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Supplementary Information
Nickel Cobalt Oxide Nanoneedles for Electrochromic Glucose
Sensors
Devesh K Pathak1, Anjali Chaudhary1,$, Manushree Tanwar1, Uttam K Goutam2, Puspen Mondal3 and Rajesh Kumar1,4,5,*
1
Materials and Device Laboratory, Department of Physics, Indian Institute of Technology Indore, Simrol-453552, India.
2
Technical Physics Division, Bhabha Atomic Research Centre, Mumbai-40008, India 3
Lithography & Microscopy Lab, Synchrotrons Utilization Section, Raja Ramanna Centre for Advanced Technology Indore, 452013, India
4
Centre for Advanced Electronics, Indian Institute of Technology Indore, Simrol-453552, India.
5
Centre for Rural Development and Technology, Indian Institute of Technology Indore, Simrol-453552, India.
$
Current address: Department of Materials Science and Engineering University of Wisconsin-Madison 1509 University Avenue Madison, WI 53706
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Figure S1: Selective Area Electron Diffraction (SAED) pattern of NiCo2O4 nanoneddle
Crystallinity of NiCo2O4 nanoneedle has been checked using High resolution TEM analysis.
The different lattice fringe present in the NiCo2O4 crystal structure shows the diffraction
pattern under the effect of light. Meanwhile, selective area electron diffraction (SAED) pattern has also been examined for checking the crystalline behaviour of material, shown in Figure S1. The diffraction image from nanoneedle is producing the discrete ring like fringes, which is an evidence of the polycrystalline nature of sample.
Figure S2: Schematic representation of spectroelectrochemistry set-up with in situ optical measurement
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This spectroelecrochemistry measurement set has been in quartz cuvette and kept inside the UV-Visible spectrometer followed by the external applied voltage, which has been
schematically shown in Figure S2. A second quartz cuvette filled with same electrolyte has also been used in the dual beam optical UV-Visible spectrometer to make the baseline at each and every wavelength during the chromic modulation of respective electrode.
Figure S3: Dimension of Carbon Cloth substrate with NiCo2O4 deposited active area
Carbon Cloth substrate of dimension (1.5cm x 0.5 cm) has been taken for the deposition in which 0.25 cm2 area were coated with NiCo2O4 nanoneddle which has been used to perform
the electrochemistry on that active material surface, shown in Figure S3 with two representation of vertical and horizontal.
Electrochemistry of NiCo2O4 Electrode:
The main advantage of prepared film is that it is completely free from the binder and strongly adhered to the substrate. The NiCo2O4@CC electrode hooked to the working electrode of this
setup and the Ag/AgCl electrode attached to the reference electrode and Pt- wire attached to the counter electrode. The voltage sweep is applied between the working and reference electrode and corresponding current is measured between the counter and working electrode.
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The different path of voltage and current in three electrode systems provide the result of only the material which is hooked to WE and this is measured using CV techniques shown in Figure 4c (main manuscript) with different scan rates in given potential window. The voltage scan follow the two different paths, mentioned here 1 and 2, in which the voltage sweep is started through the path 1 on following the potential route from -0.5V to +0.6 V known as anodic path followed by the oxidation of Ni/Co and revert back to -0.5 V through path 2 known as cathodic path followed by the reduction process of oxidised Ni/Co. This reversible process has been checked here with different possible scan rate. Therefore, these all
components are used for the glucose detection in the same electrolytic medium though the same electrochemistry route.
Observed CV curve from bare and NiCo2O4 nanoneddle deposited CC substrate is a direct
consequence of redox activity of material that has been discussed above. To make the glucose sensor, minimum electrolyte (aqueous NaOH) concentration has been chosen to make its long life in which 0.1 M NaOH electrolyte selected for the suitable, appropriate and stable
electrolytic solution for electrode response and therefore taken for all respective glucose sensing experiment.
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Figure S4: Stability of electrode under 100 continuous CV cycle at +0.4 V oxidation potential
The stability of electrode has been performed on doing the continuous CV cycles for 100 times at fixed 50 mV/Sec and the oxidation current at +0.4 V of every 10th cycle has been plotted in Figure S4 which shows little variation of current and display the flat line of current until to reach the 100th cycle. This stable current response of electrode makes it as a stable, repeatable and long life time of NiCo2O4@CC electrode for its use in commercial products.
Figure S5: Schematic representation of the mechanism of interacting Glucose to the NiCo2O4
nanoneddle via the formation of Gluconolactone ion.
Application of sensing mechanism:
The conducing Carbon Cloth (CC) substrate which having the rounded three-dimensionally active sites to deposit the material is a new thing to obtain the nanoneddle structure along all the dimensions. This provides a higher active surface area of material in same unit area of electrode and thus increases the rate of the reaction. Other thing is that the CC substrate is also flexible so it can be used to make the flexible glucose sensor. The chemical interaction
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of the target glucose analyte to the material can be control by optimizing the surface architecture of material and obviously due to the substrate as discussed in the revised
manuscript. The aqueous NaOH electrolyte has been used for recording the CV signal in the respective potential window, which gives OH- ion to oxidise the Ni and Co atom and help to change the oxidation state. Since this mechanism totally depends upon the absorption and de-absorption of ions at the surface of electrode and hence lead to rise current enhancement during the whole complete cycle by the following the redox reaction route, in which the gluconate ion as converted from glucose lead to give 2e- to this process and is responsible to rise the oxidation current.
Figure S6: Selectivity of electrode (NiCo2O4@CC) in current response on doping of
different ions.
Effect of other electrolytes having different pH are not responding to rise in current rather than doping of glucose molecule. Glucose doping into the solution is always enhancing the current makes this material exclusive for glucose sensing.
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Figure S7: Reproducibility of electrode NiCo2O4@CC in one month for 1 mM glucose
doping
The reproducibility of glucose sensor electrode has been performed for different days show little variation in the current response after addition of glucose in 1mM amount.
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Table S1: Comparison study of NiCo2O4@CC electrode to other for Glucose sensor
Material Detection Limit (M) Sensitivity(A mM-1 cm-2) Ref. ZnO Nanonails 5 24.613 1 Au nanoparticles-functionalized 3D hierarchical ZnO nanostructures
20 1.409 2
Nanoneedle-like copper oxide on N-doped reduced graphene oxide
0.01 3.4 3
Pt3Ru1 alloy nanoparticle 0.3 31.3 4
Cobalt oxide/Au/FTO hierarchical nanostructure
0.1 6000 5
Cu2O on AlOOH/reduced graphene oxide 2.6 155.1 6
ZnO Nanorod 10 23.1 7
Cu/Cu2O nanohybrid electrocatalyst 1.6 1434.12 8
CoWO4 nanospheres 0.7 1416.2 9
ZnO nanocombs 20 15.33 10
Cerium oxide 12 2.87 11
Multilayer films of chitosan, gold nanoparticles 7 555 12
Gold nanoparticles-mesoporous silica nanocomposite
45 2950 13
Fe3O4@Au/MnO2 13.2 2520 14
Fe3O4@SnO2/MWNTs 0.8 58900 15
Ferri-COs 1.38 677 16
Flower-like copper cobaltite nanosheets on graphite paper
5 3625 17
Ni(OH)2-decorated sulfur-doped carbon nanoparticles
0.028 < 1300 18
TiO2-decorated Co3O4 acicular nanotube arrays
0.3396 2008.82 19
Co3O4 nanoflowers and 3D graphene oxide hydrogel
_ 492.8 20
Nanoneddle- NiCo2O4@Carbon Cloth 2 3000 This
Work
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