Dendrimer-Gold Nanocomposite-Based Electrochemical Aptasensor for the Detection of Dopamine.

Dopamine is an important neurotransmitter and biomarker that plays a vital role in our neurological system and body. Thus, it is important to monitor the concentration levels of dopamine in our bodies. We report an aptamer-based sensor fabricated through an electro-co-deposition of a generation 3 poly(propylene imine) (PPI) dendrimer and gold nanoparticles (AuNPs) on a glassy carbon (GC) electrode by cyclic voltammetry. Through self-assembly, a single-stranded thiolated dopamine aptamer was immobilized on the GC/PPI/AuNPs electrode to prepare an aptasensor. Voltammetry and electrochemical impedance spectroscopy (EIS) were used to characterize the modified electrodes. The readout for the biorecognition event between the aptamer and various dopamine concentrations was attained from square wave voltammetry and EIS. The aptasensor detected dopamine from the range of 10-200 nM, with a limit of detection of 0.26 and 0.011 nM from SWV and EIS, respectively. The aptasensor was selective toward dopamine when different amounts of epinephrine and ascorbic acid were present. The aptasensor was applicable in a more complex matrix of human serum.

An electrochemical immunosensor for an alpha-fetoprotein cancer biomarker on a carbon black/palladium hybrid nanoparticles platform.

The early detection of cancer is a key step in cancer survival. Thus, there is a need to develop low-cost technologies, such as electrochemical immunosensor technologies, for timely screening and diagnostics. The discovery of alpha-feto protein (AFP) as a tumour-associated antigen lends AFP as a biomarker for cancer detection and monitoring. Thus, immunosensors can be developed to target AFP in cancer diagnostics. Hence, we report the application of a hybrid nanocomposite of carbon black nanoparticles (CBNPs) and palladium nanoparticles (PdNPs) as a platform for the electrochemical immunosensing of cancer biomarkers. The hybrid carbon-metal nanomaterials were immobilised by using the drop-drying and electrodeposition technique on a glassy carbon electrode, followed by the immobilisation of the anti-AFP to fabricate an immunosensor. The nanoparticles were characterised with electron microscopy, voltammetry, and electrochemical impedance spectroscopy (EIS). Square wave voltammetry (SWV) and EIS were used to study the immunosensor signal toward the bio-recognition of the AFP cancer biomarker. The hybrid nanoparticles enhanced the immunosensor performance. A linear detection range from 0.005 to 1000 ng mL-1 with low detection limits of 0.0039 ng mL-1 and 0.0131 ng mL-1 were calculated for SWV and EIS, respectively. The immunosensor demonstrated good stability, reproducibility, and selectivity. Its real-life application potential was tested with detection in human serum matrix.

Photoelectrocatalytic Degradation of Methylene Blue on Electrodeposited Bismuth Ferrite Perovskite Films.

Electrodeposited bismuth ferrite (BiFeO3) thin films on fluorine-doped tin oxide (FTO) substrate were employed as photoanodes in the photoelectrocatalytic degradation of methylene blue. The BiFeO3 thin films electrodeposited for 300 s, 600 s, 1200 s, 1800 s and 3600 s were characterised with XRD, field emission scanning electron microscopy (FESEM) and UV-vis diffuse reflectance spectroscopy. SEM images displayed different morphology at different electrodeposition times which affects the photoelectrocatalytic (PEC) performances. The FESEM cross-sectional area was used to measure the thickness of the film. The optical properties showed that the band gaps of the photoanodes were increasing as the electrodeposition time increased. The photocurrent response obtained showed that all thin film photoanodes responded to visible light and lower charge transfer resistance (from electrochemical impedance spectroscopy studies) was observed with photoanodes electrodeposited at a shorter time compared to those at a longer time. The PEC application of the photoanode for the removal of methylene blue (MB) dye in water showed that the percentage degradation decreased with an increase in electrodeposition time with removal rates of 97.6% and 70% observed in 300 s and 3600 s electrodeposition time, respectively. The extent of mineralisation was measured by total organic carbon and reusability studies were carried out. Control experiments such as adsorption, photolysis, photocatalysis and electrocatalysis processes were also investigated in comparison with PEC. The electrodeposition approach with citric acid exhibited improved electrode stability while mitigating the problem of catalyst leaching or peeling off during the PEC process.

Pregnancy rates and outcomes in a longitudinal HIV cohort in the context of evolving antiretroviral treatment provision in South Africa.

