Copper-incorporated SBA-15 with peroxidase-like activity and its application for colorimetric detection of glucose in human serum

Talanta 148 (2016) 22–28

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Copper-incorporated SBA-15 with peroxidase-like activity and its application for colorimetric detection of glucose in human serum Jianshuai Mu a,b, Yun He a, Yan Wang a,n a

Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150001, China Key Laboratory of Inorganic–Organic Hybrid Functional Material Chemistry, Ministry of Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, China

b

art ic l e i nf o

a b s t r a c t

Article history: Received 14 July 2015 Received in revised form 19 October 2015 Accepted 22 October 2015 Available online 23 October 2015

The copper incorporated SBA-15 (Cu-SBA-15) materials with different amount of Cu in framework were synthesized, and the products were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption/desorption. The Cu contents incorporated into the framework of SBA-15 were measured by inductively coupling plasma atomic emission spectrometer (ICP-AES). Cu-SBA-15 samples were found to exhibit the peroxidase-like activity, similar to the natural peroxidase. The effect of various parameters such as the content of Cu incorporated, pH and temperature on the peroxidase-like activity was studied. Based on the peroxidase-like activity, the Cu-SBA-15 was applied to the determination of H2O2. The linear range for detecting H2O2 was from 0.8 to 60 mM with a detection limit of 3.7 mM. Coupled with glucose oxidase, the Cu-SBA-15 was successfully used for the determination of glucose with the linear range of 2– 80 mM and a detection limit of 5.4 mM. The determination of glucose in human serum showed high accuracy, good reproducibility, as well as high selectivity against uric acid, ascorbic acid, dopamine and glucose analogs including fructose, maltose and lactose. & 2015 Elsevier B.V. All rights reserved.

Keywords: Cu-SBA-15 Peroxidase-like activity Colorimetric sensor Glucose detection

1. Introduction Peroxidase, present widely in plants and microorganisms, can catalyze the oxidation of some phenol and amine compounds by hydrogen peroxide [1]. It continues to attract the attention of researchers from a variety of disciplines because of its practical and commercial applications, for example as a component of clinical diagnostic kits and for immunoassays [2]. As a kind of enzyme, peroxidase has many advantages such as highly catalytic efficiency, catalytic specificity and mildly catalytic conditions. However, peroxidase possesses some disadvantages including high cost, difficult preparation, easy denaturation and etc, which limit its wide application. Therefore, the research of peroxidase mimic has been carried out for a long time [3]. The peroxidase mimics developed are usually the homogeneous catalysts such as hemin [4], cyclodextrin [5], porphyrin [6], which belong to metal complexes. Besides the homogeneous peroxidase mimics, recently some inorganic nanomaterials such as Fe3O4 nanoparticles [7], Co3O4 nanoparticles [8], CuO nanoparticles [9] and V2O5 nanowires [10] were found to exhibit the peroxidase-like activity. These n

Corresponding author. E-mail address: [email protected] (Y. Wang).

http://dx.doi.org/10.1016/j.talanta.2015.10.060 0039-9140/& 2015 Elsevier B.V. All rights reserved.

nanomaterials as heterogeneous peroxidase mimetics have received increasing attention because of their distinct properties, for example, high surface area to volume ratio, more catalytic sites on their surface than their bulk counterparts, abundance of reactive groups on their surfaces for further functionalization and easy recycle. The nanomaterial-based peroxidase mimics can take the place of natural peroxidase and have wide applications in many fields, including biosensing [11,12], pollutant removal [13], cancer diagnostics [14], and promotion of stem cell growth [15]. In the field of biosensing, these peroxidase mimics can be used for glucose determination. Diabetes in which there are high blood sugar levels over a prolonged period, is one of the most common diseases globally. It can cause many complications, which result in reduce life expectancy. Therefore, there is importance for the determination of blood glucose concentrations in order to ensure the effective treatment of prediabetes and diabetes. SBA-15, as a kind of mesoporous silica material, exhibits a twodimensional hexagonally arranged channel system [16]. The SBA15 has been applied to catalysis [17], medicine loading [18], selective adsorbents [19], sensors [20,21] and nanomaterial fabrications [22]. The SBA-15 possesses uniform mesostructures, tunable pore sizes and high surface areas, which are quite advantageous in catalytic reactions. In order to prepare the novel catalysts, the framework sites of SBA-15 can be modified with transition metal

