Chemical modification of a nanocrystalline TiO2 film for efficient electric connection of glucose oxidase

Sputter coated ZnO thin films on glass and polycarbonate: Evaluation of stability and interaction with Flavin adenine dinucleotide-dependent oxidases

Aqueous stability of sputter coated ZnO thin films were studied on two base materials, viz., polycarbonate (PC) and glass. The films showed higher stability on PC compared to glass, when exposed to aqueous buffered solution at pH-7.4, as studied by x-ray diffraction, surface reflectometry, and inductively coupled plasma-optical emission spectroscopy. Glucose oxidase (GOx) and cholesterol oxidase (Chl.Ox.) were used as model enzymes to study their electrochemical interaction with ZnO/PC. GOx showed a higher immobilization on ZnO/PC with an activity of 9.2 ± 1.7 mU cm^-2 compared to Chl.Ox. with an activity of 2.79 ± 0.5 mU cm^-2. This is attributed to the larger crystallite size and higher Zn per unit area on PC as compared to glass which enabled a higher activity of GOx on ZnO/PC compared to ZnO/glass. Immobilization was mainly dependent on the surface residue and the charge of the enzyme as indicated by zeta potential which showed -23 mV for GOx compared to -6 mV for Chl.Ox. under physiological conditions. Further under unstirred condition, the reaction was limited by diffusion of the substrate for the enzyme. Chl.Ox. showed a lower activity as compared to GOx on the surface due to low diffusional coefficient of the bulky cholesterol molecule as compared to glucose. It was confirmed by low charge transfer resistance in electrochemical impedance spectroscopy for GOx (1.51 ± 0.072 × 10⁵ Ω) as compared to Chl.Ox. (1.98 ± 0.09 × 10⁵ Ω). But under stirring condition, the diffusion limitation was overcome, and the sensitivity for Chl.Ox./ZnO was 11.2 μA cm^-2mM^-1 as compared to GOx/ZnO/PC with 3.5 μA cm^-2mM^-1. Thus, sputter coated ZnO thin films appeared to be good quality transducers for immobilization of oxidases with sensitivity dependent on the substrate diffusion and its potential application in biosensors.

Electrochemical Study and Characterization of an Amperometric Biosensor Based on the Immobilization of Laccase in a Nanostructure of TiO₂ Synthesized by the Sol-Gel Method

Laccase amperometric biosensors were developed to detect the catechol compound. The laccase enzyme (LAC) immobilization was performed on nanostructures of (a) titania (TiO₂); (b) titania/Nafion (TiO₂/NAF) (both immobilized by the sol-gel method) and a third nanostructure, which consisted of a single biosensor composite of Nafion and laccase enzyme denoted as NAF/LAC. The Nafion was deposited on a graphite electrode and used to avoid "cracking" on the matrix. The TiO₂ particle size was an average of 66 nm. FTIR spectroscopy vibration modes of different composites were determined. The electrochemical behavior of the biosensor was studied using electrochemical spectroscopy (EIS) and cyclic voltammetry (CV). The biosensor based on TiO₂/NAF/LAC presented the best electro-chemical properties with regard to sensitivity, stability and detection limit after a period of 22 days.

Bioinspired peptide nanostructures for organic field-effect transistors

Peptide-based nanostructures derived from natural amino acids are superior building blocks for biocompatible devices as they can be used in a bottom-up process without the need for expensive lithography. A dense nanostructured network of l,l-diphenylalanine (FF) was synthesized using the solid-vapor-phase technique. Formation of the nanostructures and structure-phase relationship were investigated by electron microscopy and Raman scattering. Thin films of l,l-diphenylalanine micro/nanostructures (FF-MNSs) were used as the dielectric layer in pentacene-based field-effect transistors (FETs) and metal-insulator-semiconductor diodes both in bottom-gate and in top-gate structures. Bias stress studies show that FF-MNS-based pentacene FETs are more resistant to degradation than pentacene FETs using FF thin film (without any nanostructures) as the dielectric layer when both are subjected to sustained electric fields. Furthermore, it is demonstrated that the FF-MNSs can be functionalized for detection of enzyme-analyte interactions. This work opens up a novel and facile route toward scalable organic electronics using peptide nanostructures as scaffolding and as a platform for biosensing.