Search tips
Search criteria 


Logo of sensorsMDPI Open Access JournalsMDPI Open Access JournalsThis articleThis JournalInstructions for authorssubscribe
Sensors (Basel). 2016 June; 16(6): 747.
Published online 2016 May 24. doi:  10.3390/s16060747
PMCID: PMC4934179

A Fast Strategy for Determination of Vitamin B9 in Food and Pharmaceutical Samples Using an Ionic Liquid-Modified Nanostructure Voltammetric Sensor

Xiangqun Zeng, Academic Editor, Michael T. Carter, Academic Editor, and Abdul Rehman, Academic Editor


Vitamin B9 or folic acid is an important food supplement with wide clinical applications. Due to its importance and its side effects in pregnant women, fast determination of this vitamin is very important. In this study we present a new fast and sensitive voltammetric sensor for the analysis of trace levels of vitamin B9 using a carbon paste electrode (CPE) modified with 1,3-dipropylimidazolium bromide (1,3-DIBr) as a binder and ZnO/CNTs nanocomposite as a mediator. The electro-oxidation signal of vitamin B9 at the surface of the 1,3-DIBr/ZnO/CNTs/CPE electrode appeared at 800 mV, which was about 95 mV less positive compared to the corresponding unmodified CPE. The oxidation current of vitamin B9 by square wave voltammetry (SWV) increased linearly with its concentration in the range of 0.08–650 μM. The detection limit for vitamin B9 was 0.05 μM. Finally, the utility of the new 1,3-DIBr/ZnO/CNTs/CPE electrode was tested in the determination of vitamin B9 in food and pharmaceutical samples.

Keywords: vitamin B9, ZnO/CNTs, ionic liquids, modified electrode

1. Introduction

Interest in voltammetric sensors for fast analysis has increased in the recent years [1,2,3,4,5], but the high overvoltage and low electrical signal of electroactive compounds, especially in food, pharmaceutical, biological and environmental samples, is problematic for the application of voltammetric sensors [6,7,8,9,10,11,12]. Modified electrodes have been used as voltammetric sensors with good ability for trace level analysis [13,14,15,16,17,18,19,20]. Ionic liquids (ILs) have some unique properties, such as a low vapor pressure, good thermal stability, high polarity, tunable viscosity and an ability to dissolve many compounds, a wide electrochemical window, high conductivity, high heat capacity and they can act as solvents available to control reactions. ILs represent a new class of conductive binders and mediators for the modification of electrodes for trace analysis [21,22,23,24]. In general, the structure of an IL and its high conductivity at a surface of electrodes are extremely important for evaluating and selecting ionic liquids, especially room temperature ionic liquids, for electrochemical applications [25,26,27,28,29,30].

Nanotechnology and nanoscience represent new and enabling platforms that promise to provide a broad range of novel uses and improved technologies for environmental, biological and other scientific applications [31,32,33,34,35,36,37,38,39]. Nanomaterials have been another acceptable choice for the modification of electrochemical sensors in recent years [40,41,42,43,44,45]. These kinds of materials display high conductivity and have been used in different fields to increase the efficiency of electrochemical sensors in trace level analysis [46,47,48].

Vitamin B9 (folic acid) is a water soluble vitamin that is very important for the production and maintenance of new cells. In the human body it is necessary for make normal red blood cells and to prevent anemia [49]. There is also some evidence that sufficient folic acid in the diet can reduce the risk of heart disease, although this evidence is based on population studies and not on more definitive clinical trials, so there is no definitive evidence that taking folic acid supplements would help in this respect.

Many analytical methods have been reported for the analysis of vitamin B9, including electrochemical sensors [50,51,52], spectrophotometry [53], chemiluminescence [54], Capillary electrophoresis [55] and HPLC [56]. In this project, we have developed a simple and fast method for the synthesis of ZnO/CNTs nanocomposite and its application for the preparation of electrochemical sensors in the presence of 1,3-DIBr as a high conductive IL binder. Next, the analytical performance of the novel 1,3-DIBr/ZnO/CNTs/CPE electrode was checked in the square wave voltammetric electro-oxidation of vitamin B9 in food and pharmaceutical samples. The obtained results showed the superiority of 1,3-DIBr/ZnO/CNTs/CPE over unmodified electrodes in terms of better reversibility and higher sensitivity.

