Sol–gel derived gold nanoparticles biosensing platform for Escherichia coli detection

A three dimensional polymeric network obtained by the sol–gel process was applied to develop disposable, sensitive, selective and stable electrochemical biosensors for detection and quantification of Escherichia coli. This biosensor is based on the integration of a thiolated capture probe sequence from E. coli and gold nanoparticles (AuNPs) into a sol–gel 3D polymeric network derived from (3-mercaptopropyl)-trimethoxysilane (MPTS), formed onto a screen-printed gold electrode surface. MPTS presents the advantage of forming a 3D polymeric network containing a large number of thiol tail groups distributed throughout its structure that enable both its anchoring onto gold surfaces and the AuNPs incorporation. Moreover, this matrix allows the incorporation of a high amount of capture probe and provides a biocompatible environment that preserves its original recognition capability after its immobilization, which is expected to improve the sensitivity of the final biosensing device. The hybridization event is detected using the ruthenium complex [Ru(NH3)5L]2+, where L is the ligand [3-(2-phenanthren-9-yl-vinyl)-pyridine], as redox indicator, which interacts preferentially with ds-DNA. With the use of this approach, complementary target sequences of E. coli can be quantified over the range of 21–400 pmol with a detection limit of 6.3 pmol and good reproducibility (RSD = 4.3%, n = 4, C = 10 μM). In addition, this approach is very selective allowing the detection, without the need of a hybridization suppressor, of a single mismatch. It is also quite stable under storage conditions, giving response at least for 25 days.