Immobilized Ferrous Ion and Glucose Oxidase on Graphdiyne and Its

Apr 19, 2018 - ABSTRACT: Graphdiyne (GDY) is a novel two-dimensional (2D) car- bon allotrope with sp-hybridized carbon atoms and hexagonal rings. Beca...
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Immobilized Ferrous Ion and Glucose Oxidase on Graphdiyne and Its Application on One-Step Glucose Detection Jiaming Liu,†,‡ Xiaomei Shen,ζ Didar Baimanov,†,‡ Liming Wang,† Yating Xiao,†,‡ Huibiao Liu,§ Yuliang Li,§ Xingfa Gao,*,ζ Yuliang Zhao,†,‡ and Chunying Chen*,†,‡ †

CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety & CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing 100049, China § CAS Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ζ College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, China S Supporting Information *

ABSTRACT: Graphdiyne (GDY) is a novel two-dimensional (2D) carbon allotrope with sp-hybridized carbon atoms and hexagonal rings. Because of its unique structure and electronic property, GDY was reported as a promising candidate applied in energy storage, catalysis, biosensing and so on. However, using GDY as a platform to immobilize metal ion or enzyme was still not reported. Here, we presented a GDYbased composite with dual-enzyme activity by immobilizing ferrous ion and glucose oxidase onto GDY sheet. GDY showed great adsorption capacity and maintained the high catalytic activity of ferrous ion. The ferrous ion preferred to adsorb in between the neighboring two C−C triple bonds of GDY with lower adsorption energy (−5.64 eV) if compared to graphene (−1.69 eV). Meanwhile, GDY exhibited the ability of adsorbing glucose oxidase while did not obviously influence the structure and catalytic activity of the enzyme. The as-prepared composite was successfully used in one-step blood glucose detection. This work provides a new insight on ion and enzyme immobilization by 2D material. KEYWORDS: graphdiyne, ferrous ion, glucose oxidase, enzyme immobilization, glucose detection



INTRODUCTION Graphdiyne (GDY) is a novel two-dimensional carbon material with sp- and sp2-hybridized carbon atoms. The basic structural unit of GDY is a trianglelike ring consisting of 18 carbon atoms with butadiyne (−CC−CC−) linkages and benzene rings. Such unique structure makes GDY a heterogeneously electron distributed surface.1 Since the first reported synthesis of GDY in 2010,2 GDY has been reported to be particularly useful in many fields, such as catalysis,3−7 energy,8−11 environment,12 and biosensing.13−15 However, using GDY as a substrate for immobilizing metal ion or enzyme to be an enzyme mimic is still not reported. Glucose is a major indicator of the human body, especially in the evaluation of diabetes mellitus.16 Therefore, determimation of blood glucose concentration is vital to monitor the physical condition of human body. The typical methods of glucose detection include enzymatic method, electrochemical detection17 and HPLC method.18 Glucose oxidase-peroxidase (GOx-POD) method is one of the most widely used enzymatic methods in glucose detection19 due to its high sensitivity, low detection limit and easy operation. The typical GOx-POD method includes two steps for glucose detection: First, in the presence of glucose © XXXX American Chemical Society

oxidase, glucose is oxidized into gluconic acid by oxygen to produce hydrogen peroxide; Next, the chromogenic agent is oxidized into colored product by the as-produced hydrogen peroxide, where the reaction is catalyzed by peroxidase. The current GOxPOD methods, which need two independent enzymatic reactions with different enzymes, are carried out by activating these two catalytic reactions successively.20−25 The glucose detection methods used here are separated into two steps, which make the operational procedures complicated and tedious. So immobilizing these two enzymes together to achieve one-step glucose detection is necessary. Iron is one of the transition metals whose transformation between Fe(II) and Fe(III) gives it high catalytic activity. To increase the activity and stability of iron compound, some iron-based composites were synthesized and successfully applied Special Issue: Graphdiyne Materials: Preparation, Structure, and Function Received: February 22, 2018 Accepted: April 19, 2018

