Electrochemical detection of chemical pollutants based on gold nanomaterials
Graphical abstract
Introduction
Environmental disputes are becoming a key focus of political and scientific attention because of the growing world population, intensification of agricultural and industrial activities, contamination of air, soils and aquatic ecosystems, and global climate change [1], [2], [3], [4]. A comprehensive effort is devoted to understand the stimulus of human activities on the environment, and to develop new technologies to diminish associated health, food waste, industrial products and environmental consequences [5], [6], [7]. The emerging environmental pollutants are a large group of unregulated compounds, containing of industry, human and animal fecal waste, natural toxins, drinking water disinfection byproducts, personal care products, pharmaceuticals, food materials through food preparation and packaging processes, etc. [8], [9], [10]. It is reported that approximately more than 700 new chemicals are introduced into the US marketplace every year. Over few decades, many of chemical pollutants have been investigated for environmental monitoring and food safety through various analytical strategies and the term “emerging” primarily focusing the attention on chemicals or biological species in the list of compounds with endocrine-disrupting activity and some pollutants are even suspected as a cancer promoters, which are cumulatively cause severe damage to human health [7], [11], [12], [13]. Due to the increasing the mobility and globalization of foodstuffs and associated raw materials and wastages, it is highly challengeable task to control the environmental pollution. The development of analytical platforms is an ideal to detect the environmental pollutants quickly in order to rapidly initiate remedial strategies.
The traditional analytical methods commonly employed for the detection and quantification of chemical pollutants, including atomic absorption spectrometry (AAS), flame atomic absorption spectrometry (FAAS), gas/liquid chromatography-mass spectrometry, inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectroscopy (ICP-MS), high performance liquid chromatography (HPLC)–ultraviolet (UV) and fluorescence (FL) detection, and quantitative polymerase chain reaction [14], [15]. Though, these analytical techniques are very sensitive and quantitative, but require either lengthy sample preparation events or complicate instrumentation and hence are time-consuming techniques. There is a question with the stability of natural water samples during long-term storage and measurements, as samples are subject to various biological, chemical and physical affects. In addition, these instruments are expensive and high level of expertise only may conduct the analytical performance [14]. The aforementioned limitations, the real-time, online monitoring of sensing chemical species with high sensitive and spatial resolution are highly required. Electroanalytical methods have wedged various fields, including diagnostics, environmental analysis, food sciences, enzymatic kinetics and pharmacology. The electrochemical sensing methods offer high sensitivity and selectivity, a wide linear range, rapid response space and power requirements, and low-cost instrumentation [6], [16], [17]. In addition, the electrochemical sensors are mostly easy to integrate for the detection of single and multiple pollutants simultaneously. Electrochemical sensor can be classified according to the property of obtained response: potentiometric, amperometric and conductometric methods, in which the potential, current and conductivity are measured at the sensor interface, respectively [18]. All kinds of sensors mainly consist of recognition element and physical transducer (electrode), while the sensing performance is largely dependent on the interactions between the electrode surface and the analytes [19]. For the sensing perspective, the small size and large surface of the sensing electrodes can lead to rapid responses and high sensitivity toward the target species [20]. Besides, the surface and shape modifications of various electrode materials gives specific binding performance that allow highly selective, stable and sensitive contaminants detection [21]. Therefore, considerable efforts have been devoted to the development of new sensing electrodes.
Owing to nanoscale dimensions, nanomaterials own unique properties, which may be employed to design the novel electrochemical sensor platforms with enhanced sensitivity, as they provide high surface area to volume ratios and can be tailored to encourage electrode kinetics [22], [23]. Noble metal nanoparticles are among the most extensively studied nanomaterials because of their distinctive size and shape dependent optoelectronic properties. They have led to the development of numerous analytical systems for medical and environmental applications [7], [24], [25], [26]. Nanostructured Au materials offer auspicious avenue for the development of rapid, cost-effective and highly sensitive electrochemical sensor platforms, which also demonstrate the strong potential for on-site detection of pollutants due to their superior stability and complete recovery in biochemical redox processes [25], [27], [28]. The specific functionalities of nanostructured Au materials can be easily made and are support with targeted applications with their immediate local environments. The growing interest of Au nanomaterials based electrode materials provides an active and robust research, which may be expected to provide next generation technologies for environmental applications toward enhancing the electrochemical sensing methods [29], [30]. Scheme 1 shows the schematic illustration of various Au nanomaterials based electrochemical environmental sensors. This review critically elucidates the utility and advances of Au nanomaterials toward the design and the fabrication of electrochemical sensors/biosensors for the detection of emerging chemical pollutants, enabling successful environmental monitoring. The focus of our attention on overview and the importance of the nanostructured Au electrode materials and the sensing capabilities toward environmental chemical pollutants will be reviewed.
Section snippets
Gold nanoparticles
Gold nanoparticles have employed as an outstanding materials in variety of applications such as catalysis, electronics, photonics, chemical/electrochemical sensing and imaging of environmental monitoring and biomedical applications, information storage, drug delivery and biological labeling due to their high chemical stability, tunable opto-electronic properties, high surface area and capacity for surface modification, oxidation resistance, and good biocompatibility [31]. In the advancement of
Gold nanoclusters
Gold nanoclusters (smaller than 2.0 nm) are fascinating materials among the most studied nanocluster (NC) systems because of their novel characteristics. Great interest in the development of atomically precise Au clusters with definite core numbers stabilized by organic ligand protection are greatly stable and display unique size-dependent optical, electrochemical, and catalytic properties. These properties are differing considerably from their bulk counterpart and signify the bulk-to-molecule
Gold nanoporous
Nanomaterials with hollow or porous structures have a high surface area, which can potential lead to larger currents, better S/N ratios, improved sensitivity and lower detection limits [55]. Gold nanoporous (Au NPG) is a type of open-cell metal foam, which consists of a Au ligaments and pores [56]. The pores are usually in the range of 30–40 nm and can thus be described as mesoporous according to IUPAC classification [57]. By a careful design of the fabrication conditions, the pore sizes can be
Conclusions and perspectives
Novel design of Au nanomaterials based electrochemical sensor and biosensor systems offer a potential analytical technique for the sensitive, selective, rapid, and simultaneous determination of individual and multiple environmentally toxic analytes that includes a wide diversity of applications in environmental monitoring. Owing to the exceptional physicochemical and electrocatalytic properties such as stable and exceptional electrical conductivity of the Au nanomaterials may enable the
Acknowledgements
W.J. acknowledges financial support from “CAS Pioneer Hundred Talents Program” and National Natural Science Foundation of China under Grant No. 51604253.
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