Conductive Dual Dynamic Cross-Linked H⁺-Responsive Hydrogel for Electrochemical Sensitive Monitoring of Carbonic...

Tracking the activity of carbonic anhydrase (CA) is a crucial quality-control step in algae-based carbon storage and conversion technologies. In this study, a high-performance H⁺-responsive hydrogel was developed by combining responsive dual-cross-linkers with a nanoconductive composite to construct an electrochemical biosensor for assaying CA activity. The hydrogel was synthesized by forming Schiff base bonds between oxidized dextran (ODex) and carboxymethyl chitosan, along with boronate ester bonds between ODex and borax. Upon the generation of H⁺ ions by CA catalysis (pH 7.0 to 5.0), the Schiff base and boronate ester bonds in the hydrogel rapidly break, increasing the gel's swelling degree and network porosity. This structural change facilitates the diffusion of electrochemical signal probes from the solution to the electrode surface, resulting in an enhanced current signal. Additionally, MXene nanosheets create continuous electron transport channels throughout the gel matrix. Their abundant surface functional groups (-O, -OH, -F) exhibit strong reducing properties, enabling the in situ growth of Au nanoparticles on MXene surfaces without the need for additional reductants or stabilizers, which enhances the hydrogel's conductivity and improves sensor sensitivity. Experimental results demonstrate that this sensor achieves a wide detection range of 0.035 U to 35,000 U and an ultralow detection limit of 0.005 U for CA activity in microalgal extracellular fluid. This work develops a conductive hydrogel to create a sensitive electrochemical method for detecting CA activity, which can be applied in carbon storage and conversion technologies to enhance quality control.