Measuring low concentrations of fluorescent magnetic nanoparticles by fluorescence microscopy

We introduce a new method called particle image counting (PIC) to quantify low concentrations of fluorescent magnetic nanoparticles in liquid biological samples. The biological sample is diluted with gelatin and a known volume is placed on a microscope slide. The magnetic particles are pulled down to one surface of the slide by a magnet held on the opposing surface before the gelatin is solidified to immobilize the particles. After imaging with fluorescence microscopy, the number of particles is counted using a vision algorithm. This provides an accurate measurement of particle concentration in the original biological sample. Here the method is validated by a series of experimental measurements of dilutions of a solution with a known number of fluorescent magnetic nanoparticles.