WHY SORT?

Finding needles in haystacks

🔍

🩸

Blood is crowded

About 5 billion red blood cells in every millilitre

🎯

Rare targets

A tumour cell in blood can be one in a billion

🧪

Clean samples

Many tests need plasma without cells, or one cell type alone

Before you can measure a rare cell, you have to find it.

PASSIVE BY SIZE

Let the geometry decide

📐

Deterministic lateral displacement A tilted array of posts bumps big particles sideways while small ones zigzag through

Inertial focusing At higher flow, particles settle into set positions by size, especially in spirals

Filters and weirs Gaps smaller than the target trap it

Advantage No power or labels needed, just flow

Smart channel design can sort by size with nothing but flow.

SORTING WITH SOUND

Acoustic standing waves

Sound waves set up a standing wave across a channel. Cells are pushed toward the pressure nodes at speeds that depend on their size, density and stiffness, so different cells end up in different streams, gently and without labels.

Acoustophoresis moves cells without touching them.

ACTIVE SORTING

Electric fields, magnets and lasers

⚡

Dielectrophoresis

Uneven electric fields pull cells by their electrical properties

🧲

Magnetic

Cells tagged with magnetic beads are pulled aside by a magnet

🔦

Fluorescence

A laser reads each cell's label and the chip diverts the right ones

Size, density, sound and light: each method reads a different property.

PLASMA FROM BLOOD

A common first step

🩸

Many diagnostic chips need plasma, the liquid part of blood. Cells can settle out by gravity, get caught by filters, or follow the faster branch at a channel split (the Zweifach–Fung effect), leaving cell-free plasma in the slower side channel.

Separating cells from plasma on a chip removes the need for a centrifuge.

UNIT 13 STUDY COMPLETE

🧲

Ready for the Fab Challenge?

You've seen how chips sort cells using posts, flow, sound, electric fields, magnets and light.