Vipul Bansal

Templated synthesis of single-component polymer capsules and their application in drug delivery

We report a general and facile approach for the fabrication of a new class of monodispersed, single-component and thick-walled polymer nanocapsules via the single-step assembly of macromolecules in solid core/mesoporous shell (SC/MS) silica particle templates, followed by cross-linking of the macromolecules and removal of the SC/MS templates. The general applicability of this approach is demonstrated by the preparation of nanocapsules using various polymers, including synthetic polyelectrolytes, polypeptides, and polypeptide-drug conjugates. The potential of doxorubicin (Dox)-loaded poly(L-glutamic acid) nanocapsules in tumor therapy applications is demonstrated via in vitro degradation experiments, which show a near-linear release of the Dox in the presence of a lysosomal hydrolase, nanocapsule uptake by human colorectal tumor cells, and delivery of the anticancer drug into the tumor cells, leading to tumor cell death.

Fungus-mediated biosynthesis of silica and titania particles

The synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures, pressures and neutral pH. This is exemplified by biosilicification in marine organisms such as diatoms while laboratory-based synthesis of silica involves extreme temperature and pH conditions. We show here that silica and titania particles may be produced by challenging the fungus Fusarium oxysporum with aqueous anionic complexes SiF62− and TiF62− respectively. Extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of crystalline titania particles while calcination at 300 °C is required for crystallization of silica.

Biosynthesis of zirconia nanoparticles using the fungus Fusarium oxysporum

Zirconia nanoparticles may be produced by challenging the fungus Fusarium oxysporum with aqueous ZrF62− anions; extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of nanocrystalline zirconia. Extracellular hydrolysis of the metal anions by cationic proteins of molecular weight around 24 to 28 kDa, which are rather similar in nature to silicatein, is shown to be responsible for the synthesis of zirconia nanoparticles, opening up the exciting possibility of large-scale biological synthesis of technologically important oxide materials.

Electrochemical Control of Photoluminescence in Two-Dimensional MoS2 Nanoflakes

Two-dimensional (2D) transition metal dichalcogenide semiconductors offer unique electronic and optical properties, which are significantly different from their bulk counterparts. It is known that the electronic structure of 2D MoS2, which is the most popular member of the family, depends on the number of layers. Its electronic structure alters dramatically at near atomically thin morphologies, producing strong photoluminescence (PL). Developing processes for controlling the 2D MoS2 PL is essential to efficiently harness many of its optical capabilities. So far, it has been shown that this PL can be electrically or mechanically gated. Here, we introduce an electrochemical approach to actively control the PL of liquid-phase-exfoliated 2D MoS2 nanoflakes by manipulating the amount of intercalated ions including Li(+), Na(+), and K(+) into and out of the 2D crystal structure. These ions are selected as they are crucial components in many bioprocesses. We show that this controlled intercalation allows for large PL modulations. The introduced electrochemically controlled PL will find significant applications in future chemical and bio-optical sensors as well as optical modulators/switches.

Aptamer-Controlled Reversible Inhibition of Gold Nanozyme Activity for Pesticide Sensing

This study addresses the need for rapid pesticide (acetamiprid) detection by reporting a new colorimetric biosensing assay. Our approach combines the inherent peroxidase-like nanozyme activity of gold nanoparticles (GNPs) with high affinity and specificity of an acetamiprid-specific S-18 aptamer to detect this neurotoxic pesticide in a highly rapid, specific, and sensitive manner. It is shown that the nanozyme activity of GNPs can be inhibited by its surface passivation with target-specific aptamer molecules. Similar to an enzymatic competitive inhibition process, in the presence of a cognate target, these aptamer molecules leave the GNP surface in a target concentration-dependent manner, reactivating GNP nanozyme activity. This reversible inhibition of the GNP nanozyme activity can either be directly visualized in the form of color change of the peroxidase reaction product or can be quantified using UV-visible absorbance spectroscopy. This approach allowed detection of 0.1 ppm acetamiprid within an assay time of 10 min. This reversible nanozyme activation/inhibition strategy may in principle be universally applicable for the detection of a range of environmental or biomedical molecules of interest.

Shape dependent electrocatalytic behaviour of silver nanoparticles

The electrochemical and electrocatalytic behaviour of silver nanoprisms, nanospheres and nanocubes of comparable size in an alkaline medium have been investigated to ascertain the shape dependent behaviour of silver nanoparticles, which are an extensively studied nanomaterial. The nanomaterials were synthesised using chemical methods and characterised with UV-visible spectroscopy, transmission electron microscopy and X-ray diffraction. The nanomaterials were immobilised on a substrate glassy carbon electrode and characterised by cyclic voltammetry for their surface oxide electrochemistry. The electrocatalytic oxidation of hydrazine and formaldehyde and the reduction of hydrogen peroxide were studied by performing cyclic voltammetric and chronoamperometric experiments for both the nanomaterials and a smooth polycrystalline macrosized silver electrode. In all cases the nanomaterials showed enhanced electrocatalytic activity over the macro-silver electrode. Significantly, the silver nanoprisms that are rich in hcp lamellar defects showed greater activity than nanospheres and nanocubes for all reactions studied.