2. Experimental Section

2.1. Apparatus and Chemicals

Vitamin B9 (>97%) was obtained from Sigma-Aldrich (CAS Number 59-30-3, St. Louis, MS, USA) and graphite powder (<50 µm) and paraffin oil for the preparation of carbon paste electrode were obtained from Merck (Darmstadt, Germany). A stock 0.001 M solution of vitamin B9 was prepared by dissolving 0.015 g vitamin B9 in 100 mL of buffer solution. Phosphate buffer solutions (PBS) with different pH values were used for optimization of pH. Square wave and linear sweep voltammetric investigation were performed using a μ-Autolab potentiostat/galvanostat (Eco Chemie, Utrecht, The Netherlands) connected to a three-electrode cell. An Ag/AgCl/KClsat electrode, a platinum wire, and the novel 1,3-DIBr/ZnO/CNTs/CPE electrode were used as the reference, auxiliary and working electrodes, respectively. Scanning electron microscopy (KYKY-EM3200 Digital Scanning Electron Microscope, KYKY Technology Development Ltd., Beijing, China) was used for morphological investigation. X-ray powder diffraction studies were carried out using a STOE diffractometer (EQuniox 3000, Inel, France) with Cu-Kα radiation (k = 1.54 Å). ZnO/CNTs and 1,3-DIBr were synthesized according to previous published papers [17,57].

2.2. Preparation of the Electrode

1,3-DIBr/ZnO/CNTs/CPE was prepared by mixing 1,3-dipropylimidazolium bromide (1,3-DIBr 0.25 g), paraffin oil (0.75 g), ZnO/CNTs (0.1 g), and graphite powder (0.9 g). Next, the mixture was mixed well for 75 min until a uniformly wetted paste was obtained. A portion of the paste was firmly pressed into a glass tube to prepare the 1,3-DIBr/ZnO/CNTs/CPE electrode.

2.3. Preparation of Real Samples

Mint leaves (6 g) were extracted with 0.1 M pH 9.0 phosphate buffer (100 mL) and 0.1% (v/v) 2-mercaptoethanol (0.06 g), then the thus obtained mixture was shaken for 50 min in a rotational shaker, and centrifuged at 3500 rpm for 20 min. Finally, the obtained solution filtered with a 47 mm filter (Millipore, Boston, MA, USA). For pharmaceutical analysis, five commercial vitamin B9 tablets (50.0 mg per tablet) were completely ground and homogenized. Next, suitable amounts of the powders was accurately weighed and dissolved in 100 mL of buffer solution, and the mixture was filtered through a 42 mm filter. Fortified juice samples were obtained from local supermarkets and then centrifuged for 20 min at 2000 rpm. The supernatant was filtered using a 42 mm filter and the filtrate used for the real sample analysis.

3. Results and Discussion

3.1. ZnO/CNTs Characterization

Figure 1A shows the XRD pattern for the synthesized ZnO/CNTs nanocomposite over a 2θ range of 20°–80°. XRD pattern (Figure 1) confirmed that the synthesized materials were ZnO [56]. The peak at ~26 can be nicely indexed to the (002) plane of CNTs as marked with star in Figure 1A. Also, as can be seen in Figure 1B, the outside surface of the carbon nanotubes is uniformly dotted with ZnO nanostructures, which is in agreement with results obtained from the XRD pattern.

Figure 1
(A) XRD pattern of ZnO/CNTs nanocomposite; (B) SEM images of ZnO/CNTs nanocomposite.

3.2. Voltammetric Investigation

In the first step we investigated the effect of pH on the electro-oxidation of vitamin B9 using the SWV technique (Figure 2 insert). As can be seen, the vitamin B9 peak current increased regularly from pH 6.0 to 9.0, and then conversely the current decreased when the pH value increased further from 9.0 to 11.0 (Figure 2). Therefore pH 9.0 was chosen as the optimal experimental condition for other experiments. The relationship between the oxidation peak potential and pH was also determined.

Figure 2
Plot of peak current (Ipa) vs. changing in pH value for the electro-oxidation of 100 µΜ vitamin B9 at a surface of 1,3-DIBr/ZnO/CNTs/CPE. Inset: influence of pH on square wave voltammograms of vitamin B9 at the surface of the modified ...

A linear shift of Epa towards negative potential with increasing pH can be obtained, which fitted the regression equation Epa (V) = −0.057pH + 0.985, indicating that protons are directly involved in the oxidation of vitamin B9. A slope of 57 mV/pH suggests that the number of electrons transferred is equal to the number of protons involved in the electrode reaction [39]. The current density results are shown in the insert of Figure 3 for different electrodes. The results confirmed that the joint presence of ZnO/CNTs and 1,3-DIBr causes an increase in the electrode conductivity. In order to establish a good sensitivity and highly selective electrochemical sensor for the detection of vitamin B9 with ZnO/CNTs and 1,3-DIBr as the electron mediators, we first investigated the voltammetric behavior of vitamin B9 at the surface of different electrodes. The results indicated that the oxidation peak currents of vitamin B9 at 1,3-DIBr/ZnO/CNTs/CPE can be significantly enhanced, so it’s replacement for bare CPE, ZnO/CNTs/CPE and 1,3-DIBr/CPE was subsequently exploited as an electrochemical sensor for effective sensing of vitamin B9. As also seen from this figure, the electro-oxidation peak potential of vitamin B9 at the surface of the 1,3-DIBr/ZnO/CNTs/CPE appeared at 800 mV, which was about 95 mV lower than the oxidation peak potential at the surface of the bare CPE under similar conditions. At the same time, the electro-oxidation peak current was increased by ~2.83 times at the 1,3-DIBr/ZnO/CNTs/CPE surface compared to CPE.

