Hydroxyapatite-Gold Modified Screen-Printed Carbon Electrode for Selective SARS-CoV-2 Antibody Immunosensor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or coronavirus disease 2019 (COVID-19), is still spreading worldwide; therefore, the need for rapid and accurate detection methods remains relevant to maintain the spread of this infectious disease. Electrochemical immunosensors are an alternative method for the rapid detection of the SARS-CoV-2 virus. Herein, we report the development of a screen-printed carbon electrode immunosensor using a hydroxyapatite-gold nanocomposite (SPCE/HA-Au) directly spray-coated with the immobilization receptor binding domain (RBD) Spike to increase the conductivity and surface electrode area. The HA-Au composite synthesis was optimized using the Box-Behnken method, and the resulting composite was characterized by UV-vis spectrophotometry, TEM-EDX, and XRD analysis. The specific interaction of RBD Spike with immunoglobulin G (IgG) antibodies was evaluated by differential pulse voltammetry and electrochemical impedance spectroscopy methods in a [Fe(CN)6]4-/3- solution redox system. The IgG was detected with a detection limit of 0.0561 pg mL-1, and the immunosensor had selectivity and stability of 103-122% and was stable until week 7 with the influence of storage conditions. Also, the immunosensor was tested using real samples from human serum, where the results were confirmed using the chemiluminescent microparticle immunoassay (CMIA) method and showed satisfactory results. Therefore, the developed electrochemical immunosensor can rapidly and accurately detect SARS-CoV-2 antibodies.

Electrochemical investigation of hydroxyapatite-lanthanum strontium cobalt ferrite composites (HA-LSCF) for SARS-CoV-2 aptasensors

The hydroxyapatite-lanthanum strontium cobalt ferrite (HA-LSCF) composite showed a good response on a screen-printed carbon electrode (SPCE) electrochemical aptasensor to detect SARS-CoV-2. SPCE/HA-LSCF with a thiolated aptamer has a strong affinity for the SARS-CoV-2 spike RBD protein. This occurs due to the binding of -SH to the HA-positive region. In the presence of LSCF, which is conductive, an increase in electron transfer from the redox system [Fe(CN)6]3-/4- occurs. The interaction of the aptamer with the RBD protein can be observed based on the decrease in the electron transfer process. As a result, the developed biosensor is highly sensitive to the SARS-CoV-2 spike RBD protein with a linear range of 0.125 to 2.0 ng mL-1, a detection limit of 0.012 ng mL-1, and a quantification limit of 0.040 ng mL-1. The analytical application of the aptasensor demonstrates its feasibility in the analysis of saliva or swab samples.

A review post-vaccination SARS-CoV-2 serological test: Method and antibody titer response

The development of the Coronavirus disease 2019 (COVID-19) vaccine is one of the most important efforts in controlling the pandemic. Serological tests are used to identify highly reactive human donors for convalescent plasma therapy, measuring vaccine efficacy and durability. This review article presents a review of serology tests and how antibody titers in response to vaccines have been developed. Some of the serological test methods discussed are Plaque Reduction Neutralization Test (PRNT), Enzyme-Linked Immunosorbent Assay (ELISA), Lateral flow immunoassay (LFIA), chemiluminescent immunoassay (CLIA), and Chemiluminescent Micro-particle Immunoassay (CMIA). This review can provide an understanding of the application of the body's immune response to vaccines to get some new strategies for vaccines.