Size-Selective Bubble-Array Acoustofluidic Separation Enables Colorimetric Detection of Salmonella

Rapid and reliable detection of foodborne pathogens is essential for ensuring food safety. Here, we report an integrated acoustofluidic biosensing platform for quantitative detection of Salmonella that couples a vibrating bubble-array microchannel with nanozyme-based colorimetric readout. In this design, air bubbles are reproducibly confined between paired cylindrical micropillars and organized as serial trapping units along the microchannel to support continuous-flow operation. Upon low-frequency excitation from a piezoelectric buzzer, oscillating bubbles generate stable streaming vortices that enable size-selective partitioning, preferentially retaining micron-scale bacteria-nanozyme conjugates while allowing nanoscale free Au@Pt nanozymes to pass downstream for subsequent colorimetric readout. Using smartphone-based image analysis, the Salmonella assay achieves a linear response from 8 × 101 to 8 × 105 CFU/mL with a limit of detection of 26 CFU/mL. Reliable performance was further demonstrated in Salmonella-spiked clarified chicken homogenate supernatants with 95.1-101.4% recoveries and RSD ≤ 5.4%. This work demonstrates bubble-enabled acoustofluidic partitioning, providing a simple and wash-reduced platform for foodborne pathogen analysis.