Aptamer based vanillin sensor using an ion-sensitive field-effect transistor.

An aptamer for vanillin was obtained and then used for the development of an aptasensor based on an ion-sensitive field-effect transistor (ISFET). This aptamer (a single-stranded DNA;ssDNA) was selected using the Capture-SELEX protocol, which suites well for selection of aptamers to small molecules. Among six aptamer candidates, the aptamer Van_74 with the highest affinity for vanillin was chosen (elution of 35% of the aptamer from a solid support in the presence of 2 mM of vanillin). Van_74 was characterized using nondenaturating PAGE of washouts from magnetic beads. It is shown that Van_74 binds to vanillin with an dissociation constant of >7.8 μM (determined by nondenaturating PAGE) and it was specific to vanillin in comparison with interferents: benzaldehyde, guaiacol, furaneol, ethyl guaiacol and ethyl vanillin. Also it was shown that change of buffer composition greatly affected the binding ability of Van_74. For biosensor fabrication aptamer was immobilised on the Ta2 O5 -sensitive surface of the ISFET via "click-chemistry". Detection scheme implied dehybridisation of the ssDNA probe from the aptamer and release in the solution during the addition of vanillin. As a result, the surface potential increase upon vanillin binding with the aptamer was detected by the transistor. The biosensor had a detection limit of 1.55 × 10-7  M and a dynamic range from 1.55 × 10-7  M to 1 × 10-6  M. Effective constant Kd,eff for vanillin binding on biosensor surface was calculated to be (9 ± 3) × 10-7  M. This allows selective detection of vanillin in the mixture of interferents and in samples of coffee extract. Graphical abstract A biosensor for vanillin was developed on the basis of an aptamer that was obtained via Capture-SELEX and by using an ISFET. This biosensor can be used for vanillin detection in presence of interferents and in real sample using an approach of ssDNA probe dehybridization.