Novel Platinum-Porphyrin as Sensing Compound for E ﬃ cient Fluorescent and Electrochemical Detection of H 2 O 2

: Metalloporphyrins are highly recognized for their capacity to act as sensitive substances used in formulation of optical, ﬂuorescent, and electrochemical sensors. A novel compound, namely Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl) porphyrin, was synthesized by metalation with PtCl 2 (PhCN) 2 of the corresponding porphyrin base and was fully characterized by UV-vis, ﬂuorimetry, FT-IR, 1 H-NMR, and 13 C-NMR methods. The ﬂuorescence response of this Pt-porphyrin in the presence of di ﬀ erent concentrations of hydrogen peroxide was investigated. Besides, modiﬁed glassy carbon electrodes with this Pt-porphyrin (Pt-Porf-GCE) were realized and several electrochemical characterizations were comparatively performed with bare glassy carbon electrodes (GCE), in the absence or presence of hydrogen peroxide. The Pt-porphyrin demonstrated to be a successful sensitive material for the detection of hydrogen peroxide both by ﬂuorimetric method in a concentration range relevant for biological samples (1.05–3.9 × 10 − 7 M) and by electrochemical method, in a larger concentration range from 1 × 10 − 6 M to 5 × 10 − 5 M. Based on di ﬀ erent methods, this Pt-porphyrin can cover detection in diverse ﬁelds, from medical tests to food and agricultural monitoring, proving high accuracy (correlation coe ﬃ cients over 99%) in both ﬂuorimetric and electrochemical measurements.


Introduction
The detection and quantification of oxygen in its various forms is of great importance because reactive oxygen species (ROS), such as: peroxide radicals (ROO • ), hydroxyl radical ( • OH), hydrogen peroxide (H 2 O 2 ), singlet oxygen ( 1 O 2 ), and ozone (O 3 ) are intracellularly generated during some of the enzymatic oxidation processes that are involved in the metabolism of proteins, carbohydrates and fats [1]. The normal concentrations of H 2 O 2 for plasma were determined to be 1-5 µM, while higher values, in the range of 30-50 µM, can appear during chronic inflammation [2]. In the urine of healthy subjects, the creatinine-corrected H 2 O 2 concentration varies in the range 276-1844 µM, regardless of gender [3]. Reduced oxygen levels are developed in cardiac and brain ischemia [4]. Moreover, H 2 O 2 present in blood can interact with Fe 2+ ions contributing to oxidative stress [5]. system, on a Perkin Elmer LS55 luminescence spectrometer (Perkin Elmer, Inc./UK Model/LS 55, Waltham, MA, USA). Fluorescence spectra were recorded at ambient temperature (22-24 • C), using 1 cm path length cells, without using cut-off filters, at a rate of 100 nm/min, with constant slit widths, for excitation (10 nm) and for emission (6 nm), exciting at λ = 365 nm. The fluorescence quantum yield (Φ F ) of Pt-porphyrin was calculated by using the steady-state comparative method formula: Φ sample = Φ TPP (F sample /F TPP )(A TPP /A sample )(n sample 2 /n TPP 2 ), where Φ is the relative fluorescence quantum yield, F, A, and n are the measured fluorescence area, the absorbance, and the refractive index of the solvent, respectively [21]. The method is based on comparing the Pt-porphyrin emission spectrum area with that of a fluorescence standard, meso-tetraphenylporphyrin (TPP). The emission spectra were performed in THF by exciting at λex = 330 nm. A value of Φ f = 0.10 for TPP in THF, previously calculated [22], was used. FT-IR spectra were carried out on a JASCO 430 FT-IR (Hachioji, Tokyo, Japan), from KBr pellets, in the range 4000-400 cm −1 . 1 H-NMR and 13 C-NMR spectra were registered on 400 MHz and 100 MHz respectively on a Bruker Avance DRX spectrometer equipped with a 5 mm four nuclei ( 1 H/ 13 C/ 19 F/ 29 Si) direct detection probe (Rheinsteitten, Germany), in CDCl 3 . The chemical shifts are expressed in δ (ppm). Electrochemical investigations were performed with the help of Autolab 302N EcoChemie (Eco Chemie, The Netherlands, 2007).

