A device for determining the presence or absence of at least one substance is described. The device includes an illumination component including at least one light emitting diode in the forward bias mode acting as an emitter and configured to illuminate a target with a first waveband; and a detection component including at least one light emitting diode in the reverse bias mode acting as a detector and configured to detect a second waveband emitted by the target in response to the first waveband if the target contains a threshold amount of the at least one substance, wherein, the illumination component and the detection component are included in a single head unit module.