Sustainable synthesis of truncated Au-sensors embedded within robust snipped human nails to monitor dye adulteration in real food samples
Article, Analytical Methods, 2025, DOI Link
View abstract ⏷
Natural materials with anomalous molecular machinery and hierarchies are gaining tremendous recognition in the pursuit of environmentally friendly, sustainable supports via noble metal anchoring for the analysis of organic pollutants. Herein, for the first time, we demonstrate the in situ biofabrication of AuNPs stringently tethered within snipped human nails, materialised by the hydroxy amino acids structured within the collagenous nail, which exhibit high reductive potential and Au affinity. Material characterization revealed a firm assemblage of large truncated AuNPs, including triangles, pentagons, hexagons and octagons of sizes between ∼80 and 150 nm, embedded within the highly rigid and compact three-dimensional nail, ensuring durability, shelf-life and stability against diverse physicochemical environments. Furthermore, large truncated AuNPs with sharp edges can intensify localized electromagnetic fields as “hotspots” for the direct SERS detection of organic analytes. This is validated by exposing real dye adulterants at nanomolar regimes, detecting acid orange at concentrations of 0.173-0.206 ppm in red chillies (spice) and 0.087-0.140 ppm of malachite green in green peas (pulse) collected from three distantly far vegetable markets in a radius of ∼37.28 miles. Overall, we present a highly stable, human nail waste biofabricated Au bio-substrate as a sustainable and generalized sensing technique for the identification and quantification of unsafe molecular adulterants in food samples using SERS.
Surface-enhanced Raman spectroscopy for size-resolved microplastic detection in real-world samples using thiophenol labeling
Kumar J., Jinachandran A., Renduchintala M., Soma V.R., Shanmugam V., Imamvali S., Tupakula S., Panneerselvam R.
Article, Environmental Science: Nano, 2025, DOI Link
View abstract ⏷
The widespread presence of plastic contamination in the environment presents a severe threat to human and animal health. This study introduces a toluene dispersion strategy for detecting microplastics of different sizes using surface-enhanced Raman spectroscopy (SERS). The evaporation-induced self-assembly (EISA) method was employed to prepare SERS substrates by incubating silver nanoparticles (AgNPs) of ∼40-60 nm with a microplastic solution containing polystyrene (250 μm, 2.1 mm), polypropylene (10-50 μm), and polyvinyl chloride (1-5 μm). SEM images and Raman spectroscopy confirmed the uniform decoration of AgNPs on filter paper substrates, with a relative standard deviation (RSD) of 8.22%. Thiophenol was used as a Raman reporter to monitor surface changes, showing a strong correlation (R2 = 0.986-0.995) between its SERS signal and microplastic concentration in aqueous and real samples. This is the first time a toluene dispersion strategy has been integrated with EISA to achieve highly sensitive microplastic detection, reaching a limit of 0.001 mg mL−1. The method was validated in real-world matrices, including lake water and salt samples, in the presence of interferents such as organic pollutants, inorganic ions, colloids, bio-organisms, and bisphenol A. This approach enables rapid detection of diverse microplastics in complex environmental samples.
Trapping tiny pollutants: SERS-driven strategies for microplastics and nanoplastics detection
Review, iScience, 2025, DOI Link
View abstract ⏷
Microplastics and nanoplastics are almost everywhere in biological and environmental systems, posing serious risks to human health and ecology. However, due to their complex matrices, varied sizes, and morphologies, their detection and quantification remain challenging. Particularly, Raman and surface-enhanced Raman spectroscopy (SERS) hold great promise for the detection, characterization, and quantification of micro/nanoplastics. In this review, we introduce the Raman and SERS fundamental principles, instrumentation, and SERS substrate design strategies. Particularly, emphasis is placed on SERS-enabled ultrasensitive detection, integration with chemometrics and machine learning tools, culminating in the real-world applicability. Additionally, we elaborate on the current limitations, including signal variability, lack of standardization, and sample preparation challenges. Finally, future directions involving artificial intelligence (AI) integration, substrate engineering, and multi-modal analytical approaches are discussed.
SERS detection of erythrosin B dye from fennel seed candy using silver/graphene-based cylindrical substrate
Jinachandran A., Senthilkumaran V., Surya Y.V., Kumar J., George S.D., Panneerselvam R.
Article, Sensors and Actuators B: Chemical, 2025, DOI Link
View abstract ⏷
Food safety is a growing concern due to frequent contamination. For the first time, this study introduces a novel cylindrical SERS substrate using copper rods (CuR) with electroless deposited silver nanoparticles (AgNPs) and a graphene oxide (GO) coating for efficient food monitoring. The GO/AgNPs/CuR substrate enhances signals through dense “hot spots” and superior analyte adsorption, achieving a low detection limit of 2.07 × 10⁻¹ ⁰ M for erythrosin B (ErB) with an enhancement factor of 5.19 × 10⁸. It offers excellent uniformity (RSD 7.77 %) and retains 71 % efficiency after 18 days. Notably, it detected ErB in pink fennel seed candy without spiking and achieved 85.4–97.2 % recovery in white fennel seed candy at 10⁻¹ ⁰ M. With simple fabrication, high sensitivity, and demonstrated applicability, this GO/AgNPs/CuR SERS substrate is a promising tool for real-world food safety inspection.
Highly SERS active microcomposite of silver nanoparticles-decorated nickel oxide microflowers on flexible substrates for detection of 4-nitrophenol on fish surfaces
Jinachandran A., Kokulnathan T., Wang T.-J., Panneerselvam R.
Article, Journal of Alloys and Compounds, 2025, DOI Link
View abstract ⏷
Development of high-performance flexible substrates for surface-enhanced Raman spectroscopy (SERS) is crucial for the sensitive, rapid detection of environmental pollutants in complex matrices. In this work, we report the fabrication of hydrothermally synthesized nickel oxide microflowers decorated with photoreduced silver nanoparticles on filter paper (Ag-NPs/NiO-MFs@FP) for the detection of the priority pollutant 4-nitrophenol (4-NP). The unique 3D hierarchical structure of the NiO MFs provides a wide surface area for the deposition of high-density Ag-NP and 4-NP molecules. The formation of numerous hotspots in the nanoscale gaps between adjacent Ag NPs produces a significant Raman signal enhancement. Furthermore, the energy band structure of Ag NPs and NiO MFs facilitated the efficient electron transfer to the 4-NP molecules, which further amplifies the SERS effect. The Ag-NPs/NiO-MFs@FP SERS substrate exhibits excellent performance for the detection of 4-NP, including an ultra-low limit of detection (LOD) of 3.38 × 10−12 M, an enhancement factor of 3.31 × 109, good reproducibility (RSD of 7.62 %), high uniformity, and remarkable long-term stability (70 % efficiency after 12 days). Importantly, the flexible SERS platform enables the sensitive and reliable detection of 4-NP in tap water and river water, and on fish surfaces with good recovery rates. The performance comparison results show that the proposed Ag-NPs/NiO-MFs@FP composite has superior detection performance compared to other SERS active materials and other detection methods for the detection of 4-NP. The facile fabrication approach, superior analytical capabilities, and practical feasibility of the Ag-NPs/NiO-MFs@FP SERS substrate make it a highly promising detection platform for efficient environmental monitoring and food safety applications.
