Upload
hollie-woods
View
259
Download
0
Tags:
Embed Size (px)
Citation preview
Electrochemical preparation and characterization of gold nanoparticles graphite electrode: Application to antioxidant analysis
Guan H. Tan, Ng Khan Loon, Khor Sook Mei and Lee See Mun
Contents
Introduction
Literature reviews
Objectives
Experimental
Results and discussion
Conclusions
References
IntroductionGraphite-Good electrical conductance -Renewable surface -Chemical inertness -Abundantly available (such as used batteries)
Source from www.pixshark.com
Alpha Carbon
Beta Carbon
Graphite possess a honeycomb laminar structure
The beta carbon of the upper layer is positioned above the cavity, therefore it possesses a free valence electron, which can form Van der Waals interaction with metals (Appy et al., Prog. Surf. Sci., 2014 vol. 89, pp. 219)
Introduction
Limitations with graphite
- High activation overpotential (Wring et al., Analyst, 1992, 117, pp 1215), which limits its application in electroanalysis.
-To overcome this, the surface of the graphite could be modified with nobel metal nanoparticles such as gold and platinum.
Metal Max Oxidation potential (at acidic range, pH 2-5)
Silver 0.4 V
Platinum 1.0 V
Gold 1.4 V
Palladium 0.8 V
Ruthenium 0.8 V
Source : F. Campbell, R. Compton., The use of nanoparticles in electroanalysis: an updated review. Analytical and bioanalytical chemistry, 2010, 396, Pg 241
Anti-oxidant analysis required high oxidation potential window, instead of reduction potential
GoldSilver
Introduction
- 1-step preparation: Auric acid solution and Cyclic voltammetry- High reproducibility with simple control parameter (deposition cycles, and Auric acid concentration)
- Less chemical usage
- Does not require any incubation time.
- Surface can be easily cleaned using tape and re-used.
Anti-oxidant Anti-oxidant compounds are substances that can inhibit oxidation
caused by free radicals, peroxide, and oxygen.
Electron donating
Electro-active compound that could be analyzed using electrochemical method
Anti-Oxidants peroxide
Synthetic Natural
MyricetinQuercetinRutinTocopherol
Propyl gallateButylated hydroxyanisole (BHA)Butylated hydroxytoluene (BHT)Tert-butylhydroquinone (TBHQ)
Introduction
Myricetin - Abundantly available in fruits and vegetables such as grape,
tomato, cabbage and carrot ( Huang et al., Toxicology in vitro. 2010, pp 21)
- Possess anti-oxidant properties, which is significant to health: a) anti-cancer (Shiomi et al., Food Chem., 2013, 139, pp 910)
b) therapeutic potential for diabetes mellitus( Li et al., Food science and human wellness, 2012, pp 19)
Analytical procedure used in the analysis of myricetin in food a)Liquid chromatography (Flores et al., Food Composition and Analysis, 2015, 39 , pp 55) b)Gas chromatography ( Kumar et al., Analytica Chimica Acta, 2009, 631, pp 177)
Accurate and precise method but tedious sample preparation and not possible for field analysis
Alternatively – electrochemical method could provide a rapid, and possible for on-field analysis (screen printed electrode)
Introduction
BHA, BHT and TBHQ Anti-oxidants used as the additives in food
International food safety standards, limit the usage at 200 ppm in edible oil products, biscuits, chewing gum, cream-based products,etc.
CH3
CH3
CH3
CH3
CH3
CH3
CH3
OH
Butylated hydroxytoluene (BHT) OH
O
Butylated hydroxyanisole (BHA)
OH
OH
Tert - Butylhydroquinone (TBHQ)
Safety assessment study – high concentration level in food above 3000 ppm could promote cancer (G. M. Williams, M. J. Iatropoulos, and J. Whysner, Food Chem. Toxicol., 1999, 37, pp 1027)
Introduction
Literature reviewsNo Analyte Sensor type References
1 Ascorbic acid AOx/Au-NPs/Graphite Dodevska et al., 2013
2 Dopamine and uric acid
Pencil graphite Alipour et al., 2013
3 NADH Quercetin modified Pencil graphite
Dilgin et al., 2013
4 Glucose GOx/Au-NPs/Graphite German et al., 2014
5 Lorazepam Polypyrrole/Au-NPs/pencil graphite
Rezaei et al., 2014
6 DNA interaction Topotecan immobilized pencil graphtie
Congur et al., 2015
Significance of the modified graphite electrode studies - Renewable surface ( Ref. 2) - Disposable sensor (Ref.3, 5 and 6) - Improved performance – increase surface area, electrocatalytic, and overpotential (Ref. 1,4, and 5)
