A smartphone-based bacteria sensor for rapid and portable identification of forensic saliva sample

Saliva identification provides significant evidence for forensic examinations, especially in sexual assault events. A major challenge to forensic field is to develop an effective saliva detection method that complements the existing insensitive techniques. Herein, we developed a rapid and cost-effective smartphone-based bacteria sensor for saliva identification that assays for two oral bacteria in real samples. This bacteria sensor was constructed by the blue-emitting silicon carbide quantum dots (SiC Qds) and red-emitting gold nanoclusters (AuNCs) to form a series of test strips. This method can be selectively detected two oral bacteria species (S. salivarius and S. sanguinis) with good sensitivity. Exposure of the test strips to bacteria solutions promoted dose-sensitive color evolution under a 365 nm UV lamp, which was imaged by a smartphone camera and analyzed by a color detector APP. Additional studies on 29 real samples from 4 different forensic body fluids (saliva, semen, urine, and serum) demonstrated the feasibility of the method. These findings indicate the proposed approach provides a new way for rapid and visual detection of two bacteria in saliva and screening saliva samples among forensic body fluids.