Polymeric Nanofilter Biointerface for Potentiometric Small-Biomolecule Recognition

Abstract

In this paper, we propose a novel concept of a biointerface, a polymeric nanofilter, for the potentiometric detection of small biomolecules using an extended-Au-gate field-effect transistor (EG-Au-FET). A Au electrode has the potential capability to detect various small biomolecules with ultrasensitivity at nM levels on the basis of a surface redox reaction, but it exhibits no selective response to such biomolecules. Therefore, a suitable polymeric nanofilter is designed and modified on the Au electrode, so that a small target biomolecule reaches the Au surface, resulting in an electrical signal, whereas low-molecular-weight interferences not approaching the Au surface are captured in the polymeric nanofilter. The polymeric nanofilter is composed of two layers. The first layer is electrografted as an anchor layer by a cyclic voltammetry method. Then, a filtering layer is precisely polymerized as the second layer by a photo-mediated surface-initiated atom transfer radical polymerization method. The thickness and density of the polymeric nanofilter are controlled to specifically detect a small target biomolecule with high sensitivity. As a model case, l-cysteine as the small target biomolecule at nM levels is specifically detected by filtering l-DOPA as a low-molecular-weight interference using the polymeric nanofilter-grafted EG-Au-FET on the basis of the following mechanism. The phenylboronic acid (PBA) that copolymerizes with the polymeric nanofilter captures l-DOPA through diol binding, whereas l-cysteine reaches the Au surface through the filter layer. The polymeric nanofilter can also effectively prevent the interaction between biomacromolecules such as albumin and the Au electrode. A platform based on a polymeric nanofilter-grafted EG-Au-FET biosensor is suitable for the ultrasensitive and specific detection of a small biomolecule in biological samples such as tears and sweat, which include small amounts of low-molecular-weight interferences, which generate nonspecific electrical signals.

Self-oscillating chemoelectrical interface of solution-gated ion-sensitive field-effect transistor based on Belousov–Zhabotinsky reaction

“…As the pH measurement solution, standard buffer solutions with pHs of 1.68, 4.01, 6.86, 9.18, and 10.01 (Wako Pure Chemical Industries, Ltd.) were prepared. The time course of the change in surface potential at the gate surface (Δ V out ) was monitored using a source follower circuit 35 , with which the potential change at the interface between an aqueous solution and a gate insulator can be read out directly at a constant I D (RadianceWare Inc.). In this study, V D and I D were set to 1 V and 700 μA, respectively.…”

“…In addition, the gate insulator surface of the ISFET sensor was chemically modified to specifically and selectively detect biomolecules and to reduce electrical noise from interfering species 35 , 36 . Also, such chemical modifications on the gate insulator surface contributed to the electrical detection of the phase transition (swelling and deswelling) in the poly(NIPAAm) gel 37 .…”

Self-oscillating Chemoelectrical Interface of Solution-gated Ion-sensitive Field-effect Transistor Based on Belousov–zhabotinsky Reaction

“…As the pH measurement solution, standard buffer solutions with pHs of 1.68, 4.01, 6.86, 9.18, and 10.01 (Wako Pure Chemical Industries, Ltd.) were prepared. The time course of the change in surface potential at the gate surface (Vout) was monitored using a source follower circuit, 35 with which the potential change at the interface between an aqueous solution and a gate insulator can be read out directly at a constant ID (RadianceWare Inc.). In this study, VD and ID were set to 1 V and 700 A, respectively.…”

“…In addition, the gate insulator surface of the ISFET sensor was chemically modified to specifically and selectively detect biomolecules and to reduce electrical noise from interfering species. 35,36 Also, such chemical modifications on the gate insulator surface contributed to the electrical detection of the phase transition (swelling and deswelling) in the poly(NIPAAm) gel. 37 Therefore, the self-oscillating polymer gel-coated gate ISFET sensor is expected to be used for the electrical monitoring of self-oscillation based on the phase transition on the modified surface, which is driven by the BZ reaction.…”

Biocompatible and Na+-sensitive thin-film transistor for biological fluid sensing

“…The operation of FET-based biosensors is based on the potentiometric measurement of biomolecular recognition events, which are specifically detected by modifying the gate sensing surface with various functional membranes such as ion-sensitive oxides and polymers [14,15]. That is, the changes in ionic or molecular charges caused by biological phenomena at/in such membranes contribute to the changes in the electrical properties of FET-based biosensors; therefore, FET biosensors have a significant advantage in that they enable the direct monitoring of biomolecular recognition events on the gate without using materials for labeling DNA [16][17][18][19], proteins [20,21], cells [22][23][24], and small biomarkers [25][26][27]. Moreover, a thin-film transistor (TFT) device contributes to the flexibility and stretchability [28,29] of the biosensors for the in situ monitoring of biological fluids such as sweat on the skin.…”