Flow Cytometer/Cell Sorter Instrument Types
Flow cytometers and cell sorters are two powerful tools for the accurate and efficient characterization of cells. Both instrument types measure forward scatter (FSC), side scatter (SSC) and multiple fluorescent parameters to detect specific antibody bound markers within a heterogeneous cell population. Although similar in principle and design, they are best suited to distinctly separate applications. Cytometers are most useful for multi-parameter high-throughput analysis, whereas cell sorters can take the further step of isolating specific cell populations for further analysis. The design and technology of these instruments continue to evolve rapidly to allow the measurement of more parameters with higher sensitivity and greater accuracy. Here we examine the different designs, capabilities, applications, and benefits of each instrument type.
Flow cytometers (also called cell analyzers or cell counters) detect, quantify and record fluorescent signals from individual cells as they pass through the instrument. Modern cytometers use microfluidics systems to isolate individual cells into separate fluid droplets that can pass uniformly through the instrument’s interrogation point. In most traditionally configured cytometers, lasers excite fluorescent labels on the cell, which then emit both forward and side scatter light signals. Next, lenses collect the signal from the specific cell being measured, dichroic mirrors separate the signal by wavelength, and filters block any unwanted signal from being detected. Finally, photomultiplier tube detectors amplify the signal and convert light photons to electrical current which can be recorded by the instrument and analyzed using specialized software programs. Spectral cell analyzers are a new type of cytometer instrument that uses spectral technology to gather information about the cell. Unlike conventional flow cytometers which block, reflect, or transmit a photon for detection based on its wavelength, spectral analyzers incorporate different optical approaches to achieve higher resolution with the same amount of light being distributed over more detector elements. Find more information on spectral analyzer technology here. Both types of cytometers are useful for analyzing heterogeneous cell populations and classifying cell subsets based on parameters such as cell size, morphology, or protein expression. In the research setting, they are most often used as an analysis tool to examine the effects of a specific experiment, disease, or drug.
Cell sorters also analyze heterogeneous cell populations that have been marked with detection antibodies. However, they also then physically sort the living cell subsets into tubes or multi-well plates based on specific characteristics. This method is especially useful for enriching cell populations that may then be cultured for further analysis. Fluorescent activated cell sorters (FACS) operate by placing an electrical charge on the fluid droplet as it breaks free from the fluidics stream. An electrostatic deflection system then diverts the droplets into specific containers based on their charge, allowing researchers to separate and collect two or more distinct cell population subsets. Alternatively, Magnetic Activated Cell Sorters (MACS) use superparamagnetic nanoparticles and columns to separate cells based on the presence of specific surface antigens, and Vortex Actuated Cell Sorters (VACS) that relies on a switchable microfluidic vortex stimulated by a thermal-inkjet-style actuator are being developed. Cell sorters are useful for clonal colony generation and single-cell molecular analysis. They are most often used as a starting point (i.e. sample preparation) or intermediary step (i.e. population enrichment) in a larger experiment.
In summary, both instrument types are useful for interrogating and characterizing heterogeneous cell populations, yet cell sorters offer the additional step of isolating specific subsets for further analysis. For more information on specific cytometers or sorters, see our instruments page.