Graphene oxide vs. reduced graphene oxide as carbon support in porphyrin peroxidase biomimetic nanomaterials

Talanta 148 (2016) 511–517

Contents lists available at ScienceDirect

Talanta journal homepage: www.elsevier.com/locate/talanta

Graphene oxide vs. reduced graphene oxide as carbon support in porphyrin peroxidase biomimetic nanomaterials C. Socaci a,n, F. Pogacean a, A.R. Biris a, M. Coros a, M.C. Rosu a, L. Magerusan a, G. Katona b, S. Pruneanu a,n a b

National Institute for Research and Development of Isotopic and Molecular Technologies, 67-103 Donat, 400293 Cluj-Napoca, Romania Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Arany Janos 11, Cluj-Napoca, Romania

art ic l e i nf o

a b s t r a c t

Article history: Received 6 August 2015 Received in revised form 3 November 2015 Accepted 6 November 2015 Available online 10 November 2015

The paper describes the preparation of supramolecular assemblies of tetrapyridylporphyrin (TPyP) and its metallic complexes with graphene oxide (GO) and thermally reduced graphene oxide (TRGO). The two carbon supports are introducing different characteristics in the absorption spectra of the investigated nanocomposites. Raman spectroscopy shows that the absorption of iron-tetrapyridylporphyrin is more efficient on GO than TRGO, suggesting that oxygen functionalities are involved in the non-covalent interaction between the iron-porphyrin and graphene. The biomimetic peroxidase activity is investigated and the two iron-containing composites exhibit a better catalytic activity than each component of the assembly, and their cobalt and manganese homologues, respectively. The main advantages of this work include the demonstration of graphene oxide as a very good support for graphene-based nanomaterials with peroxidase-like activity (KM ¼ 0.292 mM), the catalytic activity being observed even with very small amounts of porphyrins (the TPyP:graphene ratio¼ 1:50). Its potential application in the detection of lipophilic antioxidants (vitamin E can be measured in the 10  5–10  4 M range) is also shown. & 2015 Elsevier B.V. All rights reserved.

Keywords: Thermally reduced graphene oxide Graphene oxide nanocomposites Supramolecular assemblies Tetrapyridylporphyrin Peroxidase-like activity Vitamin E

1. Introduction Graphene is a two-dimensional nanomaterial which received an increased attention over the last decade. Nowadays, graphenebased nanocomposites have grown as a well-defined and continuously expanding domain in the large field of materials science. Their properties can be tailored by the choice of the synthesis method, from the clean carbon honeycomb surfaces obtained by chemical vapor deposition to the large quantities that can be achieved by the oxidation of graphite. Further tuning of the targeted property was accomplished by decorating the carbon surface with metallic nanoparticles, doping with heteroatoms or by covalent and non-covalent functionalization with organic molecules [1]. The organic-based supramolecular assemblies of porphyrins as biomimetic systems became extensively studied due to their potential applications, from biology to energy field [2]. It is well known that heme (an iron-containing porphyrin) is the catalytically active building-block in a variety of proteins, including peroxidases [3]. Replacement of iron with other metals, like n

Corresponding authors. E-mail addresses: [email protected] (C. Socaci), [email protected] (S. Pruneanu). http://dx.doi.org/10.1016/j.talanta.2015.11.023 0039-9140/& 2015 Elsevier B.V. All rights reserved.

manganese or cobalt, has been used to model the naturally P450 cytochrome [4,5] and for the synthesis of artificial hemoglobins. Manganese porphyrins have also been investigated for their superoxide dismutase-like activity [6] while cobalt-containing nanomaterials were recently studied for their peroxidase-like catalytic activity [7,8]. Given our recent interest in exploring the peroxidase-like activity of different graphene-based nanomaterials [9], we decided to investigate the potential of (metallo)porphyrin conjugates with graphene-based nanomaterials, to be efficiently used as peroxidase mimetic. Most of the molecularly modified graphene nanocomposites that mimic the catalytic behavior of peroxidase are decorated with inorganic nanoparticles [10,11]. Among the porphyrin-conjugates, a hemin-chemically reduced graphene nanomaterial has been investigated for its biomimetic catalytic activity in the oxidation of pyrogallol by hydrogen peroxide and also compared with an iron porphyrin-graphene conjugate [12]. Two other papers report on the ability of hemin-chemically reduced graphene nanocomposites to decompose hydrogen peroxide, by using large amounts of the organic modifier [13,14]. The peroxidase-like activity of porphyrin-based nanomaterials has been proven also in case of carbon nanoparticles as support [15]. Because the intrinsic catalytic activity of graphene is dependent on the surface modifications of the carbon lattice, we considered important to study both graphene oxide (GO) and thermally

