Flow cytometry is a laboratory technique used to analyze individual cells or particles suspended in a fluid. It provides detailed information about cell characteristics, making it a tool across scientific and medical fields. It allows researchers and clinicians to quickly assess millions of cells, offering insights not easily obtained otherwise.
The Core Principle
Flow cytometry involves controlling cell movement through a narrow channel, where a cell sample is suspended in fluid and injected into the instrument. There, a sheath fluid surrounds the sample, forcing cells to align and pass one by one through a focused laser beam. As each cell intercepts the laser, it scatters light. If cells are labeled with fluorescent dyes, these dyes become excited and emit light at different wavelengths, providing information about their properties.
How It Operates
A flow cytometer has three main systems: fluidics, optics, and electronics. The fluidics system transports cells from the sample tube to the laser interrogation point, ensuring they pass in single file. This is achieved by injecting the cell sample into a sheath fluid stream, creating a narrow core where cells are hydrodynamically focused.
The optics system includes lasers that illuminate cells, along with lenses, filters, and mirrors. These components direct laser light to the sample stream and collect scattered and fluorescent light. Optical filters separate different light wavelengths, directing them to detectors.
The electronics system converts collected light signals into electrical pulses. Photodetectors measure the intensity of the light signals. These electrical signals are amplified and processed by a computer, which translates light patterns into quantifiable data about each cell.
Information Provided
Flow cytometry measures various properties of individual cells. As cells pass through the laser, they scatter light in two ways: forward scatter (FSC) and side scatter (SSC). Forward scatter correlates with cell size, while side scatter provides information about internal complexity, such as granularity or nuclear structure.
Flow cytometry also measures fluorescence signals. Cells can be labeled with fluorescent dyes or antibodies that bind to specific cellular components. When excited by the laser, these markers emit light. The intensity and color of this light reveal the presence and abundance of specific molecules or cellular characteristics, allowing detailed analysis of heterogeneous cell populations.
Common Uses
Flow cytometry is widely applied across medical diagnostics, immunology research, and cell biology due to its ability to rapidly analyze individual cells. In medical diagnostics, it is routinely used for evaluating blood, bone marrow, and other bodily fluids. It plays a role in diagnosing blood cancers like leukemia and lymphoma by identifying abnormal cell populations based on their unique surface markers. Flow cytometry also helps monitor HIV progression by counting CD4+ T cells, which are impacted by the virus.
In immunology research, flow cytometry is indispensable for characterizing and quantifying different immune cell types, such as T cells and B cells. Researchers use it to study immune responses, track cell proliferation, and assess cell viability. This allows for a deeper understanding of how the immune system functions and responds to various stimuli.
Within cell biology, flow cytometry is used for applications like cell cycle analysis, which measures the DNA content of cells to determine their replication status. It can also detect apoptosis, or programmed cell death, and analyze cell adhesion events. The technology’s versatility and precision make it a foundational tool for examining cellular processes and identifying specific cell populations.