Figure 3
Square wave voltammograms of (a) 1,3-DIBr/ZnO/CNTs/CPE; (b) 1,3-DIBr/CPE; (c) ZnO/CNTs/CPE and (d) CPE in presence of 100 μM vitamin B9 at pH 9.0, respectively. Inset: The current density derived from square wave voltammograms responses of 100 ...

Figure 4 shows the effect of scan rate (υ) on the electro-oxidation of vitamin B9 under the optimum conditions. The results show that the peak current increased linearly as the square root of scan rate increased over a range of 10 to 100 mV/s. This result shows that the electrode process for oxidation of vitamin B9 is controlled by a diffusion step.

Figure 4
Plot of Ipa vs. ν1/2 for the oxidation of vitamin B9 at 1,3-DIBr/ZnO/CNTs/CPE. Inset shows linear sweep voltammograms of vitamin B9 at 1,3-DIBr/ZnO/CNTs/CPE at different scan rates of (a) 10; (b) 25; (c) 60 and (d) 100 mV/s in 0.1 M phosphate ...

The value of α was obtained from a Tafel plot (Figure 5). The slope of the Tafel plot is equal to 2.3RT/n (1 − α) F which comes up to 0.1686 Vdecade−1. We obtained α as 0.82. On the other hand, we obtained the value of (α) 0.22 at a surface of a bare electrode. These values clearly show that not only is the overpotential for vitamin B9 oxidation reduced at the surface of 1,3-DIBr/ZnO/CNTs/CPE, but also the rate of the electron transfer process is greatly enhanced, a phenomenon confirmed by the larger Ipa values recorded during the voltammetric responses at 1,3-DIBr/ZnO/CNTs/CPE.

Figure 5
Tafel plot for 1,3-DIBr/ZnO/CNTs/CPE in 0.1 M PBS (pH 9.0) with a scan rate of 10 mV/s in the presence of vitamin B9.

A chronoamperometric method was used for determination of the diffusion coefficient (D; can be obtained from slope of Cottrell plots) of vitamin B9 using the data derived from the raising part of the current-voltage curve (Figure 6A). From the result of Figure 6B and the Cottrell equation the mean value of the D was found to be 1.65 × 10−6 cm2/s.

Figure 6
(A) Chronoamperograms obtained at 1,3-DIBr/ZnO/CNTs/CPE in the presence of (line a) 300 and (line b) 400 μM vitamin B9 in the buffer solution (pH 9.0); (B) Cottrell plot for the data from the chronoamperograms.

3.3. Analytical Parameters for Determination of Vitamin B9

SWV was used for the sensitive determination of vitamin B9 at the 1,3-DIBr/ZnO/CNTs/CPE electrode because of its higher current sensitivity. The quantitative evaluation was based on a linear correlation between the peak currents and the concentration added, resulting in a good correlation. The equation for the measurement of vitamin B9 was Ip(A) = 0.2058 C + 4.2628 (in the range 0.08–650 μM) with a correlation coefficient of R2 = 0.9975. The detection limit was determined at 0.05 μM vitamin B9 according to the definition of YLOD = YB + 3σ. This value of the detection limit and the linear dynamic range for vitamin B9 observed on the 1,3-DIBr/ZnO/CNTs/CPE electrode are comparable and even better than those obtained for other modified electrodes (Table 1).

Table 1
Comparison of the efficiency of some electrochemical methods in the determination of vitamin B9.

3.4. Stability and Reproducibility

The repeatability and stability of 1,3-DIBr/ZnO/CNTs/CPE was investigated by square wave voltammetry measurements of 5.0 µM vitamin B9. The relative standard deviation (RSD%) for eleven successive assays was 1.5%. When using ten different electrodes, the RSD% for eleven measurements was 2.1%. When the 1,3-DIBr/ZnO/CNTs/CPE electrode is stored in the laboratory, it retains 96% of its initial response after 5 days and 94% after 30 days (Figure 7). These results indicate that 1,3-DIBr/ZnO/CNTs/CPE has good stability and reproducibility, and could be used for vitamin B9 analysis.

