Swadeshmukul Santra

Biochemically functionalized silica nanoparticles

In this report, we demonstrate the biochemical modification of silica based nanoparticles. Both pure and dye-doped silica nanoparticles were prepared, and their surfaces were modified with enzymes and biocompatible chemical reagents that allow them to function as biosensors and biomarkers. The nanoparticles produced in this work are uniform in size with a 1.6% relative standard deviation. They have a pure silica surface and can thus be modified easily with many biomolecules for added biochemical functionality. Specifically, we have modified the nanoparticle surfaces with enzyme molecules (glutamate dehydrogenase (GDH) and lactate dehydrogenase (LDH)) and a biocompatible reagent for cell membrane staining. Experimental results show that the silica nanoparticles are a good biocompatible solid support for enzyme immobilization. The immobilized enzyme molecules on the nanoparticle surface have shown excellent enzymatic activity in their respective enzymatic reactions. The nanoparticle surface biochemical functionalization demonstrates the feasibility of using nanoparticles for biosensing and biomarking applications.

Rapid and effective labeling of brain tissue using TAT-conjugated CdS∶Mn/ZnS quantum dots

TAT (a cell penetrating peptide)-conjugated CdSratioMn/ZnS quantum dots (Qdots), intra-arterially delivered to a rat brain, rapidly (within a few minutes) labeled the brain tissue without manipulating the blood-brain-barrier (BBB). Qdot loading was sufficiently high that it allowed a gross fluorescent visualization of the whole rat brain using a low power hand-held UV lamp. Histological data clearly showed that TAT-conjugated Qdots migrated beyond the endothelial cell line and reached the brain parenchyma. Qdots without TAT did not label the brain tissue confirming the fact that TAT peptide was necessary to overcome the BBB. The present study clearly demonstrated the possibility of delivering a large amount of Qdot-based imaging agents to the brain tissue.

Nanobioimaging and sensing of infectious diseases

Abstract New methods to identify trace amount of infectious pathogens rapidly, accurately and with high sensitivity are in constant demand to prevent epidemics and loss of lives. Early detection of these pathogens to prevent, treat and contain the spread of infections is crucial. Therefore, there is a need and urgency for sensitive, specific, accurate, easy-to-use diagnostic tests. Versatile biofunctionalized engineered nanomaterials are proving to be promising in meeting these needs in diagnosing the pathogens in food, blood and clinical samples. The unique optical and magnetic properties of the nanoscale materials have been put to use for the diagnostics. In this review, we focus on the developments of the fluorescent nanoparticles, metallic nanostructures and superparamagnetic nanoparticles for bioimaging and detection of infectious microorganisms. The various nanodiagnostic assays developed to image, detect and capture infectious virus and bacteria in solutions, food or biological samples in vitro and in vivo are presented and their relevance to developing countries is discussed.

TAT conjugated, FITC doped silica nanoparticles for bioimaging applications

Water-in-oil (w/o) microemulsion synthesis of 70 nm size monodisperse TAT (a cell penetrating peptide, CPP) conjugated, FITC (fluorescein isothiocyanate) doped silica nanoparticles (TAT-FSNPs) is reported; human lung adenocarcinoma (A549) cells (in vitro) and rat brain tissue (in vivo) were successfully labeled using TAT-FSNPs.

Fluorescent Nanoparticle Probes for Cancer Imaging

Optical imaging technique has strong potential for sensitive cancer diagnosis, particularly at the early stage of cancer development. This is a sensitive, non-invasive, non-ionizing (clinically safe) and relatively inexpensive technique. Cancer imaging with optical technique however greatly relies upon the use of sensitive and stable optical probes. Unlike the traditional organic fluorescent probes, fluorescent nanoparticle probes such as dye-doped nanoparticles and quantum dots (Qdots) are bright and photostable. Fluorescent nanoparticle probes are shown to be very effective for sensitive cancer imaging with greater success in the cellular level. However, cancer imaging in an in vivo setup has been recently realized. There are several challenges in developing fluorescent nanoparticle probes for in vivo cancer imaging applications. In this review, we will discuss various aspects of nanoparticle design, synthesis, surface functionalization for bioconjugation and cancer cell targeting. A brief overview of in vivo cancer imaging with Qdots will also be presented.

