THE IDEA

A tiny tube with a porous tip

A microdialysis probe is a thin tube with a semipermeable membrane at its tip, implanted in tissue. A pump slowly pushes fluid through it. Small molecules in the tissue diffuse across the membrane into the fluid, which is collected.

It is a way to sample the fluid around cells without removing tissue.

THE SETUP

Pump, probe, vial, analyzer

The fluid leaves the probe carrying a sample of whatever could cross the membrane.

Diffusion does the sampling, and a separate instrument does the measuring.

ANALYSIS

The measuring happens elsewhere

HPLC High-performance liquid chromatography separates the molecules in each sample

Detection Electrochemical or mass spectrometry detection then measures each one

Flow Typical flow rates are about 0.5 to 2 microliters per minute

One sample can reveal many different molecules.

TRADE-OFFS

Broad, but slow

✅

Strengths

Measures many molecules from one sample, including glutamate and GABA, and works in living animals

⏳

Time resolution

Samples usually cover one to several minutes, far slower than release events

📏

Size

Probes are hundreds of micrometers across, so they disturb tissue more than a microelectrode

It sees the baseline well, but not the bursts.

CALIBRATION

Recovery is not 100%

Only a fraction of the true concentration ends up in the collected fluid, called the relative recovery. Slower flow gives molecules more time to cross, so recovery is higher. Experimenters calibrate recovery so they can estimate the true level in the tissue.

The sample is a diluted copy of the tissue.

UNIT 15 STUDY COMPLETE

🧪

Ready for the Fab Challenge?

You've seen how microdialysis collects samples from living tissue and what limits its speed.