AOx: ascorbic oxidase, GOx: glucose oxidase
Literature reviewsNo Analyte Method Sample References
1 Myricetin Abrasive stripping voltammetry not performed Komorsky, S.Novak, Ivana. Electrochimica acta, 2013.
2 BHA Linear sweep voltammetry using gold nanoparticles-PVP-graphene-GCE
Soybean oil, flour
Wang et al., Talanta, 2015.
3 BHA and BHT
Linear sweep voltammetry gold disc electrode
Mineral oil M.Tomaskova et al., Fuel, 2014
4 TBHQ Differential pulse voltammetry using glassy carbon,
Mayonnaise Goulart et al,. Fuel, 2014
5 BHA and BHT
Carbon composite/Cu3PO4
/Polyester resinSoybean bio-diesel
K.Freitas, O. Fatibello., Talanta, 2010
Objectives
The objectives of this research study :
-Fabrication of a graphite electrode from a used battery and surface modification with gold nanoparticles.
-Electrochemical and morphology study of the fabricated working electrode to assess the electrode performance.
-Application of the surface modified working electrode in anti-oxidant analysis and determination in food samples.
Experimental design
ExperimentalFabrication of Au-NPs/graphite
Cleaning – Sonication in UPW and ethanol
Dry in oven at 130 °C
Cyclic voltammetry (electrodeposition)
Surface Activation (0.5 M H2SO4)
Graphite rod, diameter 3mm
PTFE insulation
Surface polish with emery paper and alumina silicate powder
Used battery
1.0 mM HAuCl4
4, 8, 12, 16, 20 and 24 cycles
Experimental – Electrode characterization
- Gold nanoparticles size - Distribution - Element analysis by EDXrF
- Cyclic voltammetry - scan rates study
- Ferri/ferro cyanide redox - Nyquist Plot- Randless-circuit
Buffer and electrolyte optimization. Example Britton-Robinson buffer, Phosphate buffer,
pH optimization
Electrochemical technique -Linear sweep voltammetry-Square wave voltammetry
Method validation - LOD, LOQ, Linearity,
sample analysis
ExperimentalApplication of Au-NPs/graphite electrode
Method development flow
Results and discussionResults and discussions
Results and discussion Gold nanoparticles deposition
0.5497 V
Anodic scan - oxidation
Reduction
Constant peak current – thermodynamic favorable nucleation growth of gold.
Peak potential shifted toward more positive potential suggesting a favorable deposition of the Au on the metal rather than carbon substrate.
0.7109 V
Graphite
8 cycles
16 cycles
Activation of Au-NPs/graphite in 0.5 M H2SO4
suppression in Au oxide formation after 20 CV scan
1st CV scan
20th CV scanReduction of Au Peak
Au-NPs without activation impedes the performance of the Au-NPs/graphite
The CV of the ferri/ferro redox of the activated Au-NPs/graphite showed an improvement in the overpotential (51mV).
activatedinactivated
bare
Peak potential difference (Epa - Epc) / V, activated = 78 mV, Bare and inactivated = 183 mV
Results and discussion
Morphology evaluation with FE-SEM
Bare graphite
8th Deposition cycles
16th Deposition cycles
24th Deposition cyclesA
B
C
D
75 nm
110 nm
180 nm
Au peak
Results and discussion
Electrochemical characterization
Effective surface area (A) (Randless-Sevcik)
Heterogeneous electron transfer (HET)rate (Laviron equation)
Electron transfer resistance
Randless Circuit fitting
(c)
Results and discussion
Electrochemical characterization (cont.)
Activated Au-NPs/graphite
Bare graphite
inactivated Au-NPs/graphite
Nyquist Plot – at16th deposition cycleThe overpotential of the activated Au-NPs/graphite was improved and the measured current was much higher than the bare graphite. The peak separation between the anodic and cathodic is much closer to the theoretical 59.16 mV (Nernst equation).
