Interferometric Scattering Microscopy

The measured signal arises from the combined optical fields, not from scattered light alone. Light scattered by a nanoscale object interferes with light reflected from the coverslip, producing an intensity contrast. Because this contrast is linked to the object’s polarizability, size, and refractive index, the measurement can reveal changes in a particle’s optical response during biochemical events.

Polarizability, size, and refractive index are the principal factors connecting an object to its observed contrast. A change in any of these properties can alter the measured intensity, so contrast should be interpreted as an optical signature rather than as a direct, isolated measurement of size alone. This relationship helps when comparing biomolecular particles or tracking their changes over time.

Unlike approaches that require fluorescent tags, Interferometric Scattering Microscopy observes the scattered-light response of the object itself. Avoiding a label can reduce perturbation to the biomolecular system while retaining sensitivity to nanoscale structures. That combination is particularly useful when tagging could influence binding, assembly, transport, or other behavior being examined.

A basic measurement begins with illumination of the sample in a configuration that provides a coverslip reflection as the reference field. The instrument then detects the intensity pattern produced by interference between that reflection and light scattered by an object. Monitoring this contrast over time supports real-time observation of individual nanoscale biological structures.

In biochemical experiments, changes in the interference contrast can be followed as molecules bind, assemble, or move through a system. The same label-free readout can support mass-related measurements, because the optical signal depends on particle properties that include size and refractive index. These capabilities let investigators connect nanoscale observations with evolving biomolecular behavior.

The method can be applied to single proteins, viruses, lipid vesicles, and other small biological structures. This range spans molecular species and larger assemblies, allowing biochemists to examine how nanoscale entities appear and change without adding fluorescent tags. Its value is therefore not limited to one class of sample, but extends across distinct biomolecular systems and their interactions.