Facile synthesis of spinel type copper cobaltite nanoplates for

Subscriber access provided by UNIV OF TEXAS DALLAS

Article

Facile synthesis of spinel type copper cobaltite nanoplates for enhanced electrocatalytic detection of Acetylcholine Paramasivam Balasubramanian, TST Balamurugan, Shen-Ming Chen, and Tse-Wei Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06021 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 14, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Facile synthesis of spinel type copper cobaltite nanoplates for enhanced electrocatalytic detection of Acetylcholine Paramasivam Balasubramanian1, T.S.T. Balamurugan1,2, Shen-Ming Chen1*, Tse-Wei Chen1,3 1

Department of Chemical Engineering and Biotechnology, National Taipei University of

Technology, Taipei 106, Taiwan, ROC. 2

Institute of Biochemical and Biomedical Engineering, National Taipei University of Technology,

No.1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan. 3

Research and Development Center for Smart Textile Technology, National Taipei University of

Technology, No.1, Section 3, Zhongxiao East Road, Taipei 106, Taiwan (ROC). Corresponding Author: *Shen Ming Chen, Fax: +886227025238, Tel: +886227017147, E-mail: [email protected]

ABSTRACT Herein, we report the preparation of novel spinel-type CuCo2O4 nanoplates (CCO NPs) through a cost-effective, soft-template (citrate) assisted method, followed by low-temperature calcination. In the synthesis process, the metal cations such as Cu2+ and Co2+ can react with citrate molecules via co-ordination interaction to form the CuCo-citrate at elevated temperature. During the calcination process at 500 °C, the citrate molecules eliminated from CuCo-citrate precursor via simple organic species, thus spinel type CuCo2O4 nanoplates were formed successfully. Surface morphology, high crystalline nature and phase purity of as-synthesized CCO NPs were assessed by Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron microscopy (XPS). As-synthesized CuCo2O4 nanoplates were used to contract a sensitive and reliable enzyme-free electrochemical sensor of Acetylcholine (ACh), shows a meaningful limit of detection (30 nM) with broad dynamic range (0.2–3500) covering the clinical range of ACh. Furthermore, the developed ACh sensor delivered long-term durability and reproducibility. The point of care utility of the ACh sensor was demonstrated in spiked blood serum samples with acceptable recovery rates. Present work demonstrates a facile synthesis method with an extensive potential towards the preparation of binary transition metal oxides (BTMOs) for divergent electrocatalytic applications.

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

Keywords: Spinel type, CuCo2O4 nanoplates, citrate mediated, electrocatalyst, Acetylcholine,

INTRODUCTION Neurotransmitters (NTs) are endogenous chemical messengers released by nerve cells to transmit the specific biochemical signals between the neurons and other cells.1 Acetylcholine (ACh) is an eminent NT, which administrates chemical transmission of neuronal signals between central and peripheral nervous system.2 In cerebral chemistry, ACh and its metabolite choline plays vital role in a range of critical physiological functions including learning, memory, sustained attention, cognition, and consciousness.3

Metabolic abnormalities of ACh results in

neuropsychiatric disorders, drop of ACh levels lead to dementia, Parkinson’s, Alzheimer’s and schizophrenia4; and the raise of ACh is conjoined with lower heart rate.3 From the aspects of biochemistry, selective and sensitive detection of ACh is essential to explore its physiological functions in cerebral and peripheral neuro systems. On the other hand, the high sensitive detection of ACh can boost the periodical monitoring of neural malfunctions, and effect of clinical treatment. The state-of-art analytical tools for the qualitative and quantitative detection of NT are electrochemiluminescence,5

high-performance

liquid

chromatography

(HPLC),6

optical

detection,7 ion-sensitive field effect transistors (ISFETs)8 and electrochemical methods.9-11 Among them, electrochemical analytical tools are emerging as a promising alternatives over conventional analytical techniques, courtesy to their high sensitivity, low-cost, portability, miniaturization and rapid assay performance.9-11 A sizable number of electrochemical ACh sensors were reported using acetylcholinesterase immobilized biosensor.12-15 The principle advantage of enzyme immobilized ACh biosensors are their excellent selectivity; however, the admirable selectivity come under the cost of poor durability, high cost of enzyme, complicated enzyme immobilization procedure, and sophisticated storage condition.16 Recent years, non-enzymatic ACh sensors has driven a considerable attention in the analytical research community; courtesy, to the direct electrocatalytic hydrolysis of ACh into choline. The nano electrocatalyst films are the emerging alternate to the high cost, less durable AChE based ACh biosensors. Heading to the design of nano-electrocatalyst for the electro oxidation of ACh; nanostructured transition metal oxides has caught our attentions due to its tunable surface morphology, dimension, and chemical compositions to deliver desired catalytic, electrical, optical 2 ACS Paragon Plus Environment

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and mechanical properties for wide range of applications.17,18 In this context, copper oxide and cobalt oxide has drawn significant attention in electrochemical community fact of its excellent electrocatalytic performance, biocompatibility, low cost, significant nano-structural morphology, superior electron-transfer ability, and remarkable physiochemical properties.19,20,21 Spinel-type (AB2O4) mixed transition metal oxides of CuCo2O4 has been utilized as auspicious electrode material for various electrochemical application, due to the outstanding electrochemical activity and higher chemical stability than the monometal oxide counter parts; the elevated physiochemical attributes can be answered by the synergic blend of the two transition elements in the crystal lattices (replacement of Co2+ from [Co2+(Co2)3+O4] by Cu2+).22,23 Catalytic efficiency and electron transportability of nano particles are specific, and fine-tuned via altering the surface morphology and dimension of nano materials.24 For this reason, the design and synthesis of nanomaterials with a unique shape and size with improved catalytic behaviors has driven special interest in material science. A CuCo2O4 nanocomposite of same chemical constituents with different dimension, and morphology can deliver district electrochemical behaviors and suitable for various electrochemical applications. For instance, Karmakar et al., designed a CuCo2O4 nano chains as an efficient OER catalyst.25 Liu et al., prepared a microsphere-like CuCo2O4 nanosheets with improved capacitance.26 Recently, Ke et al., proved that Cu2+ doping on cobalt oxide significantly improved electrochemical performance for Li–O2 batteries.27 Numerous attempts have been made in order to synthesis a morphology and dimension controlled CuCo2O4 spinels. The common molten salt approach,28 solvothermal preparation,29 and metal organic frameworks (MOFs)30,31 are the common protocols adapted for the morphology and dimension-controlled synthesis of spinal nanocomposites. On top of this synthetic protocols, soft-template (surfactants, organic molecules, copolymers etc.,) assisted synthesis of metal oxides draws sizable notice and proven to be an effective for dimension-controlled synthesis of nanomaterials.32,33 The soft-template protocol hold some significant advantages over other synthetic approaches such, easy to construct, ease to remove, and less expensive.32 To the best our knowledge, there is no literature on the fabrication of enzyme free electrochemical acetylcholine sensor employing CuCo2O4 nanoplates synthesized via citrate mediated self-assembly protocol. The citrate soft template is chosen as a credit to its special attributes such, ease to process (install, and remove) over other polymer templates, the



