Selective excitation of tryptophan fluorescence decay in proteins using a subnanosecond 295 nm light-emitting diode and time-correlated single-photon counting

We demonstrate an AlGaN light-emitting diode (LED) giving pulses of ∼600 ps full width half maximum, 0.35 μW average power, 0.6 mW peak power, and ∼12 nm bandwidth at 295 nm. This source is ideal for protein intrinsic tryptophan fluorescence decay research without the unwanted excitation of tyrosine and paves the way to lab-on-a-chip protein assays using fluorescence decay times. Fluorescence decay and anisotropy decay measurements of human serum albumin are reported and the usefulness of the 295 nm LED demonstrated in comparisons with a nanosecond flashlamp and LEDs with nominal wavelength emission of 280 nm.