512

C. Socaci et al. / Talanta 148 (2016) 511–517

reduced graphene oxide (TRGO), as supports of the (metallo)porphyrin conjugates. Besides measuring the influence of graphene on the catalytic behavior of an iron-containing porphyrin, we also synthesized the cobalt(III) and manganese(III) complexes of the porphyrin and observed their peroxidase-like activity when assembled on carbon nanostructures. The peroxidase-like activity of carbon nanomaterials found applications in the detection of different analytes [16,17,18]. The presence of functional groups at the surface of graphene oxide enables surfactant properties [19], which should also render the spectrophotometric detection of lipophilic compounds. α-Tocopherol (the main component of the vitamin E family) has a key role in our metabolism and was determined both in blood components and in foods [20,21]. The continuous interest in developing methods for the determination of this antioxidant [22,23] is justified by the difficulties related to its lipophilic nature, air and light sensitivity. Therefore, we have investigated the application of graphene oxide-iron porphyrin composite for the detection of αtocopherol.

2. Experimental 2.1. Materials and methods All the reagents were of analytical grade and used without further purification. 3,3′-dimethylbenzidine (ortho-tolidine) and 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP) were purchased from Sigma-Aldrich. Cobalt(II)chloride, manganese(II)chloride, iron(III) chloride, ethanol, dimethylformamide (DMF) and dimethylsulfoxide (DMSO) were purchased from Merck. Graphene oxide and thermally reduced graphene oxide were prepared according to a previously described synthesis [9,24]. The morphology of graphene nanocomposites were observed by transmission electron microscopy (TEM) (H-7650 120 kV Automatic TEM, Hitachi, Japan) and scanning electron microscopy (SEM) (SU-8230 STEM – Hitachi, Japan). For TEM images, the samples diluted in ethanol were droped on a copper grid. The ultraviolet–visible (UV–vis) absorption spectra of enzyme mimic and the time-dependent absorbance spectra were measured with a V-570, JASCO Spectrophotometer. The Raman spectra were collected at room temperature by using a JASCO type NRS3300 spectrophotometer arranged in a backscattering geometry, coupled to a CCD (  69 °C) detector with a 1200 l/mm grid and a spectral resolution of 7.5 cm  1. The incident laser beam with a diameter of 1 mm2 was focused through an Olympus microscope (100  objective), and the calibration was made by using the Si peak at 521 cm  1. The excitation was done by using an Ar-ion laser with a wavelength of 514 nm and a power at the sample surface of 1.1 mW. 2.2. Preparation of graphene-(metallo)porphyrin nanocomposites Graphene oxide has the molecular weight larger than TRGO so, in order to ensure the use of the same porphyrin:graphene ratio, the following reaction procedure was applied: a solution of GO (50 mg) or TRGO (25 mg) in 20 mL ethanol was sonicated for 30 min. In each solution, a volume of 350 mL of TPyP or M(III)TPyP (5 mM in DMF) was added and the final mixture was stirred at room temperature, overnight. The dispersion was then centrifuged (3000 rpm for 25 min) and the supernatant discarded. The solid was washed three more times with the same volume of ethanol, followed by centrifugation. Finally, the solid was dried at 35 °C. The resulting nanocomposites were following denoted GO-(M) TPyP or TRGO-(M)TPyP. The M(III)TPyP were synthesized by refluxing a solution of

TPyP (30.9 mg, 0.05 mmol, 10 mL DMF) with the appropriate metal chloride (0.06 mmol) for six hours (Scheme S1). 2.3. Peroxidase catalytic activity experiments The catalytic activity study of all graphene-based nanomaterials was performed as follows: 230 mL of graphene suspension (2.5 mg in 5 mL of 0.5% HCl) was added in a reaction volume of 3 mL acetate buffer solution (ABS, 0.2 M, pH 4.2) with H2O2 (1 mM) and ortho-tolidine (1 mM). The kinetic analysis were carried out with 230 mL of graphene suspension (2.5 mg of GO-FeTPyP or TRGO-FeTPyP in 5 mL of 0.5% HCl) in a reaction volume of 3 mL ABS (0.2 M, pH 4.2) with orthotolidine (0.8 mM final concentration) and variable H2O2 concentration. The reactions were carried out in a quartz cuvette with an optical path length of 1 cm and the time course measurement set at 630 nm. 2.4. Experiments for vitamin E detection A stock solution of well sonicated α-tocopherol (7.55 mM in ABS:DMSO-7:1) was used to prepare three other solutions (3  10  3 M, 3  10  4 M and 3  10  5 M) in ABS (0.2 M; pH 4.2) which were next employed to dilute α-tocopherol, down to 10  7 M. The analysis was carried out with 230 mL of graphene suspension (2.5 mg of GO-FeTPyP in 5 mL of 0.5% HCl) in a reaction volume of 3 mL ABS (0.2 M, pH 4.2) with ortho-tolidine (0.8 mM final concentration) and variable α-tocopherol concentration. The reactions were carried out in a quartz cuvette with an optical path length of 1 cm and the UV absorption spectra were measured after 10 min reaction.

