Sp-iris

Scheme of the SP-IRIS setup from [@frigerio2022Comparing digital detection platforms in high sensitivity immune-phenotyping of extracellular vesicles] (and this note).

Single-particle interferometric reflectance imaging sensing is a technique commercialized by NanoView Biosciences under the name ExoView.

They use a microarray functionalized with specific antibodies, which trap particles. Using an interferometric detection system, they can measure the presence (and the size) of the particles at each spot. In a second labelling step (like in Elisa test), the fluorescence signal can be measured.

It is a form of digital detection, with the added size-ability which is purely analog in nature. Since it is an interferometric method, it can work at smaller sizes (extracellular vesicles down to $50nm$, for example).

The interferometric detection seems similar to iSCAT, but I haven't checked the details of the interferometric approach.

A similar measurement approach is that of Simoa, just that in that case, the analytes are trapped by beads and not just by the surface.

Another company producing a relatively similar product is Myriade, under the name Video Drop.

The image below (from [@gori2020Membrane-binding peptides for extracellular vesicles on-chip analysis] and literature/202301141616 Membrane-binding peptides to detect small EVs) can give an idea of the number of particles analyzed in a single-measurement (not sure if it is representative, though)

Integrating the numbers (by eye) gives a total of around 300 particles in the histogram.

From the same paper, this figure gives a more comprehensive overview:

The image disk is $40\,\mu m$ across, which means $1350\mu m^2$. If the total number of measured particles is $200k\textrm{pcles}/\textrm{mm}^2=0.2\textrm{pcles}/\mu\textrm{m}^2$ , gives a total of $270 \textrm{particles}$ in the field of view.