Sacrificial template synthesis of ultrathin polyaniline nanosheets and their application in highly sensitive electrochemical dopamine detection

Highlights

• Ultrathin polyaniline nanosheets are prepared via a sacrificial template approach.

• The polyaniline nanosheets show a thickness of ca. 4 nm and an electrical conductivity of ca. 10 S cm⁻¹.

• A low detection limit is achieved for the proposed electrochemical dopamine sensor.

• The proposed dopamine sensor shows an exciting selectivity, reproducibility, and stability.

Abstract

Unique functional nanomaterials as electroactive media for efficiently electrochemical biosensing have always been an ever-increasing topic in biotechnology and environmental fields. In this study, we report a simple sacrificial template-guided polymerization strategy to fabricate ultrathin two-dimensional (2D) polyaniline (PANI) nanosheets for electrochemical detection of dopamine (DA). By using vanadium pentoxide nanosheets as both sacrificial templates and oxidants, the resulting PANI nanosheets show an ultrathin thickness of ca. 4 nm with a favorable electrical conductivity of ca. 10 S cm⁻¹. Furthermore, PANI nanosheets have been modified on a glass carbon electrode for highly sensitive DA detection. The proposed DA sensor delivers a linear range of 0.5–300 μM with a low detection limit of 0.118 μM (S/N = 3). In addition, the as-fabricated electrochemical sensor exhibits an outstanding selectivity, stability, reproducibility, and repeatability, enabling its feasible application for DA detection in real samples. Therefore, the ultrathin PANI nanosheets reported here are good candidates as electrodes for the sensitive and selective DA detection.

Introduction

Polyaniline (PANI) is a typical conducting polymer with the advantages of tunable electrical conductivity, ease of preparation, and favorable environmental stability, which has been utilized in variety of fields such as electronic and optical devices, biosensing, catalysis, anticorrosion, energy storage and conversion, and environment [[1], [2], [3], [4], [5], [6], [7], [8]]. To improve the performance of PANI in the abovementioned fields, varied types of its nanostructures such as nanofibers, nanowires, nanospheres, and nanotubes have been developed and stimulated significant attention because of their distinct electrical properties and excellent processibility [[4], [5], [6], [7], [8]]. Among the synthetic strategies to prepare PANI nanostructures, self-assembly and interfacial polymerization approaches are usually used to prepare PANI nanofibers and nanotubes, while template-assisted polymerization is proved to be an efficient and controllable route to prepare PANI nanotubes and hollow nanospheres with desirable inner and outer diameters, however, additional steps to remove the template are usually required when hard templates are used [[9], [10], [11]]. On the other hand, although a large variety of PANI nanostructures have been demonstrated, there are few reports to fabricate 2D PANI nanosheets with an ultrathin thickness for biosensing applications. Recently, a self-standing PANI sheet-like membrane has been achieved from a mild polymerization process on the surface of ice, whereas its thickness reaches as large as 30 nm, limiting its potential for electrochemical detection of small molecules [12].

Recognition and detection of biomolecules have a vital role to play in medical diagnostics, environmental monitoring, and food safety [[13], [14], [15]]. In particular, dopamine (DA) is a typical catecholamine neurotransmitter in mammalian brain, which is able to regulate a variety of physiological functions of the central nervous, metabolism, and cardiovascular systems [16]. Therefore, it is of significant importance to recognize and detect the level of DA in human body fluids because its abnormal content may cause a series of illnesses such as Parkinson's disease, schizophrenia, and senile dementia [17,18]. Up to now, a certain number of strategies including high-performance liquid chromatography, capillary electrophoresis, fluorimetry, chemiluminescence, enzyme-like colorimetric route, and electrochemical analysis have been demonstrated to sensitively determine DA [[19], [20], [21], [22], [23], [24]]. Among those methods, the electrochemical way usually represents the advantages of facile operation, rapid response, and high sensitivity, which might circumvent the shortcomings of other routes with time-consuming and tedious features [25]. However, an unavoidable disadvantage of the electrochemical detection of DA is the poor selectivity toward the interference of ascorbic acid (AA) and uric acid (UA) because they possess similar oxidation potentials. Thereby, a large variety of efficient functional materials like noble metals, metal oxides, metal carbides, carbons, and their hybrids have been used as efficient electrode materials toward DA detection, showing a desirable sensitivity and selectivity [[25], [26], [27], [28], [29], [30], [31], [32], [33], [34]]. Among those various materials, noble metals always exhibit excellent electrocatalytic properties, whereas porous carbon materials are commonly used as supports to improve the stability of noble metals [25,32]. Recently, some typical metal-free carbon materials such as carbon nanotubes and graphene have also been demonstrated to show a favorable performance for electrochemical sensing application [35]. Especially, graphite-based and graphene oxide-based composites have been used as modified electrodes for the sensitive detection of DA, exhibiting an outstanding sensitivity, selectivity, and storage stability [31,33,34]. Over the past years, conducting polymers have also been proved to be a new type of electrode materials to detect DA [[36], [37], [38], [39]]. For instance, a distinct tetragonal star–like PANI microstructure has been constructed for DA sensing, delivering a detection limit of 0.7 μM [36]. To further enhance the sensitivity and selectivity of the PANI materials to determine DA, it is a meaningful object to fabricate some novel structures with outstanding electrochemical properties.

In this work, ultrathin 2D PANI nanosheets have been fabricated through a mild polymerization process using vanadium pentoxide (V₂O₅·nH₂O) nanosheets as both sacrificial templates and oxidants, which can be self-degraded during the reaction. The resulting PANI nanosheets display a lateral size of several square micrometers and an ultrathin thickness of only around 4 nm, and a favorable electrical conductivity of approximately 10 S/cm. To be modified on the surface of glass carbon electrode (GCE), the obtained PANI nanosheets show an excellent electrochemical performance to detect DA in a neutral environment. The resulting sensor represents not only a high sensitivity but also excellent selectivity, stability, reproducibility, and repeatability. This work provides a straightforward approach for preparing ultrathin 2D conducting polymer nanostructures with a high performance in the application of highly sensitive biosensing field.