BACKGROUND: In South Africa, women continue to face a high burden of Human Immunodeficiency Virus (HIV) infection and the possible complications thereof during pregnancy. We assessed pregnancy incidence rates and outcomes in a longitudinal HIV cohort study over a 15-year period. METHODS: We evaluated pregnancies among women ≥ 18 years between 2004 and 2019 in the CAPRISA 002 study. We analysed pregnancy rates following HIV acquisition, CD4 counts and HIV viral load dynamics and pregnancy outcomes. We used linear regression to assess if the mean CD4 and log10 viral load close to delivery increases or decreases linearly across three different timepoints. RESULTS: In total 245 women enrolled into the HIV negative study phase, 225 into the HIV infection phase and 232 in the antiretroviral therapy (ART) phase. Median follow-up time was 2.0 years [Interquartile Range (IQR) 0.8-2.0] during the HIV negative phase, 2.6 years; (IQR) 1.2-4.8] during HIV infection and 3.7 years (IQR 1.8-5.0) on ART, with maximum follow-up time of 2, 10 and 6 years respectively. Overall, 169 pregnancies occurred in 140 women, of which 16 pregnancies were observed during acute or early HIV infection [Incidence Rate (IR) 8.0 per 100 women-years; 95% confidence interval (CI): 4.6-12.9], 48 during established infection [IR 9.3; (CI 6.8-12.3)] and 68 on ART [IR 8.9; (CI: 7.0 - 11.4)]. Birth outcomes from 155/169 (91.7%) pregnancies were 118 (76.1%) full term live births, 17 (10.9%) premature live births, 9 (5.8%) therapeutic/elective miscarriages, 8 (5.1%) spontaneous miscarriages and 3 (1.9%) spontaneous foetal deaths or stillbirths. Six mother-to-child transmission events occurred, with four documented prior to 2008. Over time, mean CD4 count in pregnant women increased from 395 cells/µL (2004-2009) to 543 cells/µL (2010-2014) and to 696 cells/µL (2015-2019), p < 0.001. Conversely, the viral load declined from 4.2 log10 copies/ml to 2.5 log10 copies/ml and to 1.2 log10 copies/ml (p < 0.001) for the corresponding periods. CONCLUSIONS: Pregnancy rates following HIV acquisition were high, emphasising a need for timeous ART provision and contraception counselling in women recently diagnosed with HIV. CD4 count and HIV viral load trajectories reflect improvements in treatment guidance for pregnant women over time.

Electrochemical detection of nicotine at a carbon Nanofiber-Poly(amidoamine) dendrimer modified glassy carbon electrode.

Development of electrochemical sensors for important drugs such nicotine (an addictive drug) is important for the society. This study reports the electrochemical detection of nicotine at a carbon nanofiber/poly (amidoamine) dendrimer modified glassy carbon electrode. The carbon nanofiber (CNF) modified GCE was prepared by drop-coating followed by the electrodeposition of generation 4 poly (amidoamine) succinamic acid dendrimer (PAMAM) to form the sensor - CNF-PAMAM GCE. Characterization of prepared materials and modified electrodes was carried out using Fourier transmission infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The CNF-PAMAM composite was confirmed by microscopy. A marked reduction in charge transfer resistance and increase in current of the CNF-PAMAM GCE in comparison to the bare electrode showed a synergic improvement electrochemical response because of the CNF-PAMAM nanocomposite. The CNF-PAMAM demonstrated an enhanced performance in the oxidation of nicotine in comparison to the bare GCE by shifting the anodic potential Epa of nicotine from 0.9 V to 0.8 V. The electrochemical sensor achieved a detection limit (LOD) of 0.02637 µM in the concentration range of 0.4815-15.41 µM of nicotine in 0.1 M PBS at pH 7.5. The sensor ability to determine nicotine in real samples was assessed in cigarettes obtaining recovery percentages of 88.00 and 97.42%. The sensor demonstrated selectivity toward nicotine in the presence of interferences. Finally, the method was validated by ultraviolet-visible spectroscopy analysis.

The application of FTO-Cu2O/Ag3PO4 heterojunction in the photoelectrochemical degradation of emerging pharmaceutical pollutant under visible light irradiation.

We report the photoelectrochemical application of a visible light active FTO-Cu2O/Ag3PO4 photoanode for the abatement of sulfamethoxazole in water. The as-synthesised photoanodes were characterised using XRD, field emission SEM, EDX, diffuse reflectance UV-vis, impedance spectroscopy and chronoamperometry. The results obtained confirmed a successful formation of p-n heterojunction at the Cu2O/Ag3PO4 interface. The highest photocurrent response of 0.62 mAcm-2 was obtained for the composite photoanode which was four times higher than pure Cu2O and about three times higher than pristine Ag3PO4. The photoanode gave 67% removal efficiency within 2 h upon its photoelectrochemical application in the degradation of sulfamethoxazole with 1.5 V bias potential at pH 6.2. The FTO-Cu2O/Ag3PO4 electrode was also applied in the treatment of a cocktail of synthetic organics containing sulfamethoxazole and orange II dye. The photogenerated holes was found to be the major oxidant and the photoanodes was stable and reusable.

Screening of Cyanobacterial Peptide Toxin, Microcystins in Hyperscum Water Samples from an Inland Sub Saharan Drinking Freshwater Reservoir.

