Rachel Fanelwa Ajayi

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.

Polyanilino-Carbon Nanotubes Derivatised Cytochrome P450 2E1 Nanobiosensor for the Determination of Pyrazinamide Anti-Tuberculosis Drugs

Pyrazinamine (PZA) is one of the most commonly prescribed anti-tuberculosis (anti-TB) drug due to its ability to significantly shorten the TB treatment period. However, excess PZA in the body causes hepatotoxicity and liver damage. This, therefore, calls for new methods for ensuring reliable dosing of the drug, which will differ from person to person due to interindividual differences in drug metabolism. A novel biosensor system for monitoring the metabolism of PZA was prepared with nanocomposite of multi-walled carbon nanotubes (MWCNTs), polyaniline (PANI) and cytochrome P450 3A4 (CYP3A4) electrochemically deposited on a glassy carbon electrode (GCE). The nanocomposite biosensor system exhibited enhanced electroactivity that is attributable to the catalytic effect of the incorporated MWCNTs. The biosensor had a sensitivity of 7.80 μA/μg mL-1 PZA and a dynamic linear range of 4.92 160 ng/mL PZA.

An Amperometric Cytochrome P450-2D6 Biosensor System for the Detection of the Selective Serotonin Reuptake Inhibitors (SSRIs) Paroxetine and Fluvoxamine

Paroxetine is the second most prescribed selective serotonin reuptake inhibitor (SSRI) antidepressant drug, characterized by extensive inter-individual variation in steady state plasma concentrations resulting in drug toxicity amongst patinets. A nanopolymeric biosensor for studying the biotransformation of paroxetine is presented. The bioelectrode system consists of cytochrome P450-2D6 enzyme encapsulated in nanotubular poly (8-anilino-1-napthalene sulphonic acid) electrochemically deposited on gold. The biosensing procedure involved the determination of the extent of modulation of fluvoxamine responses to the P450-2D6 enzyme electrode after incubation in paroxetine standard solutions. Paroxetine inhibited the activity of cytochrome P450-2D6 (CYP2D6) resulting in a decrease in the fluvoxamine signal of the biosensor. The biosensor gave a linear analytical response for the paroxetine in the interval 0.005 and 0.05 μM, with a detection limit of 0.002 μM and a response time of 30 s. Electrochemical Michaelis–Menten kinetics of the reversible competitive inhibition of the fluvoxamine responses of the biosensor by 0, 0.05 and 0.1 μM paroxetine gave apparent Michaelis–Menten constant (KMapp) values of 1.00 μM, 1.11 μM and 1.25 μM, respectively. The corresponding value for the maximum response, IMAX was 0.02 A. The dissociation constant, KI, value evaluated from Dixon analysis of the paroxetine modulation data was estimated to be-0.02 μM while Cornish-Bowden analysis confirmed the competitive inhibitory characteristics of the enzyme.

Conductive Composite Biosensor System for Electrochemical Indinavir Drug Detection

Indinavir is a protease inhibitor antiretroviral (ARV) drug, which forms part of the highly active antiretroviral therapy during the treatment of HIV/AIDS. Indinavir undergoes first-pass metabolism through the cytochrome P450 (CYP) enzymes in the human liver, of which CYP3A4 is the most influential isoenzyme. Multidrug combination therapy and, as such, therapeutic drug monitoring (TDM) during HIV/AIDS treatment are therefore critical, to prevent adverse interactions. The conventional sensitive and specific assays available for quantifying ARV drugs, however, suffer from distinct disadvantages. In this regard, biosensors can be used to provide real time information on the metabolic profile of the drug. In this study, a biosensor with cobalt(III) sepulchrate trichloride as diffusional mediator was constructed. The biosensor platform consisted of CYP3A4 immobilized onto a gold nanoparticle (GNP) overoxidized polypyrrole (OvOxPpy) carrier matrix. The biosensor exhibited reversible electrochemistry, with formal potential determined as −624 ± 5 mV, from voltammetric analysis, with overall electron transfer being diffusion controlled. The biosensor showed typical electrocatalytic response to dioxygen (O2), exemplified by the distinct increase in the cathodic peak current (). A concentration-dependent increase in was observed in response to consecutive additions of Indinavir.

