A surfactant enhanced novel pencil graphite and carbon nanotube composite paste material as an effective electrochemical sensor for determination of riboflavin

Original ArticleA surfactant enhanced novel pencil graphite and carbon nanotube composite paste material as an effective electrochemical sensor for Department of Chemistry, FMKMC College

Original Article

A surfactant enhanced novel pencil graphite and carbon nanotube

composite paste material as an effective electrochemical sensor for

Department of Chemistry, FMKMC College, Madikeri, Constituent College of Mangalore University, Karnataka, India

a r t i c l e i n f o

Article history:

Received 11 September 2019

Received in revised form

25 October 2019

Accepted 1 November 2019

Available online xxx

Keywords:

Sodium lauryl sulphate

Carbon nanotubes

Pencil graphite paste electrode

Riboflavin

Dopamine

a b s t r a c t

A novel sensor fabrication using anionic surfactant sodium lauryl sulphate modified carbonnanotube and pencil graphite composite paste electrode (SLSMCNTPGCPE) is prepared and characterized using Field Emission Scanning Electron Microscope (FE-SEM) and Cyclic Voltammetry (CV) The devised SLSMCNTPGCPE is a responsive electrode material for the determination of Riboflavin (RF) as compared

to carbon nanotube and pencil graphite composite paste electrode (CNTPGCPE) and bare pencil graphite paste electrode (BPGPE) The fabricated sensor shows a linear current response to a diverse concentration

of RF in 0.2e0.8mM and 1e5mM with a low detection limit of 1.16
108M by applying differential pulse voltammetry (DPV) The stability, reproducibility, repeatability, interference and concurrent investigation with dopamine (DA) have been done with satisfactory outcomes The new sensor was applied for the RF estimation shows good recovery in B-complex pill and natural food supplement

© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

Vitamins and neurotransmitters are biologically active

mole-cules and play a vital role in the humanoid biochemistry and

metabolism RF (vitamin B2) is aqueous soluble and a principal

component offlavoenzymes It assists the conversion of

carbohy-drates, fats, and proteins into energy and supports the body during

anxiety [1e3] RF cannot be formed in the human body, so it has to

be obtained from nutritional sources such as milk, eggs, green

vegetables, tea, wine, liver, etc The lack of RF in the human body

may lead to eye and skin disorders [4e6] Dopamine (DA) is a

neurotransmitter molecule in the mammalian central nervous

system and plays a substantial role in operating the central

ner-vous, hormonal, renal and cardiac systems Abnormal levels of DA

in the human brain cause brain diseases, such as Parkinson's and

Schizophrenia [7e13]

RF is determined using different analytical procedures such as

high-performance liquid chromatography [14], spectrophotometry

[15], Flow injection analysis [16], mass spectrometry [17], etc These

analytical techniques are expensive and time-consuming Also,

some voltammetric methods for quantification of RF are reported in the previous literature such as: mercury drop electrode [18], ZnO/ Manganese hexacyanoferrate nanocomposite/glassy carbon elec-trode [19], Highly dispersed multiwalled carbon nanotubes coupled manganese salen nanostructure [20], pre-treated GC [21], Manga-nese (III) Tetraphenyl porphyrin Modified Carbon Paste Electrode [22], pencil graphite [23], Reduced graphene oxide [24], Poly (3-methyl thiophene) Modified Glassy Carbon Electrode [25], etc Electroanalytical approaches are active and gifted analytical practices having a strong impact on human health and environ-mental monitoring The electrochemical methods are strongly recognized due to low cost, simple preparations, rapid analyzing time with the outstanding analytical performance [26e32] Pencil graphite is known to be a multipurpose tool for electroanalysis of bioactive molecules due to their sp2 hybridized carbon which shows characteristics like excellent electrical conductivity, adsorption, little background current, easy exterior modification and mechanical stability [33e35] Carbon nanotubes (CNTs) are frequently used in the fabrication of electrochemical sensors due to their excellent electronic properties, rapid renewal, extensive po-tential ranges, less residual noise with extreme stability [36e38] Surfactants (SDS, TX-100, CTAB), nanomaterials, stainless steel powder, ferrocene, etc can alter and regulate the characteristic properties of electrode surfaces, which leads to changes in the

* Corresponding author.

