This protocol describes the use of the Spectradyne nCS1 instrument to measure the particles per mL concentration and size of nanoparticles. The Spectradyne nCS1 is a particle analyzing instrument that uses microfluidic resistive pulse sensing rather than optical measurements to determine the concentration and size of samples. Microliters (typically 5 μL) of a sample are placed in a microfluidic cartridge that is inserted into the instrument for analysis; thus, low sample volumes are needed for analysis and the instrument is relatively easy to use. The size and concentration of a sample is determined by measuring the changes in voltage as particles travel through a nano-constriction in the microfluidic cartridge. This method also has the advantage over optical techniques in that measurements are not dependent on the type of material being measured ( e.g., refractive index of the sample itself is not needed for accurate analysis).