A

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Scheme 1. Schematic Illustration to Show the Preparation of Fe-GDY/GOx and Mechanism for Glucose Detection

in biosensing.26−28 Ferrous ion (Fe2+), one of the ionic forms of the iron element, is an important metal ion in many cofactors of natural enzymes, such as peroxidase,29 cytochrome oxidase,30 and dehydrogenase.31 It plays a key role in the enzymatic catalytic reaction. Meanwile, as an active transition metal ion, Fe2+ could also catalyze some chemical reactions such as Fenton reaction, which produces high-active hydroxyl radical from hydrogen peroxide.32 However, Fe2+ is easily oxidized into ferric ion (Fe3+) by oxygen in the air. Such instability of Fe2+ limits its further application. Therefore, in this study, we prepared a ferrous ion and glucose oxidase immobilized GDY composite used to one-step glucose detection (Scheme 1). GDY showed great adsorption capacity of ferrous ion and could protect it from being oxidized, which was mainly due to its heterogeneous surface of energy distribution and sp-hybridized carbon atoms.33−35 Owing to the large specific surface area of two-dimensional material, GDY could easily adsorb glucose oxidase on its surface. Surprisingly, the adsorbed enzyme showed only tiny change of structure and still kept high catalytic activity. The Fe-GDY/GOx composite, combined with peroxidase activity of Fe2+ and glucose oxidase activity, was successfully used to quantitatively determine blood glucose concentration.



into 1 mL of aqueous dispersion of Fe-GDY (1 mg/mL). The mixture was stirred gently for 1 h at room temperature. The resulting product was centrifuged and washed several times with pure water to remove the unadsorbed glucose oxidase. Measurement of Peroxidase Activity of Fe-GDY. To measure the peroxidase activity of Fe-GDY, the classical TMB colorimetric method was used in this work.36 TMB is a commonly used commercial color agent in enzyme linked immunosorbent assay (ELISA) detection, which is colorless but could be oxidized into colored product by H2O2 in the presence of peroxidase. The oxidized product shows a maximum absorbance at 655 nm and can be detected by UV−vis spectrophotometer. In a typical method, the measurement of peroxidase activity of Fe-GDY was carried out in a 1.5 mL tube with 20 μg/mL Fe-GDY and 10 mM H2O2 in sodium acetate (NaAc) buffer (pH 4.0), using 400 μM TMB as the substrate. The UV−vis spectra of the reaction solution were collected by UV−vis spectrophotometer after reaction for several minutes. Free Radical Measurements by Electron Spin Resonance Spectroscopy. To capture the hydroxyl radical generated in the reaction, we used 5-tertbutoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) as the spin trap.37 Briefly, 5 μL of Fe-GDY (2 mg/mL) and 5 μL of BMPO (250 mM) were added into 35 μL of NaAc buffer (pH 4.0), respectively. When 5 μL of H2O2 (50 mM) was added into the reaction solution, the ESR spectra for adducts BMPO/•OH were immediately collected. H2O2 Detection Using Fe-GDY. TMB chromogenic method was used in H2O2 detection. To enhance the sensitivity of the detection, H2SO4 was added into the final product to terminate the reaction and give a strong maximum absorbance at 450 nm. H2O2 was detected as the following steps: 20 μL of Fe-GDY (1 mg/mL), 10 μL of TMB solution (10 mM), and 100 μL of H2O2 solution with different concentrations were added into 120 μL of NaAc buffer (pH 4.0), respectively. The mixture was incubated at room temperature for 15 min. Then 50 μL of H2SO4 (1 M) was added into the solution to terminate the reaction and the UV−vis spectra were recorded immediately. Glucose Detection Using Fe-GDY/GOx. Glucose detection was performed as the following steps: 20 μL of Fe-GDY/GOx (1 mg/mL), 10 μL of TMB solution (10 mM), and 100 μL of glucose solution with different concentrations were added into 120 μL of NaAc buffer (pH 4.0), respectively. The mixture was incubated at room temperature for 25 min. Then 50 μL of H2SO4 (1 M) was added into the solution to terminate the reaction and the UV−vis spectra were recorded immediately. For detection of blood glucose concentration of rat, serum was collected from a newly sacrificed rat and diluted 100 times by NaAc buffer for detection. Computational Simulation Method. To compare the adsorption energies of the Fe2+ ion on the surfaces of GDY and graphene, we constructed the (2 × 2) and (4 × 4) unit cells for GDY and graphene, respectively. One Fe2+ ion was then put on each of the unit cells. To make the system electrically neutral, we added one SO42− anion to each of the adsorbed Fe2+. The Fe2+@GDY and Fe2+@graphene structures were optimized by the Vienna ab initio Simulation Package (VASP)38−40 with Perdew−Burke−Ernzerhof (PBE)41 of generalized gradient approximation (GGA) functional. Energy cutoff and Gaussian smearing were set to 500 and 0.05 eV, respectively. The 15 Å vacuum heights were used for GDY and graphene, respectively. The (3 × 3 × 1) Monkhorst−Pack mesh k-point grids42 were used for all the calculations.

