Recommended as a medical emergency,infectious keratitis with an acute and rapid disease progression can lead to serious damage of vision and even blindness.Herein,we present a kind of theranostic agents,which are made of vancomycin(Van)-modified fluorescent silicon nanoparticles(SiNPs-Van),enabling rapid and non-invasive diagnosis and treatment of Gram-positive bacteria-induced keratitis in a simultaneous manner.Typically,the resultant SiNPs-Van nanoagents have an ability of imaging bacteria in a short time both in vitro(5 min)and in vivo(10 min),making them an efficacious diagnostic agent for the detection of bacterial keratitis.In addition,the SiNPs-Van feature distinct antimicrobial activity,with superior activity of 92.5％at a concentration of 0.5 μg/mL against Staphylococcus aureus(S.aureus);comparatively,the antimicrobial rate of free vancomycin is 23.3％at the same concentration.We further explore the SiNPs-Van agents as eye drops for therapy of S.aureus-induced bacterial keratitis on rat model.Represented by slit-lamp scores,the keratitis severity of SiNPs-Van-treated corneas is 3.4,which is 59.6％and 77.3％slighter than vancomycin-(8.2 score)and PBS-treated corneas(15.0 score),respectively.The infected corneas recover to normal(1 score)after 7-d of SiNPs-Van treatment.Above results suggest that the SiNPs-Van could serve as a new kind of high-quality nanotheranostic agents,especially suitable for simultaneous diagnosis and therapy of Gram-positive bacteria keratitis.