Subhadip Mondal

A simplistic approach to green future with eco-friendly luminescent carbon dots and their application to fluorescent nano-sensor ‘turn-off’ probe for selective sensing of copper ions

Zero-dimensional fluorescent nanoparticles having specificity as molecular probe appears to be strategically balanced fluorescent nano-probes. In this work, purified lemon extract and l-arginine have been thermally coupled for the extremely acute detection of Cu2+ in aqueous medium. The Cu2+ ions may be captured by the amino groups on the surface of the nano-sensor to form cupric ammine complex resulting in quenched fluorescence via an inner filter effect. Our proposed nano-probe is N-doped carbon dots (NCDs) which are efficiently selective as fluorescent chemosensor due to enormous binding affinity towards Cu2+ in a wide range of concentration (0.05-300μM) within a few minutes.

Green approach to photoluminescent carbon dots for imaging of gram-negative bacteria Escherichia coli

Fluorescent carbon dots, zero-dimensional nanomaterials with surface ligands, have been studied extensively over the past few years in biolabelling or fluorescence-based live cell assays. In the past, synthetic organic dyes have been used as cell tracking materials, but they have severe limitations; fluorescent carbon dots may pave the way to biolabelling and cell imaging. In this work, green fluorescent carbon dots have been synthesized from a green source, gram, without any sort of covalent or ionic modifications. These gram-derived carbon dots are unique with respect to synthetic commercial cell-tracking dyes as they are non-toxic, cell internalization occurs quickly, and they have excellent bioconjugation with bacterial cells. Our aim is to establish these carbon dots in a biolabelling assay with its other physicochemical features like the tunable luminescence property, high degree of water solubility and low toxicity, towards various environments (wide range of pH, high ionic strength). Our study introduces a new perspective on the commercialization of carbon dots as a potential alternative to synthetic organic dyes for fluorescence-based cell-labelling assays.

Synthesis of polydopamine-coated halloysite nanotube-based hydrogel for controlled release of a calcium channel blocker

A stimuli-triggered drug delivery vehicle has been synthesized by self-polymerization of dopamine (DA) on the outer surface of halloysite nanotubes (HNT) followed by gelation via alginate. DA in aqueous medium is made to adhere on outer surface of lumen and self-polymerizes in alkaline medium. Self-polymerized DA (PDA)-coated HNTs have been incorporated into alginate hydrogel and ionically crosslinked. Scanning electron microscope and transmission electron microscope images imply a coating of PDA of 12–17 nm in thickness on the HNT surface. The rheological behavior of the hydrogels as prepared can reveal their shear thinning character and they show sufficient gel strength (prominent difference between elastic and loss modulus). The thermal decay profile from thermogravimetric analysis implies the superior thermal stability with respect to pristine alginate. The action of PDA as an additional effective gelator has been noticed and confirmed by swelling trends in aqueous media. Drug loading has been achieved by two procedures: one is in situ loading and the other one is post-loading. It has been noticed that in situ loading of drug molecules during polymerization process of DA on HNT surface shows better controlled release feature than post-loading. Such release behavior was also tuned by altering the synthesis parameters.

Mechanically robust dual responsive water dispersible-graphene based conductive elastomeric hydrogel for tunable pulsatile drug release

Nanohybrid hydrogels based on pristine graphene with enhanced toughness and dual responsive drug delivery feature is opening a new era for smart materials. Here pristine graphene hydrogels are synthesized by in situ free radical polymerization where graphene platelets are the nanobuiliding blocks to withstand external stress and shows reversible ductility. Such uniqueness is a mere reflection of rubber-like elasticity on the hydrogels. These nanobuilding blocks serve also the extensive physisorption which enhances the physical crosslinking inside the gel matrix. Besides the pH-responsive drug release features, these hydrogels are also implemented as a pulsatile drug delivery device. The electric responsive drug release behaviours are noticed and hypothesized by the formation of conducting network in the polyelectrolytic hydrogel matrix. The hydrogels are also tested as good biocompatibility and feasible cell-attachment during live-dead cell adhesion study. The drug release characteristics can also be tuned by adjusting the conducting filler loading into the gel matrix. As of our knowledge, this type of hydrogels with rubber-like consistency, high mechanical property, tunable and dual responsive drug delivery feature and very good human cell compatible is the first to report.

