A Combined Spectroscopic and Theoretical Analysis of Plasmonic Silver Nanoparticle Sensor Towards Detailed Microscopic Understanding of Heavy Metal Detection

Plasmonic nanoparticles are of great importance owing to their highly responsive ‘localized surface plasmon resonance’ (LSPR) behaviour to self-agglomeration/aggregation leading to the development of various nanosensors. Herein, we demonstrated the definite self-assembly of citrate functionalized silver nanoparticles (AgNPs) into a one-dimensional linear chain in presence of charged lead ions (Pb²⁺), one of the most toxic heavy metal pollutants. We have explored detail mechanism using a variety of spectroscopic tools and electron microscopy. The self-aggregation of AgNPs leads to the generation of new LSPR modes due to coupling of nearby existing modes. The conclusion of our experimental findings is duly supported by our developed numerical modelling based on the quasi-static approximation that the generated new LSPR modes are solely due to formation of chain-like aggregation of AgNPs. We have also monitored the LSPR spectra in the presence of other metal ions; however, only Pb²⁺ found to give such unique self-assembled geometry may due to its high interaction affinity with citrate. These findings play a key role for citrate functionalised AgNPs to be used as a low cost highly selective and sensitive lead ion sensor for potential application in industrial lead pollution monitoring. We have further varied several sensor parameters such as AgNPs size, concentration, and the allowed reaction time for it to be practically implemented as an efficient lead sensor meeting the Environmental Protection Agency recommendations.

Graphical abstract

The possible sensing mechanism of citrate-functionalized silver nanoparticles towards Pb2?+?followed by unique chain-like aggregation for potential atmospheric and industrial lead pollution monitoring.

     

Influence of the Bradyrhizobium japonicum Hydrogenase on the Growth of Glycine and Vigna Species

The effect of the Bradyrhizobium japonicum hydrogenase on nitrogen fixation was evaluated by comparing the growth of Vigna and Glycine species inoculated with a Hup mutant and its Hup⁺ revertant. In all experiments, the growth of plants inoculated with the strain without hydrogenase was at least equal to the growth of the strain with hydrogenase. For Glycine usuriensis and Glycine max cv. Hodgson in liquid culture, the growth was higher with the Hup⁻ strain. It is possible that reduced rates of nitrogen fixation in the presence of hydrogenase are due to O₂ depletion caused by the hydrogen oxidizing, since the oxygen pressure in the air appears to be a limiting factor of symbiotic nitrogen fixation in the soybean.     

Energetics of interaction of oligopeptide (lac 53-57) with DNA base sequences and origin of sequence-specific recognition

Computer model building with a dynamic energy minimization procedure is used here to study the interaction of a pentapeptide sequence from the lac repressor headpiece (lac 53-57) with different base sequences of DNA. The peptide fragment for this purpose was considered in the classical beta-antiparallel as well as the beta-associated conformation. The model of its interaction with DNA was optimised for various binding positions and base sequences. Partitioning of energy is analysed for different dielectric constant values and the main contributing factors to sequence-specific binding are discussed.     

Effects of 5-bromo-2-deoxy-uridine and 2-deoxy-D-glucose on the radiosensitivity of proliferating transformed mammalian cells.

Effects of 5-bromo-2-deoxy-uridine (BrdU) and 2-deoxy-D-glucose (2-DG) were studied in exponentially growing transformed mammalian (BHK-21) cells, grown as monolayer. Micronuclei formation as an index of radiation damage was studied by i) cytokinesis block technique from cytochalasin-B induced binucleated cells, and ii) conventional technique. Presence of BrdU (0.8 microM) for nearly 2 cell cycles before gamma-irradiation (2.5 Gy) significantly increased frequencies of cells with micronuclei. Post-irradiation incubation of cultures in liquid holding medium (HBSS) however, reduced micronuclei formation, especially in the BrdU treated cells. Presence of 2-DG (4 hr, equimolar with glucose) in growth as well as liquid holding medium further increased micronuclei frequencies. These observations suggest that radiation induced DNA lesions in BrdU substituted cells, leading to chromosome fragmentation are partly repairable. 2-DG increased cytogenetic damage, possibly by inhibiting the repair of such repairable lesions. Present studies suggest that combination of 2-DG could optimize BrdU-radiation therapy of brain tumors, by reducing the BrdU doses required for tumor radiosensitization.     

The dietary effects of 20-hydroxyecdysone on the development of housefly

The ingestion of 20-hydroxyecdysone adversely affected the growth and development of housefly larvae (Musca domestica) reared axenically on two synthetic diets. In a casein diet, this hormone was toxic causing 84% mortality at a concentration of 100 ppm. In an amino acid diet, the mortality was 65% at 100 ppm but the rate of larval development was greater than the controls and some puparia showing prothetely were produced for all concentrations tested. The different effects can be explained in terms of differences in the absorption and/or catabolism of 20-hydroxyecdysone in the two diets.