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Dopamine (DA) is an important neurotransmitter in the kidney, cardiovascular system, and central nervous system, which abnormality is associated with many diseases. In this work, we synthesized a functionalized multi-walled carbon nanotube/silver nanoparticle (f-MWCNT/ AgNP) nanocomposites as the biosensing material to detect DA. The SEM, EDS, and TEM characterizations indicated the success of the functionalization process with MWCNT as the base material. The values of the linear range, the limit of detection (LOD), and the selectivity of the nanocomposite were all obtained from the Differential Pulse Voltammetry (DPV) measurements. The obtained LOD value was 0.2778 mM in the linear range of 0-8 mM, which is lower than the required concentration value for detecting DA in human urine (0.3-3 mM). The biosensor's high selectivity on DA with the presence of other human-related biofluids was also reported. These results show that f-MWCNT/AgNP nanocomposites are a promising biosensor material for the detection of DA.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus identified as the cause of the Coronavirus Disease 2019 (COVID-19) outbreak. The gold standard for detecting this virus is polymerase chain reaction (PCR). The electrochemical biosensor method can be an alternative method for detecting several biomolecules, such as viruses, because it is proven to have several advantages, including portability, good sensitivity, high specificity, fast response, and ease of use. This study aims to optimize an electro­chemical aptasensor using an AuNP-modified screen-printed carbon electrode (SPCE) with an aptamer to detect RBD protein S SARS-CoV-2. Aptasensors with the streptavidin-biotin system were immobilized on the SPCE/AuNP surface via covalent bonding with linkers to 3-mercaptopropionic acid (MPA) and electrochemically characterized by the [Fe(CN)6]3-/4- redox system using differential pulse voltammetry. The results showed that the immobi­lized aptamer on the SPCE/AuNP electrode surface experienced a decrease in current from 11.388 to 4.623 µA. The experimental conditions were optimized using the Box-Behnken experimental design for the three factors that affect the current response. The results of the optimization of the three parameters are the concentration of aptamer, incubation time of aptamer, and incubation time of RBD protein S SARS-CoV-2, each of which is 0.5 µg/mL, 40 minutes, and 60 minutes, respectively. The RBD protein S SARS-CoV-2 with various concentrations was tested on an electrochemical aptasensor to determine the de­tection limit and quantification limit, and the respective results were 2.63 and 7.97 ng/mL. The electrochemical aptasensor that has been developed in this study can be applied to detect RBD protein S SARS-CoV-2 as a COVID-19 biomarker in a simple, practical, and sensitive way.

Present-day science indicates that developing sensors with excellent sensitivity and selectivity for detecting early signs of diseases is highly desirable. Electrochemical sensors offer a method for detecting diseases that are simpler, faster, and more accurate than conventional laboratory analysis methods. Primarily, exploiting non-noble-metal nanomaterials with excellent conductivity and large surface area is still an area of active research due to its highly sensitive and selective catalysts for electrochemical detection in enzyme-free sensors. In this research, we successfully fabricate Metal-Organic Framework (MOF) FeBDC-derived Fe3O4 for non-enzymatic electrochemical detection of glucose. FeBDC synthesis was carried out using the solvothermal method. FeCl2.4H2O and Benzene-1,4-dicarboxylic acid (H2BDC) are used as precursors to form FeBDC. The materials were further characterized utilizing X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier-Transform Infrared Spectroscopy (FTIR). The resulting MOF yields good crystallinity and micro-rod like morphology. Electrochemical properties were tested using Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) with a 0.1 M of Phosphate Buffer Saline (PBS pH 7.4) solution as the supporting electrolyte. The measurement results show the reduction and oxidation peaks in the CV curve of FeBDC, as well as Fe3O4. Pyrolysis of FeBDC to Fe3O4 increases the peak of oxidation and reduction currents. The Fe3O4 sample obtained has a sensitivity of 4.67 µA mM−1.cm−2, a linear range between 0.0 to 9.0 mM, and a glucose detection limit of 15.70 µM.

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A single‐chain variable fragment (scFv) is an antibody fragment composed of VH and VL linked by a hydrophilic linker that can be designed according to the shape of the target molecule and synthesized in prokaryotic or eukaryotic cells via biotechnology engineering. This study developed an electrochemical immunosensor that detects the RBD of SARS‐CoV‐2 using a screen‐printed carbon electrode modified with gold nanoparticles, and scFv as a bioreceptor. Electrochemical impedance spectroscopy was employed to measure specific interactions of antigens with antibodies. The developed immunosensor had a limit of detection and a quantification limit of 4.86 ng mL−1 and 16.20 ng mL−1, respectively. The immunosensor was stable at room temperature for up to 30 days’ storage. The immunosensor was assessed at biosafety level 3 using 33 nasopharyngeal swab specimens (clinical samples); the pieces of data were compared with quantitative Reverse Transcriptase‐PCR. The agreement of the data, the low detection limit achieved, the rapid analysis (30 min), the miniaturization, and the portability of the instrument combined with the easiness to use has the potential to become Point of Care (POC) for diagnosing the COVID‐19 disease.

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