Label-free Detection of Urine Extracellular Vesicles from Duchenne Muscular Dystrophy Patients Using Surface-Enhanced Raman Spectroscopy Combined with Machine Learning Models
Rajavel A., Kumar J., Essakipillai N., Anbazhagan R., Panneerselvam R., Ramakrishnan J., Venkataraman V., Natesan Sella R.
Article, ACS Omega, 2025, DOI Link
View abstract ⏷
Duchenne muscular dystrophy (DMD) is a neuromuscular disease that affects males in the pediatric age group. Currently, there is no painless, cost-effective prognostic method available to monitor DMD progression. The main hypothesis of this study was that the biochemical composition of extracellular vesicles (EVs) isolated from the urine of DMD patients can be distinctly differentiated from that of healthy controls using surface-enhanced Raman Spectroscopy (SERS) combined with machine learning models. This differentiation is expected to provide a noninvasive, rapid, and accurate diagnostic tool for the early detection, staging, and monitoring of DMD by identifying the molecular signatures captured by SERS and leveraging the analytical power of machine learning algorithms. We collected fasting morning urine samples from 52 DMD patients and 17 healthy controls and isolated EVs using a Total Exosome Isolation kit. The SERS substrates are prepared using silver nanoparticles, which were employed to capture the molecular fingerprints of the EVs with uniformity and reproducibility, achieving relative standard deviation values of 7.3% and 8.9%. We observed alterations in phenylalanine and α-helical proteins in patients with DMD compared to controls. These spectral data were analyzed using PCA, Support Vector Machines, and k-Nearest Neighbor (KNN) algorithms to identify distinct patterns and stage DMD based on biochemical composition. Our integrated approach demonstrated 60% sensitivity and 100% specificity in distinguishing DMD patients from healthy controls, highlighting the potential of SERS and KNN for noninvasive, accurate, and rapid diagnosis of DMD. This method offers a promising avenue for early detection and personalized treatment strategies, ultimately improving patient outcomes and quality of life.
Investigation on the reaction of sulphur with Ag–Cu–Zn-Ge alloy: Experimental and computational study
Article, Journal of Materials Research and Technology, 2024, DOI Link
View abstract ⏷
Silver and its alloys undergo tarnishing with time, which is a black stain on the surface due to the formation of Ag2S. Developing a tarnish resistant Ag alloy was attempted by alloying Ag with elements that form a passive oxide layer on the surface. Germanium is proven to provide better tarnish resistance to sterling Silver alloy (92.5 wt% pure) which is available under the trade name of Argentium©. The present work investigates the tarnish resistance behavior of sterling silver alloy (92.5 wt% pure) containing various additions of Copper, Zinc, and Germanium. The alloys were prepared by melting and casting route, followed by Passivation Heat Treatment (PHT) to create a stable and continuous oxide layer. The temperature for PHT was optimized using thermogravimetry analysis (TGA) of the alloys prepared. Accelerated tarnish test was carried out to investigate the tarnishing behavior of alloy samples obtained before and after PHT. The samples were characterized using XRD, SEM-EDX, and micro-Raman Spectroscopy. The change in reflectance of the samples after tarnish test is determined using UV–Visible reflectance spectroscopy. The mechanism behind the tarnish resistance was derived using Density Functional Theory (DFT) by comparing sulphur (S2) and Oxygen (O2) adsorption energies (BE) of the alloying elements. The lower value of S2 (BE)/O2 (BE) indicates better oxidation and tarnish resistance. The ratio ranges between 222 % (Pure Ag) and 132 % (for Ag-4.2Cu-2.8Zn-1.4Ge) and the p-p between Ge and O has contributed to the reduction in the ratio.
The Advancements and Detection Methodologies for Microplastic Detection in Environmental Samples
Balasubramaniam D.A., Panneerselvam R., Akshaya K., Rajamanickam R., De-La-torre G.E., Selvasembian R.
Book chapter, Microplastics: Environmental Pollution and Degradation Process, 2024, DOI Link
View abstract ⏷
Microplastics (MPs) contamination has emerged as a significant environmental concern due to its extensive dispersion along with potential adverse effects on aquatic as well as terrestrial ecosystems. Microplastics’ harmful effects have been seen to rise throughout the decades when they mix with other contaminants in a dynamic environmental setting. As a result, developing accurate, effective, and speedy analytical techniques for identifying MPs contamination has become a pressing issue. Understanding the origins, distribution, and implications of MPs requires reliable and efficient detection techniques in environmental samples. This chapter explores the methodologies and strategies for optical detection and identification of MPs in environmental samples, covering their potential, limitations, and the latest advances in destructive (thermal and GC-MS) and non-destructive (Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy) detection techniques. By providing a brief overview of these detection methods, this chapter aims to inform further analysis and research efforts, evaluating their applicability across various sample matrices.
Silver nanopopcorns decorated on flexible membrane for SERS detection of nitrofurazone
Jinachandran A., Kokulnathan T., Wang T.-J., Kumar K.M.A., Kumar J., Panneerselvam R.
Article, Microchimica Acta, 2024, DOI Link
View abstract ⏷
The synthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS) is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 106. This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10−9 M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10 days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10−8 M, 5.76 × 10−7 M, and 3.61 × 10−8 M, respectively, which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples. Graphical Abstract: (Figure presented.)
Surface-enhanced Raman spectroscopy: a half-century historical perspective
Yi J., You E.-M., Hu R., Wu D.-Y., Liu G.-K., Yang Z.-L., Zhang H., Gu Y., Wang Y.-H., Wang X., Ma H., Yang Y., Liu J.-Y., Fan F.R., Zhan C., Tian J.-H., Qiao Y., Wang H., Luo S.-H., Meng Z.-D., Mao B.-W., Li J.-F., Ren B., Aizpurua J., Apkarian V.A., Bartlett P.N., Baumberg J., Bell S.E.J., Brolo A.G., Brus L.E., Choo J., Cui L., Deckert V., Domke K.F., Dong Z.-C., Duan S., Faulds K., Frontiera R., Halas N., Haynes C., Itoh T., Kneipp J., Kneipp K., Le Ru E.C., Li Z.-P., Ling X.Y., Lipkowski J., Liz-Marzan L.M., Nam J.-M., Nie S., Nordlander P., Ozaki Y., Panneerselvam R., Popp J., Russell A.E., Schlucker S., Tian Y., Tong L., Xu H., Xu Y., Yang L., Yao J., Zhang J., Zhang Y., Zhang Y., Zhao B., Zenobi R., Schatz G.C., Graham D., Tian Z.-Q.
Review, Chemical Society Reviews, 2024, DOI Link
View abstract ⏷
Surface-enhanced Raman spectroscopy (SERS) has evolved significantly over fifty years into a powerful analytical technique. This review aims to achieve five main goals. (1) Providing a comprehensive history of SERS’s discovery, its experimental and theoretical foundations, its connections to advances in nanoscience and plasmonics, and highlighting collective contributions of key pioneers. (2) Classifying four pivotal phases from the view of innovative methodologies in the fifty-year progression: initial development (mid-1970s to mid-1980s), downturn (mid-1980s to mid-1990s), nano-driven transformation (mid-1990s to mid-2010s), and recent boom (mid-2010s onwards). (3) Illuminating the entire journey and framework of SERS and its family members such as tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and highlighting the trajectory. (4) Emphasizing the importance of innovative methods to overcome developmental bottlenecks, thereby expanding the material, morphology, and molecule generalities to leverage SERS as a versatile technique for broad applications. (5) Extracting the invaluable spirit of groundbreaking discovery and perseverant innovations from the pioneers and trailblazers. These key inspirations include proactively embracing and leveraging emerging scientific technologies, fostering interdisciplinary cooperation to transform the impossible into reality, and persistently searching to break bottlenecks even during low-tide periods, as luck is what happens when preparation meets opportunity.
