Room-temperature phosphorescent carbonized polymer dots as superior photoresponsive oxidase mimics for colorimetric-fluorescence dual-mode enzyme-free sensing of uric acid.

Photoresponsive nanozymes are widely used in analysis and other fields owing to their controllable catalysis and low cost, but most have relatively low catalytic efficiency. In this study, room-temperature phosphorescent carbonized polymer dots (PCPDs) were optimally prepared through a one-pot hydrothermal method using polyacrylic acid and ethylenediamine as precursors. Their photoresponsive oxidase-like activity was confirmed for the first time. The sub-fluorophore and highly-crosslinked structure endow PCPDs with excellent enzymatic properties. The PCPDs have strong affinity (Km = 0.1266 mM) and extremely high catalytic efficiency (Vmax = 2.0194 × 10-6 M s-1) over 3,3',5,5'-tetramethylbenzidine (TMB), and the reaction is dozens of times faster compared with most photoresponsive oxidases (10-8 M s-1 level). Uric acid (UA) is an important biomarker, and its sensitive detection is particularly critical. The PCPDs were irradiated for 1 min to oxidize TMB into dark blue, and the strong reducing property of UA faded the dark blue and enhanced the fluorescence (FL) of the system. The colorimetric/FL dual-mode method established has detection limits over UA of 77.8 and 48.1 nM, respectively, and linear ranges of 0.6-55 and 0.6-60 μM, respectively. Smartphones were also used to identify dual-mode RGB to detect UA. Finally, the PCPDs were successfully used to detect UA in human serum, urine and saliva. This study presents a natural-enzyme-free UA sensing platform based on PCPDs, and more importantly, provides a new type of highly efficient photoresponsive oxidases with great potential for analytical sensing and other fields.