3. Results and discussion 3.1. Synthesis and characterization of nanocomposites The formation of the non-covalent assemblies of graphenes with (metallo)tetrapyridylporphyrins is depicted in Scheme S2. The iron(III), manganese(III) and cobalt(III)tetrapyridylporphyrin were synthesized by the reaction of free porphyrin with MnCl2, CoCl2 or FeCl3 [25]. The insertion of Mn(II) and Co(II) metallic ions into the macrocyclic structure change their oxidation state, from 2þ to 3 þ. The metals oxidation was ensured by the non-anhydrous reaction conditions [26]. The formation of the more stable Mn(III)porphyrin complexes starting from Mn(II) salts has been long described [27,28] and the measured UV–vis spectra of the MnTPyP graphene nanomaterials (Fig. S1b and S4) correspond to a Mn(III)-porphyrin complex, both in shape and Soret band position [29]. Further, cobalt(II) oxidation in the presence of oxygen [30] and the blue-shift of Soret band [31] has been also previously mentioned and fit well with our data. The nanocomposites were synthesized by overnight stirring of a well-dispersed solution of GO or TRGO with a small amount of the corresponding (metallo) tetrapyridylporphyrin, the mass ratio being 50:1 and 25:1, respectively. At the end of the reaction, the careful washing of the unbounded porhyrin was performed, followed by centrifugation. In our previous study, the structural characterization of the starting GO and TRGO revealed that graphene oxide was bearing the typical oxygen functionalities, the major ones being hydroxyl groups, epoxy and carboxyl groups that caused a large space between the 2D carbon sheets. After the thermal reduction of lyophilized graphene oxide, some carboxylic groups were still present at the surface, while the aromatic carbon structure was partially restored and the interlayer distance dropped from 7.7 to 3.4 nm [24]. After the formation of the supramolecular assemblies with

C. Socaci et al. / Talanta 148 (2016) 511–517

(metallo)tetrapyridylporphyrins, we are not expecting significant changes with respect to the functional groups attached to the carbon surface. The (metallo)porphyrins can bind non-covalently to the TRGO surface by π–π stacking interactions. In the case of GO, an additional interaction between the central metal atom and the existing oxygen functional groups can take place. The morphological characterization of the GO-FeTPyP and TRGO-FeTPyP nanocomposites reveals no obvious changes compared to the starting GO and TRGO. The TEM images are displayed in Fig. 1(a) and (b) and show very small porphyrin aggregates (some indicated with arrows) on the graphene oxide sheets (a) or on the large surface sheets of the thermally reduced graphene oxide. The SEM images present the typical aspect of either GO (Fig. 1(c)) or TRGO (Fig. 1(d)) nanomaterials. The UV–vis spectra of the (metallo)tetrapyridylporphyrinsgraphene nanocomposites dispersed in pH 4.2 acetate buffer (Fig. 2(a,b) and Fig. S1, Supplementary material) show a clear redshift of the Soret band of the free porphyrins, after interaction with the two carbon nanostructures. The Soret band of the free porphyrin (in ethanol) is situated at 413 nm and is bathochromically shifted to 419 nm for CoTPyP and 461 nm for MnTPyP. As expected [32], FeTPyP shows no change in the wavelength position of the Soret band. After the formation of the non-covalent assemblies with GO and TRGO, the corresponding absorption maxima have registered a shift within the 442–448 nm range, with the exception of GO-MnTPyP, that appears at 454 nm. These results indicate the formation of graphene–porphyrins complexes, being in agreement with the observed flattening of porphyrins on the surface of graphene [33,18]. The similar values of the Soret band observed in all nanocomposites suggest that the porphyrin structures are thermodynamically stabilized by π–π interactions with a similar coplanar conformation [34]. These findings are very interesting, as the two carbon nanostructures (GO and TRGO) are differently functionalized. In the case of GO, the porphyrins are probably non-covalently attached to the locally distributed polyaromatic islands of the nanomaterial [35]. The structural changes observed so far in FeTPyP nanocomposites are also evidenced in the Raman spectra (200–2000 cm  1 spectral range, Fig. 3), where two main bands for GO and TRGO are

