Fig. 1: Concept of chiral biosensing based on extreme nanophotonics.

a Schematic of the enantiomers of OS molecules and their chiral transfer process, forming P-/M-Helices via H-bonding and P-/M-DHs via π-π interactions. The difference in the absorption of LCP and RCP light generates the CD spectra. b UV–Vis absorption and c CD spectra of P-/M-helix and their racemate. The dash lines are fitted spectra with parameters indicated in the simulation section. d Change of CD enhancement (CDE) or CDSE with decreasing mode volume of plasmonic nanostructures. Insets are schematics of several typical plasmonic nanostructures, from left to right are NPoM, chain, dimer, nanorod and nanoisland. The colors of light orange, pink, green, and blue represent the typical correlation between mode volume and CDE (CDSE) value of NPoM, chain/dimer, nanorod, and nanoisland, respectively. The dashed line serves as a guide for eyes only.