citrate ligand-metal complexation offers high crystallinity to the composite, readily available, economically cheap over polymeric templates.32,34,35 In this context, our present study provides an efficient, scalable, cost-effective protocol for the synthesis of spinel CuCo2O4 nanoplates as reliable electrocatalyst for enzymeless ACh sensor. The synthesis employs citrate molecule as thermal sensitive soft-template to induce unique shape and dimension to the CuCo2O4 nanocatalyst. The resultant CuCo2O4 nanoplates were employed as electrocatalyst for enzymeless ACh sensor. The analytical performance of the sensor has proven that the CuCo2O4 nanoplates own improved electrocatalytic activity than that of its monometallic counterparts with better limit of detection, broad dynamic range, and improved chemical stability. EXPERIMENTAL Synthesis of CuCo2O4 nanoplates (CCO NPs) In a typical synthesis, 40 mL of 0.02 M ethanolic copper nitrate was coupled with 40 mL of 0.01 M ethanolic cobalt nitrate and stirred to obtain a homogenous solution. After complete dissolution, 0.1 M (10 mL) citric acid and 0.1 M (10 mL) aqueous urea solutions were added and stirred for 15 min. The whole reaction mass was transferred to a three neck round bottom flask (RBF) and refluxed over 6 h under nitrogen atmosphere with vigorous stirring. Indeed, the condensation reactions are expected to occur between the metal ions and citrate to yield a complex network in a colloidal state. Citrate plays vital role in the synthesize process such, control the growth of nanoparticle, prevention of agglomeration and the formation of uniform size via chelation of cobalt and copper metal ions with citrate oxygen ions.35 After the completion, the reaction mass was cooled and the resulting brown precipitate (CuCo-Citrate) was harvested via centrifugation, washed thoroughly with copious amount of ethanol and water and dried at 80 °C overnight. Following, a portion of dried brown powder was subjected to annealing at 500 °C for 2 h in air with a ramp rate of 5 °C min-1. The acquired product was employed for further characterization and electrochemical studies. The overall synthetic process with electrode fabrication and electrochemical assay is illustrated in Scheme 1. RESULTS AND DISCUSSIONS Surface characterization of CCO NP


Page 4 of 24

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TEM was employed to investigate the surface morphology of the synthesized CCO NPs. In detail, Fig. 1A. shows the typical low magnification TEM images of CCO NPs, the visuals display a uniform grown of CuCo2O4 nanoplates with an average grain size as 45 nm (±5 nm) (Fig. 1B). However, a closer look at the surface of nanoplates (Fig. 1C) explores numerous lathery edges on the surface of CuCo2O4 nanoplates. Fig. 1D&E shows HRTEM image and SAED patterns of CCO NPs, calculated ‘d’ spacing value of lattice fringes from HRTEM to be 0.242 and 0.232 nm, which are corresponds to the (311) and (222) crystal planes of the cubic spinel CuCo2O4 phases and agrees with the earlier reports.36 TEM findings are supported with the X-ray powder diffraction (XRD) analysis; which proves the formation of CuCo2O4, as characterized in a plane pattern with peak at 37 and 38.7°. In addition, some lattice diffusion can be found in HRTEM image (Fig. 1D), it may due to the formation or intercalation of chemical bonds such as Co-Cu, Co-O and Cu-O.37 Elemental analysis of the catalyst was studied by energy-dispersive spectroscopy (EDS) and shown in Fig.1F. EDS measurement reveals that the co-existence of copper, cobalt and oxygen with no other elemental peaks from precursors, which further confirm the elemental purity of the bimetallic CCO NPs. Further, the crystallographic attributes of CCO NPs were studied via X-ray diffraction analysis (XRD). The Fig. 2A portrays the XRD pattern of CCO NPs, the observed major reflections support the formation of face centered cubic (fcc) structure with space group: Fd3m.38 Further, the obtained diffraction peaks at 19.1°, 31.45°, 37.06°, 38.77°, 45.07°, 55.99°, 59.72°, 65.64°, and 69.06°, were belongs to the (111), (220), (311), (222), (400), (422), (511), (440), and (531) crystal planes of spinel CuCo2O4, respectively. The originated diffraction peaks from the CCO NPs were well indexed with standard diffraction peaks of pure cubic spinel CuCo2O4 phase (JCPDS card no. 01-1155).36 Furthermore, there is no diffraction peaks observed for other possible elemental impurities of the precursor, which emphasize the high phase crystallographic purity of the synthesized CCO NPs. Fourier transformer infrared spectroscopy (FT-IR) is an effective technique to gain information about chemical linkages between the atoms present in the composite. FT-IR spectrum of CuCo-citrate precursor (a) and CCO NPs (b) were shown in Fig. 2B. FT-IR spectrum of CuCocitrate (a) reveals the characteristic peaks at 3450 and 2939 cm-1, due to the vibration of hydroxyl (–OH) and methylene (–CH2) groups.39 The peaks at 1598 and 1402 cm-1, which can be attributed 5 ACS Paragon Plus Environment


