A lab-on-a-chip is a tiny device that can carry out laboratory steps on small samples of blood, saliva, urine, or chemical reagent. Instead of using full-size tubes, pipettes, and machines, it guides fluids through microscopic channels etched into glass, plastic, or silicon. This matters because tests can become faster, cheaper, and easier to use near a patient rather than only in a central lab.
A device about the size of a stamp can help detect infections, measure biomarkers, or monitor health with only a drop of sample.
The core technology is microfluidics, where fluids move through channels that may be thinner than a human hair. At this scale, flow is usually smooth and layered, so diffusion, surface forces, and pressure control become very important. Pumps, valves, capillary action, or electric fields can move and mix tiny volumes so reactions happen in specific zones on the chip.
Sensors or color changes then convert the chemical or biological result into a readable diagnostic signal.
Key Facts
- Microfluidics studies fluid flow in channels with widths from about 1 micrometer to 1000 micrometers.
- 1 microliter = 10^-6 L and 1 nanoliter = 10^-9 L.
- Flow rate is volume per time: Q = V/t.
- Pressure-driven flow moves from high pressure to low pressure: ΔP = P1 - P2.
- Laminar flow is common in microchannels when the Reynolds number is small: Re = ρvD/μ.
- Diffusion time increases with distance squared: t ≈ x^2/(2D).
Vocabulary
- Lab-on-a-chip
- A small device that integrates several laboratory functions, such as sample transport, mixing, reaction, and detection, on one chip.
- Microfluidics
- The science and engineering of controlling very small amounts of fluid in tiny channels.
- Microchannel
- A microscopic pathway inside a chip that carries liquid samples or reagents.
- Laminar flow
- A smooth type of fluid flow in which layers of liquid move mostly side by side with little turbulent mixing.
- Biosensor
- A detector that uses a biological or chemical response to identify or measure a target substance.
Common Mistakes to Avoid
- Assuming tiny fluids behave exactly like water in a cup, because surface tension, viscosity, and diffusion often dominate at microscale sizes.
- Confusing small volume with low accuracy, because microfluidic chips can measure tiny samples precisely when channels, sensors, and calibration are well designed.
- Thinking fluids always mix quickly in microchannels, because laminar flow can keep streams separated and mixing may depend mostly on diffusion.
- Ignoring contamination control, because a very small unwanted particle or leftover sample can block a channel or change a diagnostic result.
Practice Questions
- 1 A chip moves 12 microliters of blood through a channel in 3 minutes. What is the flow rate in microliters per minute?
- 2 A diagnostic reaction chamber needs 250 nanoliters of reagent. How many chambers can be filled from 10 microliters of reagent?
- 3 A lab-on-a-chip has two side-by-side streams that do not mix quickly. Explain why this can happen in a microchannel and name one design feature that could improve mixing.