*2.3.3.1 Bacteria*

*Salmonella* is one primary risk factor for bacterial food poisoning and can be transmitted via contaminated animal-derived foods like meats, eggs milk, etc. Millions of people are infected with *Salmonella* sometimes with severe and fatal results. Most highly developed countries have zero tolerance to *Salmonella* in foods, especially to ready to eat food. Thus, ultrasensitive detection is important. However, food testing is complex and usually low concentration of *Salmonella* is found in ready to eat foods [80]. The need for rapid, sensitive and cost-effective point of care *Salmonella* screening test is of great importance. Wang *et al.* [80] developed a *Salmonella* biosensor using a platinum nanoparticle loaded manganese dioxide nanoflowers (Pt@ MnO2 NFs) and thin-film pressure detector. The biosensor test starts by separating *Salmonella* from the sample using capture antibodies (CAbs) modified magnetic nanobeads (MNB) forming MNB-CAbs-*Salmonella* complex (magnetic bacteria). Then, detection antibodies (DAb) were used for labelling magnetic bacteria to form MNB-CAb-*Salmonella-*DAb-Pt@MnO2 NFs complex (nanoflower bacteria). The nanoflower bacteria will be resuspended into H2O2 in a sealed centrifuge tube. H2O2 was catalyzed by PtMnO2 to produce O2 that results in increased pressure. This increased in pressure is monitored in real-time by piezoresistor-based pressured detector and transfer data to smartphone by Bluetooth for analysis and detection of *Salmonella* in the samples. The developed biosensor by Wang *et al* [80] can quantitatively detect *Salmonella* from 1.5 x 101 to 1.5 x 105 CFU/mL in 1.5 h with low detection limit of 13 CFU/mL.

### *2.3.3.2 Drug residues*

β2-adrenergic receptor agonists (β2-agonists) is a drug group which is usually used for the treatment of pulmonary diseases in animals [81, 82]. However, they can promote animal growth and increase feed efficiency by enhancing protein accretion and

*Application of Noble Metals in the Advances in Animal Disease Diagnostics DOI: http://dx.doi.org/10.5772/intechopen.99162*

reducing fat deposition producing "lean meats" [82–84]. The use of this drug group in veterinary medicine is illegal since prolonged consumption of residues in animalderived products can cause headache, chest tightness, nausea, and more. One of this β2-agonists is ractopamine (RAC), however RAC is a derivative of clenbuterol which causes high blood pressure and heart disease in human. Thus, the use of RAC is illegal in Europe and China but RAC is still used around the world due to its effectiveness and low cost [82]. Thus, detection of RAC and its residue using simple and accurate method is important. Sun *et al* [82] developed a colorimetric immunosensor based PtNPs immobilized on Power Vision (PV) as signal probes and Fe3O4@β-cyclodextrin as capture probes for ractopamine detection in pork. PtNPs-PV double catalyzed the chromogenic substrate 3,3′-diaminobenzidine (DAB), which induced changes in DAB's color and chromogenic absorbance. Incubation temperature, pH, and incubation time were systematically optimized, and under optimum conditions, the measured absorbance values exhibited a linear relationship with the RAC concentrations in the range of 0.03 to 8.1 ng mL−1. The detection limit was 0.01 ng mL−1. The sensor exhibited high sensitivity and specificity, which was demonstrated by testing structurally similar organic compounds such as salbutamol (SAL), clenbuterol (CLE), and dopamine (DOA). The practicality of the developed colorimetric immunosensor was supported by the successful detection of RAC in pork samples with recovery ranging from 94.00% to 106.00%.
