  Quantum measurement principle is employed to detect water quality and
presence of nano-colloids. The setup uses spatially low coherent light source,
for which the outcome of measurement is dependent on the presence of a
reflecting surface and a linear polarizer. The introduction of a reflecting
surface induces enhanced side scattering. The enhancement has specific patterns
for pure water, ions and nanoparticles and can be employed to detect refractive
index of liquids at high sensitivity. The differential enhancement can be used
as an optical magnetometer that sensitively senses magnetic moments of
colloidal magnetic nanoparticles at concentration untenable by other
measurement techniques.
