Compositions, methods, and kits are provided for treating bacterial infections with nanoparticles comprising a thiol-binding metallic core conjugated to a fluoroquinolone antibiotic. Recalcitrant infections are often difficult to treat because of the presence of persister cells, a subpopulation of bacterial cells that is highly tolerant of traditional antibiotics. Persister cells are dormant, which makes them less susceptible to many antibiotics, which are designed to kill growing cells. Administration of nanoparticles comprising a thiol-binding metallic core conjugated to fluoroquinolone antibiotics was found to be highly efficacious in eradicating persister cells and for treating infections for a broad range of bacterial species, including Gram-positive and Gram-negative bacteria. Such treatment was effective not only in eradicating planktonic bacteria but also bacteria in biofilms.