513

observed: the D band (between 1352–1362 cm  1) and the G band, around 1600 cm  1. The D band is generally associated with the structural defects present in graphene and its intensity is increasing with the sheets number [36]. The G band is characteristic to all sp2 carbon-based nanomaterials [37]. By comparing the G band position of GO (black line-a) and TRGO (black line-b), one can see a down-shift of 8 cm  1, confirming the reduction of graphene oxide after the thermal treatment [38]. The Raman spectrum of the GO-FeTPyP nanocomposite (red line, (a)), also shows a down-shift of the G band with 6 cm  1, which indicates the electron-donating properties of the attached iron porphyrin to graphene oxide [39]. In addition, the spectrum presents some shoulders or small peaks, at Raman band positions corresponding to FeTPyP (blue line, (a) and (b)): 1004.8 cm  1; 1090.6 cm  1; 1247.4 cm  1; 1458.2 cm  1; 1494 cm  1; 1557.8 cm  1. This indicates the non-covalent attachment of iron porphyrin to the graphene oxide by forming a donor–acceptor conjugated system. This can be attributed to the fact that the iron porphyrin was attached to GO by both π–π interactions with the sp2 carbon network and by coordination of the iron atoms with the oxygen atoms belonging to the functionalities. This observation was well correlated with the flattening of porphyrin molecules by π–π interactions, measured in the UV–vis spectra. The same analysis was performed on the assembly obtained with the thermally reduced graphene oxide, TRGO-FeTPyP (red line, (b)). The spectrum presents the same shoulders corresponding to the porphyrin peaks, but their intensities were significantly reduced. Also, the position of G band is unmodified. The smaller spectrum changes indicate that less amount of iron porhyrin was attached to TRGO. Based on these observations one can conclude that less amount of iron porphyrin was attached to TRGO. 3.1.1. The effect of graphene concentration The properties of (metallo)porphyrins are dependent on their supramolecular behavior both in solution and solid state. Because we observed a similar stabilized conformation of the porphyrins in the nanocomposites (see above), we were interested in the stepby-step monitorization of the interaction between MTPyP and GO

Fig. 1. TEM (a, b) and SEM (c, d) images of GO-FeTPyP (a, c),TRGO-FeTPyP (b, d).

C. Socaci et al. / Talanta 148 (2016) 511–517

GO-TPyP TPyP TRGO-TPyP

0.20 446 nm

1352.33678 1596.43216 1356.37141

443 nm

1494

0.15 0.10

1602.48411

GO GO-FeTPyP FeTPyP Intensity (a.u.)

300

350

400

450

500

550

600

500

Wavelength (nm)

1336.8

1247.4

1090.6 1147.5

0.00

1004.8

0.05

323.2

Absorbance (a.u.)

413 nm

1000

1557.8

0.25

1458.2

514

1500

2000

-1

Raman shift (cm )

Absorbance (a.u.)

447 nm

0.20 GO-FeTPyP TRGO-FeTPyP FeTPyP

0.15 0.10

442 nm 413.5 nm

0.05 0.00 400

500

600

700

800

Wavelength (nm) Fig. 2. UV–vis spectra of the GO- and TRGO-supported TPyP (a) and FeTPyP (b) (the TRGO nanocomposites have an increased overall absorbance, compared with the GO nanocomposites).

respectively TRGO. Therefore, we performed the UV–vis measurements of a series of (TR)GO-(M)TPyP mixtures in which the porphyrin concentration was kept constant and the graphene concentration was gradually increased (Fig. 4a and Figs. S2a, S3a, S4a Supplementary material). The main spectral changes were observed in the absorbance of the Soret band of the porphyrins. Hence, the interaction of all porphyrins with TRGO is less spectacular, in the used concentration ranges. The Soret band presents a hypochromism with increasing TRGO concentration, indicating that the red-shift observed in the final nanocomposites (Fig. 4b and Figs. S2b, S3b, S4b, Supplementary content) takes place at larger TRGO concentrations and longer reaction times. The TRGO-CoTPyP nanocomposite is showing a different behavior, such as a red-shift of the Soret band (at low TRGO concentrations), followed by hypochromism (at high TRGO concentrations). The interactions of the porphyrins with GO show a clear red shift of the Soret band, with the exception of MnTPyP, which exhibits a small blue-shift of the Soret band. The shift is larger for the free TPyP and is measured in the presence of less GO (120 mg/mL), in comparison with the metallic complexes (220 mg/mL). For explaining the observed behavior in the optical absorbance, we have to take into consideration that the pyridyl ring has to overcome a rotational barrier in order to become coplanar to the

Fig. 3. Raman spectra, measured between 200–2000 cm  1 for GO, GO-FeTPyP (a) and TRGO, TRGO-FeTPyP (b).

