Article pubs.acs.org/ac
Topotactic Conversion of Copper(I) Phosphide Nanowires for Sensitive Electrochemical Detection of H2O2 Release from Living Cells Zhenzhen Li, Yanmei Xin, Wenlong Wu, Baihe Fu, and Zhonghai Zhang* School of Chemistry and Molecular Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China S Supporting Information *
ABSTRACT: In this work, we clearly demonstrate for the first time the use of transition-metal phosphides to set up a new cathodic analysis platform for sensitive and selective electrochemical nonenzymatic detection of H2O2. With the help of a facile topotactic conversion method, the noble metal-free electrocatalyst of copper(I) phosphide nanowires on three-dimensional porous copper foam (Cu3P NWs/CF) is fabricated with electrochemical anodized Cu(OH)2 NWs as precursor. The Cu3P NWs/CF-based sensor presents excellent electrocatalytic activity for H2O2 reduction with a detection limit of 2 nM, the lowest detection limit achieved by noblemetal free electrocatalyst, which guarantees the possibility of sensitive and reliable detection of H2O2 release from living tumorigenic cells, thus showing the potential application as a sensitive cancer cell detection probe.
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environmental instability, and denaturation that still hinder its practical application. To overcome these issues, recently, nonenzymatic electrochemical H2O2 sensors have been proposed with effective electrocatalysts taking the place of enzymes for actively catalyzing H2O2 reduction. These new nonenzymatic sensors present many advantages, such as simple fabrication procedure, high electrocatalytic activity, wide detection range, and high stability, and they demonstrate great potential for sensitive H2O2 detection. However, up to now, only nonenzymatic sensors based on noble metal nanoparticles (NPs) have presented effective nanomolar detection limits for available detection of H2O2 release from living cells (106 mL−1).14,15 Sensors based on low-cost metal oxide materials or carbon materials, such as Co3O4, CuO, Mn2O3, carbon nanotubes, and graphene,16−20 still cannot reach the detection limit for practical sensing applications. Given the deficiency and high cost of precious noble metals, the large-scale practical utilization of noble metal-based sensor for H2O2 detection is severely impeded. A compromise strategy has been proposed by using composites of noble metal NPs and metal oxides or carbon materials, such as Au−Fe3O4, PtPd− Fe3O4, Au−MnO, Au−CuxOS, and Pt−graphene,21−25 for H2O2 detection, but the exploration of totally noble metal-free materials using earth-abundant elements with high electrocatalytic activity is still desirable. Transition-metal phosphides have been extensively studied for applications as catalysts in hydrodesulfurization and
ydrogen peroxide (H2O2) is one of the most important representatives of reactive oxygen species, generated from oxygen metabolism in cells, and is widely involved in cell growth and signal transduction.1 The concentration level of H2O2 is an essential biological parameter in monitoring and maintaining the physiological balance of a living cell, and abnormal concentration level of H2O2 will lead to cell aberrance and apoptosis and thus is closely associated with serious disorders, such as myocardial infarction, Parkinson’s disease, and even cancers.2,3 Under normal physiological conditions, H2O2 shows a concentration gradient across cellular membranes with an intracellular concentration estimated at 0.05− 0.7 μM4,5 and an extracellular concentration that is ∼10-fold higher,6,7 while in pathological conditions, the local extracellular concentrations of H2O2 can additionally elevate to as high as 10−50 μM.7−9 Therefore, it is of great significance to develop efficient and reliable methods for sensitive and selective H2O2 detection under physiological conditions. Up to now, numerous analytical techniques have been employed for H2O2 sensing, including fluorescence, colorimetry, chemiluminescence, and electrochemical methods.10−13 Among them, the electrochemical method distinguishes itself due to its simplicity, rapidness, and low cost. The conventional electrochemical H2O2 sensors are set up by anchoring horseradish peroxidase (HRP) on the surface of electrochemically active species, such as noble metals, conductive polymers, and carbon materials, where the H2O2 is reduced by HRP and the corresponding electron transfer through electrochemical materials is recorded in electronic current form. In spite of the enzyme-based sensor achieving high sensitivity and good selectivity for H2O2 detection, it has intrinsic drawbacks associated with difficult enzyme purification, complicated immobilization procedure, © XXXX American Chemical Society
Received: April 26, 2016 Accepted: July 5, 2016
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DOI: 10.1021/acs.analchem.6b01637 Anal. Chem. XXXX, XXX, XXX−XXX
Analytical Chemistry
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Article
RESULTS AND DISCUSSION Scheme 1 presents the design and synthesis strategy of Cu3P NWs/CF. CF was rationally selected as the raw material for
hydrogen evolution reactions, and many transition-metal phosphides, such as Cu3P, Ni5P4, CoP, and MoP,26−30 have shown excellent electrocatalytic reduction activity due to their metalloid characteristics and good electrical conductivity. Herein, the noble metal-free electrocatalyst of copper(I) phosphide nanowires on three-dimensional porous copper foam (Cu3P NWs/CF) is fabricated by a facile topotactic conversion method with electrochemical anodized Cu(OH)2 NWs as precursor. The Cu3P NWs/CF-based sensor presents excellent electrocatalytic activity for H2O2 reduction, and is the first to achieve a low detection limit of nanomolar level with a noble metal-free electrocatalyst, which guarantees the possibility of sensitive and reliable detection of H2O2 release from living tumorigenic cells, thus showing potential application as a sensitive cancer cell detection probe.
Scheme 1. Design and Synthesis Strategy of Cu3P Nanowires on Copper Foama
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EXPERIMENTAL SECTION Materials. All reagents are of analytical grade and were used as received without any further purification. Copper foam (CF, thickness of 1 mm) was supplied by Suzhou Taili New Energy Materials Ltd. Co. Sodium hydroxide, sodium hypophosphite, sodium chloride, dopamine, glucose, ascorbic acid, citric acid, sodium sulfate, and hydrogen peroxide were supplied by Macklin Inc., Shanghai, China. RAW 264.7 cells were supplied by KeyGEN Bio-Tech, Nanjing, China. Preparation of Cu3P Nanowires on Copper Foam Electrode. Cu3P NWs/CF was prepared as follows: first, the cleaned CF was anodized (by our previously reported method)31 in an alkali solution (3 M NaOH) for 30 min with current density 45 mA·cm−2 to form Cu(OH)2 NWs/CF. The temperature of electrochemical cells was maintained at 25 °C for all experiments. Phosphidation between NaH2PO2 (0.05 g) and Cu(OH)2 NW/CF in the tube furnace at 300 °C for 2 h under argon atmosphere converted Cu(OH)2 NWs/CF to Cu3P NWs/CF. Materials Characterization. Morphologies of samples were characterized by scanning electron microscopy (SEM, S4800, Hitachi), and high-resolution transmission electron microscopy (HR-TEM, JEOL JEM 2100). The crystalline structure of the samples was analyzed by X-ray diffraction (XRD) [Bruker D8 Discover diffractometer, using Cu Kα radiation (1.540 598 Å)]. Chemical compositions and status were analyzed by X-ray photoelectron spectroscopy (XPS) with an Axis Ultra instrument (Kratos Analytical) under ultrahigh vacuum (
