Biohybrid hydrogen-bonded organic framework sandwiched between nanoporous membranes: Novel structure for ultrasensitive electrochemical detection of urea

Biohybrids formed by encapsulating enzymes in hydrogen-bonded organic framework (HOF) have demonstrated promising applications in catalysis and biosensing. Herein, urease (Ur) was incorporated into a stable HOF named PFC-1 by initiating the self-assembly of organic monomers of PFC-1 using surface residues of the enzyme. The ultimate hybrids Ur-PFC-1 were characterized to confirm its similar structure with PFC-1 and successful Ur loading. A unique sandwich structure, using two nanoporous membranes as slices and Ur-PFC-1 as jam, was constructed. The nanochannels of the porous membranes provided ordered passageway for ion flux, which enabled the electrochemical detection of urea by measuring the ionic current. Ammonia generated by the catalytic hydrolysis of urea by Ur would affect the surface charge of the nanochannels and alter the ion current. This quantitative method exhibits a linear range of 25 pM to 2.8 μM with a detection limit of 12 pM. What’s more, this method has good repeatability and selectivity, and can be used for the detection of urea in serum samples.