Ag nanoparticle-embedded fish scales as SERS substrates for sensitive detection of forever chemical in real samples
Kumar J., Jinachandran A., Ponnusamy V.K., Huang G.G., Suresh A.K., Noothalapati H., Panneerselvam R.
Article, Applied Surface Science, 2024, DOI Link
View abstract ⏷
Biological materials with unique surface properties provide a new avenue for fabricating green and sensitive SERS-active substrates. Herein, we present a simple but efficient method to prepare surface-enhanced Raman scattering (SERS) substrates by depositing silver nanoparticles (AgNPs) on fish scale substrates using an evaporation-induced self-assembly method (EISA). Characterization of the formed flexible Ag-impregnated substrate proved outstanding SERS sensitivity, uniformity, and reproducibility properties, with a Raman enhancement factor of 1.3 × 106 and a relative standard deviation of 6.4 %. Using this powerful fish scale substrate, a toxic environmental pollutant perfluorooctane sulfonamide (PFOSA) was indirectly detected in lake water, soil, and human urine samples. Due to its chemical structure, it is difficult to detect low concentrations of PFOSA in real samples. Interestingly, malachite green (MG) was smartly used as the Raman label for PFOSA detection in real samples. One of the main appeals is that the concentration of PFOSA can be correlated with a decrease in the SERS signal of MG in real samples. In conclusion, the strategy employed and reproducible SERS substrates may have diverse applications in clinical and environmental analyses.
Sustainable golden nanoflowers grafted food-waste derived biotemplate for the direct SERS-detection of carcinogenic herbicides from agro-farms
Article, Materials Today Chemistry, 2024, DOI Link
View abstract ⏷
Surface Enhanced Raman Scattering (SERS) is emerging as a potent analytical tool for the detection of various pollutants in complex environments due to its distinctive vibrational fingerprint ability and pronounced detection sensitivity. Precautious of adverse blue-green economies and ecological impacts, sustainable generation of SERS active substrates and analyte casting matrices are getting prioritized. Herein, gold nanoflowers (AuNFs) of ∼75 ± 15 nm were initially biofabricated using an expended cell culture medium as a one-step synthesis cum stabilization strategy. Then the heavy architecture of multi-faceted AuNFs with deep pits and edges, that acted as hotspots for enhancing the localized electromagnetic fields, was utilized for the direct SERS detection of commonly used carcinogenic herbicides collected from agro-farms at nanomolar regimes with 0.44 ppm and 0.27 ppm for Glyphosate and amino methyl phosphonic acid, respectively. Such a low level detection is superior by 8.33% when compared to the reported values. Computational finite-difference time-domain (FDTD) simulations affirmed the enhanced SERS effect from the multi-faceted nanostructure of AuNFs with structural heterogeneities that provide numerous hotspots to amplify the localized electromagnetic field. More eminently, fish scale derived biotemplate through AuNF-analyte drop casting contributed to the exceptional intensities, attributed to the naturally grooved hierarchically porous hydrophilic lamellar structures contact angle of 73°. Overall, the adapted bioengineering of SERS substrate is safe, robust, affordable and reproducible, fostered by bioderived durable biomatrix offering potent sustainable SERS detection of various biomedically and environmentally relevant molecules.
Clinical detection of total homocysteine in human serum using surface-enhanced Raman spectroscopy
Zheng X.-B., Liu S.-H., Panneerselvam R., Zhang Y.-J., Wang A., Zhang F.-L., Jin S., Li J.-F.
Article, Vibrational Spectroscopy, 2023, DOI Link
View abstract ⏷
Cardiovascular diseases cause enormous morbidity and mortality worldwide. Excessive blood total homocysteine (tHcy) is an independent risk factor for cardiovascular diseases. Therefore, it is imperative to measure the content of tHcy in human blood. However, the currently available analytical methods have the disadvantages such as being time-consuming and expensive. Herein, we propose a rapid clinical quantification of tHcy in human serum using high-performance Ag Nanopolyhedra (Ag NPOLY) as surface-enhanced Raman spectroscopy (SERS) substrates. Generally, 80% of homocysteine (Hcy) in serum is oxidized, and only 20% of Hcy is free. To understand this behavior, we explored the reduction effect of tris(2-carboxyethyl) phosphine (TCEP) on serum Hcy at different pH. The results confirmed that our method can detect 2 µM of Hcy in human serum. As a proof-of-concept, the developed method was applied to the actual clinical detection of human serum tHcy, and the serum of 5 hyperhomocysteinemia (HHcy) patients was verified. Moreover, the obtained, results were consistent with high-performance liquid chromatography (HPLC) results. The linear correlation coefficient of the two methods was 0.9766. Importantly, our analysis can be completed within 15 min, while HCLP requires more than 1 h. Overall, we have successfully developed a rapid SERS-based quantitative method for human serum tHcy, which can provide a new solution for the clinical diagnosis of cardiovascular diseases in the future.
Surface-Enhanced Raman Spectroscopic Probing in Digital Microfluidics through a Microspray Hole
Das A., Fehse S., Polack M., Panneerselvam R., Belder D.
Article, Analytical Chemistry, 2023, DOI Link
View abstract ⏷
We report a novel approach for surface-enhanced Raman spectroscopy (SERS) detection in digital microfluidics (DMF). This is made possible by a microspray hole (μSH) that uses an electrostatic spray (ESTAS) for sample transfer from inside the chip to an external SERS substrate. To realize this, a new ESTAS-compatible stationary SERS substrate was developed and characterized for sensitive and reproducible SERS measurements. In a proof-of-concept study, we successfully applied the approach to detect various analyte molecules using the DMF chip and achieved micro-molar detection limits. Moreover, this technique was exemplarily employed to study an organic reaction occurring in the DMF device, providing vibrational spectroscopic data.
Au nanocakes as a SERS sensor for on site and ultrafast detection of dioxins
Wang T., Li H.-M., Wen B.-Y., Panneerselvam R., Zhang Y.-J., Wang A., Zhang F.-L., Jin S., Li J.-F.