J. Mu et al. / Talanta 148 (2016) 22–28

1 2 3

Transmittance

Intensity

(100)

(110) (200)

1 2

4 959

2

3

814

459

3 4 1

23

1088

4

5

2 (degree)

1500

1000

500 -1

Wavenumber (cm )

Fig. 1. XRD patterns (a) and FT-IR spectra (b) of SBA-15 (1), 1% Cu-SBA-15 (2), 3% Cu-SBA-15 (3) and 5% Cu-SBA-15 (4).

ions. And the catalytic properties of SBA-15 can be regulated by the incorporation of various metals. So far, a number of transition metal incorporated SBA-15 have been developed for catalytic reactions. For example, Fe-SBA-15 was applied to the catalytic hydride transfer reaction of aromatic nitro compounds into amino compounds [23]. Al-SBA-15 was employed as catalysts in the methanolysis of sunflower oil [24]. Cu-SBA-15 had high catalytic activity in hydroxylation of phenol [25]. However the research about the metal substituted mesoporous materials in the field of peroxidase-mimetic catalysis has been scarcely reported by far. To our knowledge, only Fe-SBA-15 was reported to be a peroxidaselike catalyst for H2O2 detection [26]. In this work, we demonstrated that Cu-SBA-15 mesoporous materials owned the peroxidase-like activity, which could catalyze the oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 to develop a blue color in the system, leading to a simple approach to colorimetric determination of H2O2. With glucose oxidase, a sensitive and selective colorimetric method for the determination of glucose was developed and successfully applied to the determination of glucose in human serum. This work may facilitate the research and utilization of metal substituted mesoporous materials as peroxidase-mimetics in medical diagnostics.

temperature naturally. The solid product was filtered, washed with water and absolute ethanol for several times, dried at 353 K for 24 h. After that, the surfactant template was removed by calcination in air at 550 °C for 6 h. Thus, the SBA-15 product was collected. The Cu-SBA-15 samples were prepared with addition of CuSO4
5H2O in the SBA-15 solution during the above procedures. The amount of CuSO4
5H2O was 0.2, 0.6 and 1 mmol, respectively. The Cu-SBA-15 samples were denoted as xCu-SBA-15 where x denoted the nCu/nSi molar ratio in the gel. 2.3. Characterization of products

2. Experimental

The X-ray diffraction patterns were collected on a D8 Advance X-ray diffractometer (Bruker, Germany). Scanning electron microscopy (SEM) was measured by a SU-8000 SEM (Hitachi, Japan). Transmission electron microscopy (TEM) was carried out using transmission electron microscope (FEI TecnaiG2S-Twin, USA) with a field emission gun operating at 200 kV. FT-IR spectra were measured by a Spectrum 100 Frontier IR Spectrometer (PerkinElmer, USA). The N2 adsorption and desorption isotherms were obtained at 77 K using ASAP 2020 Physisorption Analyzer (Micromeritics, USA). Chemical compositions were determined by inductively coupled plasma atomic emission spectroscopy (ICPAES) with an Optima 8000 ICP-OES spectrometer (PerkinElmer, USA).

2.1. Materials

2.4. Study of peroxidase-like activity

Tetraethyl orthosilicate (TEOS), HCl, CuSO4
5H2O, H2O2, acetic acid, sodium acetate and glucose were obtained from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). PEO20PPO70PEO20, 3,3′,5,5′-Tetramethylbenzidine (TMB), Glucose oxidase (GOx) were purchased from Sigma (St Louis, MO, USA). Human serum samples were supplied by a local hospital.

