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Enhancing electrochemical detection on graphene oxide-CNT nanostructured electrodes using magneto-nanobioprobes.

Sharma P, Bhalla V, Dravid V, Shekhawat G - Sci Rep (2012)

Bottom Line: Sensitive detection was achieved by precisely designing the nanohybrid and correlating the available metal ions with analyte concentration.We confirmed the ultrahigh sensitivity of this method for a new generation herbicide diuron and its analogues up to sub-picomolar concentration in standard water samples.The novel immune-detection platform showed the excellent potential applicability in rapid and sensitive screening of environmental pollutants or toxins in samples.

View Article: PubMed Central - PubMed

Affiliation: Institute of Microbial Technology (CSIR), Sector 39-A, Chandigarh 160036, India.

ABSTRACT
Graphene and related materials have come to the forefront of research in electrochemical sensors during recent years due to the promising properties of these nanomaterials. Further applications of these nanomaterials have been hampered by insufficient sensitivity offered by these nanohybrids for the type of molecules requiring lower detection ranges. Here, we report a signal amplification strategy based on magneto-electrochemical immunoassay which combines the advantages of carbon nanotube and reduced graphene oxide together with electrochemical bursting of magnetic nanoparticles into a large number of metal ions. Sensitive detection was achieved by precisely designing the nanohybrid and correlating the available metal ions with analyte concentration. We confirmed the ultrahigh sensitivity of this method for a new generation herbicide diuron and its analogues up to sub-picomolar concentration in standard water samples. The novel immune-detection platform showed the excellent potential applicability in rapid and sensitive screening of environmental pollutants or toxins in samples.

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(a) Response curves of rGO/CNT modified SPE The signal response was measured by a differential pulse voltammetry technique at amplitude 50 mV, pulse width 0.2 s, pulse period 0.5 s.(b) Competitive inhibition response curve for diuron at different concentrations. Each point in the graph was the mean of three successive measurements (n = 3).
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f6: (a) Response curves of rGO/CNT modified SPE The signal response was measured by a differential pulse voltammetry technique at amplitude 50 mV, pulse width 0.2 s, pulse period 0.5 s.(b) Competitive inhibition response curve for diuron at different concentrations. Each point in the graph was the mean of three successive measurements (n = 3).

Mentions: The formation of rGO/CNT nanocomposite on the working electrode of SPE increased the surface area enabling it to capture a large amount of metal ions liberated from Au/Fe nanoparticles after electrochemical conversion in the developed magneto-electrochemical immunoassay (MEI). The assay was carried out by coating the ELISA plates with hapten-protein (DCPU–BSA) conjugate. Optimum dilution of synthesized Ab-Au/Fe nanobioprobes pre-mixed with different concentrations of standard samples were used and incubated on the plates. The quick formation of nanobioprobe mediated immunocomplex on the plates was assisted by the application of magnetic field using bar magnet. The plates were washed and acid dissolved for the desorption of nanoparticles by using a mild acid followed by partial neutralization to retain pH 5.2. The intact magnetic core remain unaffected as mild weak acids are not capable of forming complexes with Fe in order to break the Fe-O bonds in the nanoparticles21. However, a reductive electrochemical scan is capable of liberating the Fe2+ ions from the magnetic nanoparticles22. The Fe2O3 nanoparticles were converted into metal ions (Fe2+) by applying a potential sweep between 0 to −1.6 V vs. Ag/AgCl. A characteristic broad reductive peak appeared at −0.75 V as shown in inset of figure S4 (see supplementary information, S4). Thus liberated reduced metal ions (Fe2+) on rGO/CNT modified SPE were monitored by differential pulse voltammetry (DPV). The competitive inhibition curve for diuron and other herbicides prepared at different concentrations in double distilled water ranging from 0.01 pg/mL to 1 µg/mL is shown in figure 6. The figure shows a linear decrease in current signal response with increasing concentrations of diuron (i to viii). At the highest concentration of diuron (1 µg/mL), the signal response was almost negligible demonstrating that there were no available metal ions on modified electrode surface. The percentage cross reactivity to related diuron analogues (linuron and fenuron) and other non related herbicides (atrazine and 2, 4-dichlorophenoxyacetic acid) was calculated on the basis of standard calibration curves see supplementary information Fig. S5). In the figure 6b, the standard inhibition curve for diuron is depicted. Data analysis was performed by normalizing the absorbance values using the following formula: Where I, I0, and Iex are the relative current intensities of the sample, hapten at zero concentration, and hapten at excess concentration, respectively. The limit of detection for diuron was found to be approximately 0.01 ng/mL in standard samples. The sensitivity of the assay was higher than the existing chromatography techniques (GC or HPLC) where the detection limits were 0.25 and 2.0 µg/L respectively for diuron samples23. The developed immunoassay showed excellent sensitivity and specificity demonstrating detection limit up to 0.1 pg/mL (sub-ppt) for diuron samples with high degree of reproducibility (n = 3) and good signal precision (~2%).