Synthesis of Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl)-porphyrin (Pt(II)-TAPP)
The synthesis of Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl)-porphyrin, shown in Figure 1, was performed by adapting the method of Yamashita [27], optimized according to [28], as follows: 0.105 g (12.5 mmole) 5,10,15,20-tetra-(4-allyloxy-phenyl)porphyrin dissolved in 35 mL chlorobenzene were vigorously stirred together with a mixture containing 0.0933 g (19.7 mmole) PtCl 2 (PhCN) 2 and 0.072 g (52.9 mmole) NaAc × 3H 2 O dissolved in 24 mL chlorobenzene. The molar ratio between the reactants was TAPP:PtCl 2 (PhCN) 2 :CH 3 COONa × 3H 2 O = 1:1.5:4 chosen in order to favor the generation of the Pt-complex and to prevent the HCl generation. Then, the reaction mixture was refluxed for 2 h and the reaction progress was monitored by UV-vis spectroscopy, as can be seen in Figure 2.  The completion of the reaction was evidenced in the UV-vis spectra by both the hypsochromic shift of the Soret band and the reducing of the Q bands number to only two, as shown in Figure 2. The reaction mixture was then cooled to room temperature, filtered, and repeatedly washed with warm water (4 × 60 mL). The filtrate was several times washed with 100 mL water in a separatory funnel. The organic extract was dried over Na2SO4 and the chlorobenzene was removed by vacuum  The completion of the reaction was evidenced in the UV-vis spectra by both the hypsochromic shift of the Soret band and the reducing of the Q bands number to only two, as shown in Figure 2. The reaction mixture was then cooled to room temperature, filtered, and repeatedly washed with warm water (4 × 60 mL). The filtrate was several times washed with 100 mL water in a separatory funnel. The organic extract was dried over Na 2 SO 4 and the chlorobenzene was removed by vacuum distillation. The resulting orange-reddish solid was recrystallized from dichloromethane. The pure crystalline powder was finally kept for 10 h at 90 • C in vacuum.

Electrochemical Measurements
Before each electrochemical determination, the working electrode (WE) was cleaned with fine sandpaper (0.3 µm), washed with water, electrochemically cleaned (10 cycles in 0.5 M sulfuric acid in the range −1 to 1.2 V), and exposed to ultrasound bath for 3 minutes in water, acetone, and ethanol.
The porphyrin films were deposited on clean GCE surfaces by drop-casting from a 5.84 mM Pt(II)-TAPP solution in CH 2 Cl 2 , by successively depositing 3 × 1 drops. The films were left to dry, then the surfaces were washed with CH 2 Cl 2 and water and then dried and stored in the dark. The modified electrode thus prepared was marked as Pt-Porf-GCE. All electrochemical measurements were performed at room temperature in a conventional one-compartment three-electrode cell. The electrochemical cell contains the platinum wire as auxiliary electrode, the Ag/AgCl as reference electrode and the working electrode: glassy carbon (GCE 0.0314 cm 2 ) unmodified and modified with metal porphyrin film (Pt-Porf-GCE).
The electrocatalytic effect of the Pt-metalloporphyrin on hydrogen peroxide transformation was carried out in morpholine-ethane-sulfonic acid (MES) buffer solution, pH 5.6, at a scan rate of 50 mV/s, in open atmosphere, without removing oxygen (this did not have a significant effect on the oxidation process) [20].

UV-vis Monitoring of the Metalation Reaction
As represented in Figure 2, the UV-vis spectrum of the (TAPP) porphyrin-base is etio type shape with the Soret band generated by the transition from a 1u (π) -e g * (π) and the four Q-bands in the visible region, corresponding to a 2u (π) -e g * (π) transitions.
Monitoring the metalation reaction by UV-vis, as represented in Figure 2, shows that after a short period of time the Soret band of TAPP is splitting into two bands of equal intensity, revealing the equilibrium between porphyrin base (λ = 425 nm) and the generation of Pt(II)-TAPP. The forming of Pt-TAPP is shown by the significant hypsochromic shift of the Soret band with 15 nm, to 410 nm. After 100 min of reflux, the QI and the QIII bands disappeared and the intensity of the Soret band located at 410 nm is continuously increasing, proving that the equilibrium of the reaction is moved to the formation of the Pt-complex.