E-mail address: manju1853@gmail.com (J.G Manjunatha).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

https://doi.org/10.1016/j.jsamd.2019.11.001

2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ).

reaction rates and pathways Surfactant-modified electrodes have

been extensively applied in the organic electroanalysis, including

nutrition, medicinal, and bio-samples assessment [39e46] The

present effort is the fabrication of a surfactant modified carbon

nanotube and pencil graphite powder composite paste electrode

for the electroanalysis of RF in the presence of DA

2 Experimental

2.1 Apparatus

The Electroanalytical experiments were carried out through

CHI-6038E (electrochemical workstation - USA) It is assembled

with a standard three-electrode arrangement with a computer for

information storage and selection of analytical parameters The

fabricated bare and chemically modified electrodes were executed

as a working electrode, a saturated calomel electrode (SCE) and a

platinum wire were executed as a reference electrode and counter

electrode correspondingly Field emission scanning electron

mi-croscopy (FE-SEM) was obtained using the instrument operating at

5.00 kV (DST-PURSE Laboratory, Mangalore University) All current

measurements were taken with background current All

experi-ments were done at lab temperature

2.2 Reagents and chemicals

RF (99%) was purchased from Molychem, India DA (99%)

and CNTs were bought from Sigma Aldrich, US Silicone oil

(99%) was bought from Nice Chemicals, India 8B pencil is

purchased from the local market Other chemicals are of assay

98.5%, A.R grade used as received The RF and DA standard

so-lution of 2.5 mM was prepared just before the experiment with

distilled water 25 mM SLS was prepared using distilled water

The 0.1 M Phosphate buffer solutions (PBS) of different pH values

were prepared by mixing the suitable quantity of 0.1 M Na2HPO4

and 0.1 M NaH2PO4

2.3 Preparation of pencil graphite powder

The acid-treated pencil graphite, polymer, and surfactant

modified pencil graphite are previously reported for electroanalysis

of electroactive species The present effort of sensor fabrication

provides advantages like less impurity electrode, easy surface

renewal as like carbon paste, simple procedure, easy activation

approach, low cost with good sensitivity and selectivity The 8B

pencil lead is cut into small pieces and crushed in an agate mortar

to afine pencil powder and the obtained powder is stirred with

2 N H2SO4(1:5 ratio) for 30 min, kept 12 h for digestion at 30C and

then washed with dilute acid followed by distilled water The

washed product is dried in the oven at 60C [47e49]

2.4 Development sodium lauryl sulphate modified carbon

nanotube and pencil graphite composite paste electrode

The carbon nanotube and pencil graphite composite electrode

was equipped by hand mixing of 55% pencil graphite powder, 15%

carbon nanotube, 30% silicone oil in a mortar and grounded well

for 20 min to get an homogenous paste; the obtained paste was

filled into a hollow tube of Teflon and it was smoothed out by a

tissue paper The electrical connection was provided through a

wire of copper joined to the end of the tube The surface

modi-fication of the electrode was done by immobilization 10mL SLS

surfactant on the carbon nanotube and pencil graphite composite

3 Result and Interpretations 3.1 FE-SEM and electrochemical characterization of BPGPE, CNTPGCPE, SLSMCNTPGCPE

Fig 1(a), (b) and (c) depict the FE-SEM images of BPGPE, CNTPGCPE, and SLSMCNTPGCPE The BPGPE morphology appears flat whereas CNTPGCPE shows spheres and a fibrous morphology, therefore it was successfully modified with CNTs SLSMCNTPGCPE shows an agglomerated surface with white patches which indicates that the electrode surface is modified with SLS The three electrodes having different topographical properties show different electro-chemistry with electroactive species

SLSMCNTPGCPE for the standard 1 mM K4[Fe(CN)6] in 0.1 M KCl is presented in Fig 1(d) The SLSMCNTPGCPE (curve c) senses

K4[Fe(CN)6] oxidation at 0.268 V, and reduction at 0.204 V, with elevated current signals and a lesserDEp value (0.064V) But in case

of BPGPE (Curve a) and CNTPGCPE (curve b) theDEp values are 0.173, 0.154 V, respectively, with lower current responses So, SLSMCNTPGCPE exhibits higher electrochemical amplification with

SLSMCNTPGCPE might deliver a conducting track through the surfactant layer for quicker electron transfer kinetics Hence, SLSMCNTPGCPE acts as an electron exchange negotiator

The effective surface area of SLSMCNTPGCPE, CNTPGCPE, BPGPE can be calculated by using the Randles-Sevcik equation [50]

Ip¼ 2.69
105n3/2A D1/2C0y1/2

where Ip is the anodic/cathodic peak current in A, Co is the concentration of electroactive species (mol cm3), n is the number

of electrons interchanged, D is the coefficient of diffusion (cm2/s),y

is the potential scan rate (V/s), A is the effective surface area (cm2) The surface area is found to be extremely large for SLSMCNTPGCPE (0.04 cm2) as compared to CNTPGCPE (0.025 cm2), BPGPE (0.016 cm2)

3.2 Optimization of the quantity of carbon nanotubes and SLS The amount of carbon nanotubes used for the preparation of CNTPGCPE effects the electrochemical response of RF (0.1 mM)

