Accelerating the peroxidase-like activity of Co²⁺ by quinaldic acid: Mechanism and its analytical applications

Although enzyme mimics have been widely developed, limited catalytic efficiency is still a bottleneck, especially under neutral condition. Herein, we reported the bioactive quinaldic acid (QA) significantly boosted the peroxidase-like activity of Co²⁺ in the presence of bicarbonate (HCO₃^-). With 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonate) (ABTS) as the substrate, the catalytic activity of Co²⁺ (1 μM) was increased by over 300 times upon adding 100 μM QA. The formed Co²⁺ complex had much higher turnover number (5.52 min^-1) than that of cobalt-based nanozymes (0.011-0.51 min^-1) in decomposing H₂O₂. Based on this system, ultrasensitive colorimetric methods for the detection of Co²⁺, bicarbonate and urease activity were achieved with limits of detection of 4.6 nM, 40 μM and 0.00125 U/mL, respectively. For the first time, this work established an ultrasensitive method for the detection of urease activity by activating a peroxidase-like mimic with the produced HCO₃^-.