Rapid and Sensitive Biosensing of Salmonella Using Mechanical Step Rotation and Gold@platinum Nanozymatic Amplification

Inspired by ballpoint pen, an optical biosensor is developed for detection of Salmonella using a mechanical step rotator with a dropper to greatly simplify operation, a high gradient magnetic field with immune magnetic nanobeads to specifically separate bacteria, and immune gold@platinum nanozymes with a smartphone to sensitively detect bacteria. First, the preloaded bacterial sample is drawn by the dropper to react with the immune magnetic nanobeads through repeated squeezing and releasing of the dropper, and the rotator is successively rotated and the dropper is repeatedly squeezed and released to achieve mixing of the bacteria, magnetic nanobeads and gold@platinum nanozymes, followed by magnetic separation to remove the background. Then, the conjugates are effectively washed with skim milk and ultrapure water, and the substrate are rapidly catalyzed into the product. Finally, the blue product is photographed and analyzed using a smartphone to obtain the Salmonella concentration. This biosensor could detect Salmonella as low as 56 CFU/mL in ~ 25 min.