Metal Wire Networks Functionalized with Nickel Alkanethiolate for

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Metal Wire Networks functionalized with Ni Alkanethiolate for Transparent and Enzymeless Glucose Sensors Ajay B Urgunde, Akshay Kumar, Kiran P Shejale, Rakesh K Sharma, and Ritu Gupta ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01115 • Publication Date (Web): 01 Oct 2018 Downloaded from http://pubs.acs.org on October 4, 2018

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ACS Applied Nano Materials

Metal Wire Networks functionalized with Ni Alkanethiolate for Transparent and Enzymeless Glucose Sensors Ajay B. Urgunde, Akshay Kumar, Kiran P. Shejale, Rakesh K. Sharma and Ritu Gupta*

Department of Chemistry, Indian Institute of Technology Jodhpur, Karwad, Rajasthan-342037, India Corresponding Author: Dr. Ritu Gupta ([email protected]) Abstract The futuristic healthcare technology including glucose sensors demand for wearable components that ought to be transparent and flexible. Ni nanostructures have proven to be highly efficient as an electrocatalyst for glucose sensors. In this study, we explore single source precursors of Ni alkylthiolate, Ni(SR)2 complexes as an active electrode material and coat them on transparent Au mesh network to fabricate a transparent and highly efficient glucose sensor. The metal thiolate complex is electro-oxidized in the alkaline medium by repeated Cyclic Voltammetry measurements to give rise to Ni redox-active centers with sharp anodic and cathodic peaks. Among different chain length metal alkylthiolates, Ni butanethiolate with the shortest carbon chain (C4) is found to be most efficient in retaining sharp oxidation at low potential value and high current density. Electrochemical property of Ni butanethiolate towards glucose oxidation is examined on different electrode surfaces such as Au thin film, Au mesh and FTO. Interestingly, the glucose oxidation takes place most efficiently on Au mesh network as compared to Au film and FTO substrates. The Ni(SC4H9)2/Au mesh exhibited two linear ranges of detection from 0.5 1 ACS Paragon Plus Environment

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2 mM and 2 - 11 mM with the sensitivity value of 675.97 µA.mM-1cm-2 and Limit of Detection (LOD) of 2.2 µM along with excellent selectivity and reproducibility. The present study demonstrates that Ni butanethiolate on Au mesh acts as a promising functional and transparent electrode material with a possibility of large-scale production for practical glucose detection. Keywords: Ni alkylthiolate, electrochemical, transparent, glucose sensing, sensitivity, detection 1. Introduction Glucose sensors have gained popularity due to their wide applicability not only as healthcare device for diabetic patients but also for food industries in chemical analysis.1–3 Most of the currently used glucose either involve electrochemical methods or spectrophotometry based on optical absorption.4 Optically transmitting yet conducting electrodes in biosensors are gaining popularity as they can be used in daily lives such as in contact lenses and display devices.5 Moreover, simultaneous detection by electrochemical and optical methods requires the development of functional yet transparent electrodes. In literature, Indium Tin oxide (ITO) and Fluorine-doped Tin oxide (FTO) have been used for the fabrication of transparent optical biosensors as these are conductors and transparent in the visible region.6 However, ITO and FTO thin film have limited surface area due to planar geometry that limits either the transparency or the ultimate performance of the device. In addition, the ITO/FTO itself is not a redox-active material and requires functionalization that reduces the overall transmittance of the sensor. Thus, the applicability of the currently available transparent conducting electrodes is limited because of their poor selectivity, poor stability, less robustness, and fabrication intricacy. The noble-metals such as Au, Pd, Pt provide a robust platform for functionalization with the biomolecular systems, but these are reflective and non-transparent.6 As an alternative, non-ITO and non-FTO based transparent metal electrodes have been fabricated by various techniques such as

