This paper describes a selective and sensitive detection of bronchodilators (theophylline) using an aloe vera plant extract decorated iron tungstate nanorods (AFW) immobilized Nafion (Nf) modified glassy carbon electrode (GCE) (AFW/Nf/GCE).
Trang 1Original Article
Eco-friendly synthesis of aloe vera plant extract decorated iron
determination of theophylline in blood serum, black tea and urine
samples
A Karthikaa, C Sudhakarb, A Suganthia,**, M Rajarajanb,*
a PG & Research Department of Chemistry, Thiagarajar College, Madurai 625009, Tamil Nadu, India
b Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India
a r t i c l e i n f o
Article history:
Received 9 May 2019
Received in revised form
5 September 2019
Accepted 7 September 2019
Available online 14 September 2019
Keywords:
Nanocomposite
Theophylline
Sensitivity
Selectivity
Electrochemical sensor
a b s t r a c t
This paper describes a selective and sensitive detection of bronchodilators (theophylline) using an aloe vera plant extract decorated iron tungstate nanorods (AFW) immobilized Nafion (Nf) modified glassy carbon electrode (GCE) (AFW/Nf/GCE) The AFW was synthesized by the co-precipitation method and characterized by UVevisible spectroscopy, x-ray diffraction (XRD), Fourier transform infrared spectros-copy (FT-IR), scanning electron microsspectros-copy (SEM), elemental analysis (EDX) and electrochemical studies Interestingly, the oxidation of theophylline with AFW/Nf/GCE displayed a superior electrocatalytic ac-tivity as compared to bare GCE and iron tungstate (FW) modified GCE The oxidation of theophylline in an electrochemical sensor also revealed a linear current response range from 0.1 to 160mM and a low detection limit (LOD) of 0.0028mM This sensor showed high selectivity, stability and reproducibility to tested biological and food samples It has been successfully applied for the selective determination of theophylline in human serum, black tea, and urine samples
© 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
Theophylline (1, 3-dimethylxanthine (scheme (S1))) is one of
the most important xanthine alkaloid derivatives, which is often
present in coffee, tea, chocolate, and traditional medicines
Remarkably, 6% of people (infants, children, women, and men)
were commonly affected by respiratory disorder every year
Therefore, pharmaceutical chemists developed active and
effec-tive drugs to cure different respiratory disorders [1] The drug
was clinically used in several pharmacological treatments such as
asthma, neonatal apnea, airway diseases and chronic obstructive
pulmonary diseases[2] Theophylline was found that the normal
human blood plasma level of 5e20mg/mL was safe to our health
However, overdose [20 mg/mL] and continuous usage of
theophylline cause several critical issues, such as arrhythmia; cardiac arrhythmias, insomnia, anorexia, fever, heartburn tachy-cardia, vomiting, and dehydration fever [3e5] As aforemen-tioned, the high concentration (40mg/mL) of theophylline shows some clinical cases in patients that would pass on with respira-tory and cardiac arrests[6] Besides, theophylline is developed and determined in some analytical methods reported by immu-noassay, spectrophotometry, gas chromatography, mass spec-trometry, thin layer chromatography, capillary electrophoresis, high-performance liquid chromatography, chemiluminescence and electrochemical methods [7e14] These methods require expert monitoring with trained technicians, complicated facil-ities, high cost, a huge amount of reagents and long time of sample analysis Compared with other methods, the electro-chemical method is simple, low cost, user-friendly, portable, se-lective, sensitive, accurate, easy handling, which enables the speedy analysis of theophylline determination Using various modified electrodes, several electrochemical theophylline sensors have been developed and industrialized in recent years Vol-tammetric performance of theophylline based on multiwalled carbon nanotubes in pharmacological drugs and urine samples
* Corresponding author.
** Corresponding author PG & Research Department of Chemistry, Thiagarajar
College, Madurai 625009, Tamil Nadu, India.
E-mail addresses: suganthiphd09@gmail.com (A Suganthi), rajarajanchem1962@
gmail.com (M Rajarajan).
