SAMPLE REAGENT ADSORPTION ON ALUMINA VERSUS PYREX SUBSTRATES OF MICROFABRICATED ELECTROCHEMICAL SENSORS

Platinum redox sensors have been microfabricated for potentiometric de tection in diffusional microtitration of microliter-size fluid samples . Two different materials, alumina ceramic and Pyrex glass, have been studied for their suitability as sensor substrates. Adsorptions of rea gent and/or sample on an alumina ceramic substrate and a Pyrex glass s ubstrate are compared. Using iodimetric redox titration, significant a dsorption of both reagent and sample occurs on alumina ceramic substra tes. This causes contamination and cross-contamination of samples, lea ding to highly irreproducible results. Reproducibility with a 1.6% coe fficient of variation has been achieved using a platinum redox sensor deposited on a Pyrex substrate for the analysis of 20 mu L sample micr odroplets. Due to the large surface area relative to the small sample volume, surface processes can have a significant effect on the analysi s of microsamples. Therefore, precautions must be taken to minimize pr oblems arising from air interference and sensor/sample, sensor/reagent and reagent/sample interfaces.