An optical rotation bio-sensor based on the photonic spin Hall effect was established and applied to detecting the concentration varieties of chiral molecules. The optical rotation, introduced by sample solutions, was exploited to modulate the postselected polarization of a weak measurement system. Much work has been done in the case of glucose and fructose. However, little attention has been paid for biomolecules, such as proteins and amino acids. With this modulation, the optical rotation can be determined through the direction and spin accumulation of light spots, thus mirroring the concentration of solutions. A resolution of 2×10–4 degree was achieved.