Mediator-free interaction of glucose oxidase, as model enzyme for immobilization, with Al-doped and undoped ZnO thin films laser-deposited on polycarbonate supports

Abstract

Research Highlights: Electrochemical interaction of ZnO and AZO thin films with the enzyme glucose oxidase was studied.  Nature of interaction of GOx with AZO was explored using XPS.  Mechanism of the electron transfer between GOx and AZO/ZnO was studied using EIS.  The results show that AZO is preferable to ZnO for GOx immobilization and glucose sensor development. Abstract:Al doped and undoped ZnO thin films were deposited by pulsed-laser deposition on polycarbonate sheets. The films were characterized by optical transmission, Hall effect measurement, XRD and SEM. Optical transmission and surface reflectometry studies showed good transparency with thicknesses ~100 nm and surface roughness of 10 nm. Hall effect measurements showed that the sheet carrier concentration was -1.44 x 10 15 cm -2 for AZO and -6 x 10 14 cm -2 for ZnO. The films were then modified by drop-casting glucose oxidase (GOx) without the use of any mediators. Higher protein concentration was observed on ZnO as compared to AZO with higher specific activity for ZnO (0.042 U mg -1 ) compared to AZO (0.032 U mg -1 ), and was in agreement with cyclic voltemmetry (CV). X-ray photoelectron spectroscopy (XPS) suggested that the protein was bound by dipole interactions between AZO lattice oxygen and the amino group of the enzyme. Chronoamperometry showed sensitivity of 5.5 µA mM -1 cm -2 towards glucose for GOx/AZO and 2.2 µA mM -1 cm -2 for GOx/ZnO. The limit of detection (LoD) was 167 µM of glucose for GOx/AZO, as compared to 360 µM for GOx/ZnO. The linearity was 0.28-28 mM for GOx/AZO whereas it was 0.6-28 mM for GOx/ZnO with a response time of 10s. Possibly due to higher enzyme loading, the decrease of impedance in presence of glucose was larger for GOx/ZnO as compared to GOx/AZO in electrochemical impedance spectroscopy (EIS). Analyses with clinical blood serum samples showed that the systems had good reproducibility and accuracy. The characteristics of novel ZnO and AZO thin films with GOx as a model enzyme, should prove useful for the future fabrication of inexpensive, highly sensitive, disposable electrochemical biosensors for high throughput diagnostics.

Biocatalytic Membrane Based on Polydopamine Coating: A Platform for Studying Immobilization Mechanisms

“…The concentration of H 2 O 2 was calculated using the following equation where ε is the molar extinction coefficient of 4-AAP at 505 nm and equals 12.88 mM –1 cm –1 , L is the effective width of the cuvette used, and the factor 1/2 corresponds to the 2 mol of H 2 O 2 required to reduce 1 mol of 4-AAP …”

Doping Ag in ZnO Nanorods to Improve the Performance of Related Enzymatic Glucose Sensors

“…As shown in Table 1 , the detection limits of the ZnO-Ag-based glucose sensors are slightly smaller than those reported in the literature [ 13 , 14 , 17 ], whilst the linear ranges are close to the corresponding values. Whereas the sensitivities of the ZnO-Ag-based glucose sensors approach that of the ZnO-Al-based one, they are much smaller than that of the ZnO-Ni- and ZnO-Co-based ones.…”

“…[ 12 , 13 , 14 ] or excellent conductivity (such as Au, C, and Al, etc.) [ 15 , 16 , 17 ]. For example, Anusha coated Pt nanoparticles on ZnO nanoporous structures, and confirmed that the Pt nanoparticles enhance both the catalytic activity and electron transfer ability of the glucose sensor [ 12 ].…”

“…Wei hydrothermally synthesized Au nanocrystals on the surface of ZnO nanorods, and demonstrated that the nanocrystals promote the direct electron transfer between GOx and ZnO nanorods [ 15 ]. Fidal doped Al in ZnO thin films, and proved that doping with Al increases the carrier concentration of the ZnO thin film as well as the sensitivity of the glucose sensor [ 17 ]. Obviously, these nanoparticles enhance the catalytic character of the glucose sensors, and more redox electrons are generated and transferred from the redox active centers of GOx to the ZnO surface.…”