Experiments were carried out using 10 μg mL  1 Cu-SBA-15 samples in a reaction volume of 3 ml buffer solution (100 mM acetate buffer, pH 3.0) with 0.5 mM TMB and 100 mM H2O2 as substrates. After reacting some time, the solutions were measured on a Lambda 750 UV–vis–NIR spectrophotometer (Perkin Elmer, American).

2.2. Preparation of samples 2.5. Determination of glucose The mesoporous SBA-15 sample was synthesized using the nonionic triblock copolymer PEO20PPO70PEO20 (P123) as a template in acid conditions [27]. Typically, 1.78 g P123 template was dissolved in a solution of 40 mL of 2 M HCl, stirring for 2 h. And 20 mmol of tetraethyl orthosilicate (TEOS) were added and this mixture was continuously stirred at 40 °C for 24 h to attain a transparent sol. Then, the sol was put into the Teflon autoclave and maintained at 100 °C for 48 h and then cooled to room

The determination of glucose was realized as follows: (1) 20 μL of 5.0 mg mL  1 GOx and 180 μL of serum were incubated at 37 °C for 30 min; (2) 20 μL of 25 mM TMB, 100 μL of 0.45 mg mL  1 CuSBA-15-3, and 180 μL of 200 mM acetate buffer (pH 3.0) were added into the above 200 μL serum samples; (3) the mixed solution was incubated at room temperature for 30 min, and used for absorption spectroscopy measurement.

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J. Mu et al. / Talanta 148 (2016) 22–28

Fig. 2. SEM images of SBA-15 (a), 1% Cu-SBA-15 (b), 3% Cu-SBA-15 (c) and 5% Cu-SBA-15 (d) TEM images of 5% Cu-SBA-15 in the direction perpendicular to the pore axis (e) and in the direction of the pore axis (f).

3. Results and discussion 3.1. Characterization of Cu-SBA-15 As shown in Fig. 1a, the SBA-15 exhibits a strong peak and two weak peaks on its XRD patterns in the 2θ range of 0.5–2°, which can be indexed to (100), (110) and (200) diffraction planes [25]. The result indicates the synthesized SBA-15 has a well-ordered two-dimensional (2D) mesostructure (p6mm) [28]. Similar to SBA15, the three Cu-SBA-15 samples also exhibit the three diffraction

planes, showing that the incorporation of Cu does not alter the two-dimensional (2D) mesostructure. The FT-IR spectra of SBA-15 and Cu-SBA-15 samples are shown in Fig. 1b. The bands at 1088 cm  1, 814 cm  1 and 459 cm  1 are attributed to antisymmetric stretching vibration, symmetric stretching vibration and rocking vibration of Si–O–Si in SBA-15, respectively [25]. The band at 959 cm  1 of Cu-SBA-15 samples is observed, and it can be assigned to a Si–O–Cu vibration in the framework structure of Cusubstituted SBA-15 samples [29]. The Cu–O stretch vibration band at 536 cm  1 is not observed in the FT-IR spectra of the Cu-SBA-15

Quantity Adsorbed

Pore volume

J. Mu et al. / Talanta 148 (2016) 22–28

the hexagonal array of uniform channels (Fig. 2e and f), which confirms that the structural ordering is still maintained after the incorporation of Cu in SBA-15 matrix. The nitrogen adsorption/desorption isotherms of SBA-15 and Cu-SBA-15 samples exhibit type IV isotherms with hysteresis loops in the relative pressure range from 0.45 to 0.80, which confirm the mesoporousnature of these materials (Fig. 3) [30]. The pore size distributions of SBA-15 and Cu-SBA-15 samples are shown in the insert of Fig. 3, and the Brunauer–Emmete–Teller (BET) surface areas and the pore volumes are listed in Table 1. In order to obtain the final Cu content incorporated into SBA-15 matrix, Cu determinations were performed by ICP and the actual nCu/nSi values of the products are as listed in Table 1. It can be seen that the actual nCu/nSi ratios of the Cu-SBA-15 samples increase with increasing the input nCu/nSi ratio in the synthesis sources, which also show Cu species is indeed incorporated into the silica framework.

