Yes, EOSIN is a Scrabble word!

Letter values in Scrabble US: E 1, O 1, S 1, I 1, N 1.

Is it a valid word?

EOSIN is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a red fluorescent dye resulting from the action of bromine on fluorescein; used in cosmetics and as a biological stain for studying cell structures

Not playable in Scrabble US: BROMEOSIN.