Anodic potential at 0.3210 V (solid line) shifted to 0.2698 V (dotted line)
0.1M Ferricyanide solution
Results and discussion
Application to anti-oxidant analysis – myricetin
Method: Square wave voltammetry (SWV)
Electrolyte: Britton-Robinson Buffer 0.1M
Highest peak current at pH 2
At 0.0591, n =1 Nernst slope
Results and discussion
Results and discussion
From Nernst equation, it suggests an equal ratio of electron to proton transfer, i.e. n=1.
3 oxidation potential
BA
Oxidation mechanism at peak , 0.4 V
C. Goncalo et. al. J. Mol. Chem., 2010, 16, 863S. Komorsky-Lovrić et. al.,Electrochim. Acta, 2013, 98, 53.
The first oxidation occurs at the 2nd hydroxyl group of pyrogallol group also reported by Goncalo et. al and Komorsky et al.
Application to anti-oxidant analysis – myricetin
Au-NPs /graphite
Bare graphite
Au-NPs/graphite - Improvement in the sensitivity of myricetin analysis.
Au-NPs /graphite
Bare graphite
Results and discussion
SWV of myricetin with concentration increment corresponding to 0.2, 0.4, 0.6, 0.8 and 1.0 µg mL-1 .
The detection limit (LOD)of myricetin = 0.4 µg mL-1
The limit of quantitation (LOQ) was calculated based on 10 times the standard deviation of LOD (n=5).
The LOQ of myricetin = 0.8 µg mL-1
Results and discussion
To test the method accuracy and precision in sample analysis, solutions of myricetin in ethanol were prepared at 0.8 and 1.0 µg mL-1 ( n=5)
Concentration / µg mL-1
SWV Analysis / µg mL-1
Standard error / µg mL-1, (p=0.05)
Recovery (%)
0.80 0.81 0.03 98.31
1.00 1.00 0.03 99.32
Results and discussion
Sample Myricetin /mg Kg-1 RSD / %
Green tea 16.9 4.33
Analysis in green tea samples (n =2)
Other Anti-Oxidants in Food
TBHQ (Tertiary Butyl Hydroquinone) BHA (Butylated Hydroxy Anisole) BHT (Butylated Hydroxy Toluene)
Results and Discussion
TBHQ
BHABHT
Au-NPs/Graphite
Bare graphite
Results and Discussion
BHA
TBHQ
BHT
(b)
64 µg mL-1
4 µg mL-1
(a) BHA
TBHQ
BHT
Blank
Linear sweep voltammetry (LSV) analysis of TBHQ, BHA and BHT standards
Linear correlation of peak current against concentration
SampleTBHQ , mgKg-1 BHA, mg Kg-1 BHT, mg Kg-1
Result Std error Result Std error Result Std errorMargarine - - 55.2 2.3 - -Ghee - - 140.8 3.2 - -Mayonaise - - - - - -
Peanut Butter 33.6 1.2 - - - -Sunflower Oil 190.3 8.3 - - - -Biscuit - - - - - -Corn Oil - - - - - -
Salad Dressing - - 105.0 3.0 - -
Results and Discussion
Analysis of TBHQ, BHA and BHT in food samples using linear sweep voltammetry and Au-NPs/graphite working electrode. (n =5)All within the allowed limits of 200 mg/kg
Conclusions
In this study a gold nanoparticles graphite electrode was successfully fabricated from a used battery graphite.
The electrochemical and morphology characterization showed improvement in the effective surface area, overpotential and heterogeneous electron transfer rate of the Au-NPs/graphite electrode.
It can be inferred that at the 16th deposition cycle the Au-NPs/graphite electrode reached an optimum performance.
The Au-NPs/graphite was successfully applied in the myricetin analysis using square wave voltammetry. The electrode sensitivity was improved by 2.5 fold when compared to the bare graphite. The LOD and LOQ were determined at 1.26 x 10-6 mol L-1 and 2.51 x 10-6
mol L-1
The 3 anti-oxidants can be simultaneously analyzed using the Au-NPs/graphite electrode. It was successfully applied in the determination of TBHQ, BHA, and BHT in some food samples.
Acknowledgment This work was financially supported by :
- The University of Malaya Research Grant (UMRG-Programme RP012C-14SUS/PG177-2014B),
- Fundamental Research Grant Scheme (FRGS) from the Ministry of Higher Education of Malaysia (MOHE) FP014-2013A and FP058-2014A.