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Ag and CuO metal nanowire network and other template-based metal networks along with conventional lithographic techniques for the fabrication of transparent biosensors.7 Crackle lithography has emerged as an unconventional method for fabrication of transparent metal mesh network.8,9 Using this technique, a transparent Au metal wire network is prepared as a current collecting electrode and functionalized with redox-active species for fabrication of a transparent glucose sensor. In an enzymeless glucose sensor, electrocatalysts play an important role in ascertaining its efficiency as well as its performance.10 Various nanomaterials of noble metals,11 metal oxides,12 nitrides,13-14 carbides15 and chalcogenides16 with different morphologies, shape, size and crystallinity have been employed as active electrocatalytic material for fabrication of glucose sensors. Ni-based nanomaterials are well known as efficient electrocatalyst due to their easily reversible redox couple.17–19 Moreover, Ni is also abundant and cost-effective that makes it highly suitable for glucose sensing. The nanostructured Ni/NiO and their composite materials with high surface area are usually synthesized by variety of techniques such as electrodeposition, physical vapor deposition, anodization and hydrothermal synthesis.13 Literature is bound with enormous examples of glucose sensors based on nickel oxide nanostructures due to their high sensitivity, specificity and selectivity.20 Various 3-dimensional, porous architectures with high surface area are fabricated for the improvement of the sensor characteristics such as operating voltage, detection range, sensitivity and limit of detection (LOD). Shen et al. used one-step method for fabrication of glassy carbon electrode modified with Ni nanoparticles-AttapulgiteGO hybrid electrode using electrodeposition technique which showed LOD as low as 0.37 µM.21 Yang et al. synthesized hierarchical Ni(OH)2 hollow nanorods using chemical bath sonication for obtaining high sensitivity of 2904 µA.mM-1 cm-2 and LOD limit of 2 µM however the linear



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detection range is only up to 3.86 mM and does not meet the physiological range of glucose levels.22 Liu and his coworkers have developed Ni-doped diamond-like carbon film using magnetron radio frequency co-sputtering process for high sensitivity up to 10 mM glucose concentration without any influence from interfering species with excellent reversibility for glucose detection.23 Clearly, Ni/NiO based nanostructures are found to be excellent materials for the fabrication of glucose sensors, however, none of the sensors reported are transparent in nature. Further, there is a dire need for the development of easily scalable production methods for commercialization of these glucose sensors. Most of the literature methods are based on nonscalable synthetic techniques and thus, not yet commercialized.

Ni alkyl thiolate based

precursors in toluene can be easily prepared as ink for direct application by a solution based process. Moreover, thiolate ink is known to bind well with metallic substrates such as Au and Ag. In this paper, a series of Ni alkyl thiolate are synthesized as single source precursors and electrodes are fabricated by drop casting these on conducting substrate. It is further electrooxidized resulting in a thin electrocatalytic layer for electrochemical glucose sensing. The method has an advantage of obtaining well-distributed redox-active centres without any aggregation resulting in reproducible and stable results. Among different chain length thiolates, Ni butyl thiolate with short alkyl chain results in high current density at lower voltage as thus acts as an optimum coating for sensing application. The transparent Au mesh showed high electrochemical sensing performance for non-enzymatic detection of glucose due to high electrocatalytic activity of Ni butanethiolate.

