%0 Journal Article
%T Solid State pH Sensor Based on Light Emitting Diodes (LED) As Detector Platform
%A King Tong Lau
%A R. Shepherd
%A Danny Diamond
%A Dermot Diamond
%J Sensors
%D 2006
%I MDPI AG
%R 10.3390/s6080648
%X 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.
%K pH sensing
%K solid-state pH sensor
%K optical sensing
%K colorimetric sensor
%K light emitting diode
%K light dependent resistor.
%U http://www.mdpi.com/1424-8220/6/8/848