Enhanced anti-interference on electrochemical detection of arsenite with nanoporous gold in mild condition

Abstract

Determination of arsenite [As(III)] without interference in mild condition is crucial for portably assessing arsenic contamination using electrochemical method. We have developed high-surface area nanoporous gold (np-Au) with a three dimensional, interconnected ligaments and nanoporous structure for the electrochemical detection of As(III) in 0.1 M HAc-NaAc solution (pH 5.0) without using strong acidic electrolyte. Square wave anodic stripping voltammetry (SWASV) using the np-Au modified glassy carbon electrode (GCE) confirms the successful detection of As(III) with almost no interference from some commonly coexisting ions. Furthermore, the sensitivity of the np-Au modified GCE exhibited approximately 10-fold enhancement as compared to Au nanoparticles (Au NPs) modified GCE. Finally, the proposed method is successfully applicable for analysis of As(III) in real water samples with satisfactory recoveries. The np-Au modified GCE shows enhanced anti-interference and excellent sensing performance may be attribute to its special surface structure and the fast transports of analytes and electron in the interface of electrode.

Introduction

The presence of arsenic (As) in food and water is a serious worldwide threat to public health, exposure to which can cause a lot of health problems, including skin lesions, keratosis (skin hardening), respiratory, mutagenic, and carcinogenic effects [1], [2]. The contamination of groundwater by arsenic has been reported in 20 countries where arsenic levels in drinking water are above the World Health Organization (WHO) guideline value of 10 ppb [3], [4], [5]. In the natural environment, Arsenic is predominantly present as trivalent arsenite [As(III)] and pentavalent arsenate [As(V)], and As(III) is reported to be 40–70 fold more toxic than As(V) [6], [7], [8]. So it is of utmost urgent to develop sensitive, fast, selective, and reliable analytical methods for As(III) detection.

Up to now, a variety of methods including graphite furnace absorption spectrometry (GFASS), electro-spray MS (ES-MS) coupled to chromatographic separation (HPLC,GC), neutron-activation analysis (NAA), inductive coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF), atomic emission spectrometry (AES) generally with inductively coupled plasma (ICP-AES), and so on [2], [6], [9], [10], [11], [12], [13], [14], have been used for the determination of As(III). Nevertheless, these techniques require expensive instruments, time-intensive, laboratory setup, and well trained technicians for their handling, which can not be routinely used for in-situ analysis. Compared to these techniques mentioned above, the low-cost electrochemical methods, particularly stripping voltammetry analysis may provide an attractive alternative for their excellent sensitivity, simple operation, and ease of portability [15], [16].

