Plasmon enhanced silver quantum cluster fluorescence for biochemical applications

S. Bernard, J.P. Kutter, K.B. Mogensen
Technical University of Denmark, DK

Keywords: quantum cluster fluorescence, microchip, plasmonics, photoactivation, cyanide

Summary:

Silver quantum clusters (AgQCs) consisting of typically 4-10 atoms and known to be highly fluorescing in the visible wavelength range. Here, plasmon-enhanced silver quantum cluster fluorescence is employed for chemical sensing in a simple microfluidic device. Oil-immersion microscopy is used through the lid of the chip (x100 objective), which makes imaging of individual silver clusters possible inside the channel. The bottom substrate contains plasmonic silver particles (AgNPs) that are both used for cluster photoactivation and fluorescence detection. Initially, plasmon-enhanced photoreduction of Ag-cations in solution (1 mM AgNO3) is employed for synthesis of the quantum clusters (< 1nm) at the surface of the larger AgNPs (d~20nm). The photoactivation is shown to obey Hill/Langmuir kinetics with a time constant of only 31s. The novelty of this work is that here, a scheme based on oxidative dissolution is employed for subsequent detection, where the clusters are dissolved upon interaction with the analyte, resulting in a large change in signal. On-chip indirect fluorescence detection of dilute cyanide samples are demonstrated. Two time constants are needed to fit the exponential decay of the quantum cluster fluorescence, showing an initial fast decay (mean lifetime of only 15s).