  This work demonstrates an original and ultrasensitive approach for
surface-enhanced Raman spectroscopy (SERS) detection based on evaporation of
self-lubricating drops containing silver supraparticles. The developed method
detects an extremely low concentration of analyte that is enriched and
concentrated on sensitive SERS sites of the compact supraparticles formed from
drop evaporation. A low limit of detection of 10^-16 M is achieved for a model
hydrophobic compound rhodamine 6G (R6G). The quantitative analysis of R6G
concentration is obtained from 10^-5 to 10^-11 M. In addition, for a model
micro-pollutant in water triclosan, the detection limit of 10^-6 M is achieved
by using microliter sample solutions. The intensity of SERS detection in this
approach is robust to the dispersity of the nanoparticles in the drop but
became stronger after a longer drying time. The ultrasensitive detection
mechanism is the sequential process of concentration, extraction, and
absorption of the analyte during evaporation of self-lubrication drop and hot
spot generation for intensification of SERS signals. This novel approach for
sample preparation in ultrasensitive SERS detection can be applied to the
detection of chemical and biological signatures in areas such as environment
monitoring, food safety, and biomedical diagnostics.
