Hierarchical aqueous self-assembly of gold nanoparticles (Au NPs) triggered by macrocyclic molecules, cucurbiturils (CBs), provides a facile method to fabricate surface-enhanced Raman spectroscopy (SERS) substrates for potential applications in homeland security, environmental monitoring, therapeutic drug monitoring and disease diagnostics. In contrast to conventional techniques which suffer from non-specificity and false signals, the Au NP: CB SERS system offers numerous advantages for on-site detection such as high sensitivity, selectivity, reproducibility, cost-effectiveness and minimal sample preparation. The molecular recognition in the system is mediated by a combination of CB host-guest complexation and formation of precise nanojunctions between Au NPs, leading to very strong and reproducible SERS signals. Herein, supramolecular chemistry between CBs and various attractive analyte targets including explosives (2,4- dinitrotoluene, DNT), drugs (methylxanthines, MeX) and biomarkers (creatinine, CRN) was investigated using experimental and computational approaches to quantify the key binding parameters for the subsequent SERS studies. The host-guest complexes can be used to modify the aggregation kinetics of the Au NP: CB nanoaggregates meanwhile bulky guests can be quantified in the SERS system with highly reproducible signals when they are just positioned in close proximity to the plasmonic nanojunctions. The ability of the SERS system to differentiate structurally similar molecules has been verified by multiplexed detection of isomers while the tolerance against possible signal perturbation from background molecules has been investigated in synthetic urine. This research has provided new fundamental insights into the Au NP: CB SERS system and demonstrated its potential to be extended to multiplexed detection of analyte targets in complex media, thus paving the way towards in-field and point-of-care applications
