In this paper, we report the concept of an aptamer (Ap)-based nanofilter interface for the suppression of nonspecific signals generated by interfering species in biological samples. As a model of the target small biomolecule, l-3,4-dihydroxyphenylalanine (l-DOPA) is used to demonstrate its electrical discrimination from dopamine (DA) despite their similar chemical structures using a DA–Ap nanofilter-coated Au gate field-effect transistor (FET). A Au gate electrode is employed to assess the electrical response of the FET to l-DOPA on the basis of oxidative reactions. In particular, the proposed nanofilter interface is based on the DA–Ap layer immobilized at the aryl-diazonium-based anchor monolayer, which is electrochemically grafted on the Au gate electrode via diazonium chemistry. As a result, the electrical signal from l-DOPA is clearly discriminated from that from DA at a concentration of 1 μM or higher using the DA–Ap nanofilter-coated Au gate FET.

That is, DA is trapped by the DA–Ap nanofilter through the formation of complexes, the molecular charges of which are shielded by counter ions that are not in contact with the Au gate surface, whereas l-DOPA reaches and electrochemically reacts with the Au gate surface, generating an electrical signal regardless of the nanofilter. The surface properties of the DA–Ap nanofilter modified on the Au gate electrode are investigated by cyclic voltammetry, chronocoulometry, atomic force microscopy, and X-ray photoelectron spectroscopy. A platform based on the FET biosensor with the Ap-based nanofilter interface contributes to the electrical monitoring of small biomarkers while suppressing the nonspecific signals of interfering species in biological samples.

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Jenny
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Journal of Nano Research & Applications