Electrochemical Immunosensor Using Nanoparticle-Based Signal Enhancement for <italic>Escherichia Coli</italic> O157:H7 Detection

An electrochemical immunosensor based on the assembly of three nanoparticles for the rapid detection of Escherichia coli O157:H7 has been developed. The biosensor assay consists of magnetic separation using antibody-functionalized magnetic nanoparticles (MNPs) and electrochemical reporters using gold nanoparticle (AuNP)-conjugated lead sulfide (PbS) nanoparticles via oligonucleotide linkage. The AuNPs were also functionalized with polyclonal anti-E. coli O157:H7 antibodies in order to bind the target bacterial cells which were captured and separated from the sample by antibody-functionalized MNPs. Because each AuNP was linked to multiple PbS nanoparticles, each binding event to the target resulted in substantial amplification. The signal of PbS was measured on screen-printed carbon electrode by square wave anodic stripping voltammetry. Results show that the biosensor could detect E. coli O157:H7 in the range of 10 ¹ -10 ⁶ colony forming units per milliliter (cfu/ml) with a signal-to-noise ratio ranging from 2.77 to 4.31. With sample preparation being minimized, results were obtained in 1 h from sample processing to final readout. Due to its high sensitivity, this trinano immunosensor has great potential applications in public health, biodefense, and food/water safety monitoring.