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.2019.09.004
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
Journal of Science: Advanced Materials and Devices 4 (2019) 554e560
Trang 2was studied by Malode et al.[15] Gao et al investigated carbon
nanotube-large mesoporous/Nafion/GCE in determining
theoph-ylline in human serum samples [16] Chen et al developed a
highly sensitive electrochemical apt sensor for theophylline
detection, based on gold nanoparticles[17] A theophylline sensor
based on manganese oxide nanoparticle/ionic liquids/chitosan
nanocomposite modified GCE was fabricated [14] Besides, a
se-lective determination of theophylline based on an imprinted
solegel film immobilized on a carbon nanoparticle modified
electrode [18] and the WS2/Ag nanoparticle based
electro-chemical determination of theophylline [19] were reported
Recently, nanomaterials have been synthesized and found to
exhibit different properties from their bulk counterparts The
intensive research of metal tungstate focused on a variety of
applications such as scintillator materials, semiconductors,
pho-toluminescence, water splitting, humidity sensor, catalysis, Li-ion
batteries, and an optical sensor However, dual metal oxides
(combining two metals with single phase oxygen atom) display
large reactive sites, good conductivity, and higher stability as
compared to their primary ones[20e24] Over the past decades,
inorganic nanostructured materials have found a tremendous
interest due to their unique physicochemical properties In
particular, inorganic FeWO4 transition metal oxides have drawn
significant interest in technological applications with
photo-catalysis, gas sensor, photo-catalysis, conducting electrode,
sensitized-dye using solar cells by lithium-ion batteries [25e30] The
Wolframite structure of FeWO4 nanoparticles with different
shapes and sizes was obtained, and their optical, magnetic and
electrical properties were reported [31] The oxygen binding
closed pack of a hexagonal structure consisted of FeWO4
(fer-rierite) nanoparticles showed a superior performance of the
electron transport process[32,33]
Green chemistry as playing a major role of synthesis of
nanomaterials is currently reported The main compensation for
nanomaterials was synthesized and used for plants, microbes,
and algae Nowadays, synthesized nanomaterials are usually
used as intermediary for plants, which should be low cost, easily
prepared by a single step method, and eco-friendly[34e36] The
Aloe is a genus, and the species for A vera (syn: Aloe barbadensis
Mill) go to the subfamily Asphodeloideae with the main member
for Liliaceae Aloe vera (Aloe Barbadensis) leaves possess a
triangular saw-like structure and an ornamental plant They can
be used as an important medicine in siddha, homeopathy,
ay-urveda and unani Particularly, the extract of agave is used in the
treatment of skin disease In this work, a novel, eco-friendly
plant leaf extract decorated FeWO4 was synthesized by a
co-precipitation method Nafion is an electrode modifier to
immo-bilize the AFW nanocomposite drop cast on the surface GCE The
immobilization of catalytic molecules on the electrode surface
has several advantages over the bare electrodes, as (i) modified
electrodes alter the overall rate of electrochemical reactions, (ii)
the catalyst is readily separated from the solution medium, and
(iii) a very small amount of catalyst is required for the
electro-catalytic reactions [37,38] The simplest drop coating method
has been adapted to coat AFW/Nf/GCE surface using
micro-syringe This type of electrode modification allows the
electro-catalyst to be dispersed into the molecular level with good
electrocatalytic activity in many electrocatalytic reactions [39]
The AFW was characterized by a variety of spectroscopic,
analytical and electrochemical sensing methods The fabricated
AFW/Nf/GCE showed good selectivity, sensitivity, low detection
limit and good electrocatalytic behavior towards the detection of
theophylline in various (human blood serum, back tea, and
urine) samples
2 Experimental 2.1 Materials and methods Ferric chlorites, sodium tungstate, theophylline, cystine, citric acid, dopamine, glucose, ascorbic acid, oxalic acid, lactic acid, L -tyrosine, starch, and quercetin all the chemicals were purchased from SigmaeAldrich The buffer solution of pH 3.0 to 8.0 (NaH2PO4 and Na2HPO4) was used to prepare the standard (0.1 M) solutions and the pH values were adjusted using 0.1 M NaOH and 0.1 M orthophosphoric acid The stock solution of theophylline was pre-pared using triple distilled water and stored in a dark condition All the solutions were prepared using analytical grade chemicals and triple distilled water
XRD pattern was obtained using an X-ray diffraction unit with (l¼ 1.5418A) on X-ray diffraction (Model: JDX-8.30, JEOL, Japan).