to the symmetric and antisymmetric vibration of carboxylate (–COO) groups of citrate.40 The typical vibration bands at 1238, 1075 and 855 cm-1 arising from the C–H, C–OH and C–C bond vibrations.35 This characteristic peaks symbolize the existence of citrate molecules in the uncalcined CuCo-citrate samples. The typical FT-IR spectrum of CCO NPs (b) exhibited two extremely strong vibration peaks at 564 and 663 cm-1, resulted by the Co-O and Cu-O bond vibrations, respectively. These newly formed vibrational bands confirm the successful formation of spinel CCO NPs and the results were in agreement with the earlier reports of CCO NPs.41 In order to prove the synthetic process proceeds through the removal of citrate molecules from CuCo-citrate to spinel CuCo2O4 in detail, Thermogravimetric analysis (TGA) were carried out with CuCo-citrate precursor sample (un-calcined) (curve-a) and CCO NPs (curve-b). Fig. 2C displays the TGA graphs of CuCo-citrate precursor (un-calcined) (curve-a). The thermograph revealed three major weight loss steps at the temperatures of 185, 305 and 495 °C. The first, weight loss of about 4.5 % at 185 °C was most likely resulted from the evaporation of physically absorbed water molecules on the surface of sample. The observed weight loss of 5 % at 305 °C which was likely due to the decomposition of CuCo-citrate precursor.42 Finally, a 10 % weight loss at 495 °C can be ascribed the removal or evaporation of organic species in various forms and crystallization of spinel CuCo2O4.43 In addition, a weight loss step were observed at 880 °C, which may attributed to the decomposition of spinel structure of CuCo2O4 into Co-O and Cu-O.41 TGA analysis confirms that the all the organic species were evaporated or degraded during the annealing process and the spinel structure has been obtained. In contrast, TGA curve of the calcined CuCo2O4 sample (curveb), does not show any significant degradation stage before 850 °C, the weight loss step in the temperature range of 850-1000 °C, which could be related to the decomposition of spinel CuCo2O4 phase. The observed results authenticate that the calcined samples are free from the trace of precursors and confirm the formation pure spinel CuCo2O4 phase. This results of the TGA observations are consistent with the results of EDX, FT-IR and other elemental analysis studies discussed earlier. According to the above experimental observation and analysis, when the citrate molecules were added into the metal precursor solution, copper and cobalt ions were chelated by the oxygen moieties (-OH) of citrate molecules, thus replacing the protons. As a result, the CuCo-Citrate complex was formed. Further, high temperature calcination of CuCo-Citrate the nitrates of metals 6 ACS Paragon Plus Environment

Page 6 of 24

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reduced into ammonium citrate and combusted in to gaseous products with instantaneous growth of metal oxide nano structure with leathery surface.44 Following the sequence of elemental analysis, the synthesized CuCo2O4 nanoplates were subjected to X-ray photoelectron spectroscopy (XPS) in order to investigate the electronic states of the representative elements. The XPS survey spectrum CCO NPs displayed in Fig. 3A specifies the CuCo2O4 nanocatalyst is composed of copper, cobalt and oxygen. Employing a Gaussian fitting, the high-resolution spectrum of Cu 2p (Fig. 3B) fitted into four peaks. The peaks at 933 (Cu 2p3/2) and 955.4 eV (Cu 2p1/2) correspond to the Cu2+ ion. These results authenticate the prevalence of Cu ion in the CCO NPs and the output is matching with that of earlier reports.45 Added to this, two shake-up satellite peaks were appeared at 943.59 and 963.52 eV for Cu 2p3/2 and Cu 2p1/2. Following, the Co 2p spectrum (Fig.3C) displays two Co2p3/2 and Co2p1/2 peaks located at 780.7 and 795.7 eV (spin orbit splitting value= 15 eV) accompanied with two little shake-up satellite peaks (791.2 and 806 eV).46 After refined fitting, the spectrum can be deconvoluted into at four peaks. Where, the peaks at 780.2, and 795.1 eV can be assigned to the Co3+, while other two peaks at 781.2 and 796.8 eV indicates the presence of Co2+. Further, the refined XPS analysis manifest the presence of Co2+ and Co3+ in the CCO NPs.47 The highresolution O1s spectrum in Fig.3D, O1s spectrum was fitted with two peaks indicating the existence of lattice oxygen and adsorption oxygen on the surface of sample. The peak at 530.9 eV respect to the lattice oxygen species (O2-, O-), which reveal the redox behavior of the metal. While another peak at 532.8 eV corresponds to the adsorption oxygen species (O2-, O22-), obvious the concentration of oxygen vacancy in the CCO NPs.48 Also a peak at 534.5 eV may be due to the physically, or chemically bounded water molecules on the surface of CCO NPs.43 In summary, the elemental analysis of the CCO NPs displayed the coexistence of Cu(II), Co(II), Co(III), O- and O2electronic states of constituent elements of the composite which emphasize the synergic mixing of Cu and Co in the crystal lattice of each other in the resultant CCO NPs.22,23 Electrochemical impedance spectroscopy (EIS) EIS is a powerful tool to study the surface properties of the electrode and monitor the associated interfacial properties and thus allowing understanding the chemical alteration allied with the electrode surface. The interface properties of the CCO NPs film modified GCE was demonstrated by EIS. In the Nyquist plots (equivalent circuit diagram shown in inset of Fig. 4A), 7 ACS Paragon Plus Environment