porphyrin ring. This rotational barrier depends on the type of central metal atom, which explains the different GO concentrations needed for each metallic complex. In the case of free TPyP, this process is probably facilitated by the hydrogen bonds between the two hydrogen atoms inside the porphyrin ring and the oxygen functional groups on the surface of GO. Also, the manganese(III), cobalt(III) and iron(III) have axial ligands which can delay the interaction with graphene, compared to the uncomplexed TPyP. 3.2. Peroxidase-like activity Further, we have explored the biomimetic catalytic behavior of graphene-(metallo)porphyrins nanocomposites, during the oxidation of 3,3′-dimethylbenzidine (o,o′-tolidine) in the presence of hydrogen peroxide. The experiments were carried out at the same concentration for all nanocomposites, with 1 mM o,o′-tolidine and 1 mM hydrogen peroxide, in acetate buffer solution (0.2 M, pH 4.2). The oxidation of dimethylbenzidine is producing a charge transfer complex, blue colored, with a maximum absorbance at 630 nm [9]. The slopes of the time course measurements at 630 nm are indicative of the peroxidase-like activity of various porphyrin–graphene assemblies. Fig. 5a,b is clearly showing a

C. Socaci et al. / Talanta 148 (2016) 511–517

Absorbance (a.u.)

0.21 0.18 0.15 0.12 0.09 0.06 0.03

0.27

Abs. at 630 nm (a.u.)

FeTPyP-5.9µM + 18.52 µg/mL GO + 37.04 µ g/mL GO + 74.08 µg/mL GO + 148.16 µ g/mL GO + 222.24 µg/mL GO

0.24

400

0.21 0.18 0.15

GO-FeTPyP

Fe-TPyP

0.12

GO

0.09 0.06 0.03

500

600

700

-0.03

800

Wavelength (nm)

0.06

0.03

400

500

600

200

400

600

800

1000

1200

0.35

Abs. at 630 nm (a.u.)

0.09

0

Time (s)

FeTPyP 5.9 µM + 18.52 µM/mL TRGO + 37.04 µM/mL TRGO + 74.08 µM/mL TRGO + 148.16 µM/mL TRGO

0.12

Absorbance (a.u.)

GO-TPyP GO-MnTPyP GO GO-CoTPyP GO-FeTPyP FeTPyP

0.24

0.00

0.00

0.00 300

515

700

800

TRGO TRGO-CoTPyP TRGO-TPyP TRGO-MnTPyP TRGO-FeTPyP FeTPyP

0.30 0.25 0.20 0.15

TRGO-FeTPyP

FeTPyP

0.10 0.05 0.00 -0.05 -0.10

0

200

400

Wavelength (nm)

600

800

1000 1200

Time (s)

Fig. 4. UV–vis spectra of the GO- (a) and TRGO-supported FeTPyP (b).

large improvement in the catalytic activity of both GO and TRGO, by noncovalently attaching small amounts of iron tetrapyridylporphyrin. The assemblies formed with the free porphyrinic macrocycle and with the manganese and cobalt-containing ones are showing no improvement in the catalytic behavior of GO and TRGO, for the oxidation of 3,3′-dimethylbenzidine in the presence of hydrogen peroxide. The iron complexed porphyrins are showing improved peroxidase-like activity when supported on both graphene oxide and thermally reduced graphene oxide. The increased catalytic activity of TRGO when

Fig. 5. The time-dependent absorbance changes of GO-based porphyrin nanomaterials (a) and TRGO-based porphyrin nanomaterials (b) in pH 4.2 acetate buffer at room temperature. The recordings were performed at 630 nm.

forming the π–π complex with FeTPyP is really large, especially considering the small amount needed for our studies. In the previous reports (see Table 1) the iron porphyrin or hemin were supported on chemically reduced graphene oxide. Our experimental results are showing that the graphene oxide nanocomposite is giving similar results. Nevertheless, using the TRGO brings major benefits, such as the avoiding of harmful reducing agents (e.g. hydrazine).

Table 1 The comparison of the kinetic parameters of various nanomaterials. Nanomaterial

Km (mM)-H2O2 as substrate

Graphene/porphyrin ratio (w/w)

Experimental conditions

Ref.

GO-FeTPyPa TRGO-FeTPyPa Ch. reduced GO-Au-heminb Heminb Ch. reduced GO-heminb N-doped graphenea HRPb

0.292 1.17 3.1 2.74 2.256 0.486 3.70 0.214 1.579

50/1 50/1 1/1 – 1/1 – – – –

Room temperature, 0.2 M acetate buffer pH 4.2 Room temperature, 0.2 M acetate buffer pH 4.2 Room temperature, 0.02 M acetate buffer pH 4 Room temperature, 0.025 M phosphate buffer pH 5 Room temperature, 0.025 M phosphate buffer pH 5 Room temperature, 0.2 M acetate buffer pH 4.2 Temperature: 40 °C, 0.2 M acetate buffer pH 3.5 Temperature: 35 oC, 0.025 M phosphate buffer pH 4 Room temperature, 0.2 M acetate buffer pH 4.2

This work This work [13] [14] [14] [9] [40] [41] [9]

HRPa a b

Measured with dimethylbenzidine. Measured with tetramethylbenzidine.

