Detection of H2O2 using Carbon Nanotubes Covalently Attached to Nanostructured Au Electrode

Abstract

Detection of hydrogen peroxide (H 2 O 2 ) has practical significance in various fields, including pharmaceutical, clinical and food industries. The enzyme based H 2 O 2 biosensors allow for the detection at lower potentials, thus avoiding possible interference from reducing agents. However, this type of sensors is inherently less stable, difficult to fabricate and more expensive. Due to high electroactive surface area and electrocatalytic properties, gold nanoparticles and their combination with carbon nanotubes (CNTs) are commonly used in H 2 O 2 sensor design. To avoid fabrication inconveniences and improve stability of a H 2 O 2 sensor, we designed a new hybrid material in which CNTs are covalently attached to a gold surface. First, a highly homogeneous nanostructured gold surface was formed on top of the SiO 2 substrate with an intermediate layer of Ti, using E-beam evaporation technique. The average height of the gold nanostructures was 3.9 nm. The gold surface was then electrochemically grafted with aminophenyl groups. Further, plasma-functionalized densified CNT film made from CNT array was attached to the gold surface via amide formation reaction. An introduction of CNTs led to a 40-fold increase in current response. Formation of nanostructured gold surface without actual attachment of nanoparticles to the substrate, as well as covalent bonding of CNTs to the surface, provide a very high stability of the fabricated material, which, in turn, improves the repeatability of measurements. A designed electrode was used for non-enzymatic H 2 O 2 detection. Under optimized parameters of square wave voltammetry and optimum pH, analysis of H 2 O 2 can be performed using 5 independent oxidation peaks. The presence of multiple peaks is due to oxidation of gold, CNTs and H 2 O 2 itself. All peaks increase when H 2 O 2 is added in solution, because of chemical reduction of CNT and gold surfaces, and their consecutive electrochemical oxidation. Using the peak at -0.6 V allows for the H 2 O 2 detection at very low potential, that can minimize interference from various reducing agents. For the -0.6 V peak, the limit of detection was 1.4 mM. Using the peak at -0.05 V allows for much higher sensitivity with the limit of detection of 500 nM. Almost no signal deterioration was observed after 200 measurements, proving high stability of the fabricated electrodes.