Lab-on-a-Syringe Biosensing of Salmonella using Magnetic Grid Separation with Nanozyme Signal Amplification

This work aimed to use a syringe as an experimental platform, and Salmonella typhimurium as a research model to develop a simple, cheap, rapid, and disposable optical biosensor. First, an elaborate separator with multiple fluidic channels and high-gradient magnetic fields, consisting of permanent magnets, was 3D printed and installed inside a 10 mL syringe. Then, the mixture of bacterial samples, immune magnetic nanoparticles and immune gold@platinum nanozymes was repeatedly pulled and pushed by the syringe to realize sufficient mixing and immunoreaction for the formation of nanoparticle-bacteria-nanozyme conjugates, which were subsequently captured in the fluidic channels. After washing with skim milk and ultrapure water, colorless TMB substrate was drawn into the fluidic channels and catalyzed by the nanozymes to produce blue TMBox catalysate. Finally, a self-developed smartphone APP was employed to analyze the image of catalysate for Salmonella detection. The biosensor could detect as low as 87 CFU/mL Salmonella in 25 min with a linear range of 1.08 × 10²–1.08 × 10⁶ CFU/mL.