Many electrochemical sensors operate by binding selective antibodies to a conductive nanomaterial (e.g., carbon nanotube) and then monitoring changes to the material’s conductivity when the target analyte binds to the antibodies.
For example, conduction changes which occur when Microcystin-LR (MCLR), a toxin produced by cyanobacteria, binds to the surface of anti-MCLR-coated single-walled carbon nanotubes are easily detectable down to MCLR concentrations of 0.6 nM, which easily satisfies guidelines set by the World Health Organization for this substance in drinking water [363]; this technique improves the sampling time over traditional MCLR measurement methods (e.g., ELISA) by an order of magnitude.
A similar strategy utilizing AuNPs and glucose-sensitive enzymes can be used to measure glucose concentrations in commercial beverages [364], and a reusable piezoelectric AuNP immunosensor has been developed which detects the presence of aflatoxin-B17 in contaminated milk samples down to a concentration of 0.01 ng/mL.
Other electrochemical systems based on nanomaterials include: an immunosensor based on a cerium oxide nanoparticle and chitosan nanocomposite which detects ochratoxin-A, a food-borne fungal contaminant ; detection of staphylococcal enterotoxin B and cholera-toxin using silicon nanowire transistors and carbon nanotubes (CNTs), respectively; and detection and quantification of food colorants8 (Ponceau 4R and Allura Red in soft drinks and Sudan 1 in ketchup or chili powder) using CNTs and the concentration dependent intensity changes of the colorant-specific oxidation peaks.
Note that analytes are not limited to harmful substances: one study showed that CNT-based electrochemical detection in microfluidic devices can be used to measure antioxidant, flavor compound and vitamin content in vanilla beans and apples . Numerous other examples of electrochemical detection of various biomolecules using nanomaterials are provided in a recent review of the topic