4 3 2 1 10

20

Pore size (nm)

30

4 3 2 1 0.0

0.2

0.4

0.6

0.8

1.0

P/Po

3.2. The peroxidase-like activity of Cu-SBA-15

Fig. 3. N2 adsorption/desorption isotherms of SBA-15 (1), 1% Cu-SBA-15 (2), 3% CuSBA-15 (3) and 5% Cu-SBA-15 (4), the insert shows the pore size distribution curves.

The natural peroxidases can catalyze the oxidation of 3,3′,5,5′tetramethylbenzidine (TMB) in presence of H2O2 to develop the color change. As shown in Fig. 4a, TMB can be oxidazed in presence of H2O2 and 1% Cu-SBA-15 to produce the typical blue color. The maximum absorbance of blue solution is 652 nm, originating from the oxidation of TMB. Additional control experiments using TMB in the absence of 1% Cu-SBA-15 or H2O2 show no oxidative reaction indicating that both the components are required for the reaction. This means 1% Cu-SBA-15 has the ability of catalyzing the TMB oxidation with utilizing H2O2. The phenomenon is similar to that of horseradish peroxidase (HRP) [31], showing that 1% CuSBA-15 exhibits the peroxidase-like activity. As shown in Fig. 4b, in presence of three Cu-SBA-15 samples with different Cu contents, the solutions of TMB and H2O2 display a blue color, but there is a difference in absorbance intensity for different Cu contents. The absorbance intensity follows the order: 5% Cu-SBA-154 3% Cu-SBA-154 1% Cu-SBA-15. The difference of the absorbance intensity attributes to the different peroxidase-like activities of the three Cu-SBA-15 samples, which is proportionate to the Cu contents in different Cu-SBA-15 samples. However, in presence of SBA-15, the solution containing TMB and H2O2 does not produce a blue color and has no absorption in the range from 350 to 750 nm. The above results show that the catalytic activity of

Table 1 Texture properties of the SBA-15 and Cu-SBA-15 samples. Samples

nCu/nSi

Surface area (m2 g  1)

Pore size (nm)

Pore volume (cm3 g  1)

Sources Producta SBA-15 1% Cu-SBA15 3% Cu-SBA15 5% Cu-SBA15 a

25

─ 1%

─ 0.259%

844.870 814.662

7.739 7.709

0.625 0.614

3%

1.285%

695.438

7.758

0.535

5%

2.863%

647.930

7.747

0.604

Calculated from the results determined by ICP.

samples, indicating there is no CuO in the structure of Cu-SBA-15 samples [29]. The results of FT-IR demonstrate that the Cu is successfully incorporated into the framework sites of the SBA-15. Morphology and microstructure were investigated using SEM and TEM. The SEM images of SBA-15 and Cu-SBA-15 samples reveal that the materials consisted of homogeneously dispersed rodlike particles (Fig. 2a–d). TEM images of 5% Cu-SBA-15 show

0.15

0.10

Absorbance

Absorbance

2

4

0.05

3

5% Cu-SBA-15 3% Cu-SBA-15

1

1% Cu-SBA-15 SBA-15

2 0.00 550

1 600

650

Wavelength(nm)

0

700

750

400

500

600

700

Wavelength(nm)

Fig. 4. (a) The absorption spectra of different reaction systems after 5 min, TMB þH2O2 (1), TMB þ1%Cu-SBA-15 (2), TMB þ H2O2 þHRP (3) and TMB þ H2O2 þ1% Cu-SBA-15 (4). The photograph showed the color development of different samples after 15 min. Reaction conditions: 0.25 mM TMB, 10 μg mL  1 1% Cu-SBA-15, 100 mM H2O2 in 100 mM NaAc buffer (pH 3.0). (b) The relative peroxidase-like activity of SBA-15 and different Cu-SBA-15 samples. Reaction conditions: 0.25 mM TMB, 10 μg mL  1 Cu-SBA-15 samples, 100 mM H2O2 in 100 mM NaAc buffer (pH 3.0) for 30 min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

