Rakesh Kumar Singhal

Preparation of multicolor emitting carbon dots for HeLa cell imaging

We have synthesized biocompatible fluorescent carbon dots (CDs) by a one-step hydrothermal method using Solanum tuberosum (potato) as a raw material. The CDs were characterized by UV-visible, fluorescence, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS) and high-resolution transmission electron microscopic (HR-TEM) techniques. We found that the carbonization of potato at ∼170 °C for 12 h produces highly fluorescent CDs of 0.2–2.2 nm size. The synthesized CDs are well dispersed in water and exhibited strong blue and bright blue emissions under UV illumination (λex = 302, 365 nm). The CDs showed a strong emission peak at 455 nm at an excitation wavelength of 374 nm. The CDs acted as fluorescent probes for multicolor (blue, green and red) imaging of HeLa cells and the CDs did not induce cell death, which indicates that the CDs are biocompatible and nontoxic to HeLa cells. Therefore, the CDs can be used as probes for cell-imaging applications in vitro and in vivo.

One-step green synthetic approach for the preparation of multicolor emitting copper nanoclusters and their applications in chemical species sensing and bioimaging.

One-step green microwave synthetic approach was developed for the synthesis of copper nanoclusters (Cu NCs) and used as a fluorescent probe for the sensitive detection of thiram and paraquat in water and food samples. Unexpectedly, the prepared Cu NCs exhibited strong orange fluorescence and showed emission peak at 600 nm, respectively. Under optimized conditions, the quenching of Cu NCs emission peak at 600 nm was linearly proportional to thiram and paraquat concentrations in the ranges from 0.5 to 1000 µM, and from 0.2 to 1000 µM, with detection limits of 70 nM and 49 nM, respectively. In addition, bioimaging studies against Bacillus subtilis through confocal fluorescence microscopy indicated that Cu NCs showed strong blue and green fluorescence signals, good permeability and minimum toxicity against the various bacteria species, which demonstrates their potential feasibility for chemical species sensing and bioimaging applications.

Microwave assisted synthesis of tyrosine protected gold nanoparticles for dual (colorimetric and fluorimetric) detection of spermine and spermidine in biological samples

In this work, tyrosine-protected gold nanoparticles (Tyr-Au NPs) were fabricated by one-step reduction of Au3+ ion using Tyr as a reducing and capping agent under microwave irradiation. The Tyr-Au NPs were successfully used as a dual probe for colorimetric and fluorescence turn-on assays of spermine and spermidine in biological samples. Upon addition of spermine and spermidine, the characteristic surface plasmon resonance (SPR) band of Tyr-Au NPs was red-shifted to 596 and 616nm and the emission peak (Tyr) at 410nm was gradually increased with increasing concentration of both analytes, confirming the aggregation of Tyr-Au NPs induced by spermine and spermidine, which results to restore fluorescence of Tyr on the surfaces of Au NPs. In addition, it shows high selectivity for sensitive detection of prostatic cancer biomarkers spermine and spermidine in real clinical applications with reduced sample preparations.

Colorimetric and fluorescence “turn-on” methods for the sensitive detection of bromelain using carbon dots functionalized gold nanoparticles as a dual probe

Bromelain is a group of sulfhydryl-containing proteolytic enzymes, which exhibit antiedematous, anti-inflammatory, antithrombotic and fibrinolytic activity. Herein, we report a dual-mode nanosensor with both colorimetric and fluorescence detection of bromelain using carbon dots capped gold nanoparticles (CDs-Au NPs) as a dual probe. Upon the addition of bromelain to the CDs-Au NPs dispersed in an aqueous solution, the probe shows a dramatic color change from red to blue and a remarkable ratiometric fluorescence enhancement, which are based on two distance-dependent phenomena: the color change of CDs-Au NPs and the displacement of the CDs from the surface of the Au NPs. A red-shift in the surface plasmon resonance (SPR) peak from 523 to 576 nm and an enrichment of the fluorescence emission at 425 nm was observed, which resulted in good linear relationships between A576/A523 and I/I0, and at concentrations of 1.0–260 μM (R2 = 0.991) and 1.0–100 nM (R2 = 0.993), the limits of detection for bromelain at a signal-to-noise ratio of 3 were 18.9 nM and 0.52 nM using UV-visible and fluorescence spectroscopy, respectively. This dual probe allows for the quantification and detection of bromelain in real samples such as pineapple extracts and biological samples.

Spatial distribution and accumulation of 226Ra, 228Ra, 40K and 137Cs in bottom sediments of Mumbai Harbour Bay

The present work shows the activity levels of 226Ra, 228Ra, 40K and 137Cs in bottom sediments collected from eight locations of Mumbai Harbour Bay. The study has shown that 40K and 228Ra concentration is nearly uniform throughout the studied area while 226Ra and 137Cs are more concentrated in the southern regions of the bay. The significant variation in the activity levels of radionuclides within the study site might be due to their sorption/desorption processes onto the surface of sediment materials. The low mean value of 226Ra/228Ra ratio (0.72) in the sediments indicates that 238U has relatively greater solubility and mobility than 232Th. Similarly, low activity ratio (0.18) for 137Cs/40K reflects the presence of very high content of 40K in sediment due to presence of primary minerals in sediment. Silt and clay were reported to dominate the composition of the sediment. A significant positive correlation between 226Ra and 228Ra and 137Cs and 40K suggest a similar origin of their geochemical sources and identical behavior during transport in the sediment system.

