Microfluidic Resistive Pulse Sensing (MRPS)
The Microfluidic Resistive Pulse Sensing (MRPS) instrument used at PTL to measure nanoparticles in suspension is based on the Coulter Principle also known as the Electric Sensing Zone technique. Simply stated, the Coulter Principle refers to the use of an electric field for counting and sizing particles suspended in a conducting liquid.
PTL utilizes microfluidic resistive pulse sensing technology from Spectradyne. The Spectradyne nCS1, a patented nanoparticle analyzer features a microfluidic cartridge. This cartridge allows the electrical detection of nanoparticles which are counted and sized at a high resolution as they pass one by one through a constricted flow path.
As shown in the diagram, particles in a conductive fluid pass through a nanoscale constriction (NC). A voltage is applied continuously across the two sides of the NC. As particles pass through, the voltage signal increases, due to the electrical resistance of the particle within the NC. The voltage signal is proportional to the volume of the particle’s resistance based on Ohm’s Law. As the particle exits the NC, the voltage signal returns to constant levels. Particles are measured individually, with no dependence on particle composition or optical properties.
Only 3 microliters of analyte are required for any material type including transparent/opaque as well as conducting/insulating, etc. The size range of measurement is from 50 nm to 2 μm diameter. The instrument also can determine the particle concentration of a nanosuspension in the range of approximately 107 to 1011 particles/mL. Applications include active pharmaceutical ingredients (APIs), excipients, nanoemulsions, proteins, exosomes, virosomes, and their aggregates, as well as general nanoparticles including gold/silver, colloidal silicon dioxide, metal-oxide nanoparticles, etc.