A study which probed the occurrence and quantitative variations hepatotoxic microcystin in a Sub Saharan drinking freshwater reservoir was carried out between November 2014 and March 2015. Results reveal the presence of MCYST-YR, MCYST-LR, MCYST-RR, MCYST-LA and MCYST-LF variants either in cells collected directly from bloom or toxic isolates cultured under laboratory conditions. Two minor microcystin congeners (MCYST-(H4)YR) and (D-Asp3, Dha7) MCYST-RR) were identified, but not quantified. Variants dominance were in the order MCYST-LR > MCYST-RR > MCYST-YR > MCYST-LA > MCYST-LF across sampling sites. Maximum and minimum concentrations of quantified MCYSTs congeners were (489.25, 50.95 µg toxin/g DW), (98.92, 9.11 µg toxin/g DW), (140.25, 12.07 µg toxin/g DW), (56.99, 6.20 µg toxin/g DW) and (50.46, 3.65 µg toxin/g DW) for MCYST-LR, MCYST-YR, MCYST-RR, MCYST-LA and MCYST-LF, respectively. Analysis of variance (ANOVA) revealed there was a high significant difference between mean microcystin concentrations across sampling sites (p < 0.05).

Bioaccumulation and Quantitative Variations of Microcystins in the Swartspruit River, South Africa.

The bioaccumulation and quantitative variations of cyanobacterial peptide hepatotoxin intracellular microcystin in floating scums of cyanobacterium microcystis flos aquae collected from predetermined sampling sites in the Swartspruit River was investigated. Three distinct MCs variants (MC-YR, MC-LR, and MC-RR) were isolated, identified, and quantified. Additionally, two minor microcystin congeners (MC-(H4) YR), (D-Asp(3), Dha(7))MC-RR) also were identified but were not quantified. Quantitative analysis was achieved using peak areas substituted on linear regression equations: Y = 10085x - 19698 (R (2) = 0.9998), Y = 201387x + 20328 (R (2) = 0.9929), Y = 2506x + 15659 (R (2) = 0.9999), and 9859x + 208694 (R (2) = 0.9929) of standard curves for 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 µg/mL MC-LR, MC-RR, MC-YR respectively. Variant dominance followed the order MC-LR > MC-RR > MC-YR across the sampling sites. Analysis of maximum and minimum concentrations of quantified MCs variants showed 270.7, 14.10 (µg/g), 141.5, 1.43 (µg/g), and 72.28, 0.15 (µg/g) for MC-LR, MC-RR, and MC-YR, respectively. This implies there was quantitative variations of microcystin congeners across the sampled sites. Significant differences between means were assessed by an analysis of variance with P < 0.05 being considered significant. Results showed that there were no significant difference between mean MCs concentrations across the sampling periods (P > 0.05) and significant difference between mean MCs concentrations across sampling sites (P < 0.05).

Heterogeneous electron transfer kinetics and electrocatalytic behaviour of mixed self-assembled ferrocenes and SWCNT layers.

The electron transfer dynamics and electrocatalytic behaviour of ferrocene-terminated self-assembled monolayers (SAMs), co-adsorbed with single-walled carbon nanotubes (SWCNTs) on a gold electrode, have been interrogated for the first time. Ferrocene monocarboxylic acid (FMCA) or ferrocene dicarboxylic acid (FDCA) was covalently attached to the cysteamine (Cys) monolayer to form Au-Cys-FMCA and Au-Cys-FDCA, respectively. The same covalent attachment strategy was used to form the mixed SWCNTs and ferrocene-terminated layers (i.e. Au-Cys-SWCNT/FMCA and Au-Cys-SWCNT/FDCA). Using cyclic voltammetry and electrochemical impedance spectroscopy, the impact of neighbouring SWCNTs on the electron transfer dynamics of the ferrocene molecular assemblies in an acidic medium (0.5 M H(2)SO(4)) and in a solution of an outer-sphere redox probe ([Fe(CN)(6)](4-)/[Fe(CN)(6)](3-)) was explored. The electron transfer rate constants in both media essentially decreased as Au-Cys-FMCA > Au-Cys-SWCNT/FDCA > Au-Cys-FDCA > Au-Cys-SWCNT/FMCA. This trend has been interpreted in terms of several factors such as the locations of the ferrocene species in a range of environments with a range of potentials, the proximity/interactions of the ferrocenes with one another, and electrostatic interaction or repulsion existing between the negatively-charged redox probe and the modified electrodes. The thiocyanate ion (SCN(-)) was used as a model analyte to examine the influence of the neighbouring SWCNTs on the electrocatalytic ability of the ferrocene assemblies. The Au-Cys-SWCNT/FDCA showed the best catalytic activity (in terms of onset potential and catalytic peak current height) for the oxidation of SCN(-), possibly due to the repulsive interactions between the negatively charged SCN(-) and high number of surface -COOH species at the SWCNT/FDCA. This study has provided some useful insights as to how CNTs co-assembled with ferrocene-terminated thiols could impact on the electron transfer kinetics as well as the electrocatalytic detection of the self-assembled ferrocene layers.