A colorimetric biosensor based on 3D printed spiral mixer and magnetic continuous-flow separation for sensitive detection of Salmonella in centrifuge tubes.

Early screening of foodborne pathogens is effective to prevent food poisoning. In this work, a portable colorimetric biosensor was innovatively developed on a centrifugal tube using a 3D printed spiral mechanical mixer for rapid immune reaction, a 3D printed magnetic field generator for continuous-flow bacterial capture, Au@Pt nanozymes for effective signal amplification, and a smartphone application for accurate image processing. The rapid and efficient mixing of specific antibodies on the magnetic beads and Au@Pt nanozymes with target bacteria was simply achieved through repeated press-and-release actions on the mixer to produce the vortex turbulence in the sample chamber and thus form the magnetic bead-bacteria-nanozyme conjugates. The air pressure in the centrifuge tube was adjusted by manual operation on the disposable syringe. More importantly, the entire bacterial detection procedure from separation and labelling, then to washing and catalysis, and finally to measurement and analysis, was achieved on a single centrifugal tube. Besides, all the wastes were collected inside the tube to avoid cross-contamination risks. This disposable biosensor was featured with easy operation, low cost and high sensitivity, and was able to detect Salmonella typhimurium as low as 16 CFU/mL in 1 h, which might pave a pathway for on-site screening of foodborne pathogens to ensure food safety.