UV-vis Monitoring of the Metalation Reaction
As represented in Figure 2, the UV-vis spectrum of the (TAPP) porphyrin-base is etio type shape with the Soret band generated by the transition from a1u (π) -eg* (π) and the four Q-bands in the visible region, corresponding to a2u (π) -eg* (π) transitions. Monitoring the metalation reaction by UV-vis, as represented in Figure 2, shows that after a short period of time the Soret band of TAPP is splitting into two bands of equal intensity, revealing the equilibrium between porphyrin base (λ = 425 nm) and the generation of Pt(II)-TAPP. The forming of Pt-TAPP is shown by the significant hypsochromic shift of the Soret band with 15 nm, to 410 nm. After 100 min of reflux, the QI and the QIII bands disappeared and the intensity of the Soret band located at 410 nm is continuously increasing, proving that the equilibrium of the reaction is moved to the formation of the Pt-complex.
The reaction was completed after approximately two hours, when all the porphyrin was transformed into its Pt-complex. As a consequence, UV-vis spectrum presents solely a narrow Soret band located at 410 nm and only two Q bands, the first located at 513 nm, blue shifted in comparison with the porphyrin base and representing the Q(0-1) vibration and the second one at 596 nm respectively, representing Q(0-0) electronic transition. The intensity of the remaining Q(0-0) band is increased as compared to the original QI(0-0) band of the porphyrin base. According to this behavior [29] the novel obtained Pt-porphyrin is belonging to the second group of metalloporphyrins.

FT-IR Characterization
A comparison of the FT-IR spectra of the porphyrin base TAPP with the corresponding Pt(II)-TAPP, as presented in Figure 3, shows that the Pt-complex gave a simplified spectrum, due to the higher symmetry of the novel compound, which increases from D2h to D4h. The reaction was completed after approximately two hours, when all the porphyrin was transformed into its Pt-complex. As a consequence, UV-vis spectrum presents solely a narrow Soret band located at 410 nm and only two Q bands, the first located at 513 nm, blue shifted in comparison with the porphyrin base and representing the Q(0-1) vibration and the second one at 596 nm respectively, representing Q(0-0) electronic transition. The intensity of the remaining Q(0-0) band is increased as compared to the original QI(0-0) band of the porphyrin base. According to this behavior [29] the novel obtained Pt-porphyrin is belonging to the second group of metalloporphyrins.

FT-IR Characterization
A comparison of the FT-IR spectra of the porphyrin base TAPP with the corresponding Pt(II)-TAPP, as presented in Figure 3, shows that the Pt-complex gave a simplified spectrum, due to the higher symmetry of the novel compound, which increases from D 2h to D 4h .
The peak located at 3318 cm −1 and attributed to internal N-H bond is no more present in the Pt(II)-TAPP spectrum, proving the complete metalation. Due to the increased symmetry, the band corresponding to C-H stretching and bending vibrations, located at 1289 cm −1 in the spectrum of the porphyrin base is missing in the case of Pt-porphyrin. The large band of OH group caused by intramolecular H-bonding and located at 3426 cm −1 covers the C-H stretching vibrations of phenyl ring from 3033 cm −1 [30]. The C=N bonding vibration has a lower frequency (1452 cm −1 ) in Pt(II)-TAPP than in the porphyrin base (1472 cm -1 ) due to the influence of the platinum atom [31,32]. Another significant band is the vibration of the C-O-C bond, located at 1006 cm −1 in the Pt-porphyrin [33].

NMR Analysis
The investigation of the 1 H-NMR spectrum, represented in Figure 4A, reveals the absence of the signal of the two internal protons, proving the bonding of the platinum in the inner core of the porphyrin. All the signals for the distinctive protons that prove the proposed structure of the compound are identifiable. Thus, the β-pyrrolic protons present a singlet at 8.70 ppm; the eight ortho  The peak located at 3318 cm −1 and attributed to internal N-H bond is no more present in the Pt(II)-TAPP spectrum, proving the complete metalation. Due to the increased symmetry, the band corresponding to C-H stretching and bending vibrations, located at 1289 cm −1 in the spectrum of the porphyrin base is missing in the case of Pt-porphyrin. The large band of OH group caused by intramolecular H-bonding and located at 3426 cm −1 covers the C-H stretching vibrations of phenyl ring from 3033 cm −1 [30]. The C=N bonding vibration has a lower frequency (1452 cm −1 ) in Pt(II)-TAPP than in the porphyrin base (1472 cm -1 ) due to the influence of the platinum atom [31,32]. Another significant band is the vibration of the C-O-C bond, located at 1006 cm −1 in the Pt-porphyrin [33].