Starch functionalized biodegradable semi-IPN as a pH-tunable controlled release platform for memantine

Sequentially prepared semi-interpenetrating polymer network (semi-IPN) has been developed here via Michael type addition of acrylic acid (AA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) on to starch. The semi-IPN hydrogel have proficiency in fast water imbibition towards gel network and swelling tunable character with pH alteration in ambient condition. The synthesized gel has been characterized by Fourier transformed infrared spectroscopy (FTIR) to confirm Michael type grafting of monomers on to starch. The surface morphology, observed from Scanning Electron Microscopy (SEM) exhibited corrugated rough surface on hydrogel which enhances the fast water uptake feature by anomalous Fickian case II diffusion mechanism. Grafting reaction also improves its thermal stability which has been confirmed by thermogravimetric analysis (TGA). Biodegradation study with hen egg lysozyme medium reveals the accelerated enzymatic scission of the starch backbone and progressive mass loss. Degradation of the hydrogel around 60% of its primary mass has been observed within 7days. The physicochemical characterizations of this hydrogel suggest this as a promising pH-tunable, biodegradable candidate for control drug delivery vehicle.

Zinc and nitrogen ornamented bluish white luminescent carbon dots for engrossing bacteriostatic activity and Fenton based bio-sensor

Carbon dots with heteroatom co-doping associated with consummate luminescence features are of acute interest in diverse applications such as biomolecule markers, chemical sensing, photovoltaic, and trace element detection. Herein, we demonstrate a straightforward, highly efficient hydrothermal dehydration technique to synthesize zinc and nitrogen co-doped multifunctional carbon dots (N, Zn-CDs) with superior quantum yield (50.8%). The luminescence property of the carbon dots can be tuned by regulating precursor ratio and surface oxidation states in the carbon dots. A unique attribution of the as-prepared carbon dots is the high monodispersity and robust excitation-independent emission behavior that is stable in enormously reactive environment and over a wide range of pH. These N, Zn-CDs unveils captivating bacteriostatic activity against gram-negative bacteria Escherichia coli. Furthermore, the excellent luminescence properties of these carbon dots were applied as a platform of sensitive biosensor for the detection of hydrogen peroxide. Under optimized conditions, these N, Zn-CDs reveals high sensitivity over a broad range of concentrations with an ultra-low limit of detection (LOD) indicating their pronounced prospective as a fluorescent probe for chemical sensing. Overall, the experimental outcomes propose that these zero-dimensional nano-dots could be developed as bacteriostatic agents to control and prevent the persistence and spreading of bacterial infections and as a fluorescent probe for hydrogen peroxide detection.

Selective cross-linking of carboxylated acrylonitrile butadiene rubber and study of their technological compatibility with poly(ethylene-co-methyl acrlylate) by means of mechanical, thermal, and chemical analysis

Technologically compatible blend becomes an interesting arena of polymer blend industry for their significant properties and fascinating morphologies. This work encompasses the fabrication of technologically compatible blend through melt blending of poly(ethylene-co-methyl acrylate) (EMA) and carboxylated acrylonitrile butadiene rubber (XNBR) in five different ratios to study their compatibility by employing various techniques, like Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). To observe the reinforcing effect of blend specific amount of metal oxide, zinc oxide (ZnO) was incorporated into the system. Curing characterization, FTIR, and morphological analysis confirm that ZnO selectively forms cross-link with XNBR through the coordination complex and does not show any substantial effect on EMA. DMTA reveals high-temperature relaxation of the carboxylic salt of XNBR phase which reinforces the EMA/XNBRZnO-cross-linked blends and also verified by FTIR analysis. Although DSC shows single glass transition temperature (Tg) for all blend systems in between the Tg of pure polymer component, DMTA confirms the presence of two different Tg for plastic and rubber phases with close proximity, specifying technological compatibility in blend compounds. Increasing XNBR improves tensile strength of blends by sacrificing elongation at break. Therefore, our aim is to tune and optimize the blend features by judicial mixing of EMA and XNBR to mitigate the blend failure during service tenure and develop a novel technologically compatible blend.Graphical abstract

