Department of Chemistry

Inspite of being a plentiful and inexpensive metal, the use of copper nanoclusters is limited in bio-medical research because of their toxicity and low stability due to its easily oxidizable nature. It also has a low quantum yield. The interdisciplinary publication of the researchers at SRM University-AP successfully addressed these constraints, resulting in strong fluorescence, superior colloidal stability, and non-toxicity of copper nanoclusters for bio imaging applications. The research was a collective work of Dr Manjunatha Thondamal from the Department of Biological Sciences, Dr Mahesh Kumar Ravva and Dr Sabyasachi Chakrabortty from the Department of Chemistry along with their PhD scholars; Mr Kumar Babu Busi, Ms Kotha Jyothi, Ms Sheik Haseena, Ms Shamili Bandaru and Ms Jyothi Priyanka Ghantasala.

The article titled ‘“Engineering colloidally stable, highly fluorescent and nontoxic Cu nanoclusters via reaction parameter optimization” was featured in the prestigious Q1 journal RSC Advances (IF: 4.036), published by the ‘Royal Society of Chemistry’. They successfully prepared the protein stabilised copper nanoclusters inside the aqueous medium with exceptional optical properties. To the best of their knowledge, the reported colloidal stability and quantum yield of their as-synthesized Cu NCs are the highest reported in the literature, where the emission wavelength is in the red region. Also, optimised copper nanoclusters showed excellent biocompatibility towards solid cancer cell lines and C. elegans as in vitro and in vivo environments. Thus, these red colour luminescent copper nanoclusters were becoming a suitable fluorescent probe for deep tissue penetration, photodynamic, photothermal and diagnostic applications.

Abstract of the Research

Metal Nanoclusters (NCs) composed of the least number of atoms (few to tens) became very attractive for their emerging properties owing to their ultrasmall size. Preparing copper nanoclusters (Cu NCs) in an aqueous medium with high emission properties, strong colloidal stability, and low toxicity has been a long-standing challenge. Although they are earth-abundant and inexpensive, they are comparatively less explored due to their limitations such as ease of surface oxidation, poor colloidal stability, and high toxicity. To overcome these constraints, we established a facile synthetic route by optimizing the reaction parameters, especially altering the effective concentration of the reducing agent to influence their optical characteristics. The improvement of photoluminescence intensity and superior colloidal stability was modelled from a theoretical standpoint. Moreover, the as-synthesized Cu NCs showed a significant reduction of toxicity in both in vitro and in vivo models. The possibilities of using such Cu NCs as a diagnostic probe towards C. elegans were explored. Also, the extension of this approach towards improving the photoluminescence intensity of the Cu NCs on other ligand systems was demonstrated.

The Department of chemistry has always been a dynamic space for innovative and inspiring research. Recently, Assistant Professor Dr Nimai Mishra published his fifteenth research paper from SRM university-AP as a corresponding author. The paper is titled Post-synthesis Treatment with Lead Bromide for Obtaining Near Unity Photoluminescence Quantum Yield and Ultra-Stable Amine Free CsPbBr 3 Perovskite Nanocrystal and is published in the Q1 journal, The Journal of Physical Chemistry C with an impact factor of 4.2. The research group is comprised of Dr Mishra’s PhD students Mr Syed Akhil, Dr V G Vasavi Dutt, and Mr Rahul Singh. This is the group’s fifth consecutive article published in the American Chemical Society.

About the article

The article reports Ultra-Stable and Near Unity Photoluminescence Quantum Yield Amine Free CsPbBr 3 Perovskite Nanocrystal Post-synthesis Treatment with Lead Bromide. Herein, the researchers have introduced a simple lead bromide (PbBr 2 ) post-treatment process to achieve the near-unity PLQY (>95 %) in amine-free CsPbBr 3 PNCs. Furthermore, PbBr 2 treatment enables these materials to drastically improve stability in different environmental conditions (polar solvents, light, and heat). In addition, a green-emitting down- converted light-emitting diode was fabricated using PbBr 2 treated amine-free CsPbBr 3 PNCs, which shows its considerable prospects for display applications. Thus, the results of the research will promote these PbBr 2 treated amine-free inorganic perovskite nanocrystals for commercial development in optoelectronic applications.