So, it was optimized by varying the magnitude of carbon nano-tubes from 5 mg to 25 mg using CV in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s as shown inFig 2(a) The highest electro-chemical activity for RF (0.1 mM) is obtained at the 15 mg carbon nanotube amount, so it is an optimized carbon nanotube amount for electrode fabrication throughout the experiment The sur-factant amount optimization is an essential parameter in elec-troanalysis The surfactant optimization from 5 to 20 mL at CNTPGCPE for the detection of RF (0.1 mM) was performed using

CV in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s as shown in

Fig 2(b) The elevated current is reached at 10mL SLS because at

10mL SLS the critical aggregation concentration was reached At any further increase in the amount of SLS, the cathodic peak current decreases

3.3 Electroanalysis of RF at different electrodes The electrocatalytic behavior of RF (0.1 mM) at BPGPE, CNTPGCPE and SLSMCNTPGCPE was investigated in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s and is presented inFig 3(a) At BPGPE (curve a) the cyclic voltammogram for 0.1 mM RF reveals poor oxidation and reduction responses at 0.445 V and 0.579 V,

G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 2

Fig 1 FE-SEM Depiction of (a) BPGPE (b) CNTPGCPE (c) SLSMCNTPGCPE (d) Electrochemical performance of BPGPE (curve a), CNTPGCPE (curve b) SLSMCNTPGCPE (curve c) for

1 mM K 4 [Fe (CN) 6 ] in 0.1 M KCl at sweep rate of 0.1 V/s.

Fig 2 (a) Calibration of carbon nanotube weight for the preparation of CNTPGCPE for reduction of RF (0.1 mM) (b) Effect SLS quantity for RF (0.1 mM) electroanalysis.

Fig 3 (a) Cyclic voltammetric output of RF (0.1 mM) at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) in 0.1 M PBS of pH 6.5, sweep rate of 0.1 V/s (b) Cyclic voltammetric behavior in the presence of RF (curve b) and absence of RF (curve a) at SLSMCNTPGCPE, under optimal conditions.

activity of RF was increased at CNTPGCPE (curve b) with

quasi-reversible behavior The anodic and cathodic potential for RF at

CNTPGCPE were detected at - 0.464 V and0.577 V, respectively,

with elevated current responses The current sensitivity obtained at

CNTPGCPE was two times higher than that at BPGPE The

SLSMCNTPGCPE (curve c) creates further enhancement in the

cur-rent signal for 0.1 mM RF with anodic and cathodic detection

po-tentials of 0.467 V and 0.678 V, respectively The current

produced at SLSMCNTPGCPE for 0.1 mM RF is four times higher

than the current signal produced at CNTPGCPE The results show

that the electrochemical response is amplified at each step of

modification The CV analysis in the presence and absence of RF was

performed at the optimal condition as shown inFig 3(b) In the

absence of RF (curve a) the characterized CV portrays no peak at

SLSMCNTPGCPE But under parallel conditions in the presence of RF

(0.1 mM), the sharp oxidation and reduction were observed

at0.467 V and 0.678 V, respective;y, with an excellent current

response (curve b)

3.4 Influence of potential sweep rate

The impact of the potential scan rate on the RF oxidation/

reduction was analyzed to identify the electrode kinetics By

altering the sweep rate from 0.1 to 0.3 V/s in 0.1 M PBS of pH 6.5, the

voltammograms are found as inFig 4(a) As the sweep rate

in-creases the peak current also inin-creases and the anodic potential

shifts to the more positive side and the cathodic peak potential

shifts to the more negative side with a significant change inDEp

values It shows that the RF process is quasi-reversible The

po-tentialfluctuations were due to the kinetic limitation of diffusion

layers, which is formed at the upper current density

The plot of Ipcvs v1/2(Fig 4(b)) is found to be linear and it is

(A)¼ 2.49
105þ3.39
104v1/2(V/s)1/2with a value for the

correlation coefficient of 0.99 This discloses that the process is

diffusion rather than adsorption-controlled, so it is the ideal

instance for a quantitative assessment

3.5 Effect of pH

pH is a key factor that affects the electrocatalytic sensing

phe-nomena and is helpful in the prediction of biomolecular reaction

pathways.Fig 5(a) illustrates the cyclic voltammograms of 0.1 mM

RF at various pH ranging from 5.5 to 7.5 of 0.1 M PBS at a sweep rate

of 0.1 V/s A plot of Ipcvs pH (Fig 5(b)) confirms that the reduction peak current was maximum at pH 6.5 At a further increase and decrease in pH, the reduction peak current values decrease and so a

pH value of 6.5 was preferred to complete the electrochemical experiments Meanwhile, at this pH, a swift electron transfer re-action will occur The basic pH is not appropriate for an estimate of

RF since it may be influenced by the creation of unstable lumiflavin molecules with irradiation of light

