Colorimetric two-dimensional photonic crystal biosensors for label-free detection of hydrogen peroxide

Hydrogen peroxide (H2O2) detection is highly desirable for both environment and health concerns and a number of methods have been developed to monitor H2O2. However, most methods are limited due to the need of sophisticated instrument and high cost. Here we report a label-free two-dimensional (2-D) photonic crystal (PhC) horseradish peroxidase/bovine serum albumin (HRP/BSA) protein composite hydrogel sensor to monitor H2O2. Our 2-D PhC HRP/BSA protein composite hydrogel sensor is fabricated by mild protein cross-linking of BSA and HRP with glutaraldehyde, where BSA acts as a scaffold of HRP while HRP acts as the recognition molecule. The 2-D PhC HRP/BSA protein composite hydrogel sensor selectively detects H2O2 since HRP can specifically decompose H2O2 accompanying with heme inactivation. This protein hydrogel undergoes a volume phase transition as a result of peroxidase inactivation. The inactivation-induced conformational change of HRP gives rise to a decreased cross-linking density, which enlarges the particle spacing and decreases the Debye ring of the 2-D photonic crystals (PhCs). Our optimized 2-D PhC HRP/BSA-75 protein composite hydrogel sensors show a good linear range from 8.8 × 10-6 M to 60.6 × 10-6 M and an excellent sensitivity with a limit of detection of 8.8 × 10-6 M. This sensor fabrication method demonstrates the proof-of-concept for utilizing proteins with few lysine groups to develop smart PhC protein composite hydrogel sensors to determine H2O2 concentration in solution, which makes it possible for developing protein organogel sensors to detect gaseous H2O2 in the future.