In Vitro Diagnostics, Immunology Spurring Advances in Flow Cytometry

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Clever innovation and disciplined engineering are helping to create better, smaller and less expensive flow cytometers.


A white blood cell (WBC) and a microvesicle (MV), labeled for surface protein CD45 and captured on a Millipore ImageStreamX imaging flow cytometer under 640-nm excitation. This MV is near the resolution limit at 60× magnification. Courtesy of Joanne Lannigan, Flow Cytometry Core/Uta Erdbrügger, University of Virginia School of Medicine.

Cells are the building blocks of organisms. From yeast and bacteria to elephants and whales, cells are the fundamental units of both biological structure and function. They have long been the subject of intense study: to better understand how they work, to help develop safer and more effective drug compounds, and to serve as diagnostic proxies of disease.

Most flow cytometers work by funneling cells from a liquid sample into a narrow stream so they’re in single file, and passing them one by one at high speed through one or more interrogating laser beams. The resulting interactions generate scattered and fluorescent light, and an analysis of these allows counting, identification and characterization of the cells in the sample.

Main applications and unmet needs

But for all the advances since its inception a half century ago, flow cytometry is constantly being pushed further.

In some fields of research, requirements are bumping up against rather fundamental physical limitations. For example, in recent years it has been increasingly recognized that tiny particles (microvesicles and exosomes) shed from cells can tell us a lot about physiology, disease and recovery. These particles (see Figure 2) can be even smaller than bacteria, however, and they are very challenging to detect on current flow cytometers. Instruments capable of reliably detecting and characterizing these extracellular vesicles would help translate this new area of research into clinical practice.

Sensitivity for nanoparticles

The recognition that smaller-than-cells particles can be important harbingers of certain disease states, and diagnostic entities in their own right, has spurred the field to push the envelope in terms of sensitivity of detection. One approach is to label the microvesicles and exosomes (broadly, extracellular vesicles — EVs) with fluorophores and detect them using standard instrumentation. The challenge there is that EVs, due to their size, do not support the levels of fluorescence staining normally seen in whole cells. Therefore higher-sensitivity instruments are needed

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