Molecularly imprinted polymers (MIPs) are generally a more stable material for sensing application. The high selectivity and sensitivity of MIPs for sensors can be achieved if the template molecule is imprinted in the polymer and this makes them an ideal alternative as a recognition element for sensors. A new electrochemical sensor based on molecularly imprinted polymeric microspheres (MIPs) and multi-walled carbon nanotube/gold nanoparticle (MIP–MWCNT–AuNP) modified carbon screen-printed electrodes (SPEs) for the rapid detection of 17β-estradiol (E) hormone in serum samples has been successfully developed. Hydrophobic MIPs were synthesized using photopolymerization in emulsion form. The multi-walled carbon nanotube grafted with gold nanoparticles was firstly deposited onto a carbon screen-printed electrode for the purpose of accelerating electron transfer to the surface of the electrode. The MIP microspheres specific to the 17β-estradiol hormone, prepared via a facile photopolymerization technique, were coated onto the MWCNT–AuNP modified SPE. The presence of 17β-estradiol in biological samples could be detected with the sensor via absorption of 17β-estradiol into the deposited MIPs and this was monitored by differential pulse voltammetry (DPV) at 0.6 V for the reduction of 17β-estradiol. Under optimal conditions, the sensor could detect the concentrations of 17β-estradiol from 1.0 × 10⁻¹⁵ to 1.0 × 10⁻⁶ M (R² = 0.9921), with a detection limit of 2.5 × 10⁻¹⁶ M. The sensor based on MIP microspheres and the MWCNT–AuNP modified electrode demonstrated a stability of 55 days with good reproducibility (RSD < 5%, n = 5) and regenerability (RSD < 4%, n = 5). Using this sensor, the gender of the arowana fish determined via the level of 17β-estradiol using fish serum samples demonstrated good agreement with a conventional test kit based on the immuno-assay method.

This article details an investigation on the mechanism of corrosion inhibition of mild steel using amylose-acetate-blended carboxymethyl chitosan (AA-CMCh) in acidic media in the context of kinetic and thermodynamic parameters. The surface of mild steel was exposed to test solutions and evaluated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The activation energy (E_a), free energy of adsorption (ΔG), enthalpy of activation (ΔH_ads), and entropy of activation (ΔS_ads) were determined in order to elucidate the mechanism of corrosion inhibition. The results confirmed that AA could be improved using CMCh as a corrosion inhibitor. The corrosion rate decreased from 1109.00 to 229.70 mdd (79.29%), while corrosion inhibition increased from 35.13 to 89.72%. Sulfate acid (H₂SO₄) of 0.25 M also helped in decreasing the corrosion rate from 2664.4 to 1041.67 mdd (60.9%) while also in increasing corrosion inhibition from 56.94 to 68.31%. The calculated values for ΔG, ΔH_ads, and ΔS_ads were −33.22 kJ·mol⁻¹, −48.56 kJ·mol⁻¹, and 0.0495 kJ·mol⁻¹·K⁻¹, respectively. The mechanism of corrosion inhibition of mild steel in the acidic condition is dominated and precipitated by the formation of the Fe-chelate compound, which was confirmed by the SEM/EDS spectrum. The reactions were spontaneous, exothermic, and irregular and takes place on the surface of mild steel.

In this article a luminescence fiber optic biosensor for the microdetection of heavy metal toxicity in waters based on the marine bacterium Aliivibrio fischeri (A. fischeri) encapsulated in alginate microspheres is described. Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(II) were selected as sample toxic heavy metal ions for evaluation of the performance of this toxicity microbiosensor. The loss of bioluminescence response from immobilized A. fischeri bacterial cells corresponds to changes in the toxicity levels. The inhibition of the luminescent biosensor response collected at excitation and emission wavelengths of 287 ± 2 nm and 487 ± 2 nm, respectively, was found to be reproducible and repeatable within the relative standard deviation (RSD) range of 2.4–5.7% (n = 8). The toxicity biosensor based on alginate micropsheres exhibited a lower limit of detection (LOD) for Cu(II) (6.40 μg/L), Cd(II) (1.56 μg/L), Pb(II) (47 μg/L), Ag(I) (18 μg/L) than Zn(II) (320 μg/L), Cr(VI) (1,000 μg/L), Co(II) (1700 μg/L), Ni(II) (2800 μg/L), and Fe(III) (3100 μg/L). Such LOD values are lower when compared with other previous reported whole cell toxicity biosensors using agar gel, agarose gel and cellulose membrane biomatrices used for the immobilization of bacterial cells. The A. fischeri bacteria microencapsulated in alginate biopolymer could maintain their metabolic activity for a prolonged period of up to six weeks without any noticeable changes in the bioluminescence response. The bioluminescent biosensor could also be used for the determination of antagonistic toxicity levels for toxicant mixtures. A comparison of the results obtained by atomic absorption spectroscopy (AAS) and using the proposed luminescent A. fischeri-based biosensor suggests that the optical toxicity biosensor can be used for quantitative microdetermination of heavy metal toxicity in environmental water samples.

An ultrasensitive electrochemical biosensor for the determination of pathogenic Vibrio cholerae (V. cholerae) DNA was developed based on polystyrene-co-acrylic acid (PSA) latex nanospheres-gold nanoparticles composite (PSA-AuNPs) DNA carrier matrix. Differential pulse voltammetry (DPV) using an electroactive anthraquninone oligonucleotide label was used for measuring the biosensor response. Loading of gold nanoparticles (AuNPs) on the DNA-latex particle electrode has significantly amplified the faradaic current of DNA hybridisation. Together with the use of a reported probe, the biosensor has demonstrated high sensitivity. The DNA biosensor yielded a reproducible and wide linear response range to target DNA from 1.0 × 10−21 to 1.0 × 10−8 M (relative standard deviation, RSD = 4.5%, n = 5) with a limit of detection (LOD) of 1.0 × 10−21 M (R 2 = 0.99). The biosensor obtained satisfactory recovery values between 91 and 109% (n = 3) for the detection of V. cholerae DNA in spiked samples and could be reused for six consecutive DNA assays with a repeatability RSD value of 5% (n = 5). The electrochemical biosensor response was stable and maintainable at 95% of its original response up to 58 days of storage period.