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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

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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 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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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