The present invention relates to an optical sensing chip, which has various applications and may be used repetitively. The optical sensing chip can qualitatively identify different types of molecules and quantitatively analyze small molecules in minute amounts. Regarding a conventional optical sensing chip, an additional sample of known concentration is required as a reference in signal comparison for quantitative determination. In the disclosure, it is unnecessary to add the additional sample of known concentration, but the optical sensing chip itself provides a fixed optical signal that is not varied along with environmental changes to serve as a reference for quantitative determination. In addition, the optical sensing chip also possesses the ability to concentrate or filter sample in real-time.