Stimuli-responsive colorimetric sensor based on bifunctional pyrophosphate-triggered controlled release and enhancing activity of CoOOH nanozyme

As a class of intelligent materials, stimuli-responsive hydrogels enable attractive sensors for sensitive and selective detection along with the potential for low production costs. Herein, we proposed a stimuli-responsive colorimetric sensor based on Cu2+-crosslinked alginate hydrogel loaded with CoOOH nanozyme. Upon binding of Cu2+ to pyrophosphate ion (PPi), the hydrogel would be disassembled by PPi, which controlled the release of CoOOH nanoflakes. Interestingly and importantly, it was found that PPi and PPi-Cu2+ could further enhance the catalytic activity of the released CoOOH nanozyme. Since alkaline phosphatase (ALP) can catalyze the hydrolysis of PPi to phosphate ion (Pi), a sensitive colorimetric sensor for ALP detection was constructed based on PPi-triggered controlled release and enhancing activity of CoOOH nanozyme. The as-constructed sensor exhibited good linear response to ALP over the range from 0.1 to 250 mU/mL with a detection limit of 0.07 mU/mL. Additionally, this sensor was also extended to measure two typical ALP inhibitors (Na3VO4 and EDTA) with reasonable results. Last but not least, it was confirmed that the detection results of ALP in real serum samples with the proposed sensor were in accordance with the data from clinical test, which indicates the robustness and practicability of this stimuli-responsive colorimetric sensor.