Uric acid sensing based on sandwich carbon electrode sets decorated with gold nanoparticles

Department of Mechanical EngineeringThis study reports an enzymatic uric acid sensor with enhanced electrochemical sensing performance by electrodepositing gold nanoparticles on sandwich carbon electrodes. The improvement of sensor performance was based on the structural advantage of sandwich carbon electrode sets, consisting of suspended carbon mesh electrode (SME) and substrate bound interdigitated electrodes (IDE). The uricase enzyme was selectively immobilized to IDE and by-product generated from uricase-uric acid reaction was detected in SME to track the uric acid concentration. As the SME is completely covering the IDE, the by-product can be detected with SME before being diffused into the bulk solution. The electrode structure was fabricated using simple and cost-effective technique known as carbon-microelectromechanical-systems (C-MEMS). The polymer structure was patterned using successive photolithography and converted into carbon electrode by vacuum pyrolysis. This unique technique enabled the wafer-level fabrication of two separate but adjacent electrodesSME and IDE. To enhance the surface reactivity and surface area of electrodes, gold nanoparticles were electrodeposited to the sandwich carbon electrodes. As the surface area of IDE is larger compared to the simple planar electrode, the electrodeposition of gold nanoparticles is improved on IDE. The uricase enzyme was selectively immobilized to the IDE with selective electrochemical surface modification using aryl diazonium reduction. Uricase enzyme was selectively immobilized by bonding with diazonium deposited to IDE. The selective immobilization of enzyme allowed the maintenance of SME surface electroactivity. Uric acid sensing performance was evaluated by conducting chronoamperometry test with the sensor structure for the uric acid concentration range of 0 to 1000 ??M. From structural advantage of sandwich carbon electrodes and high electrochemical reactivity of gold nanoparticles, the developed uric acid sensor was capable of sensitive uric acid sensing with low lower limit of detection (LOD) of 6.25 ??M. As uric acid concentration of healthy person???s blood is ranged from 120 to 450 ??M, the sensing range of this uric acid sensor is appropriate in detecting uric acid concentration in human blood. The sensitivity was calculated as change in current signal per uric acid concentration change divided with sensor operation area. The sandwich electrode structure showed high sensitivity with two linear ranges of uric acid concentration. The calculated sensitivity was 742.11 ??A??mM???1??cm???2 for low concentration range (0 ??? 100 ??M) and 553.26 ??A??mM???1??cm???2 for high concentration range (100 ??? 1000 ??M).clos