Detecting matter at a single-molecule level is the ultimate target in many branches of study. Nanosensors based on plasmonics have garnered significant interest owing to their ultrahigh sensitivity even at single-molecule level. However, currently, plasmonic-enhanced nanosensors have not achieved excellent performances in practical applications and their detection at femtomolar or attomolar concentrations remains highly challenging. Here we show a plasmonic sensing strategy, called buoyant plasmonic-particulate-based few-to-single particle-nanosensors. Large-sized floating particles combined with a slippery surface may prevent the coffee-ring effect and enhance the spatial enrichment capability of the analyte in plasmonic sensitive sites via the aggregation and lifting effect. Dimer and single particle-nanosensors demonstrate an enhanced surface-enhanced Raman spectroscopy (SERS) and a high fluorescence sensitivity with an enrichment factor up to an order of ∼104 and the limit of detection of CV molecules down to femto- or attomolar levels. The current buoyant particulate strategy can be exploited in a wide range of plasmonic enhanced sensing applications for a cost-effective, simple, fast, flexible, and portable detection.