Hirakendu Basu

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).

Highly efficient removal of TiO2 nanoparticles from aquatic bodies by silica microsphere impregnated Ca-alginate

A novel material, “calcium-alginate–silica microsphere” (Cal-Alg–SM) beads, was developed by impregnating silica microspheres in calcium alginate. These beads were highly efficient in the removal of TiO2 nanoparticles from aquatic bodies without disturbing their physicochemical characteristics. The optimum composition of the beads was 10% loading of silica microspheres into a 4% Ca-alginate matrix. They were formed by the controlled addition of a homogenised mixture of SMs and Na-alginate solution into 0.4 M CaCl2 solution. Cal-Alg–SM beads were characterized by measuring zeta potential, recording Fourier Transform infrared spectra and scanning electron microscopy coupled with energy dispersive spectrometry mapping both before and after the uptake. Uptake studies carried out in batch mode showed that Cal-Alg–SM beads are very effective for the removal of TiO2 nanoparticles in the pH range of 3–5 and the sorption was more than 90% in the concentration range of 10–500 μg mL−1. Beads were successfully tested with lake and groundwater samples spiked with TiO2 nanoparticles. The sorption isotherm was seen to follow the Langmuir model and the uptake capacity evaluated was 29.9 mg g−1. The mechanism of sorption was proposed based on the zeta potential values of SMs and TiO2 nanoparticles at different pH values.

Ammonium molybdate phosphate functionalized silicon dioxide impregnated in calcium alginate for highly efficient removal of 137Cs from aquatic bodies

In this study, silica functionalized with ammonium molybdate phosphate (AMP) impregnated in calcium alginate (SiO2-AMP–Cal-Alg) was developed for the highly efficient removal of radioactive cesium from aquatic media. During the synthesis, a compact protective interlayer of silica was deliberately constructed to stabilize the AMP. The optimum composition of the SiO2-AMP–Cal-Alg beads was evaluated as 6% AMP modified SiO2 loaded into 4% calcium alginate. Because of high ion exchange capacity of the AMP functional layer, the SiO2-AMP–Cal-Alg has high removal efficiency (>91%) of radioactive cesium from 137Cs spiked solutions (3000–35 000 Bq L−1) and contaminated seawater. Batch experiments revealed that adsorption equilibrium was rapidly achieved within 30 min and the maximum sorption capacity was up to 37.52 mg g−1. Kinetic models and adsorption isotherm equations (Langmuir/Freundlich) were used to fit the experiment data for describing the sorption process. These SiO2-AMP–Cal-Alg beads are proposed to hold great promise for the clean-up of radiocesium contaminated water around nuclear facilities after nuclear accidents.

Microwave-assisted synthesis of water-soluble Eu3+ hybrid carbon dots with enhanced fluorescence for the sensing of Hg2+ ions and imaging of fungal cells

In this work, a fluorescent nanosensor based on Eu3+ hybrid carbon dots (Eu3+-CDs) was fabricated by single-step microwave heating using ethylenediaminetetraacetic acid (EDTA), L-cysteine and europium(III) nitrate as reagents. The as-synthesized Eu3+ hybrid CDs exhibited a characteristic fluorescence emission peak at 427 nm upon excitation at a wavelength of 343 nm. Upon the addition of Hg2+ ions, the emission peak of the Eu3+ hybrid CDs was quenched and a linear relationship was observed between the fluorescence quenching intensity and the concentration of Hg2+ ions in the range of 5.0–250 μM with a detection limit of 2.2 μM. The developed nanosensor not only enables selective and sensitive detection of Hg2+ ions but also offers excellent applications in the confocal imaging of fungal cells (Fomitopsis sp.), which holds great promise in biomedical applications.

Assessment of radioactivity in the soil samples from Imphal city, India, and its radiological implication

The radioactivity concentration and the natural gamma absorbed dose rates of the terrestrial radionuclides (226Ra, 232Th, and 40K) have been determined in soil samples collected from twenty different locations of Imphal city, India, using high-purity germanium detector. The range of activity concentration of 226Ra, 232Th, and 40K in the soil from the studied areas varies from 30.3 Bq/kg (Phayeng) to 155.5 Bq/kg (Lamphel), 21.2 Bq/kg (Yairipok) to 257.1 Bq/kg (Lamphel), and 287.4 Bq/kg (Uchiwa) to 2209.3 Bq/kg (Changangei) with overall mean values of 94.1 Bq/kg, 146.5 Bq/kg and 1222.9 Bq/kg, respectively. The absorbed dose rate and annual effective outdoor dose in the study area range from 61.0 nGyh−1 and 0.4 mSv (Laphupat Tera) to 294.4 nGyh−1 and 1.1 mSv (Lamphel) with an average value of 182.9 nGyh−1 and 1.1 mSv. The external hazard index ranged from 0.4 to 1.8 with an average of 1.1. It was significant in 12 locations as it exceeded unity.

Association and migration behavior of trace metals with humus colloidal particles in aquatic subsurface medium

In this study, we investigate the influence of humic acid on the migration of trace metals (Fe, Ca, Mg, Cu, Sr, Zn) in the saturated subsurface medium. Migration study was carried out in a specially fabricated soil column. The results of this study demonstrate that presence of humic acid in the colloidal form play a key role in mobility of trace metals in aquatic subsurface medium. Migration of elements like Fe, Ca, Mg, Cu were facilitated by the presence of the humus colloids whereas presence of Zn, Sr in the hydrated form was evident from the experimental results. The observation was explained based on the linear attenuation coefficient (LAC).