2. Experimental Section (a) Chemicals 4 ACS Paragon Plus Environment

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Ni(II) chloride hexahydrate (CAS No. 7791-20-0) and glucose were purchased from Fischer Scientific Inc. All the thiols of different chain length, butanethiol (CAS No. 109-79-5), octanethiol (CAS No. 111-88-6), dodecanethiol (CAS No.112-55-0), hexadecanethiol (CAS No. 2917-26-2) were purchased from Sigma Aldrich in highest purity. Fluorine-doped tin oxide (FTO) substrates of sheet resistance 7 Ω/sq were purchased from Techinstro (Product Code TISXZ001) (b) Fabrication of Electrode Ni(II) chloride hexahydrate in ethanol (1 M) was heated at 70°C with 2 M triethylamine followed by addition of 2 M alkanethiol (RSH; R= C4H9, C8H17, C12H25, and C16H33) and continuously stirring for 12 hrs. The product obtained was washed thoroughly in acetonitrile and methanol for removing excess of unreacted thiols and vacuum dried. The obtained Ni alkylthiolates were solubilized in toluene to make 1 mg/mL of solution for electrode fabrication. The Au film and FTO working electrodes of 3 mm diameter circular region were fabricated by patterning using toner masking technique developed in this study followed by Au metal evaporation. Crackle lithography was employed for the fabrication of Au mesh electrodes as detailed below. Different Ni alkylthiolates complex solutions (5 µL) in toluene were drop coated and allowed to dry for 2 hr before use. The Au mesh is prepared by crack template method. Briefly, a commercially-available crackle finish paint (DecoArt, USA) is mixed with IPA and water in 80:20 to a concentration of 0.5 mg/mL, sonicated for 10 min and spin-coated on glass substrates at 800 rpm for 30 s. Upon drying, the coated layer forms a network of well-connected cracks. The Au metal is deposited by physical vapor deposition (PVD) in the active area of 5 mm diameter by using a physical mask, and the crack template is removed by dissolving in chloroform leaving behind Au network on a



glass substrate. The patterned substrates were examined using an Optical Microscope (Laben, India). The physical mask of the toner was first printed on PET sheet and transferred to the glass substrate by hot pressing the toner printed side of PET towards the glass substrate at an optimum temperature of 200˚C. The FTO and Au films were patterned by physical masking created using hot press toner transfer technique on standard FTO and glass substrates respectively. (c) Characterization The absorbance spectra were recorded using UV-Vis spectrophotometer (Varian Cary 4000) over a wavelength range of 200-800 nm. Fourier Transform Infrared spectroscopy (FTIR) was performed using Bruker Vertex 70 V+ PMA50 spectrometer in the range of 600 to 3000 cm-1. The sample preparation was done by pelletizing the complex with standard KBr (analytical grade). FESEM measurements were performed Nova NanoSEM600 instrument (FEI., The Netherlands). XPS characterization was carried out on Omicron Nanotechnology (Oxford Instruments). Samples for XPS were prepared by drop-coating Ni thiolate on Au/glass substrates. Electrochemical measurements were performed using electrochemical workstation (CHI660ECH Instruments Inc.). The cyclic voltammetry (CV) was done in three-electrode geometry with Ni alkylthiolate coated Au metal network, FTO and Au film as working electrodes, Ag/AgCl as the reference electrode and Pt as the counter electrode. NaOH (0.1 M) was used as an electrolyte. A voltage range of 0.2 - 0.8 V was chosen and measurements were performed at different scan rates (10 - 350 mV/s). Glucose solutions were made in 0.1 M NaOH. Electrochemical measurements were carried out with various electrodes in different concentration of glucose solutions. The CV measurements of blank Au electrode were carried out in 0.1 M blank NaOH at a scan rate of 50 mV/s as control (SI, Figure S3). The reproducibility of the glucose sensor was


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examined by testing five different electrodes under same conditions as described in the experimental section.

3.Results and Discussion The Ni alkylthiolate complexes of different chain length were synthesized following the previously reported procedure as explained in the experimental section.24,25 Briefly, solution of nickel chloride and alkylthiol were mixed in the presence of triethylamine in ethanol at 70 °C with vigorous stirring resulting in a precipitate due to complex formation. All the complexes were characterized by FTIR and UV-vis spectroscopy as shown in Figures S1 and S2. In FTIR spectra, all the peaks are indexed as shown in Figure S1. With the increasing chain length, there is a clear increase in peak intensity of anti-symmetric CH2 peak. In the UV-vis spectra (Figure S2), all the signatures are ascribed to ligand to metal charge transfer and since there is no peak corresponding to d-d transition for tetrahedral Ni(II), it suggests a square planar arrangement of Ni(II). These complexes are dissolved in toluene and drop-coated on Au film as shown by schematic in Figure 1a. The Ni alkylthiolate complexes on drop coating form a uniform thin film on electrode surface despite of random orientation of molecules due to the lamellar structure of these complexes.26 The Ni alkylthiolates molecules on Au electrode are subjected to consecutive cyclic voltammetry cycles for electroxidation of the Ni alkylthiolate chains leading to self assembly of molecules under applied field (Figure 1a). The FESEM image in Figure 1b shows the well distributed random nanoparticles present on the electrode surface after electro-oxidation. The CV cycles are repeated until a saturated voltage and current is obtained as shown in Figure 1c-f. The first voltammetric curve represents the oxidation of the Ni ions to Ni(OH)2 in 0.1 M



