Inaccurate diagnoses contributes to the high mortality rate of breast cancer. Human epidermal growth factor receptor 2 (HER2) is overexpressed in breast cancer tumors at around 20–30%. This study aims to develop an electrochemical biosensor for HER2 based on a gold nanoparticle-aptamer bioconjugate (AuNP@HER2 aptamer) and investigate the interaction between DNA aptamer and HER2 using computational methods. The bioconjugate was synthesized using maleimide and polyethylene glycol as a linker. The –NH2 group of cysteamine that modified the gold electrode can form a covalent bond with the bioconjugate maleimide. The interaction of the bioconjugated aptamer with HER2 was measured electrochemically based on the [Fe(CN)6]3−/4− redox system. The limit of detection, the linear range of HER2, precision, and accuracy in this study were 1.52 ng mL–1, 0.01 to 15.0 ng mL–1, 0.1298, and 94.06%, respectively. The structure of the DNA aptamer was modeled using mFold, Assemble2, and Chimera, with the interaction between the DNA aptamer and HER2 explored by NPDock. The modeling of the aptamer with HER2 showed that electrostatic interactions dominated the attractive forces. The resulting interaction pattern can be used as a template to improve the binding energy of the aptamer, thus providing insight into the development of aptamer-based biosensors.

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Two years after SARS-CoV-2 caused the first case of COVID-19, we are now in the “new normal” period, where people’s activity has bounced back, followed by the easing of travel policy restrictions. The lesson learned is that the wide availability of accurate and rapid testing procedures is crucial to overcome possible outbreaks in the future. Therefore, many laboratories worldwide have been racing to develop a new point-of-care diagnostic test. To aid continuous innovation, we developed a plasmonic-based biosensor designed explicitly for portable Surface Plasmon Resonance (SPR). In this study, we designed a single chain variable fragment (scFv) from the CR3022 antibody with a particular linker that inserted a cysteine residue at the second position. It caused the linker to have a strong affinity to the gold surface through thiol-coupling and possibly become a ready-to-use bioreceptor toward a portable SPR gold chip without purification steps. The theoretical affinity of this scFv on spike protein was −64.7 kcal/mol, computed using the Molecular Mechanics Generalized Born Surface Area (MM/GBSA) method from the 100 ns molecular dynamics trajectory. Furthermore, the scFv was produced in Escherichia coli BL21(DE3) as a soluble protein. The binding activity toward Spike Receptor Binding Domain (RBD) SARS-CoV-2 was confirmed with a spot-test, and the experimental binding free energy of −10.82 kcal/mol was determined using portable SPR spectroscopy. We hope this study will be useful in designing specific and low-cost bioreceptors, particularly early in an outbreak when the information on antibody capture is still limited.

More than 6,000,000 people have died due to the coronavirus (COVID‐19) pandemic. This disease spread quickly due to its highly contagious nature. The SARS‐CoV‐2 virus that causes the disease can be transmitted through saliva droplets secreted by infected people at a distance of less than 1 m. As a result, saliva has been accepted as an alternative specimen for COVID‐19 detection by the Centers for Disease Control and Prevention (CDC). Furthermore, WHO recommended the use of rapid antigen tests based on lateral flow immunoassay when reverse transcription‐polymerase chain reaction (RT‐PCR) is not available. We developed a saliva‐based rapid antigen test by optimizing the antibody concentration and optimum pH for the conjugation of antibody and gold nanoparticles. We found that the best running buffer formulation consisted of 75 mM sodium phosphate buffer, 1% NaCl, 1% Triton X‐100, 0.5% N‐acetyl‐L‐cysteine, and 0.02% sodium azide. The addition of a mucolytic agent in the buffer can reduce the viscosity of saliva, thus improving sensitivity. The rapid test developed detected the lowest concentration of nucleocapsid protein at 0.1 μg/mL. Our study revealed 100% specificity against negative COVID‐19 saliva and no cross‐reaction with avian influenza virus hemagglutinin.