electrophoresis
/ ih-lek-troh-fuh-REE-sis /
Rub a balloon on your hair and it tugs charged bits of paper across a table. Now imagine that pull made steady and gentle across a wet slab of jelly, with charged molecules drifting toward one end. Electrophoresis is that idea harnessed: a sustained electric field that nudges charged molecules through a medium, sorting them as they go.
Formally, electrophoresis is the migration of charged particles or molecules through a fluid or gel under an applied electric field. Each species moves toward the oppositely charged electrode at a speed set by its charge, size, and shape, and by the resistance of the medium; in a sieving gel, smaller molecules thread through more easily and pull ahead of larger ones, so a mixture spreads into separated bands.
It matters because it is the bedrock technique for separating proteins, DNA, and RNA by size or charge — the basis of DNA fingerprinting, genome sequencing, and countless biology and clinical tests. Its honest caveats are that it can be slow and somewhat manual in its classic slab-gel form, that resolution depends on carefully matched gels and buffers, and that heating from the current must be controlled to keep bands sharp.
A genetics lab loads DNA fragments into wells at one end of an agarose gel and switches on a voltage; over half an hour the negatively charged fragments creep toward the positive electrode, the smallest racing farthest, forming a ladder of bands under ultraviolet light.
An electric field marches charged molecules through a gel, sorting them by size and charge.
The name combines 'electro' (electricity) and the Greek 'phoresis' (a carrying), literally 'carrying by electricity' — a good picture of charged molecules being ferried by the field.