A plot of Epcvs pH (Fig 5(c)) demonstrates the impact of pH on the cathodic peak potential of 0.1 mM RF over the range of 5.5e7.5 The plot shows that the electrocatalytic peak is lifted towards a more negative potential with an increase in pH ac-cording to the equation Epc(V)¼ 0.0574 pH-0.31 The slope value

of 0.0574 is close to the accepted value 0.059 which indicates that the electrons and protons involved in the electrochemical reac-tion are in the ratio 1:1 So the sequence of reducreac-tion/oxidareac-tion of

RF comprises two electrons and two protons as revealed in

Scheme 1 3.6 Linearity, limit of detection and quantification For the quantitative estimate of RF, the more responsive DPV technique was executed The effect of change in RF concentration

vs oxidation peak current was obtained at SLSMCNTPGCPE using 0.1 M PBS of pH 6.5 as presented inFig 6(a) and (b) Thesefigures indicate that, under optimal conditions, the change in concen-tration of RF is directly proportional to the oxidation peak current values in the concentration domain 0.2e0.8mM and 1e5mM We considered thefine linear range 1e5mM The linearity is described

by an equation as Ipc(A)¼ 8.60
106þ 0.733 (M) and LOD and LOQ were calculated as 3sd/m and 10sd/m [51], respectively Here,

‘sd’ is the standard deviation of the buffer solution current values (5 replicates) and‘m’ is the slope of the calibration graph The LOD and LOQ were found to be 1.16
108 M and 3.87
108 M (±0.065), respectively.Table 1[52e56] depicts the comparison of the established electrode with previously reported electrodes The SLSMCNTPGCPE yields higher detection values as compared

[52,53], detection values that are near to those of GCE/ AuNPS@PDA-RGO [54] and a smaller detection limit value as compared to that of SnO2/RGO/GCE, CreSnO2/GCE [55,56] Comparatively, the fabricated sensors provide advantages such as low cost, non-toxic nature, simple sensor development with good biosensing ability

Fig 4 (a) Cyclic voltammograms of RF (0.1 mM) at SLSMCNTPGCPE with different potential sweep rates, i.e 0.1e0.3 V/s in 0.1 M PBS of pH 6.5 (b) Graphical plot of (v) 1/2 vs I

G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 4

Fig 5 (a) Cyclic voltammetric characterization of RF (0.1 mM) at various pH from 5.5 to 7.5 at SLSMCNTPGCPE with a potential scan rate of 0.1 V/s (b) Plot of cathodic peak current

vs pH (c) Plot of cathodic peak potential vs pH.

Scheme 1 The Electron transfer mechanism of RF.

Fig 6 (a) Differential voltammetric curves for RF from a to m i.e., 0.2e5mM at a sweep rate of 0.05 V/s in 0.1 M PBS of pH 6.5 (b) Standard calibration plot for the concentration of

RF vs the oxidation peak current.

3.7 Analytical applicability

The devised SLSMCNTPGCPE was applied to estimate the

amount of RF in the B-complex pill and in a natural food

supple-ment solution, using the DPV technique at optimal conditions A

suitable quantity of the B-complex powder and food supplement to

a standard solution of a concentration of 1.0
104M was prepared

using distilled water The determination of RF was performed using

the standard addition method in a 0.1 M PBS solution The

re-coveries in the B-complex pill and food supplement were about

95e100.7% The estimates and recovery assessments are tabulated

inTable 2So, the electrochemical sensor offers good recovery in

both B-complex tablets and natural food supplements, which shows the practicability of the developed sensor

3.8 Determination, repeatability and stability of the devised sensor Repeatability for the detection of 0.1 mM RF was assessed through CV in 0.1 M PBS (pH 6.5) with sweep rate 0.1 V/s at SLSMCNTPGCPE The fabricated electrode yields an admirable repeatability for 5 distinct measurements with the relative stan-dard deviation (RSD) of 1.81% The stability of the proposed sensor for the electrochemical detection of 0.1 mM RF was investigated by

30 uninterrupted cycles It has been noticed that 95% of the primary current signal was retained even after 30 cycles, so the established sensor has a high stability

3.9 Electrochemical behavior DA (0.1 mM) and sweep rate effects The electrochemical enhancement of DA (0.1 mM) behavior was inspected by CV at SLSMCNTPGCPE, CNTPGCPE and BPGPE in 0.1 M PBS of pH 6.5 as shown in Fig 7(a) The DA detection using SLSMCNTPGCPE (curve c) was achieved with oxidation and

Table 1

Comparison of the proposed electrochemical sensor with previously reported sensor for voltammetric quantization of RF.

PdeCuNPS - palladium-copper nanoparticles, DPV- differential pulse voltammetry, MBeSO 3 HeMSM- Methylene blue incorporated mesoporous silica microsphere, AuNPs@PDA-RGO- gold nanoparticle/polydopamine/reduced graphene oxide, SnO 2 /RGO- reduced graphene oxide, SWV-square wave voltammetry, LSV- linear sweep voltammetry.