EXPERIMENTAL SECTION

Materials. 3,3′,5,5′-Tetramethylbenzidine (TMB), D-(+)-glucose, and glucose oxidase (GOx, ≥ 180 U/mg) were purchased from Shanghai Aladdin Biochemical Technology Co.,Ltd . Ferrous sulfate heptahydrate (FeSO4·7H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 30% hydrogen peroxide (H2O2) was purchased from Beijing Chemical Reagent Research Institute. Characterization. The morphologies of materials were measured by a Tecnai G2 20 S-TWIN transmission electron microscopy (TEM) at an accelerating voltage of 200 kV and a scanning electron microscopy (SEM, Hitachi S4800). The heights of materials were measured by a Bruker Multimode-8 atomic force microscope (AFM). Zeta potential of the materials was measured by a Zeta Sizer Nano series Nano-ZS (Malvern Instruments Ltd., Malvern, UK). The UV−visible absorption spectra were measured by a Cary UV spectrophotometer (PerkinElmer Lambda 850). XPS spectra were collected by an X-ray photoelectron spectroscopy (ESCALAB 250, Thermo Fisher) instrument. The enzyme structure was determined by a circular dichroism spectrophotometer (J-1500, JP). Electron spin resonance (ESR) spectra were collected by a Bruker EMX ESR Spectrometer (Billerica, MA). Preparation of Fe-GDY. GDY powder was supplied from Li’s group (Chinese Academy of Sciences), which was synthesized according to the previously published procedure.2 Graphene was purchased from Nanjing XFNANO Materials Tech Co., Ltd. In a typical synthesis of Fe-GDY, FeSO4 solution (0.5 mL, 10 mM) was added into aqueous dispersion of GDY (1.5 mL, 1 mg/mL) at room temperature under gentle stirring for 30 min. The resulting product was centrifuged and washed several times with pure water. Fe-graphene was synthesized in the same method. Preparation of Fe-GDY/GOx. In a typical synthesis of Fe-GDY/ GOx, 1 mL of glucose oxidase aqueous solution (1 mg/mL) was added B

DOI: 10.1021/acsami.8b03118 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 1. Characterization of Fe-GDY. (a) SEM image of Fe-GDY; (b, c) TEM images of Fe-GDY; (d) EDX mapping of Fe-GDY for C, O, and Fe; (e) XRD patterns of GDY (black) and Fe-GDY (red); (f) survey XPS spectrum of Fe-GDY; (g) high-resolution Fe 2p XPS spectrum of Fe-GDY. During the calculations, all the atoms were relaxed with the conjugated gradient algorithm, and the electronic energy and force convergence criteria were set to 10−6 eV and 0.01 eV/Å, respectively. The adsorption energies were calculated with

Eads = E FeSO4 @sheet − (E FeSO4 + Esheet)

