Specific and ultrasensitive ciprofloxacin detection by responsive photonic crystal sensor

A new approach for specific and ultrasensitive measurement of ciprofloxacin has been developed by integrating ternary complexes into responsive photonic crystal (RPC). Tryptophan was first immobilized within the polyacrylamide hydrogel substrates of RPC. The determination of ciprofloxacin was via the existence of zinc(II) ions that function as a 'bridge' to form specific tryptophan-zinc(II)-ciprofloxacin complexes step by step, which resulted in a stepwise red-shift of the diffraction wavelength. A maximum wavelength shift from 798 to 870 nm for ciprofloxacin was observed when the RPC film was immersed in 10−4 M ciprofloxacin. A linear relationship has been obtained between the Δλ of diffraction peak and logarithm of ciprofloxacin concentration at pH 5.0 in the range of 10−10 to 10−4 M. And the least detectable concentration in present work is about 5 × 10−11 M. The results demonstrated that the as-designed ternary complexes-based RPC sensor exhibited high sensitivity, satisfactory specificity and excellent recoverability for sensing of ciprofloxacin in aqueous media and were validated by detecting ciprofloxacin in the eye-drop sample.