NMR Analysis
The investigation of the 1 H-NMR spectrum, represented in Figure 4A, reveals the absence of the signal of the two internal protons, proving the bonding of the platinum in the inner core of the porphyrin. All the signals for the distinctive protons that prove the proposed structure of the compound are identifiable. Thus, the β-pyrrolic protons present a singlet at 8.70 ppm; the eight ortho phenyl protons gave signal in the 7.94-7.96 ppm interval and the eight meta phenyl protons as doublet at 7.18-7.20 ppm, respectively. The four protons from O-CH 2 -CH=CH 2 are identified as multiplet at 6.13-6.22 ppm, the other eight belonging to =CH 2 are resonating as two doublets from 5.51 to 5.55 ppm and from 5.34 to 5.36 ppm; the protons in the vicinity of oxygen O-CH 2 -gave a doublet at 4.73-4.74 ppm.
The chemical shifts (δ) of 13 C-NMR are attributed in Figure 4B, taking into consideration the distinct aspect and zone for the assignment of each carbon. The 3-line triplet signal around 77 is due to CDCl 3 in which the sample was diluted. [33].

NMR Analysis
The investigation of the 1 H-NMR spectrum, represented in Figure 4A, reveals the absence of the signal of the two internal protons, proving the bonding of the platinum in the inner core of the porphyrin. All the signals for the distinctive protons that prove the proposed structure of the compound are identifiable. Thus, the β-pyrrolic protons present a singlet at 8. The chemical shifts (δ) of 13 C-NMR are attributed in Figure 4B, taking into consideration the distinct aspect and zone for the assignment of each carbon. The 3-line triplet signal around 77 is due to CDCl3 in which the sample was diluted.

Fluorimetric Detection of H2O2
The method for testing the capacity of Pt(II)-TAPP to act as a sensitive material for the fluorimetric detection of hydrogen peroxide was performed by adding 0.6 mL H2O2 solution with different concentrations to each sample containing 5.4 mL solution of 9.93 × 10 −6 M Pt(II)-TAPP in DMSO. The concentrations of the added H2O2 solution were: 1.05 × 10 −6 M; 1.1 × 10 −6 M; 1.6 × 10 −6 M; 2.59 × 10 −6 M; 2.9 × 10 −6 M; 3.17 × 10 −6 M; 3.43 × 10 −6 M; 3.67 × 10 −6 M; 3.9 × 10 −6 M. Each sample was stirred, and the emission spectra were recorded, as shown in Figure 5. It can be observed that the quenching of fluorescence is taking place when adding hydrogen peroxide to the Pt(II)-TAPP solution in DMSO, as represented in Figure 5. The intensity of emission decreases after a linear equation, characterized by an excellent confidence coefficient of 99.76%, in 1.05-3.9 × 10 −7 M H2O2 concentration range.

Study of Interfering Analytes
The selectivity of the fluorimetric sensor toward the H 2 O 2 detection is a very important aspect. Taking into consideration that this fluorimetric sensor is destined for medical tests, the interference study, shown in Figure 6, was focused on those anions, cations or compounds that are frequently present in the targeted environments (human serum and urine), such as: glucose (Glu); NaCl; ascorbic acid (AA); phosphate buffer (PSB), AA + NaCl, PSB + NaCl, Glu + NaCl, lactic acid (LA), I 2 + LA, potassium dichromate (Cr 2  The method used for investigation of interfering analytes is described as follows: to each 10 mL of 9.93 × 10 −6 M Pt(II)-TAPP solution in DMSO, 1 mL solution containing the mentioned above interfering analytes was added. Each sample was vigorously stirred for 1 minute in the ultrasonic bath and the fluorescence spectra were recorded. Each measurement was performed three times. The method used for investigation of interfering analytes is described as follows: to each 10 mL of 9.93 × 10 −6 M Pt(II)-TAPP solution in DMSO, 1 mL solution containing the mentioned above interfering analytes was added. Each sample was vigorously stirred for 1 minute in the ultrasonic bath and the fluorescence spectra were recorded. Each measurement was performed three times.
The average percentage errors for H 2 O 2 fluorescence detection are calculated as |∆I|/I × 100 (where I represents the emission intensity of the sample containing H 2 O 2 and |∆I|, the difference in module between I and the emission intensity of each studied interference analyte or mixtures of analytes), as displayed in Figure 7. The method used for investigation of interfering analytes is described as follows: to each 10 mL of 9.93 × 10 −6 M Pt(II)-TAPP solution in DMSO, 1 mL solution containing the mentioned above interfering analytes was added. Each sample was vigorously stirred for 1 minute in the ultrasonic bath and the fluorescence spectra were recorded. Each measurement was performed three times.
The average percentage errors for H2O2 fluorescence detection are calculated as |ΔI|/I × 100 (where I represents the emission intensity of the sample containing H2O2 and |ΔI|, the difference in module between I and the emission intensity of each studied interference analyte or mixtures of analytes), as displayed in Figure 7. As can be seen from Figure 7, glucose, lactic acid, dichromate anion, iodine, acetic acid, NaCl and permanganate anion, solely or in combined mixtures, have no significant influence toward H 2 O 2 detection, although their concentration was 100-times higher than the concentration of detected H 2 O 2 .
Other interferences, such as: ascorbic acid, dilauryl phosphite and phosphate buffer introduced significant average percentage errors, below 5%. Instead, by performing the measurements in samples comprising at least three different interference analytes, each of them containing NaCl, the measurements are lacking in precision (errors between 5.5% and 7.3%), probably because of the induced higher ionic strength.