Table 2

Estimate of RF in the B-complex pill and in the natural food supplement.

Sample Added (mM) Detected (mM) Recovery (%) RSD

RSD-relative standard deviation.

Fig 7 (a) Cyclic voltammetry of DA (0.1 mM) at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) (b) Scan rate studies of DA from 0.1 to 0.3 V/s in 0.1 M PBS of pH

G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 6

reduction potentials of 0.231 V and 0.165 V, respectively, with a

swift current response Whereas in CNTPGCPE (curve b), DA was

characterized at 0.221 V and 0.118 V with less current as compared

to SLSMCNTPGCPE At BPGPE (curve a) the DA voltammetric

sensing was very poor with oxidation and reduction potentials of

0.230 V and 0.139 V, respectively So, the cyclic voltammetric

sensing of DA was enhanced at SLSMCNTPGCPE

The scan rate effect from 0.1 V/se 0.3 V/s on DA oxidation/

reduction was studied using CV in 0.1 M PBS of pH 6.5 displayed in

Fig 7(b) The graphical plot of Ipcvs v1/2(Fig 7(c)) gives a straight

Ipc(A)¼ 3.16
105þ1.48
104v1/2(V/s)1/2, R¼ 0.99 This

illu-minates that the electrochemical DA interaction with the electrode

surface was diffusion controlled

3.9.1 Instantaneous analysis of RF in the presence of DA using CV

and DPV

The electrochemical separation of RF (0.1 mM) and DA (0.1 mM)

at SLSMCNTPGCPE is achieved using CV in 0.1 M PBS of pH 6.5, with

a 0.1 V/s scan rate as displayed inFig 8(a) At BPGPE (curve a) RF

and0.576 V, respectively, with a low current value But after bulk

modification with CNT i.e CNTPGCPE (curve b) the RF oxidation and

reduction peaks appeared at0.490, 0.608 V and DA anodic and

cathodic potential peaks were detected at 0.165 V and 0.037 V,

respectively, with an improved current response as compared to

BPGPE However, a clear separation and current enhancement was

achieved at SLSMCNTPGCPE (curve c), the RF anodic and cathodic

characteristic oxidation and reduction potentials appeared at 0.247 V and - 0.017 V, respectively, with enriched current signals

So, the electrochemical separation is amended at SLSMCNTPGCPE The concurrent study of RF and DA at different electrodes

SLSMCNTPGCPE (curve c) the RF and DA detection potentials were at0.536 and 0.080 V with a peak separation of 0.456 V and with high current responses in contrast to CNTPGCPE and BPGPE The RF and DA separation at CNTPGCPE (curve b) were charac-terized at the potentials 0.536 and 0.063 V with less current

as compared to SLSMCNTPGCPE At BPGPE (curve a) minor

current sensitivity

3.9.2 Determination of RF in the presence of DA using DPV The feasibility of RF (0.1 mMe0.110 mM) determination in the presence of DA was analyzed by using DPV technique in 0.1 M PBS

of pH 6.5 at a sweep rate of 0.05 V/s in the potential domain1.0 to 0.4 V as demonstrated inFig 9(a) The RF concentration was varied from 0.1 mM to 0.110 mM while the DA concentration was kept constant as 0.1 mM For each successive addition of RF, there is a rise in current values without affecting much to the DA peak So, it may be concluded that SLSMCNTPGCPE is the dominant electro-chemical sensor for the estimate of RF in the presence of DA The plot of the concentration variation of RF from 100mM to 110mM against the peak current (Fig 9(b)) gives a straight line It follows the linear regression equation Ipc(A)¼ 8.14
106þ 0.21 (M) with

a coefficient of correlation of 0.99 It underlines the feasibility of RF determination in the presence of DA

Fig 8 (a) CV concurrent analysis of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at sweep rate of 0.1 V/s in 0.1 M PBS of pH 6.5 (b) Instantaneous separation of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at a 0.05 V/s sweep rate in 0.1 M PBS of pH 6.5 using DPV.

Fig 9 (a) Differential pulse voltammograms for RF concentration variations from a to f i.e., 0.1 mMe0.110 mM in the presence of DA at a scan rate of 0.05 V/s in 0.1 M PBS of pH 6.5 (b) Calibration graph for RF (0.1 mMe0.110 mM) in the presence of 0.1 mM DA.