Figure 7
Square wave voltammograms of 1,3-DIBr/ZnO/CNTs/CPE in the presence of 100 μM vitamin B9 at a pH 9.0 at a different times.

3.5. Interference Study

For a successful voltammetric sensor for the detection of vitamin B9 in food and pharmaceutical samples, good selectivity and high sensitivity are the two most important requirements. To assess the selectivity of the 1,3-DIBr/ZnO/CNTs/CPE, some potential interferents were investigated in the presence of 10.0 μM vitamin B9. As can be seen in Table 2, the 1,3-DIBr/ZnO/CNTs/CPE has a good selectivity for the determination of vitamin B9.

Table 2
Interference study for the determination of 10.0 µM vitamin B9.

3.6. Real Sample Analysis

For the purposes of this study, vitamin B9 was electrochemically measured with the developed voltammetric sensor in vitamin B9 tablets and food samples. The data obtained by the proposed method was compared with a published method too [39] (see Table 3; a modified carbon paste electrode prepared with N-hexyl-3-methylimidazolium hexafluorophosphate and Pt:Co was used for comparing the obtained data). As can be seen from Table 3, the amounts of vitamin B9 determined by our 1,3-DIBr/ZnO/CNTs/CPE electrode in real samples were very similar to the labelled amount and there was no difference at the 95% confidence level (paired t test; n = 3) when compared with the published method [39]. Therefore, the 1,3-DIBr/ZnO/CNTs/CPE is very suitable for the voltammetric determination of vitamin B9 in real samples.

Table 3
Determination of vitamin B9 in real samples (n = 3).

4. Conclusions

In the present work, the combination of the features of ZnO/CNTs nanocomposite and 1,3-dipropylimidazolium bromide were exploited for the development of a voltammetric sensor for the determination of vitamin B9. The developed voltammetric sensor based on carbon nanotubes-ionic liquid composite was shown to be simple, quick to prepare, reproducible, stable and precise for the voltammetric determination of vitamin B9. The new 1,3-DIBr/ZnO/CNTs/CPE electrode was successfully used for the determination of vitamin B9 in some food and pharmaceutical samples.


The authors wish to thank The Health of Plant and Livestock Products Research Center, Mazandaran University of Medical Sciences, Sari, Iran for their support.

Author Contributions

Author Contributions

Fatemeh Khaleghi had done experimental analysis for this work. Roya Sadeghi synthesized the ZnO/CNTs nanocomposite. Yangping Wen suggests the idea of the work. Elyasi Irai help to financial support and some of experimental part and Vinod K. Gupta revised the English language. All authors of article provided substantive comments.

Conflicts of Interest

Conflicts of Interest

The authors declare no conflict of interest.


