Recent research progress on surface-enhanced spectra of chiral molecules

Chiral molecules are ubiquitous in natural world. Molecular chirality determines their physical and chemical properties. Detection and characterization of these chiral enantiomers are of considerable importance for biochemical and pharmaceutical industries. Conventional chiroptical spectroscopy techniques nowadays can not meet the needs in practical applications, with the disadvantages of small signal and large noise, etc. It is necessary to solve these problems and characterize chiral enantiomers fast and sensitively. Surface-enhanced spectroscopic techniques delivered through specifically designed nanostructures have been proved to be highly successful for ultrasensitive chiral detection, with dramatic enhanced interactions between light and chiral molecules induced by nanostructures. There are considerable researches on surface-enhanced spectroscopic techniques in recent years, and the enhancement effect on the circular dichroism (CD), vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectrum is excellent. In this review, we present a survey of the recent work about surface-enhanced spectroscopic techniques in the two aspects of metal and dielectric nanostructures, respectively. Plasmonic nanostructures based on metallic elements can provide highly enhanced electric fields, which ensures the generation of strong chiral near fields, showing promise for the enhancement of detection sensitivities of chiral spectroscopies. The dielectric nanostructures exhibit strong enhancement of the electric near-field while simultaneously providing intense magnetic resonances, which can generate uniform-sign superchiral field, ensuring the untrasensitive chiral sensing. Besides, dielectric nanostructures show extremely low optical losses, which is very beneficial for the detection of enhanced chiroptical spectroscopy. With surface-enhanced spectroscopic method, it is promising to solve the problems in the chirality characterization techniques nowadays and lead to unprecedented levels of chiroptical sensitivity.