A “turn-on” fluorescence assay for lead(II) based on the suppression of the surface energy transfer between acridine orange and gold nanoparticles

The authors describe a strategy for fluorometric determination of lead(II) that is based on the suppression of the surface energy transfer that occurs between acridine orange and gold nanoparticles (AuNPs). As a result, the fluorescence of the system is recovered. Under optimized conditions, the enhancement of fluorescence intensity is related to the concentration of lead(II) in the 44 nM to 4.8 μM range, with a detection limit of 13 nM. The relative standard deviations for 11 determinations at concentrations of 0.386 μM, 1.93 μM and 2.89 μM are 1.02 %, 1.06 % and 1.75 %, respectively. This result suggests that the method can potentially be used to monitor the level of lead(II) in environmental samples. Lead(II) ion is found to bind to citrate capped gold nanoparticles (AuNPs) which prevents binding of acridine orange (AO) to the AuNPs. As a result, the surface energy transfer from AO to AuNPs cannot occur and fluorescence is restored. This effect was used to quantify lead(II) ion.