the diameter of the semicircle at higher frequency depicts the charge transfer resistance (Rct) that control the electron transfer kinetics of the redox probe at the electrode surface. Fig. 4A displays the obtained Nyquist plots (-Z’’ vs Z’) of bare GCE (a), Co3O4/GCE (b), and CCO NPs/GCE (c) under open-circuit potential condition in 0.1 M KCl solution containing 5 mM Fe(CN)63-/4- (1:1). The estimated charge transfer resistance (Rct) values of bare GCE (a), Co3O4/GCE (b), and CCO NPs/GCE (c) were 180, 615, and 301 Ω, respectively. The higher Rct value of Co3O4/GCE (b) demonstrates the semiconducting nature of Co3O4. The CCO NPs/GCE shows a lower charge transfer resistance (Rct) over the Co3O4/GCE, in other words the electron transport kinetics of CCO NPs film is much higher than that of Co3O4/GCE and favors ease diffusion of Fe(CN)63-/4- to the electrode surface. These results designating that the doping of copper into Co3O4 significantly enhanced the ionic conductance and accelerated electron transfer kinetics of CCO NPs which is favorable for electrochemical sensing applications. Electrochemical behavior of ACh at CCO NPs modified electrode Cyclic voltammetry technique was adapted to analyses the electrochemical behavior of ACh on the surface of CCO NPs catalyst film. A control experiments were conducted for comparison; CVs of ACh at CCO NPs/GCE (a), Co3O4/GCE (b), and bare GCE (c) in 0.1 M NaOH solution (N2-saturated) containing 2 mM ACh at a sweep rate 50 mV s-1 were shown in Fig. 4B. No peak currents were observed for CCO NPs/GCE, and control electrodes in blank electrolyte. The cyclic voltammograms of CCO NPs/GCE, and control electrodes in presence of ACh is illustrated in Fig. 4B. There is no sizable current response can be observed on GCE in presence of 2 mM Ach symbolizing the necessity of redox mediator. Interestingly, the obtained anodic current response of ACh oxidation at CCO NPs/GCE (Ipa= 0.154 mA) is much higher (1.9 times) than that of Co3O4/GCE (Ipa= 0.08 mA) control electrode, which may be raised by improved electrical conductance resulted by Cu doping on the crystal lattices of CuCo2O4 nanoplates. The CuCo2O4 nanoplates catalyze the oxidation process at favorable potentials with enhanced anodic current over other control electrodes. The enriched electrocatalytic activity may be attributed by high electrical conductivity, a unique lathery nanoplates-like morphology, and synergistic effect of CuCo2O4 nanoplates. Based on the earlier literature, the mechanism of electrocatalytic oxidation Ach catalyzed by CuCo2O4 nanoplates can be stated as follows,49 8 ACS Paragon Plus Environment

Page 8 of 24

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CuCo2O4 + OH- + H2O → CuOOH + 2CoOOH + e-

(1)

After that the oxidation of ACh takes place via following reaction: CuOOH + ACh → Cu(OH)2 + HOOCCH2N+(CH3)3 + H2O

(2)

Reaction (2) occurring via two steps as follows.11 CH3COO(CH2)2N+(CH3)3 + H2O → CH3COOH + HO(CH2)2N+(CH3)3

(3)

Followed by oxidation of hydroxyethyl groups of ammonium ion: CuOOH + HO(CH2)2N+(CH3)3 + OH- → HOOCCH2N+(CH3)3 + H2O + Cu(OH)2 (4) In detail, ACh was hydrolyzed in alkaline solution to yield acetic anion and choline, later CCO NPs modified electrode was oxidized to form Cu(II)/Cu(III) catalytic system with absorbed choline molecules, then the alcohol group of choline was oxidized to respective carboxylic acid by Cu(III)/Cu(II) redox mediator.49,

50

Based on these elucidations, obvious that the electro

oxidation of Ach were investigated using CuCo2O4 nanoplates modified electrode occurring via the active Cu(III)/Cu(II) redox species. Further, the electrocatalytic activity of CCO NPs/GCE for ACh detection was assessed via CVs with increasing concentration of ACh. Fig. 4C shows CV curves of CCO NPs/GCE in absence and cumulative addition of ACh concentrations from 2 to 10 mM in 0.1 M NaOH solution at a scan rate of 50 mV-1. The cyclic voltammograms displays a linear increment in response current with increase in ACh concentration with excellent correlation coefficient (R² = 0.9982 (Fig. 4D)). The steady state increase of anodic current with increasing the concentration of ACh verify the rapid and superior electrocatalytic activity of the CCO NPs modified GCE. Next, the effect electrolyte concentration towards the anodic current of ACh was analyzed with various concentration of electrolyte, since the incorporation of suitable medium is vital for the reliability of the assay. It is well known that the concentration of OH– play a crucial role in the electrocatalytic oxidation of ACh at the CCO NPs electrocatalyst film. Fig. S1A display the anodic current response of the CCO NPs modified electrode in the different concentration of NaOH (0.01, 0.05, 0.1, 0.15, and 0.2 M) in presence of 2 mM ACh at a sweep rate 50 mV s-1. The anodic current response was increases intensely and reach the maximum at 0.1 M NaOH, a further increase in



electrolyte concentration resulted in drop of response current. Thus, 0.1 M NaOH was chosen for further electrochemical studies as the optimal supporting electrolyte. Furthermore, the effect of scan rate towards electrocatalytic performance is analyzed with cyclic voltammograms as a function of sweep rate, varying from 50 to 500 mV s-1 (Fig. 4E). The CV curves displays increment of anodic current response with a gradual potential shift of the oxidation peak potential towards positive direction as the scan rate increases. The oxidation peak current (Ipa) of ACh linearly increased with the square root of the scan rate in the range of 50 – 500 mV s-1 (Fig. 4F) with the correlation coefficient of 0.9905, which indicates that the electrochemical oxidation of ACh on CCO NPs electrocatalyst film is a typical diffusioncontrolled process.9 The obtained results consistent with the previous report of copper-based sensors under diffusion controlled electrocatalysis process.13 In order to extend the response efficiency and quantitative dynamic range of the developed sensor, amperometric technique was employed. The electrochemical performance of the sensor at amperometric detection of an analyte is depends upon the applied potential as it has a great impact on the sensitivity and selectivity of amperometric assays. In order to select an adequate operating potential, the effect of applied potential was studied on the current response of the ACh sensor. As depicted in Fig. S1B, the effect of applied potential on the electrochemical oxidation of ACh were studied in the potential range of 0.6-0.75 V in 0.1 M NaOH solution. A maximal response signal was achieved at applied potential of +0.65 V, and it was chosen as the optimal working potential for amperometric detection of ACh. The amperometric response of the CCO NPs film electrode towards successive injection of ACh were investigated in 0.1 M NaOH solution under applied potential of +0.65 V, and displayed in Fig. 5A. The amperometric results explore the rapid increase in response current after the addition of ACh to the electrolyte solution, the oxidation current increases and reaches a steady state within 4s of analyte addition, this can be ascribed to the high electrocatalytic activity of the CCO NPs towards ACh oxidation. The amperometric current response of ACh oxidation increased linearly in the concentration range of 0.2 µM to 3.5 mM. As depicted in Fig. 5B, the oxidation current response has a good linearity against concentration of ACh with a linear regression equation of Ip (mA) = 0.0001 [ACh] + 0.0121; R² = 0.9913. The detection limit of the sensor determined to be 30 nM from the intercept of the regression plot and standard deviation, under 10 ACS Paragon Plus Environment

