Digital Holographic Reconstruction Applied to iSCAT Data for Nanoparticle Tracking (DH-iSCAT)

Characterizing nanoparticles freely diffusing in solution using label-free techniques is crucial for numerous applications across physics, chemistry, and life sciences. Current challenges include the quantitative measurement of concentrations, particularly for mixtures of particles with different sizes or refractive index and the ability to detect dielectric particles smaller than 30 nm. Here, we describe an in-line digital holographic technique that enables to address these challenges. Owing to its intrinsic interferometric stability, empty viruses as small as 26 nm in diameter and 10 nm gold nanoparticles can be detected. Reconstruction of the scattered field within a well-controlled volume yields the precise three-dimensional positions of the particles enabling an absolute concentration measurement. We illustrate the technique’s potential by measuring the hydrodynamic diameter, refractive index, and concentration of a variety of metallic, dielectric, and biological nanoparticles, including complex mixtures.