oxygen and iron. The oxygen signal was mainly due to the existence of oxygen-containing groups in GDY.43 The high resolution asymmetric C 1s XPS spectra showed no obvious change before and after Fe2+ adsorption of GDY (Figure S3), which consisted of four main peaks: C−C (sp2) at 284.6 eV, C−C(sp) at 285.2 eV, C−O at 286.6 eV, and CO at 288.8 eV.44 The chemical state of iron adsorbed on GDY was determined by high resolution Fe 2p XPS spectra (Figure 1g). The two specific Fe(II) satellites were observed: Fe(II) Fe 2p3/2 satellite at 715.8 eV and Fe(II) Fe 2p1/2 satellite at 729.4 eV. Meanwhile, according to the Fe 2p1/2 and Fe 2p3/2 main peak, the major chemical state of the adsorbed iron was Fe (II) rather than Fe (III).15,45 The sustainability of Fe2+ was probably due to the low reduction potential of GDY.46 Peroxidase Activity of Fe-GDY and Mechanism. TMB chromogenic method was used to measure the activity of Fe-GDY and Fe-graphene. At the same concentration of carbon materials, the reaction solution containing Fe-GDY showed the strongest absorbance at 655 nm, which was about 7.2 times higher than Fe-graphene (Figure 2a). Such high peroxidase activity of Fe-GDY could be mainly attributed to the high Fe2+ adsorption capacity of GDY. The optimum pH of catalytic reaction was measured by using NaAc buffer with different pH values from 2.0 to 7.0. The results showed that the optimum pH value of reaction was 4.0 (Figure 2b), so pH 4.0 was adopted as standard condition in the next experiment. The reaction of TMB oxidation by H2O2 was a key step in the glucose detection by Fe-GDY/GOx, which was derived from the adsorbed Fe2+. So the capacity of H2O2 detection by Fe-GDY was determined. Figure 2c showed the H2O2 concentration dependent absorbance variations in the catalytic reaction, which were related to the concentration of oxidized TMB. The result demonstrated that

(1)

where EFeSO4@sheet is the total energy of the carbon sheet with the adsorbed FeSO4, EFeSO4, and Esheet are the total energies of the isolated FeSO4 and the carbon sheet, respectively.



RESULTS AND DISCUSSION Synthesis and Characterization of Fe-GDY. Fe-GDY was prepared by simply mixing FeSO4 aqueous solution and GDY suspension together under gentle stirring. The morphology of Fe-GDY was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As shown in Figure 1a−c, the size of Fe-GDY was several hundred nanometer and the structure was stratified. There was no visible nanocluster or nanoparticle on the surface of GDY (Figure 1a, c) compared with pure GDY sheet (Figure S1). Energy-dispersive X-ray (EDX) element mapping was used to investigate the distribution of Fe element on GDY sheet. Figure 1d showed that Fe was uniformly distributed on GDY sheet, which was well overlapped with C and O element of GDY. The XRD pattern of Fe-GDY showed no observed specific peaks came from lattice plane of iron (Figure 1e). These results suggested that iron ion were adsorbed onto the surface of GDY rather than forming crystal structures. The increase of zeta potential of Fe-GDY also demonstrated the adsorption of iron ion on GDY (Figure S2). The chemical composition in Fe-GDY and its elementary chemical form were investigated by X-ray photoelectron spectroscopy (XPS). As shown in Figure 1f, Fe-GDY was composed of carbon, C

DOI: 10.1021/acsami.8b03118 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 2. POD activity of Fe-GDY: (a) UV−vis spectra of buffer solution containing 400 μM TMB, 10 mM H2O2, and different materials after 5 min reaction; (b) pH-dependence POD activity of Fe-GDY, (c) linear calibration plot for H2O2 using Fe-GDY, (d) ESR spectra of reaction solution containing 25 mM BMPO with 10 mM H2O2 (black line) or 200 μg/mL Fe-GDY (red line) or H2O2 and Fe-GDY together (blue line).

H2O2 could be detected with a broad linear range from 1 μM to 200 μM by Fe-GDY. To better understand the mechanism of the peroxidase activity of Fe-GDY, we performed ESR spectroscopy measurement to detect the probable generated free radical during the catalytic reaction. Strong ESR signal of radical spin adduct was observed after mixing Fe-GDY and H2O2 together in pH 4.0 NaAc buffer for 5 min, whereas H2O2 or Fe-GDY alone did not show any significant spectra (Figure 2d). The ESR spectrum of Fe-GDY and H2O2 containing solution showed four main lines with the relative intensities of 1:2:2:1, which was considered as the specific signal of BMPO/•OH.47 These results illustrated the generation of •OH from H2O2 in the presence of Fe-GDY, which could be explained by the Fenton reaction between the Fe2+ ion on GDY and H2O2 (showed in eq 2).48 Fe 2 + + H 2O2 → Fe3 + + OH− + ·OH

