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Ultrasonics - Sonochemistry

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Ultrasonic preparation and nanosheets supported binary metal oxidenanocomposite for the effective application towards the electrochemicalsensor

Tse-Wei Chena, Rameshkumar Arumugamb, Shen-Ming Chenc,⁎, Mohammad Altafd,e,Salim Manohardase, Mohammed Saeed Ali Abuhasilf, Mohammad Ajmal Alig

a Department of Materials, Imperial College London, London SW7 2AZ, United KingdombDepartment of Chemistry, Bannari Amman Institute of Technology, Sathyamangalam, Erode, Indiac Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, No. 1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan, ROCdDepartment of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabiae Central Laboratory, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi ArabiafDepartment of Food Science and Nutrition, College of Food & Agriculture Sciences, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabiag Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia

A R T I C L E I N F O

Keywords:Methyl nicotinate detectionBinary metal oxideNanocompositeUltrasonic preparationCyclic voltammetryReduced graphene oxide

A B S T R A C T

Binary metal oxides (La2O3@SnO2) decorated reduced graphene oxide nanocomposite was synthesized by ul-trasound process in an environmentally benign solvent with a working frequency of 25 and 40 kHz (6.5 l200 H,Dakshin, India and maximum input power 210 W). Further, to enhance the electrocatalytic activity, the reducedgraphene oxide (rGO) was prepared from graphene oxide by ultrasonication method. As prepared La2O3@SnO2/rGO was scrutinized using XRD, TEM, EDX and quantitative test for the structural and morphology properties. Asmodified La2O3@SnO2/rGO nanocomposite exhibits better electrochemical activity towards the oxidation ofmethyl nicotinate with higher anodic current compared to other modified and unmodified electrode for thedetection of methyl nicotinate with larger linear range (0.035–522.9 µM) and lower limit of detection(0.0197 µM). In addition, the practical feasibility of the sensor was inspected with biological samples, reveals theacceptable recovery of the sensor in real samples.

1. Introduction

Ultrasound assistant synthesis of different types of particles andnanostructured nanomaterials composed of transition metal oxides,metal sulfides, carbon nanomaterials, and polymer covered nanoma-terials have underwent great attention in fast few years [1,2]. Because,the unique chemical reaction routes induced by acoustic cavitationprocess in solution, which gives reaction conditions of transient tem-perature and pressure within the collapsing bubbles, wave and radicalformation stages [2,3]. Binary metal oxide based nanomaterials havebeen developed due to their unique potential catalytic applications invarious areas such as electrochemical and gas sensors, lasers and pho-tonics, transistors, Li- ion based batteries, electronics, and photo-detectors have implicated much more [4–7]. Moreover, transition na-nomaterials (TNM) and lanthanides based nanomaterials (LBN) havebeen recognized as an electrocatalyst due to their physical and chemical(catalytic) properties, such as high surface area, and highly stable in

high temperature and pressure [8,9]. In addition, many methods areavailable for synthesis of binary metal oxide based carbon nano-composite including cetrimonium bromide/assisted hydrothermal andmechano-chemical methods have been applied to synthesis for variousnanomaterials [10–13]. In this work, the development of a simple andfast synthetic sonochemical method that can control the composition ofnanostructures and reduced process graphene oxide to reduced gra-phene oxide under ambient conditions remained an important topic ofinterrogated [14,15]. We are developing binary metal oxide of lan-thanum(III) oxide and stannic oxide (La2O3@SnO2) based nanomater-ials with reduced graphene oxide nanocomposite. Because, nano-composite of La2O3@SnO2/rGO possessing high surface area andexcellent electrochemical properties [16–18]. Besides, the significantphysical and chemical properties of two dimensional and layered na-nostructured, reduced graphene oxide (rGO) has similar electro-chemical properties, as compared with graphene oxide and graphite[14,18–21]. In addition, it’s exploring the higher surface area, larger

https://doi.org/10.1016/j.ultsonch.2020.105007Received 27 December 2019; Received in revised form 29 January 2020; Accepted 6 February 2020

⁎ Corresponding author.E-mail address: smchen78@ms15.hinet.net (S.-M. Chen).

Ultrasonics - Sonochemistry 64 (2020) 105007

Available online 07 February 20201350-4177/ © 2020 Elsevier B.V. All rights reserved.