1. Karimi-Maleh H., Tahernejad-Javazmi F., Ensafi A.A., Moradi R., Mallakpour S., Beitollahi H. A high sensitive biosensor based on fept/cnts nanocomposite/N-(4-hydroxyphenyl)-3,5-dinitrobenzamide modified carbon paste electrode for simultaneous determination of glutathione and piroxicam. Biosens. Bioelectron. 2014;60:1–7. doi: 10.1016/j.bios.2014.03.055. [PubMed] [Cross Ref]
2. Karimi-Maleh H., Biparva P., Hatami M. A novel modified carbon paste electrode based on nio/cnts nanocomposite and (9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)-4-ethylbenzene-1,2-diol as a mediator for simultaneous determination of cysteamine, nicotinamide adenine dinucleotide and folic acid. Biosens. Bioelectron. 2013;48:270–275. [PubMed]
3. Eren T., Atar N., Yola M.L., Karimi-Maleh H. A sensitive molecularly imprinted polymer based quartz crystal microbalance nanosensor for selective determination of lovastatin in red yeast rice. Food Chem. 2015;185:430–436. doi: 10.1016/j.foodchem.2015.03.153. [PubMed] [Cross Ref]
4. Sanghavi B.J., Mobin S.M., Mathur P., Lahiri G.K., Srivastava A.K. Biomimetic sensor for certain catecholamines employing copper (II) complex and silver nanoparticle modified glassy carbon paste electrode. Biosens. Bioelectron. 2013;39:124–132. doi: 10.1016/j.bios.2012.07.008. [PubMed] [Cross Ref]
5. Mobin S.M., Sanghavi B.J., Srivastava A.K., Mathur P., Lahiri G.K. Biomimetic sensor for certain phenols employing a copper (II) complex. Anal. Chem. 2010;82:5983–5992. doi: 10.1021/ac1004037. [PubMed] [Cross Ref]
6. Yaghoubian H., Karimi-Maleh H., Khalilzadeh M.A., Karimi F. Electrocatalytic oxidation of levodopa at a ferrocene modified carbon nanotube paste electrode. Int. J. Electrochem. Sci. 2009;4:993–1003.
7. Raoof J.B., Ojani R., Karimi-Maleh H. Carbon paste electrode incorporating 1-[4-(ferrocenyl ethynyl) phenyl]-1-ethanone for electrocatalytic and voltammetric determination of tryptophan. Electroanalysis. 2008;20:1259–1262. doi: 10.1002/elan.200704176. [Cross Ref]
8. Yola M.L., Atar N., Eren T., Karimi-Maleh H., Wang S. Sensitive and selective determination of aqueous triclosan based on gold nanoparticles on polyoxometalate/reduced graphene oxide nanohybrid. RSC Adv. 2015;5:65953–65962. doi: 10.1039/C5RA07443F. [Cross Ref]
9. Atar N., Eren T., Yola M.L., Karimi-Maleh H., Demirdögen B. Magnetic iron oxide and iron oxide@ gold nanoparticle anchored nitrogen and sulfur-functionalized reduced graphene oxide electrocatalyst for methanol oxidation. RSC Adv. 2015;5:26402–26409. doi: 10.1039/C5RA03735B. [Cross Ref]
10. Ensafi A.A., Karimi-Maleh H., Mallakpour S., Hatami M. Simultaneous determination of N-acetylcysteine and acetaminophen by voltammetric method using N-(3, 4-dihydroxyphenethyl)-3, 5-dinitrobenzamide modified multiwall carbon nanotubes paste electrode. Sens. Actuators B Chem. 2011;155:464–472. doi: 10.1016/j.snb.2010.12.048. [Cross Ref]
11. Sanghavi B.J., Hirsch G., Karna S.P., Srivastava A.K. Potentiometric stripping analysis of methyl and ethyl parathion employing carbon nanoparticles and halloysite nanoclay modified carbon paste electrode. Anal. Chim. Acta. 2012;735:37–45. doi: 10.1016/j.aca.2012.05.029. [PubMed] [Cross Ref]
12. Sanghavi B.J., Sitaula S., Griep M.H., Karna S.P., Ali M.F., Swami N.S. Real-time electrochemical monitoring of adenosine triphosphate in the picomolar to micromolar range using graphene-modified electrodes. Anal. Chem. 2013;85:8158–8165. doi: 10.1021/ac4011205. [PMC free article] [PubMed] [Cross Ref]
13. Moradi R., Sebt S., Karimi-Maleh H., Sadeghi R., Karimi F., Bahari A., Arabi H. Synthesis and application of FePt/CNTs nanocomposite as a sensor and novel amide ligand as a mediator for simultaneous determination of glutathione, nicotinamide adenine dinucleotide and tryptophan. Phys. Chem. Chem. Phys. 2013;15:5888–5897. doi: 10.1039/c3cp00033h. [PubMed] [Cross Ref]
14. Shahmiri M.R., Bahari A., Karimi-Maleh H., Hosseinzadeh R., Mirnia N. Ethynylferrocene-NiO/MWCNT nanocomposite modified carbon paste electrode as a novel voltammetric sensor for simultaneous determination of glutathione and acetaminophen. Sens. Actuators B Chem. 2013;177:70–77. doi: 10.1016/j.snb.2012.10.098. [Cross Ref]