Enhancing electrochemical detection on graphene oxide-CNT nanostructured electrodes using magneto-nanobioprobes.

Sharma P, Bhalla V, Dravid V, Shekhawat G - Sci Rep (2012)

(a) Response curves of rGO/CNT modified SPE The signal response was measured by a differential pulse voltammetry technique at amplitude 50 mV, pulse width 0.2 s, pulse period 0.5 s.(b) Competitive inhibition response curve for diuron at different concentrations. Each point in the graph was the mean of three successive measurements (n = 3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3500845&req=5

f6: (a) Response curves of rGO/CNT modified SPE The signal response was measured by a differential pulse voltammetry technique at amplitude 50 mV, pulse width 0.2 s, pulse period 0.5 s.(b) Competitive inhibition response curve for diuron at different concentrations. Each point in the graph was the mean of three successive measurements (n = 3).
Mentions: The formation of rGO/CNT nanocomposite on the working electrode of SPE increased the surface area enabling it to capture a large amount of metal ions liberated from Au/Fe nanoparticles after electrochemical conversion in the developed magneto-electrochemical immunoassay (MEI). The assay was carried out by coating the ELISA plates with hapten-protein (DCPU–BSA) conjugate. Optimum dilution of synthesized Ab-Au/Fe nanobioprobes pre-mixed with different concentrations of standard samples were used and incubated on the plates. The quick formation of nanobioprobe mediated immunocomplex on the plates was assisted by the application of magnetic field using bar magnet. The plates were washed and acid dissolved for the desorption of nanoparticles by using a mild acid followed by partial neutralization to retain pH 5.2. The intact magnetic core remain unaffected as mild weak acids are not capable of forming complexes with Fe in order to break the Fe-O bonds in the nanoparticles21. However, a reductive electrochemical scan is capable of liberating the Fe2+ ions from the magnetic nanoparticles22. The Fe2O3 nanoparticles were converted into metal ions (Fe2+) by applying a potential sweep between 0 to −1.6 V vs. Ag/AgCl. A characteristic broad reductive peak appeared at −0.75 V as shown in inset of figure S4 (see supplementary information, S4). Thus liberated reduced metal ions (Fe2+) on rGO/CNT modified SPE were monitored by differential pulse voltammetry (DPV). The competitive inhibition curve for diuron and other herbicides prepared at different concentrations in double distilled water ranging from 0.01 pg/mL to 1 µg/mL is shown in figure 6. The figure shows a linear decrease in current signal response with increasing concentrations of diuron (i to viii). At the highest concentration of diuron (1 µg/mL), the signal response was almost negligible demonstrating that there were no available metal ions on modified electrode surface. The percentage cross reactivity to related diuron analogues (linuron and fenuron) and other non related herbicides (atrazine and 2, 4-dichlorophenoxyacetic acid) was calculated on the basis of standard calibration curves see supplementary information Fig. S5). In the figure 6b, the standard inhibition curve for diuron is depicted. Data analysis was performed by normalizing the absorbance values using the following formula: Where I, I0, and Iex are the relative current intensities of the sample, hapten at zero concentration, and hapten at excess concentration, respectively. The limit of detection for diuron was found to be approximately 0.01 ng/mL in standard samples. The sensitivity of the assay was higher than the existing chromatography techniques (GC or HPLC) where the detection limits were 0.25 and 2.0 µg/L respectively for diuron samples23. The developed immunoassay showed excellent sensitivity and specificity demonstrating detection limit up to 0.1 pg/mL (sub-ppt) for diuron samples with high degree of reproducibility (n = 3) and good signal precision (~2%).

Bottom Line: Sensitive detection was achieved by precisely designing the nanohybrid and correlating the available metal ions with analyte concentration.We confirmed the ultrahigh sensitivity of this method for a new generation herbicide diuron and its analogues up to sub-picomolar concentration in standard water samples.The novel immune-detection platform showed the excellent potential applicability in rapid and sensitive screening of environmental pollutants or toxins in samples.

View Article: PubMed Central - PubMed

Affiliation: Institute of Microbial Technology (CSIR), Sector 39-A, Chandigarh 160036, India.

ABSTRACT
Graphene and related materials have come to the forefront of research in electrochemical sensors during recent years due to the promising properties of these nanomaterials. Further applications of these nanomaterials have been hampered by insufficient sensitivity offered by these nanohybrids for the type of molecules requiring lower detection ranges. Here, we report a signal amplification strategy based on magneto-electrochemical immunoassay which combines the advantages of carbon nanotube and reduced graphene oxide together with electrochemical bursting of magnetic nanoparticles into a large number of metal ions. Sensitive detection was achieved by precisely designing the nanohybrid and correlating the available metal ions with analyte concentration. We confirmed the ultrahigh sensitivity of this method for a new generation herbicide diuron and its analogues up to sub-picomolar concentration in standard water samples. The novel immune-detection platform showed the excellent potential applicability in rapid and sensitive screening of environmental pollutants or toxins in samples.

Show MeSH