Bright far-red/near-infrared gold nanoclusters for highly selective and ultra-sensitive detection of Hg2+

In this paper, we developed a simple one-pot method, employing inexpensive chicken egg white (EW) as a reducing/capping reagent, for microwave-assisted synthesis of water-soluble and well-dispersed chicken egg white-protected gold nanoclusters (EW@AuNCs) with far-red/near-infrared (FR/NIR) emission. The resultant AuNCs showed strong emission at 667   nm with a quantum yield of 7.23%. The excellent photostability, large Stokes shift (>350   nm), microsecond-scale lifetime and strong emission endowed EW@AuNCs potential as a sensing probe. The photoluminescence of EW@AuNCs could be quenched upon addition of either Hg 2+ or Cu 2+ ion. After ethylenediamine (En) was used as a masking agent, the EW@AuNCs offered highly selective for determination of Hg 2+ ion. Also, the resultant EW@AuNCs probe exhibited ultra-high sensitivity toward Hg 2+ ion with a detection limit as low as 20 pM, which is 500 times lower than the limit value (10   nM) defined by the U.S. Environmental Protection Agency in drinkable water. The proposed AuNCs probe for Hg 2+ ion has a linear range of 0.0446–5.90   nM and good repeatable response to 2.0   nM Hg 2+ with a relative standard deviation of 2.8% ( n   =   5). Additionally, the applicability of the sensing system was also verified by analysis of Hg 2+ ion in tap water and pond water samples.