All-solid-state flexible visualization sensor based on sandwich structure and light-induced potential variation

A novel all-solid-state flexible electrochromic sensor without liquid electrolytes and external power sources is reported which simplifies device construction and instrumentation requirement and offers high stability and energy efficiency. A polyacrylamide hydrogel was used as the solid electrolyte, and prussian blue (PB) on one end of a flexible bipolar electrode (BPE) served as the electrochromic region. Molecularly imprinted polymers (MIPs) modified on the other pole of the BPE, as electron injection regions, recognized targets and formed a sandwich structure with the aptamer functionalized light-responsive zirconium-based metal-organic frameworks (UiO-66) coated TiO₂ (Apt-UiO-66@TiO₂) quantitatively. Under ultraviolet light-irradiation, the captured TiO₂@UiO-66 triggered potential differences between the two poles of the BPE, causing the discoloration of PB. The degree of PB color change correlated with the concentration of bisphenol A (BPA) in the range 1.0 × 10^-6 to 1.0 × 10^-12 M. BPA could be quantified via the intelligent RGB analysis, and the limit of detection reaches 5.96 × 10^-13 M. The sensor has been applied to the assay of BPA in bottled water samples with satisfactory results. This all-solid-state flexible sensor can be integrated into flexible devices with enhanced portability for field applications.