*Article* **Exploring Protein-Inorganic Hybrid Nanoflowers and Immune Magnetic Nanobeads to Detect** *Salmonella* **Typhimurium**

#### **Lei Wang 1, Xiaoting Huo 1, Ruya Guo 2, Qiang Zhang 3 and Jianhan Lin 1,\***


Received: 30 October 2018; Accepted: 30 November 2018; Published: 4 December 2018

**Abstract:** Early screening of pathogenic bacteria is key to preventing and controlling outbreaks of foodborne diseases. In this study, protein-inorganic hybrid nanoflowers were synthesized for signal amplification and used with a calcium ion selective electrode (Ca-ISE) to establish a new enzyme-free assay for rapid and sensitive detection of *Salmonella*. Calcium hydrophosphate crystals were first conjugated with polyclonal antibodies against *Salmonella* to synthesize immune calcium nanoflowers (CaNFs), and streptavidin modified magnetic nanobeads (MNBs) were conjugated with biotinylated monoclonal antibodies against *Salmonella* to form immune MNBs. After target bacteria were separated using immune MNBs to form magnetic bacteria, immune CaNFs were conjugated with magnetic bacteria to form nanoflower conjugated bacteria. Then, hydrogen chloride was used to release calcium ions from nanoflower conjugated bacteria. After magnetic separation, the supernatant was finally injected as a continuous-flow to fluidic chip with Ca-ISE for specific detection of calcium ions. The supernatant's potential had a good linear relationship with bacteria concentration, and this assay was able to detect the *S.* Typhimurium cells as low as 28 colony forming units/mL within two hours. The mean recovery of target bacteria in spiked chicken samples was 95.0%. This proposed assay shows the potential for rapid, sensitive, and on-line detection of foodborne pathogens.

**Keywords:** protein-inorganic hybrid nanoflower; continuous-flow potentiometric detection; ion selective electrode; *Salmonella*
