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).
Journal of Science: Advanced Materials and Devices (2019) 554e560 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Eco-friendly synthesis of aloe vera plant extract decorated iron tungstate nanorods immobilized Nafion for selective and sensitive determination of theophylline in blood serum, black tea and urine samples A Karthika a, C Sudhakar b, A Suganthi a, **, M Rajarajan b, * a b PG & Research Department of Chemistry, Thiagarajar College, Madurai 625009, Tamil Nadu, India Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India a r t i c l e i n f o a b s t r a c t Article history: Received May 2019 Received in revised form September 2019 Accepted September 2019 Available online 14 September 2019 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 spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis (EDX) and electrochemical studies Interestingly, the oxidation of theophylline with AFW/Nf/GCE displayed a superior electrocatalytic activity 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 160 mM and a low detection limit (LOD) of 0.0028 mM 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/) Keywords: Nanocomposite Theophylline Sensitivity Selectivity Electrochemical sensor 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 effective 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 5e20 mg/mL was safe to our health However, overdose [20 mg/mL] and continuous usage of * 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 theophylline cause several critical issues, such as arrhythmia; cardiac arrhythmias, insomnia, anorexia, fever, heartburn tachycardia, vomiting, and dehydration fever [3e5] As aforementioned, the high concentration (40 mg/mL) of theophylline shows some clinical cases in patients that would pass on with respiratory and cardiac arrests [6] Besides, theophylline is developed and determined in some analytical methods reported by immunoassay, spectrophotometry, gas chromatography, mass spectrometry, thin layer chromatography, capillary electrophoresis, high-performance liquid chromatography, chemiluminescence and electrochemical methods [7e14] These methods require expert monitoring with trained technicians, complicated facilities, high cost, a huge amount of reagents and long time of sample analysis Compared with other methods, the electrochemical method is simple, low cost, user-friendly, portable, selective, 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 Voltammetric performance of theophylline based on multiwalled carbon nanotubes in pharmacological drugs and urine samples 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 (http://creativecommons.org/licenses/by/4.0/) A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 was studied by Malode et al [15] Gao et al investigated carbon nanotube-large mesoporous/Nafion/GCE in determining theophylline 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 selective determination of theophylline based on an imprinted solegel film immobilized on a carbon nanoparticle modified electrode [18] and the WS2/Ag nanoparticle based electrochemical 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, photoluminescence, 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 photocatalysis, gas sensor, catalysis, conducting electrode, sensitizeddye 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 (ferrierite) 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, ayurveda 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 coprecipitation method Nafion is an electrode modifier to immobilize 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 electrocatalytic reactions [37,38] The simplest drop coating method has been adapted to coat AFW/Nf/GCE surface using microsyringe This type of electrode modification allows the electrocatalyst 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 555 Experimental 2.1 Materials and methods Ferric chlorites, sodium tungstate, theophylline, cystine, citric acid, dopamine, glucose, ascorbic acid, oxalic acid, lactic acid, Ltyrosine, 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 prepared 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 (l ¼ 1.5418 A) on X-ray diffraction (Model: JDX-8.30, JEOL, Japan) The UVevisible spectra were carried out using UVevisible spectrophotometer (Model: Hitachi, U-3300) FT-IR data of the nanocomposite were obtained using PerkineElmer spectrophotometer in the range of 400e4000 cmÀ1 (Model 460plus, Jasco, Japan) Morphology aspects of nanocomposite and its particle were evaluated 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 (Model660E, 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 was filtered 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 180 C for h The resultant product was filtered using NO Whatman paper with ethanol and water A brown color precipitate was obtained and that was dried at 400 C for h using drier 2.4 Synthesis of aloe vera plant extracts using iron tungstate 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 followed by vigorous stirring for 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 h The obtained precipitate was washed with triple distilled water, ethanol and dried at 400 C (3 h) muffle furnace 556 A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 2.5 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 nanocomposite on GCE, mg AFW/Nf was dispersed into the solution by an ultra-sonication method for 30 After it was sonicated, mL 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 Finally, the obtained nanocomposite modified GCE was used to sense theophylline in the present study (scheme (S2)) Results and discussion 3.1 Characterization UVeVis absorption spectra were observed the electronic/optical properties of FW and AFW nanoparticle was shown in Fig 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 in Fig 1b [40] The nanocomposite can be recognized 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 in Fig 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, b ¼ 5.718 Å, c ¼ 4.965 Å was shown in Fig 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 in Fig 3(a, b) Fig shows the peak at 3352 and 