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This article reviews the progress made in the past 5 years in the field of direct and non-enzymatic electrochemical sensing of glucose. Following a brief discussion of the merits and limitations of enzymatic glucose sensors, we discuss the history of unraveling the mechanism of direct oxidation of glucose and theories of non-enzymatic electrocatalysis. We then review non-enzymatic glucose electrodes based on the use of the metals platinum, gold, nickel, copper, of alloys and bimetals, of carbon materials (including graphene and graphene-based composites), and of metal-metal oxides and layered double hydroxides. This review contains more than 200 refs.

We report on a simple and reliable method for the determination of trace cadmium ion using a glassy carbon electrode (GCE) modified with cupferron, s-naphthol and MWCNTs. The operational mechanism consists of several steps: first, the ligand cupferron on the modified electrode reacts with Cd2+ ion to form a chelate compound. Next, this chelate is adsorbed by the carrier s-naphthol following the principle of organic co-precipitation. Finally, the coprecipitated complex is detected by the GCE. This scheme is interesting because it combines preconcentration and electrochemical detection. Two linear responses are obtained, one in the concentration range of 5.0 × 10−11 to 1.6 × 10−8 M, the other in the range of 1.6 × 10−8 to 1.42 × 10−6 M, with a lower detection limit of 1.6 × 10−11 M. This modified GCE does not suffer from significant interferences by Cu(II), Hg(II), Ag(I), Fe(III), Pb(II), Cr(III), Zn(II), NO3−, Cl−, SO 4 2− ions and EDTA. The response of the electrode remained constant for at least 3 weeks of successive operation. The method presented here provides a new way for the simultaneous separation, enrichment, and electrochemical detection of trace cadmium ion.

A hydrothermal technique was used to synthesize nickel ferrite nanoparticles (NF-NPs) deposited on multi-walled carbon nanotubes (MWCNTs). The material was characterized by scanning electron microscopy, energy dispersive spectrometry, and X-ray powder diffraction which showed that the NF-NPs are located on the surface of the carboxylated MWCNTs. The material was used to modify a glassy carbon electrode which then was characterized via cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry. The electrode displays strong electrochemical response to hydrazine. A potential hydrazine sensing scheme is suggested.

An electrode sensitive to uric acid was prepared by electrodeposition of nickel(II) hexacyanoferrate(III) on the surface of a glassy carbon electrode modified with multi-walled carbon nanotubes. The morphology of the material was characterized by scanning electron microscopy and Fourier transform infrared spectrometry. The modified electrode were characterized via cyclic voltammetry and amperometry (i - t). It exhibited efficient electron transfer ability and a strong and fast (< 3 s) response towards uric acid which is linear in the range from 0.1 μM to 18 μM, with a lower detection limit of 50 nM (at an S/N ratio of 3). In addition, the electrode exhibited good reproducibility and long-term stability.

An electrochemical sensor for theophylline (ThPh) was prepared by electropolymerizing o-phenylenediamine on a glassy carbon electrode in the presence of ThPh via cyclic voltammetry, followed by deposition of gold nanoparticles using a potentiostatic method. The effects of pH, ratio between template molecule and monomer, number of cycles for electropolymerization, and of the solution for extraction were optimized. The current of the electro-active model system hexacyanoferrate(III) and hexacyanoferrate(IV) decreased linearly with successive addition of ThPh in the concentration range between 4.0 × 10−7 ~ 1.5 × 10−5 mol·L−1 and 2.4 × 10−4 ~ 3.4 × 10−3 mol·L−1, with a detection limit of 1.0 × 10−7 mol·L−1. The sensor has an excellent recognition capability for ThPh compared to structurally related molecules, can be regenerated and is stable.

We are presenting a sensor for hydroxylamine that is based on an glassy carbon electrode modified with nanoparticles of Prussian Blue and with multi-walled carbon nanotubes (MWCNTs). The sensing material was synthesized using a mixture of ferric chloride and potassium ferricyanide solution in the presence of MWCNTs under ambient conditions. Characterization was done by scanning electron microscopy, UV-vis spectroscopy, Fourier transform infrared absorption spectrum and cyclic voltammetry. The modified electrode showed two well-defined pairs of redox peaks and dramatic catalytic activity towards the electro-oxidation of hydroxylamine with a linear response ranging from 1.5 µM to 2.0 mM. In addition, tests show the sensor exhibited outstanding stability and reproducibility.

A non-enzymatic amperometric glucose is reported that is based on an glassy carbon electrode modified with a Cu-CuO nanowire (NW) composite. The morphology and the composition of the nanowire were characterized by scanning electron microscopy and X-ray diffraction, respectively. The modified electrode efficiently catalyzes the oxidation of glucose at less-positive potential (0.30 V) in 0.10 M NaOH solution in the absence of any enzymes or redox mediators. The sensor was successfully used for the amperometric sensing of glucose. Linear response was obtained over the concentration range from 0.1 to 12 mM. The common interfering agents ascorbic acid and uric acid do not interfere with the determination of glucose. The modified electrode features high sensitivity, low working potential, excellent stability, and fast amperometric sensing of glucose. Thus it is promising for the future development of non-enzymatic glucose sensors.

