The development of immunosensors to detect antibodies or antigens has stood out in the face of traditional methods for diagnosing emerging diseases such as the one caused by the SARS-CoV-2 virus. The present study reports the construction of a simplified electrochemical immunosensor using a graphene-binding peptide applied as a recognition site to detect SARS-CoV-2 antibodies. A screen-printed electrode was used for sensor preparation by adding a solution of peptide and reduced graphene oxide (rGO). The peptide-rGO suspension was characterized by scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical characterization (electrochemical impedance spectroscopy—EIS, cyclic voltammetry—CV and differential pulse voltammetry—DPV) was performed on the modified electrode. The immunosensor response is based on the decrease in the faradaic signal of an electrochemical probe resulting from immunocomplex formation. Using the best set of experimental conditions, the analytic curve obtained showed a good linear regression (r² = 0.913) and a limit of detection (LOD) of 0.77 μg mL⁻¹ for antibody detection. The CV and EIS results proved the efficiency of device assembly. The high selectivity of the platform, which can be attributed to the peptide, was demonstrated by the decrease in the current percentage for samples with antibody against the SARS-CoV-2 S protein and the increase in the other antibodies tested. Additionally, the DPV measurements showed a clearly distinguishable response in assays against human serum samples, with sera with a response above 95% being considered negative, whereas responses below this value were considered positive. The diagnostic platform developed with specific peptides is promising and has the potential for application in the diagnosis of other infections that lead to high antibody titers.

Here, a carbon paste modified electrode (CPME) with Zn/Al-layered double hydroxide (Zn/Al-LDH) was developed for the simultaneous electrochemical detection of dopamine (DA) and uric acid (UA). The surface morphology and structural features of the synthesized Zn/Al-LDH were analyzed using scanning electron microscopy and X-ray diffraction analysis. The LDH-modified sensor exhibited enhanced adsorptive properties, significantly improving the preconcentration and detection of the targets. Electrochemical characterization using square wave voltammetry demonstrated that the Zn/Al-LDH structure plays a crucial role in increasing sensitivity due to its high surface area and favorable electrostatic interactions by adsorptive preconcentration separate from the electrochemical cell. Under optimized conditions (preconcentration pH of 6.0 and an electrochemical cell pH of 7.0), the sensor demonstrated excellent linearity across biologically relevant concentrations, ranging from 0.2 to 20 μM, in phosphate-buffered saline (PBS), synthetic urine, and synthetic cerebrospinal fluid, with limits of detection of 68 nM for UA and 71 nM for DA. Recovery studies confirmed the sensor’s reliability in complex biological matrices, with recoveries ranging from 90% to 120%. Compared to existing electrochemical sensors, the Zn/Al LDH-modified CPE offers a promising, selective, and efficient platform for neurotransmitter and metabolite analysis in biological samples.