The UVevisible spectra were carried out using UVevisible spec-trophotometer (Model: Hitachi, U-3300) FT-IR data of the nano-composite were obtained using PerkineElmer spectrophotometer
in the range of 400e4000 cm1 (Model 460plus, Jasco, Japan) Morphology aspects of nanocomposite and its particle were eval-uated from SEM (Model: Vega3, TESCAN, USA) The following electrochemical methods were adopted in a usual three-electrode system with nanocomposite modified GCE as a working electrode, platinum (Pt) wire as a counter electrode and saturated KCl/Ag/ AgCl as a reference electrode All the electrochemical techniques are performed using CHI-electrochemical workstation (Model-660E, USA) under a nitrogen gas atmosphere at room temperature Electrochemical investigations were performed at least 3e5 times for getting the reproducible results
2.2 Preparation of aloe vera plant extract Aloe Vera plants were collected from Thiagarajar College campus and about 25 g was thoroughly washed in distilled water and cut into fine gel pieces The gel pieces were dribbled with mortar The plant extract solution wasfiltered using a Whatman filter paper (model: 300W) Finally, the extract was used for all experiments
2.3 Synthesis of iron tungstate The starting material of 0.1 M (4.28 g) of ferric chloride was dissolved in (50 mL) deionized water with constant stirring, and then 0.2 M (5.47 g) of sodium tungstate was added in drops into above mixture solution at pH ¼ 9e11 (NaOH) The precipitate solution was transferred into an autoclave (Teflon lined stainless steel) heated at 180C for 3 h The resultant product wasfiltered using NO 1 Whatman paper with ethanol and water A brown color precipitate was obtained and that was dried at 400C for 4 h using drier
2.4 Synthesis of aloe vera plant extracts using iron tungstate
1 g of ferric chloride and 2.03 g of sodium tungstate dissolved were dispersed in 50 mL deionized water After appearing a brown precipitate solution, 20 mL extract was added into the dispersive solution of sodium tungstate and ferric chloride fol-lowed by vigorous stirring for 3 h To adjust the pH value 9e11, NaOH solution (0.1 M) was added The mixture solution was transferred into an autoclave (Teflon lined stainless steel) heated
at 160 C for 5 h The obtained precipitate was washed with triple distilled water, ethanol and dried at 400 C (3 h) muffle furnace
Trang 32.5 Fabrication of theophylline modified electrode
The polished mirror-like surface of GCE with 0.3 mm was used
for surface modifications With the aim of fixation of
nano-composite on GCE, 1 mg AFW/Nf was dispersed into the solution by
an ultra-sonication method for 30 min After it was sonicated, 5mL
of AFW/Nf was the dispersive solutions was pipetted and drop cast
onto the GCE surface and dried in air at room temperature for
10 min Finally, the obtained nanocomposite modified GCE was
used to sense theophylline in the present study (scheme (S2))
3 Results and discussion
3.1 Characterization
UVeVis absorption spectra were observed the electronic/optical
properties of FW and AFW nanoparticle was shown inFig 1 In
Fig 1a a broad absorption band onset was observed at 350 nm Aloe
Vera plant extract showed the shift with a small wavelength
(380 nm) shown inFig 1b[40] The nanocomposite can be
recog-nized to the electron charge transfer conversion of d electron metal
ions found the conduction or valence band by FW and AFW The
bandgap energy was calculated for FW (1.8 eV) and AFW (2.1 eV)
The crystallographic nature of the materials synthesized was
studied by powder XRD pattern shown inFig 2 Crystalline nature
of diffraction peaks was indexed monoclinic phase JCPDS number
file No 46-1446, through the lattice parameters of a ¼ 4.739 Å,
b¼ 5.718 Å, c ¼ 4.965 Å was shown inFig 2a The intensity was
clear that the full width of half maximum (FWHM) of the strongest
characteristic peak for AFW nanoparticles are stronger and broader
than that of FW indicating the crystal size of AFW is smaller than
that of FW The crystalline size was calculated by Debye Scherer
equation and was found 30 nm and 15.83 nm, respectively[33] The
FT-IR spectra of FW and AFW nanocomposites are shown inFig 3(a,
b).Fig 3shows the peak at 3352 and 2924 cm1, which correspond
to the OeH and CeH stretching vibration peak appeared The
observed peak at 878 and 824 cm1, which corresponds to WO2and
W2O8stretching vibrations exist in FW The two bridge of oxygen
(W2O2) shows symmetric stretch at 629 cm1 In addition, the band
observed at 450 cm1confirms the stretching vibration of the FeO6
polyhued building validating the formation of FeWO4 structure
Then the peaks were positioned (1647 cm1) C]C aromatic
stretching vibration with associated OeH vibration (1452 and
1251 cm1), CeN and NeH stretching vibration located at 663 and
1045 cm1 The structure and morphology of the surface consequential were examined using SEM The morphology shows a nanorod-like shape with aggregation of nanorods, as displayed inFig 4a How-ever, such aggregation is absent when a plant extract was added, as shown inFig 4b The plant extract acts as a capping agent which is established by EDX spectrum [41,42] The corresponding EDX spectrum was confirmed by the presence of Fe, W, O, and C that appeared as strong signal peaks This showed a good agreement with the functionalized AFW nanocomposite
3.2 Electrochemical performance The cyclic voltammogram (CV) behavior was investigated as oxidation of theophylline in the various modified and unmodified
Fig 1 UVeVis-spectra of a) FW and b) AFW nanocomposites.
