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Here we report on a novel optical sensing configuration for Lab-on-a-disc colorimetric analysis applications. The system employs a wireless paired emitter detector diode device (PEDD), which consists of two light emitting diodes (LEDs). One LED, forward biased, serves as the light source whereas the other, in reverse bias mode, serves as the light detector. A simple timer circuit is used to measure the time taken for the photocurrent generated by the emitter LED to discharge the detector LED from 5 V (logic 1) to 1.7 V (logic 0) to give a digital output directly. The light dependent discharging process has been deployed for the measurement of concentrations of colored solutions in a microfluidic platform. The PEDD sensor was validated versus standard optical detection systems showing close correlation and similar limits of detection to UV-VIS spectroscopy.