Electrochemical Immunoassay ofEscherichia coliO157:H7 Using Ag@SiO₂Nanoparticles as Labels

Abstract

Silica coated silver (Ag@SiO2) nanoparticles were prepared and characterized by transmission electron microscope (TEM) and UV-vis absorption, and the nanoparticles were used as labels in sandwich-type immunosensor of Escherichia coli O157:H7 (E. coli O157:H7). The labels involved in immunoreaction were dissolved by mixed acid of hydrofluoric acid and nitric acid, and the released Ag+ ions were electrochemical stripping analyzed (via differential pulse voltammetry, DPV) at poly(acrylic acid)/poly(diallyldimethylammonium chloride)/carbon nanotubes (PAA/PDCNT) modified glass carbon electrode (GCE), which obviously enhanced the signal of Ag+ stripping. Then, the number of E. coli O157:H7 could be indirectly reflected by the signal intensity of labeled Ag+. And the results showed that the DPV signals were proportional to the logarithm of the E. coli O157:H7 concentration in the range from 20 cfu/mL to 8.0 × 103 cfu/mL with the detection limit of 13 cfu/mL.

A robust electrochemical immunosensor based on core–shell nanostructured silica-coated silver for cancer (carcinoembryonic-antigen-CEA) diagnosis

“…52 The layering of silica on the outer surface of silver was implemented by a modified “Stober” (sol–gel) procedure. 47 Our first observation was that the stability of the silica shells depended on the conditions under which they were formed. The initial change in the color from yellow to black indicates the evolution of steady Ag nanoparticles.…”

“…The silica coating on Ag NPs were done by modified “Stober” method. 47 The as formed concentrated silver nanoparticles were put into mixture of pure ethanol (100 mL, 99.9%), liquid ammonia (28 to 30%), and deionized water. After 35 min of sonication, various amount TEOS (tetraethyl orthosilicate) were added dropwise (gradually starting from 2 to 15 μL) then the mixture was correctly agitated for 15 h at ambient RT.…”

“…Ag nanoparticles were prepared by an improvised chemical reduction method in the present work using citrate and then the coating of Ag nanoparticles was carried out with silica by the modied Stober method (sol-gel). 40,47,48 According to the work done by Thorat et al, 49 silica provides a biocompatible environment. The electrochemical experiments were carried out by cyclic voltammetric (CV) studies.…”

Detection and Typing Strategies for Pathogenic Escherichia coli

“…There is no strict definition of an immunosensor and various formats and technologies are developing quickly, but many immunosensors use the same principles as an ELISA assay. These assays incorporate the use of nanoparticles which are coupled with specific oligonucleotides that can detect complementary DNA strands through a color change (Chen and Yin 2014;Ma et al 2014). There are various formats that are described by Tokarskyy and Marshall (2008).…”