T

thermal conductivity of the nanocomposite. Therefore, it’s widely usedfor various applications such as photonics, transistors, Li- ion basedbatteries, hydrogen evaluation reactions (HER), CO oxidation and re-duction reactions [22–24]. In my research group has been focused onthe rGO development in the electrocatalytic application of electro-chemical sensor [25,26]. Therefore, we are focusing a two dimensionalrGO as the current enhancing nanomaterial combine with La2O3@SnO2

through an ultra-sonication method for the effective detection of me-thyl nicotinate Scheme 1.

Tuberculosis is one of the diseases caused by bacteria ofMycobacterium tuberculosis and also, one of the leading airborne chronicdiseases that affect millions of millions peoples across the world wide[27,28]. In addition, according to the World Health Organization(WHO) report has Tuberculosis in 2019, an estimated above 2.0 milliondeaths in 2018 have been reported due to Tuberculosis [28]. It has beenestimated that around 5 to 10 million peoples have affected Tubercu-losis and 25% of the peoples affected in India alone [28,29]. Conse-quently, it is clear that an early and also, regular diagnosis of Tu-berculosis diseases can help to save millions of lives across the world[28,30]. Methyl nicotinate is one of the key metabolites of Myco-bacterium tuberculosis and identified as a key biomarker of Tuberculosisdiseases in breath [28,31]. Trained rats and monkeys have been ef-fectively used under clinical research to detect the scent of the Myco-bacterium tuberculosis metabolite vapors including methyl nicotinate,and diagnose Tuberculosis in both healthy as well as infected peoples.The efforts made in the electrochemical detection of methyl nicotinatein biological samples using the binary metal oxides (La2O3@SnO2)decorated reduced graphene oxide nanocomposite.

In this work, hydrothermal methods followed by ultra-sonicationmethods were utilized for the synthesis of La2O3@SnO2 nanoparticleswith reduced graphene oxide for the effective determination of methylnicotinate. The prepared nanocomposite was successfully characterizedwith help of XRD, TEM, elemental analysis and electrochemical studies.Besides, the glassy carbon electrode modified with La2O3@SnO2/rGOnanocomposite exhibits enhanced electrochemical behavior with na-nomolar detection limit, higher sensitivity, wide linear range and highstability in electrocatalytic detection of methyl nicotinate biomarker.

2. Experimental section

2.1. Sonochemical synthesis of binary metal oxide decorated rGOnanocomposite

10 mg of graphene oxide powder was added into 10 mL DD water.The solution was sonicated 15 min. Then, 20 mg of SnO2 nanoparticleswas added into 10 mL of graphene oxide solution. Then, the solutionwas ultrasonicated 30 min and then, 10 mg of La2O3 nanoparticles wasadded into the above solution and again the solution was ultrasonica-tion 30 min (ultrasonic bath model 6.5 l200 H, Dakshin, India) with aworking frequency of 25 and 40 kHz and a maximum input power of upto 210 W). Finally, the SnO2@GOS@La2O3 nanocomposite was ob-tained by vacuum drying the powder at 75 °C (more details of metaloxide and graphene oxide synthesis is given Supporting information).

2.2. Fabrication of La2O3@SnO2/rGO/GCE modified electrode

Prior to modify the surface of glassy carbon electrode (GCE) waspolished with 0.05 µm alumina slurry and washed with DD water anddried at room temperature and then, 8 µL of the La2O3@SnO2/rGOnanocomposite was drop casted over the clean surface of glassy carbonelectrode. The La2O3@SnO2/rGO/GCE modified electrode was dried atroom temperature. Similar electrode procedure is applied to preparedGO/GCE and SnO2/GCE. Finally, as modified electrodes was applied forelectrochemical detection of methyl nicotinate.

3. Result and discussion

3.1. XRD analysis of SnO2 and La2O3@SnO2/rGO nanocomposite

The XRD patterns of as-prepared SnO2 and La2O3@SnO2/rGOsamples are represented in Fig. 1. The crystalline nature of SnO2 na-noparticles was analyzed using X-ray diffraction spectrometry. Therutile-like crystalline structure of SnO2 nanoparticles displayed thecharacteristic diffraction peaks at the 2θ angles are corresponds to(1 1 0), (1 0 1), (2 0 0), (1 1 1), (2 1 0), (2 2 0), (0 0 2), (3 1 0), (1 1 2),(3 0 1), (3 0 2), and (3 2 1) miller indices, respectively. The diffractionpattern of SnO2 nanoparticles perfectly matched with the JCPDSnumber 41–1445 [32,33]. Furthermore, the diffraction peaks of

Scheme 1. Synthesis route for the preparation of La2O3@SnO2/rGO and modified with GCE for the detection of methyl nicotinate.

