Microsensor characterization in an integrated blood gas measurement system

In the healthcare sector, the monitoring of blood gases and other chemicals in the blood is crucial as they provide vital signs of the respiratory and metabolic well being of the human body. The measurement of blood gases is conventionally done using glass electrode sensors. The development of ion-sensitive field effect transistor (ISFET) has created a high potential in multiparameter chemical sensor devices. This microsensor is essentially based on the established MOSFET technology. In the design and characterisation of a pH ISFET sensor, the ISFET model was characterised and a final design has been evolved with the assistance of MATLAB and HSPICE software. Silicon nitrate (Si/sub 3/N/sub 4/) and aluminium oxide (Al/sub 2/O/sub 3/) were the ion-sensitive membranes considered in the model. pH analyses were performed on both the membranes to evaluate the electrical responses of the sensor to the change in pH. The effect of the physical parameters of the ISFET on the drain-source current output is studied. Various physical and electrical parameters have been analysed to propose an optimal output response of the ISFET sensor. The sensor achieved an average sensitivity of 50 mV/pH, which is comparable to other published works. By being capable of miniaturization, further advantages are gained, namely easier fabrication, better performance characteristics of the sensor, and the ability to integrate with other biomedical sensors on the same die without any electrical or spatial interferences.

1. Introduction

The advancements in medical and life sciences in recent years have promoted the growth and demand for biosensors in new diagnostic techniques and applications. Blood gas measurement plays a very vital role in medical diagnosis. Clinicians are increasingly dependent on the rapid and reliable measurement of the various chemical variables in blood for accurate diagnostic decisions. The objective in this paper is to design and characterise blood gas sensors as a front-end component for measurement of concentration of hydrogen ions in blood, with very small sample volumes. Suitable modelling of the sensor response has been carried out, and appropriate signal processing of the sensor output proposed.