NaOH (indicated by the first cycle with different peak potential). Since blank Au electrode did not exhibit any peak around 0.4 - 0.6 V in CV measurement (SI, Figure S3), this indicates that the redox peaks in Figure 1c correspond to Ni alkylthiolates only. This is also the reason for selecting Au as the current collecting electrode. The progressive increase in anodic and cathodic peak currents can be seen with the oxidation of Ni(OH)2 to NiOOH.28,29 As seen in Figure 1c, the repeated measurements increase current density and peak shifting towards lower potential values. The highest anodic peak current was observed in case of Ni(SC4H9)2/Au (henceforth abbreviated as Ni-C4SH/Au) with the current density of 1.06 mA/cm2 whereas Ni-C16SH/Au exhibits the lowest current density of 0.12 mA/cm2 even after 25 cycles. The increase in current could be due to the reorientation of molecular ligands during redox activity.17 Moreover, Ni-C4SH is known to possess distorted structure as compared to other long chain thiols where ordering is lamellar in nature.24 The measurements were continued for 25 cycles till the saturated current was obtained along with a constant peak potential. This process helps in getting rid of the ligands on the surface and exposes the Ni redox-active centres directly to the electrolyte. The anodic peak current for the thiolates increases with respect to descending carbon chain length (IC4>IC8>IC12>IC16). The peak shift is much more drastic from 0.70 V to 0.55 V in case of NiC4SH/Au as compared to other longer chain thiolates (inset, Figure 1c). In case of Ni-C8SH/Au and Ni-C12SH/Au, the peak shift occurs only after several cycles (inset Figure 1d and e) while in case of Ni-C16SH/Au in Figure 1f, the redox peak is absent in the beginning and takes several odd cycles for a low current peak (31.97 µA) to originate at 0.65 V. Moreover, the peak in first cycle has different potential than that of the rest of the cycles. The insets of the Figure 1c-f represent the anodic peak potential (VA,p) values of the respective thiolates. After the preelectrooxidation, it is observed that with the number of cycles, the peak potential stabilizes to a


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particular potential with the oxidation of Ni(OH)2 to NiOOH.19,30 The stability in the peak potential for initial 25 cycles can be seen from insets of Figure 1c-f. From Figure 1g, it can be seen that the peak position of the Ni alkanethiolates changes with the increasing number of carbon atoms. Increase in anodic peak current with increasing number of alkyl carbon atoms is shown in Figure 1h. A steep decrease in anodic peak current is observed with increasing number of alkyl carbon atoms. Peaks are seen to be shifting more towards positive side with an increased peak current which could be probably due to electron hopping across the alkyl carbon chain.31 As the carbon chain length increases, more potential is required for the electron transfer; hence a change in peak position towards positive side is observed (SI, Figure S4). Similarly, with the decrease in the carbon chain, the number of electrons hoping through increases, leading to an increase in current at much lower peak potential which is essential for electrochemical activity. The butyl chains in Ni butyl thiolate are known to be defective and attains various conformations that may result in highly exposed Ni(II) redox centres.24 This lead to higher redox activity within the same area as compared to the other Ni based alkyl thiolates. The detailed surface composition and oxidation was carried out by X-ray photoelectron spectroscopy (XPS) on the Ni-C4SH/Au electrode before and after electrooxidation by applying 100 cycles of CV at 50 mV/s. The full survey spectra show presence of peaks corresponding to Ni 2p, O 1s, S 2p , Au 4f, and C 1s as seen in Figure S5. In the high resolution spectrum of Ni 2p regime, two peaks were observed at 853.8 eV and 871.04 eV corresponding to Ni 2p3/2 and Ni 2p1/2 due to the Ni(II) species in the thiolate complex. After electrooxidation, there is a shift in Ni(II) peaks to lower binding energy (853.6 eV and 870.64 eV) due to weakening of Ni-S linkage and emergence of new peaks at 855.6 eV and 873.2 eV corresponding to Ni(OH)2 formation at the surface.17 The spin energy separation of ~17 eV is attributed the formation of Ni(OH)2. A satellite peak is as well observed



