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Figure 2. SEM images of (A) NPG obtained by 30 min dealloying treatment; (B) Pd&Pt@NPG, which are delivered as a reference to the TEM images in large scale.

Figure 2 SEM images of (A) NPG obtained by 30 min dealloying treatment; (B) Pd&Pt@NPG, which are delivered as a reference to the TEM images in large scale.

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Figure 1. Illustrative fabrication process of the Pd&Pt@NPG/graphene paper electrode for the biosensor application. In addition to temperature, pH, and toxic chemicals for sterilization, the responses of glucose sensors are a function of humidity. Both high and low humidity may be significantly harmful to the sensors in use as well as storage. Therefore, the poor stability of enzymatic sensors and the interference of some electro-oxidizable species remain as problems for application (Feng, D. et al., 2009). So preference is given to non-enzymatic sensor which means the direct electrochemical oxidation of glucose without enzyme. Nonenzymatic electrode would exhibit conveniences and advantages to avoid the drawbacks of enzymatic sensors. Dealloyed Au/Ag alloy membranes have a three-dimension nanoporous structure, consisting of gold ligaments and nanopore channels (Fujita, T. et al., 2008). Hence, the dealloyed nanoporous gold (NPG) possesses high electric conductivity and a large surface area, which offer a arge number of adsorption sites for proteins and enzymes and could increase the signal-to-noise ratio in he miniaturization systems (Yu, C. ef al., 2007). Furthermore, NPG has excellent stability and biocompatibility for use in biosensors and reactors Sotiropoulou, S. et al., 2005). The striking properties of he nanoporous gold have motivated intensive interest in I a NPG is formed from Au50Ag50 alloy membrane (weight ratio) by 30min dealloying process on concentrated nitric acid and subsequently maintained on Ultra-pure water. Chloroplatinic acid hydrate and palladium chlorine acid and formic acid are mixed and dispersed under 25 °C water bath. Then, NPG is carefully transferred to the mixed solution. After this process, the reaction container is kept out of light and under 25 °C water bath for 3 h to obtain Pd&Pt@NPG (Figure 1).
Figure 1. Illustrative fabrication process of the Pd&Pt@NPG/graphene paper electrode for the biosensor application. In addition to temperature, pH, and toxic chemicals for sterilization, the responses of glucose sensors are a function of humidity. Both high and low humidity may be significantly harmful to the sensors in use as well as storage. Therefore, the poor stability of enzymatic sensors and the interference of some electro-oxidizable species remain as problems for application (Feng, D. et al., 2009). So preference is given to non-enzymatic sensor which means the direct electrochemical oxidation of glucose without enzyme. Nonenzymatic electrode would exhibit conveniences and advantages to avoid the drawbacks of enzymatic sensors. Dealloyed Au/Ag alloy membranes have a three-dimension nanoporous structure, consisting of gold ligaments and nanopore channels (Fujita, T. et al., 2008). Hence, the dealloyed nanoporous gold (NPG) possesses high electric conductivity and a large surface area, which offer a arge number of adsorption sites for proteins and enzymes and could increase the signal-to-noise ratio in he miniaturization systems (Yu, C. ef al., 2007). Furthermore, NPG has excellent stability and biocompatibility for use in biosensors and reactors Sotiropoulou, S. et al., 2005). The striking properties of he nanoporous gold have motivated intensive interest in I a NPG is formed from Au50Ag50 alloy membrane (weight ratio) by 30min dealloying process on concentrated nitric acid and subsequently maintained on Ultra-pure water. Chloroplatinic acid hydrate and palladium chlorine acid and formic acid are mixed and dispersed under 25 °C water bath. Then, NPG is carefully transferred to the mixed solution. After this process, the reaction container is kept out of light and under 25 °C water bath for 3 h to obtain Pd&Pt@NPG (Figure 1).
