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

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. Both the LED sensor and the LDR sensor responded to various pH buffer solutions in a similar way to obtain sigmoidal curves expected of the dye. The pKa value obtained for the sensors was found to agree with the literature value.

Optical sensing system based on wireless paired emitter detector diode device and ionogels for lab-on-a-disc water quality analysis

“…It was previously demonstrated that when pH indicator dyes are immobilised within solid gels, the micro-environment of the matrix shifts the pK a of the dye slightly, on occasions by over 0.5 pH unit 56 .…”

A wireless paired emitter detector diode device as an optical sensor for Lab-on-a-disc applications

“…[10,11]. Diamond and co-workers further described the development of PEDD based sensors with regard to configuration and applications [12,13].…”

Light-Emitting Diodes for Analytical Chemistry

“…Unique properties of LEDs make them attractive for sensor applications, e.g., the measurement of pH (36,37); oxygen (38); and other reactive gases (39,40), water (41), soil nutrients (42), and smoke (43). Most commercial flow-through RI detectors today use LEDs as light sources.…”