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Amperometric urea biosensors based on sulfonated graphene/polyaniline nanocomposite.

Das G, Yoon HH - Int J Nanomedicine (2015)

Bottom Line: The biosensor achieved a broad linear range of detection (0.12-12.3 mM) with a notable response time of approximately 5 seconds.Moreover, the fabricated biosensor retained 81% of its initial activity (based on sensitivity) after 15 days of storage at 4°C.The ease of fabrication coupled with the low cost and good electrochemical performance of this system holds potential for the development of solid-state biosensors for urea detection.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Gachon University, Seongnam, Gyeonggi-do, South Korea.

ABSTRACT
An electrochemical biosensor based on sulfonated graphene/polyaniline nanocomposite was developed for urea analysis. Oxidative polymerization of aniline in the presence of sulfonated graphene oxide was carried out by electrochemical methods in an aqueous environment. The structural properties of the nanocomposite were characterized by Fourier-transform infrared, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques. The urease enzyme-immobilized sulfonated graphene/polyaniline nanocomposite film showed impressive performance in the electroanalytical detection of urea with a detection limit of 0.050 mM and a sensitivity of 0.85 (μA · cm(-2)·mM(-1). The biosensor achieved a broad linear range of detection (0.12-12.3 mM) with a notable response time of approximately 5 seconds. Moreover, the fabricated biosensor retained 81% of its initial activity (based on sensitivity) after 15 days of storage at 4°C. The ease of fabrication coupled with the low cost and good electrochemical performance of this system holds potential for the development of solid-state biosensors for urea detection.

No MeSH data available.


cyclic voltammogram obtained at 20 mV·s−1.Notes: (A) ITO/SG-PANI in 1 M HCl. (B) (a) ITO/GO, (b) ITO/GO in 10 mM urea, (c) ITO/SGO, (d) ITO/SGO in 10 mM urea, (e) ITO/SG-PANI/Urs in PBS (ph 7.4), and (f) ITO/SG-PANI/Urs in 10 mM urea (PBS, ph 7.4).Abbreviations: GO, graphene oxide; ITO, indium tin oxide; PBS, phosphate-buffered saline; SGO, sulfonated graphene oxide; SG-PANI, sulfonated graphene/polyaniline; Urs, urease; vs, versus.
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f8-ijn-10-055: cyclic voltammogram obtained at 20 mV·s−1.Notes: (A) ITO/SG-PANI in 1 M HCl. (B) (a) ITO/GO, (b) ITO/GO in 10 mM urea, (c) ITO/SGO, (d) ITO/SGO in 10 mM urea, (e) ITO/SG-PANI/Urs in PBS (ph 7.4), and (f) ITO/SG-PANI/Urs in 10 mM urea (PBS, ph 7.4).Abbreviations: GO, graphene oxide; ITO, indium tin oxide; PBS, phosphate-buffered saline; SGO, sulfonated graphene oxide; SG-PANI, sulfonated graphene/polyaniline; Urs, urease; vs, versus.

Mentions: The electrochemical properties of the SG-PANI electrode were studied using CV. Figure 8 shows the cyclic voltammogram of ITO/SG-PANI recorded in 1 M HCl, and that of ITO/SG-PANI/Urs with and without 10 mM urea (PBS, pH 7.4). The cyclic voltammogram of ITO/GO and ITO/SGO were also recorded in PBS and in 10 mM urea (PBS, pH 7.4), respectively. However, no significant differences were observed in the voltammogram (Figure 8B) for the ITO/GO and ITO/SGO in PBS and urea, indicating that GO and SGO played no role in oxidation of urea. Two pairs of redox peaks were distinctly visible for ITO/SG-PANI when the CV was measured in the presence of 1 M HCl (Figure 8A), which is in agreement with earlier published reports.46,47 These peaks correspond to the variable oxidation states of PANI. The peaks merged upon increasing the pH of the medium, as shown in Figure 8Be and Bf. Tian et al46 reported that the merging of the peaks usually occurred at pH >5. PANI has been reported to lose its electrochemical activity in the neutral or basic medium.48 However, with a neutral medium, the ITO/SG-PANI/Urs biosensor showed a stable electrochemical behavior in the cyclic potential range between −0.2 and +0.4 V, due to the doping effect of SG. The CV of the SG-PANI biosensor can be traced to a visibly distinct redox pair, ie, an oxidation peak of ~64 mV and a corresponding reducing peak approximately −93 mV in PBS. This peak is a combination of two peaks generally observed in an acidic medium, corresponding to the transitions of leucoemeraldine and emeraldine and between the emeraldine and pernigraniline redox states of PANI.49 The electrochemical activity of the SG-PANI electrode is thus promising considering the practical applications as the bioactivity of the enzyme is denatured at lower pH (<6). A similar observation was also reported by Liu et al for PANI/poly(aminobenzenesulfonic acid)-modified single-walled carbon nanotubes prepared by the layer-by-layer method.47 The extension of the electroactivity of PANI to a medium of pH 7.4 is indicative of the doping influence on the SO3− groups of SG. Figure 4 represents the possible transformation of the doped PANI structure under this condition. Figure 8B shows that in the presence of urea, the intensity of the anodic and cathodic peaks increases, with a simultaneous shift in the peak potential, ie, the oxidation peak potential shifts to 107 mV and the corresponding reduction peak potential to −47 mV, with a peak-to-peak separation (ΔEp) potential of ~66 mV. The low ΔEp indicates a very fast electron transfer, as generally observed for one-electron systems.50,51


Amperometric urea biosensors based on sulfonated graphene/polyaniline nanocomposite.