Article, Vibrational Spectroscopy, 2023, DOI Link
View abstract ⏷
Dioxin is a highly toxic and carcinogenic pollutant created during industrial production and waste incineration. Pollutant monitoring has made extensive use of surface-enhanced Raman spectroscopy (SERS) as a quick, non-destructive, sensitive, and affordable analytical method. However, the fabrication of a SERS substrate with ultrahigh sensitivity is a challenging task, the detection cost is expensive. Currently, these are the challenges faced by SERS technique for the detection of dioxin pollutants. In this paper, we present Au nanocakes (Au NCs) as an easy-to-build SERS substrate for sensitive SERS detection of dioxins in real samples. Based on three-dimensional finite-difference time-domain (3D-FDTD) calculations, the enhancement factor of the substrate following aggregation is approximately 1010. Using a portable Raman spectrometer, the limit of detection for dioxins such as 1-chloro-dibenzo-p-dioxin (1-CDD), 2,8-dichloro-dibenzo-p-dioxin (2,8-DCDD), and 2,3,7-trichloro-dibenzo-p-dioxin (2,3,7-TrCDD) in clean water reached as low as 5, 5, and 10 ng/mL, respectively. As a real-world application, the same toxic pollutants were detected in sewage water samples. Our findings could lead to the development of novel SERS-based sensors for the rapid detection of dioxins in real-world scenarios. Moreover, a portable Raman spectrometer is used to detect the pollutants, which is easy to use and inexpensive.
Raman Spectroscopy for Hydrogen Production
Book chapter, ACS Symposium Series, 2023, DOI Link
View abstract ⏷
Renewable Energy Solutions for Fueling the Future. Green hydrogen, which is produced by using renewably generated electricity that splits water molecules into hydrogen and oxygen, holds significant promise to meet global energy demand while contributing to climate action goals. Currently, the production of green hydrogen is not yet economical or efficient enough. The key to solving this problem is through the development of innovative electrocatalysts. This book reviews recent research and perspectives on these essential areas of focus and provides must-have information for moving new research in green energy forward.
Promise of nano-carbon to the next generation sustainable agriculture
Chandel M., Kaur K., Sahu B.K., Sharma S., Panneerselvam R., Shanmugam V.
Review, Carbon, 2022, DOI Link
View abstract ⏷
The impact of the carbon nanomaterials (CNMs) wave in agro-application has been growing in recent years. The carbon nanomaterials family includes graphene oxide (GO), carbon nanotube (CNT), carbon nanofiber (CNF), carbon nanohorns (CNH), carbon nanodots (CND), carbon nano-onions (CNO), fullerene, and nano-diamond. The former seven belong to the sp2 carbon and the later belong to sp3 carbon. Based on the selection of the forms of allotropes, morphology, size, and the potential combination to form hybrids; the CNMs have shown different performance in the agro activities. Hence, in this review, all these studies along with our contributions are detailed briefly with the information about material synthesis, characterization, and application efficiency; the application includes the role in pesticide, fertilizer, and preservative sector. The review is finally concluded with the highlights about advantages, gaps/risks identified for the industry application, quality assurance status, and future perspectives.
Microfluidics and surface-enhanced Raman spectroscopy, a win-win combination?
Panneerselvam R., Sadat H., Hohn E.-M., Das A., Noothalapati H., Belder D.
Review, Lab on a Chip, 2022, DOI Link
View abstract ⏷
With the continuous development in nanoscience and nanotechnology, analytical techniques like surface-enhanced Raman spectroscopy (SERS) render structural and chemical information of a variety of analyte molecules in ultra-low concentration. Although this technique is making significant progress in various fields, the reproducibility of SERS measurements and sensitivity towards small molecules are still daunting challenges. In this regard, microfluidic surface-enhanced Raman spectroscopy (MF-SERS) is well on its way to join the toolbox of analytical chemists. This review article explains how MF-SERS is becoming a powerful tool in analytical chemistry. We critically present the developments in SERS substrates for microfluidic devices and how these substrates in microfluidic channels can improve the SERS sensitivity, reproducibility, and detection limit. We then introduce the building materials for microfluidic platforms and their types such as droplet, centrifugal, and digital microfluidics. Finally, we enumerate some challenges and future directions in microfluidic SERS. Overall, this article showcases the potential and versatility of microfluidic SERS in overcoming the inherent issues in the SERS technique and also discusses the advantage of adding SERS to the arsenal of microfluidics.
Surface-enhanced Raman spectroscopy for food quality and safety monitoring
Panneerselvam R., Kanagarajan S., Jinachandran A.
Book chapter, Nanotechnology Applications for Food Safety and Quality Monitoring, 2022, DOI Link
View abstract ⏷
Surface-enhanced Raman spectroscopy (SERS) is a nanostructure-based analytical technique that can render chemical and fingerprint information of food adulterants, contaminants, and pathogens. Due to its high sensitivity and simplicity, this vibrational spectroscopic technique has been widely used for food quality and food safety applications. In the first section of this chapter provides a basic understanding of Raman spectroscopy and SERS technique. Then, it introduces the different fabrication methods for plasmonic nanostructures (SERS substrates) and its importance in SERS measurements. The potential applications of SERS (i) detection of residual pesticides and insecticides, (ii) detection of chemical contaminants and pathogens, (iii) application of SERS in plant science, and (iv) nutritional quality analysis are discussed in detail. Finally, it also presents an outlook on the challenges and future directions of SERS as a powerful analytical tool in food analysis.
Advances of surface-enhanced Raman and IR spectroscopies: from nano/microstructures to macro-optical design
Wang H.-L., You E.-M., Panneerselvam R., Ding S.-Y., Tian Z.-Q.
Review, Light: Science and Applications, 2021, DOI Link
View abstract ⏷
Raman and infrared (IR) spectroscopy are powerful analytical techniques, but have intrinsically low detection sensitivity. There have been three major steps (i) to advance the optical system of the light excitation, collection, and detection since 1920s, (ii) to utilize nanostructure-based surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) since 1990s, and (iii) to rationally couple (i) and (ii) for maximizing the total detection sensitivity since 2010s. After surveying the history of SERS and SEIRA, we outline the principle of plasmonics and the different mechanisms of SERS and SEIRA. We describe various interactions of light with nano/microstructures, localized surface plasmon, surface plasmon polariton, and lightning-rod effect. Their coupling effects can significantly increase the surface sensitivity by designing nanoparticle–nanoparticle and nanoparticle–substrate configuration. As the nano/microstructures have specific optical near-field and far-field behaviors, we focus on how to systematically design the macro-optical systems to maximize the excitation efficiency and detection sensitivity. We enumerate the key optical designs in particular ATR-based operation modes of directional excitation and emission from visible to IR spectral region. We also present some latest advancements on scanning-probe microscopy-based nanoscale spectroscopy. Finally, prospects and further developments of this field are given with emphasis on emerging techniques and methodologies.
A microfluidic device enabling surface-enhanced Raman spectroscopy at chip-integrated multifunctional nanoporous membranes
Krafft B., Panneerselvam R., Geissler D., Belder D.