26

J. Mu et al. / Talanta 148 (2016) 22–28

100

Relative Activity (%)

Relative Activity(%)

100

Cu-SBA-15 HRP

50

50

Cu-SBA-15 HRP

0 2

4

6

8

10

0

12

20

30

pH

40

50

60

Temperature ( C)

Fig. 5. Effects of pH (a) and temperature (b) on the peroxidase-like activity of 5% Cu-SBA-15. Experiments were carried out using 10 μg mL  1 5% Cu-SBA-15 samples or 0.075 U HRP in 3 mL buffer (different pHs), with 0.25 mM TMB and 100 mM H2O2 as substrates. The maximum point in each curve was set as 100%.

0.12

0.25

0.08

y=1.26966x+0.02938 r=0.99778

0.04

0.00

0.02

0.04

[H2O2]/mol L

Absorbance

Absorbance

0.20

0.15

0.10

0.06

y=1.94078x+0.07003 r=0.99955

0.00

0.02

0.04

0.06

0.08

-1

-1

[glucose]/mol L )

Fig. 6. The linear calibration plots for H2O2 (a) and glucose (b) determination.

(A-A0)/A0

10

5

Scheme 1. Schematic illustration of colorimetric determination of H2O2 and glucose by using glucose oxidase (GOx) and Cu-SBA-15-catalyzed reactions.

e os uc

e

gl

m

in

id

pa do

rb co

as

ur

ic

ic

ac

ac

id

e os ct la

to al

m

fru

ct

os

se

e

0 Cu-SBA-15 is derived from the Cu incorporation into the Cu-SBA15. Similar to HRP, the peroxidase-like activity of Cu-SBA-15 is pHdependent (Fig. 5a). And the optimal pH of Cu-SBA-15 and HRP is pH 3 and pH 5, respectively, indicating that Cu-SBA-15 has high peroxidase-like activity even in highly acidic conditions. As shown in Fig. 5b, the catalytic activity of Cu-SBA-15 is also dependent on temperature, and the optimal temperature is 55 °C and 35 °C for Cu-SBA-15 and HRP, respectively. At higher temperature, the catalytic activity of HRP decrease dramatically due to its denaturation. However, there is no denaturation for of Cu-SBA-15, which shows Cu-SBA-15 is more robust than natural peroxidase even under

Fig. 7. The selectivity of glucose determination by monitoring the relative absorbance. 5 mM fructose, 5 mM maltose, 5 mM lactose, 1 mM glucose, 1 mM UA, 1 mM AA and 1 mM dopamine.

J. Mu et al. / Talanta 148 (2016) 22–28

27

Table 2 Comparison between the values obtained by our proposed method and hospital for the determination of glucose in serum samples. Samples

C1a (mM)

C2a (mM)

C3a (mM)

Ca (mM)

RSD (%)

Cb (mM)

Added (mM)

Found (mM)

Recovery (%)

1 2 3

6.2 8.0 6.7

5.8 7.8 6.5

5.6 8.2 6.8

5.9 7 0.3 8.0 7 0.2 6.7 7 0.2

5.2 2.5 2.3

6.0 8.1 6.7

5.0 5.0 5.0

11.1 70.2 13.1 70.3 11.6 70.2

102.0 100.0 98.0

a b

Determined by our method. Determined in the hospital.