Electrochemical Detection of H 2 O 2
The response of GCE and GCE electrodes modified with Pt-porphyrin film (Pt-Porf-GCE) in MES buffer solution at pH = 5.6 was studied comparatively. The cyclic voltammograms are shown in Figure 8A. Different cyclic voltammograms were obtained on modified GCE electrode. The modified electrode has oxidation peaks at the potentials of 0.35 V and 0.8 V and reduction peaks at −0.125 V and −0.6 V, corresponding to the Pt-porphyrin film and thus confirming its presence on the electrode surface. The response of GCE and GCE electrodes modified with Pt-porphyrin film (Pt-Porf-GCE) in MES buffer solution at pH = 5.6 was studied comparatively. The cyclic voltammograms are shown in Figure 8A. Different cyclic voltammograms were obtained on modified GCE electrode. The modified electrode has oxidation peaks at the potentials of 0.35 V and 0.8 V and reduction peaks at −0.125 V and −0.6 V, corresponding to the Pt-porphyrin film and thus confirming its presence on the electrode surface. Cyclic voltammograms for GCE in MES buffer solution at pH = 5.6 in the absence and in the presence of H 2 O 2 , are presented in Figure 8B. The GCE presents a light response in the presence of H 2 O 2 . The comparison of the cyclic voltammograms shown in Figure 8C for GCE (curve 1) and for modified Pt-Porf-GCE (curve 2) in the presence of the same concentration of H 2 O 2 (28.95 mM), reveals that the GCE has no significant response but the modified Pt-Porf-GCE strongly changed both its anodic and cathodic responses. On modified Pt-Porf-GCE the oxidation process takes place at a lower potential and the reduction process at a higher potential than in the case of GCE.
The oxidation current of H 2 O 2 on the modified Pt-Porf-GCE, represented in Figure 9, increased due to electrocatalytic oxidation (~0.7 V), as well as that of reduction (−0.5 V).
H2O2. The comparison of the cyclic voltammograms shown in Figure 8C for GCE (curve 1) and for modified Pt-Porf-GCE (curve 2) in the presence of the same concentration of H2O2 (28.95 mM), reveals that the GCE has no significant response but the modified Pt-Porf-GCE strongly changed both its anodic and cathodic responses. On modified Pt-Porf-GCE the oxidation process takes place at a lower potential and the reduction process at a higher potential than in the case of GCE.
The oxidation current of H2O2 on the modified Pt-Porf-GCE, represented in Figure 9, increased due to electrocatalytic oxidation (~0.7 V), as well as that of reduction (−0.5 V). The significant increase of the reduction current in the presence of H2O2 is due to the electrocatalytic effect of the Pt-metalloporphyrin (Pt-Porf) on the H2O2 reduction, illustrated by Equations (1) and (2). The reduced form of Pt-metalloporphyrin (Pt-Porf − ) can reduce the H2O2 and transforms into the initial form (Pt-Porf) on the electrode surface (Equation (2)).
The oxidation current is due to the electrochemical oxidation of water and hydrogen peroxide. The hydrogen peroxide oxidation is mediated by the Pt-metalloporphyrin immobilized on the GCE, as can be seen in the following simplified mechanism, presented in Equations (3) and (4): 2Pt-Porf + + H2O2 ⟶ 2Pt-Porf + O2 + 2H + (4) Similar observations were reported by other authors [4,37].
In the studied concentration range, the anodic and cathodic response currents of the Pt-Porf-GCE are directly proportional to the H2O2 concentration, as illustrated in Figure 10 (A, B).  (1) and (2). The reduced form of Pt-metalloporphyrin (Pt-Porf − ) can reduce the H 2 O 2 and transforms into the initial form (Pt-Porf) on the electrode surface (Equation (2)).
The oxidation current is due to the electrochemical oxidation of water and hydrogen peroxide. The hydrogen peroxide oxidation is mediated by the Pt-metalloporphyrin immobilized on the GCE, as can be seen in the following simplified mechanism, presented in Equations (3) and (4): Similar observations were reported by other authors [4,37].
In the studied concentration range, the anodic and cathodic response currents of the Pt-Porf-GCE are directly proportional to the H 2 O 2 concentration, as illustrated in Figure 10A,B). The results indicate that the detection of hydrogen peroxide by using the modified Pt-Porf-GCE is accurate. The oxidation and reduction currents were found to increase linearly with increasing H2O2 concentration. The calibration graphs from Figure 10A, B, plotted between the catalytic current and H2O2 concentration on the Pt-Porf-GCE give a linear dependence in the concentration range from 1 × 10 −6 M to 5 × 10 −5 M, R 2 = 0.999, for both diagrams. The results indicate that the detection of hydrogen peroxide by using the modified Pt-Porf-GCE is accurate. The oxidation and reduction currents were found to increase linearly with increasing H 2 O 2 concentration. The calibration graphs from Figure 10A, B, plotted between the catalytic current and H 2 O 2 concentration on the Pt-Porf-GCE give a linear dependence in the concentration range from 1 × 10 −6 M to 5 × 10 −5 M, R 2 = 0.999, for both diagrams.
This is a range of concentration larger than that obtained in the case of fluorimetric detection and is appropriate for measurements in technical gold cyanidation [38] cosmetics [39] and agriculture [10].

