Electronic Supplementary Material (ESI) for ChemComm.
This journal is © The Royal Society of Chemistry 2016
Electronic Supplementary information (EIS) for
Bimetal-Organic-Frameworks-Derived
Yolk-shell-structured
Porous
Co2P/ZnO@PC/CNTs Hybrids for Highly Sensitive Non-Enzymatic
Detection of Superoxide Anion Released from Living Cells
Min-Qiang Wang,a,+ Cui Ye,b,+ Shu-Juan Bao,a,* Yan Zhang,a Mao-Wen Xu,a and Zhe Li, a
a
Institute for Clean Energy & Advanced Materials, Faculty of Materials and Energy, Southwest
University, Chongqing 400715, PR China
b Key Laboratory of Eco-environments in Three Gorges Reservoir Region (Ministry of
Education), School of Chemistry and Chemical Engineering, Southwest University, Chongqing
400715, PR China.
* Corresponding author
Fax: +86-23-68254969; Tel:+86-23-68254969;
E-mail: baoshj@swu.edu.cn
Experimental section
Materials: Analytical grade cobalt nitrate hexahydrate (Co(NO3)2·6H2O), zinc nitrate
hexahydrate (Zn(NO3)2·6H2O), 2-methyllimidazole and Nafion solution (5 wt %) were purchased
from Aladdin Industrial Co., (Shanghai, China). Potassium superoxide (KO2), Zymosan A (Zym,
from Saccharomyces cerevisiae), SOD (from bovine erythrocytes), and 0.01 M PH 7.4 Phosphate
buffer solution (PBS) were obtained from Sigma-Aldrich. The O2•− solutions were prepared by the
addition of KO2 solid powder to PBS (N2 saturated). The concentration of O2•− was determined by
recording the reduction of ferri cytochrome c spectrophotometrically and using the extinction
coefficient (21.1 mM−1 cm−1) of ferri cytochrome c at 550 nm. The other chemicals were
purchased from Sigma-Aldrich and used without further purification. Deionized water (18.2 MX)
was used throughout the experiments.
Synthesis of Zn/Co-ZIF and ZIF-67 precursors: The Zn/Co-ZIF precursors were first
synthesized via a simple method according to the previous report. In a typical synthesis, 2methyllimidazole (0.616g), Co(NO3)2·6H2O (0.546g), and Zn(NO3)2·6H2O (0.558g) were
dissolved in 15mL methanol, 7.5mL methanol, and 7.5mL methanol, respectively under
ultrasound for 5min at room temperature. After forming homogeneous solution, Co(NO3)2·6H2O
in methanol solution was mixed with ligand solution (2-methylimidazole) slowly in 1min under
ultrasound for 2 min at 40℃ by syringe. Next, Zn(NO3)2·6H2O in methanol solution was further
added in the above-mentioned solution by inches keeping ultrasound for 10min. The resulting
suspension was transferred to 50mL Teflon-lined stainless-steel autoclaves and then heated at
120℃ for 4h. Finally, the mixture were washed via centrifugation at 11000 rpm for 5 min with
methanol for several times and then dried under vacuum at 60℃ to get the final Zn/Co-ZIF
product. For the synthesis of ZIF-67, the same procedure was conducted without the addition of
Zn(NO3)2.
Synthesis of Co2P/ZnO@PC/CNTs and Co2P@PC: The Co2P/ZnO@PC/CNTs was prepared
by using a simple low-temperature phosphidation of the obtained Zn/Co-ZIF precursors. In a
typical synthesis, 20 mg Zn/Co-ZIF precursors and 400 mg NaH2PO2 were placed at two separate
positions in one quartz boat with NaH2PO2 at the upstream side of the furnace. Then, the samples
were heated to 350 ℃ for 1.5 h with a heating rate of 2 ℃min-1 in a N2 atmosphere. After cooling
to room temperature, the porous Co2P/ZnO@PC/CNTs was collected. The same procedure was
conducted to fabricate Co2P@PC used ZIF-67 as precursor.
Fabrication of modified electrodes: The glassy carbon electrode (GCE, Φ= 3 mm) was
respectively polished with 0.3 and 0.05mm alumina slurry followed by rinsing thoroughly with
double distilled water, and then ultrasonically cleaned in ethanol and double distilled water to
obtain a mirror-like surface. The as-prepared Co2P/ZnO@PC/CNTs aqueous dispersion (5mL, 2
mg ml-1) was dropped onto the well-polished bare GCE and then evaporated in air. Then, Nafion
(5mL, 2.5%) was dropped on the surface of Co2P/ZnO@PC/CNTs composite to form a Nafion
membrane. Similar procedure was also applied to prepare Co2P@PC modified electrode for a
comparative study.
Material characterizations and electrochemical measurements: Powder X-ray diffraction
(XRD) patterns were obtained with a XRD-7000 (XRD, Shimadzu XRD-7000) with Cu Kα source
radiation at a scanning rate of 2° min−1 from 10 to 80°. The morphologies and microstructures
were investigated by field-emission scanning electron microscopy (FESEM, JEOL-7800F),
transmission electron microscope (TEM, JEM- 2100), and Energy-dispersive X-ray spectroscopy
(EDX, INCA X-Max 250). The surface properties of the samples were studied by X-ray
photoelectron spectroscopy (XPS, Escalab 250xi, Thermo Scientific). The electrochemical
measurements were carried out on a conventional three electrode system with the as-prepared
electrodes as the working electrode, a platinum wire as the counter electrode, and a saturated
calomel electrode (SCE) as the reference electrode on a CHI660 electrochemical workstation (CHI
Instruments Inc.).
Cell Cultures and real time monitoring cell released O2•− molecules: A375 (human
malignant melanoma cells) cell line was cultured in RPMI-1640 medium supplemented with 10%
heat inactivated fetal bovine serum, 1 mol L−1 ampicillin and 1 mol L−1 kanamycin and was grown
in a humidified incubator (95% air with 5% CO2) at 37 °C. The cell density applied to our
experiments was the average cell number counted from 6 different areas of 1.8 mm2 on three
samples through inverted microscopy. Real time monitoring O2•― molecules released from cells
was performed by chronoamperometry. In order to ensure accuracy of measured O2•―
concentrations, cell culture medium inside device was mildly stirred during cell released O2•―
measurement
Fig. 5. The electrochemical impedance spectroscopy (EIS) of Co2P/PC and Co2P/ZnO@PC/CNTs
hybrid based electrodes in a 0.2 M [Fe(CN)6]3-/4- mixture (1:1) containing 0.1 M KCl at open
potential.