harsh conditions. 3.3. Analytical performance for glucose detection with Cu-SBA-15 Because H2O2 is one of the two substrates for Cu-SBA-15 sample, the peroxidase-like activity of Cu-SBA-15 is H2O2-dependent. Therefore, Cu-SBA-15 sample can be used to detect H2O2. The corresponding calibration curve of absorbance versus H2O2 concentration is shown in Fig. 6a. The linear range for detecting H2O2 is from 0.8 to 60 mM with a detection limit of 3.7 mM. The detection limit is of the same order of magnitude as that of Fe3O4 nanoparticles (3 mM) [32] and Au nanoparticles (4 mM) [33], lower than that of [FeIII(biuret-amide)] on mesoporous silica (10 mM) [34] and Au@Pt core–shell nanorods (45 mM) [35]. Glucose oxidase (GOx) can catalyze the oxidation of beta-D-glucose by utilizing molecular oxygen to gluconic acid and H2O2[36, 37]. When the glucose oxidation catalyzed by GOx is coupled with the catalytic reaction by the Cu-SBA-15 sample, the colorimetric determination of glucose could be realized (Scheme 1). As shown in Fig. 6b, the linear range for glucose is from 2 to 80 mM and the detection limit is 5.4 mM. The detection limit is lower than those of previous works based on [FeIII(biuret-amide)] on mesoporous silica (10 mM) [34], Fe3O4 nanoparticles (30 mM) [32] and Au@Pt core–shell nanorods (45 mM) [35]. 3.4. Selectivity for glucose determination The selectivity of the demonstrated determination system was tested with other glucose analogs including fructose, maltose and lactose. Even the control samples were used at concentrations of five times of that of glucose, their signals were less than 20.3% of glucose signal (Fig. 7). The selectivity of the system for glucose determination was also evaluated against ascorbic acid (AA), dopamine and uric acid (UA), in view of a possible application of the system to determine glucose in human serum. It can be seen that the responses to AA, dopamine and UA were 2.5%, 5.4% and 18.6% of that of glucose at the same concentration, respectively (Fig. 7), therefore the interferences of AA and dopamine are not significant. Since the normal physiological levels of UA and glucose are 0.1 and 3–8 mM, respectively. The concentration of glucose in human blood is more than 30 times higher than that of UA. The actual interference of UA would be much smaller than 18.6%. The above results demonstrate that the method may be suitable for the reliable glucose determination in human blood. 3.5. Determination of glucose in serum samples In order to validate the reliability of the proposed method, it was applied to detect the concentration of glucose in human serum samples. The serum samples were drawn from three different persons, and each serum sample was measured three times to evaluate the reproducibility. As shown in Table 2, The biggest relative standard deviation (R.S.D.) is 5.2% for the three serum samples, demonstrating good reproducibility of the method. The values of glucose concentrations in serum samples measured by

the above method are compared with those obtained from the hospital. It can be seen the biggest bias is 0.1 mM, showing that our results agree satisfactorily with those obtained in the hospital. Upon adding 5 mM glucose to the serum samples, the recoveries were found to be from 98.0% to 102.0%. The above results imply the demonstrated biosensing system can be applicable for the reliable determination of glucose in human blood samples.

4. Conclusions The Cu-SBA-15 materials with different Cu contents in the framework were synthesized. The Cu-SBA-15 samples were found to possess the peroxidase-like activity, which relates to the Cu incoporation. The optimal pH and temperature of their catalytic activity is pH 3 and 50 °C. With the peroxidase-like reaction catalyzed by Cu-SBA-15, H2O2 can be detected with a linear range from 0.8 to 60 mM and a detection limit of 3.7 mM. Coupled with glucose oxidase, the Cu-SBA-15 sample is then used for glucose determination with a linear range from 2 to 80 mM and a detection limit of 5.4 mM. The method has high selectivity against other interferents including fructose, maltose, lactose, ascorbic acid and uric acid. The demonstrated biosensing system is then applied to the glucose determination in human serum, and the values of glucose levels agree very well with those obtained in hospital, exhibiting good accuracy and reproducibility. These findings imply the applicability of Cu-SBA-15 materials as a sensor for the determination of glucose in human serum.

Acknowledgments The authors acknowledge the support of the National Natural Science Foundation of China (No. 31470489 and 21273057).

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