The peroxidase activity of Fe-GDY/GOx was tested after preparation. The result showed that the peroxidase activity of Fe-GDY/GOx was about 83% of Fe-GDY (Figure 3d). The slender decline of the catalytic activity of Fe-GDY after glucose oxidase absorption was probably due to the coverage of Fe2+ by glucose oxidase. The optimum pH value for glucose detection was measured by incubating 100 μM glucose, 400 μM TMB and 80 μg/mL Fe-GDY/GOx in NaAc buffer with different pH value from 2.0 to 7.0. The result showed the optimum pH for glucose detection by Fe-GDY/GOx was 4.5, which was very close to the optimum pH for the peroxidase activity of Fe-GDY (pH 4.0) (Figure 3e). The temperature-dependence activity of Fe-GDY/ GOx was also measured (Figure 3f). The optimum temperature for glucose detection was 35°C. Meanwhile, Fe-GDY/GOx showed a broad temperature range (20−40 °C) with more than 90% activity of the highest. According to the experimental results above, the peroxidase activity of Fe-GDY did not significantly change after glucose oxidase adsorption. The glucose detection was carried out by adding Fe-GDY/ GOx, TMB and different concentration of glucose solution into pH 4.5 NaAc buffer solution. As the increase of glucose concentration, the absorbance of reaction solution at 450 nm was increasing accordingly (Figure 3g). Figure 3h showed the linear calibration plot for glucose. The curve exerted great linearity from 5 to 160 μM of the glucose concentration with a high R-square (0.9985), which demonstrated that the as-prepared Fe-GDY/GOx could be used as a sensitive one-step glucose detection agent. The limit of detection is 0.89 μM. Compared with other colorimetric method-based sensors for glucose detection, Fe-GDY/GOx showed higher sensitivity and shorter detection time (Table 2). To investigate the selectivity of Fe-GDY/GOx to glucose, we used different sugars as control in the detection experiment. The absorbance at 450 nm was measured after 100 μM sugar incubated with Fe-GDY/ GOx in the same reaction time (Figure S4). The result showed that Fe-GDY/GOx exhibited high selectivity to glucose detection. To verify the feasibility of the above method on detection of blood glucose, we used rat serum as the tested sample. Figure 3i

(2)

Synthesis of Fe-GDY/GOx and Glucose Detection Tests. Fe-GDY/GOx was prepared by incubating Fe-GDY with glucose oxidase at room temperature. The GOx adsorption was confirmed by atomic force microscope (AFM) image. As shown in Figure 3a, b, the height of GDY without GOx adsorption was about 5 nm, which was in accordance with the previous reported work,49 whereas the increasing height on the GDY sheet was considered as the GOx clusters (white arrow). CD (circular dichroism) technique was used to determine the structure of GOx after adsorption. As shown in Figure 3c, the CD spectrum of Fe-GDY/GOx was very close to the pure GOx. The slight decrease of the peak intensity of Fe-GDY/GOx indicated the successful adsorption of GOx on GDY sheet.50 The secondary structure proportion was estimated and showed in Table 1. After adsorption, the percentage of α-helix slightly increased from 25.2 to 26.5%, while the ratio of α-helix to β-sheet increased from 0.514 to 0.538. It was demonstrated that the secondary structure of GOx did not obviously change after adsorbed on GDY sheet.51 D

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Figure 3. Characterization of Fe-GDY/GOx and glucose detection test. (a) AFM image of Fe-GDY/GOx; (b) thickness of Fe-GDY/GOx; (c) CD spectra of pure GOx (black) and Fe-GDY/GOx (red); (d) POD activity of Fe-GDY before and after GOx adsorption; (e) pH-dependence and (f) temperature-dependence glucose detection by Fe-GDY/GOx; (g) UV−vis spectra of buffer solution containing 400 μM TMB, 80 μg/mL Fe-GDY/ GOx, and glucose with different concentrations after 25 min reaction; (h) linear calibration plot for glucose using Fe-GDY/GOx; (i) UV−vis spectra of buffer solution containing 400 μM TMB, 80 μg/mL Fe-GDY/GOx, and diluted rat serum (red line) or water (black line).

simulation to compare the adsorption energy of Fe2+ ion on these two materials. The results showed that Fe2+ ion preferred to adsorb in between the neighboring two C−C triple bonds of GDY (Figure 4a). The calculated adsorption energy was −5.64 eV. In contrast, the Fe2+ ion preferred to adsorb atop the hexatomic ring of graphene (Figure 4b), which had a relatively less negative adsorption energy of −1.69 eV. Therefore, the Fe2+ ion was more immobilized on GDY than it was on graphene. This computational result corresponded with the previous experimental result, which demonstrated that Fe2+ ion was much easier to be immobilized onto GDY than graphene. As an innovative 2D carbon material holding many unique features, graphdiyne can be rationally designed for potential application in biosensing and medical purposes.57,58

