Tuning the NiO Thin Film Morphology on Carbon Nanotubes by Atomic Layer Deposition for Enzyme‐Free Glucose Sensing

Abstract

Nanocomposites made of stacked‐cup carbon nanotubes coated with NiO (NiO/SCCNTs) via atomic layer deposition (ALD) were synthesized in order to obtain a material exhibiting enhanced and optimized electrochemical performance towards detections of glucose. The structure and morphology were characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). NiO deposited as nanocrystalline particles in the cubic modification, were well dispersed and directly anchored on SCCNTs forming a smooth particulate thin film, which becomes more dense with the increase of the number of ALD cycles. The NiO/SCCNTs samples with various thicknesses of the NiO coating (0.8 nm, 1.7 nm, 4.0 nm, 6.5 nm, 14.0 nm and 21.8 nm) were applied for enzyme‐free glucose sensing. Their electrochemical performance strongly depends on the thickness of the deposited NiO thin film. The best performing glucose sensors respond over a wide concentration range from 2 μM to 2.2 mM (R2=0.9979) with remarkably enhanced sensitivity (1252.3 μA cm−2 mM−1), with a limit of detection (LOD) of 0.10 μM (S/N=3) and with a fast response time (lower than 2 s). The significant performance improvement can be attributed to the conformal NiO coating, high surface to volume ratio and to the optimized thickness of the NiO thin film. The advantage of our sensors is also associated with the conductive supporting material (SCCNTs), simplicity of fabrication, high sensitivity, selectivity, stability and reproducibility for the rapid quantification of glucose.

Gas Sensing of NiO‐SCCNT Core–Shell Heterostructures: Optimization by Radial Modulation of the Hole‐Accumulation Layer

“…The GPC determined from the thickness of the NiO films grown on the SCCNTs for various number of ALD cycles is almost constant. The linear fitting ( R 2 = 0.993) of the NiO thickness versus the number of ALD cycles passes by the origin with a slope of 0.32 Å cycles −1 corresponding to a GPC of 0.32 Å cycles −1 , as also reported recently by us . The average thickness calculated for the NiO‐SCCNT samples from TEM images are similar to the values calculated from ellipsometry data ( Table 1 and Figure S1, Supporting Information).…”

“…It can be seen that both, NiO/Al 2 O 3 /SCCNTs and Al 2 O 3 /SCCNTs, did not show any reflection that can be assigned to the Al 2 O 3 showing the amorphous nature of the ALD deposited Al 2 O 3 film. Moreover, all the NiO‐SCCNTs heterostructures with 50, 100, 200, and 400 deposition cycles of NiO show the diffraction peaks corresponding to the reflections of face‐centered cubic NiO, but with higher number of ALD cycles the reflection from the SCCNTs becomes less pronounced compared to the reflections originating from NiO, reported in our previous article …”

“…Figure shows HRTEM images for the samples coated by 100, 200, 400, and 700 NiO ALD cycles. Some additional HRTEM images to differentiate between the thickness of the NiO shell layer for the SCCNT samples coated with 25, 50, 100, 200, 400, and 700 NiO ALD cycles can also be found in our recent report . It can be seen that the SCCNTs are equally and conformally coated from the inner and the outer surfaces with NiO nanoparticles.…”

“…Fabrication and Characterization of NiO‐SCCNTs and NiO‐Al 2 O 3 ‐SCCNTs Heterostructures : The comprehensive of the experimental procedure can be found in an earlier report elsewhere . Briefly, stacked‐cup carbon nanotubes were treated with nitric acid (HNO 3 , 67%) at 105 °C under reflux for 6 h. The mixture was repeatedly washed and filtered with distilled water until the pH = 7.…”

MOF‐Derived Spinel NiCo2O4 Hollow Nanocages for the Construction of Non‐enzymatic Electrochemical Glucose Sensor

“…The apparent formal potential of the redox process is calculated to be about 0.40 V if the arithmetic mean of two peak values are taken, which is obviously much smaller than that of Co(III)/Co(IV) (0.52 V) and Ni(II)/Ni(III) (0.55 V) as well . This implies the redox reaction of NiCo 2 O 4 features an improved kinetics, which is assumed to be ascribed to the synergistic effect between two metal species in spinel structure, which further favors the catalytic oxidation of glucose significantly.…”