15. Afsharmanesh E., Karimi-Maleh H., Pahlavan A., Vahedi J. Electrochemical behavior of morphine at zno/cnt nanocomposite room temperature ionic liquid modified carbon paste electrode and its determination in real samples. J. Mol. Liq. 2013;181:8–13. doi: 10.1016/j.molliq.2013.02.002. [Cross Ref]
16. Ensafi A.A., Karimi-Maleh H. Modified multiwall carbon nanotubes paste electrode as a sensor for simultaneous determination of 6-thioguanine and folic acid using ferrocenedicarboxylic acid as a mediator. J. Electroanal. Chem. 2010;640:75–83. doi: 10.1016/j.jelechem.2010.01.010. [Cross Ref]
17. Bavandpour R., Karimi-Maleh H., Asif M., Gupta V.K., Atar N., Abbasghorbani M. Liquid phase determination of adrenaline uses a voltammetric sensor employing CuFe2O4 nanoparticles and room temperature ionic liquids. J. Mol. Liq. 2016;213:369–373. doi: 10.1016/j.molliq.2015.07.054. [Cross Ref]
18. Beitollah H., Goodarzian M., Khalilzadeh M.A., Karimi-Maleh H., Hassanzadeh M., Tajbakhsh M. Electrochemical behaviors and determination of carbidopa on carbon nanotubes ionic liquid paste electrode. J. Mol. Liq. 2012;173:137–143. doi: 10.1016/j.molliq.2012.06.026. [Cross Ref]
19. Zhao Y., Gao Y., Zhan D., Liu H., Zhao Q., Kou Y., Shao Y., Li M., Zhuang Q., Zhu Z. Selective detection of dopamine in the presence of ascorbic acid and uric acid by a carbon nanotubes-ionic liquid gel modified electrode. Talanta. 2005;66:51–57. doi: 10.1016/j.talanta.2004.09.019. [PubMed] [Cross Ref]
20. Tavana T., Khalilzadeh M.A., Karimi-Maleh H., Ensafi A.A., Beitollahi H., Zareyee D. Sensitive voltammetric determination of epinephrine in the presence of acetaminophen at a novel ionic liquid modified carbon nanotubes paste electrode. J. Mol. Liq. 2012;168:69–74. doi: 10.1016/j.molliq.2012.01.009. [Cross Ref]
21. Elyasi M., Khalilzadeh M.A., Karimi-Maleh H. High sensitive voltammetric sensor based on Pt/CNTs nanocomposite modified ionic liquid carbon paste electrode for determination of Sudan I in food samples. Food Chem. 2013;141:4311–4317. doi: 10.1016/j.foodchem.2013.07.020. [PubMed] [Cross Ref]
22. Najafi M., Khalilzadeh M.A., Karimi-Maleh H. A new strategy for determination of bisphenol A in the presence of Sudan I using a ZnO/CNTs/ionic liquid paste electrode in food samples. Food Chem. 2014;158:125–131. doi: 10.1016/j.foodchem.2014.02.082. [PubMed] [Cross Ref]
23. Sun W., Yang M., Jiao K. Electrocatalytic oxidation of dopamine at an ionic liquid modified carbon paste electrode and its analytical application. Anal. Bioanal. Chem. 2007;389:1283–1291. doi: 10.1007/s00216-007-1518-2. [PubMed] [Cross Ref]
24. Safavi A., Maleki N., Moradlou O., Tajabadi F. Simultaneous determination of dopamine, ascorbic acid, and uric acid using carbon ionic liquid electrode. Anal. Biochem. 2006;359:224–229. doi: 10.1016/j.ab.2006.09.008. [PubMed] [Cross Ref]
25. Bijad M., Karimi-Maleh H., Khalilzadeh M.A. Application of ZnO/CNTs nanocomposite ionic liquid paste electrode as a sensitive voltammetric sensor for determination of ascorbic acid in food samples. Food Anal. Methods. 2013;6:1639–1647. doi: 10.1007/s12161-013-9585-9. [Cross Ref]
26. Baghizadeh A., Karimi-Maleh H., Khoshnama Z., Hassankhani A., Abbasghorbani M. A voltammetric sensor for simultaneous determination of vitamin C and vitamin B6 in food samples using ZrO2 nanoparticle/ionic liquids carbon paste electrode. Food Anal. Methods. 2015;8:549–557. doi: 10.1007/s12161-014-9926-3. [Cross Ref]
27. Arabali V., Ebrahimi M., Abbasghorbani M., Gupta V.K., Farsi M., Ganjali M., Karimi F. Electrochemical determination of vitamin C in the presence of NADH using a CdO nanoparticle/ionic liquid modified carbon paste electrode as a sensor. J. Mol. Liq. 2016;213:312–316. doi: 10.1016/j.molliq.2015.10.001. [Cross Ref]
28. Shayeh J.S., Ehsani A., Ganjali M., Norouzi P., Jaleh B. Conductive polymer/reduced graphene oxide/Au nanoparticles as efficient composite materials in electrochemical supercapacitors. Appl. Surf. Sci. 2015;353:594–599. doi: 10.1016/j.apsusc.2015.06.066. [Cross Ref]