3.9.3 Anti-interference ability analysis

The effects of diverse species that can have interference with

the 0.1 mM RF electroanalysis, such as folic acid, ascorbic acid,

biotin, pyridoxine, alanine, glycine, estriol, tartrazine (0.1 mM)

were evaluated at optimal conditions using the DPV technique

The results showed that there was no significant effect on peak

potential and peak current value of 0.1 mM RF So, the proposed

sensor has an excellent selectivity with low interference effects

(below±3%)

4 Conclusion

The established electrode is a low cost and an active sensor for

the determination of RF in the presence of DA The projected sensor

offers a low detection limit, good linearity, comparable with

pre-vious sensores reported in literature The presented sensing

strat-egy was applied to pharmaceutical and food samples with an

excellent recovery So, the demonstrated sensor can be applied to

routine analysis of RF in real samples Moreover, the electrode

ex-hibits a high stability, low interference effects, good repeatability

and is eco-friendly From these discussions, we conclude that the

devised sensor is the best alternative for the electrochemical

quantification of RF in the presence of DA

Declaration of Competing Interest

The authors declare no conflict of interest

Acknowledgement

We gratefully acknowledge the financial support from the

VGST, Bangalore under Research Project No

KSTePS/VGST-KFIST(L1)2016e2017/GRD-559/2017-18/126/333, 21/11/2017

References

[1] P Xu, C Qiao, S Yang, L Liu, M Wang, J Zhang, Fast determination of vitamin B 2

based on molecularly imprinted electrochemical sensor, Eng 4 (2012) 129e134

[2] B Kaur, R Srivastava, Metallosilicate modified electrodes for the

simulta-neous, sensitive, and selective determination of riboflavin, Rutin, and

Pyri-doxine, Electroanalysis, Electroanalysis 26 (2014) 1078e1089

[3] L.S Anisimova, E.V Mikheeva, V.F Slipchenko, Voltammetric determination of

riboflavin in vitaminized supplements and feeds, J Anal Chem 56 (2001)

658e662

[4] A.M Bagoji, S.T Nandibewoor, Redox behavior of Riboflavin and its

deter-mination in Real samples at Graphene modified glassy carbon electrode, Phys.

Chem Commun 3 (2016) 65e76

[5] Z Zhang, J Xu, Y Wen, T Wang, A highly-sensitive VB 2 electrochemical sensor

based on one-step co-electrodeposited molecularly imprinted WS2-PEDOT

film supported on graphene oxide-SWCNTs nanocomposite, Mater Sci Eng.

C 92 (2018) 77e87

[6] T Nie, J.K Xu, L.M Lu, K.X Zhang, L Bai, Y.P Wen, Electroactive species-doped

poly (3,4-ethylenedioxythiophene) films: enhanced sensitivity for

electro-chemical simultaneous determination of vitamins B 2 , B 6 and C, Biosens

Bio-electron 50 (2015) 244e250

[7] J.G Manjunatha, B.E Kumara Swamy, G.P Mamatha, C Raril, L Nanjunda

Swamy, Santosh Fattepur, Carbon paste electrode modified with boric acid

and TX-100 used for electrochemical determination of dopamine, Material

today proc 5 (2018) 22368e22375

[8] J.G Manjunatha, M Deraman, N.H Basri, N.S Mohd Nor, I.A Talib, N Ataollahi,

Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel

sensor for the simultaneous determination of dopamine, ascorbic acid, and

uric acid, C R Chimie 17 (2014) 465e476

[9] J.G Manjunatha, M Deraman, N.H Basri, I.A Talib, Fabrication of poly (Solid

Red A) modified carbon nanotube paste electrode and its application for

simultaneous determination of epinephrine, uric acid and ascorbic acid, Arab.

J Chem 11 (2018) 149e158

[10] C Raril, J.G Manjunatha, Carbon nanotube paste electrode for the

determi-nation of some neurotransmitters: a cyclic voltammetric study, Mod Chem.

Appl 6 (2018)

[11] R Shashanka, D Chaira, B.E Kumara Swamy, Fabrication of yttria dispersed

duplex stainless-steel electrode to determine dopamine, ascorbic and uric

acid electrochemically by using cyclic voltammetry, Int J Sci Eng Res 7

[12] R Shashanka, D Chaira, B.E Kumara Swamy, Electrochemical investigation of duplex stainless steel at carbon paste electrode and its application to the detection of dopamine, ascorbic and uric acid, Int J Sci Eng Res 6 (2015) 1863e1871

[13] G.K Jayaprakasha, B.E Kumara Swamy, B.N Chandrashekar, R Flores-Mor-enod, Theoretical and cyclic voltammetric studies on electrocatalysis of ben-zethonium chloride at carbon paste electrode for detection of dopamine in presence of ascorbic acid, J Mol Liq 240 (2017) 395e401

[14] B.J Petteys, E.L Frank, Rapid determination of vitamin B₂ (riboflavin) in plasma by HPLC, Clin Chim Acta 412 (2011) 38e41

[15] R Bartzatt, Detection and assay of riboflavin (vitamin B2) utilizing UV/VIS spectrophotometer and citric acid buffer, J Sci Res Rep 3 (2014) 799e809

[16] A Safavi, M.A Karimi, M.R Hormozi Nezhad, Flow injection analysis of riboflavin with chemiluminescence detection using a N-halo compoundseluminol system, Luminescence 20 (2005) 170e175

