Aptamer-based sandwich assay for on chip detection of Ochratoxin A by an array of amorphous silicon photosensors

A multichannel glass-PDMS microfluidic chip functionalized with a novel aptasensor has been developed for the detection of Ochratoxin A (OTA). The aptasensor is built on a glass substrate covered with a poly(2-hydroxyethtyl methacrylate) brush layer, which is subsequently functionalized with an aptamer having high affinity towards OTA. The assay relies on an aptamer-linked immobilized sorbent assay (ALISA) using two different OTA aptamers, which, in presence of OTA, assemble to form a sandwich-like structure generating a chemiluminescent signal. The chip is combined with an array of amorphous silicon photosensors that transduce the chemiluminescent signal into an electrical signal that can be processed to detect and quantify the OTA in the sample. The successful detection of OTA has been demonstrated in standard solutions and in beer samples spiked with OTA. The results shows that the values measured for OTA, applying the ALISA assay, are comparable to those measured by the reference methods. The sensitivity of the proposed analytical method is 0.32 pA L/mg, while the LOD and the LOQ are 0.82 and 2.5 mg/L, respectively. Taking into account both the LOD of the ALISA and the method applied for OTA extraction from beer samples, we extrapolated that 1.1 g of beer sample is sufficient to detect OTA contamination under the regulatory limits.