Article, Analytical and Bioanalytical Chemistry, 2020, DOI Link
View abstract ⏷
A three-dimensional microfluidic chip that combines sample manipulation and SERS detection on-chip was developed. This was successfully achieved by chip integration of a nanoporous polycarbonate track-etched (PCTE) membrane which connects microfluidic channels on two different levels with each other. The membrane fulfills two functions at the same time. On the one hand, it enables sample enrichment by selective electrokinetic transport processes through the membrane. On the other hand, the silver nanoparticle–coated backside of the same membrane enables SERS detection of the enriched analytes. The SERS substrate performance and the electrokinetic transport phenomena were studied using Rhodamine B (RhB) by Raman microscopy and fluorescence video microscopy. After system validation, the approach was attested by on-chip processing of a complex food sample. In a proof-of-concept study, the microfluidic device with the SERS substrate membrane was used to detect a concentration of 1 ppm melamine (705 cm−1) in whole milk. Electrokinetic transport across the nanoporous SERS substrate facilitates the extraction of analyte molecules from a sample channel into a detection channel via a potential gradient, thus easily removing obscuring compounds present in the sample matrix. The SERS signal of the analyte could be significantly increased by on-target sample drying. This was achieved by guiding an additional gas flow over the membrane which further extends the microfluidic functionality of the chip device. The proposed method possesses the advantages of combining a rapid (within 15 min) sample clean-up using electrokinetic transport in a three-dimensional microfluidic device which is highly suitable for sensitive and selective SERS detection of chemical and biological analytes. [Figure not available: see fulltext.].
Raman spectroscopic detection in continuous microflow using a chip-integrated silver electrode as an electrically regenerable surface-enhanced raman spectroscopy substrate
Article, Analytical Chemistry, 2019, DOI Link
View abstract ⏷
An electrochemical approach to enable surface-enhanced Raman spectroscopy (SERS) detection in continuous microflow is presented. This is achieved by the integration of a silver electrode as SERS substrate in a microfluidic chip device. By the application of actuation pulses of about 4 V, otherwise irreversibly adsorbed analytes are stripped off, which enables quasi-real-time SERS detection in a continuous microflow. The approach opens up a way for in situ SERS monitoring of compounds in microflow with high application potential in microseparation techniques like HPLC and lab-on-a-chip devices.
A rapid and simple chemical method for the preparation of Ag colloids for surface-enhanced Raman spectroscopy using the Ag mirror reaction
Panneerselvam R., Xiao L., Waites K.B., Atkinson T.P., Dluhy R.A.
Article, Vibrational Spectroscopy, 2018, DOI Link
View abstract ⏷
Colloidal silver (Ag) nanoparticles (AgNP) have been widely used for surface-enhanced Raman spectroscopy (SERS) applications. We report a simple, rapid and effective method to prepare AgNP colloids for SERS using the classic organic chemistry Ag mirror reaction with Tollens’ reagent. The AgNP colloid prepared with this process was characterized using SEM, and the reaction conditions further optimized using SERS measurements. It was found that Ag mirror reaction conditions that included 20 mM AgNO3, 5 min reaction time, and 0.5 M glucose produced AgNP colloids with an average size of 319.1 nm (s.d ± 128.1). These AgNP colloids exhibited a significant SERS response when adenine was used as the reporter molecule. The usefulness of these new AgNP colloids was demonstrated by detecting the nucleotides adenosine 5′-mono-phosphate (AMP), guanosine 5′-monophosphate (GMP), cytidine 5′-monophosphate (CMP), and uridine 5′-monophosphate (UMP). A detection limit of 500 nM for AMP was achieved with the as-prepared AgNP colloid. The bacterium Mycoplasma pneumoniae was also easily detected in laboratory culture with these SERS substrates. These findings attest to the applicability of this AgNP colloid for the sensitive and specific detection of both small biomolecules and microorganisms.
Quantitative detection using two-dimension shell-isolated nanoparticle film
Yang J.-L., Yang Z.-W., Zhang Y.-J., Ren H., Zhang H., Xu Q.-C., Panneerselvam R., Sivashanmugan K., Li J.-F., Tian Z.-Q.
Article, Journal of Raman Spectroscopy, 2017, DOI Link
View abstract ⏷
Surface-enhanced Raman spectroscopy (SERS) can provide a fingerprint of molecules with ultrahigh sensitivity, down to the single-molecule level. However, accurate quantitative detection in practical samples using SERS is still a great challenge. Herein, a highly uniform shell-isolated Ag@SiO2 nanoparticle (Ag SHIN) monolayer film was prepared and employed as a substrate for the quantitative determination of melamine in milk samples through shell-isolated nanoparticle-enhanced Raman spectroscopy. The Ag SHIN film exhibits excellent reproducibility, high stability, as well as ultrahigh sensitivity with a limit of detection of 0.03 ppm. A linear relationship between the Raman intensity and the melamine concentration in a wide range (1 ppb to 5 ppm) was obtained. These results demonstrate that the Ag SHIN monolayer film is a promising and reliable substrate for the quantitative SERS analysis of practical samples. Copyright © 2017 John Wiley & Sons, Ltd.
Surface-enhanced Raman spectroscopy: Bottlenecks and future directions
Panneerselvam R., Liu G.-K., Wang Y.-H., Liu J.-Y., Ding S.-Y., Li J.-F., Wu D.-Y., Tian Z.-Q.
Article, Chemical Communications, 2017, DOI Link
View abstract ⏷
In this feature article, we discuss in detail developmental bottleneck issues in Raman spectroscopy in its early stages and surface-enhanced Raman spectroscopy (SERS) in the past four decades. We divide SERS research into two different directions with different targets. Fundamental research is extending the limits of SERS to single-molecule, sub-nanometer resolution and femtosecond processes. In contrast, practical research is expanding the range of applications with the aim of providing versatile analytical tools for surface, materials, life, environmental, forensic and food sciences and also commercial instruments for use in daily life. In the second direction there have continually been many complex bottlenecks to be overcome. We attempt to enumerate the key issues in detail and also describe the achievements made to overcome the bottlenecks. In the last, but not least important part, we discuss the remaining bottlenecks and possible strategies for overcoming them to enable SERS to be an even more powerful and versatile technique.
Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) of Electrode Surfaces
Book chapter, Advances in Electrochemical Science and Engineering: Nanopatterned and Nanoparticle-Modified Electrodes: Volume 17, 2017, DOI Link
View abstract ⏷
This chapter shows that nanoparticles (NPs) and nanostructures can play a key role in developing the new shell-isolated mode for characterizing various electrochemical systems. Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) has overcome the long-standing material-specific and morphology-specific limitations of the direct contact mode of surface-enhanced Raman spectroscopy (SERS). SHINERS has enabled one to identify the species present in the passive layer formed during the gold leaching reaction in practical applications. More importantly, the strategy of quantitative analysis of SHINERS on electrode surface species is very useful for both fundamental and practical applications. The most important step in the SHINERS investigation is to prepare and characterize the pinhole-free shell-coated NPs. High-resolution transmission electron microscopy (HRTEM) images and SERS spectra from pyridine molecules on gold substrates are primarily used to ensure that the shell is pinhole-free.
Shell-isolated nanoparticle-enhanced Raman spectroscopy
Book chapter, Recent Developments In Plasmon-Supported Raman Spectroscopy: 45 Years of Enhanced Raman Signals, 2017, DOI Link
Core-shell nanoparticle-enhanced raman spectroscopy
Li J.-F., Zhang Y.-J., Ding S.-Y., Panneerselvam R., Tian Z.-Q.
