Precise conversion electron intensities of low energy gamma transitions for efficiency calibration of electron detectors.

Precise energies and relative intensities of gamma transitions and conversion electrons in the electron capture decay of 153Gd have been determined independently with our well-tested and optimized gamma and electron spectrometers - a large-volume (60 cc) HPGe detector and a mini-orange electron transporter paired to a Si(Li) detector, respectively. The experimental internal conversion coefficients of the gamma transitions in 153Eu have been determined using Normalized Peak to Gamma method and compared with the theoretical values adopted by Nuclear Data Sheets to assign multipolarities of all the transitions. The precise internal conversion electron intensities of the low energy transitions can be used as standards for calibration purposes of electron detectors and spectrometers.

Computational design and clinical demonstration of a copper nanocluster based universal immunosensor for sensitive diagnostics.

Nanoparticle based sensors are good alternatives for non-enzymatic sensing applications due to their high stability, superior photoluminescence, biocompatibility and ease of fabrication, with the only disadvantage being the cost of the synthesis process (owing to the expensive precursors and infrastructure). For the first time, we report the design of an immunosensor employing streptavidin conjugated copper nanocluster, developed at a much lower cost compared to other nanomaterials like noble metal nanoparticles and quantum dots. Using in silico tools, we have tried to establish the dynamics of conjugation of nanocluster to the streptavidin protein, based on EDC-NHS coupling. The computational simulations have successfully explained the crucial role played by the components of the immunosensor leading to an efficient design capable of high sensitivity. In order to demonstrate the functioning of the Copper Nanocluster ImmunoSensor (CuNIS), HIV-1 p24 biomarker test was chosen as the model assay. The immunosensor was able to achieve an analytical limit of detection of 23.8 pg mL-1 for HIV-1 p24 with a linear dynamic range of 27-1000 pg mL-1. When tested with clinical plasma samples, CuNIS based p24 assay showed 100% specificity towards HIV-1 p24. With the capability of multiplexed detection and a cost of fabrication 100 times lower than that of the conventional metal nanoclusters, CuNIS has the potential to be an essential low-cost diagnostic tool in resource-limited settings.

Sub-picogram level sensitivity in HIV diagnostics achieved with the europium nanoparticle immunoassay through metal enhanced fluorescence.

We describe a novel application of Metal Enhanced Fluorescence (MEF) to immunoassays for boosting the signal through a single step modification of the europium nanoparticle based immunoassay with addition of gold nanoparticles. The new limit of detection was found to be 0.19 pg mL-1 which was much lower than that of the conventional assay which was around 1.80 pg mL-1, thus achieving a ten-fold increase in the limit of detection of p24, an early biomarker for HIV infections. Real world applications of the new technique were demonstrated with the commercially available Perkin Elmer Alliance kits greatly improving their sensitivity limits, thus demonstrating that the sensitivity and reproducibility of this approach are as good as those of high-end, sensitive immunoassays. The results of this study pave the way for the development of a highly sensitive screening protocol based on any fluorescent nanoparticle based immunoassay.

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.

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

The aqueous based reflux method useful for the green synthesis of nanostructures is described in detail. In this method, the parameters: the order of addition of precursors, the time of the reflux and the cooling rate should be optimized in order to obtain the desired phase and morphology of the nanostructures. The application of this method is discussed with reference to the synthesis of CZTS nanoparticles which have great potential as an absorber material in the photovoltaic devices. The highlights of this method are:•Simple.•Low cost.•Aqueous based.

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.

C60 as an active smart spacer material on silver thin film substrates for enhanced surface plasmon coupled emission.

In this study, we present the use of C60 as an active spacer material on a silver (Ag) based surface plasmon coupled emission (SPCE) platform. In addition to its primary role of protecting the Ag thin film from oxidation, the incorporation of C60 facilitated the achievement of a 30-fold enhancement in the emission intensity of rhodamine B (RhB) fluorophore. The high signal yield was attributed to the unique π-π interactions between C60 thin films and RhB, which enabled efficient transfer of energy of RhB emission to Ag plasmon modes. Furthermore, minor variations in the C60 film thickness yielded large changes in the enhancement and angularity properties of the SPCE signal, which can be exploited for sensing applications. Finally, the low-cost fabrication process of the Ag-C60 thin film stacks render C60 based SPCE substrates ideal, for the economic and simplistic detection of analytes.