A differential amplifier includes an unmatched pair, including first quantum dots and second quantum dots, and a matched pair, including first and second phototransistors. The unmatched pair has a difference between a first spectrum absorbed by the first quantum dots and a second spectrum absorbed by the second quantum dots. Each of the first and second phototransistors includes a channel. The first quantum dots absorb the first spectrum from incident electromagnetic radiation and gate a first current through the channel of the first phototransistor, and the second quantum dots absorb the second spectrum from the incident electromagnetic radiation and gate a second current through the channel of the second phototransistor. The first and second phototransistors are coupled together for generating a differential output from the first and second currents, the differential output corresponding to the difference between the first and second spectrums within the incident electromagnetic radiation.