Mukesh Kumar Kumawat

Multifunctional graphene quantum dots for combined photothermal and photodynamic therapy coupled with cancer cell tracking applications

Graphene quantum dots (GQDs) have gained enormous attention due to their unique optical properties and emerging employment in biology. Herein, we report the synthesis of highly crystalline GQDs having superior physicochemical and near infrared (NIR)-responsive properties using simple waste, withered leaves of Ficus racemosa, an Indian fig tree, as a carbon source. A considerably large production yield was obtained (ca. 18%) with a competitive quantum yield of 14.16%. The GQDs exhibited excellent dispersibility in both organic as well as aqueous solvents and were highly photostable. High-resolution transmission electron microscopy showed the presence of ultra-small honey-combed as well as self-assembled GQDs. Cell cycle analysis using flow cytometry and biocompatibility studies showed that the GQDs were cytocompatible and were used as in situ labeling probes for normal as well as cancer cells. Furthermore, upon irradiation with an 808 nm laser (0.5 W cm−2), a concentration-dependent photothermal response and production of reactive oxygen species were observed. Confocal laser scanning microscopy showed that GQDs did not lose their fluorescence despite continuous laser irradiation (30 min) on MDA-MB-231 breast cancer cells. Thus, cell death could be traced using GQD-labeled MDA-MB-231 cells post-therapy using the photostability of GQDs, unlike photo-bleachable organic dyes. Thus, a low-cost, scalable, green-synthesis of GQDs with highly efficient optical properties will pave the way for new therapeutics and imaging in biomedical cancer research.

Graphene Quantum Dots for Cell Proliferation, Nucleus Imaging, and Photoluminescent Sensing Applications

We report a simple one-pot microwave assisted “green synthesis” of Graphene Quantum Dots (GQDs) using grape seed extract as a green therapeutic carbon source. These GQDs readily self-assemble, hereafter referred to as “self-assembled” GQDs (sGQDs) in the aqueous medium. The sGQDs enter via caveolae and clathrin-mediated endocytosis and target themselves into cell nucleus within 6–8 h without additional assistance of external capping/targeting agent. The tendency to self-localize themselves into cell nucleus also remains consistent in different cell lines such as L929, HT-1080, MIA PaCa-2, HeLa, and MG-63 cells, thereby serving as a nucleus labelling agent. Furthermore, the sGQDs are highly biocompatible and act as an enhancer in cell proliferation in mouse fibroblasts as confirmed by in vitro wound scratch assay and cell cycle analysis. Also, photoluminescence property of sGQDs (lifetime circa (ca.) 10 ns) was used for optical pH sensing application. The sGQDs show linear, cyclic and reversible trend in its fluorescence intensity between pH 3 and pH 10 (response time: ~1 min, sensitivity −49.96 ± 3.5 mV/pH) thereby serving as a good pH sensing agent. A simple, cost-effective, scalable and green synthetic approach based sGQDs can be used to develop selective organelle labelling, nucleus targeting in theranostics, and optical sensing probes.

Benzothiazoles-substituted tetraphenylethylenes: synthesis, structure, aggregation-induced emission and biological studies

New tetraphenylethylene (TPE) bearing benzothiazoles at the ortho-position to OH and OCH3 groups, 1a and 1b, respectively, were prepared. Benzothiazole tetraphenylethylenes 1a/1b were synthesized by the acid-catalysed condensation reaction of an appropriate di-aldehyde, such as 5,5′-(2,2-diphenylethylene-1,1-diyl)bis(2-hydroxybenzaldehyde) 2a or 5,5′-(2,2-diphenylethylene-1,1-diyl)bis(2-methoxybenzaldehyde) 2b, with 2-aminothiophenol. Compound 1a exhibited an excited state intramolecular proton transfer (ESIPT) phenomenon. The photophysical properties of compounds 1a/1b in solution and aggregated form, along with their structure–property relationships, were comparatively investigated. The study showed that the substituent groups on TPE at the ortho position to benzothiazole have a great influence on the electronic structure, molecular packing, and aggregation-induced emission properties. Moreover, the cell viability studies by MTT assay and fluorescence cell imaging experiments proved the low-toxicity of 1a and that it can be used as a potential contrasting agent in cell imaging studies.

Highly selective optical and reversible dual-path chemosensor for cyanide detection and its application in live cells imaging

A new biocompatible fluorescent receptor 1 was synthesized by conjugating diaminomaleonitrile (DMN) with benzothiazole unit, and characterized by single X-ray. In DMF/water (1:1, v/v), the receptor 1 showed a selectivity turn-on fluorescence at 517nm in the presence of CN-. Receptor 1 showed a detection limit down to 0.16µM without any interference from other tested anions. The reversibility and reusability of 1 for the detection of CN- ion was also tested for five cycles indicating the probe 1 could be used in a reversible manner. Importantly, the receptor 1 showed excellent cells viability and was successfully applied for the detection of CN- in live mouse fibroblast cells L929 cells.

Evolution of thiol-capped gold nanoclusters into larger gold nanoparticles under electron beam irradiation

We report in situ transformation of glutathione-capped red-fluorescent gold nanoclusters (AuNCs) into larger gold nanoparticles (AuNPs) embedded on a copper grid under high energy electron beam of Field Emission Gun Transmission Electron Microscope (FEG-TEM). Electron beam irradiation causes coalescing of individual finer AuNCs into bigger discrete AuNPs as a function of electron dose rate and time. The coalescence was closely studied over time and the mechanism is discussed. The study will help to understand the structural and morphological changes that occur in AuNCs inside FEG-TEM due to prolonged electron beam exposure.