An Acid-Responsive Microfluidic Salmonella Biosensor Using Curcumin as Signal Reporter and ZnO-Capped Mesoporous Silica Nanoparticles for Signal Amplification

• This was first time to use HAc to release curcumin as reporter. • ZnO NPs were used to cap MSNs to avoid premature release of curcumin. • Koch fractal mixer was developed and verified with excellent performance. • The biosensor was able to detect Salmonella as low as 10 1 CFU/mL in 1.5 h. • The mean recovery of the spiked chicken samples was ∼104 %. An acid-responsive microfluidic biosensor using curcumin (CUR) as signal reporter and ZnO-capped mesoporous silica nanoparticles (MSNs) for signal amplification was developed for sensitive and rapid detection of Salmonella in colorimetric and fluorescent modal. The MSNs were first incubated with CUR to obtain MSN@CUR nanoparticles (MC NPs). The MC NPs were then capped with ZnO nanoparticles to form MSN@CUR@ZnO nanoparticles (MCZ NPs) to prevent CUR from premature release, followed by modification with polyclonal antibodies (pAbs) against Salmonella Typhimurium ( S. Typhimurium) to obtain immune MSN@CUR@ZnO@pAbs nanoparticles (MCZP NPs). The immune magnetic nanoparticles (MNPs), the S. Typhimurium cells and the MCZP NPs were conjugated in the microfluidic chip with a Koch fractal mixing channel to form MNP-bacteria-MCZP complexes. Finally, the acetic acid (HAc) was first time introduced to release CUR from the complexes, and both the color and fluorescence changes were measured to determine the concentration of Salmonella . This proposed biosensor was able to quantitatively detect S. Typhimurium ranging from 10 2 to 10 7 CFU/mL in 1.5 h and the lower detection limits were calculated to be 63 CFU/mL for colorimetric measurement and 40 CFU/mL for fluorescent measurement, respectively. The mean recovery was about 104 % for Salmonella in the spiked chicken samples.