Conclusions
Metalloporphyrins(II) are highly recognized for their capacity to act as sensitive substances used in formulation of optical, fluorescent, and electrochemical sensors. In this respect, a novel Pt-porphyrin structure, namely: Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl) porphyrin, was successfully synthesized and was fully characterized by UV-vis and fluorimetry (Supplementary Materials), FT-IR, 1 H-NMR and 13 C-NMR methods.
The fluorescence response of this Pt-porphyrin in the presence of different concentrations of hydrogen peroxide was investigated. It was proved that in the detection domain 1.05-3.9 × 10 −7 M H 2 O 2 (that is highly relevant for biological testing) the investigated porphyrin can act as fluorescent sensitive substance, with a high confidence coefficient of 99.7%. In comparison with other previous strategies [8,16,17], this fluorescent approach gave a 40 times lower detection limit of 0.3 × 10 −7 M, and the procedure is simpler, less expensive and less time consuming. The fluorimetric response is accurate and stable in the presence of several interfering mixtures of anions, cations and strongly oxidizing species frequently present in the targeted environments. Glucose, lactic acid, dichromate anion, iodine, acetic acid, NaCl, and permanganate anion, solely or in combined mixtures, have no significant influence on H 2 O 2 detection, although their concentration was 100-times higher than that of detected H 2 O 2 .
On the other hand, Pt-Porf-GCE was realized and several electrochemical characterizations were comparatively performed with the bare GCE, in the absence or presence of hydrogen peroxide. The oxidation and reduction currents were found to increase linearly with increasing H 2 O 2 concentration on modified Pt-Porf-GCE. The calibration graphs plotted between the catalytic current (both anodic and cathodic currents) and H 2 O 2 concentration on the Pt-Porf-GCE gave a linear response in the concentration range from 1×10 −6 M to 5×10 −5 M with exceptional confidence coefficient of 99.9%.
Different methods for the determination of hydrogen peroxide, based on several sensitive materials were accomplished in order to improve the linear concentration range and the limit of detection and are summarized in Table 1. Based on two different fluorimetric and electrochemical methods, this Pt-porphyrin has the potential to cover detection of hydrogen peroxide in diverse fields, from medical tests to technical, cosmetics, food, and agriculture monitoring, with high accuracy. The future implications will be focused on obtaining of the Pt-porphyrin from recovered platinum from spent automotive catalysts producing added value from this recovery and decreasing costs.