Rapid, point-of-care, visual detection of RBD of SARS-CoV-2 spike protein using an acrylamide-free photonic crystal aptasensor.

As COVID-19 continues to reemerge with new variants, it has become a persistent challenge to public health, causing disruptions in society and the economy. We report a facile photonic crystal-based aptasensor for the rapid visual detection of the receptor-binding domain (RBD) of the severe acute respiratory syndrome (SARS-CoV-2) spike (S) protein. Monodispersed polystyrene@poly(2-hydroxyethyl methacrylate-acrylic acid) [PS@poly(HEMA-AA)] core-shell microspheres were synthesized to fabricate a stimuli-responsive photonic crystal (RPC). The integration of the RBD target-specific aptamer into the poly(HEMA-AA) hydrogel network facilitated the development of a biosensor that enabled RPCs to selectively bind to the SARS-CoV-2 spike protein using coupling chemistry. The interaction between the RBD and a single-stranded DNA aptamer causes the hydrogel to expand, leading to a color change and a shift in the photonic bandgap (PBG). This phenomenon can be used to detect the RBD of the SARS-CoV-2 spike protein. The addition of the RBD of SARS-CoV-2-S-protein to the Apt-RPC aptasensor resulted in a rapid visual color shift from violet to green. The detection range of the developed aptasensor was estimated to be 100-1000 ng with excellent selectivity. Thus, the developed aptasensor offers distinct advantages over conventional detection methods. Our study also facilitates the development of a straightforward point-of-care self-testing kit that does not rely on toxic acrylamide-based chemicals. Furthermore, the sensor eliminates the need for complex sample preparation or signal amplification steps, making it a promising platform for point-of-care diagnosis.