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A novel approach to suppress the side reactions observed in the reaction-based gold-sensing systems based on the alkyne activation is disclosed. By elevating steric strain around the reaction site, the gold ion promoted ring-opening process in rhodamine-lactam probes is significantly accelerated, which also leads to suppression of those possible side reactions. As a result, the probes show very high sensitivity in addition to excellent selectivity toward gold species. Furthermore, bioimaging of gold species in live cells was demonstrated with a FRET version.

A rhodamine-derived alkyne shows turn-on fluorescence change only toward Au(I)/Au(III) species among various other metal species examined. A formyloxazole compound is formed as the major product in aqueous media, presumably via a vinylgold intermediate, which casts new mechanistic implications on vinylgold intermediates.

To alleviate side reactions identified in an N-propargyl-rhodamine lactam sensing system, we devised the novel reaction-based sensing scheme for gold species based on the alkynophilicity. A fluorescein (2-ethynyl)benzoate underwent Au(III)-promoted ester hydrolysis selectively over other metal ions with high sensitivity, which accompanies a turn-on fluorescence change in pH 7.4 HEPES buffer. The work offers a versatile reactive moiety for the development of gold probes with improved sensing properties.