Visual test of subparts per billion-level mercuric ion with a gold nanoparticle probe after preconcentration by hollow fiber supported liquid membrane

With the combination of the gold nanoparticle (AuNP)-based visual test with hollow fiber supported liquid membrane (HFSLM) extraction, a highly sensitive and selective method was developed for field detection of mercuric ion ([Hg.sup.2+]) in environmental waters. [Hg.sup.2+] in water samples was extracted through HFSLM and trapped in the aqueous acceptor and then visually detected based on the red-to-blue color change of 3-mercaptopropionic acid-functionalized AuNP (MPA-AuNP) probe. The highest extraction efficiency of [Hg.sup.2+] was obtained by using a 600 mL sample (pH 8.0, 2.0% (w/v) NaCl), ~35 [micro]L of acceptor (10 mM of 2,6-pyridinedicarboxylic acid, pH 4.0) filled in the lumen of a polypropylene hollow fiber tubing (55 cm in length, 50 [micro]m wall thickness, 280 [micro]m inner diameter), a liquid membrane of 2.0% (w/v) trioctycphosphine oxide in undecane, and a shaking rate of 250 rpm. The chromegenic reaction was conducted by incubating the mixture of MPA-AuNP stock solution (12 [micro]L, 15 nM), Tris-borate buffer solution (18 [micro]L, 0.2 M, pH 9.5), and acceptor (30 [micro]L) at 30[degrees]C for 1 h. The detection limit can be adjusted to 0.8 [micro]g/L [Hg.sup.2+] (corresponding to an enrichment factor of ~1000 in the HFSLM) and 2.0 [micro]g/L [Hg.sup.2+] (the U.S. Environmental Protection Agency limit of [[Hg.sup.2+]] for drinkable water) by using extraction times of 3 and 1 h, respectively. The proposed method is extremely specific for [Hg.sup.2+] with tolerance to at least 1000-fold of other environmentally relevant heavy and transition metal ions and was successfully applied to detect [Hg.sup.2+] in a certified reference water sample, as well as real river, lake, and tap water samples. 10.1021/ac100541s