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La2O3@SnO2/rGO nanocomposite showed at the 2θ angles are evi-dently proves that the crystalline nature of La2O3 nanoparticles arehexagonal and miller indices corresponds to (1 0 1), (2 2 2), (3 0 0),(4 0 0), and (6 2 2) planes. The obtained diffraction peaks of La2O3

nanoparticles were clearly matched with the JCPDS card no 04–0856[34,35]. Furthermore, reduced graphene oxide (rGO) peak was ob-served above 26° (2θ angles) [36]. Therefore, graphene oxide was re-duced to change reduced graphene oxide by sonochemical process.These results indicate that the prepared La2O3@SnO2/rGO is pure andwell assigned.

3.2. Morphological analysis of La2O3@SnO2/rGO nanocomposite

The surface morphology of as-obtained nanocomposite and

nanoparticles were studied by TEM. The TEM images of La2O3@SnO2/rGO and rGO was given in Fig. 2. Fig. 2A clearly showed a sphere likeshaped La2O3 and SnO2 nanoparticles combined during the sono-chemical process. Furthermore, layered like nanosheets were observedfor the formation of reduced graphene oxide in Fig. 2B and C. More-over, the high resolution TEM image of La2O3@SnO2/rGO nano-composite was also shown in Fig. 2B and C. In that the La2O3@SnO2

well covered with the sheet liked rGO after the ultra-sonication processand its indicating the successful formation of La2O3@SnO2/rGO nano-composite. Besides, the EDS analysis (Energy-dispersive X-ray spectro-scopy) of La2O3@SnO2/rGO composite was measured and it shown inFig. 2D. The corresponding elementals of La2O3@SnO2/rGO nano-composite was presented such as lanthanum (La), tin (Sn), oxygen (O)and carbon (C) and quantitative analysis of the La2O3@SnO2/rGO na-nocomposite was displayed in Fig. 2E. Therefore, the results are con-firming that the successful formation of La2O3@SnO2/rGO nano-composite by hydrothermal and sonochemical methods.

3.3. Electrochemical detection of methyl nicotinate based on modified andunmodified electrodes

The pH of the electrolyte analysis has serious effect on the elec-trochemical reactions of the pharmaceutical and biological compo-nents. For that reason, the effect of pH on the electrochemical oxidationbehavior of methyl nicotinate was studied by using 0.05 mol phosphatebuffer solutions (PBS), ranging from pH 3.0–11.0, as the supportingelectrolyte. phosphate buffer solutions were used as a supportingelectrolyte, which covers all the pH-value ranges (from 3.0 to 11.0) andin comparison to phosphate buffer solution (PBS) in the optimum pHvalue (pH = 7.0), shows much higher intensity in the oxidation peakcurrent of 100 µM methyl nicotinate (Fig. 3A) based on La2O3@SnO2/rGO/GCE. Because, the anodic peak currents were gradually increasedfrom the electrolyte pH from 3.0 to 7.0. Meanwhile, the anodic peakcurrents of methyl nicotinate were decreased while using the pH 7.0 to11.0 and its indicating higher oxidation peak current of methyl nico-tinate on pH 7.0. Therefore, pH 7.0 is considered as optimized pH and

Fig. 1. XRD patterns of SnO2 (blue) and La2O3@SnO2/rGO nanocomposite(red).

Fig. 2. TEM of La2O3@SnO2/rGO nanocomposite (A-C). EDS analysis of La2O3@SnO2/rGO nanocomposite (D) and quantitative analysis of La, Sn, C, and O.

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its used for all other electrochemical experiments. Furthermore, a linearcalibration plot was plotted against anodic peak potential (Epa) anddifferent pH solutions with the linear regression equation of Epa(V) = 0.5385 + 0.009 and co efficient value of R2 = 0. 9941 (Fig. 3B).The feasible electrochemical oxidation mechanism of methyl nicotinateat La2O3@SnO2/rGO modified GCE is shown in Scheme 2.

