Nanoparticle-Based Immunochemical Biosensors and Assays: Recent Advances and Challenges.

We review the progress achieved during the recent five years in immunochemical biosensors (immunosensors) combined with nanoparticles for enhanced sensitivity. The initial part introduces antibodies as classic recognition elements. The optical sensing part describes fluorescent, luminescent, and surface plasmon resonance systems. Amperometry, voltammetry, and impedance spectroscopy represent electrochemical transducer methods; electrochemiluminescence with photoelectric conversion constitutes a widely utilized combined method. The transducing options function together with suitable nanoparticles: metallic and metal oxides, including magnetic ones, carbon-based nanotubes, graphene variants, luminescent carbon dots, nanocrystals as quantum dots, and photon up-converting particles. These sources merged together provide extreme variability of existing nanoimmunosensing options. Finally, applications in clinical analysis (markers, tumor cells, and pharmaceuticals) and in the detection of pathogenic microorganisms, toxic agents, and pesticides in the environmental field and food products are summarized.

Enzymatic Precipitation Enhanced Surface Plasmon Resonance Immunosensor for the Detection of Salmonella in Powdered Milk.

Contamination of food by pathogenic bacteria has always been a serious threat for human health. The amount of food exports and imports has been increasing in recent years which requires precise food quality control with short analysis time and simplified sample treatment. Surface plasmon resonance (SPR) immunosensor enhanced by biocatalyzed precipitation was developed for the analysis of Salmonella in dairy products. The specific capture antibody was immobilized on the SPR chip which allowed a direct label-free detection of Salmonella Typhimurium with the limit of detection (LOD) of 104 CFU·mL-1 and the analysis time of 10 min. Alternatively, the secondary detection antibody was conjugated with horseradish peroxidase to provide a signal enhancement by the biocatalyzed conversion of 4-chloro-1-naphthol to insoluble benzo-4-chlorocyclohexadienone. The formation of precipitate was studied in detail by atomic force microscopy (AFM). The sensitivity was increased 40 times in case of the precipitation-enhanced detection compared to the label-free approach. The optimized method provided LOD of 100 CFU·mL-1 with linear range up to 106 CFU·mL-1. The total time of analysis including bacteria binding and enhancement step was below 60 min. The capability to analyze real samples with complex matrices was demonstrated on the detection of Salmonella in powdered milk. The developed sensor represents simple and robust approach for routine monitoring of food contamination.