[17] M Aranda, G Morlock, Simultaneous determination of riboflavin, pyridoxine, nicotinamide, caffeine and taurine in energy drinks by planar chromatography-multiple detection with confirmation by electrospray ioni-zation mass spectrometry, J Chromatogr., A 1131 (2006) 253e260 [18] M.M Guida, M Salvatore, F Salvatore, Riboflavin (vitamin B2) assay by adsorptive cathodic stripping voltammetry (adcsv) at the hanging mercury drop electrode (HMDE), Biochem Physiol 4 (2015) 1e10

[19] S Selvarajan, A Suganthi, M Rajarajan, A facile synthesis of ZnO/Manganese hexacyanoferrate nanocomposite modified electrode for the electrocatalytic sensing of riboflavin, J Phys Chem Solids 121 (2018) 350e359

[20] P K Sonkar, V Ganesan, S.K Sen Gupta, D.K Yadav, Highly dispersed multi-walled carbon nanotubes coupled manganese salen nanostructure for simultaneous electrochemical sensing of vitamin B2 and B6, J Electroanal Chem 807 (2017) 235e243

[21] H.Y Gu, A.M Yu, H.Y Chen, Electrochemical behavior and simultaneous determination of vitamin B2, B6, and C, at electrochemically pre-treated glassy carbon electrode, Anal Chem Lett 34 (2001) 2361e2374

[22] S.S Khaloo, S Mozaffari, P Alimohammadi, H Kargar, J Ordookhanian, Sen-sitive and selective determination of riboflavin in food and pharmaceutical samples using manganese (III) tetraphenyl porphyrin modified carbon paste electrode, Int J Food Prop (2016) 19

[23] A.A Ensafi, E Heydari-Bafrooei, M Amini, DNA-functionalized biosensor for riboflavin based electrochemical interaction on pre-treated pencil graphite electrode, Biosens Bioelectron 31 (2011) 376e381

[24] Z Qianfen, W Yong, N.I Yongnian, Electrochemical sensor for the detection of riboflavin based on nanocomposite film of polydeoxyadenylic acid/reduced graphene oxide, Chem J Chinese U 36 (2015) 1674e1680

[25] H Zhang, J Zhao, H Liu, H Wang, R Liu, J Liu, Application of poly (3-methylthiophene) modified glassy carbon electrode, Int J Electrochem Sci.

5 (2010) 295e300 [26] H Beitollahi, M.A Taher, M Ahmadipour, R Hosseinzade, Electrocatalytic determination of captopril using a modified carbon nanotube paste electrode: application to determination of captopril in pharmaceutical and biological samples, Measurement 47 (2013) 770e776

[27] H Beitollahi, M Mostafavi, Nanostructured base electrochemical sensor for simultaneous quantification and voltammetric studies of levodopa and car-bidopa in pharmaceutical products and biological samples, Electroanalysis 26 (2014) 1090e1098

[28] S.Z Mohammadi, H Beitollahi, E.B Asadi, Electrochemical determination of hydrazine using a ZrO 2 nanoparticles-modified carbon paste electrode, Envi-ron Monit Assess 187 (2015) 4039e4099

[29] B Uslu, S.A Ozkan, Electroanalytical methods for the determination of pharmaceuticals: a review of recent trends and developments, Anal Chem Lett 44 (2011) 2644e2702

[30] M Labib, E.H Sargent, S.O Kelley, Electrochemical methods for the analysis of clinically relevant biomolecules, Chem Rev Chem Rev 116 (2016) 9001e9090

[31] R Shashanka, Effect of sintering temperature on the pitting corrosion of ball milled duplex stainless steel by using linear sweep voltammetry, Anal Bio-anal Electrochem 10 (2018) 349e361

[32] G.K Jayaprakash, B.E Kumara Swamy, H.N Gonzalez Ramirez, M.T Ekanthappa, R Flores-Moreno, Quantum chemical and electrochemical studies of lysine modified carbon paste electrode surface for sensing dopa-mine, New J Chem 42 (2018) 4501e4506

[33] I.G David, D.E Popa, M Buleandra, Pencil graphite electrodes: a versatile tool

in electroanalysis, J Anal Methods Chem 2017 (2017) 1e22 [34] A Torrinha, C.G Amorim, C.B.S.M Montenegro, A.N Araujo, Biosensing based

on pencil graphite electrodes, Talanta 190 (2018) 235e247 [35] K Skrzypczynska, K Kusmierek, A Swia ˛tkowski, L Da˛bek, The influence of pencil graphite hardness on voltammetric detection of pentachlorophenol, Int J Electrochem Sci 13 (2018) 88e100

[36] N Punbusayakul, Carbon nanotubes architectures in electroanalysis, Procedia Eng 32 (2012) 683e689

[37] J.G Manjuntha, G.K Jayaprakash, Electrooxidation and determination of es-triol using a surfactant modified nanotube paste electrode, Eurasian J Anal Chem 14 (2019) 1e11

[38] J.G Manjunatha, Surfactant modified carbon nanotube paste electrode for the sensitive determination of mitoxantrone anticancer drug, Electrochem Sci.

