Double nanohole optical tweezers allow for trapping of nanoparticles down to single digit nanometer range, including individual proteins, viruses, DNA fragments and quantum dots. Here we demonstrate dual magnetic force / optical force analysis for the characterization of magnetic nanoparticles. From this single platform we can isolate individual nanoparticles and determine their size, permeability, remanence and permittivity. This is of interest for characterizing magnetic nanoparticles in mixtures, isolating ones of desired characteristics and pick-and-place assembly of magnetic nanoparticles in nanoscale magnetic devices.
The magnetic nanoparticle is characterized by analysis of the optical transmission through a double-nanohole aperture with an applied magnetic gradient force. The optical transmission step at trapping, autocorrelation of transmission intensity, distribution of transmission values and variations with applied magnetic field amplitude provide information of individual magnetic nanoparticles that allows for determining their individual material characteristics. The values obtained agree well with past published values for iron oxide, and the size distribution over repeated measurements matches well with scanning electron microscope characterization (and manufacturer specifications).