The electrochemical oxidation analysis of methyl nicotinate waschecked by cyclic voltammetry (CV) method. The CV analysis at theGCE modified with GO, SnO2, La2O3@SnO2/rGO nanocomposite andunmodified GCE was investigated such as (a) bare GCE, GO/GCE,SnO2/GCE, La2O3@SnO2/rGO NC/GCE was shown in Fig. 4A. The ex-periment condition is scan rate 50 mVs−1 and 100 µM of methyl ni-cotinate in PBS (pH = 7.0). This condition is optimized by variouselectrochemical studies. Furthermore, the current response of un-modified electrode showed low and other control electrode (GO/GCEand SnO2/GCE), also appeared minimum peak currents with a higheranodic peak potential. However, the La2O3@SnO2/rGO modified elec-trode indicated the high anodic peak current (Ipa) at low anodic peakpotential (Epa). Therefore, nanocomposite was enhanced the electro-catalytic activity towards methyl nicotinate due to the La2O3@SnO2

and rGO. The binary metal oxide and reduced graphene oxide could bea significant modified material towards the electrocatalytic oxidation of

methyl nicotinate. The La2O3@SnO2/rGO modified electrode showedthat the synergistic effect of La2O3@SnO2 and rGO nanosheets can in-volve the electrochemical oxidation of methyl nicotinate on the elec-trode and electrolyte interface in pH 7.0. The obtained anodic peakcurrent of modified and unmodified electrodes (bare GCE, SnO2/GCE,rGO/GCE and La2O3@SnO2/rGO/GCE) were shown in Fig. S1. Theenhanced anodic peak current of methyl nicotinate using La2O3@SnO2/rGO modified electrode is due to the direct oxidation and further moredetails of electrochemical oxidation mechanism of methyl nicotinate isgiven in Scheme 2. Besides, the electrochemical peak shows that theirreversible reaction at La2O3@SnO2/rGO modified GCE towards me-thyl nicotinate. These results confirm that the La2O3@SnO2/rGO na-nocomposite modified GCE was better modified electrode for the elec-trochemical detection of methyl nicotinate.

To further verify the anti-fouling effect of methyl nicotinate atLa2O3@SnO2/rGO/GCE, CV investigations were carried out using var-ious concentrations from 25 µM to 125 µM at 50 mVs−1 in 0.05 M PBS(pH 7.0), as shown in Fig. 4B. While increasing the methyl nicotinateconcentrations, the anodic peak currents is gradually increased and itsindicating the superior electrocatalytic activity of the La2O3@SnO2/rGO modified GCE. Furthermore, the corresponding calibration plot fordifferent concentrations of methyl nicotinate (µM) versus anodic peak

Fig. 3. (A) Bar diagram of different pH vs Current (µA) at La2O3@SnO2/rGO modified GCE in 100 µM of methyl nicotinate at 50 mVs−1, (B) Plot diagram for pH vs.anodic peak potential (Epa).

Scheme 2. Electrochemical oxidation mechanism of methyl nicotinate based on La2O3@SnO2/rGO modified electrode.

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current (µA) is displayed a linear calibration plot in Fig. 5A. Moreover,the linear regression equation and correlation coefficient of the reactionis Ipc = −0.221–15.931 and R2 = 0.9928, as shown in Fig. 5A. Fur-thermore, the corresponding slope value is almost 1 and its suggeststhat the electrochemical oxidation reaction of methyl nicotinate is in-volved first order kinetic based on the La2O3@SnO2/rGO modified GCE.

3.4. Effect of scan rate at La2O3@SnO2/rGO modified GCE towards methylnicotinate

The effect of different scan rates on La2O3@SnO2/rGO modifiedelectrode was further studied by CV towards electrochemical oxidationof methyl nicotinate in 0.05 M PBS (pH 7.0) containing 100 µM ofmethyl nicotinate at 20–200 mVs−1 and it’s irreversible anodic peakcurrent of methyl nicotinate based La2O3@SnO2/rGO modified elec-trode at pH 7.0 (PBS). The peak currents were increased when in-creasing the scan rates from 20 to 200 mVs−1 and the linear calibrationplot for square root of scan rate versus peak current (µA) in Fig. 5B. Thelinear regression equation and correlation coefficient of the oxidationreaction is Ipa = −0.059 + 9.11 and R2 = 0.9916, indicating theelectrochemical reduction of methyl nicotinate was adsorption-con-trolled electrochemical process. Also, the calibration plot of log scanrate vs anodic peak potential (Epc) showed a good linear relationshipwith the linear regression equation and correlation co-efficient ofIpc = −48.977–15.391 and R2 = 0.9908 from Fig. 5B. Therefore, theresults conclude that the electrochemical oxidation of methyl nicotinateat La2O3@SnO2/rGO modified GCE is diffusion controlled process in pH7.0 (PBS).