Table 1. Conformation of Pure GOx and Fe-GDY/GOx α-helix (%)

β-sheet (%)

α/β

25.2 26.5

49 49.3

0.514 0.538

GOx Fe-GDY/GOx

Table 2. Comparison of Analytical Performance for Glucose Detection by Various Sensors sensor V2O5 nanozymes Fe/CeO2 NRs H2TCPP-γ-Fe2O3 NPs Por-CeO2 NPs Cu−Ag/rGO nanocomposite Fe-GDY/GOx

linear range limit of total time for (μM) detection (μM) detection (min)

ref

10−2000 1−100 5−25

10 3.41 2.54

65 40 40

25 52 53

40−150 1−30

19 3.82

>30 60

54 55

5−160

0.89

25



CONCLUSION In summary, we have prepared a GDY-based composite with dual-enzymatic activity by immobilizing ferrous ion and glucose oxidase on GDY sheet. Fe-GDY/GOx was prepared by simply mixing FeSO4 aqueous solution and GDY suspension, then incubating with glucose oxidase. Iron adsorbed on GDY was stable and maintained Fe2+ ion form due to the sp-hybridized carbon atoms of GDY. The computational results showed that Fe2+ was much easier to adsorb on GDY than graphene because of the lower adsorption energy. Meanwhile, Fe2+ on GDY showed high peroxidase activity through Fenton reaction. GDY had a negligible influence on adsorbed glucose oxidase, which still retained high enzymatic catalytic activity. The as-prepared Fe-GDY/GOx

This work

showed the increasing absorbance at 450 nm of the solution containing diluted rat serum, TMB, and Fe-GDY/GOx. According to the linear calibration curve, the calculated glucose concentration in rat serum was 10.92 ± 0.21 mM, which was in the normal range of blood glucose concentration of rat.56 This result demonstrated the feasibility of Fe-GDY/GOx on blood glucose detection. Computational Simulation of Stability of Fe2+ cation on GDY and graphene. To further understand the Fe2+ ion adsorption on GDY and graphene, we carried out ab initio E

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Figure 4. Top (up) and side (down) views of the most stable configurations for Fe2+ adsorbed on (a) GDY and (b) graphene. Data in parentheses are adsorption energies. In the top view structures, the metal−carbon distances are selectively marked; in the bottom view structures, the distances between the Fe atoms and the carbon sheets are marked. The gray and cyan atoms denote C and Fe atoms, respectively, and the SO42− anions are not shown for simplicity.



combined both peroxidase and glucose oxidase activities and was successfully used in one-step glucose detection. These results suggested that GDY was capable of adsorbing a considerable amount of metal ions through its sp-hybridized carbon atoms. So GDY could be promisingly applied in ion immobilization, water purification, and in situ catalysis in the future.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b03118. SEM image of GDY (Figure S1); zeta potential of GDY and Fe-GDY (Figure S2); high-resolution asymmetric C 1s XPS spectra of GDY and Fe-GDY (Figure S3); and selectivity analysis for glucose detection using Fe-GDY/ GOx (Figure S4) (PDF)



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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jiaming Liu: 0000-0002-6619-6443 Liming Wang: 0000-0003-1382-9195 Huibiao Liu: 0000-0002-9017-6872 Yuliang Li: 0000-0001-5279-0399 Xingfa Gao: 0000-0002-1636-6336 Yuliang Zhao: 0000-0002-9586-9360 Chunying Chen: 0000-0002-6027-0315 Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS The authors appreciated the financial support from the Ministry of Science and Technology of China (National Basic Research Program 2016YFA0201600), the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (11621505), the CAS Interdisciplinary Innovation Team, the CAS Key Research Program for Frontier Sciences (QYZDJSS-SLH022), and the National Science Fund for Distinguished Young Scholars (11425520). F

DOI: 10.1021/acsami.8b03118 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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DOI: 10.1021/acsami.8b03118 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX