Venkataramaniah Kamisetti

Aqueous based reflux method for green synthesis of nanostructures: Application in CZTS synthesis

Graphical abstract

Flexible Ag–C60 nano-biosensors based on surface plasmon coupled emission for clinical and forensic applications

The relatively low sensitivity of fluorescence detection schemes, which are mainly limited by the isotropic nature of fluorophore emission, can be overcome by utilizing surface plasmon coupled emission (SPCE). In this study, we demonstrate directional emission from fluorophores on flexible Ag-C60 SPCE sensor platforms for point-of-care sensing, in healthcare and forensic sensing scenarios, with at least 10 times higher sensitivity than traditional fluorescence sensing schemes. Adopting the highly sensitive Ag-C60 SPCE platform based on glass and novel low-cost flexible substrates, we report the unambiguous detection of acid-fast Mycobacterium tuberculosis (Mtb) bacteria at densities as low as 20 Mtb mm(-2); from non-acid-fast bacteria (e.g., E. coli and S. aureus), and the specific on-site detection of acid-fast sperm cells in human semen samples. In combination with the directional emission and high-sensitivity of SPCE platforms, we also demonstrate the utility of smartphones that can replace expensive and cumbersome detectors to enable rapid hand-held detection of analytes in resource-limited settings; a much needed critical advance to biosensors, for developing countries.

One-Step Synthesis of Colloidal Quantum Dots of Iron Selenide Exhibiting Narrow Range Fluorescence in the Green Region

The instantaneous isolation of green fluorescent colloidal quantum dots of iron selenide capped with biocompatible oleic acid is reported in this study. These iron-containing quantum dots also serve as a safe alternative to the conventionally used metal-chalcogenide systems in which the heavy metal component is usually toxic. The isolated colored colloidal solutions exhibited intense green fluorescence on exposure to ultraviolet light, which was also confirmed by photoluminescence spectroscopy. The isolated product was subjected to dynamic light scattering and transmission electron microscopy, and the particles were found to exhibit spherical morphology with an average diameter of 6–8 nm, confirming the isolation of quantum dots. The isolated iron selenide quantum dots have promising potential towards bioimaging and sensing, due to the biocompatible coating of oleic acid and iron, which also allows possibility of further chemical derivatization.

Vanadium pentoxide nanoparticles based saturable absorbers

Vanadium pentoxide (V2O5) nanoparticles were synthesized by solution combustion method. The particle size reduction of the as-synthesized sample was achieved through ball milling. The as-synthesized and the ball milled samples were further characterized using XRD, TEM, EDX, UV-Visible and FTIR spectroscopy. Open-aperture z-scan technique was employed to study the nonlinear optical behavior of the synthesized samples and the commercially available V2O5 (bulk) using a second harmonic (532 nm) of Nd: YAG laser with 15 ns pulse width. We observed that the nonlinear absorption process was dependent on particle size as the synthesized and ball milled nanoparticles exhibited saturable absorption behavior while bulk V2O5 exhibited a transition to reverse saturable absorption behavior at the same incident laser intensity.

Femtogram Level Sensitivity achieved by Surface Engineered Silica Nanoparticles in the Early Detection of HIV Infection

We have engineered streptavidin labelled Europium doped fluorescent silica nanoparticles which significantly increased sensitivity without compromising the specificity of the immunoassay. As a proof of concept, a time resolved fluorescence based sandwich immunoassay was developed to detect HIV-1 p24 antigen in clinical specimens. The detection range of the silica nanoparticle based immunoassay (SNIA) was found to be between 0.02 to 500 pg/mL in a linear dose dependent manner. SNIA offers 1000 fold enhancement over conventional colorimetric ELISA. Testing of plasma samples that were HIV negative showed no false positive results in the detection of HIV-1 p24 antigen. This highly sensitive p24 assay can help improve blood safety by reducing the antibody negative window period in blood donors in resource limited settings where nucleic acid testing is not practical or feasible. This technology can also be easily transferred to a lab-on-a-chip platform for use in resource limited settings and can also be easily adopted for the detection of other antigens.

Fluorescent silver nanoparticle based highly sensitive immunoassay for early detection of HIV infection

For the first time, we have engineered streptavidin labeled fluorescent silver nanoparticles for their application in immunosensing of biomolecules which will significantly increase sensitivity without compromising the specificity. A computational perspective for understanding the efficiency of the conjugation process is provided as a proof of concept. The fluorescence based sandwich immunoassay was demonstrated to detect HIV-1 p24 antigen in clinical specimens with improved sensitivity and specificity. The detection range of the fluorescent silver nanoparticle-based immunoassay (FSNIA) was found to be between 10 and 1000 pg mL−1 in a linear dose dependent manner. False positives were not observed with plasma samples from healthy adults (HIV−ve), hepatitis B (HBV+ve) and hepatitis C (HCV+ve). Plasma samples that were HIV−ve showed no interference with detection of HIV-1 p24 antigen. This technology can be used in resource limited settings and easily adopted for the detection of other pathogen antigens.

Carbon nanotubes as novel spacer materials on silver thin-films for generating superior fluorescence enhancements via surface plasmon coupled emission

In this study, we report the first time implementation of single/multi-walled carbon nanotubes, as novel spacer materials, on a silver (Ag) thin-film based surface plasmon coupled emission (SPCE) platform. The engineered Ag-CNT SPCE substrates enabled the realization of up to ~10-fold enhancement in fluorescence signal intensity, of the rhodamine b dye. This study addresses the issue that, while many of the biochemical sensing strategies are based on fluorescence, they are all fundamentally limited by the isotropic nature of the phenomenon that results in low signal collection efficiency ( 50% signal collection efficiency. Considering the easy functionalization of these carbon nano-allotropes, and their high sensitivity; the economical Ag-CNT SPCE platforms can be effectively extended towards sensing applications.

Enhanced dissolution characteristics of piroxicam–Soluplus® nanosuspensions

ABSTRACT In the present study, we have prepared nanosuspensions of piroxicam using Soluplus® as the matrix using aqueous-based conventional ball milling. The comparative physico-chemical characteristics were assessed using PXRD (powder X-ray diffraction), DSC (differential scanning calorimetry), FESEM (field emission scanning electron microscopy) and FTIR (Fourier transform infrared spectroscopy) analysis, indicating the nanoformulations displayed lower crystallinity with no chemical interactions between the drug and polymer molecules. The cytotoxicity of the formulations was established from MTT assay performed on Caco-2 cell lines. The release rate of piroxicam from various ratios of drug/polymer nanoparticles was investigated using a USP paddle apparatus. The nanoformulations exhibited higher release of the drug in comparison with the pure drug. The enhanced dissolution characteristics of the drug in the nanoformulations could possibly increase the anti-inflammatory effects of the drug owing to superior bioavailability characteristics.

Effect of sulfur doping on thermoelectric properties of tin selenide – A first principles study

In this work we present the thermoelectric properties of tin selenide (SnSe) and sulfur doped tin selenide(SnSe(1-x)Sx, x= 0.125 and 0.25) obtained using first principles calculations. We investigated the electronic band structure using the FP-LAPW method within the sphere of the density functional theory. Thermoelectric properties were calculated using BOLTZTRAP code using the constant relaxation time approximation at three different temperatures 300, 600 and 800 K. Seebeck coefficient (S) was found to decrease with increasing temperature, electrical conductivity (σ/τ) was almost constant in the entire temperature range and thermal conductivity (κ/τ) increased with increasing temperature for all samples. Sulfur doped samples showed enhanced seebeck coefficient, decreased thermal conductivity and decreased electrical conductivity at all temperatures. At 300 K, S increased from 1500 µV/K(SnSe) to 1720μV/K(SnSe0.75S0.25), thermal conductivity decreased from 5 × 1015 W/mKs(SnSe) to 3 × 1015 W/mKs(SnSe0.75S0....

Surface plasmon coupled emission as a novel analytical platform for the sensitive detection of cysteine

Abstract Thiolated amino acids are biologically important molecules due to their role in protein folding and structure. One such molecule is cysteine (Cys), which acts as a biomarker for diseases like cancer, HIV, sepsis, etc., making its rapid detection imperative and essential. In this study, we report the sensitive detection of the thiolated amino acid Cys, from the non-thiolated amino acid arginine (Arg), using the novel surface plasmon coupled emission (SPCE) platform, characterized with high signal-to-noise ratios. Our studies were performed on the conventional silver (Ag) SPCE substrate, where Cys was detected to a nanomolar level, which is a major improvement to the previously reported level of sensitivity. This can be attributed to the highly sensitive SPCE platform and the unique thiol-Ag interactions associated specifically with Cys. We have also shown the role and influence of the coating process on sensitivity of detection and substantiated the advantages of SPCE over the SPR-based strategy of detection. The simplistic and economical SPCE platform enabled the sensitive detection of Cys that is of biological and medical relevance.