of the Pt4f, Pd 3d and Au 4f regions are shown in Figure 4 The spectrum is composed of the Pt 4f7/2 and Pt 4f5/2 peaks having a binding energy difference of 3.33 eV. The Pt 4f7/2 and Pt 4f5/2 peak was deconvoluted into two and three component peaks, respectively, i.e. component peaks A and B for the Pt 4f7/2 peak, and component respond to the Pd3d5/2 and Pd 3d3/2 in
of the Pt4f, Pd 3d and Au 4f regions are shown in Figure 4 The spectrum is composed of the Pt 4f7/2 and Pt 4f5/2 peaks having a binding energy difference of 3.33 eV. The Pt 4f7/2 and Pt 4f5/2 peak was deconvoluted into two and three component peaks, respectively, i.e. component peaks A and B for the Pt 4f7/2 peak, and component respond to the Pd3d5/2 and Pd 3d3/2 in
Figure 4. (A, B, C) XPS spectra of the Pt 4f, Pd 3d and Au 4f of Pt&Pd@NPG Janata, J. 1983). Besides the composition, we obtained the elements content of the catalyst, as show in Table 3.1. It is clear that the atomic ration of Pd&Pt-NPs (ac. 27%) is much smaller than that of Au-NPs (ac. 73%). palladium nanoparticles (Jaramillo, T. F. et al., 2003). The Au 4f712 peak appeared at a binding energy of 84.1 eV and the Au 4f3/2 peak appeared at 87.7 eV, confirming the formation of metallic gold (Oesch, U., & Table 1: Elements content of Pt&Pd@NPG catalyst from XPS analysis.
Figure 4. (A, B, C) XPS spectra of the Pt 4f, Pd 3d and Au 4f of Pt&Pd@NPG Janata, J. 1983). Besides the composition, we obtained the elements content of the catalyst, as show in Table 3.1. It is clear that the atomic ration of Pd&Pt-NPs (ac. 27%) is much smaller than that of Au-NPs (ac. 73%). palladium nanoparticles (Jaramillo, T. F. et al., 2003). The Au 4f712 peak appeared at a binding energy of 84.1 eV and the Au 4f3/2 peak appeared at 87.7 eV, confirming the formation of metallic gold (Oesch, U., & Table 1: Elements content of Pt&Pd@NPG catalyst from XPS analysis.
Table 2: The real surface areas and roughness factors of NPG and Pd&Pt@NPG samples. Table 3: Rs and Ret of NPG/GP and Pd&Pt@NPG/GP electrodes, bare GP electrode is also included for comparison.
Table 2: The real surface areas and roughness factors of NPG and Pd&Pt@NPG samples. Table 3: Rs and Ret of NPG/GP and Pd&Pt@NPG/GP electrodes, bare GP electrode is also included for comparison.
Electrocatalytic activity of modified electrod toward glucose detection is increased with the glucose concentration increase. For comparison, the NPG electrode is also investigated in the 0.1M PBS + 10mm glucose solution, and due to the absence of Pd&Pt-NPs/graphene paper in the surface of NPG, there is nearly no redox peaks in the CV curve, which indicates the highly enhanced catalytic property
Electrocatalytic activity of modified electrod toward glucose detection is increased with the glucose concentration increase. For comparison, the NPG electrode is also investigated in the 0.1M PBS + 10mm glucose solution, and due to the absence of Pd&Pt-NPs/graphene paper in the surface of NPG, there is nearly no redox peaks in the CV curve, which indicates the highly enhanced catalytic property
Figure 5. (A) CVs of the fabricated Pt&Pd@NPG (dark line) and NPG (red line) electrodes in 0.5M H,SO, solution in order to obtain the surface roughness factor. Scan rate: 50 mV/s. (B) EIS Nyquist plots of GP, NPG@GP and Pd&Pt@NPG@GP electrodes (inset: equivalent circuit diagram proposed for analysis of the EIS data)
Figure 5. (A) CVs of the fabricated Pt&Pd@NPG (dark line) and NPG (red line) electrodes in 0.5M H,SO, solution in order to obtain the surface roughness factor. Scan rate: 50 mV/s. (B) EIS Nyquist plots of GP, NPG@GP and Pd&Pt@NPG@GP electrodes (inset: equivalent circuit diagram proposed for analysis of the EIS data)
Pd&Pt @ NPG/graphene Figure 6.B shows the tyy paper can effectively catalyze glucose oxidation on the modified electrode surface. pical amperometric responses of the Pd&Pt@NPG/graphene paper upon the successive injection of glucose into the PBS solution (PH=7.4). Upon each addition of glucose, the response of the Pd&Pt@NPG/GP electrode based-sensor rapidly reaches 95% of the steady-state value within 3s. A good inear dependence on t he glucose concentration in the range of 0.1-20mM was achieved, with a sensitivity of 39.05 uA mM™'cm” and a detection limit down to 50 uM at a signal-to-noise (S/N) ratio of 3 (Figure 6.C). of Pd&Pt@NPG/graphene paper. Multiple anodic peaks attributed to the oxidation of glucose and resulting intermediates are observed for the positive scan. During the cathodic potential scan, the oxidation of glucose is suppressed in the high potential range because of the presence of surface oxide. With the reduction of Pt oxide, more surface-active sites are available for the oxidation of glucose, resulting in large and broad oxidation peak. These results can be explained by a well-accepted mechanism of glucose oxidation on a Pt electrode in neutral media (Habrioux, A. et al., 2007). These results explain and indicate _ that Figure 6. (A) CV curves of Pt&Pd@NPG/graphene paper electrode in 0.1 M PBS