Silica-based multimodal/multifunctional nanoparticles for bioimaging and biosensing applications

In the last decade, the field of nanoparticle (NP) technology has attracted immense interest in bioimaging and biosensing research. This technology has demonstrated its capability in obtaining sensitive data in a noninvasive manner, promising a breakthrough in early-stage cancer diagnosis, stem cell tracking, drug delivery, pathogen detection and gene delivery in the near future. However, successful and wide application of this technology relies greatly on robust NP engineering and synthesis methodologies. The NP development steps involve design, synthesis, surface modification and bioconjugation. Each of these steps is critical in determining the overall performance of NPs. It is desirable to obtain NPs that are highly sensitive, stable, imageable, biocompatible and targetable. It is also desirable to obtain multimodal/multifunctional NPs that will enable imaging/sensing of the target using multiple imaging/sensing modalities. In this review, we focus on silica NPs that have been developed for biosensing applications and silica-based multimodal/multifunctional NPs for bioimaging applications.

Fabrication and testing of a magnetically actuated micropump

A micropump has been fabricated in a modular fashion using silicone elastomers, which are cheap, tough, durable and inert. For modular assembly, molded bodies capture a thin valve membrane, and a diaphragm is glued on top. After attaching a novel, magnetically oriented permanent magnet composite membrane, as well as inlet and outlet tubes, the pump is activated by an electromagnet. Under a differential water head, the valve opened at ∼600 Pa. A pump 15 mm in diameter, 20 mm long, weighing 10 g, had a maximum pump rate for air of 260 μl/min at 1.9 W.

Gold-Speckled Multimodal Nanoparticles for Noninvasive Bioimaging

In this report the synthesis, characterization, and functional evaluation of a multimodal nanoparticulate contrast agent for noninvasive imaging through both magnetic resonance imaging (MRI) and photoacoustic tomography (PAT) is presented. The nanoparticles described herein enable high resolution and highly sensitive three-dimensional diagnostic imaging through the synergistic coupling of MRI and PAT capabilities. Gadolinium (Gd)-doped gold-speckled silica (GSS) nanoparticles, ranging from 50 to 200 nm, have been prepared in a simple one-pot synthesis using nonionic microemulsions. The photoacoustic signal is generated from a nonuniform, discontinuous gold nanodomains speckled across the silica surface, whereas the MR contrast is provided through Gd incorporated in the silica matrix. The presence of a discontinuous speckled surface, as opposed to a continuous gold shell, allows sufficient bulk water exchange with the Gd ions to generate a strong MR contrast. The dual imaging capabilities of the particles have been demonstrated through in silicio and in vitro methods. The described particles also have the capacity for therapeutic applications including the thermal ablation of tumors through the absorption of irradiated light.

Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots.

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.

Excited-state intramolecular proton transfer in 2-(2′-aminophenyl) benzimidazole

Abstract An excited-state intramolecular proton transfer process has been studied in 2-(2′-aminophenyl)benzimidazole (2-APBI) in different solvents using steady state and time resolved fluorescence spectroscopy. Semi-empirical quantum mechanical calculations (AM1 and CNDO/S-CI) have also been carried out. Dual fluorescence (normal and tautomer fluorescence) is observed in non-polar solvents. Based on the fluorescence excitation spectra recorded at different wavelengths, it is concluded that the normal fluorescence originates from rotamer II or IV and tautomer fluorescence from rotamer V. The tautomer fluorescence intensity decreases with increase in the polarity and hydrogen bonding capacity of the solvents. Different fluorescence lifetimes of the normal and tautomer bands indicate that rotamer I and II are not in equilibrium in the excited state. Semi-empirical quantum mechanical calculations have shown that the rotamer II is slightly more stable than the rotamer I in the ground state whereas in polar solvents, the stability of rotamer II increases due to extra solvation. For isolated molecule the activation energy for the interconversion of rotamers is 2.71 kJ mol−1 in the ground state, whereas it is 36 kJ mol−1 in the first excited singlet state.