at 861.16 eV. To further confirm the presence Ni(OH)2, high resolution O 1s spectra were deconvoluted as seen in Figure 2b. For the pristine electrode, a small peak was observed at 532.5 eV which corresponds to M-O bond due to surface oxygen species. On electrooxidation, two highly intense peaks appear at 530.9 eV and 531.5 eV corresponding to the oxide species along with surface hydroxylation. Thus, from XPS measurements, it can be concluded that the Ni-C4SH transforms into NiO and Ni(OH)2 after electroxidation which is as well observed electrochemically in Ni alkylthiolate complexes by an evolution of redox peak in Figure 1c-f. Thus, Ni-C4SH/Au is used further for testing the electrochemical performance towards glucose sensing. In most of the Ni based materials, it is well known that the surface of all these active material converts to metal hydroxide in presence of alkali based electrolyte which is responsible for sensing. However, it is important to examine the influence of the nature of nanoparticles formed from these complexes on the extent of electrocatalytic activity. The electrochemical sensing properties of Ni-C4SH/Au were investigated using cyclic voltammetry in presence and absence of 1 mM glucose solution in 0.1 M NaOH at different scan rates as shown in Figure 3. The redox peaks obtained for Ni-C4SH/Au in blank NaOH and 1 mM glucose are shown in black and red color curves respectively (Figure 3a and b). The well-defined redox peaks at 0.50 V (cathodic peak) and at 0.55 V (anodic peak) in Figure 3a-d correspond to Ni2+/Ni3+ redox couple formation which increases with increase in scan rate. However, for the same scan rate, an apparent increase in current is observed upon addition of 1 mM glucose to the blank NaOH solution. The slight shift in peak potential and increased current is observed with successively increasing scan rate as shown in Figure 3a-d.32 The plausible reason is because of the oxidation of glucose to gluconolactone by NiO(OH) accompanied with formation of Ni(OH)2.33,34 Figure 3e and f demonstrates the linearity of anodic and cathodic peak current (IA,p 10 ACS Paragon Plus Environment

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and IC,p) with square root of different scan rates for blank and 1 mM glucose respectively. It can be seen that IA,p and IC,p both increases linearly with the increasing scan rate. The linear relationship in both cases is important for the sensing device as it indicates reversibility of electron transfer process taking place during the electrochemical reaction. The correlation coefficient, R2 = 0.998 in Figure 3f confirms that Ni nanostructures formed by the electrooxidation of Ni butanethiolate possess excellent electrocatalytic activity for enzymeless glucose oxidation.33 The above results in Figure 3 show that Ni nanostructures derived from Ni-C4SH layer is electrocatalytic active towards glucose sensing. The Au mesh electrodes were fabricated by combination of toner transfer patterning and crackle lithography as shown schematically in Figure 4a. The crackle precursor spontaneously cracks resulting in an interconnected network of empty space that is filled with Au metal by physical vapor deposition in masked region. The physical masking is done by transferring laser jet printed toner on PET sheet to glass substrate by hot pressing as demonstrated in Figure 4a. The resulting Au network possess a sheet resistance of Au mesh is ~ 4 Ω /sq which is slightly higher than the Au film ~ 2 Ω/sq however appears to be significantly transparent (Figure 4b). The transmittance of Au mesh coated with Ni-C4SH was measured to be ~ 60 % which is slightly lower than Ni-C4SH/FTO however sufficient enough for clear visibility (Figure 4c). The transparency of metal mesh is attributed to the voids present between the seamlessly connected wire networks (Figure S6) fabricated by crackle lithography technique.27 The electrochemical behavior of the electrode is further examined for their application as functional material in glucose sensors. Au film and Au mesh electrodes were functionalized with Ni-C4SH layer and electro-oxidized as described before to understand if there are any differences in their electrochemical response with and without glucose due to changes in the 11 ACS Paragon Plus Environment