Page 10 of 24

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


signal-to-noise ratio of 3 (S/N=3). The physiological abundance of ACh in mammalian nervous system (synapse) is around 2.4 mM,10 which is well within the linear response of our amperometric ACh sensor. The CCO NPs based ACh sensor exhibits a good resolution to the trace level detection of ACh. The CCO NPs film catalyzed ACh assay possess better detection limit towards ACh than that of previously reported non-enzymatic ACh sensors listed in Table 1. As the shape and dimension of nanomaterials holds a decisive influence on the physiochemical properties which attribute the electrocatalytic performance of the catalyst; the enhanced electrocatalytic activity of the proposed sensor can be attributed to the unique lathery nano-plate morphology of CuCo2O4, which own abundant surface area, high electrochemical conductivity and lathery edges of the CCO NPs allowed the oxidation of ACh in the electrode surface.51 Exclusion of biological interfering species is a challenge task in non-enzymatic ACh detection. Human blood is rich redox active biomolecules, which can have oxidized simultaneously with ACh at the modified electrode surface and resulted in false positive electrochemical signals. Therefore, the selectivity test was conducted by the consecutive addition of 500 µM dopamine (a), uric acid (b), ascorbic acid (c), epinephrine (d), norepinephrine (e), tryptamine (f), glutamate (g) and serotonin (i) towards the determination of 5 µM ACh (Fig. 5C). There is no sizable alteration in the response current was observed for the interfering agents; while UA displays a faint amount of current response, indicating the good selectivity of the proposed sensor. In order to verify the durability and long-term stability of the developed sensor, amperometric measurement were recorded using CCO NPs modified electrode in 0.1 M NaOH solution and shown in Fig. 5D. The electrode retains 94.4 % of its initial current response over 2000 s advocating reliable performance of CCO NPs film modified electrode towards ACh detection. The reproducibility of the sensor is an essential parameter in practical detection application. The reproducibility of CCO NPs based ACh sensor was examined by measuring the amperometric current responses of ACh oxidation at five different CCO NPs modified electrodes fabricated via the protocol stated earlier. These five electrodes yielded a relative standard deviation (RSD) of 3.4 % for the determination of ACh, denoting the dependable reproducibility of the sensor.



Page 12 of 24

The point-of-care utility of the CCO NPs based ACh sensor was evaluated by determining the ACh concentration in blood serum samples via amperometric method. Fresh blood serum samples were collected from Chang Cung University, Taoyuan, Taiwan.

The quantitative

detection of ACh in blood serum samples were determined by CCO NPs-ACh sensor, following the standard addition protocol. The obtained recovery value of the ACh in blood serum samples are in the range of 98.4% -100.1% (Table 2). These analytical results demonstrate the practical feasibility of the developed ACh sensor based on the CCO NPs electrocatalyst film modified electrode. CONCLUSION In this work, we have reported a novel and efficient soft-template mediated synthesis protocol for the synthesis of spinel CuCo2O4 nanoplates. In the synthesis process, the metal cations such as Cu2+ and Co2+ can react with citrate molecules via co-ordination interaction to form the CuCo-citrate at elevated temperature. During the calcination process at 400 °C, the citrate molecules eliminated from CuCo-citrate precursor via simple organic species, thus spinel type CuCo2O4 nanoplates were formed successfully. As-synthesized CuCo2O4 nanoplates was used to contract a sensitive and reliable enzyme free electrochemical sensor of Acetylcholine (ACh). The CCO NPs-ACh sensor owns dependable selectivity and meaningful limit of detection (30 nM) with broad dynamic range (0.2–3500) covering clinical range of ACh. The practical applicability of CCO NPs-ACh sensor was demonstrated in blood serum samples with dependable recovery rates. Such a unique BTMOs prepared via rationally designed metal-citrate precursors followed by consequent low temperature annealing can provide great promise for the facile, proficient synthesis of BTMOs for various electrochemical applications. SUPPORTING INFORMATION Materials and methods, Fabrication of CCO NPs modified electrode, Optimization of NaOH concentration and applied potential towards ACh detection. ACKNOWLEDGMENT The authors gratefully acknowledge the financial support of the Ministry of Science and Technology, Taiwan through contract no. MOST 107-2113-M-027-005-MY3.


Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References (1)

Perry, E. K.; Ashton, H.; Young, A. H. Neurochemistry of consciousness: Neurotransmitters in mind. John Benjamins Publishing. 2002.

(2)

Cooper, J. R.; Bloom, F. E.; Roth, R. H. The biochemical basis of neuropharmacology, Oxford University Press, USA. 2003.

(3)

Çevik, S.; Timur, S.; Anik, Ü. Biocentri-voltammetric biosensor for acetylcholine and choline. Microchim. Acta. 2012, 179 (3-4), 299-305.