Gold Nanoparticle-Decorated Keggin Ions/TiO2 Photococatalyst for Improved Solar Light Photocatalysis

We demonstrate a facile localized reduction approach to synthesizing a Au nanoparticle-decorated Keggin ion/TiO(2) photococatalyst for improved solar light photocatalysis application. This has been achieved by exploiting the ability of TiO(2)-bound Keggin ions to act as a UV-switchable, highly localized reducing agent. Notably, the approach proposed here does not lead to contamination of the resultant cocatalyst with free metal nanoparticles during aqueous solution-based synthesis. The study shows that for Keggin ions (phosphotungstic acid, PTA), being photoactive molecules, the presence of both Au nanoparticles and PTA on the TiO(2) surface in a cocatalytic system can have a dramatic effect on increasing the photocatalytic performance of the composite system, as opposed to a TiO(2) surface directly decorated with metal nanoparticles without a sandwiched PTA layer. The remarkable increase in the photocatalytic performance of these materials toward the degradation of a model organic Congo red dye correlates to an increase of 2.7-fold over that of anatase TiO(2) after adding Au to it and 4.3-fold after introducing PTA along with Au to it. The generalized localized reduction approach to preparing TiO(2)-PTA-Au cocatalysts reported here can be further extended to other similar systems, wherein a range of metal nanoparticles in the presence of different Keggin ions can be utilized. The composites reported here may have wide potential implications toward the degradation of organic species and solar cell applications.

Quasi-cubic magnetite/silica core-shell nanoparticles as enhanced MRI contrast agents for cancer imaging

Development of magnetic resonance imaging (MRI) contrast agents that can be readily applied for imaging of biological tissues under clinical settings is a challenging task. This is predominantly due to the expectation of an ideal MR agent being able to be synthesized in large quantities, possessing longer shelf life, reasonable biocompatibility, tolerance against its aggregation in biological fluids, and high relaxivity, resulting in better contrast during biological imaging. Although a repertoire of reports address various aforementioned issues, the previously reported results are far from optimal, which necessitates further efforts in this area. In this study, we demonstrate facile large-scale synthesis of sub-100 nm quasi-cubic magnetite and magnetite/silica core-shell (Mag@SiO2) nanoparticles and their applicability as a biocompatible T2 contrast agent for MRI of biological tissues. Our study suggests that silica-coated magnetite nanoparticles reported in this study can potentially act as improved MR contrast agents by addressing a number of aforementioned issues, including longer shelf life and stability in biological fluids. Additionally, our in vitro and in vivo studies clearly demonstrate the importance of silica coating towards improved applicability of T2 contrast agents for cancer imaging.

Detect, Remove and Reuse: A New Paradigm in Sensing and Removal of Hg (II) from Wastewater via SERS-Active ZnO/Ag Nanoarrays

Mercury being one of the most toxic heavy metals has long been a focus of concern due to its gravest threats to human health and environment. Although multiple methods have been developed to detect and/or remove dissolved mercury, many require complicated procedures and sophisticated equipment. Here, we describe a simple surface enhanced Raman spectroscopy (SERS) active ZnO/Ag nanoarrays that can detect Hg(2+), remove Hg(2+) and can be fully regenerated, not just from Hg(2+) contamination when heat-treated but also from the SERS marker when exposed to UV as a result of the self-cleaning ability of this schottky junction photocatalyst. The sensors are also highly selective because of the unique way mercury (among other chemicals) interacts with Ag nanoparticles, thus reducing its SERS activity.

Bicontinuous cubic phase nanoparticle lipid chemistry affects toxicity in cultured cells

Gaining an increased understanding of the toxicity of new lipid nanoparticle formulations such as the class of cubic and hexagonal phase forming nanomaterials called cubosomes™ and hexosomes™ is crucial for their development as therapeutic agents. Surprisingly, the literature on the in vitro and in vivo toxicity of cubic and hexagonal phase forming lipid nanoparticles is negligible, despite a rapidly growing number of publications on their potential use in various therapeutic applications. In this work we have developed methods to study the in vitro cytotoxicity of two chemically distinct cubic phase nanoparticle dispersions using the lipids glycerol monooleate and phytantriol respectively. We have found that the toxicity of phytantriol cubosomes is considerably greater than that of glycerol monooleate cubosomes. The increased toxicity of phytantriol appears to result from its greater ability to disrupt the cellular membrane (haemolytic activity) and oxidative stress. This finding has significant impact and can provide useful guidelines for those conducting further research on the use of cubic phase forming lipids for therapeutic and diagnostic applications both in vitro and in vivo.