Immobilization of cellulase on iron tolerant Pseudomonas stutzeri biosynthesized photocatalytically active magnetic nanoparticles for increased thermal stability.

Bacteria mediated synthesis of magnetic nanoparticles (MNPs) for biotechnological applications is an important area of nanotechnology. This study demonstrates the use of iron tolerant bacterium for synthesis of MNPs for cellulase immobilization and photocatalytic activity. The enrichment, isolation, screening and molecular identification led to the selection of Pseudomonas stutzeri KDP_M2 with high degree of iron tolerance. The synthesis parameters such as 1 mM ferric quinate, pH 9 and 96 h static incubation were found optimum for maximum yield of 210 mg/L. The characterization using various techniques indicated that MNPs were Hematite (Fe2O3) with particle size between 10 and 20 nm. Further, vibrating sample magnetometer and thermogravimetric analyses demonstrated the superparamagnetic nature with high thermal stability. The MNPs were found an excellent support for immobilization of industrially important cellulase with 96.5% binding efficiency. The immobilization which was confirmed by Fourier transform infrared spectroscopy indicated that immobilization did not reduce the cellulase activity, rather enhanced the thermal stability and operational temperature range of cellulase. The immobilized cellulase showed maximum cellulolytic activity at pH 4.6 and retained 80% activity upto 3rd cycle of reuse, therefore, can be utilized repeatedly at acidic conditions.The monitoring the photocatalytic activity showed rapid degradation of methyl violet and methylene blue within initial 10 min. of reaction.

Selective and sensitive colorimetric detection of platinum using Pseudomonas stutzeri mediated optimally synthesized antibacterial silver nanoparticles.

In this work, Pseudomonas stutzeri was used for the optimum biogenic synthesis of antibacterial silver nanoparticles (AgNPs) which were applied for colorimetric detection of platinum ions (Pt+2). The optimum synthesis conditions were 2 mM AgNO3, pH 9 and incubation at 60 °C for 24 h. The FTIR spectra indicated that biomolecules such as amino acids, proteins or enzymes from P. stutzeri were involved in the synthesis of AgNPs in the size range of 10-50 nm. Among the various metal ions tested and screened initially, the colloidal AgNPs probe-based colorimetric assay selectively detected Pt+2 with 50 ppm as the limit of detection (LOD). The assay demonstrated in the present study quantitatively recovered Pt+2 in the range of 70-150 % with good accuracy and precision. Further, the test of antibacterial activity of AgNPs alone, and in combination with ampicillin showed excellent activity against four of the six tested bacteria.

Selective interaction between phytomediated anionic silver nanoparticles and mercury leading to amalgam formation enables highly sensitive, colorimetric and memristor-based detection of mercury.

Presently, nanotechnology is being foreseen to play an important role in developing analytical assays for the detection of pollutants like mercury (Hg2+). In this study, Kokum fruit mediated silver nanoparticles (AgNPs) were differentially centrifuged to prepare anionic, monodispersed AgNPs to develop a highly sensitive, colorimetric and memristor-based assay for detection of Hg2+ in water samples. The investigation of the highly selective reaction between AgNPs and Hg2+ using HAADF-STEM images and EDS spectrum indicated the amalgam formation through etching and under potential deposition which resulted in a visible color change from brown to colorless, change in SPR intensity and also change in memristive switching like property of AgNPs. The developed colorimetric assay detected Hg2+ with a limit of detection (LOD) of 6.2 ppb and limit of quantification (LOQ) of 18.9 ppb and, quantitatively recovered Hg2+ with good accuracy and precision (RSD < 2%). Further, the test of memristive switching like property of AgNPs demonstrated frequency-dependent shrinkage of I-V hysteresis loop indicating memristive switching like property. The test of the sensitivity of Hg2+ detection was estimated to be 8.7 ppb as the LOD and 26.4 ppb as LOQ. Like the colorimetric assay, the memristor-based assay also recovered Hg2+ with good accuracy and precision.