Publication
This work has been accepted by the journal of Analytical Sciences:
Khan Loon Ng, See Mun Lee, Sook Mei Khor, Guan Huat Tan. 2015. Electrochemical preparation and characterization of gold nanoparticles graphite electrode: Application to myricetin antioxidant analysis. Analytical Sciences. Accepted for publication. (ISI-Cited Publication)
References
1. S. a. Wring and J. P. Hart, “Chemically modified, carbon-based electrodes and their application as electrochemical sensors for the analysis of biologically important compounds. A review,” Analyst, vol. 117, no. August, p. 1215, 1992.
2. D. Appy, H. Lei, C.-Z. Wang, M. C. Tringides, D.-J. Liu, J. W. Evans, and P. a. Thiel, “Transition metals on the (0001) surface of graphite: Fundamental aspects of adsorption, diffusion, and morphology,” Prog. Surf. Sci., vol. 89, no. 3–4, pp. 219–238, Aug. 2014.
3. T. Hezard, K. Fajerwerg, D. Evrard, V. Collière, P. Behra, and P. Gros, “Gold nanoparticles electrodeposited on glassy carbon using cyclic voltammetry: Application to Hg(II) trace analysis,” J. Electroanal. Chem., vol. 664, pp. 46–52, Jan. 2012.
4. E. Alipour, M. Reza, and A. Saadatirad, “Electrochimica Acta Simultaneous determination of dopamine and uric acid in biological samples on the pretreated pencil graphite electrode,” Electrochim. Acta, vol. 91, pp. 36–42, 2013.
5. Y. Dilgin, B. Kızılkaya, D. G. Dilgin, H. İ. Gökçel, and L. Gorton, “Electrocatalytic oxidation of NADH using a pencil graphite electrode modified with quercetin.,” Colloids Surf. B. Biointerfaces, vol. 102, pp. 816–21, Feb. 2013.
6. B. Rezaei, M. K. Boroujeni, and A. a. Ensafi, “A novel electrochemical nanocomposite imprinted sensor for the determination of lorazepam based on modified polypyrrole@sol-gel@gold nanoparticles/pencil graphite electrode,” Electrochim. Acta, vol. 123, pp. 332–339, Mar. 2014.
7. G. Congur, A. Erdem, and F. Mese, “Bioelectrochemistry Electrochemical investigation of the interaction between topotecan and DNA at disposable graphite electrodes,” Bioelectrochemistry, vol. 102, pp. 21–28, 2015.
8) B. Sultana and F. Anwar, “Flavonols (kaempeferol, quercetin, myricetin) contents of selected fruits, vegetables and medicinal plants,” Food Chem., vol. 108, pp. 879–884, 2008.
9) Y. Li and Y. Ding, “Minireview: Therapeutic Potential of Myricetin in Diabetes Mellitus,” Food Sci. Hum. Wellness, vol. 1, no. 1, pp. 19–25, 2012.
10)G. Flores and M. Luisa, “Journal of Food Composition and Analysis Variations in ellagic acid , quercetin and myricetin in berry cultivars after preharvest methyl jasmonate treatments,” J. Food Compos. Anal., vol. 39, pp. 55–61, 2015.
11)K. Shiomi, I. Kuriyama, H. Yoshida, and Y. Mizushina, “Inhibitory effects of myricetin on mammalian DNA polymerase, topoisomerase and human cancer cell proliferation,” Food Chem., vol. 139, no. 1–4, pp. 910–918, 2013.
12)A. Kumar, A. K. Malik, and D. K. Tewary, “A new method for determination of myricetin and quercetin using solid phase microextraction-high performance liquid chromatography-ultra violet/visible system in grapes, vegetables and red wine samples.,” Anal. Chim. Acta, vol. 631, no. 2, pp. 177–81, Jan. 2009.
13)A. L. Eckermann, D. J. Feld, J. a Shaw, and T. J. Meade, “Electrochemistry of redox-active self-assembled monolayers.,” Coord. Chem. Rev., vol. 254, no. 15–16, pp. 1769–1802, Aug. 2010.
14) Š. Komorsky-Lovrić and I. Novak, “Abrasive stripping voltammetry of myricetin and dihydromyricetin,” Electrochim. Acta, vol. 98, pp. 153–156, May 2013.
References
THANK YOU