29. Tizfahm J., Aghazadeh M., Maragheh M.G., Ganjali M.R., Norouzi P., Faridbod F. Electrochemical preparation and evaluation of the supercapacitive performance of MnO2 nanoworms. Mater. Lett. 2016;167:153–156. doi: 10.1016/j.matlet.2015.12.158. [Cross Ref]
30. Aghazadeh M., Maragheh M.G., Ganjali M.R., Norouzi P., Faridbod F. Electrochemical preparation of MnO2 nanobelts through pulse base-electrogeneration and evaluation of their electrochemical performance. Appl. Surf. Sci. 2016;364:141–147. doi: 10.1016/j.apsusc.2015.12.146. [Cross Ref]
31. Naderi H.R., Norouzi P., Ganjali M.R. Electrochemical study of a novel high performance supercapacitor based on MnO2/nitrogen-doped graphene nanocomposite. Appl. Surf. Sci. 2016;366:552–560. doi: 10.1016/j.apsusc.2016.01.058. [Cross Ref]
32. Ganjali M.R., Larijani B., Pourbasheer E. Fabrication of an all solid state (ASS) polymeric membrane sensor (PME) for tramadol and its application. Int. J. Electrochem. Sci. 2016;11:2119–2129.
33. Aghazadeh M., Asadi M., Maragheh M.G., Ganjali M.R., Norouzi P., Faridbod F. Facile preparation of MnO2 nanorods and evaluation of their supercapacitive characteristics. Appl. Surf. Sci. 2016;364:726–731. doi: 10.1016/j.apsusc.2015.12.227. [Cross Ref]
34. Aghazadeh M., Maragheh M.G., Ganjali M., Norouzi P. One-step electrochemical preparation and characterization of nanostructured hydrohausmannite as electrode material for supercapacitors. RSC Adv. 2016;6:10442–10449. doi: 10.1039/C5RA20498D. [Cross Ref]
35. Ariga K., Yamauchi Y., Ji Q., Yonamine Y., Hill J.P. Research update: Mesoporous sensor nanoarchitectonics. APL Mater. 2014;2 doi: 10.1063/1.4868177. [Cross Ref]
36. Nakanishi W., Minami K., Shrestha L.K., Ji Q., Hill J.P., Ariga K. Bioactive nanocarbon assemblies: Nanoarchitectonics and applications. Nano Today. 2014;9:378–394. doi: 10.1016/j.nantod.2014.05.002. [Cross Ref]
37. Goyal R.N., Gupta V.K., Chatterjee S. Simultaneous determination of adenosine and inosine using single-wall carbon nanotubes modified pyrolytic graphite electrode. Talanta. 2008;76:662–668. doi: 10.1016/j.talanta.2008.04.011. [PubMed] [Cross Ref]
38. Goyal R.N., Gupta V.K., Chatterjee S. Voltammetric biosensors for the determination of paracetamol at carbon nanotube modified pyrolytic graphite electrode. Sens. Actuators B Chem. 2010;149:252–258. doi: 10.1016/j.snb.2010.05.019. [Cross Ref]
39. Jamali T., Karimi-Maleh H., Khalilzadeh M.A. A novel nanosensor based on Pt:Co nanoalloy ionic liquid carbon paste electrode for voltammetric determination of vitamin B9 in food samples. LWT-Food Sci. Technol. 2014;57:679–685. doi: 10.1016/j.lwt.2014.01.023. [Cross Ref]
40. Ariga K., Li J., Fei J., Ji Q., Hill J.P. Nanoarchitectonics for dynamic functional materials from atomic-/molecular-level manipulation to macroscopic action. Adv. Mater. 2016;28:1251–1286. doi: 10.1002/adma.201502545. [PubMed] [Cross Ref]
41. Ariga K., Ishihara S., Abe H., Li M., Hill J.P. Materials nanoarchitectonics for environmental remediation and sensing. J. Mater. Chem. 2012;22:2369–2377. doi: 10.1039/C1JM14101E. [Cross Ref]
42. Karimi-Maleh H., Ahanjan K., Taghavi M., Ghaemy M. A novel voltammetric sensor employing zinc oxide nanoparticles and a new ferrocene-derivative modified carbon paste electrode for determination of captopril in drug samples. Anal. Methods. 2016;8:1780–1788. doi: 10.1039/C5AY03284A. [Cross Ref]
43. Karimi-Maleh H., Tahernejad-Javazmi F., Atar N., Yola M.L.T., Gupta V.K., Ensafi A.A. A novel DNA biosensor based on a pencil graphite electrode modified with polypyrrole/functionalized multiwalled carbon nanotubes for determination of 6-mercaptopurine anticancer drug. Ind. Eng. Chem. Res. 2015;54:3634–3639. doi: 10.1021/ie504438z. [Cross Ref]
44. Jafari S., Faridbod F., Norouzi P., Dezfuli A.S., Ajloo D., Mohammadipanah F., Ganjali M.R. Detection of aeromonas hydrophila DNA oligonucleotide sequence using a biosensor design based on ceria nanoparticles decorated reduced graphene oxide and fast Fourier transform square wave voltammetry. Anal. Chim. Acta. 2015;895:80–88. doi: 10.1016/j.aca.2015.05.055. [PubMed] [Cross Ref]
