A nozzle-type ultra-micro-volume multi-ion sensor using a rear-gate SIS/ISFET

A nozzle-type micro multi-ion (NMM) sensor suitable for ultra-micro-volume sample-solution analysis has been developed using a newly designed rear-gate silicon-insulator-silicon (SIS) three-layer structure ISFET chip. The sensor inner volume is only 2.5 μl from the nozzle tip to the ISFET part for sensing the temperature and three types of ions. The outer body of the sensor is also sufficiently small to be dipped into the standard miniature sample vessels used in automatic blood analysers. K⁺, Na⁺ and Cl^- ion-sensing membranes are formed on the ISFET, and their basic characteristics and durabilities are checked. Furthermore, the sample solution volume needed for the sensor is estimated from pH and K⁺ ion flow-through sensing measurements. As a result, the sensor durability to cleaning by a detergent solution has been more than doubled by means of the membrane-locking structure of the ISFET chip. Also, the sample volume needed for the measurement has been drastically reduced to about 20 μl including prior sample-solution rinsing.