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

We demonstrate an AlGaN light-emitting diode (LED) giving pulses of ∼600ps full width half maximum, 0.35μW average power, 0.6mW peak power, and ∼12nm bandwidth at 295nm. 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 295nm LED demonstrated in comparisons with a nanosecond flashlamp and LEDs with nominal wavelength emission of 280nm.