Particle-Resolved Holographic Molecular Binding Assays

Holographic molecular binding assays use holographic video microscopy to monitor changes in the light-scattering properties of functionalized probe beads as target molecules bind to their surfaces. This label-free assay relies on the ability of holographic microscopy to resolve nanometer-scale changes in the diameter of a micrometer-scale colloidal sphere. Previous implementations have relied on large statistical samples obtained with thousands of beads to monitor population shifts with subnanometer precision. Recent advances in high-speed adaptive aberration correction bring the same level of precision to single-particle measurements and make possible complete binding assays with a single probe bead. We demonstrate this technique with probe beads functionalized with protein A that are immobilized with holographic optical traps while being incubated with target antibodies. The success of this approach not only creates new opportunities for medical diagnostic testing, but also illustrates the growing range of applications for holographic particle characterization that are made possible by recent advances in the technique.