A method for detecting nanoparticles dispersed in a liquid dispersion sample, using an electronic data processor for classifying the sample as having, or not having, nanoparticles present, and using the electronic data processor for pre-training a machine learning classifier with a plurality of nanoparticles liquid dispersion specimens, while dispersed, the method comprising the steps of:
- emitting a laser modulated by a modulation frequency onto each specimen;
- capturing a temporal signal from laser light backscattered by each specimen for a plurality of temporal periods of a predetermined duration for each specimen;
- calculating specimen DCT or Wavelet transform coefficients from the captured signal for each of the temporal periods;
- using the calculated coefficients to pre-train the machine learning classifier;
- using a laser emitter having a focusing optical system coupled to the emitter to emit a laser modulated by a modulation frequency onto the sample;
- using a light receiver to capture a signal from laser light backscattered by the sample for a plurality of temporal periods of a predetermined duration;
- calculating sample DCT or Wavelet transform coefficients from the captured signal for each of the temporal periods;
- and
- using the pre-trained machine learning classifier to classify the calculated sample coefficients as having, or not having, nanoparticles present,
- wherein the nanoparticles have a particle size, in any particle direction, below 1 μm,
- and further wherein the focusing optical system is a focusing optical system suitable to provide a field gradient pattern.