Pd&Pt @ NPG/graphene Figure 6.B shows the tyy paper can effectively catalyze glucose oxidation on the modified electrode surface. pical amperometric responses of the Pd&Pt@NPG/graphene paper upon the successive injection of glucose into the PBS solution (PH=7.4). Upon each addition of glucose, the response of the Pd&Pt@NPG/GP electrode based-sensor rapidly reaches 95% of the steady-state value within 3s. A good inear dependence on t he glucose concentration in the range of 0.1-20mM was achieved, with a sensitivity of 39.05 uA mM™'cm” and a detection limit down to 50 uM at a signal-to-noise (S/N) ratio of 3 (Figure 6.C). of Pd&Pt@NPG/graphene paper. Multiple anodic peaks attributed to the oxidation of glucose and resulting intermediates are observed for the positive scan. During the cathodic potential scan, the oxidation of glucose is suppressed in the high potential range because of the presence of surface oxide. With the reduction of Pt oxide, more surface-active sites are available for the oxidation of glucose, resulting in large and broad oxidation peak. These results can be explained by a well-accepted mechanism of glucose oxidation on a Pt electrode in neutral media (Habrioux, A. et al., 2007). These results explain and indicate _ that Figure 6. (A) CV curves of Pt&Pd@NPG/graphene paper electrode in 0.1 M PBS
Figure 7. (A) CV curves of Pd&Pt@ NPG/graphene paper electrode in 0.1 M PBS (pH 7.4) solution with HO, concentration of (5 mM). Scan rate: 50mV/s. (B) Amperometric responses of Pd& Pt @ NPG/graphene paper electrode for successive additions of H,O,. The supporting electrolyte is 0.1 M PBS (pH 7.4). The inset shows a close look of red oval region. (C) Calibration curve with different concentrations of H,O, (0.1 M PBS, pH 7.4) with Pd&Pt@NPG/graphene paper electrode with amperometry method. (D) The amperometric responses to the consecutive addition of the 1 mM H,0, and the | mM interfering species: Cl, SO,”, CO;”, NO;,, Fe** in a stirred PBS solution. Applied potential: 0.25V. KSOCIO Schwann cells and Human Umbilical Vein Endothelial cells (HUVEC) were chosen as the probes for real-time electrochemical determination of HO, released upon being stimulated. Our results demonstrate that after being incubated with the Pd&Pt@NPG/grapheme paper for over 2h, the Hela cells, RSC96 cells and HUVEC cells still maintained their viability and activity, and did not show any changes in cell morphology and viability, as shown in the bright-field and dark-field microscope image (Figure 8. A-F), indicating the good biocompatibility of Pd&Pt@NPG/graphene paper electrode. The cells of 80% confluency are induced to release HO) by injecting N-formylmethionyl-leucyl-phenylalanine (f{MLP), which is one of the synthetic N-formyl methionyl peptides that can stimulate the secretion of several effectors molecules including interleukin 1, lysosomal enzymes, tumor necrosis factor, nitric oxide and reactive oxygen intermediates (ROD) by living cells. Figure 8. G-I depicts the amperometric response changes of Pd&Pt@NPG/graphene paper electrode located near the living cells lines in a culture medium consisting of Dulbecco's modified Eagle medium (DMEM) at 37°C. After the injection of 10 ul fMLP (0.1 mm), a significant decreased current is observed for all the living cells at the applied potential of 0.25 V, followed by a gradual increase of current, and finally reaches a plateau (Figure 8. G-I). However, the contro wells containing no living cells do not generate any signal response to the addition of fMLP (Figure 8. J). These results together suggest that the generated increase of amperometric responses are ascribed to the electrochemical reduction HO, released by living cells upon being simulated by fMLP. Moreover, the increased current densities and the times to reach the plateau for these three types of living cells are investigated in details. As shown in Figure 8. K and 8. F, upon the additinn of eanal amount of fMIP the increace