Review, Chemical Reviews, 2017, DOI Link
View abstract ⏷
Core-shell nanoparticles are at the leading edge of the hot research topics and offer a wide range of applications in optics, biomedicine, environmental science, materials, catalysis, energy, and so forth, due to their excellent properties such as versatility, tunability, and stability. They have attracted enormous interest attributed to their dramatically tunable physicochemical features. Plasmonic core-shell nanomaterials are extensively used in surface-enhanced vibrational spectroscopies, in particular, surfaceenhanced Raman spectroscopy (SERS), due to the unique localized surface plasmon resonance (LSPR) property. This review provides a comprehensive overview of core-shell nanoparticles in the context of fundamental and application aspects of SERS and discusses numerous classes of core-shell nanoparticles with their unique strategies and functions. Further, herein we also introduce the concept of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) in detail because it overcomes the long-standing limitations of material and morphology generality encountered in traditional SERS. We then explain the SERS-enhancement mechanism with core-shell nanoparticles, as well as three generations of SERS hotspots for surface analysis of materials. To provide a clear view for readers, we summarize various approaches for the synthesis of core-shell nanoparticles and their applications in SERS, such as electrochemistry, bioanalysis, food safety, environmental safety, cultural heritage, materials, catalysis, and energy storage and conversion. Finally, we exemplify about the future developments in new core-shell nanomaterials with different functionalities for SERS and other surfaceenhanced spectroscopies.
Theoretical study of normal Raman spectra and SERS of benzyl chloride and benzyl radical on silver electrodes
Chen Y.-L., Panneerselvam R., Wu D.-Y., Tian Z.-Q.
Article, Journal of Raman Spectroscopy, 2017, DOI Link
View abstract ⏷
Electrochemical surface-enhanced Raman spectroscopy has been used to characterize adsorbed species widely but rarely to reaction intermediates on electrodes. In previous studies, the observed surface-enhanced Raman spectroscopy signals were proposed from benzyl species due to the electrochemical reduction of benzyl chloride on silver electrode surfaces. In this work, we reinvestigated the vibrational assignments of benzyl chloride and benzyl radical as the reaction intermediate. On the basis of density functional theory calculations and normal mode analysis, our systematic results provide more reasonable new assignments for both surface species. Further, we investigated adsorption configurations, binding energies, and vibrational frequency shifts of benzyl radical interacting with silver. Our calculated results show that the wagging vibration displays significant vibrational frequency shift, strong coupling with some intramolecular modes in the phenyl ring, and significant changes in intensity of Raman signals. The study also provides absolute Raman intensity in benzyl halides and discusses the enhancement effect mainly due to the binding interaction with respect to free benzyl radical. Copyright © 2016 John Wiley & Sons, Ltd.
Self-assembly of subwavelength nanostructures with symmetry breaking in solution
Tian X.-D., Chen S., Zhang Y.-J., Dong J.-C., Panneerselvam R., Zhang Y., Yang Z.-L., Li J.-F., Tian Z.-Q.
Article, Nanoscale, 2016, DOI Link
View abstract ⏷
Nanostructures with symmetry breaking can allow the coupling between dark and bright plasmon modes to induce strong Fano resonance. However, it is still a daunting challenge to prepare bottom-up self-assembled subwavelength asymmetric nanostructures with appropriate gaps between the nanostructures especially below 5 nm in solution. Here we present a viable self-assembly method to prepare symmetry-breaking nanostructures consisting of Ag nanocubes and Au nanospheres both with tunable size (90-250 nm for Au nanospheres; 100-160 nm for Ag nanocubes) and meanwhile control the nanogaps through ultrathin silica shells of 1-5 nm thickness. The Raman tag of 4-mercaptobenzoic acid (MBA) assists the self-assembly process and endows the subwavelength asymmetric nanostructures with surface-enhanced Raman scattering (SERS) activity. Moreover, thick silica shells (above 50 nm thickness) can be coated on the self-assembled nanostructures in situ to stabilize the whole nanostructures, paving the way toward bioapplications. Single particle scattering spectroscopy with a 360° polarization resolution is performed on individual Ag nanocube and Au nanosphere dimers, correlated with high-resolution TEM characterization. The asymmetric dimers exhibit strong configuration and polarization dependence Fano resonance properties. Overall, the solution-based self-assembly method reported here is opening up new opportunities to prepare diverse multicomponent nanomaterials with optimal performance.
Microwave-Assisted Synthesis of Highly Dispersed PtCu Nanoparticles on Three-Dimensional Nitrogen-Doped Graphene Networks with Remarkably Enhanced Methanol Electrooxidation
Peng X., Chen D., Yang X., Wang D., Li M., Tseng C.-C., Panneerselvam R., Wang X., Hu W., Tian J., Zhao Y.
Article, ACS Applied Materials and Interfaces, 2016, DOI Link
View abstract ⏷
A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.
Stable 16.2% Efficient Surface Plasmon-Enhanced Graphene/GaAs Heterostructure Solar Cell
Lin S.-S., Wu Z.-Q., Li X.-Q., Zhang Y.-J., Zhang S.-J., Wang P., Panneerselvam R., Li J.-F.
Article, Advanced Energy Materials, 2016, DOI Link
Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials
Ding S.-Y., Yi J., Li J.-F., Ren B., Wu D.-Y., Panneerselvam R., Tian Z.-Q.
Review, Nature Reviews Materials, 2016, DOI Link
View abstract ⏷
Since 2000, there has been an explosion of activity in the field of plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS hotspots-nanoscale regions with a strongly enhanced local electromagnetic field-that allow trace-molecule detection, biomolecule analysis and surface characterization of various materials. In particular, we discuss a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials, which feature a strong local electromagnetic field on the surface of the probe material. Enhancement of surface Raman signals up to five orders of magnitude can be obtained from materials that are weakly SERS active or SERS inactive. We provide a detailed overview of future research directions in the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the broad application prospect for materials science and technology.
In-situ electrochemical shell-isolated Ag nanoparticles-enhanced Raman spectroscopy study of adenine adsorption on smooth Ag electrodes
Li C.-Y., Chen S.-Y., Zheng Y.-L., Chen S.-P., Panneerselvam R., Chen S., Xu Q.-C., Chen Y.-X., Yang Z.-L., Wu D.-Y., Li J.-F., Tian Z.-Q.
Article, Electrochimica Acta, 2016, DOI Link
View abstract ⏷
Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to investigate the electrochemical behavior of adenine molecules on smooth Ag electrodes. To attain this goal, pinhole-free shell-isolated Ag nanoparticles (Ag SHINs) have been synthesized and then used as signal "amplifiers" in the gap-mode configuration (Ag SHINs are coupled with a Ag electrode surface). The as-prepared Ag SHINs exhibit remarkable plasmonic performance under 488, 532, and 633 nm excitations as revealed by finite-difference time-domain (FDTD) simulations and SHINERS experiments. Furthermore, wavelength-dependent SHINERS investigation of adenine on Ag electrodes is excellently combined with the electrochemical technique. With outstanding chemical stability and plasmonic property, the Ag SHINs are extraordinarily suitable for fundamental studies at various electrochemical interfaces.
A facile method for the synthesis of large-size Ag nanoparticles as efficient SERS substrates
Zhao Y., Zhang Y.-J., Meng J.-H., Chen S., Panneerselvam R., Li C.-Y., Jamali S.B., Li X., Yang Z.-L., Li J.-F., Tian Z.-Q.
