Chapter 2 - Biosensors for Intracellular and Less Invasive Measurements Based on Nanostructured Metal Oxides

Abstract

Nanostructured metal oxides have opened innovative and exciting opportunities for exploring intracellular biosensing applications. Metal-oxides-based nanostructures such as zinc oxide/copper oxide (ZnO/CuO) is relatively a biosafe, biocompatible, and large surface area nanostructures with polar surface that can be used for biomedical applications. Metal oxide nanostructures have been widely explored to develop biosensors with high sensitivity, fast response time, and sufficient stability for the determination of intracellular metal ions and glucose by electrochemical methods. In this chapter, we report on a functionalized ZnO-nanostructure-based selective electrochemical sensor for intracellular metal ions and glucose. To apply the biosensor concept to intracellular and less invasive measurements based on nanostructured metal oxides, hexagonal ZnO nanorods were grown on the tip of a silver-covered borosilicate glass capillary (0.7µm diameter) and coated with the membrane/enzyme. The membrane/enzyme-coated ZnO nanorods exhibited a metal ions/glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference was linear over a wide concentration range of interest. The effect of the hormone insulin and extracellular injected metal ions, which increased the concentration of intracellular glucose/metal ions, was also demonstrated. These results demonstrate the capability to perform biologically relevant measurements of metal ions/glucose within living cells. The ZnO nanorod metal ions/glucose electrode thus holds promise for minimally invasive dynamic analyses of single cells. The measured metal ions/glucose concentration in human adipocytes or frog oocytes using ZnO nanorod sensor was consistent with values reported in the literature. This microelectrode device represents a simple but powerful technique to measure intracellular metal ions/glucose concentration which is of particular importance with regard to investigations into bone destruction/diabetes and its consequences.