Photophysical Characterization and α-Type Delayed Luminescence of Rapidly Prepared Au Clusters

Abstract

A new and perspective addition to traditional fluorescent probes is the Au clusters (8–25 atoms) which can label proteins, rendering them extremely bright and photostable. In this paper, we show that albumins can quickly and effectively be labeled using microwave acceleration, which shortens the time of Au labeling from several hours to <30 s. Chromatography of Au proteins and FLIM (fluorescence lifetime imaging microscopy) reveals that Au clusters readily form and remain associated with the proteins. Subsequently, luminescence of the Au proteins (BSA, biotinylated-BSA, HSA) was studied using 3D-emission spectroscopy, time-resolved spectroscopy, and FLIM. We show that the red luminescence of the 25-atom gold cluster attached to the proteins has a broad range of emission lifetimes: about 95% of the total emission has a lifetime component ranging from 0.4 to 105 ns, and ∼5% is a delayed (alpha) emission with a range of lifetimes from 1 to 280 μs. The spectrum of Au delayed emission coincides with its fluorescence spectrum, suggesting that the Au delayed emission is actually delayed fluorescence (possibly, classical α-type), and emitting from the same electronic state. Our findings for the Au proteins suggest their broad applicability as new long-lived luminescence probes for the life sciences.