Metabolic and biochemical changes caused by gamma irradiation in plants

Applications involving radioisotopes and radiations reveal a great promise particularly for the welfare of the society. However, in the event of a nuclear accident, the direct and indirect effect of radionuclide and radiation transfers in soil–plant–air environment are envisaged on almost all the components of the food chain. It also assumes significance as we often overlook the fact that radiations, emitted by any radioisotope although cannot be seen or felt, interacts with matter and could alter its biochemical, biophysical and biological characteristics. The interaction of ionizing radiation with human body and consequent biological effects are well characterized and quantified using data derived from the radiation workers and/or the nuclear accidents around the world. However, radiation impact on agriculture viz a viz economic productivity are not well understood and available data is scanty, scattered and inconclusive. At the plant level the effects could be visualized at morphological, biochemical, physiological and/or biophysical levels, where the magnitude of the effected change depends heavily on the exposure dose, soil, farm management and other environmental variables. This review attempts to collate and critically analyze the available researches on how the ionizing radiation might interact with crops at the whole plant or tissue or cell level to affect economic yield under various edaphic variables where not only the productivity but also the quality of the agri-produce may become vulnerable.

Evaluation of doses from ionising radiation to non-human species at Trombay, Mumbai, India.

In order to meet the proposed regulatory compliances for the protection of non-human species from the ionising radiation, a comprehensive dose-evaluation process for terrestrial and aquatic biota was worked out at Trombay. During this work, dose rate (external and internal) from ionising radiation to the terrestrial plants and marine organisms (mixed varieties of fish) was evaluated by estimating the concentration of anthropogenic ((137)Cs, (90)Sr) and natural radionuclides ((238)U, (232)Th and (40)K) in environmental matrices, such as soil, vegetation, sea water and sediment. The samples were processed as per the International Atomic Energy Agency protocol for the estimation of naturally occurring and anthropogenic radionuclides. The average values of radiation exposure to the terrestrial plants for (40)K, (90)Sr, (137)Cs, (232)Th and (238)U were 632.8 +/- 40.5, 167.4 +/- 48.2, 691.2 +/- 29.9, 48769 +/- 13203 and 1801 +/- 1495 microGy y(-1), respectively. In the case of marine organisms (fish), the maximum external exposure was 195 microGy y(-1) due to (40)K concentration in bottom sediment, whereas the minimum was 0.004 microGy y(-1) due to (137)Cs in sea water. Internal exposure to fish was maximum (700 microGy y(-1)) due to (40)K, whereas the minimum of 0.12 microGy y(-1) was due to (90)Sr. Considering the dose limit of 10 mGy d(-1) (3.65 Gy y(-1)), proposed by the US Department of Energy, evaluated radiation exposure (external + internal) and dose rate in the present study to the terrestrial plants and marine organisms are orders of magnitude less.

Selective separation of iron from uranium in quantitative determination of traces of uranium by alpha spectrometry in soil/sediment sample

During this work, controlled redox potential methodology was adopted for the complete separation of traces of uranium from the host matrix of mixed hydroxide of Iron. Precipitates of Fe(+2) and Fe(+3) along with other transuranic elements were obtained from acid leached solution of soil by raising the pH to 9 with 14N ammonia solution. The concentration of the uranium observed in the soil samples was 200-600 ppb, whereas in sediment samples, the concentration range was 61-400 ppb.

Mg2+ ion as a tuner for colorimetric sensing of glyphosate with improved sensitivity via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles

Silver nanoparticles based analyte recognition has received a wide range of interest in the assaying of trace target analytes in environmental samples. In this work, a simple colorimetric assay was developed for the rapid and selective detection of glyphosate in water and food samples via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles (MNBZ-Ag NPs) using Mg2+ ions as a tuner and trigger. Initially, Ag NPs were synthesized with sodium borohydrate as a reducing agent and capped with MNBZ which showed a yellow color. The addition of Mg2+ ions did not cause aggregation of MNBZ-Ag NPs, but the subsequent addition of glyphosate resulted a drastic decrease in interparticle distance through complex formation between MNBZ-Ag NPs–Mg2+ ion and glyphosate, yielding a color change from yellow to orange-red, which results in a red-shift in the characteristic surface plasmon resonance (SPR) peak from 399 to 517 nm. Based on this, sensitive and selective detection of glyphosate was achieved with a limit of detection of 17.1 nM. This probe was successfully applied to detect glyphosate in water and food samples, which proves a very simple and selective platform for on-site monitoring of glyphosate in agriculture samples.

Simultaneous colorimetric detection of four drugs in their pharmaceutical formulations using unmodified gold nanoparticles as a probe

We have developed a simple UV-visible spectrometric method for parallel detection of four drugs (venlafaxine, imipramine, amlodipine and alfuzosin) by using unmodified gold nanoparticles (Au NPs) as a colorimetric probe. The citrate was self-assembled onto the Au NPs to form a probe that undergoes a color change from red to blue by the addition of the four drugs. It is presumed that the color change is a result of the aggregation of the Au NPs induced by the four drugs, resulting a red-shift in their absorption spectra from 521 to 653, 695, 688 and 636 nm for venlafaxine, imipramine, amlodipine and alfuzosin, respectively. The method was validated in the concentration range of 0.001–100 μM, where it demonstrated good linearity (R2 = 0.997, 0.997, 0.995 and 0.998) with limits of detection in the range of 0.9–9.3 nM. The aggregation of the Au NPs induced by the four drugs was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The applicability of the method was demonstrated by determining the drugs contents in pharmaceutical and biological samples (urine and plasma).