Enzyme-free hydrogen peroxide sensor based on Au@Ag@C core-double shell nanocomposites
Graphical abstract
Introduction
Hydrogen peroxide (H2O2) is a kind of excellent antioxidant and one of the products in a variety of biochemical reactions catalyzed by oxidases, such as glucose catalyzed by glucose oxidase, choline catalyzed by cholinesterase, and lactic acid catalyzed by lactalase. H2O2 is also a major reactive oxygen species (ROS) involved in various diseases, such as cancer [1], cardiovascular disorders [2], and Alzheimer's disease [3]. Therefore, it is very important to detect H2O2 rapidly and accurately in the fields of clinic, pharmaceutical, food security and environmental protection [4], [5], [6]. The measurement methods for H2O2 have been explored by various researchers, including resonance light scattering [7], cell imaging [8], electrochemical methods [9], and so on. Compared with other methods, considerable attention has been paid on the electrochemical approach due to its practical advantages which include high sensitivity and selectivity, rapid response, low cost, operation simplicity, easy miniaturization, etc. In the early stage, according to the specificity response of enzyme to the substrate, various nanomaterials were used to immobilize enzyme in order to construct highly sensitive H2O2 sensors [10]. However, it was ineluctable that the catalytic effect of enzyme just preserved in some appropriate conditions. Therefore, it is very important to develop a simple enzyme-free H2O2 sensor.
Bimetallic core−shell nanoparticles (NPs) have attracted growing attention owing to their unique properties, which are different from those of monometallic counterparts and alloys [11]. The well physicochemical properties of synergy between two metals could be coordinated by shape, size and composition [12]. Meanwhile, the bimetallic metal nanoparticles can also exhibit favorable electrocatalytic activity, which takes place on the shell of the NPs and the core metal can markedly affect the performance of the whole NPs. Thus, many bimetallic metal nanoparticles, such as core−shell AuAg [13], AgPt alloy [14] and so on, were used to prepare enzyme-free H2O2 sensor. Au and Ag are ideal choices of the basal material to construct bimetallic metal nanoparticles due to their unique electronic and catalytic properties as well as their good stability, convenience of electron transfer and biocompatibility [15], [16], and can be used to develop H2O2 sensor. The synthesized Au−Ag core−shell nanocomposites are generally covered with a layer of carbon nanomaterials, which could protect Au and Ag nanoparticles from oxidation and aggregation. Carbon dots (CDs), a new class of carbon-based nanomaterials, is famous for its water solubility, superior fluorescent, low toxicity, high chemical stability, simple synthesis, remarkable conductivity and biocompatibility [17]. CDs have promising application in the field of bioimaging, pollutant detection and photocatalysis [18].
In this work, we first chose CDs as reductant and raw materials to form carbon film around Au core and obtained Au@C core−shell nanoparticles. The carbon membrane which covered to the Au core was not a dense layer. Usually, the surface of gold nanoparticles presents negative charges. Therefore, the Ag+ may be adsorbed to the surface of Au nanoparticles across the non-dense carbon membrane. After joining with the AA reductant, Ag ions react with AA on the surface of Au particles and become Ag layer between Au and carbon layer. Thus, the Au@Ag@C core-double shell nanocomposites were obtained. The nanocomposites were used to fabricate Au@Ag@C-modified glassy carbon electrode (GCE). The Au@Ag@C/GCE showed well electrocatalytical activity toward the reduction of H2O2, and can be used as a nice H2O2 sensor. Furthermore, Au@Ag@C/GCE also exhibits excellent selectivity and stability.
Section snippets
Reagents
Sodium hydroxide, silver nitrate, hydrogen peroxide (30 wt%), oil acid, polyethylene glycol-200 (PEG-200), sodium dihydrogen phosphate and 12 hydrated sodium hydrogen phosphate were purchased from Xilong Chemical Co., Ltd. (Guangdong, China). Glucose (GL), ascorbic acid (AA) was purchased from Instrument Co., Ltd. (Beijing, China). Chloroauric acid, polyvinylpyrrolidone (PVP) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All other chemicals were analytical reagents
Characterization of CDs, Au@C and Au@Ag@C
Fig. 1a is the TEM image of the prepared CDs. Most of the particles are amorphous and the diameter is 10 ± 2 nm. The optical properties of metal nanoparticles are affected by the nanoparticle size, shape and dielectric environment [22]. Fig. 1b shows typical UV−vis absorption spectra and fluorescence spectra of the CDs, a strong UV−vis absorption band appeared at 277 nm and the fluorescence excitation and emission wavelengths appeared at 360 and 455 nm, respectively, on behalf of the CDs launching
Conclusions
We synthesized core-double shell structure Au@Ag@C nanocomposites via a facile approach and used to construct H2O2 sensor. The nanocomposites have good electrocatalytic activity toward H2O2 reduction. Morever, the modified electrode performs a wonderful sensitivity, selectivity, low detection limit, fast response, good stability and anti-interference ability toward the determination of H2O2. These experimental results demonstrate that Au@Ag@C nanocomposites are an attractive material for the
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 21175115), Natural Science Foundation of Fujian province in China (2012J05031 and 2012Y0065), and the Innovation Base Foundation for Graduate Students Education of Fujian Province.
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