Smartphone-Based Molecularly Imprinted Photonic Crystal Hydrogel Sensor for the Label-Free Detection of Bisphenol A

Here, the implementation of a smartphone-based portable molecularly imprinted photonic crystal hydrogel (MIPCH) colorimetric sensor for the visual and label-free detection of bisphenol A (BPA) in water samples is reported. The sensor is prepared by photopolymerizing BPA-added hydrogel precursor solution within the voids of a photonic crystal opal film, followed by the extraction of BPA molecules. Rebinding of the BPA analyte to the MIPCH causes the hydrogel to swell, leading to a significant redshift in the diffracting spectrum. The MIPCH sensor exhibits a low limit of detection of 0.96  ×  10⁻¹⁵ m. The sensor also shows linear response in the femtomolar range, rapid responsiveness (≤6 min), selective detection of BPA in complex matrices, long-term stability, and reproducibility. Images of the sensor responses are used to train a deep-learning-based regression model on a smartphone to predict the BPA concentration quantitatively. Integration of the regression model with the developed sensor provides an accurate and portable smart sensor platform well-suited for real-time and on-field monitoring of BPA.