solid state ph sensor based on light emitting diodes (led) as detector platform固态ph传感器基于发光二极管(led)作为探测器平台.pdf

Sensors 2006, 6, 848-859 sensors ISSN 1424-8220 © 2006 by MDPI /sensors Full Research Paper Solid State pH Sensor Based on Light Emitting Diodes (LED) As Detector Platform King Tong Lau*, R. Shepherd, Danny Diamond and Dermot Diamond* National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Dublin, Ireland E-mails: kim.lau@dcu.ie, roderick.shepherd@dcu.ie, danny.diamond@dcu.ie, dermot.diamond@dcu.ie. * Author to whom correspondence should be addressed, kim.lau@dcu.ie (King Tong Lau), Dermot.diamond@dcu.ie (Dermot Diamond) Received: 7 March 2006 / Accepted:1 May 2006 /07/03/2006 / Published: 23 August 2006 Abstract: A low-power, high sensitivity, very low-cost light emitting diode (LED)-based device developed for low-cost sensor networks was modified with bromocresol green membrane to work as a solid-state pH sensor. In this approach, a reverse-biased LED functioning as a photodiode is coupled with a second LED configured in conventional emission mode. A simple timer circuit measures how long (in microsecond) it takes for the photocurrent generated on the detector LED to discharge its capacitance from logic 1 (+5 V) to logic 0 (+1.7 V). The entire instrument provides an inherently digital output of light intensity measurements for a few cents. A light dependent resistor (LDR) modified with similar sensor membrane was also used as a comparison method. Bot