Article, Journal of Raman Spectroscopy, 2016, DOI Link
View abstract ⏷
Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface-enhanced Raman spectroscopy (SERS). However, large-scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed-mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as-prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785-nm excitation, respectively. Significantly, 150-nm Ag NPs exhibit an enhancement factor exceeding 108 for pyridine (Py) molecules in electrochemical SERS (EC-SERS) measurements. Furthermore, finite-difference time-domain (FDTD) calculation is employed to explain the size-dependent SERS activity. Finally, the potential of the as-prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd.
Erratum: Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces (Analyst (2016) DOI: 10.1039/c6an00180)
Wen B.-Y., Jin X., Li Y., Wang Y.-H., Li C.-Y., Liang M.-M., Panneerselvam R., Xu Q.-C., Wu D.-Y., Yang Z.-L., Li J.-F., Tian Z.-Q.
Erratum, Analyst, 2016, DOI Link
Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces
Wen B.-Y., Jin X., Li Y., Wang Y.-H., Li C.-Y., Liang M.-M., Panneerselvam R., Xu Q.-C., Wu D.-Y., Yang Z.-L., Li J.-F., Tian Z.-Q.
Article, Analyst, 2016, DOI Link
View abstract ⏷
For the first time, we used the electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) technique to in situ characterize the adsorption behaviour of four DNA bases (adenine, guanine, thymine, and cytosine) on atomically flat Au(111) electrode surfaces. The spectroscopic results of the various molecules reveal similar features, such as the adsorption-induced reconstruction of the Au(111) surface and the drastic Raman intensity reduction of the ring breathing modes after the lifting reconstruction. As a preliminary study of the photo-induced charge transfer (PICT) mechanism, the in situ spectroscopic results obtained on single crystal surfaces are excellently illustrated with electrochemical data.
Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy at Single-Crystal Electrode Surfaces
Dong J.-C., Panneerselvam R., Lin Y., Tian X.-D., Li J.-F.
Article, Advanced Optical Materials, 2016, DOI Link
View abstract ⏷
As an innovative technique, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) eliminates the material and morphology generality problems of surface-enhanced Raman spectroscopy (SERS). For the past few years, SHINERS has been extensively employed in many fields, especially in the electrochemistry field. This article renders a brief overview of the developments of SHINERS technique and its applications in electrochemistry. First, we clearly explain the basic principles of the SHINERS technique, such as design principles, materials synthesis, characterization methods, and related theoretical calculation methods. We then describe about the significant applications of electrochemical SHINERS (EC-SHINERS) with a focus of study on various single-crystal electrode surfaces. Finally, we summarize the recent developments and give an outlook for future developments in the SHINERS field.
Probing the Electronic Structure of Heterogeneous Metal Interfaces by Transition Metal Shelled Gold Nanoparticle-Enhanced Raman Spectroscopy
Zhang Y.-J., Li S.-B., Duan S., Lu B.-A., Yang J., Panneerselvam R., Li C.-Y., Fang P.-P., Zhou Z.-Y., Phillips D.L., Li J.-F., Tian Z.-Q.
Article, Journal of Physical Chemistry C, 2016, DOI Link
View abstract ⏷
In heterogeneous catalysis, characterization of heterogeneous metal interfaces of bimetallic catalysts is a crucial step to elucidate the catalytic performance and is a key to develop advanced catalysts. However, analytical techniques such as X-ray photoelectron spectroscopy can only work in vacuum conditions and are difficult to use for in situ analysis. Here, we present efficient and convenient core-shell nanoparticle-enhanced Raman spectroscopy to explore the in situ electronic structures of heterogeneous interfaces (Au@Pd and Au@Pt core-shell NPs) by varying the shell thickness. The experimental observations reported here clearly show that Pd donates electrons to Au, while Pt accepts electrons from Au at the heterogeneous interfaces. This conclusion gains further support from ex situ X-ray photoelectron spectroscopy results. The Au core greatly affects the electronic structures of both the Pd and Pt shells as well as catalytic behaviors. Finally, the as-prepared core-shell nanoparticles were used to demonstrate their improved catalytic properties in real electrocatalytic systems such as methanol oxidation and oxygen reduction reactions.
Potential dependent thiocyanate adsorption on gold electrodes: a comparison study between SERS and SHINERS
Cabello G., Chen X.-J., Panneerselvam R., Tian Z.-Q.
Article, Journal of Raman Spectroscopy, 2016, DOI Link
View abstract ⏷
Potential dependent adsorption of target molecules on electrode surface has long been analyzed by several analytical techniques at the electrochemical interfaces. Here, the adsorption of thiocyanate (SCN−) on gold electrodes [Au (111) and Au (poly)] is investigated by electrochemical shell isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) and surface-enhanced Raman spectroscopy. Based on the experimental observation, C − N stretching mode of N-bound SCN− can be observed around 2080 cm−1 throughout the whole potential range. The band corresponding to νC−N of S-bound SCN− appears as a shoulder at more negative potentials, and as a well-defined band are more positive potentials. However, the overlapped bands provoke a negative shift in the frequency of S-bound thiocyanate. Therefore, a change in the calculated Stark slope is observed. Interestingly, SHINERS has been employed to demonstrate the thiocyanate orientation and its effect on Raman spectra. Our results widen the opportunities of SHINERS to unravel the potential-dependent adsorption behavior of target molecules on single-crystal electrode surfaces. Copyright © 2016 John Wiley & Sons, Ltd.
Large scale synthesis of pinhole-free shell-isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications
Zhang W., Dong J.-C., Li C.-Y., Chen S., Zhan C., Panneerselvam R., Yang Z.-L., Li J.-F., Zhou Y.-L.
Article, Journal of Raman Spectroscopy, 2015, DOI Link
View abstract ⏷
Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) as a new member of Raman technique garnered great attention among scientific community. In this work, we used an improved experimental setup to float the bare silver nanoparticles in air with the help of extraneous airflow, and used atomic layer deposition (ALD) method to coat ultra-thin inert shell without pinholes. Under optimal conditions, we successfully prepared three kinds of SHINERS NPs (Ag@Al2O3, Ag@SiO2 and Ag@TiO2) in large quantity without pinholes. The ultra-thin inert shell maintains the SERS activity of silver nanoparticles for long period of time. Transmission electron microscopy (TEM) images confirm the uniform coating of shell material on silver nanoparticles. Finally, the as-prepared SHINs have been applied to detect various samples to demonstrate the applications. The presented ALD method offers a unique way to coat ultrathin shell (1-10 nm) on metal nanoparticles in large quantity (1-10 g) for practical applications.
“Smart” Ag Nanostructures for Plasmon-Enhanced Spectroscopies
Li C.-Y., Meng M., Huang S.-C., Li L., Huang S.-R., Chen S., Meng L.-Y., Panneerselvam R., Zhang S.-J., Ren B., Yang Z.-L., Li J.-F., Tian Z.-Q.
Article, Journal of the American Chemical Society, 2015, DOI Link
View abstract ⏷
Silver is an ideal candidate for surface plasmon resonance (SPR)-based applications because of its great optical cross-section in the visible region. However, the uses of Ag in plasmon-enhanced spectroscopies have been limited due to their interference via direct contact with analytes, the poor chemical stability, and the Ag+ release phenomenon. Herein, we report a facile chemical method to prepare shell-isolated Ag nanoparticle/tip. The as-prepared nanostructures exhibit an excellent chemical stability and plasmonic property in plasmon-enhanced spectroscopies for more than one year. It also features an alternative plasmon-mediated photocatalysis pathway by smartly blocking "hot" electrons. Astonishingly, the shell-isolated Ag nanoparticles (Ag SHINs), as "smart plasmonic dusts", reveal a 1000-fold ensemble enhancement of rhodamine isothiocyanate (RITC) on a quartz substrate in surface-enhanced fluorescence. The presented "smart" Ag nanostructures offer a unique way for the promotion of ultrahigh sensitivity and reliability in plasmon-enhanced spectroscopies.
