Label‐free optical detection of C‐reactive protein by nanoimprint lithography‐based 2D‐photonic crystal film

The development of high‐sensitive, and cost‐effective novel biosensors have been strongly desired for future medical diagnostics. To develop novel biosensor, the authors focused on the specific optical characteristics of photonic crystal. In this study, a label‐free optical biosensor, polymer‐based two‐dimensional photonic crystal (2D‐PhC) film fabricated using nanoimprint lithography (NIL), was developed for detection of C‐reactive protein (CRP) in human serum. The nano‐hole array constructed NIL‐based 2D‐PhC (hole diameter: 230 nm, distance: 230, depth: 200 nm) was fabricated on a cyclo‐olefin polymer (COP) film (100 µm) using thermal NIL and required surface modifications to reduce nonspecific adsorption of target proteins. Antigen‐antibody reactions on the NIL‐based 2D‐PhC caused changes to the surrounding refractive index, which was monitored as reflection spectrum changes in the visible region. By using surface modified 2D‐PhC, the calculated detection limit for CRP was 12.24 pg/mL at an extremely short reaction time (5 min) without the need for additional labeling procedures and secondary antibody. Furthermore, using the dual‐functional random copolymer, CRP could be detected in a pooled blood serum diluted 100× with dramatic reduction of nonspecific adsorption. From these results, the NIL‐based 2D‐PhC film has great potential for development of an on‐site, high‐sensitivity, cost‐effective, label‐free biosensor for medical diagnostics applications