A Novel Sensor Platform Based on Aptamer‐Conjugated Polypyrrole Nanotubes for Label‐Free Electrochemical Protein Detection

Abstract

We first present a simple yet versatile strategy for the functionalization of polymer nanotubes in a controlled fashion. Carboxylic-acid-functionalized polypyrrole (CPPy) nanotubes were fabricated by using cylindrical micelle templates in a water-in-oil emulsion system, and the functional carboxyl groups were effectively incorporated into the polymer backbone during the polymerization by using pyrrole-3-carboxylic acid (P3CA) as a co-monomer without a sophisticated functionalization process. It was noteworthy that the chemical functionality of CPPy nanotubes was readily controlled in both qualitative and quantitative aspects. On the basis of the controlled functionality of CPPy nanotubes, a field-effect transistor (FET) sensor platform was constructed to detect specific biological entities by using a buffer solution as a liquid-ion gate. The CPPy nanotubes were covalently immobilized onto the microelectrode substrate to make a good electrical contact with the metal electrodes, and thrombin aptamers were bonded to the nanotube surface via covalent linkages as the molecular recognition element. The selective recognition ability of thrombin aptamers combined with the charge transport property of CPPy nanotubes enabled the direct and label-free electrical detection of thrombin proteins. Upon exposure to thrombin, the CPPy nanotube FET sensors showed a decrease in current flow, which was probably attributed to the dipole-dipole or dipole-charge interaction between thrombin proteins and the aptamer-conjugated polymer chains. Importantly, the sensor response was tuned by adjusting the chemical functionality of CPPy nanotubes. The efficacy of CPPy nanotube FET sensors was also demonstrated in human blood serum; this suggests that they may be used for practical diagnosis applications after further optimization.

Conducting‐Polymer Nanomaterials for High‐Performance Sensor Applications: Issues and Challenges

“…We have developed another way to anchor conducting-polymer nanomaterials onto an electrode substrate. [32,33,68] The overall reaction steps are illustrated in Figure 9a and b. First, PPy nanotubes with controlled carboxyl functionalities were synthesized by copolymerizing pyrrole with pyrrole-3-carboxylic acid (P3CA).…”

“…We recently employed aptamers as bioreceptors for label-free electrochemical detection of proteins. [32] Aptamers, which synthetic DNA or RNA oligonucleotide probes, have great potential over antibodies in biological applications because of their ability to selectively bind specific target molecules. As shown in Figure 9b and c, amineterminated thrombin aptamers were covalently bound to the carboxyl groups of the nanotubes.…”

“…Conducting polymer nanomaterials have been employed to detect diverse analytes such as toxic gases, volatile organic compounds, and biological species. We have also explored the fabrication of sensors based on conducting polymer nanomaterials, consisting of polyanilne (PANI), [31] polypyrrole (PPy), [32][33][34][35][36] and poly(3,4-ethylenedioxythiophene) (PEDOT), [37,38] during the past few years. These studies strongly support the fact that conducting polymer nanomaterials may be excellent candidates for fabricating high-performance sensors.…”

Recent Advances in Nanostructured Conducting Polymers: from Synthesis to Practical Applications

“…mechanism, many different types of FET sensors have been developed to detect glucose [189], odorants [190], proteins [191,192], and hormones [193]. Recently, a high-performance dopamine FET sensor was successfully demonstrated using human dopamine receptor-containing nanovesicles as the gate-potential modulator on a PEDOT nanotube channel (Figure 12) [184].…”

Conducting Polymers in Sensor Design

“…An alternative strategy of using PPy nanoparticles was presented by Yoon et al [54]. Covalent links between polypyrrole nanotubes and a microelectrode were formed to obtain convenient electrical communication in solution.…”