Microfluidic Colorimetric Biosensors Based on MnO₂ Nanozymes and Convergence–Divergence Spiral Micromixers for Rapid and Sensitive Detection of Salmonella

Abstract

In-field screening of foodborne pathogens plays an important role in ensuring food safety. Thus, a microfluidic biosensor was developed for rapid and sensitive detection of Salmonella using manganese dioxide nanoflowers (MnO2 NFs) for amplifying the biological signal, a microfluidic chip with a convergence–divergence spiral micromixer for performing automatic operations, and a smartphone app with a saturation calculation algorithm for processing the image. First, immune magnetic nanoparticles (MNPs), the sample, and immune MnO2 NFs were fully mixed and sufficiently incubated in the spiral micromixer to form MNP–bacteria–MnO2 sandwich complexes, which were magnetically captured in a separation chamber in the microfluidic chip. Then, a 3,3′,5,5′-tetramethylbenzidine (TMB) substrate was injected and catalyzed by a MnO2 NF nanomimetic enzyme on the complexes, resulting in the production of yellow catalysate. Finally, the catalysate was transferred into a detection chamber and its image was measured and processed using the smartphone app to determine the number of bacteria. This biosensor was able to detect Salmonella from 4.4 × 101 to 4.4 × 106 CFU/mL in 45 min with a detection limit of 44 CFU/mL, and has the potential to provide a promising platform for on-site detection of foodborne bacteria.

The recent development of nanozymes for food quality and safety detection

“…6). 82 In their system, a microfluidic chip with a convergence-divergence spiral micromixer was chosen for rapid and sensitive bacterial detection. Immune magnetic nanoparticles, food samples, and MnO 2 NFs were added to the corresponding input channels in turn.…”

Research progress on detection techniques for point-of-care testing of foodborne pathogens

“… Xue et al (2021) developed a microfluidic biosensor for rapid and sensitive detection of Salmonella using manganese dioxide nanoflowers (MnO 2 NFs), a microfluidic chip with a convergence-divergence spiral micromixer, and a smartphone app with a saturation calculation algorithm ( Figure 4A ). This biosensor was able to detect Salmonella from 4.4 × 10 1 to 4.4 × 10 6 CFU/ml in 45 min with a detection limit of 44 CFU/ml.…”

“… (A) Schematic of this Colorimetric Biosensor for Detection of Salmonella ( Xue et al, 2021 ); (B) Making the process of the microchip ( Zhang et al, 2021b ); (C) The whole process of a microfluidic platform for detection of S. aureus by fluorescence labeling ( Song et al, 2020 ); (D) Schematics of the i-Gene ( Nguyen et al, 2020 ). …”

On-site colorimetric detection of Salmonella typhimurium based on peroxidase-like activity of aptamer-functionalized 3D covalent organic frameworks embedded with gold nanoparticles

“…Therefore, the colorimetric method based on enzymatic catalysis is a good way and it has been rapidly developed in recent years [7]. Due to the poor stability and expense of natural enzymes, more attention has been paid to nanozyme as biosensors in colorimetric assay systems, especially nanozyme mimicking peroxidase has been widely reported [13]. At present, numerous nanomaterials with peroxidase-like activity have been explored, such as noble metal NPs (Au, Ag, Pt), manganese dioxide NPs and carbon-based nanomaterials (graphene oxide (GO)) [14,15].…”