Flexible microfluidic colorimetric detection chip integrated with ABTS? plus and Co@MnO2 nanozyme catalyzed TMB reaction systems for bio-enzyme free detection of sweat uric acid

Background: The development of wearable detection devices that can achieve noninvasive, on -site and real-time monitoring of sweat metabolites is of great demand and practical significance for point -of -care testing and healthcare monitoring. Monitoring uric acid (UA) content in sweat provides a simple and promising way to reduce the risk of gout and hyperuricemia. Traditional bioenzyme based UA assays suffer from high cost, poor stability, inconvenience for storage and easy deactivation of bioenzymes. Wearable microfluidic colorimetric detection device for sweat UA detection has not been reported. The development of novel wearable microfluidic colorimetric detection chip with no requirement of bioenzymes for sweat UA detection is of great importance for health care monitoring. Results: Firstly, Co@MnO2 nanozyme with high oxidase-like activity was synthesized and characterized. Co@MnO2 can catalyze the oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB) directly to generate blue-green colored ox-TMB. Green colored 2,2 '-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) radical (ABTS & sdot;+) was produced by the oxidation of ABTS by potassium persulfate. UA exhibits distinct quenching effect on Co@MnO2 catalyzed TMB colorimetric reaction system and ABTS & sdot;+ based colorimetric system, leading to obvious color fading of the two colorimetric systems. Then, a flexible microfluidic colorimetric detection chip for UA detection was fabricated by assembling Co@MnO2/TMB modified paper chips and ABTS & sdot;+ modified paper chips into a polydimethylsiloxane (PDMS) microfluidic chip. The fabricated microfluidic colorimetric detection chip exhibits good linear relationship for sweat UA detection. The linear range is from 20 to 200 mu mol/L with detection limit as low as 6.6 mu mol/L. Good results were obtained for the detection of UA in actual sweat from three volunteers. Significance: This work provides two bio-enzyme free colorimetric detection systems for UA detection. Furthermore, a simple, low-cost and selective flexible wearable microfluidic colorimetric detection chip was fabricated for noninvasive and on -site detection of sweat UA, which holds great application potential for personal health monitoring and point -of -care testing.