Hexagonal β-Ni(OH)2 nanosheets were synthesized by a simple template- and surfactant-free hydrothermal approach. They were characterized by scanning electron microscopy, X-ray powder diffraction, and thermal gravimetric analysis. The nanosheets were incorporated, along with chitosan, into an amperometric sensor which displayed a good performance in terms of detection of hydrogen peroxide. The linear range is from 5.0 µM to 0.145 mM, the sensitivity is 24.76 µA mM−1, the detection limit is 0.5 µM, and the response time is

A novel route is presented for the fabrication of chromium (III) hexacyanoferrate(II) (Crhf) nanoparticles attached to single-walled carbon nanotubes (SWNTs) modified glassy carbon electrodes (GCE). The morphological character of the Crhf/SWNTs nanocomposites was examined using scanning electron microscopy (SEM), transmission electron microscopy, UV-Vis spectroscopy and Fourier transform infrared spectrometry. The performance of the Crhf/SWNTs nanocomposite modified electrode was characterized using cyclic voltammetry and amperometry. The electrode exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. Moreover it showed a wide linear working range (0.5–500 μM hydrazine), with a detection limit of 0.45 μM estimated at a signal to noise ratio of 3. Response time is fast (about 3 s) and the electrode exhibited good reproducibility and long-term stability.

LaFeO3 nanoparticles of approximately 22 nm in size were synthesized and characterized by XRD and TEM. A novel glassy carbon electrode modified with LaFeO3 nanoparticles was constructed and characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.145 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The anodic peak current (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range from 1.5 × 10−7 to 8.0 × 10−4 M. The detection limit was 3.0 × 10−8 M. The relative standard deviation of eight successive scans was 3.47% for 1.0 × 10−6 M DA. The interference by ascorbic acid was eliminated efficiently. The method was used to determine DA in dopamine hydrochloride injections and showed excellent sensitivity and recovery.

Silver nanoparticles (AgNP) were synthesized with NaBH4 as reducing agent and oleate as stabilizer. AgNP and L-cysteine (L-cys) were co-deposited on a gold electrode surface to fabricate the AgNP/L-cys modified electrode (AgNP/L-cys/Au). First, we prepared the L-cysteine self-assembled film modified gold electrode through S-Au bond, then it was rinsed into the Ag colloid solution to prepare the Ag nanoparticles/L-cysteine modified electrode through interaction of the silver surface and the carboxylate and amino groups of L-cysteine. After the self-assembled electrode was prepared, the electrochemical behavior of the modified electrode was investigated. The electrochemical response of neutral red (NR) on the modified electrode was investigated. The electrochemical response of cyclic voltammetry and determination by differential pulse voltammetry of neutral red on the modified electrode were reported. We also observed that the modified electrode catalyzes the redox process of neutral red, which provided another way of applying Ag nanoparticles in composite neutral red-AgNP films.

A glassy carbon electrode (GCE) modified with ferrocenecarboxamide, gold nanoparticles and multiwall carbon nanotubes was constructed and characterized by field emission scanning electron microscopy and cyclic voltammetry. The electrochemical behavior of bilirubin (BR) on the modified electrode was investigated and it was found that the modified electrode had an obvious electrocatalytic effect on bilirubin. Compared with a bare GCE, the modified electrode exhibited a marked enhancement in the current response for bilirubin. Amperometry was employed to investigate the electrocatalytical oxidation of bilirubin on the modified electrode. As a result, it exhibits an excellent electrocatalytic response to bilirubin with a response time of less than 5 s, a broad linear range of 1 to 100 μmol L−1, as well as good long-term stability and reproducibility.

A carbon nanotube (CNTs)/lanthanum hydroxide(La(OH)3)nanocomposite was firstly synthesized, and characterized in terms of structure and morphology through X-ray diffraction analysis and transmission electron microscopy. The electrochemical behavior and potential electrochemical applications of the nanocomposite modified electrode were also studied. Cyclic voltammetry was used to probe the characterization of the modified electrode. The modified electrode was used for the determination of adenine and guanine, and the, accelerated electron transfer mechanism was investigated. The result demonstrated that the CNTs/La(OH)3 modified electrode provides an effective method for the determination of adenine and guanine with detection limits 0.22 and 0.26 µM, respectively.

CeO2 nanoparticles approximately 12 nm in size were synthesized and subsequently characterized by XRD, TEM and UV-vis spectroscopy. Then, a gold electrode modified with CeO2 nanoparticles was constructed and characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode demonstrated strong catalytic effects with high stability towards electrochemical oxidation of rutin. The anodic peak currents (measured by differential pulse voltammetry) increased linearly with the concentration of rutin in the range of 5.0 × 10−7–5.0 × 10−4 mol · L−1. The detection limit (S/N = 3) was 2.0 × 10−7 mol · L−1. The relative standard deviation (RSD) of 8 successive scans was 3.7% for 5.0 × 10−6 mol · L−1 rutin. The method showed excellent sensitivity and stability, and the determination of rutin in tablets was satisfactory.

A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452 nm, the linear ranges of calibration curves were 0–0.8 µg mL−1 for bovine serum albumin (BSA), 0–1.2 µg mL−1 for human serum albumin (HSA), and 0–2.5 µg mL−1 for human γ-IgG (γ-IgG), respectively. The detection limits were 1.3 ng mL−1 for BSA, 10 ng mL−1 for HAS, and 5.7 ng mL−1 for γ-IgG.