Rapid and accurate detection of SARS-CoV-2 spike protein by aptamer conformation change based on a reusable aptasensor.

Timely and accurate detection of the virus is of great significance to prevent the virus's harm and control the epidemic. Here, an aptasensor based on the principle of promoting hybridization through aptamer conformational change was designed to quantitatively detect the spike (S) protein of SARS-CoV-2. When the S protein binds to the 3' end of the aptamer, the 5' end of the aptamer tansforms into a straight hybridization region, which will greatly facilitate the hybridization with complementary DNA (cDNA). In the absence of S protein, hybridization is less likely to occur due to the complex G-quadruplex structure of aptamer. According to this principle, cDNA is modified onto magnetic beads (MBs) or onto the optical fiber probe of an evanescent wave fluorescence aptasensor (EWFA) detection platform to capture the fluorescently labeled aptamer-S protein conjugate, two kinds of quantitative detection methods for SARS-CoV-2 S protein were established. In particular, simple, rapid and sensitive detection could be obtained based on the EWFA detection platform, in which the whole detection procedure including the measurement and regeneration takes  only 14 min, the LOD is 5.34 ng/mL, the linear response range is 141.49 to 9507.36 ng/mL, and the optical fiber probe could be reused for 19 times. The EWFA detection platform is also potentially applicable to detect other protein biomarkers only by replacing the specifically modified optical fiber probes.