Graphene aids optical detection of Ochratoxin A

Ochratoxin A (OTA) – a toxin produced by different fungus species – is one of the most abundant food-contaminating mycotoxins. It is also a frequent contaminant of water-damaged houses and of heating ducts that can have a detrimental effect on human health. Rapid detection of OTA would reduce the cost of food production processes and increase human health safety in many circumstances. Now, scientists have developed an optical method to rapidly detect small quantities of OTA on a sensor made of aptamer-functionalized graphene-coated glass. The results were published in the international journal Nanomaterials.

Figure: OTA detection with aptamer-modified graphene. From Nekrasov et al, Nanomaterials 11, 226 (2021).

The sensor was produced by transferring monolayer CVD graphene onto a glass slide. The graphene was made sensitive to OTA by immobilizing aptamers on the graphene surface. Aptamers are molecules that bind to a specific target molecule only, in this case OTA. The detection of small concentrations of OTA in solution was performed by optical spectral-phase interferometry (SPI). SPI is a quick, precise and contact-free method that makes use of a beam of white light that probes the surface of the sensor chip. Tiny changes on the surface, such as the binding of OTA to the aptamer, are observed as changes in the reflection spectrum of the light beam.

The researchers demonstrated proof of concept by detecting a 10 nM concentration of OTA, corresponding to the maximum tolerable level of toxin concentration in food. For comparison, a control process of OTA introduced onto the sensor chip without the aptamer coating produced no changes in the spectrum. The sensor detects the presence of OTA in only 6 minutes, which is about 40% faster than previously reported optical OTA sensors based on thin gold layers instead of graphene. The limit of detection is projected to 1 nM OTA concentration.

Previously, researchers also reported OTA detection within minutes and with high sensitivity with graphene field effect transistors (GFET). The optical method presented here has several advantages over GFET-based methods, such as remote detection and multiplexing, opening pathways for use in drug discovery, food, and medical analyses. The approach can be generalized to develop other kinds of biosensors for different analytes, with applications in health analysis, environmental and food control, and agriculture.