**4. Conclusions**

A novel potentiometric assay based on effective amplification of biological signals using protein-inorganic hybrid CaNFs, efficient separation of target bacteria using immune MNBs, and continuous-flow detection of calcium ions using Ca-ISE was successfully developed for rapid and sensitive detection of *Salmonella*. The proposed assay was able to detect *S.* Typhimurium cells as low as 28 CFU/mL within two hours. The Ca-ISE embedded in the fluidic chip is capable of online

monitoring calcium ions and has potential for the development of a lab-on-a-chip potentiometric biosensing device for sensitive detection of foodborne pathogens.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/8/12/1006/ s1, Figure S1: (a) The platform for proof of the proposed assay; (b) The fluidic chip with the Ca-ISE. Figure S2: Calibration curve of the flame photometer (*N* = 3).

**Author Contributions:** L.W. and J.L. designed the concept; L.W., Q.Z. and J.L. carried out Methodology, Validation, and Formal Analysis; Investigation and Resources were conducted by X.H. and R.G.; Writing—Original draft preparation was performed by L.W.; J.L. supervised all the work and revised the manuscript.

**Funding:** This research was funded by the National Science Foundation of China [31802219] and Walmart Foundation [SA1703161].

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
