Analytical Sciences

Microfluidic Polymer Chip Integrated with an ISFET Detector for Cationic Surfactant Assay in Dental Rinses

Takashi MASADOME,* Kensuke YADA,* and Shin-ichi WAKIDA**

*Department of Applied Chemistry, Faculty of Engineering, Shibaura Institute of Technology, Toyosu, Koto-ku, Tokyo 135-8548, Japan
**Human Stress Signal Research Center (HSS), National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan

A cationic surfactant ion-selective field-effect transistor (cationic surfactant-ISFET) has been developed based on the tetraphenylborate derivative known as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. The cationic surfactant-ISFET shows an almost Nernstian response to tetradecyldimethylbenzylammonium chloride (Zephiramine) over a concentration range between 1.0 × 10^-6 M and 1.0 × 10^-3 M, with a slope of 58.5 ± 1.7 mV/decade. The cationic surfactant-ISFET can be used over a range of pH values, between pH 3 and 9. The cationic surfactant-ISFET shows excellent selectivity for Zephiramine over small inorganic cations, but shows similar selectivity for other cationic surfactants, such as hexadecyltrimethylammonium and stearyltrimethylammonium ions. A microfluidic polymer chip was integrated with the cationic surfactant-ISFET, and this was fabricated using polystyrene plates and stainless wires as a template for the channel. Cationic surfactant-ISFETs used in a batch system and microchips integrated with cationic surfactant-ISFETs showed very similar performance in terms of low detection limits, slope sensitivity and the stability of the potential response. The microfluidic polymer chip was then applied to the determination of cationic surfactants in dental rinses.

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