electrode geometry (Figure 5). CV curves of Ni-C4SH/Au film and Ni-C4SH/Au mesh after electro-oxidation in 0.1 M NaOH are shown in Figure 5a and b. The oxidation peak corresponding to Ni2+ is obtained at much lower potential using Au mesh electrode as compared to the Au film. However, the reversibility of Ni-based redox reaction is lowered for Au mesh as indicated by the higher peak-peak separation as well as the ratio of peak currents. Clearly, Au mesh based electrodes can enable sensing at lower operating voltage due to low oxidation potentials in contrast to Au film. For understanding the glucose response, CV curves were obtained in the range of 0.2 - 0.8 V versus Ag/AgCl for Au film and 0.2 - 0.6 V versus Ag/AgCl for Au mesh (Figure 5c and d). The current density is observed to be linear with respect to square root of scan rate for Ni-C4SH/Au mesh electrode with and without glucose as shown in Figure S7 indicating the catalytic activity of Ni based electrode is not compromised by using modified Au mesh electrodes as well. A constant increase in the anodic peak current and decrease in cathodic peak current is seen with the increasing glucose concentrations in both the cases (seen in Figure 5a and b) in accordance with literature.35–37 However, the onset potential and the voltage range for electrocatalytic activity is different for Au mesh and Au film. The Au mesh is made of seamless wire network that offers high surface area to glucose molecules and reduces the overpotential for oxidation to (Vp,mesh = 0.45 V) in comparison to Au film (Vp, film = 0.55 V). The electrocatalytic activity in Au mesh is relatively more pronounced in reverse cathodic scan at positive potentials as seen by the raised current with respect to that of Au film based electrode. The reversibility of the mesh based electrode in presence of high concentration of glucose (< 4 mM) is relatively low, however sufficient enough for one-time glucose sensing application. The highest anodic peak current of the CV curves of Au film and Au mesh for each glucose concentration is plotted and fitted linearly to obtain two different ranges of concentration. The


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higher region was observed from 1 - 8 mM for Au film and 2 - 8 mM for Au mesh. The lower ranges lie between 0.03 - 1 mM and 0.2 - 1.5 mM for Au film and Au mesh respectively. The glucose concentration versus current density obtained from anodic peak current values display a excellent linearity with a correlation coefficient value, R2 = 0.944 and R2 = 0.998 of glucose concentration below 1 mM and 1.5 mM in case of Ni-C4SH/Au film, and Ni-C4SH/Au mesh respectively (Figure 5e and f). Similarly, for the higher region, the R2 values were 0.986 and 0.996. The results obtained with transparent Au mesh electrode are comparable with Au film electrode. However, FTO electrode possess a very narrow range of detection (0.5 - 5.5 mM) and R2 = 0.971 indicating lower electrocatalytic activity of Ni-C4SH/FTO towards glucose oxidation probably due to lesser electron conduction compared to Au (SI, Figure S8). The performance metrics of different electrodes are compared in SI, Table S2. The value of sensitivity and LOD is calculated as given in Note S1. The value of R2 for Au mesh specifically indicates high electrocatalytic activity with high sensitivity in lower ranges of glucose. To further study the performance of the Ni-C4SH/Au mesh and Ni(SC4H9)2/FTO electrodes as sensors, I-t measurements were performed for both the electrodes in three-electrode geometry at an applied voltage of 0.6 V as shown in Figure 6a and b respectively. Systematic jumps in the current are observed with time in an otherwise constant current density at 0.6 V upon successive addition of aliquots of 50 mM glucose in 10 mL of 0.1 M NaOH. In case of Au mesh, it takes more time to respond to the glucose as compare to that of FTO. This may be due to lower 2-D surface area of the wire electrode thus giving a time delay in the current response. The glucose is added to the system until no change in current is observed. A saturation limit is obtained after glucose concentration becomes 11 mM for Au mesh and 5.3 mM, in case FTO electrode suggesting faster coverage of actives sites on FTO surface by intermediates formed 13 ACS Paragon Plus Environment


