Fluidics

Abstract

The use of fluidics is implicit in a technology named "flow cytometry," which flows a cell or particle through a sensing volume to obtain serial analysis of particles on a one by one basis. This flow of particles enables flow cytometry to collect information on multiple particle populations, giving it a distinct advantage over bulk analysis approaches. Moreover, flow cytometers can analyze thousands of particles per second in a single flowing stream. Additionally, use of volumetric sample delivery makes it possible for flow cytometers to accurately count cells and particles. Furthermore, the analysis results can be coupled with a fluidic diversion mechanism to sort and collect particles based on desired properties. Finally, when high-throughput sampling technologies are employed to rapidly change the input of the sample stream, a flow cytometer can become an integral tool for high-throughput screening. The above properties have made flow cytometry useful in a wide range of biomedical applications. In this unit we will present an overview of fluidic systems that make flow cytometry possible. This will introduce historical approaches, explanations of the commonly implemented current fluidics, and brief discussions of potential future fluidics where appropriate.

Figure 1

A conceptual diagram of the three primary functions of the fluidics of a flow cytometer. Many options are possible to accomplish each of these functions. Potential examples are shown.

Figure 2

The principle of hydrodynamic focusing. Sheath fluid (Black arrows) flows at a high linear velocity compared to the slow moving sample stream (Gray with white arrows). The fast moving sheath accelerates and focuses the sample stream to a narrow core as it exits the flow cell or nozzle, or the capillary tapers towards the exit orifice.

Figure 3

Optical analysis of a focused sample stream in a typical hydrodynamic focusing flow cytometer. The sample stream is surrounded by a clean sheath fluid that is not pictured.

Figure 4

Typical configurations of flow cytometer flow cells for (A) analysis, (B) electrostatic droplet sorting after analysis in a flow cell, and (C) analysis directly in the jet-inair system after ejection from a nozzle.

Figure 5

Traditional delivery methods. (A) Pressure differential, where a pressure head is introduced into a sealed sample tube to drive sample to the flow cytometer. (B) Syringe pumps in combination with automatic valves that can first fill a fill line and then drive the sample to the cytometer. (C) A simple peristaltic pump that pumps an unsealed sample to the flow cytometer.