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).

The lower size limit for this technique is approximately 50 nm; however, a wide range of cartridges are available through the manufacturer that allow measurement of particles of up to 2000 nm. Most samples examined at the NCL use a 300 nm cartridge, meaning that the cartridges measure from 50-300 nm. The instrument requires that the running buffer and sample dilutions contain a low concentration of surfactant. Spectradyne recommends PBS with 1% Tween as the standard running buffer and sample diluent. Note though, this may cause some samples to be incompatible with this technique and will be discussed later.

Detailed explanations of how the instrument works, use of the instrument, and data analysis are available in the instrument handbook and on the company website; the intention of this protocol is to provide guidance and detail for the types of nanoparticles typically analyzed at the NCL. Our experience with this instrument has provided us with some additional helpful techniques and insight for the samples frequently examined in the NCL.