during reaction making them less available for incoming glucose molecules as compared to Au mesh. Clearly, the projected surface area of Au mesh that is electrochemically active is comparatively higher than FTO due to the lateral contribution from the thickness of the wire network even though the geometrical area of metal mesh is lower (25%). It is important to note that the concentration range of detection is wider for Au mesh as compared to FTO and human blood glucose range lies between 1- 8 mM that makes Au mesh based electrode ideal for glucose sensing. The calibration plot obtained from the I-t measurement in Figure 6c shows two different concentration regimes where the current response is linear. The R2 value is 0.999 in lower concentration region of 0.5 - 2 mM with and 0.988 for Au mesh in the higher region of 2 - 11 mM. These values are comparatively better than that of FTO and Au film based electrodes (Figure 6c, and SI, Figure S9). The sensitivity and LOD were found to be 675.97 µA.mM-1cm-2 and 2.167 µM (S/N = 3) for Au mesh for lower region. The Ni-C4SH/FTO electrode exhibited the sensitivity of 852.05 µA.mM-1cm-2 and a LOD of 6.082 µM (S/N = 3) as obtained from the slope and extrapolation of linear calibration curve of I-t measurements, respectively (SI, Table S2). The wide range of glucose detection in Au mesh can be attributed to the interconnected 2Dwire network with high electrode/electrolyte interface that provides more active sites to the glucose molecules. Figure 6d shows the actual range of values of glucose present in body fluids such as urine, saliva, and sweat. The higher range of detection was experimentally observed to be 2 - 11 mM for Ni-C4SH/Au mesh electrode which can be easily used for detecting blood glucose simultaneously the lower range of detection is from 0.5 - 2 mM and which can be used for a variety of body fluids. For Au mesh, glucose detection range is wider as compared to FTO and thus it can be used for the blood glucose detection as well. Interference tests were also performed with other molecules that might be present in low quantities in blood (0.1 mM) along with higher


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concentrations of glucose (3 - 8 mM).38 I-t measurement was performed with the successive addition of glucose and other interfering sugars such as 0.1 mM maltose, 0.1 mM fructose, 0.1 mM sucrose, 0.1 mM lactose and 0.1 mM of ascorbic acid with Ni-C4SH/Au electrode (SI, Figure S10). Since, the other molecules are usually present in much lower concentrations compared to the concentration of the glucose in blood sample, we have used 0.1 mM concentration of the interfering molecules. The change in the current density is observed to be marginal as compared to the change in the current density upon exposure to 1 mM concentration of glucose. After addition of interfering molecules, a further addition of 2 mM glucose resulted in a significant increase in the current density (Figure S10) indicating negligible influence of interfering molecules on electrocatalytic activity of Ni-C4SH/Au electrode towards glucose oxidation. The electrochemical response of Ni-alkanethiolate films/ Au mesh electrode towards glucose is comparable to the state-of-the-art results in literature (Table S3).17-22 The bar graph representing variation in current ratio response with the respective electrodes is shown in Figure S10. The fluctuation in the current response for glucose detection was found to lie within the limit (

Metal Wire Networks Functionalized with Nickel Alkanethiolate for

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