A gallium telluride quantum dots bioelectrode system for human epidermal growth factor receptor-2 (Her2/neu) oncogene signalling

Human epidermal growth factor receptor 2 (Her2/neu) is a biomarker that is overexpressed in human breast cancers. A quantum dots (QDs) -based genosensor for Her2/neu oncogene was developed with gallium telluride QDs and amine-terminated probe ssDNA (NH2-5′-AATTCCAGTGGCCATCAA-3′), that is complementary to the DNA sequence of a section of the ERF gene of HER-2/neu (i.e. 5′-GAACATGAAGGACCGGTGGGC-3′). The QDs were highly crystalline, 6 nm (from XRD) in size and had band gap values of 3.3 eV and 3.5 eV calculated from fluorescence emission and UV-visible absorption data, respectively. The sensor sensitivity and limit of detection values were 10.0 μA ng−1 mL−1 and 0.2 pg mL−1 Her2/neu oncogene, respectively.

Electrochemical Ultra-Low Detection of Isoniazid Using a Salicylaldamine Functionalised G1-DAB-(NH2)4 Dendritic Sensor vs. UV-VIS Spectrophotometric Detection

A poly(propyleneimine) based dendrimer was synthesised and successfully functionalised with a copper centre within its branches. The dendrimer and corresponding metallodendrimer were successfully characterised using FTIR, HR-TEM and HR-SEM in order to determine the effect of the inclusion of copper into the dendritic structure. The incorporation of copper caused crystallinity as revealed in the HR-TEM and a sheet-like morphology as shown in the HR-SEM images. The resulting metallodendrimer was then applied as an electrocatalytic platform for the sensing of a first line TB drug called isoniazid. This method was compared to a routine laboratory detection using UV-Vis and was found to be much more sensitive to trace amounts of isoniazid in solution. The electrochemical detection was found to have a limit of detection (LOD) of 0.233 nM compared to 11.47 nM using the Ultraviolet-visible spectroscopy method.

A Novel Polyaniline Nanocomposite with Doping Effects of Poly(Methyl Methacrylate) and TiO2 Nanoparticles

Polyaniline (PANI) is a globally investigated conductive polymer with a variety of applications in various fields due to its ease of synthesis and modification. One method of enhancing the physico-chemical properties and processability of PANI is the incorporation of polymers and nanoparticles to form composite and hybrid materials with new features. This study reports the electrochemical synthesis of a polyaniline nanocomposite that incorporates titanium dioxide nanoparticles (TiO2) and poly (methyl methacrylate) (PMMA). The significant effects of PMMA and TiO2 nanoparticles on structural, morphological, optical and electrochemical properties of native polyaniline were investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The formation and deformation of relevant peaks observed from the FTIR spectra confirm the intrusion of PMMA and TiO2 into PANI while the voltammetric results show that the incorporation of both dopants significantly enhanced the electroactivity of PANI in a neutral pH medium.

Cytochrome P450-3A4/Copper-Poly(Propylene Imine)-Polypyrrole Star Co-Polymer Nanobiosensor System for Delavirdine - A Non-Nucleoside Reverse Transcriptase Inhibitor HIV Drug