3.5. Electrochemical determination of methyl nicotinate at La2O3@SnO2/rGO modified electrode

Differential pulse voltammetry (DPV) analysis for different con-centrations of methyl nicotinate in PBS of pH 7.0 was recorded underthe optimum experimental conditions (Figs. 3–5). The sequential ad-ditions of methyl nicotinate from 0.035 μM to 522.9 μM, the anodicpeak currents (Ipc) were gradually increased and its indicating theelectrochemical oxidation ability of the La2O3@SnO2/rGO modifiedGCE towards various additions of methyl nicotinate in pH 7.0 (PBS).The linear relations were observed between the anodic peaks currentsand methyl nicotinate concentration and linear dynamic ranges of0.035–522.9 μM for electrochemical oxidation peak in Fig. 6A.

Furthermore, the correspondence linear relationship between thedifferent additions methyl nicotinate concentration and anodic peakcurrent ranging with the linear regression equation and correlationcoefficient of Ipa = 0.325 + 1.854 and R2 = 0.9907, respectively. Thelimit of detection (LOD) was also calculated using LOD = 3σ/S, σ isstandard deviation and S is the slope value from the linear calibrationplot in Fig. 6A (inset). Using the LOD equation, the limit of detectionwas calculated as a 0.019 µM and the sensitivity of the proposed sensorwas calculated to be 4.577 µA µM−1 cm−2. Furthermore, the con-sidered limit of detection, sensitivity and linear response range werealso compared with previously reported methods (Table 1), includingelectrochemical method and more details given in Table 1. According toobtained results, the La2O3@SnO2/rGO modified GCE is a suitable forelectrochemical modified sensor towards the methyl nicotinate oxida-tion. Moreover, the storage stability analysis of the La2O3@SnO2/rGOmodified GCE was also examined in presence of 100 µM methyl

Fig. 4. (A) The electrochemical detection of methyl nicotinate at modified (b; rGO/GCE, c; SnO2/GCE and d; La2O3@SnO2/rGO/GCE) and a; unmodified electrodes.(B) Different concentration analysis at La2O3@SnO2/rGO/GCE (0.05 M PBS (pH 7.0) and 50 mVs−1).

Fig. 5. (A) Calibration plot of different concertation (methyl nicotinate/µM) and oxidation peak current (µA) at La2O3@SnO2/rGO modified GCE (B) correspondingcalibration linear plot for square root of the different scan rate vs anodic peak current.

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nicotinate containing 0.05 M PBS (pH 7.0) by DPV technique, as shownin Fig. 6B. The anodic peak current responses of methyl nicotinate werereasonably decreased from 1st day to 14th day (95.78%), proves thatthe as-prepared La2O3@SnO2/rGO modified GCE has a good stabilitytowards methyl nicotinate detection.

3.6. Selectivity, reproducibility and repeatability of the modified electrode

The selectivity of the modified sensor is more important for thedeveloped real time sensor in practical applications. In order to studythe selectivity and anti-interference ability of the sensor, the La2O3@SnO2/rGO/GCE was investigated by DPV in the presence of methylnicotinate and interfering compounds such as glucose (Glu), UA (uricacid), folic acid (FA), AA (ascorbic acid), epinephrine (EP), DA (dopa-mine), isoniazid (IND), chloramphenicol (CAP), methyl parathion (MP)and norepinephrine (NEP) in 0.05 M PBS (pH 7.0) containing methylnicotinate. The appeared DPV anodic current response was displayed inFig. 7. It can be clearly regard that no obvious current variations werenoted even in the presence of 10-fold excess concentration of co-in-terfering compounds, suggests that the La2O3@SnO2/rGO modifiedGCE has good anti-interference ability and excellent selectivity onmethyl nicotinate detection.

