Impedimetric nano-collision Escherichia coli analysis based on Silver-Gold bimetallic nanoparticles

An impedimetric detection of E. coli was developed using chemically synthesised bimetallic Ag-Au (1:2) nanoparticles (NPs). The UV-visible spectra of the NPs had absorption bands at 470 and 580 nm for Ag NPs and Au NPs, respectively. In the presence of E. coli, a negative potential shift and a blue shift was observed in the voltammograms and spectra respectively. The complex formed had an oxidation potential at + 0.95 V. Technique choice was based on sensitivity comparison of Differential pulse voltammetry, cyclic voltammetry and impedance spectroscopy in 0.1 M PBS with Impedance being the best choice. Optimum sensing conditions of the NPs-E. coli complex for NPs concentration, incubation period, method modulation amplitude and applied potential were 5 mM, 20 min, 10 mV and + 0.5 V, respectively. The sensor's linearity range, lower limits of detection and quantification were found to be 10¹-10⁷, 1.88 × 10¹, 2.34 × 10² cells/mL, respectively. The sensor's applicability was validated by repeatability, stability and selectivity studies showing minimum changes in signal. Potential usage of the sensor in real samples was demonstrated by standard addition analysis of sea and River water samples as well as recovery of spiked water and fruit juices with acceptable % RSD < 2%.

The impact of silver nanoclay functionalisation on optical and electrochemical properties

Three different fractions of nanoclay (nanomer 1.44P) were functionalised with Ag forming silver nanoclay composites (Ag/nanomer 1.44P). The optical and electrochemical properties of the functionalised nanoclay were studied. Optical, morphology, and electrochemical techniques were used for the characterisation of the synthesised Ag/nanomer 1.44P nanocly composites. The presence and the absence of functional groups observed in the FTIR spectrum of Ag/nanomer 1.44P, compared with those found in the spectra of silver and pure nanomer 1.44P prove that a reaction occurred, thus a successful functionalisation of nanomer 1.44P nanoclay with silver. The XRD data of all composites showed four diffraction peaks within the silver spectrum range, with the intensity of silver decreasing with increasing concentration of nanomer 1.44P. SEM represented well-dispersed particles of different shapes with average particle sizes of 2.5, 27.5, and 5 nm with the enhanced concentration of nanomer 1.44P nanoclay. The decrease in diffusion coefficient values from 4.26 × 10^-10, 2.50 × 10^-13 , 1.40 × 10^-13 cm² s^-1 and electron transfer rates of 1.50 × 10^-5, 3.94 × 10^-7, 2.86 × 10^-7 cm s^-1 are respectively proportional to an increase in nanomer 1.44P concentration depicting changes in nanocomposites sizes.

Electrochemistry as a Complementary Technique for Revealing the Influence of Reducing Agent Concentration on AgNPs

The synthesis process of AgNPs has been attracting a lot of attention in the fields of biosensors/sensors, diagnostics, and therapeutic applications. An attempt to understand the effect of different concentrations of reducing agents on the synthetic design process has been made. In this paper, we gather information on voltammetry studies and relate it with UV-vis and scanning electron microscopy (SEM) analyses. Given the kinetics, localized surface plasmon absorption (LSPR) band, and narrow size distribution of these methods, it was possible to compare the obtained measurements and clearly distinguish sizes and aggregation. AgNPs measured by SEM showed a statistically significant reduction of the nanoparticle sizes from 65 to 37.5 nm as the reducing agent increased. Well-matched d-spacing data calculated from selected area electron diffraction (SAED) patterns and X-ray diffraction (XRD) were obtained for all of the samples. The UV-vis studies showed that the SPR bands shift toward the blue region as the reducing agent concentration is increased, indicating a decrease in particle sizes. It is worth emphasizing that cyclic voltammetry (CV) and differential pulse voltammetry (DPV) coincide well with SEM on the aggregation of AgNPs at higher concentrations. A 10 mM reducing agent concentration resulted in uniform outcomes for producing AgNPs with the smallest size in terms of full width at half-maximum (FWHM) in all of the methods used in this study, while UV-vis band gaps increase with increasing reducing agent concentration. In agreement with all of the methods investigated, the results suggested that the best concentration of the reducing agents is 10 mM for a target application. These findings suggest the usefulness of voltammetry as a complementary method that can be used as a qualitative guide to identify the size and aggregation of NPs.

Cytotoxicity, fluorescence tagging and gene-expression study of CuInS/ZnS QDS - meso (hydroxyphenyl) porphyrin conjugate against human monocytic leukemia cells

The toxicity of heavy metals present in binary semiconductor nanoparticles also known as quantum dots (QDs) has hindered their wide applications hence the advent of non-toxic ternary quantum dots. These new group of quantum dots have been shown to possess some therapeutic action against cancer cell lines but not significant enough to be referred to as an ideal therapeutic agent. In this report, we address this problem by conjugating red emitting CuInS/ZnS QDs to a 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin -photosensitizer for improved bioactivities. The glutathione capped CuInS/ZnS QDs were synthesized in an aqueous medium using a kitchen pressure cooker at different Cu: In ratios (1:4 and 1:8) and at varied temperatures (95 °C, 190 °C and 235 °C). Optical properties show that the as-synthesized CuInS/ZnS QDs become red-shifted compared to the core (CuInS) after passivation with emission in the red region while the cytotoxicity study revealed excellent cell viability against normal kidney fibroblasts (BHK21). The highly fluorescent, water-soluble QDs were conjugated to 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) via esterification reactions at room temperature. The resultant water-soluble conjugate was then used for the cytotoxicity, fluorescent imaging and gene expression study against human monocytic leukemia cells (THP-1). Our result showed that the conjugate possessed high cytotoxicity against THP-1 cells with enhanced localized cell uptake compared to the bare QDs. In addition, the gene expression study revealed that the conjugate induced inflammation compared to the QDs as NFKB gene was over-expressed upon cell inflammation while the singlet oxygen (1O2) study showed the conjugate possessed large amount of 1O2, three times than the bare porphyrin. Thus, the as-synthesized conjugate looks promising as a therapeutic agent for cancer therapy.