Carbon Nanostructures Based Mechanically Robust Conducting Cotton Fabric for Improved Electromagnetic Interference Shielding

Herein, an intelligent cotton fabric was fabricated using a non-ionic surfactant based macro structured carbonaceous coating through the ‘knife-over-roll’ technique. The developed novel fabric was tested as flexible, mechanically robust with prolonged chemical/moisture resistance. Various characterization techniques were thoroughly used to analyze the fabric. The as-prepared fabric shows an outstanding electromagnetic interference (EMI) shielding efficiency (SE) of about 21.5 dB even at the lowest possible coating thickness (0.20 mm) where the highest EMI SE of 30.8 dB is obtained at only 0.30 mm coating thickness over the X-band frequency range (8.2-12.4 GHz), possibly due to the three-dimensionally interconnected network structure of conducting carbon particles. The micro-computed tomography disclosed the porous architecture and “void-filler” arrangement within the fabrics. For the betterment of serviceability and practicability of the coated fabric, the water tolerance and contact angle studies were conducted. The relatively high contact angle than pure cotton fabric, and excellent water resistance after coating ensure improved endurance for external or industrial uses. Therefore, this proof-of-construct manifests commercialization of the developed fabric for multipurpose applications in a facile, less-hazardous and economical way.

Preparation and Properties of Halloysite Nanotubes/Poly(ethylene methyl acrylate)-Based Nanocomposites by Variation of Mixing Methods

ABSTRACT Halloysite nanotube-based inorganic–organic polymer nanocomposite has been developed with improved mechanical strength in one direction by solution mixing followed by melt mixing. Melt mixing, solution mixing, and melt-cum-solution mixing were performed to optimize the mechanical strength of the nanocomposites. The field emission scanning electron microscopic images and small-angle X-ray scattering spectrum can support the unidirectional array of halloysite nanotubes in the matrix. The tensile properties revealed that solution–melt mixing is the most desired way to develop clay-based nanocomposites. Thermal characterizations implied that thermal stability was improved after nanoclay incorporation. Dynamic mechanical analysis showed the flow properties and the “Payne effect” of the nanocomposites. GRAPHICAL ABSTRACT

Polysaccharide and poly(methacrylic acid) based biodegradable elastomeric biocompatible semi-IPN hydrogel for controlled drug delivery

Nanoparticles embedded semi-interpenetrating (semi-IPNs) polymeric hydrogels with enhanced mechanical toughness and biocompatibility could have splendid biomedical acceptance. Here we propose poly(methacrylic acid) grafted polysaccharide based semi-IPNs filled with nanoclay via in situ Michael type reaction associated with covalent crosslinking with N,N-methylenebisacrylamide (MBA). The effect of nanoclay in the semi-IPN hydrogel has been investigated which showed significant improvement of mechanical robustness. Meanwhile, the hydrogels showed reversible ductility up to 70% in response to cyclic loading-unloading cycle which is an obvious phenomenon of rubber-like elasticity. The synthesized semi-IPN hydrogel show biodegradability and non-cytotoxic nature against human cells. The live-dead assay showed that the prepared hydrogel is a viable platform for cell growth without causing severe cell death. The in vitro drug release study in psychological pH (pH = 7.4) reveals that the controlled drug release phenomena can be tuned by simulating the environment pH. Such features in a single hydrogel assembly can propose this as high performance; biodegradable and non-cytotoxic 3D scaffold based promising biomaterial for tissue engineering.