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Sensors 2006, 6(8), 848-859; doi:10.3390/s6080648
Article

Solid State pH Sensor Based on Light Emitting Diodes (LED) As Detector Platform

* ,
,
 and
*
National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Dublin, Ireland
* Authors to whom correspondence should be addressed.
Received: 7 March 2006 / Accepted: 1 May 2006 / Published: 23 August 2006
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Abstract

A low-power, high sensitivity, very low-cost light emitting diode (LED)-baseddevice developed for low-cost sensor networks was modified with bromocresol greenmembrane to work as a solid-state pH sensor. In this approach, a reverse-biased LEDfunctioning as a photodiode is coupled with a second LED configured in conventionalemission mode. A simple timer circuit measures how long (in microsecond) it takes for thephotocurrent 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 lightintensity measurements for a few cents. A light dependent resistor (LDR) modified withsimilar sensor membrane was also used as a comparison method. Both the LED sensor andthe LDR sensor responded to various pH buffer solutions in a similar way to obtainsigmoidal curves expected of the dye. The pKa value obtained for the sensors was found toagree with the literature value.
Keywords: pH sensing; solid-state pH sensor; optical sensing; colorimetric sensor; light emitting diode; light dependent resistor. pH sensing; solid-state pH sensor; optical sensing; colorimetric sensor; light emitting diode; light dependent resistor.
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Lau, K.T.; Shepherd, R.; Diamond, D.; Diamond, D. Solid State pH Sensor Based on Light Emitting Diodes (LED) As Detector Platform. Sensors 2006, 6, 848-859.

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