In addition, the repeatability of La2O3@SnO2/rGO/GCE was

examined by utilizing the GCE towards the sensing of methyl nicotinate(100 µM) with consecutive 12 measurements with the similar time in-terval displayed in Fig. S2. The anodic current response of methyl ni-cotinate at initial and final measurement does not show much moredifference, illustrates that the La2O3@SnO2/rGO modified GCE hasbetter repeatability. Furthermore, to investigate the reproducibility ofthe experiment was performed with the aid of ten different La2O3@SnO2/rGO modified GCEs depict in Fig. S3. The anodic peak currentresponse of methyl nicotinate displayed the same anodic current forfour different electrodes. Therefore, the identical current responses ofanodic peaks proves that the offered La2O3@SnO2/rGO modified GCEelectrode has better selectivity, stability, repeatability and reproduci-bility towards the electrochemical detection of methyl nicotinate.

3.7. Real sample analysis

To investigate the practicality of the La2O3@SnO2/rGO modifiedsensor was evaluated for the detection of methyl nicotinate in biologicalsamples. The human serum and urine samples were collected fromchang gung medical hospital, Taiwan. The DPV technique was used todetermine the methyl nicotinate and human serum and urine samplesdid not show any response for methyl nicotinate, which reveals that nomethyl nicotinate was found in the collected samples. Prior to theanalysis, the human serum and urine samples were diluted with bufferand spiked with known concentrations of methyl nicotinate by usingthe standard addition method. Then, the samples were applied to thepracticality of the La2O3@SnO2/rGO nanocomposite modified sensor.Furthermore, the obtained peak current responses have calculated bystandard addition method. The results were calculated and tabulated inTable 2. These good recovery results and RSDs of the proposed sensorprove the valuable practically towards the methyl nicotinate in

Fig. 6. (A) DPV responses of different addition of methyl nicotinate concentrations ranging from 0.035 to 522.9 μM in 0.05 PBS (pH 7.0) and (inset) correspondinglinear calibration plot for different concentration of methyl nicotinate vs anodic peak current (Ipa). (B) Stability analysis.

Table 1Comparison between the sensor performances of La2O3@SnO2/rGO modifiedGCE with other previously reported towards methyl nicotinate sensor.

Electrodes Linear range Limit of detection Reference

Co/RGO/GCE 0.15–14 mg/mL 0.4 μM [28]La2O3@SnO2/rGO/GCE 0.035–522.9 µM 19.7 nM This work

Fig. 7. Selectivity analysis of La2O3@SnO2/rGO modified GCE at 100 µMconcentration of methyl nicotinate (MN) and 50-fold excess of other analytes.

Table 2Determination of methyl nicotinate in real samples based on La2O3@SnO2/rGOmodified GCE.

Real Samples Added (µM) Found (µM) Recovery (%) *RSD (%)

Blood Serum 0 0 – –100 98.26 98.26 3.25200 195.2 97.6 3.42

Urine 0 0 – –100 98.92 98.92 2.94200 197.5 98.75 2.72

* Related standard deviation (RSD) of n = 3 independent experiments.

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biological samples.

4. Conclusion

In summary, we have prepared a La2O3@SnO2 nanoparticles deco-rated on rGO based nanocomposite for the electrochemical detection ofmethyl nicotinate biomarker. The XRD and TEM results reveal that theformation of La2O3@SnO2 and rGO nanocomposite with crystallinenanostructure. As prepared La2O3@SnO2/rGO modified GCE provideshigher anodic current in PBS (pH 7.0). The prepared La2O3@SnO2 de-corated reduced graphene oxide modified GCE showed high sensitivity(4.577 μA μM−1 cm−2) towards methyl nicotinate, with low detectionlimit (19.7 nM) over the concentration range of 0.035–522.9 μM withgood linearity (R2 = 0.9907). The sensor also exhibited good re-producibility and selectivity for the biomarker detection thus con-firming its clinical applicability. Thus from all the results, the La2O3@SnO2/rGO modified GCE proves to be an efficient electrocatalyst formethyl nicotinate detection.

Declaration of Competing Interest

The authors declare that they have no known competing financialinterests or personal relationships that could have appeared to influ-ence the work reported in this paper.

Acknowledgement

The authors would like to extend their sincere appreciation to theDeanship of Scientific Research at king Saud University for funding thiswork through research group project number RG-1439-076. The au-thors gratefully acknowledge the financial support of the Ministry ofScience and Technology, Taiwan through contract number. MOST 107-2113-M-027-005-MY3.

Declaration of Competing Interest

The authors declare that they have no conflicts of interest to thisresearch work.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ultsonch.2020.105007.

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