Quantitative SERS using the sequestration of small molecules inside precise plasmonic nanoconstructs.

We show how the macrocyclic host, cucurbit[8]uril (CB[8]), creates precise subnanometer junctions between gold nanoparticles while its cavity simultaneously traps small molecules; this enables their reproducible surface-enhanced Raman spectroscopy (SERS) detection. Explicit shifts in the SERS frequencies of CB[8] on complexation with guest molecules provides a direct strategy for absolute quantification of a range of molecules down to 10(-11) M levels. This provides a new analytical paradigm for quantitative SERS of small molecules.