Recently, many kinds of electrode materials including platinum [8], [17], mercury [18], [19], boron-doped diamond [20], [21], modified GCE [22], and gold electrode [23], [24], [25], have been developed for determination of As(III). Because of their high hydrogen overvoltage, highly sensitive, and reversibility, the nanosized Au and Au-based materials have received more attention in the electrochemical detection of As(III). Srivastava et al. [26] determined As(III) at a graphene paste electrode modified with the thiacrown 1,4,7-trithiacyclononane (TTCN) and gold nanoparticles (AuNPs) with potentiometric stripping analysis (PSA), and obtained an LOD of 8 pM, more importantly, the modified electrode displays a 15-fold enhancement in the PSA signal (dt/dE) compared to a conventional graphene paste electrode. Using SWV, Ohsaka et al. [15] found a limit of detection of 0.28 ppb with a sensitivity of 27.27 ± 0.01 μA cm⁻² μM⁻¹ for As(III) in 0.1 M phosphate buffer (PB) solution (pH 1) on a Au(111)-like poly-Au electrode. Dar et al. [27] measured As(III) on silver nanoparticle (AgNPs)-graphene oxide (GO) composite modified glassy carbon electrode (GCE) in 0.1 M H₂SO₄ solution by SWV (square wave voltammetry), and obtained a sensitivity of 180.5 μA μM⁻¹ with a LOD of 0.24 nM. Raj et al. [24] used a gold nanoelectrode ensembles (GNEEs) to determine As(III) by SWV in 1 M HCl media and obtained an LOD of 0.02 ppb with a sensitivity of 235.5 μA μM⁻¹. Compton’s group [5] investigated As(III) detection by SWV in 1 M HCl media on a gold nanoparticle modified GCE giving an LOD of 4.4 ppb with a sensitivity of 95 μA μM⁻¹. Chen et al. [25] determined As(III) on a gold-nanoparticle embedded nafion composite modified on glassy carbon electrode using SWV in a medium containing 0.1 M EDTA and 0.1 M PB buffer (pH 5.0) and achieved an LOD of 0.047 ppb with a sensitivity of 23.98 μA μM⁻¹. Huang et al. [28] measured As(III) in 0.1 M PB aqueous solution with 0.01 M EDTA by SWV and obtained an LOD of 0.0025 ppb with a sensitivity of 16.15 μA μM⁻¹ on Au NPs modified GCE. Xiao et al. [16] detected As(III) in 0.1 M HCl media on a Au NPs modified carbon nanotubes and an LOD of 0.1 ppb but more importantly a sensitivity of 1985 μA μM⁻¹ was obtained with SWV. Hossain et al. [29] prepared gold nanoparticle-modified GCE by electrodeposition for As(III) determination in 3 M HCl by LSV (linear sweep voltammetry) with an LOD of 1.8 ppb and a sensitivity of 320 μA cm⁻² μM⁻¹. Other approaches include that of Huang and coauthors [30], who used Au micro wire electrodes to determine As(III) in N₂H₄·2HCl electrolyte (pH 0.5) by SWV obtained an LOD of 5.01 ppb and a sensitivity of 35.4 nA μM⁻¹. Zen et al. [31] reported a poly(L-lactide) stabilized gold nanoparticles (designated as PLA-Au^NP) modify a disposable SPE (screen-printed carbon electrode) for the detection of As(III) by DPASV (differential pulse anodic stripping voltammeter) in 1 M HCl media and obtained an LOD of 0.09 ppb with a sensitivity of about 6.43 μA μM⁻¹. Giacomino et al. [8] detected As(III) in 0.25 M HCl media on a lateral gold electrode with an LOD of 0.06 ppb. Through careful investigation, we found that most of the reported on As(III) detection using Au or Au-based electrodes under strongly acidic media (such as HCl, H₂SO₄, HNO₃), which could suffer the problems from generating toxic arsine gas and the interference from H₂ evolution. Furthermore, the major problems associated with the available Au or Au-based electrodes are the interference from some commonly coexisting ions such as Cu(II), Hg(II) present in the real water sample, and the interference due to supporting electrolyte anions. Among these, anodic stripping voltammetric detection of As(III) without interference of Cu(II) remains a big challenging aspect since the presence of Cu(II) favor the formation of intermetallic compounds such as Cu₂As₃ which restricts the design of As(III) sensors for the real sample analysis. Thus, it is expected to develop an efficient sensing materials for realizing the sensitive detection of As(III) without interference from commonly coexisting ions in mild medium.

Importantly, the performance of electrochemical sensors is highly dependent on the structural properties of electrodes. To date, considerable efforts have been devoted to innovational materials for coordinate mass- and charge- transport and electron transfer kinetics: electrochemical reaction occurring at electrolyte/electrode interface, mass transport of analyte in electrolyte and electrode, and the electron conduction in electrode and current collector [32]. Touilloux et al. [33] developed the gold nanoparticles plated 2.1 μm iridium-based microelectrode for determining As(III) at pH 8. The interference by copper can be negligible for an As: Cu concentration ratio of 1:20. This demonstrates that the structure of electrode directly affects the electrochemical performance. Recently, nanoporous gold (np-Au) has received tremendous scientific attention, since it has excellent electrocatalytic performance, structural integrity, chemical stability, and electrical conductivity [34]. At present, np-Au material can be produced by simple electrochemical treatment of polycrystalline gold [35], chemical dealloying gold alloys [36], [37], [38], the use of templates [39], [40], and so on. In particular, chemical dealloying Au alloys, selective removal of one component from within an alloy, has become a popular method for simple and low-cost generation of np-Au. The dealloying process gives rise to a unique bicontinuous nanostructure consisting of nanosized interconnected ligaments and nanoporous channels, which enables np-Au to have good electrical conductivity, enhancing the transports of electron and offers a relatively large specific surface area of electrode/electrolyte interface, facilitating the full use of the enhanced electrocatalysis [41], [42], [43]. The np-Au has been demonstrated beneficial for a wide variety of different applications, including electrocatalysts [34], [39], [44], [45], electrochemical sensors [46], [47], energy storage [48], and electrochemical actuators [42]. Considering the special surface structure, fast mass transportation, and high current density of np-Au, it might enhance the As(III) electroanalysis performance, such as anti-interference, sensitivity etc. However, to the best of our knowledge, the application of np-Au modified electrodes for stripping voltammetry electroanalysis of As(III) has not been explored.

We report here np-Au modified GCE electrode constructed with an in-situ chemical dealloying of AuCu nanoparticles (AuCu NPs), which is performed on electroanalysis of As(III) in mild condition (acetate buffer solution pH 5.0) by SWASV for the first time. The anti-interference, reproducibility, and stability have been systematically investigated. And also, the proposed method has been successfully applied to determination of As(III) in real water samples.