Figure 7. (A) CV curves of Pd&Pt@ NPG/graphene paper electrode in 0.1 M PBS (pH 7.4) solution with HO, concentration of (5 mM). Scan rate: 50mV/s. (B) Amperometric responses of Pd& Pt @ NPG/graphene paper electrode for successive additions of H,O,. The supporting electrolyte is 0.1 M PBS (pH 7.4). The inset shows a close look of red oval region. (C) Calibration curve with different concentrations of H,O, (0.1 M PBS, pH 7.4) with Pd&Pt@NPG/graphene paper electrode with amperometry method. (D) The amperometric responses to the consecutive addition of the 1 mM H,0, and the | mM interfering species: Cl, SO,”, CO;”, NO;,, Fe** in a stirred PBS solution. Applied potential: 0.25V. KSOCIO Schwann cells and Human Umbilical Vein Endothelial cells (HUVEC) were chosen as the probes for real-time electrochemical determination of HO, released upon being stimulated. Our results demonstrate that after being incubated with the Pd&Pt@NPG/grapheme paper for over 2h, the Hela cells, RSC96 cells and HUVEC cells still maintained their viability and activity, and did not show any changes in cell morphology and viability, as shown in the bright-field and dark-field microscope image (Figure 8. A-F), indicating the good biocompatibility of Pd&Pt@NPG/graphene paper electrode. The cells of 80% confluency are induced to release HO) by injecting N-formylmethionyl-leucyl-phenylalanine (f{MLP), which is one of the synthetic N-formyl methionyl peptides that can stimulate the secretion of several effectors molecules including interleukin 1, lysosomal enzymes, tumor necrosis factor, nitric oxide and reactive oxygen intermediates (ROD) by living cells. Figure 8. G-I depicts the amperometric response changes of Pd&Pt@NPG/graphene paper electrode located near the living cells lines in a culture medium consisting of Dulbecco's modified Eagle medium (DMEM) at 37°C. After the injection of 10 ul fMLP (0.1 mm), a significant decreased current is observed for all the living cells at the applied potential of 0.25 V, followed by a gradual increase of current, and finally reaches a plateau (Figure 8. G-I). However, the contro wells containing no living cells do not generate any signal response to the addition of fMLP (Figure 8. J). These results together suggest that the generated increase of amperometric responses are ascribed to the electrochemical reduction HO, released by living cells upon being simulated by fMLP. Moreover, the increased current densities and the times to reach the plateau for these three types of living cells are investigated in details. As shown in Figure 8. K and 8. F, upon the additinn of eanal amount of fMIP the increace
Table 4: Comparison of the nonenzymatic glucose and HO, detection Performance
Table 4: Comparison of the nonenzymatic glucose and HO, detection Performance
Figure 8. The bright-field images of (A): Hela cells, (B): HUVEC cells and (C): RSC96 cells. The dark-field images of (D): Hela cells, (E): HUVEC cells and (F): RSC96 cells. Amperometric responses of the Pd&Pt@NPG/GP electrode in 0.1 M PBS (pH=7.4) with the addition of 10 uM fMLP in the absent of cell, as (J) shows, and in the present of (G): Hela cells, (H): HUVEC cells and (1) RSC96 cells. Applied potential: 0.25V. (K): Increase amperometric current densities of these cells. (L):Times needed to reach the plateau of these cells. substantially demonstrate that the proposed biosensor based on Pd&Pt@NPG/GP establishes a_ sensitive, reliable and robust method for the qualitative determination of H,O, secreted by different living cells and could potentially be useful for further physiological and pathological investigations. amperometric current densities for Hela cells, HUVEC cells and RSC96 cells are 29, 11 and 51 uA cm’. And the times to reach the plateau for these three types of living cells also increase in the order of Hela cells > RSC96 cells > HUVEC cells. Although the clear reason is still unknown at the present stage, these observations
Figure 8. The bright-field images of (A): Hela cells, (B): HUVEC cells and (C): RSC96 cells. The dark-field images of (D): Hela cells, (E): HUVEC cells and (F): RSC96 cells. Amperometric responses of the Pd&Pt@NPG/GP electrode in 0.1 M PBS (pH=7.4) with the addition of 10 uM fMLP in the absent of cell, as (J) shows, and in the present of (G): Hela cells, (H): HUVEC cells and (1) RSC96 cells. Applied potential: 0.25V. (K): Increase amperometric current densities of these cells. (L):Times needed to reach the plateau of these cells. substantially demonstrate that the proposed biosensor based on Pd&Pt@NPG/GP establishes a_ sensitive, reliable and robust method for the qualitative determination of H,O, secreted by different living cells and could potentially be useful for further physiological and pathological investigations. amperometric current densities for Hela cells, HUVEC cells and RSC96 cells are 29, 11 and 51 uA cm’. And the times to reach the plateau for these three types of living cells also increase in the order of Hela cells > RSC96 cells > HUVEC cells. Although the clear reason is still unknown at the present stage, these observations
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