Development and characterization of an all-solid-state potentiometric biosensor array microfluidic device for multiple ion analysis

A microfluidic device with an all-solid-state potentiometric biosensor array was developed using microfabrication technology. The sensor array included a pH indicator, and potassium and calcium ion-selective microelectrodes. The pH indicator was an iridium oxide thin film modified platinum microelectrode and the iridium oxide was deposited by an electrochemical method. The potassium and calcium ion-selective microelectrodes were platinum coated with silicon rubber based ion-selective membranes with respectively potassium (valinomycin) and calcium (ETH 1001) ionophores. The detection system was integrated with a micro-pneumatic pump which can continuously drive fluids into the microchannel through sensors at flow rates ranging from 52.4 μl min^-1 to 7.67 μl min^-1. The sensor array microfluidic device showed near-Nernstian responses with slopes of 62.62 mV ± 2.5 mV pH ^-1, 53.76 mV ± 3 mV -log[K⁺]^-1 and 25.77 mV ± 2 mV -log[Ca²⁺]^-1 at 25°C ± 5°C, and a linear response within the pH range of 2-10, with potassium and calcium concentrations between 0.1 M and 10^-6 M. In this study the device provided a convenient way to measure the concentration of hydrogen, potassium and calcium ions, which are important physiological parameters.