Development of a package-free transparent disposable biosensor chip for simultaneous measurements of blood constituents and investigation of its storage stability.

A package-free transparent disposable biosensor chip was developed by a screen-printing technique. The biosensor chip was fabricated by stacking a substrate with two carbon electrodes on its surface, a spacer consisting of a resist layer and an adhesive layer, and a cover. The structure of the chip keeps the interior of the reaction-detecting section airtight until use. The chip is equipped with double electrochemical measuring elements for the simultaneous measurement of multiple items, and the reagent layer was developed in sample-feeding path. The sample-inlet port and air-discharge port are simultaneously opened by longitudinally folding in two biosensor units with a notch as a boundary. Then the shape of the chip is changed to a V-shape. The reaction-detecting section of the chip has a 1.0 microl sample volume for one biosensor unit. Excellent results were obtained with the chip in initial simultaneous chronoamperometric measurements of both glucose (r=1.00) and lactate (r=0.998) in the same samples. The stability of the enzyme sensor signals of the chip was estimated at ambient atmosphere on 8 testing days during a 6-month period. The results were compared with those obtained for an unpackaged chip used as a control. The package-free chip proved to be twice as good as the control chip in terms of the reproducibility of slopes from 16 calibration curves (one calibration curve: 0, 100, 300, 500 mg dl(-1) glucose; n=3) and 4.6 times better in terms of the reproducibility of correlation coefficients from the 16 calibration curves.