Das G, Yoon HH - Int J Nanomedicine (2015)

cyclic voltammogram obtained at 20 mV·s−1.Notes: (A) ITO/SG-PANI in 1 M HCl. (B) (a) ITO/GO, (b) ITO/GO in 10 mM urea, (c) ITO/SGO, (d) ITO/SGO in 10 mM urea, (e) ITO/SG-PANI/Urs in PBS (ph 7.4), and (f) ITO/SG-PANI/Urs in 10 mM urea (PBS, ph 7.4).Abbreviations: GO, graphene oxide; ITO, indium tin oxide; PBS, phosphate-buffered saline; SGO, sulfonated graphene oxide; SG-PANI, sulfonated graphene/polyaniline; Urs, urease; vs, versus.
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f8-ijn-10-055: cyclic voltammogram obtained at 20 mV·s−1.Notes: (A) ITO/SG-PANI in 1 M HCl. (B) (a) ITO/GO, (b) ITO/GO in 10 mM urea, (c) ITO/SGO, (d) ITO/SGO in 10 mM urea, (e) ITO/SG-PANI/Urs in PBS (ph 7.4), and (f) ITO/SG-PANI/Urs in 10 mM urea (PBS, ph 7.4).Abbreviations: GO, graphene oxide; ITO, indium tin oxide; PBS, phosphate-buffered saline; SGO, sulfonated graphene oxide; SG-PANI, sulfonated graphene/polyaniline; Urs, urease; vs, versus.
Mentions: The electrochemical properties of the SG-PANI electrode were studied using CV. Figure 8 shows the cyclic voltammogram of ITO/SG-PANI recorded in 1 M HCl, and that of ITO/SG-PANI/Urs with and without 10 mM urea (PBS, pH 7.4). The cyclic voltammogram of ITO/GO and ITO/SGO were also recorded in PBS and in 10 mM urea (PBS, pH 7.4), respectively. However, no significant differences were observed in the voltammogram (Figure 8B) for the ITO/GO and ITO/SGO in PBS and urea, indicating that GO and SGO played no role in oxidation of urea. Two pairs of redox peaks were distinctly visible for ITO/SG-PANI when the CV was measured in the presence of 1 M HCl (Figure 8A), which is in agreement with earlier published reports.46,47 These peaks correspond to the variable oxidation states of PANI. The peaks merged upon increasing the pH of the medium, as shown in Figure 8Be and Bf. Tian et al46 reported that the merging of the peaks usually occurred at pH >5. PANI has been reported to lose its electrochemical activity in the neutral or basic medium.48 However, with a neutral medium, the ITO/SG-PANI/Urs biosensor showed a stable electrochemical behavior in the cyclic potential range between −0.2 and +0.4 V, due to the doping effect of SG. The CV of the SG-PANI biosensor can be traced to a visibly distinct redox pair, ie, an oxidation peak of ~64 mV and a corresponding reducing peak approximately −93 mV in PBS. This peak is a combination of two peaks generally observed in an acidic medium, corresponding to the transitions of leucoemeraldine and emeraldine and between the emeraldine and pernigraniline redox states of PANI.49 The electrochemical activity of the SG-PANI electrode is thus promising considering the practical applications as the bioactivity of the enzyme is denatured at lower pH (<6). A similar observation was also reported by Liu et al for PANI/poly(aminobenzenesulfonic acid)-modified single-walled carbon nanotubes prepared by the layer-by-layer method.47 The extension of the electroactivity of PANI to a medium of pH 7.4 is indicative of the doping influence on the SO3− groups of SG. Figure 4 represents the possible transformation of the doped PANI structure under this condition. Figure 8B shows that in the presence of urea, the intensity of the anodic and cathodic peaks increases, with a simultaneous shift in the peak potential, ie, the oxidation peak potential shifts to 107 mV and the corresponding reduction peak potential to −47 mV, with a peak-to-peak separation (ΔEp) potential of ~66 mV. The low ΔEp indicates a very fast electron transfer, as generally observed for one-electron systems.50,51

Bottom Line: The biosensor achieved a broad linear range of detection (0.12-12.3 mM) with a notable response time of approximately 5 seconds.Moreover, the fabricated biosensor retained 81% of its initial activity (based on sensitivity) after 15 days of storage at 4°C.The ease of fabrication coupled with the low cost and good electrochemical performance of this system holds potential for the development of solid-state biosensors for urea detection.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Gachon University, Seongnam, Gyeonggi-do, South Korea.

ABSTRACT
An electrochemical biosensor based on sulfonated graphene/polyaniline nanocomposite was developed for urea analysis. Oxidative polymerization of aniline in the presence of sulfonated graphene oxide was carried out by electrochemical methods in an aqueous environment. The structural properties of the nanocomposite were characterized by Fourier-transform infrared, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques. The urease enzyme-immobilized sulfonated graphene/polyaniline nanocomposite film showed impressive performance in the electroanalytical detection of urea with a detection limit of 0.050 mM and a sensitivity of 0.85 (μA · cm(-2)·mM(-1). The biosensor achieved a broad linear range of detection (0.12-12.3 mM) with a notable response time of approximately 5 seconds. Moreover, the fabricated biosensor retained 81% of its initial activity (based on sensitivity) after 15 days of storage at 4°C. The ease of fabrication coupled with the low cost and good electrochemical performance of this system holds potential for the development of solid-state biosensors for urea detection.

No MeSH data available.