Pullulan-stabilized gold nanoparticles tablet as a nanozyme sensor for point-of-care applications

In this article, we first report the fabrication of pullulan-stabilized gold nanoparticles tablet (AuNPs-pTab) as a point-of-care (POC) analytical device using pullulan-AuNPs solution (AuNPs-pSol) without any additional tablet forming ingredient and then use AuNPs-pTab as a colorimetric sensor for glucose detection in human saliva samples. The AuNPs-pTab sensor fabrication comprises three steps: 1) synthesis of AuNPs-pSol, 2) formation of AuNPs-pTab in an oven at 50 C for 30 min, and 3) colorimetric detection of glucose using AuNPs-pTab as peroxidase-mimic enzymatic activity employing TMB-H2O2 system. AuNPs-pSol was synthesized by one-pot two-steps method using gold (III) chloride and pullulan as an all-in-one reagent; reducing/stabilizing/tablet forming agent followed by casting of AuNPs-pTab. The fabricated tablet was characterized using UV-vis, FTIR, TEM, DLS, and zeta potential analysis, and results were compared with AuNPs-pSol. The morphology of nanoparticles in tablet was similar to the AuNPs in solution phase. The AuNPs-pTab is stable for > 6 months as compared to AuNPs-pSol which lost stability after one month. The peroxidase-mimic enzymatic behavior of AuNPs-pTab was 25% better than AuNPs-pSol as depicted by the development of intense blue color of oxidized TMB. The effect of pH, temperature, and concentration of TMB as well as AuNPs-pTab was studied to see their impact on glucose assay. The reaction rate was calculated using Michaelis Menten's model of TMB oxidation while the calibration curve for glucose monitoring is fitted using a dose-response equation with a linear range of 0-5 mu M of glucose. The limit of detection (LoD) for H2O2 was found to be 28.7 mu M in the buffer while it was 38.2 and 163.04 mu M for glucose in buffer and artificial human saliva, respectively. Percentage recovery for real human saliva was calculated as 93.6-107.7%. Our newly proposed AuNPs-pTab sensor has shown excellent peroxidase-like activity and provides an easy substitute for AuNPs solution with enhanced catalytic efficiency. Moreover, the AuNPs-pTab sensor is a promising platform for POC devices due to its fulfillment of ASSURED criteria. AuNPs-pTab sensor opens a new horizon in disease diagnosis due to its ability to detect H2O2 which is a potential biomarker for many diseases. Our work is appealing to researchers working in nanotechnology, and the devel-opment of new bioassays as well as POC devices.