(4)

Bolat, E. Ö.; Tığ, G. A.; Pekyardımcı, Ş. Fabrication of an amperometric acetylcholine esterase-choline oxidase biosensor based on MWCNTs-Fe3O4 NPs-CS nanocomposite for determination of acetylcholine. J. Electroanal. Chem. 2017, 785, 241-8.

(5)

Deng, S.; Lei, J.; Cheng, L.; Zhang, Y.; Ju, H. Amplified electrochemiluminescence of quantum dots by electrochemically reduced graphene oxide for nanobiosensing of acetylcholine. Biosens Bioelectron. 2011, 26 (11), 4552-8.

(6)

Kuribayashi, M.; Tsuzuki, M.; Sato, K.; Abo, M.; Yoshimura E. A rapid analytical method for free choline by LC and its application for bacterial culture medium samples, Chromatographia, 2007, 67 (3-4), 339-41.

(7)

Wang, C. I; Periasamy, A. P.; Chang, H. T.; Photoluminescent C-dots@RGO probe for sensitive and selective detection of acetylcholine, Anal Chem. 2013, 85 (6), 3263-70.

(8)

Kharitonov, A. B.; Zayats, M.; Lichtenstein, A.; Katz, E.; Willner, I. Enzyme monolayerfunctionalized field-effect transistors for biosensor applications, Sensor Actuat. B-Chem. 2000, 70 (1-3), 222-31.

(9)

Ju, J.; Bai, J.; Bo, X.; Guo, L. Non-enzymatic acetylcholine sensor based on Ni–Al layered double hydroxides/ordered mesoporous carbon, Electrochim. Acta 2012, 78, 569-75.

(10)

Wang, L.; Chen, X.; Liu, C.; Yang, W. Non-enzymatic acetylcholine electrochemical biosensor based on flower-like NiAl layered double hydroxides decorated with carbon dots. Sensor Actuat. B-Chem. 2016, 233, 199-205.

(11)

Sattarahmady, N.; Heli, H.; Moosavi-Movahedi, A. A. An electrochemical acetylcholine biosensor based on nanoshells of hollow nickel microspheres-carbon microparticlesNafion nanocomposite. Biosens Bioelectron. 2010, 25 (10), 2329-35.



(12)

Chauhan, N.; Chawla, S.; Pundir, C. S.; Jain, U. An electrochemical sensor for detection of neurotransmitter- acetylcholine using metal nanoparticles, 2D material and conducting polymer modified electrode. Biosens Bioelectron. 2017, 89, 377-83.

(13)

Heli, H.; Hajjizadeh, M.; Jabbari, A.; Moosavi-Movahedi, A. A. Copper nanoparticlesmodified carbon paste transducer as a biosensor for determination of acetylcholine, Biosens Bioelectron. 2009, 24 (8), 2328-33.

(14)

Sattarahmady, N.; Heli, H.; Vais. R. D. An electrochemical acetylcholine sensor based on lichen-like nickel oxide nanostructure. Biosens Bioelectron. 2013, 48, 197-202.

(15)

Shibli, S. M.; Beenakumari, K. S.; Suma, N. D. Nano nickel oxide/nickel incorporated nickel composite coating for sensing and estimation of acetylcholine, Biosens Bioelectron. 2006, 22 (5), 633-8.

(16)

He, C.; Wang, Z.; Wang, Y.; Hu, R.; Li, G. Non-enzymatic all-solid-state coated wire electrode for acetylcholine determination in vitro Biosens Bioelectron. 2016, 85, 679-83.

(17)

Yuan, C., Wu, H. B.; Xie, Y.; Lou, X. W. Mixed transition‐ metal oxides: design, synthesis, and energy‐ related applications. Angew Chem Int Ed. 2014, 53 (6), 1488-504.

(18)

Lan, W. J.; Kuo, C. C.; Chen, C. H. Hierarchical nanostructures with uniqueY-shaped interconnection networks in manganese substituted cobalt oxides:the enhancement effect on electrochemical sensing performance. Chem Commun. 2013, 49 (29), 3025-7.

(19)

Sun, S.; Sun, Y.; Chen, A.; Zhang, X.; Yang, Z. Nanoporous copper oxide ribbon assembly of free-standing nanoneedles as biosensors for glucose. Analyst, 2015, 140 (15), 5205-15.

(20)

Li, M.; Han, C.; Zhang, Y.; Bo, X.; Guo, L. Facile synthesis of ultrafine Co3O4 nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors. Anal Chim Acta 2015, 861, 25-35.

(21)

Balasubramanian, P.; Annalakshmi, M.; Chen, S. M.; Sathesh, T.; Peng, T. K.; Balamurugan, T. S. T. Facile solvothermal preparation of Mn2CuO4 microspheres: Excellent electrocatalyst for real-time detection of H2O2 released from live cells. ACS Appl. Mater. Interfaces. 2018, 10 (50), 43543–43551.

(22)

Liu, S.; Hui, K. S.; Hui, K. N. Flower-like copper cobaltite nanosheets on graphite paper as high-performance supercapacitor electrodes and enzymeless glucose sensors. ACS Appl Mater Interfaces, 2016, 8 (5), 3258-67.


Page 14 of 24

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23)

Jia, J.; Li, X.; Chen, G. Stable spinel type cobalt and copper oxide electrodes for O 2 and H2 evolutions in alkaline solution. Electrochim Acta 2010, 55 (27), 8197-206.

(24)

Wang, F.; Han, Y.; Lim, C. S.; Lu, Y.; Wang, J.; Xu, J.; Chen, H.; Zhang, C.; Hong, M.; Liu, X. Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping. Nature. 2010, 463 (7284), 1061.

(25)

Karmakar, A.; Srivastava, S. K. Interconnected Copper Cobaltite Nanochains as Efficient Electrocatalysts for Water Oxidation in Alkaline Medium. ACS Appl. Mater. Interfaces 2017, 9 (27), 22378-87.

(26)

Liu, S.; San Hui, K.; Hui, K. N.; Yun, J. M.; Kim, K. H. Vertically stacked bilayer CuCo2O4/MnCo2O4 heterostructures on functionalized graphite paper for highperformance electrochemical capacitors. J Mater. Chem. A, 2016, 4 (21), 8061-8071.