HIV and AIDS are among the world’s pandemics that pose serious concern to almost every individual in the world. With the current level of availability of anti-retroviral (ARV) drugs and the ease of accessibility of treatment in many countries such as South Africa, the disease can be controlled by suppressing the viral load of an infected individual. These anti HIV drugs such as delavirdine are metabolised by enzymes which are found in the liver microsomes, particularly those of the cytochrome P450 family. Due to the fact that the metabolic rate of a patient determines the effect of the drug, the drug could either have a beneficial or an adverse effect once it is administered. It is therefore imperative that the metabolic profile of a patient is determined to ensure proper dosing of the ARV drugs. In this study a nanobiosensor system was devised and used for the determination of the metabolism of delavirdine (DLV), a non-nucleoside reverse transcriptase inhibitor (NNRTI) ARV drug. The nanobiosensor was prepared by the entrapment of the isoenzyme CYP3A4 into a pre-formed electro active carrier matrice consisting of a dendrimeric copper generation-2 poly(propylene imine)-co-polypyrrole star copolymer (Cu(G2PPI)-co-PPy). The metallo-dendrimer was used as a host for the enzyme and provided the necessary bio-compatible environment that allowed the direct transfer of electrons between the enzyme’s active centres and platinum electrode surface. (Cu(G2PPI)-co-PPy) was prepared by the incorporation of the copper metal into the G2PPI and the electropolymerization of pyrrole onto the Cu(G2PPI). The incorporation of Cu into G2PPI was determined by Fourier transform infrared (FTIR) spectroscopy which did not show the presence of the Cu but showed an increase in the intensities of the peaks after the incorporation. The surface morphology of Cu(G2PPI-2Py) was confirmed by the use of high resolution scanning electron microscopy (HRSEM) which showed a difference in the surface morphology of the dendrimer moiety with the addition of the copper metal. The HRSEM images after Cu incorporation resulted in the change from rough surface to smooth surface with open cavities which were essential for the entrapment of the biological systems (CYP3A4). The energy band gap of (Cu(G2PPI)-co-PPy) were determined to be 3.85 eV, signifying that the copolymer is characteristic of a biocompatible semiconductive platform for applications in biosensors. The star copolymer (Cu(G2PPI)-co-PPy) was characterized using cyclic voltammetry where it was confirmed that the material was electroactive and conducting due to electron movement along the polymer chain. A diffusion co-efficient (Do) value of 8.64 x 10-5 cm2/s was determined for the material indicating a slow electron transfer kinetics within the diffusion layer. The resultant nanobiosensor parameters include a dynamic linear range (DLR) of 0.01-0.06 nM, a limit of detection (LOD) of 0.025 nM and a sensitivity value of 0.379 μA/nM.

Tin Selenide Quantum Dots Electrochemical Biotransducer for the Determination of Indinavir - A Protease Inhibitor Anti-Retroviral Drug

Biocompatibility of tin selenide quantum dots was achieved by the incorporation of 3-mercaptopropionic acid (3-MPA) as a capping agent, which also improved the stability and the solubility of the material. The UV-Vis spectrophotometric analysis of the quantum dots revealed a broad absorption band at ~ 330 nm (with a corresponding band gap, Eg, value of 3.75 eV), which is within the range of values expected for quantum dots materials. The 3-mercaptopropionic acid-capped tin selenide (3-MPA-SnSe) quantum dots were used to develop an electrochemical biosensor for indinavir, which is a protease inhibitor antiretroviral (ARV) drug. The biosensor was prepared by the self-assembly of L-cysteine on a gold electrode that was functionalised with 3-MPA-SnSe quantum dots, followed by cross-linking with cytochrome P450-3A4 (CYP3A4) using 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The electrocatalytic properties of the biosensor included a characteristic cyclic voltammetric reduction peak at-380 mV, which was used to detect the response of the biosensor to indinavir. The sensor performance parameters included response time and limit of detection (LOD) values of 11 s and 3.22 pg/mL, respectively. The test concentration range studied (0.014 – 0.066 ng/mL) gave a linear calibration plot for indinavir, and it was lower than the physiological plasma concentration index (i.e. maximum plasma concentrations, Cmax,) of indinavir (5 - 15 ng/mL) normally observed 8 h after intake. This indicates that the biosensor can be very useful in the case of ultra-rapid metabolisers where very low Cmax values are expected