Abstract

Fluorescence Microfluidic Resistive Pulse Sensing: A Rapidly Emerging Method for Flow Cytometry at the Nanoscale

Jean-Luc Fraikin, CEO, Spectradyne

Nanoparticle-based biotechnologies including virus-mediated cell and gene therapies, lipid nanoparticles (LNPs), and extracellular vesicles (EVs) hold enormous promise as vaccines and therapeutics. These revolutionary technologies derive their potency from payload-carrying particles as small as 20 nanometers in diameter.  At this size scale, basic physical properties of the particles directly dictate the efficacy and safety of the overall product and are therefore critical parameters that must be measured to effectively develop and produce products based on these materials. The realization of the potential of these medicines is limited, however, by a lack of practical analytical tools for measuring three key particle properties that critically impact dose and bioavailability: Particle size, concentration, and payload. Despite new developments that stretch the limits of its sensitivity, optical flow cytometry is fundamentally limited in its ability to accurately detect and measure nanoscale particles in heterogeneous samples. Fluorescence Microfluidic Resistive Pulse Sensing (F-MRPS) is rapidly emerging as a powerful alternative to optical flow cytometry that accurately measures nanoparticle concentration, size, and payload in complex samples. F-MRPS combines two orthogonal analytical techniques into a single measurement:  A cartridge-based electrical method for counting and sizing particles (MRPS), and simultaneous high sensitivity single-particle fluorescence measurements for quantifying payload.  In contrast with purely optical flow cytometry methods, the detection limit of F-MRPS is not limited by light scattering intensity, and measurements of particle size are completely independent of the particle’s optical properties.  F-MRPS is therefore uniquely suited to analyzing complex heterogeneous samples and is rapidly being adopted by industrial and academic users for quantification of EVs, virus and LNPs. A technical overview of the F-MRPS technology will be presented, together with measurement examples from key impact areas including virus and gene therapy, extracellular vesicles, lipid nanoparticles (LNPs), and liposomes.  The fluorescence sensitivity of F-MRPS is demonstrated with measurements of synthetic particles cross-calibrated to NIST-traceable fluorescence intensity standards.