Peter M. Ndangili

Determination of Anthracene on Ag-Au Alloy Nanoparticles/Overoxidized-Polypyrrole Composite Modified Glassy Carbon Electrodes

A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO3 and HAuCl4 using C6H5O7Na3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20–50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10−6 to 3.56 × 10−4 M with a detection limit of 1.69 × 10−7 M. The proposed method was simple, less time consuming and showed a high sensitivity.

Polyester Sulphonic Acid Interstitial Nanocomposite Platform for Peroxide Biosensor

A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (∼90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.

3-Mercaptopropionic Acid Capped Ga2Se3 nanocrystal-CYP3A4 Biosensor for the Determination of 17-Alpha-Ethinyl Estradiol in Water

Water soluble and biocompatible 3-mercaptopropionic acid capped gallium selenide nanocrystals, were synthesized from hydrated gallium (III) perchlorate and selenide ions. The 3-mercaptopropionic acid capped gallium selenide nanocrystals, was non-fluorescent but showed a sharp UV-vis absorption maximum at 250 nm.The synthesized nanoparticle was used to develop an electrochemical biosensor for the detection of 17-alpha-ethinyl estradiol, an estrogenic endocrine disrupting compound (e-EDC). The biosensor was fabricated by potentiostatic deposition of novel gallium selenide nanocrystals on a L-cystine modified gold electrode, followed by covalent coupling of genetically engineered cytochrome P450-3A4 (CYP3A4), a Heme containing enzyme. The biosensor gave an electrochemical response at about-220 mV. The results revealed that 3-Mecarptopropanoic acid capped Gallium Selenide nanocrystals can be used in conjunction with CYP3A4 as an electrode modifier for the detection of 17-alpha ethinyl estradiol. The 3-Mecarptopropanoic acid capped Gallium Selenide nanoparticles exhibited a semiconductor like behaviour.

Optoelectronics of Stochiometrically Controlled Palladium Telluride Quantum Dots

Water dispersed PdTe semiconducting nanocrystals were synthesized and stabilised with 3-mercaptopropionic acid (3-MPA). HRTEM studies revealed the formation of spherical nanoparticles of average size ~4 nm with good crystallinity. UV-visible spectral analysis and band gap measurements confirmed that the nanocrystals are indeed semiconductors. This semiconducting characteristic was supported by electrochemical impedance spectroscopy (EIS) data which gave Bode plots with absolute frequency and a maximum frequency phase angle values of 38.3° and 75°, respectively. Electroanalysis of the film on glassy carbon electrode (GCE) verified the retention of the ability of Pd to adsorb hydrogen on its surface as well as absorb hydrogen within its lattice.