Explanation of the research

Cesium lead halide perovskite nanocrystals (PNCs) have been the flourishing area of research in the field of photovoltaic and optoelectronic applications because of their excellent optical and electronic properties. Mainly, cesium lead bromide (CsPbBr 3 ) NCs with bright green photoluminescence (PL) and narrow full-width at half-maximum (FWHM) of < 25 nm is the most desirable for television displays and green-emitting LEDs. Improving the photoluminescence quantum yields (PLQYs) and optimizing the stability have been challenging tasks to promote cesium lead halide (CsPbX3; X=Cl, Br and I) perovskite nanocrystals (PNCs) for real optoelectronic applications. In recent years, the amine- free synthesis route has become an option for making stable CsPbX 3 PNCs.

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Proteins are the most vital life forms which maintain close coordination with almost living activities through their biological functions. Nevertheless, in most cases, proteins suffer from low charge (electron) transfer efficiency as they are mainly made of insulating organic molecules. The interdisciplinary research publication, of Dr Sabyasachi Mukhopadhyay and Dr Sabyasachi Chakrabortty from the Department of Physics & Department of Chemistry respectively, along with their PhD scholars: Ms Ashwini Nawade, Mr Kumar Babu Busi and Ms Kunchanapalli Ramya, envisions the molecular-level understanding of the charge transport behaviour of various protein-metal nanocluster hybrid.

The article titled ‘“Improved Charge Transport across Bovine Serum Albumin – Au Nanoclusters’ Hybrid Molecular Junction” was featured in the prestigious Q1 journal ACS Omega (IF: 3.512), published by the ‘American Chemical Society’. They successfully incorporated Gold Nanoclusters inside the protein backbone leading to an increase in their conductivity. This will provide new avenues for the rational design of bioelectronic devices with optimized features. The BSA-Au cluster has been a promising model for bioelectronic functionalities. With an increase in their current carrying capacity, they can be used for many more applications, especially as the interface between tissue and organ in biocompatible devices. The research team is also planning to work with various protein dopants to understand their charge transport mechanism. These studies will help in using the protein for various applications mainly in bioimplants or biosensors for drug testing and diagnostics purposes.

Abstract of the Research

Proteins, a highly complex substance, have been the essential element in the living organism where various applications are envisioned due to their biocompatible nature. Apart from protein’s biological functions, contemporary research mainly focuses on their evolving potential associated with nanoscale electronics. Here, we report one type of chemical doping process in model protein molecules (BSA) to modulate its electrical conductivity by incorporating metal (Gold) nanoclusters on the surface or within it. The as-synthesized Au NCs incorporated inside the BSA (Au 1 to Au 6) were optically well characterized with UV-Vis, time-resolved photoluminescence (TRPL), X-ray photon spectroscopy, and high-resolution transmission electron microscopy techniques. The PL quantum yield for Au 1 is 6.8% whereas Au 6 is 0.03%. In addition, the electrical measurements showed ~10-fold enhancement of conductivity in Au 6 where maximum loading of Au NCs was predicted inside the protein matrix. We observed a dynamic behaviour in the electrical conduction of such protein-nanocluster films, which could have real-time applications in preparing biocompatible electronic devices.

Surface-enhanced Raman Spectroscopy (SERS) is a nuanced chemical technique that amplifies the Raman scattering of molecules by utilising plasmonic nanostructured materials. SERS operates as a powerful detection tool that allows for the structural fingerprinting of a molecule. The ultra-high sensitivity and selectivity of the process offer it a vast array of applications in surface and interface chemistry, nanotechnology, biology, biomedicine, food science, environmental analysis and other areas.

Dr J P Raja Pandiyan and his PhD scholar, Ms Arunima Jinachandran from the Department of Chemistry have been keenly involved in exploring the possibilities of SERS technology in food science and other fields. The safety and quality concerns related to food were the primary reasons that impelled them to step into this domain. Their article “Surface-enhanced Raman spectroscopy for food quality and safety monitoring” was published in the book Nanotechnology Applications for Food Safety and Quality Monitoring, published by Elsevier. The article was published in collaboration with Dr Selvaraju Kanagarajan from the Swedish University of Agricultural Sciences.

As an analytical technique, SERS possesses several advantages such as non-destructive, sensitive, and selective. In the chapter, the necessity, and applications of SERS in food science are elaborately discussed. They have also discussed all the possible food contaminants and how to identify them using SERS to ensure food quality. This book will serve as an enlightening read to research groups who are working on Raman, surface-enhanced Raman spectroscopy, analytical chemistry, and food quality analysis.