Gold nanoclusters as a quenchable fluorescent probe for sensing oxygen at high temperatures.

Gold nanoclusters (AuNCs) capped with lipoic acid (LA) or templated with bovine serum albumin (BSA) are shown to be viable fluorescent probes for oxygen (O2) which acts as a collisional quencher. Quenching of fluorescence, with its lifetimes in the order of 123 ± 9 ns (LA) and 153 ± 15 ns (BSA) (in aqueous solution), is best measured at excitation/emission wavelengths of 400/680 nm and 375/650 nm respectively. It follows the Stern-Volmer model, whose quenching constants (Ksv) and quenching efficiencies (γ) are 1400 M-1 and 0.52 for AuNC@LA and 4479 M-1 and 0.90 for AuNC@BSA. The probes were immobilized on a silica support and tested for response to O2 in gas phase using a commercial instrument. The effect of temperature on the fluorescence of AuNC@LA was studied in the range from 30 to 210 °C. Fluorescence intensity slightly decreases with temperature in the first heating cycle but remains constant in further cycles. The AuNC@LA were studied for their response to O2 in the temperature range from 30 to 100 °C, and even at 100 °C they respond to O2, with a Ksv that slightly drops with increasing temperature. Measuring in gas phase at 100 °C, the sensor has a detection limit of 3% (V/V) of O2 at a signal-to-noise ratio of 3. Graphical Abstract Gold-nanoclusters (AuNCs) fluorescence intensity (λexc = 400 nm, λem = 680 nm) remains constant from 30 to 210 °C and is quenched by O2 following a collisional mechanism. The Stern-Volmer constant (Ksv) slightly changes from 25 °C to 100 °C (at least).