The mother of a 12-year-old Brooklyn boy who died earlier this month from antibiotic resistant staph infection put the city on notice Tuesday that she planned a $25 million lawsuit.

Aileen Rivera said Kings County Hospital improperly diagnosed the illness of her son, Omar, and sent him home after treatment with allergy medicine. He died of methicillin-resistant Staphylococcus aureus two days later, on Oct. 14.

Rivera, speaking in a calm, firm voice, said her son got much worse the following night.

When she took him to another emergency room, at Brookdale Hospital, staff said they would do their best. Then, she said, "They tell me 'he don't make it."'

She announced her intention to sue the city and its hospital system at the offices of the Cochran law firm in Manhattan. A notice of claim is the first step in bringing a lawsuit.

Kings County said this week that it was closely examining whether it could have done anything more to detect the infection.

Derek Sells, one of her lawyers, said that the law required them to set a monetary figure for the damages. "Although you can never put a price on a life ... we put this figure in to represent the significant nature of our claim," he said.

"What my son go through, I don't want any kid, no mother, to go through," said Rivera.