Abstract: Disclosed is a system for detecting contaminants in a sample fluid. The system has a colloidal dispersion circuit with a reservoir containing a colloidal dispersion with colloidal particles capable of exhibiting localized surface plasmon resonance (“LSPR particles”), a Raman spectrometer/flow cell and a pump for circulating the colloidal dispersion through the colloidal dispersion circuit. A colloidal dispersion level sensor measures the extent of colloidal dispersion in the colloidal dispersion circuit. A permeation valve diverts the colloidal dispersion in the colloidal dispersion circuit through an ultra-filtration membrane with a pore size smaller than the LSPR particles, thus preventing the LSPR particles from passing through. The sample may be introduced into the colloidal dispersion circuit through a fluid sample injection valve. A processor is connected to the Raman spectrometer/flow cell, the pump, the permeation valve, the colloidal dispersion level sensor, and the fluid sample injection port.