Fig 2 XRD patterns of a) FW and b) AFW nanocomposites.
A Karthika et al / Journal of Science: Advanced Materials and Devices 4 (2019) 554e560 556
Trang 4electrodes, as shown inFig 5 It shows that the CV performance
on theophylline on a) bare, b) FW and c) AFW/Nf/GCE in presence
of 50mM theophylline and pH¼ 7 (0.1 M PBS) at a scan rate of
50 mV/s.Fig 5shows the potential range fromþ0.2 to 1.2 V, and
the unmodified GCE (bare GCE) was not observed for an anodic current peak, the bare GCE was not separated by the anodic peak current of theophylline Compared with FW/GCE, bare GCE observed with weak anodic peak current presented at an elec-trochemical performance in theophylline, as shown inFig 5(b& c) In Fig 5c (AFW/Nf/GCE) a very sharp and high anodic peak current was observed with a large surface area and an excellent electrochemical activity As a result, the AFW/Nf/GCE nano-composite displays a good electrocatalytic activity towards the oxidation of theophylline
3.3 Effect of scan rate and pH The influence of scan rate on the oxidation of theophylline with AFW/Nf immobilized modified GCE in 50 mM theophylline (0.05 M PB¼ 7) was investigated by CV and the obtained result was displayed in Fig 6 These results revealed that the anodic peak current was gradually increased with increasing the scan rate from 10 to 160 mV/s and slightly shifted towards the posi-tive potential side Fig 6b exhibits the linear relationship be-tween anodic current peak and different scan rate and a linear regression equation can be expressed as Ipa¼ 0.0191x þ 1.1859 with a correlation coefficient (R2) ¼ 0.9963 respectively This result indicates that the electrochemical detection of theophyl-line at AFW/Nf/GCE which is an adsorption-controlled process [43e45]
The pH of the electrolyte can affect the performance of AFW/Nf/ GCE to the oxidation of theophylline FromFig 7(aec), it is clearly
Fig 4 SEM images for a) FW and b) AFW and EDX spectra of c) AFW nanocomposites.
Fig 5 a) Cyclic voltammetric response of bare GCE (a), FW/GCE (b) AFW/Nf/GCE (c) in
the presence of 50mM theophylline containing 0.1 M (pH ¼ 7) PBS at a scan rate of
50 mV/s.
Trang 5understood that increasing the pH value from 3 to 8 (0.1 M PBS) the
anodic peak current of theophylline increases with increase in the
pH above 7 Therefore, we selected optimum pH¼ 7 were used for
further electrochemical studies Predominant pHs, the more
hydroxyl particles are collaborated with the theophylline and prompt the de-protonation, subsequently, the electrocatalytic movement decreased[46,16] The linear plot of anodic peak po-tential and different pH is shown inFig 7b By increasing the pH
Fig 6 a) Cyclic voltammetric response of FW/GCE, AFW/Nf/GCE in 50mM theophylline containing 0.1 M (pH ¼ 7) PBS at different scan rates from 10 to 160 mV/s (curve aep) and (b) the linear plot of anodic peak current response of theophylline vs square root of scan rate.
Fig 7 a) Cyclic voltammetric response of different pH on 50mM theophylline in 0.1 MPBS at AFW/Nf/GCE at the scan rate 50 mV/s, (b) the linear plot of anodic peak current and c) effect of different pH.
