Motivated by reported aptamers targeting the RBD of S protein , we decided to use aptamer as a recognition element to develop protein assays using isothermal amplification to achieve high sensitivity. Several isothermal amplification methods, for example, hybrid chain reaction (HCR) and rolling circle amplification (RCA) , are suitable for in situ signal amplification on the surface of solid materials. As DNA-encoded information is stable and can be converted easily into optical or electrochemical signals, DNA-based probes are routinely used in bioanalytical assays. The nucleic acid sequences can also be designed to form various interesting structures for signal output .