G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices xxx (xxxx) xxx 8

[39] N.F Atta, S.A Darwish, S.E Khalil, A Galal, Effect of surfactants on the

vol-tammetric response and determination of an antihypertensive drug, Talanta

72 (2007) 1438e1445

[40] R Vittal, H Gomathi, K.J Kim, Beneficial role of surfactants in

electrochem-istry and in the modification of electrodes, Adv Colloid Interface Sci 119

(2006) 55e68

[41] G Tigari, J.G Manjunatha, C Raril, N Hareesha, Determination of riboflavin at

carbon nanotube paste electrodes modified with an anionic surfactant,

Chemistry select 4 (2019) 2168e2173

[42] R Shashanka, D Chaira, B.E Kumara Swamy, Electrocatalytic response of

duplex and yittria dispersed duplex stainless-steel modified carbon paste

electrode in detecting folic acid using cyclic voltammetry, Int J Electrochem.

Sci 10 (2015) 5586e5598

[43] R Shashanka, B.E Kumara Swamy, S Reddy, D Chaira, Synthesis of silver

nanoparticles and their applications, Anal Bioanal Electrochem 5 (2013)

455e466

[44] R Shashanka, Synthesis of nano-structured stainless-steel powder by

me-chanical alloying-an overview, Int J Sci Eng Res 8 (2017) 588e594

[45] G.K Jayaprakasha, R Flores-Morenob, Quantum chemical study of TX-100

modified graphene surface, Electrochim Acta 248 (2017) 225e231

[46] G.K Jayaprakash, B.E Kumara Swamy, N Casillas, R Flores-Moreno, Analytical

Fukui and cyclic voltammetric studies on ferrocene modified carbon

elec-trodes and effect of Triton X-100 by immobilization method, Electrochim.

Acta 258 (2017) 1025e1034

[47] A Wankhade Amey, V.N Ganvir, Preparation of low cost activated carbon

from tea waste using sulphuric acid as activating agent, Int Res J Environ Sci.

2 (2013) 53e55

[48] O Koyun, S Gorduk, M.B Arvas, Y Sahin, Electrochemically treated pencil

graphite electrodes prepared in one step for the electrochemical

determina-tion of paracetamol, Russ J Electrochem 54 (2018) 796e808

[49] O Koyun, Y Sahin, Poly(L-Cysteine) modified pencil graphite electrode for determination of sunset yellow in food and beverage samples by differential pulse voltammetry, Int J Electrochem Sci 13 (2018) 159e174

[50] C Raril, J.G Manjunatha, Sensitive electrochemical analysis of resorcinol using polymer modified carbon paste electrode: a cyclic voltammetric study, Anal Bioanal Electrochem 10 (2018) 488e498

[51] C Sumathi, P Muthukumaran, R Radhakrishnan, G Ravi, J Wilson, Riboflavin detection bya-Fe2O3/MWCNT/AuNPs-based composite and a study of the interaction of riboflavin with DNA, RSC Adv (9) (2019) 34095e34101 [52] A Sangili, P Veerakumar, S M Chen, C Rajkumar, K C Lin, Voltammetric determination of vitamin B2 by using a highly porous carbon electrode modified with palladium-copper nanoparticles, Mikrochim Acta 186 (2019)

299 [53] R Gupta, P.K Rastogi, U Srivastava, G Vellaichamy, K.S Piyush, K.Y Dharmendra, Methylene blue incorporated mesoporous silica microsphere-based sensing scaffold for the selective voltammetric determi-nation of riboflavin, RSC Adv 6 (2016) 65779e65788

[54] L Pengfei, L Zhenping, Y Zhibin, W Xin, M.A Eser, J Mingliang, Z Guofu,

S Lingling, An electrochemical sensor for determination of vitamin B2 and B6 based on AuNPs@PDA-RGO modified glassy carbon electrode, J Electrochem Soc 166 (2019) B821eB829

[55] R Sriramprabha, M Divagar, N Ponpandian, C Viswanathan, Tin oxide/ reduced graphene oxide nanocomposite-modified electrode for selective and sensitive detection of riboflavin, J Electrochem Soc 165 (2018) B498eB507

[56] N Lavanya, S Radhakrishnan, C Sekar, M Navaneethan, Y Hayakawa, Fabrication of Cr doped SnO 2 nanoparticles-based biosensor for the selective determination of riboflavin in pharmaceuticals, Analyst 138 (2013) 2061e2067