Measurement of Chiral Molecular Parameters Based on a Combination of Surface Plasmon Resonance and Weak Value Amplification

A novel combination of surface plasmon resonance (SPR) and weak value amplification (WVA) is employed to measure the optical rotation angle and refractive index of chiral enantiomers such as sugars and amino acids. An extremely low optical rotation change (2.73 × 10^-4 rad) is readily measurable, with a resolution of 6.75 × 10^-7 rad, 1 order of magnitude higher than that obtained using weak value amplification with intensity modulation, and a refractive index change of 1.13 × 10^-6 RIU is also detected, with a resolution of 1.99 × 10^-9 RIU, a nearly 1-order-of-magnitude increase in sensitivity over weak measurement based on a Mach-Zehnder interferometer. The optical activity and refractive index changes of chiral molecules are determined in real time by measurements of the output light intensity variation, whereby the absolute configuration of the chiral molecule is identified through the relation between intensity and molecular orientation. The SPR-WVA combination sensing scheme fills the gap of capability for detecting the optical activity of a molecular solution, which has not been possible with conventional SPR alone.