(27)

He, L.; Wang, Y.; Wang, F.; Zhang, S.; Wu, X.; Wen, Z.; Liu, J.; Zhang, W. Influence of Cu2+ doping concentration on the catalytic activity of CuxCo3−xO4 for rechargeable Li–O2 batteries. J Mater. Chem. A, 2017, 5 (35), 18569-18576.

(28)

Reddy, M. V.; Yu, C.; Jiahuan, F.; Loh, K. P.; Chowdari, B. V. Molten salt synthesis and energy storage studies on CuCo2O4 and CuO·Co3O4. RSC Adv. 2012, 2 (25), 9619-25.

(29)

Ning, R., Tian, J., Asiri, A. M., Qusti, A. H., Al-Youbi, A. O., Sun, X. Spinel CuCo2O4 nanoparticles supported on N-doped reduced graphene oxide: a highly active and stable hybrid electrocatalyst for the oxygen reduction reaction. Langmuir, 2013, 29 (43), 1314613151.

(30)

Ma, J., Wang, H., Yang, X., Chai, Y., Yuan, R. Porous carbon-coated CuCo2O4 concave polyhedrons derived from metal–organic frameworks as anodes for lithium-ion batteries. J Mater. Chem. A, 2015, 3 (22), 12038-12043.

(31)

Salunkhe, R. R., Kaneti, Y. V., Yamauchi. Y. Metal−Organic Framework-Derived Nanoporous Metal Oxides toward Supercapacitor Applications: Progress and Prospects. ACS Nano, 2017, 11 (6), 5293-308.

(32)

Zhang, Y., Li, L., Su H., Huang, W., Dong, X. Binary metal oxide: advanced energy storage materials in supercapacitors. J Mater. Chem A, 2015, 3 (1), 43-59.

(33)

Wang, Z., Wang, Z., Liu, W., Xiao, W., Lou, X. W. Amorphous CoSnO3@ C nanoboxes with superior lithium storage capability. Energy Environ. Sci., 2013, 6 (1), 87-91.



(34)

Dandan, H., Pengcheng, X., Xiaoyan, J., Jun, W., Piaoping, Y., Qihui, S., Jingyuan, L., Dalei Song, Zan Gao, Milin Z. Trisodium citrate assisted synthesis of hierarchical NiO nanospheres with improved supercapacitor performance J. Power Sources 2013, 235, 4553

(35)

Huang, Z., Zhao, Y., Song, Y., Zhao, Y., Zhao, J. Trisodium citrate assisted synthesis of flowerlike hierarchical Co3O4 nanostructures with enhanced catalytic properties. Colloids and Surfaces A: Physicochem. Eng. Aspects 2017, 516, 106-14.

(36)

Han, D., Hu, H., Liu, B., Song, G., Yan, H., Di, J. CuCo2O4 nanoparticles encapsulated by onion-like carbon layers: A Promising solution for high-performance lithium ion battery. Ceram. Int. 2016, 42 (10), 12460-6.

(37)

Feng, Y., Liu, J., Wu, D., Zhou, Z., Deng, Y., Zhang, T., Shih, K. Efficient degradation of sulfamethazine with CuCo2O4 spinel nanocatalysts for peroxymonosulfate activation. Chem. Eng. J. 2015, 280, 514-524.

(38)

Bhardwaj, M., Suryawanshi, A., Fernandes, R., Tonda, S., Banerjee, A., Kothari, D., Ogale, S. CuCo2O4 nanowall morphology as Li-ion battery anode: Enhancing electrochemical performance through stoichiometry control. Mater. Res. Bull. 2017, 90, 303-10.

(39)

Xiang, Y., Wu, H., Zhang, K. H., Coto, M., Zhao, T., Chen, S., Dong, B., Lu, S., Abdelkader, A., Guo, Y., Zhang, Y. Quick one-pot synthesis of amorphous carbon coated cobalt–ferrite twin elliptical frustums for enhanced lithium storage capability. J Mater. Chem A, 2017, 5 (17), 8062-9.

(40)

Jiang, J., Huang, L., Liu, X., Ai, L. Bioinspired Cobalt−Citrate Metal−Organic Framework as an Efficient Electrocatalyst for Water Oxidation. ACS Appl. Mater. Interfaces 2017, 9 (8), 7193-201.

(41)

Shanmugavani, A., Selvan, R. K. Improved electrochemical performances of CuCo2O4/CuO nanocomposites for asymmetric supercapacitors. Electrochim Acta 2016, 188, 852-62.

(42)

Hsiao, Y. J., Liu, C. W., Dai, B. T., Chang, Y. H. Sol–gel synthesis and the luminescent properties of CaNb2O6 phosphor powders. J Alloys Compd. 2009, 475 (1-2), 698-701.

(43)

Jadhav, H. S., Pawar, S. M., Jadhav, A. H., Thorat, G. M., Seo, J. G. Hierarchical mesoporous 3D flower-like CuCo2O4/NF for high-performance electrochemical energy storage. Sci Rep. 2016, 6, 31120. 16 ACS Paragon Plus Environment

Page 16 of 24

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44)

Mudsainiyana, R. K., Jassala, A. K., Munish, G., Chawla, S. K. Study on structural and magnetic properties of nanosized M-type Ba-hexaferrites synthesized by urea assisted citrate precursor route. J. Alloy Compd. 2015, 645, 421-428.

(45)

Shao, L., Wang, Q., Fan, L., Wang, P., Zhang, N., Sun, K. Copper cobalt spinel as a highperformance cathode for intermediate temperature solid oxide fuel cells. Chem Commun., 2016, 52 (55), 8615-8.

(46)

Kaverlavani, S. K., Moosavifard, S. E., Bakouei, A. Self-templated synthesis of uniform nanoporous CuCo2O4 double-shelled hollow microspheres for high-performance asymmetric supercapacitors. Chem Commun. 2017, 53 (6), 1052-5.