2924 cmÀ1, which correspond to the OeH and CeH stretching vibration peak appeared The observed peak at 878 and 824 cmÀ1, which corresponds to WO2 and W2O8 stretching vibrations exist in FW The two bridge of oxygen (W2O2) shows symmetric stretch at 629 cmÀ1 In addition, the band observed at 450 cmÀ1 confirms the stretching vibration of the FeO6 polyhued building validating the formation of FeWO4 structure Then the peaks were positioned (1647 cmÀ1) C]C aromatic Fig UVeVis-spectra of a) FW and b) AFW nanocomposites Fig XRD patterns of a) FW and b) AFW nanocomposites stretching vibration with associated OeH vibration (1452 and 1251 cmÀ1), CeN and NeH stretching vibration located at 663 and 1045 cmÀ1 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 in Fig 4a However, such aggregation is absent when a plant extract was added, as shown in Fig 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 FT-IR spectra of a) FW and b) AFW nanocomposites A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 557 Fig SEM images for a) FW and b) AFW and EDX spectra of c) AFW nanocomposites electrodes, as shown in Fig It shows that the CV performance on theophylline on a) bare, b) FW and c) AFW/Nf/GCE in presence of 50 mM theophylline and pH ¼ (0.1 M PBS) at a scan rate of 50 mV/s Fig shows the potential range from ỵ0.2 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 electrochemical performance in theophylline, as shown in Fig 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 nanocomposite displays a good electrocatalytic activity towards the oxidation of theophylline 3.3 Effect of scan rate and pH Fig a) Cyclic voltammetric response of bare GCE (a), FW/GCE (b) AFW/Nf/GCE (c) in the presence of 50 mM theophylline containing 0.1 M (pH ¼ 7) PBS at a scan rate of 50 mV/s The influence of scan rate on the oxidation of theophylline with AFW/Nf immobilized modified GCE in 50 mM theophylline (0.05 M PB ¼ 7) was investigated by CV and the obtained result was displayed in Fig 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 positive potential side Fig 6b exhibits the linear relationship between anodic current peak and different scan rate and a linear regression equation can be expressed as Ipa ẳ 0.0191x ỵ 1.1859 with a correlation coefficient (R2) ¼ 0.9963 respectively This result indicates that the electrochemical detection of theophylline 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 From Fig 7(aec), it is clearly 558 A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 Fig a) Cyclic voltammetric response of FW/GCE, AFW/Nf/GCE in 50 mM 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 a) Cyclic voltammetric response of different pH on 50 mM 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 understood that increasing the pH value from to (0.1 M PBS) the anodic peak current of theophylline increases with increase in the pH above Therefore, we selected optimum pH ¼ 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 potential and different pH is shown in Fig 7b By increasing the pH A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 medium 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 À 2.352 (R2 ¼ 0.998) According to this equation [47] dEpc 2:303 mRTị ẳ nFị dpH 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 Epc is 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 pH ¼ PBS, as shown in Fig Electrochemical performance of theophylline concentration was increased from lower to higher level in the linear range of 0.1e160 mM 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) ẳ 0.0531 ỵ 2.615 (R2 ¼ 0.991) with a lower limit (0.0028 mM) and a higher sensitivity (2.573 mMÀ1 cmÀ2), as shown in Fig 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 in Table (ST2) [46,47,51,53e57,16,19] 559 (Aa), Oxalic acid (Oa), Lactic acid (La), L-tyrosine (L-tyr), Starch (Str) and Quercetin (Qcerti), as shown in Fig 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 50 mM 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 pH ¼ and in 0.1 M PBS The AFW/Nf/GCE achieved a good recovery when electrochemically sensing block tea, urine, and blood serum samples 3.5 Electrochemical sensor performance test The electrochemical sensor was newly developed for a significant selectivity [58e60] The selectivity was evaluated for the AFW/ Nf/GCE containing interference for amperometric current potential applied ỵ1.1 V at 1200 pm rotation speed continuously stirred with pH ¼ (0.1 M PBS) The electrochemical sensor response for the modified GCE was well defined through adding 50 mM of theophylline, 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 Fig Amperometric iet curve response of 50 mM 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 Fig DPV response of the AFW/Nf/GCE in 0.1 MPBS (pH 7.0) with theophylline concentration varying from 0.1 to 160 mM (a) and the insert calibration plot for the linear dependence of peak current vs concentration of theophylline (b) 560 A Karthika et al / Journal of Science: Advanced Materials and Devices (2019) 554e560 [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 recovery 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 recoveries were ranging between 98.6% and 99.3% for the theophylline black tea, urine and serum samples, and the results are summarized in Table (ST2) [16] [17] [18] [19] Conclusion [25] [26] 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 electrochemical techniques AFW/Nf/GCE exhibited a tremendous electrocatalytic activity for the oxidation of theophylline The fabricated AFW/Nf immobilized modified GCE using DPV technique yielded the linear range (0.1e160 mM), and the low LOD (0.0028 mM) and the high sensitivity (2.573 mMÀ1 cmÀ2) 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 [27] [28] [29] [20] [21] [22] [23] [24] [30] [31] [32] [33] [34] [35] Conflict of interest The authors have declared no conflict of interest [36] [37] [38] [39] Acknowledgments [40] 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 [41] Appendix A Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jsamd.2019.09.004 [42] [43] [44] [45] [46] [47] [48] [49] References [50] [1] J.V 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