C. Socaci et al. / Talanta 148 (2016) 511–517

Further informations regarding the catalytic reactions were obtained by determining the apparent steady state kinetic parameters, both for GO-FeTPyP and TRGO-FeTPyP. The maximum velocity (Vmax) and the Michaelis–Menten constant (KM) obtained from the Lineweaver-Burk linearization of the experimental data, are shown in Fig. 6 a,b-insets. The comparison of the kinetic parameters of GO-FeTPyP and TRGO-FeTPyP, with those of other similar nanomaterials and HRP is given in Table 1. The low KM value obtained for GO-FeTPyP nanocomposite indicates that less hydrogen peroxide is needed to achieve the maximum catalytic activity. The above experimental results clearly indicate that the GOFeTPyP/o-tolidine system can be used to detect hydrogen peroxide, since its catalytic activity is H2O2 concentration dependent. By representing the absorbance value (at 630 nm) vs. hydrogen peroxide concentration, we have obtained a linear curve within 2  10  5– 5  10  4 M (Fig. 7) and a detection limit (LOD) of 7.2  10  5 M. We also performed preliminary experiments to exploit the peroxidase-like activity of the GO-FeTPyP nanocomposite for detecting a liposoluble antioxidant, α-tocopherol (the main component of the vitamin E family). Being aware of the surfactant properties of graphene oxide, we recorded the UV–vis spectra of the GO-FeTPyP/o,o′-tolidine/H2O2 system in the presence of increasing concentrations of α-tocopherol (Fig. 8a). The final solutions were spectroscopic clear and the gradual discoloration (from blue to colorless) was observable with naked-eye, as opposite to

Fig. 6. Steady-state kinetic assay of GO-FeTPyP (a), TRGO-FeTPyP (b) and the corresponding Lineweaver–Burk plots (insets). Experiments were carried out in acetate buffer (0.2 M; pH 4.2) with a concentration of 0.8 mM for ortho-tolidine.

0.12

Abs. at 630 nm (a.u.)

516

0.10 0.08 0.06

y = - 0.0033 + 178.9 x C SD = 0.0043 LOD = 7.2 x 10-5 M

0.04 0.02 0.00 0.0 1.0x10-4 2.0x10-4 3.0x10-4 4.0x10-4 5.0x10-4

CH O (M) 2

2

Fig. 7. Absorbance at 630 nm vs. H2O2 concentration for the GO-FeTPyP nanocomposite. The absorbance values were determined from the time course measurements and correspond to the 10 min reaction with the GO-FeTPyP/o-tolidine system.

Fig. 8. UV–vis absorption spectra of dimethylbenzidine-H2O2 system catalyzed by GO-FeTPyP, with increasing α-tocopherol concentrations (normalized spectra) (a); Absorbance at 630 nm as a function of α-tocopherol concentration for the GOFeTPyP nanocomposite (b).

C. Socaci et al. / Talanta 148 (2016) 511–517

the opaque solutions obtained with TRGO-FeTPyP. The α-tocopherol concentration fitted linearly well with the 630 nm absorbance, within the 10  4–10  5 M range (Fig. 8b). This range is comparable with the concentrations found in blood plasma [20] or in certain vegetable oils [21].

[13]

[14]

[15]

4. Conclusions We have synthesized catalytically efficient composites starting from graphene oxide and thermally reduced graphene oxide, by using small quantities of (metallo)tetrapyridylporphyrins. The spectroscopic characterization showed that these macrocycles are non-covalently attached to the GO or TRGO, mainly by π–π interactions. More porphyrin is attached to GO in comparison to TRGO, because the oxygen atoms on GO surface are able to coordinate the central iron atom. The GO-FeTPyP and TRGO-FeTPyP are showing good catalytic activity, during the oxidation of 3,3′-dimethylbenzidine with hydrogen peroxide. Furthermore, by taking advantage of the surfactant behavior of GO, we were able to introduce as “proof of principle” the potential application of GOFeTPyP in the naked-eye detection of vitamin E, as a simple, fast and cost efficient method.

Acknowledgment This paper was supported by a grant of MEN-UEFISCDI, Romania; Project no. PN-II-PT-PCCA-2013-4-1282 (230/2014), (PN-IIProgram 4, Partnership in Priority Areas, PCCA-type 2).

[16]

[17]

[18] [19]

[20]

[21] [22]

[23]

[24]

[25] [26]

Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.talanta.2015.11. 023.