45. Alizadeh T., Ganjali M.R., Akhoundian M., Norouzi P. Voltammetric determination of ultratrace levels of Cerium (III) using a carbon paste electrode modified with nano-sized cerium-imprinted polymer and multiwalled carbon nanotubes. Microchim. Acta. 2016;183:1123–1130. doi: 10.1007/s00604-015-1702-6. [Cross Ref]
46. Karimi-Maleh H., Rostami S., Gupta V.K., Fouladgar M. Evaluation of ZnO nanoparticle ionic liquid composite as a voltammetric sensing of isoprenaline in the presence of aspirin for liquid phase determination. J. Mol. Liq. 2015;201:102–107. doi: 10.1016/j.molliq.2014.10.042. [Cross Ref]
47. Cheraghi S., Taher M.A., Karimi-Maleh H. A novel strategy for determination of paracetamol in the presence of morphine using a carbon paste electrode modified with CdO nanoparticles and ionic liquids. Electroanalysis. 2016;28:366–371. doi: 10.1002/elan.201500357. [Cross Ref]
48. Atta N.F., El-Kady M.F., Galal A. Simultaneous determination of catecholamines, uric acid and ascorbic acid at physiological levels using poly(N-methylpyrrole)/Pd-nanoclusters sensor. Anal. Biochem. 2010;400:78–88. doi: 10.1016/j.ab.2010.01.001. [PubMed] [Cross Ref]
49. Atta N.F., El-Kady M.F., Galal A. Palladium nanoclusters-coated polyfuran as a novel sensor for catecholamine neurotransmitters and paracetamol. Sens. Actuators B Chem. 2009;141:566–574. doi: 10.1016/j.snb.2009.07.002. [Cross Ref]
50. Taherkhani A., Jamali T., Hadadzadeh H., Karimi-Maleh H., Beitollahi H., Taghavi M., Karimi F. ZnO nanoparticle-modified ionic liquid-carbon paste electrode for voltammetric determination of folic acid in food and pharmaceutical samples. Ionics. 2014;20:421–429. doi: 10.1007/s11581-013-0992-0. [Cross Ref]
51. Unnikrishnan B., Yang Y.-L., Chen S.-M. Amperometric determination of folic acid at multi-walled carbon nanotube-polyvinyl sulfonic acid composite film modified glassy carbon electrode. Int. J. Electrochem. Sci. 2011;6:3224–3237.
52. Xiao F., Ruan C., Liu L., Yan R., Zhao F., Zeng B. Single-walled carbon nanotube-ionic liquid paste electrode for the sensitive voltammetric determination of folic acid. Sens. Actuators B Chem. 2008;134:895–901. doi: 10.1016/j.snb.2008.06.037. [Cross Ref]
53. Nagaraja P., Vasantha R.A., Yathirajan H.S. Spectrophotometric determination of folic acid in pharmaceutical preparations by coupling reactions with iminodibenzyl or 3-aminophenol or sodium molybdate-pyrocatechol. Anal. Biochem. 2002;307:316–321. doi: 10.1016/S0003-2697(02)00038-6. [PubMed] [Cross Ref]
54. Song Z., Zhou X. Chemiluminescence flow sensor for folic acid with immobilized reagents. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2001;57:2567–2574. doi: 10.1016/S1386-1425(01)00441-3. [PubMed] [Cross Ref]
55. Zhao S., Yuan H., Xie C., Xiao D. Determination of folic acid by capillary electrophoresis with chemiluminescence detection. J. Chromatogr. A. 2006;1107:290–293. doi: 10.1016/j.chroma.2005.11.052. [PubMed] [Cross Ref]
56. Amidžić R., Brborić J.S., Čudina O.A., Vladimirov S.M. Rp-HPLC determination of vitamins, folic acid and B12 in multivitamin tablets. J. Serb. Chem. Soc. 2005;70:1229–1235. doi: 10.2298/JSC0510229A. [Cross Ref]
57. Sadeghi R., Karimi-Maleh H., Bahari A., Taghavi M. A novel biosensor based on ZnO nanoparticle/1,3-dipropylimidazolium bromide ionic liquid-modified carbon paste electrode for square-wave voltammetric determination of epinephrine. Phys. Chem. Liq. 2013;51:704–714. doi: 10.1080/00319104.2013.782547. [Cross Ref]
58. Wan Q., Yang N. The direct electrochemistry of folic acid at a 2-mercaptobenzothiazole self-assembled gold electrode. J. Electroanal. Chem. 2002;527:131–136. doi: 10.1016/S0022-0728(02)00836-7. [Cross Ref]
59. Arvand M., Dehsaraei M. A simple and efficient electrochemical sensor for folic acid determination in human blood plasma based on gold nanoparticles-modified carbon paste electrode. Mater. Sci. Eng. C. 2013;33:3474–3480. doi: 10.1016/j.msec.2013.04.037. [PubMed] [Cross Ref]

Articles from Sensors (Basel, Switzerland) are provided here courtesy of Multidisciplinary Digital Publishing Institute (MDPI)