The ubiquitous ring stain formation, upon evaporation of a sessile droplet, is known to be driven by a capillary flow taking the dispersed particles toward the three-phase contact line (TPCL) for gradual deposition with a rapid acceleration of the flow in the final leg of drying. However, we report that the process is akin to phase transition, with particles depositing at the contact line in a short span of time and well before the complete drying of the droplet. We used surface-enhanced Raman spectroscopy (SERS) when aqueous droplets of sodium 4-marcaptobenoate-stabilized nanomolar plasmonic gold nanoparticles (NaMBA-AuNPs) were evaporated under ambient conditions. The Raman signals of the molecules were observed to have sharply increased in a short window of time that matched well with simultaneous digital photographing of the deposition. Higher initial AuNP concentrations led to faster phase transitions; however, the final concentration at the TPCL was about 13 μM for 25 nm AuNPs, irrespective of the initial concentrations studied. The time for phase transitions decreased with increasing particle size at a fixed initial AuNP concentration.