[27] [28]

[29]

References [1] Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Graphene and graphene oxide: synthesis, properties and applications, Adv. Mater. 22 (2010) 3906–3924. [2] Y. Zhao, Q. Shang, J. Yu, Y. Zhang, S. Liu, Nanostructured 2D diporphyrin honeycomb film: photoelectrochemistry, photodegradation and antibacterial activity, Appl. Mater. Interfaces 7 (2015) 11783–11791. [3] T.L. Poulos, Heme enzyme structure and function, Chem. Rev. 114 (2014) 3919–3962. [4] B. Hu, C. Sun, Q. Deng, Z. Liu, Synthesis and catalytic properties of a series of cobalt porphyrins as cytochrome P450 model: the effect of substituents on the catalytic activity, J. Incl. Phenom. Macrocycl. Chem. 76 (2013) 345–352. [5] M.C. Feiters, A.E. Rowan, R.J.M. Nolte, From simple to supramolecular cytochrome P450 mimics, Chem. Soc. Rev. 29 (2000) 375–384. [6] K.M. Faulkner, S.I. Liochev, I. Fridovich, Mn(I.I.I) Stable, porphyrins mimic superoxide dismutase in vitro and substitute for it in vivo, J. Biol. Chem. 269 (1994) 23471–23476. [7] Y. Chen, H. Cao, W. Shi, H. Liu, Y. Huang, Fe-Co bimetallic alloy nanoparticles as a highly active peroxidase mimetic and its application in biosensing, Chem. Commun. 49 (2013) 5013–5015. [8] J. Xie, H. Cao, H. Jiang, W. Shi, H. Zheng, Y. Huang, Co3O4-reduced graphene oxide nanocomposite as an effective peroxidase mimetic and its application in visual biosensing of glucose, Anal. Chim. Acta 796 (2013) 92–100. [9] F. Pogacean, C. Socaci, S. Pruneanu, A.R. Biris, M. Coros, L. Magerusan, G. Katona, R. Turcu, G. Borodi, Graphene based nanomaterials as chemical sensors for hydrogen peroxide – a comparison study of their intrinsic peroxidase behavior, Sens. Actuators B 213 (2015) 474–483. [10] X. Zhang, G. Wu, Z. Cai, X. Chen, Dual functional Pt-on-Pd supported on reduced graphene oxide: peroxidase-mimic activity and a enhanced electrocatalytic oxidation characteristics, Talanta 134 (2015) 132–135. [11] J. Liu, Z. Liu, C.J. Barrow, W. Yang, Molecularly engineered graphene surfaces for sensing applications: a review, Anal. Chim. Acta 859 (2015) 1–19. [12] T. Xue, S. Jiang, Y. Qu, Q. Su, R. Cheng, S. Dubin, C.-Y. Chiu, R. Kaner, Y. Huang,

[30] [31]

[32] [33]

[34]

[35] [36]

[37]

[38]

[39]

[40]

[41]

