Background: Metal-free, water-soluble and highly stable meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS₄) has been studied for their singlet oxygen quantum yield. However, TPPS₄ suffers from inherent shortcomings. To address these, TPPS₄ was conjugated to ternary copper indium sulphide/ zinc sulphide (CuInS₂/ZnS) quantum dots (QDs). Purpose: We herein report for the first time the synthesis of TPPS₄–CuInS/ZnS QDs conjugate as an improved photosensitizer. Methods: Water-soluble TPPS₄ was synthesized from tetraphenylporphyrin (TPPH₂) after silica-gel purification. The CuInS/ZnS QDs were synthesized by hydrothermal method at a Cu:In ratio of 1:4. The porphyrin–QDs conjugate was formed via the daggling sulfonyl bond of the porphyrin and amine bond of the QDs. The effect of pH on the optical properties of TPPS₄ was evaluated. The effect of Zn:Cu + In ratio on the ZnS shell passivation was examined to reduce structural defects on the as-synthesized QDs. Results: Various spectroscopic techniques were used to confirm the successful conversion of the organic TPPH₂ to water-soluble TPPS₄. The singlet oxygen generation evaluation shows an improved singlet oxygen quantum yield from 0.19 for the porphyrin (TPPS₄) alone to 0.69 after conjugation (CuInS/ZnS-TPPS₄) with an increase in the reaction rate constant (k (s-1)).

An electrochemical immunosensor based on a silver nanoparticles (Ag NPs)-doped polyaniline (PANI) modified glassy carbon electrode (GCE) transducer, wherein polyclonal anti-polychlorinated biphenyl (PCB) antibody (Ab) was immobilized by a covalent linkage with glutaraldehyde (GA), was developed. The optimum conditions for the fabrication of the immunosensor were immersion, 30 min incubation in 1.0% GA. Electrochemical measurements of PCB 28 were done using the square wave voltammetry (SWV) technique. The optimum methodology conditions were a 20 mV s⁻¹ scan rate, sweep potential range of −1 to 1 V and PCB incubation period of 2 h. The electrochemical response obtained under these optimum conditions was linear within 0.2 and 1.2 ng mL⁻¹ with limit of detection (LOD) and limit of quantitation (LOQ) values of 0.063 ng mL⁻¹ and 0.209 ng mL⁻¹, respectively. The specificity of the developed sensor towards PCB 28 against benzyl chloride (BnCl) and PCB 180 was poor due to structural similarities. However, the PCB 180 results correspond to total PCB, thus indicating the sensor's applicability to regular total PCB determination. Cations and anions tested had a minimum effect on the sensor. Recoveries in water and guava juice ranged from 90% to 102%. Thus, proving the immunosensor's selectivity to PCBs and its possible application in the detection and monitoring of PCBs in food, water bodies and general environmental samples.

This study assesses the physical and electrochemical changes of bimetallic Ag-Au nanoparticle-functionalized bentonite nanoclay. Nanoclay was studied to deduce a better sensing material/film. A chemical co-reduction method was used to synthesize bimetallic Ag-Au c nanoparticles, which were used to prepare a Ag-Au/PGV bentonite composite. Bimetallic Ag-AuNPs and their nanoclay composite were optically characterized using the scanning electron microscope, ultraviolet visible spectroscopy, X-ray diffraction, and Fourier transform infrared, whilst cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to ascertain their electrochemical activity and properties. The results of surface morphological inspection showed an average size of 10nm, in agreement with XRD. The bimetallic Ag-AuNPs UV/Vis characteristic wavelengths of 414nm and 516nm confirmed the presence of Ag and Au metals, respectively. XRD exhibited diffraction planes related to 2θ values of Ag and Au metals, whilst FTIR indicated mainly COO- functional groups from the citrate capping of bimetallic Ag-Au NPs. CV and DPV showed that bentonite nanoclay is largely insulated by silicates but exhibited a small electroactivity of Fe. The electroactivity of Ag-Au/PGV bentonite exhibited peak potentials due to Ag/Ag+ and Au/Au³⁺ redox couples at 0.19V/0.20V and 1.37V/0.42, respectively. The Ag-Au/PGV bentonite nanocomposite exhibited the highest surface concentration of 3.25×10⁻²cm², a diffusion coefficient of 2.36×11cm²/s, and an electron transfer rate constant (Ks) of 1.99×10⁻⁴cm². The outcome of these results indicated that the Ag-Au/PGV bentonite nanocomposite was more electroactive than PGV. Therefore, this study accentuates Ag-Au/PGV bentonite nanocomposite as a novel and promising platform for electrochemical sensing with higher sensitivity and efficiency than other sensing materials.

A study of nanosensor comprising of a glassy carbon electrode modified with a composite of multiwall carbon nanotube (MWCNT) and bimetallic (Ag‐PtNPs) for the determination of Nevirapine. The GCE/MWCNT/Ag‐PtNPs sensor had remarkable electrocatalytic properties with enhanced response towards Nevirapine under optimized conditions. The platform electrochemical characterisation in 0.01 M NaOH solution, with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) is detailed. The limit of the detection (LOD) was 0.021 μM. The nanosensor was validated for real sample study using spiked pharmaceutical dose form, milk and urine samples, which showed acceptable recoveries (90‐ 112 %), good precision (RSD=3.3 %, N=3), reproducibility (RSD=4.3 %) and excellent selectivity towards Nevirapine from studied interferents.

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.