Rapid detection of melamine in milk liquid and powder by surface-enhanced Raman scattering substrate array
Article, Food Control, 2015, DOI Link
View abstract ⏷
To determine the artificial additives in dairy products, we demonstrate a simple method for rapid and massive determination of melamine in milk liquid and powder samples by surface-enhanced Raman spectroscopy (SERS) technique. The developed method utilizes silver nanoparticles (AgNPs) decorated on a cylindrical support for detecting as low as 5μL of sample without any drying procedure. Importantly, the linear range for melamine in water was 5-400parts per billion (ppb) with a low detection limit of 2.5ppb (S/N=3). In addition, for analysis of melamine in milk liquid and powder, the dilution method was successfully applied to suppress the matrix effect from real samples. Interestingly, our results indicate that a dilution factor of 75 could effectively reduce the matrix effect with partially sacrificing the sensitivity in detection. The detection limit is increased to 2parts per million (ppm) in real sample detection, which is close to the acceptable limits regulated in milk products. More importantly, the elimination of complicated sample pre-treatments and the acceptable sensitivity in melamine detection attest our proposed method as a potential tool for rapid and massive food inspections.
In Situ Monitoring of Electrooxidation Processes at Gold Single Crystal Surfaces Using Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy
Li C.-Y., Dong J.-C., Jin X., Chen S., Panneerselvam R., Rudnev A.V., Yang Z.-L., Li J.-F., Wandlowski T., Tian Z.-Q.
Article, Journal of the American Chemical Society, 2015, DOI Link
View abstract ⏷
Identifying the intermediate species in an electrocatalytic reaction can provide a great opportunity to understand the reaction mechanism and fabricate a better catalyst. However, the direct observation of intermediate species at a single crystal surface is a daunting challenge for spectroscopic techniques. In this work, electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) is utilized to in situ monitor the electrooxidation processes at atomically flat Au(hkl) single crystal electrode surfaces. We systematically explored the effects of crystallographic orientation, pH value, and anion on electrochemical behavior of intermediate (AuOH/AuO) species. The experimental results are well correlated with our periodic density functional theory calculations and corroborate the long-standing speculation based on theoretical calculations in previous electrochemical studies. The presented in situ electrochemical SHINERS technique offers a unique way for a real-time investigation of an electrocatalytic reaction pathway at various well-defined noble metal surfaces.
Electrochemical shell-isolated nanoparticle-enhanced raman spectroscopy: Correlating structural information and adsorption processes of pyridine at the Au(hkl) single crystal/solution interface
Li J.-F., Zhang Y.-J., Rudnev A.V., Anema J.R., Li S.-B., Hong W.-J., Rajapandiyan P., Lipkowski J., Wandlowski T., Tian Z.-Q.
Article, Journal of the American Chemical Society, 2015, DOI Link
View abstract ⏷
Electrochemical methods are combined with shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) for a comprehensive study of pyridine adsorption on Au(111), Au(100) and Au(110) single crystal electrode surfaces. The effects of crystallographic orientation, pyridine concentration, and applied potential are elucidated, and the formation of a second pyridine adlayer on Au(111) is observed spectroscopically for the first time. Electrochemical and SHINERS results correlate extremely well throughout this study, and we demonstrate the potential of EC-SHINERS for thorough characterization of processes occurring on single crystal surfaces. Our method is expected to open up many new possibilities in surface science, electrochemistry and catalysis. Analytical figures of merit are discussed.
Photochemical method for decoration of silver nanoparticles on filter paper substrate for SERS application
Conference paper, Journal of Raman Spectroscopy, 2014, DOI Link
View abstract ⏷
A facile photoreduction strategy to attach silver nanoparticles on filter paper (AgNPs@FP) to form surface-enhanced Raman scattering (SERS) substrate array was proposed and examined. As prepared, SERS substrate array was applied to detect low concentration of adenine and other nucleobases in aqueous solutions. In addition, the formed SERS substrate array allows mass analysis of aqueous samples with a requirement of only 10 μL in sample volume. To optimize and understand the parameters in preparations, factors such as the concentrations of citrate and silver nitrate, photoreduction time, and concentration of sodium hydroxide were varied and examined. Para-nitrothiophenol was used as a Raman probe molecule and scanning electron microscope (SEM) images of the substrates were used to explore the influences of experimental factors in the preparation of SERS array. Results indicated that silver ions could be effectively reduced and deposited in/on filter paper with the presence of citrate. The formed AgNPs@FP exhibits a three-dimensional structure as the particles formed on and beneath the surface of the cellulosic fibers could be observed. Deposition of analyte on restricted substrate array rendered reproducible results and the spot-to-spot SERS intensity varied within 8%. At optimal conditions, the substrate enhancement factor approached 107. We demonstrated that the filter paper-based SERS substrates can be used as a suitable tool for biological analysis, and a limit of detection better than 160 nM was obtained in detection of adenine molecules in aqueous solutions with a linear range up to 20 μM. Copyright © 2014 John Wiley & Sons, Ltd.
Sensitive cylindrical SERS substrate array for rapid microanalysis of nucleobases
Article, Analytical Chemistry, 2012, DOI Link
View abstract ⏷
In this work, a cylindrical-substrate array for surface-enhanced Raman scattering (SERS) measurements was developed to enable analysis of nucleobases in a few microliters of liquid. To eliminate uncertainties associated with SERS detection of aqueous samples, a new type of cylindrical SERS substrate was designed to confine the aqueous sample at the tip of the SERS probe. Poly(methyl methacrylate) (PMMA) optical fibers in a series of different diameters were used as the basic substrate. A solution of poly(vinylidene fluoride)/ dimethylformamide (PVDF/DMF) was used to coat the tip of each fiber to increase the surface roughness and facilitate adsorption of silver nanoparticles (AgNPs) for enhancing Raman signals. A chemical reduction method was used to form AgNPs in and on the PVDF coating layer. The reagents and reaction conditions were systematically examined with the aim of estimating the optimum parameters. Unlike the spreading of aqueous sample on most SERS substrates, particularly flat ones, the new SERS substrates showed enough hydrophobicity to restrict aqueous sample to the tip area, thus enabling quantitative analysis. The required volume of sample could be as low as 1 μL with no need for a drying step in the procedure. By aligning the cylindrical SERS substrates into a solid holder, an array of cylindrical substrates was produced for mass analysis of aqueous samples. This new substrate improves both reproducibility and sensitivity for detection in aqueous samples. The enhancement factor approaches 7 orders in magnitude with a relative standard error close to 8%. Using the optimized conditions, nucleobases of adenine, cytosine, thymine, and uracil could be detected with limits approaching a few hundreds nanomolar in only a few microliters of solution. © 2012 American Chemical Society.