(47)

Wang, P. X., Shao, L., Zhang, N. Q., Sun, K. N. Mesoporous CuCo2O4 nanoparticles as an efficient cathode catalyst for Li-O2 batteries. J. Power Sources. 2016, 325, 506-12.

(48)

Yang, W., Hao, J., Zhang, Z., Lu, B., Zhang, B., Tang, J. Synthesis of hierarchical MnCo2O4.5 nanostructure modified MnOOH nanorods for catalytic degradation of methylene blue. Catal Commun. 2014, 46, 174-178.

(49)

Heli, H., Jafarian, M., Mahjani, M. G., Gobal, F. Electro-oxidation of methanol on copper in alkaline solution. Electrochim. Acta 2004, 49 (27), 4999.

(50)

Casella, I. G., Cataldi, T. R., Guerrieri, A., Desimoni, E. Copper dispersed into polyaniline films as an amperometric sensor in alkaline solutions of amino acids and polyhydric compounds. Anal Chim Acta 1996, 335 (3), 217.

(51)

Solla-Gullo´on, J., Vidal-Iglesias, F. J., Feliu, J. M. Shape dependent electrocatalysis. Annu. Rep. Prog. Chem., Sect. C, 2011, 107, 263–297.

(52)

Balasubramanian, P.; Balamurugan, T. S. T. Chen, S. M.; Sathesh, T.; Chen, T. W. Rational design of Cu@Cu2O nanospheres anchored B, N co-doped mesoporous carbon: A sustainable electrocatalyst to assay eminent neurotransmitters Acetylcholine and Dopamine. ACS Sustain Chem Eng., 2018. DOI: 10.1021/acssuschemeng.8b04473



Figures and Tables Cu(NO3)2

Co(NO3)2

10 nm Citric acid Urea

500 0C/2 h

Refluxing 180 0C/6 h

CuCo2O4 nanoplates CuCo-citrate

Acetylcholine

CCO NPs/GCE

Ethanol

Calcination

I/mA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

T/s

Scheme 1. Schematic representation of the present work.

Fig. 1. TEM images (A-C), HRTEM image (D), SAED pattern (E), EDS analysis (F) of CCO NPs. 18 ACS Paragon Plus Environment

Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 2. XRD pattern (A) CCO NPs. FT-IR spectrum (B) of CuCo-citrate precursor sample (uncalcined) (a), CCO NPs (b). TGA spectrum (C) of CuCo-citrate precursor sample (un-calcined) (a), CCO NPs (b).



Fig. 3. The X-ray photoelectron spectroscopy (XPS) spectrum of CCO NPs: survey (A), Cu 2p (B), Co 2p (C), O 1s (D).


Page 20 of 24

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 4. (A) EIS curves of bare GCE (a), Co3O4/GCE (b), and CCO NPs/GCE (c). (B) CVs of CCO NPs/GCE (a), Co3O4/GCE (b), and bare GCE (c) in 0.1 M NaOH solution (N2- saturated) containing 2 mM ACh at a scan rate of 50 mV s-1. In absence of 2 mM ACh is denoted as (a’), (b’) and (c’) respective electrodes. (C) CVs for CCO NPs/GCE in 0.1 M NaOH in the presence of various concentration of ACh: 2, 4, 6, 8, and 10 mM, sweep rate: 50 mV s-1. (D) The corresponding calibration plot of various concentration of ACh: [ACh] vs Ipa. Error bars= ±standard deviation 21 ACS Paragon Plus Environment


(n=3) (E) CVs for CCO NPs/GCE in 2 mM ACh at different scan rate in the range of 50 – 500 mV s-1. (F) The corresponding calibration plots of anodic current response (Ipa) vs scan rates. Error bars= ±standard deviation (n=3)

Fig. 5. (A) Typical amperometric current response of CCO NPs modified electrode upon cumulative injection of ACh into 0.1 M NaOH solution at an applied potential +0.65 V. Inset, oxidation current response of low concentrations, (B) The corresponding calibration curve of ACh: [ACh] vs Ipa. Error bars= ±standard deviation (n=3) (C) Amperometric current response of CCO NPs modified electrode toward the addition of ACh and various interfering species (dopamine (a), uric acid (b), ascorbic acid (c), epinephrine (d), norepinephrine (e), tryptamine (f), glutamate (g) and serotonin (i)) in 0.1 M NaOH. (D) Operational stability of the developed sensor. Table 1. Comparison of analytical performance of the proposed ACh sensor with previously reported sensors.


Page 22 of 24

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electrode material

Linear range (µM)

LOD (µM)

ref

Ni–Al LDHs/OMC/GC

2–4922

0.042

9

NiAl-LDH/CD

5–6885

1.7

10

0.24–828

0.049

11

copper nanoparticles

120–2680

39

13

nickel oxide

250–5880

26.7

14

Cu@Cu2O-BNDC

0.3–2602

17

52

CuCo2O4 nanoplates

0.2–3500

0.030

This work

composites hollow nickel microspheres/carbon

nanostructure

Table 2. Acetylcholine levels in blood serum samples, as determined by proposed sensor based on CCO NPs modified glassy carbon electrode. Sample

Found (µM)

Added (µM)

Recovery (µM)

RR (%) (n=3)

1

19.3

50

49.2

98.4

2

18.9

100

99.8

99.8

3

19.5

500

500.5

100.1



For Table of Contents Use Only Cu(NO3)2

Co(NO3)2

10 nm Citric acid Urea

500 0C/2 h

Refluxing 180 0C/6 h

CuCo2O4 nanoplates

CuCo-citrate

Acetylcholine

CCO NPs/GCE

Ethanol

Calcination

I/mA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

T/s

Synopsis A novel and efficient soft-template mediated protocol for the synthesis of spinel CuCo2O4 nanoplates is reported and it was used to contract a sensitive and reliable enzyme free electrochemical sensor of Acetylcholine.


Facile synthesis of spinel type copper cobaltite nanoplates for

Recommend Documents