Ferrocene-functionalized nanocomposites as signal amplification probes for electrochemical immunoassay of Salmonella typhimurium.

An electrochemical immunosensor based on ferrocene (Fc)-functionalized nanocomposites was fabricated as an efficient electroactive signal probe to amplify electrochemical signals for Salmonella typhimurium detection. The electrochemical signal amplification probe was constructed by encapsulating ferrocene into S. typhimurium-specific antimicrobial peptides Magainin I (MI)-Cu3(PO4)2 organic-inorganic nanocomposites (Fc@MI) through a one-step process. Magnetic beads (MBs) coupled with antibody were used as capture ingredient for target magnetic separation, and Fc@MI nanoparticles were used as signal labels in the immunoassays. The sandwich of MBs-target-Fc@MI assay was performed using a screen-printed carbon electrode as transducer surface. The immunosensor platform presents a low limit of detection (LOD) of 3 CFU·mL-1 and a linear range from 10 to 107 CFU·mL-1, with good specificity and precision, and was successfully applied for S. typhimurium detection in milk. Graphical abstract One-pot process antimicrobial peptides Magainin I-Cu3(PO4)2 organic-inorganic nanocomposites (Fc@MI) were used as ideal electrochemical signal label, integrating both essential functions of biological recognition and signal amplification. Screen-printed carbon electrode (SPCE) was used as the electrochemical system for Salmonella typhimurium detection.

Immunoassay for pathogenic bacteria using platinum nanoparticles and a hand-held hydrogen detector as transducer. Application to the detection of Escherichia coli O157:H7.

An innovative approach is presented for portable and sensitive detection of pathogenic bacteria. A novel synthetic hybrid nanocomposite encapsulating platinum nanoparticles, as a highly efficient catalyst, catalyzes the hydrolysis of the ammonia-borane complex to generate hydrogen gas. The nanocomposites are used as a label for immunoassays. A portable hand-held hydrogen detector combined with nanocomposite-induced signal conversion was applied for point-of-care testing of pathogenic bacteria. A hand-held hydrogen detector was used as the transducer. Escherichia coli O157:H7 (E. coli O157: H7), as detection target, formed a sandwich structure with magnetic beads and hybrid nanocomposites. Magnetic beads were used for separation of the sandwich structure, and hybrid nanocomposites as catalysts to catalyze the generation of hydrogen from ammonia-borane. The generated hydrogen was detected by a hydrogen detector using an electrochemical method. E. coli O157:H7 has a detection limit of 10 CFU·mL-1. The immunosensor made the hand-held hydrogen detector a point-of-care meter to be used outdoors for the detection and quantification of targets beyond hydrogen. Graphical abstract Schematic presentation of one-pot synthetic peptide-Cu3(PO4)2 hybrid nanocomposites embedded PtNPs (PPNs), encapsulating many Pt particles. The PPNs acts as an ideal immunoprobe for hand-held H2 detector signal readouts, by transforming pathogenic bacteria recognition events into H2 signals.

Disposable syringe-based visual immunotest for pathogenic bacteria based on the catalase mimicking activity of platinum nanoparticle-concanavalin A hybrid nanoflowers.

Disposable syringes were used in a novel point-of-care visual test for detecting pathogenic bacteria (Escherichia coli O157:H7 and Salmonella typhimurium). Hybrid nanoflowers composed of platinum nanoparticles and concanavalin A (Pt-nanoflowers) were prepared through a one-pot reaction and were found to be viable catalase mimics. They catalyze the decomposition of hydrogen peroxide (H2O2) to generate O2. When used as labels in immunoassays, they integrate both the functions of biological recognition and signal amplification. The disposable syringe pressure readout was combined with Pt-nanoflower signal conversion and successfully applied to a visual bacteria detection scheme. Both Escherichia coli O157:H7 and Salmonella typhimurium can be quantified with detection limits of as low as 15 and 7 CFU·mL-1, respectively. Graphical abstract One-pot synthetic platinum nanoparticle (PtNP)-concanavalin A hybrid nanoflowers (Pt-nanoflowers), have been used as ideal signal labels for immunoassays and integrating both essential functions of biological recognition and signal amplification. Disposable syringes were used as a readout to detect pathogenic bacteria.

Hemin-incorporated nanoflowers as enzyme mimics for colorimetric detection of foodborne pathogenic bacteria.

Rapid, sensitive and point-of-care detection of foodborne pathogenic bacteria is essential for food safety. In this study, we found that hemin-concanavalin A hybrid nanoflowers (HCH nanoflowers), as solid mimic peroxidase, could catalyze oxidation of 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) in the presence of H2O2 to a green-colored product. HCH nanoflowers, integrating the essential functions of both biological recognition and signal amplification, meet the requirements of signal labels for colorimetric immunoassay of bacteria. In view of the excellent peroxidase mimetic catalytic activity of HCH nanoflowers, a colorimetric biosensing platform was newly constructed and applied for sensitive detection of foodborne Escherichia coli O157:H7 (E. coli O157:H7). The corresponding detection limits was as low as 4.1 CFU/mL with wide linear ranges (101-106 CFU/mL).