A Karthika et al / Journal of Science: Advanced Materials and Devices 4 (2019) 554e560 558
Trang 6medium from lower to a higher level, peak current potential was
shifted to the positive side The linear equation for anodic peak
potential (V)¼ 4.4812x 2.352 (R2 ¼ 0.998) According to this
equation[47]
dEpc
dpH¼ð2:303 mRTÞ
ðnFÞ
where R is the gas constant, n is the transfer electron number, T is
the standard temperature, m is the proton number, F is the Faraday
constant and Epcis the cathodic peak potential[48e50]
3.4 Differential pulse voltammetry (DPV)
DPV is considered to be more sensitive as compared with CV
[51e53] The DPV found the calibration of a linear plot used at
pH¼ 7 PBS, as shown inFig 8 Electrochemical performance of
theophylline concentration was increased from lower to higher
level in the linear range of 0.1e160mM Besides, the DPV manifested
addition of theophylline in the sharp anodic peak, and the observed
value was at 1.1 V The calibration curve followed a linear equation
Ipc (mA) ¼ 0.0531 þ 2.615 (R2 ¼ 0.991) with a lower limit
(0.0028mM) and a higher sensitivity (2.573mM1cm2), as shown
inFig 8b The low-level theophylline has appeared in movement,
with fast response of AFW/Nf/GCE with a superior electrocatalytic
current The discovered result was obtained from the high linear
range, the lower detection limit and good sensitivity showed an
enhanced or a similar performance as reported inTable 1 (ST2)
[46,47,51,53e57,16,19]
3.5 Electrochemical sensor performance test
The electrochemical sensor was newly developed for a signi
fi-cant selectivity[58e60] The selectivity was evaluated for the AFW/
Nf/GCE containing interference for amperometric current potential
appliedþ1.1 V at 1200 pm rotation speed continuously stirred with
pH¼ 7 (0.1 M PBS) The electrochemical sensor response for the
modified GCE was well defined through adding 50mM of
theoph-ylline, as (a) presently considerable addition of hundredfold excess
showed no response while the response by the addition of 100 fold
excess in biological samples was co-interference, such as Cystine
(Cys), Citric acid (Ca), Dopamine (Dp), Glucose (Glu), Ascorbic acid
(Aa), Oxalic acid (Oa), Lactic acid (La),L-tyrosine (L-tyr), Starch (Str) and Quercetin (Qcerti), as shown inFig 9 The determination of theophylline used for three independent electrodes at present in the (3.9%) relative standard deviation indicating the anodic peak current promised a superior reproducibility Besides, the unique response appeared at 50mM storage stability of 91% AFW/Nf/GCE, suggestive of a satisfactory storage capacity
3.6 Analysis of theophylline in real samples The AFW/Nf/GCE was analyzed in block tea, urine and human blood serum samples The human serum and urine samples were collected from a governmental hospital, while Madurai and black tea samples were collected from the local market in Madurai The prepared sample was subjected to suitable dilution at pH¼ 7 and in 0.1 M PBS The AFW/Nf/GCE achieved a good recovery when elec-trochemically sensing block tea, urine, and blood serum samples
Fig 8 DPV response of the AFW/Nf/GCE in 0.1 MPBS (pH 7.0) with theophylline concentration varying from 0.1 to 160mM (a) and the insert calibration plot for the linear
Fig 9 Amperometric iet curve response of 50mM theophylline in each CYS (b), CA (c),
DP (d), GLU (e), AA (f), OA (g), LA (h), L-TYR (i), STR (j) and QUER (k) 0.1 M PBS (pH 7.0)
at AFW/Nf/GCE recorded at the scan rate of 50 mV/s.
Trang 7[61] The samples were diluted 100 times with PBS (pH 7.0), and
different amounts of theophylline were spiked in them without
further treatment These studies demonstrated that the good
re-covery was achieved by AFW/Nf/GCE for the human urine, blood
serum and black tea samples The standard addition method used
in previous studies was also considered The obtained good
re-coveries were ranging between 98.6% and 99.3% for the
theophyl-line black tea, urine and serum samples, and the results are
summarized inTable 2 (ST2)
4 Conclusion
We successfully synthesized the aloe vera plant extract using FW
nanocomposite through a simple co-precipitation method The AFW
nanorods were characterized via the spectral, analytical and
trochemical techniques AFW/Nf/GCE exhibited a tremendous
elec-trocatalytic activity for the oxidation of theophylline The fabricated
AFW/Nf immobilized modified GCE using DPV technique yielded the
linear range (0.1e160mM), and the low LOD (0.0028mM) and the
high sensitivity (2.573mM1cm2) for the theophylline detection
The modified electrode displayed with great stability, selectivity, and
reproducibility It can also be utilized for real-time monitoring of
drugs in pharmaceutical and biological samples
Conflict of interest
The authors have declared no conflict of interest
Acknowledgments
The authors thank the UGC Networking Resource Centre, School
of Chemistry, University of Hyderabad, Telangana, India, for
providing necessary laboratory facilities to carry out this work The
authors thank the Management of Thiagarajar College for providing
necessary laboratory facilities to carry out this work
Appendix A Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jsamd.2019.09.004
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