517

X. Duan, Graphene‐supported hemin as a highly active biomimetic oxidation catalyst, Angew. Chem. 124 (2012) 3888–3891. X. Lv, J. Weng, Ternary composite of hemin, gold nanoparticles and graphene for highly efficient decomposition of hydrogen peroxide, Sci. Rep. 3 (2013) 3285. Y. Guo, L. Deng, J. Li, S. Guo, E. Wang, S. Dong, Hemin-graphene hybrid nanosheets with intrinsic peroxidase-like activity for label-free colorimetric detection of single-nucleotide polymorphism, ACS Nano 5 (2011) 1282–1290. X. Wang, K. Qu, B. Xu, J. Ren, X. Qu, Multicolor luminescent carbon nanoparticles: synthesis, supramolecular assembly with porphyrin, intrinsic peroxidase-like catalytic activity and applications, Nano Res. 4 (2011) 908–920. Y. Shi, J. Huang, J. Wang, P. Su, Y. Yang, A magnetic nanoscale Fe3O4/Pβ-CD composite as an efficient peroxidase mimetic for glucose detection, Talanta 143 (2015) 457–463. K. Zhao, W. Gu, S. Zheng, C. Zhang, Y. Xian, SDS-MoS2 nanoparticles as highlyefficient peroxidase mimetics for colorimetric detection of H2O2 and glucose, Talanta 141 (2015) 47–52. Y. Song, W. Wei, X. Qu, Colorimetric biosensing using smart materials, Adv. Mater. 23 (2011) 4215–4236. P. Guo, P. Chen, M. Liu, One-dimensional porphyrin nanoassemblies assisted via graphene oxide: sheetlike functional surfactant and enhanced phtocatalytic behaviours, Appl. Mater. Interfaces 5 (2013) 5336–5345. A.L. Sowell, D.L. Huff, P.R. Yeager, S.P. Caudill, E.W. Gunter, Retinol, α-tocopherol, lutein/zeaxanthin, β-cryptoxanthin, lycopene, α-carotene, trans-βcarotene, and four retinyl esters in serum determined simultaneously by reversed-phase HPLC with multiwavelength detection, Clin. Chem. 40 (1994) 411–416. D.C. Herting, E.-J.E. Drury, Vitamin E content of vegetable oils and fats, J. Nutr. (1963) 335–342. Y. Hirowatari, H. Yoshida, H. Kurosawa, D. Manita, N. Tada, Automated measurement method for the determination of vitamin E in plasma lipoprotein classes, Sci. Rep. 4 (2014) 1–6. M. Mejean, A. Brunelle, D. Touboul, Quantification of tocopherols and tocotrienols in soybean oil by supercritical-fluid chromatography coupled to highresolution mass spectrometry, Anal. Bioanal. Chem. 407 (2015) 5133–5142. D. Olteanu, A. Filip, C. Socaci, A.R. Biris, X. Filip, M. Coros, M.C. Rosu, F. Pogacean, C. Alb, I. Baldea, P. Bolfa, S. Pruneanu, Cytotoxicity assessment of graphene-based nanomaterials on human dental follicle stem cells, Colloids Surf. B: Biointerfaces 136 (2015) 791–798. A.D. Adler, F.R. Longo, F. Kampas, J. Kim, On the preparation of metalloporphyrins, J. Inorg. Nucl. Chem. 32 (1970) 2443–2445. R.F. Pasternack, E.J. Gibbs, J.J. Villafranca, Interactions of porphyrins with nucleic acids, Biochemistry 22 (1986) 2406–2414. L.J. Boucher, Manganese porphyrin complexes, Coord. Chem. Rev. 7 (1972) 289–329. E. Fagadar-Cosma, M.C. Mirica, I. Balcu, C. Bucovicean, C. Cretu, I. Armeanu, G. Fagadar-Cosma, Synthesis, spectroscopic and AFM characterization of some manganese porphyrins and their hybrid silica nanomaterials, Molecules 14 (2009) 1370–1388. I. Creanga, A. Palade, A. Lascu, M. Birdeanu, G. Fagadar-Cosma, E. FagadarCosma, Manganese(III)porphyrin sensitive to H2O2 detection, Dig. J. Nanomater. Biostructures 10 (2015) 315–321. P. Hambright, The coordination chemistry of metalloporphyrins, Coord. Chem. Rev. 6 (1971) 247–268. J. Li, B.C. Noll, A.G. Oliver, G. Ferraudi, A.G. Lappin, W.R. Scheidt, Oxygenation of cobalt porphyrinates: coordination or oxidation? Inorg. Chem. 49 (2010) 2398–2406. J.T. Groves, T.E. Nemo, Aliphatic hydroxylation catalyzed by iron porphyrin complexes, J. Am. Chem. Soc. 105 (1983) 6243–6248. J. Geng, H.-T. Jung, Porphyrin functionalized graphene sheets in aqueous suspensions: from the preparation of graphene sheets to highly conductive graphene films, J. Phys. Chem. C 114 (2010) 8227–8234. Y. Xu, L. Zhao, H. Bai, W. Hong, C. Li, G. Shi, Chemically converted graphene induced molecular flattening of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin and its application for optical detection of cadmium(II) ions, J. Am. Chem. Soc. 131 (2009) 13490–13497. S. Park, R.S. Ruoff, Chemical methods for the production of graphenes, Nat. Nanotechnol. 4 (2009) 217–224. K.S. Subrahmanyam, S.R.C. Vivekchand, A. Govindaraj, C.N.R. Rao, A study of graphenes prepared by different methods: characterization, properties and solubilization, J. Mater. Chem. 18 (2008) 1517–1523. M.S. Dresselhaus, A. Jorio, M. Hofmann, G. Dresselhaus, R. Saito, Perspectives on carbon nanotubes and graphene Raman spectroscopy, Nano Lett. 10 (2010) 751–758. A. Kaniyoor, T.T. Baby, S. Ramaprabhu, Graphene synthesis via hydrogen induced low temperature exfoliation of graphite oxide, J. Mater. Chem. 20 (2010) 8467–8469. Y. Chen, Z.-H. Huang, M. Yue, F. Kang, Integrating porphyrin nanoparticles into a 2D graphene matrix for free-standing nanohybrid films with enhanced visible-light phtocatalytic activity, Nanoscale 6 (2014) 978–985. L.Z. Gao, J. Zhuang, L. Nie, J.B. Zhang, Y. Zhang, N. Gu, T.H. Wang, J. Feng, D. L. Yang, S. Perrett, X.Y. Yan, Intrinsic peroxidase-like activity of ferromagnetic nanoparticles, Nat. Nanotechnol. 2 (2007) 577–583. Y. Song, K. Qu, C. Zhao, J. Ren, X. Qu, Graphene oxide: intrinsic peroxidase catalytic activity and its application to glucose detection, Adv. Mater. 22 (2010) 2206–2210.