Cops have busted a woman suspected of randomly assaulting a female straphanger with a “sharp object’’ that may have been a hypodermic needle on a subway train.

Nicole Brown, 47, of The Bronx, was taken into custody at the 59th Street and Lexington Avenue station shortly after Saturday’s 11:30 a.m. attack, police said.

Brown faces charges including assault. The victim, 26, is in stable condition at a hospital