Synthesis of Ta/Ni microcavity array film for highly sensitive uric acid detection

H2O2/Glucose Sensor Based on a Pyrroloquinoline Skeleton-Containing Molecule Modified Gold Cavity Array Electrode

H₂O₂-related metabolites are essential indicators in clinical diagnosis because the accumulation of such reactive oxygen species could cause the risk of cardiovascular disease. Herein, we reported an electrochemical sensor to determine H₂O₂ and glucose. The pyrroloquinoline skeleton containing molecules (PQT) were used as the electrocatalyst and the gold cavity array (GCA) electrodes as the supporting electrode. The GCA electrode was fabricated by electrodeposition using high-ordered two-dimensional polystyrene spheres as the template. The strong absorbability of iodide ions (I^-) displaced adventitious materials from the metal surface and the I^- monolayer was subsequently removed by electrochemical oxidation to get a clean electrode surface. PQT molecules were firmly immobilized on the GCA electrode and performed an excellent electrocatalytic effect on H₂O₂/glucose detection, manifested by a small overpotential and a significantly increased reduction current. A good linear correlation was observed over a wide range of 0.2 μmol/L-1.0 mmol/L with the limit of detection of 0.05 μmol/L. Moreover, the sensor can realize sensitive, accurate, and the highly selective detection of actual samples, proving its application prospect in clinical diagnosis.

Dual-signal uric acid sensing based on carbon quantum dots and o-phenylenediamine

Fluorescent carbon quantum dots (CQDs), which showed excitation-dependent emission characteristics, were prepared using a facile hydrothermal method. The structure and optical properties of CQDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-Vis spectroscopy, and fluorescence spectroscopy. These CQDs also showed peroxidase-like activity and could catalyze the H₂O₂-mediated oxidation of o-phenylenediamine (OPD) to form 2,3-diaminophenazine (DAP) with an absorption peak at 420 nm. DAP exhibited an obvious fluorescence emission at 550 nm under the excitation of 360 nm. On the other hand, it decreased the fluorescence of CQDs at 450 nm via inner filter effect. The experimental results indicated that the H₂O₂ concentration affected the color of DAP and the fluorescence intensity of CQDs and DAP. Thus, a colorimetric and ratiometric fluorescence dual-signal method was established for measuring the concentrations of H₂O₂ and uric acid (UA). The effects of pH, incubation temperature, incubation time, and OPD concentration on the response were investigated. Under the conditions of pH 7.5, temperature 50 °C, incubation time 30 min, and OPD 1.5 mM, the absorbance and fluorescence intensity ratio responses were linearly dependent on UA concentration ranging from 5.0 μM to 100 μM. The limits of detection were 0.7 and 0.5 μM with a colorimetric method and ratiometric fluorescence method, respectively. More importantly, this dual responsive method has been applied to the determination of UA in urine samples with satisfactory results.

Electrochemical synthesis and characterization of poly(thionine)-deep eutectic solvent/carbon nanotube-modified electrodes and application to electrochemical sensing

Electropolymerization of thionine (TH) on multiwalled carbon nanotube (MWCNT)-modified glassy carbon electrodes (GCE) in ethaline deep eutectic solvent (DES) was carried out for the first time, to prepare poly(thionine) (PTH) films with different nanostructured morphologies. PTH films were formed on MWCNT/GCE by potential cycling electropolymerization in ethaline with the addition of different acid dopants CH₃COOH, HClO₄, HNO₃, H₂SO₄ and HCl, acetic acid being the best. The electropolymerization process was monitored with an electrochemical quartz crystal microbalance. The polymerization scan rate was a key factor affecting the electrochemical and morphological properties of the PTH_Ethaline-CH₃COOH/MWCNT/GCE; electrodeposition at 200 mV s^-1 showing the best performance. The PTH/MWCNT/GCE platform was characterized using cyclic and differential pulse voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The analytical characteristics of the PTH films were evaluated for sensing of ascorbic acid and biosensing of uric acid. The developed sensor exhibited a low detection limit (1.1 μM), wide linear range (2.8-3010 μM) and high sensitivity (1134 μA cm^-2 mM^-1) for ascorbic acid. After immobilization of uricase, UOx, on PTH/MWCNT/GCE, the biosensor was successfully applied to the determination of uric acid, with fast response (˂ 7 s), good sensitivity (450 μA cm^-2 mM^-1, wide linear range (0.48-279 μM) and low detection limit (58.9 nM), better than in the literature and than with PTH prepared in aqueous solution. The determination of uric acid in synthetic urine samples was successfully tested and the mean analytical recovery was 100.8 ± 1.4%. This is a promising approach for the determination of uric acid in real samples. Graphical abstract.

A highly sensitive uric acid electrochemical biosensor based on a nano-cube cuprous oxide/ferrocene/uricase modified glassy carbon electrode

A uric acid (UA) electrochemical biosensor was constructed using ferrocene (Fc) decorated cuprous oxide (Cu₂O) enhanced electro-active characteristics and covalently immobilized with uricase (UOx) on glassy carbon electrode (GCE). The electrochemical characteristics of the fabricated electrode was analysed by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV). DPV studies revealed rapid response of fabricated electrode UOx/Fc/Cu₂O/GCE towards UA in a wide concentration range of 0.1–1,000 μM with a sensitivity of 1.900 μA mM⁻¹ cm⁻² and very low detection limit of 0.0596 μM. A very low magnitude Michaelis–Menten constant (Km) value was evaluated as 34.7351 μM which indicated the chemical attraction of the enzyme towards the UA was much higher. The developed biosensor was successfully applied to detect UA in human urine samples. Moreover, reproducibility and stability studies demonstrated the fabricated UOx/Fc/Cu₂O/GCE biosensor had high reproducibility with a RSD of 2.8% and good reusability with a RSD of 3.2%. Specificity studies results showed the fabricated biosensor had strong anti-interference ability. The improved sensor performance was attributed to the synergistic electronic properties of Cu₂O and Fc that provided enhances delectrocatalytic activity and electron transfer. The present biosensor can be extended for use in clinical settings.

Synthesis of an ordered nanoporous Cu/Ni/Au film for sensitive non-enzymatic glucose sensing

Ordered nanoporous Cu/Ni/Au film was prepared by electrochemical deposition and magnetron sputtering using an anodic aluminium oxide template. The fabricated porous film has a uniform hexagonal pore size structure, a long-range ordered arrangement, and a pore diameter of approximately 40 nm. Following the dissolution of the template, the independent Cu/Ni/Au film is devolved to an ITO substrate as an effective non-enzyme glucose detection sensor. The sensor has good electrocatalytic performance with two specific linear ranges of 0.5 μM to 3.0 mM and 3.0–7.0 mM and high sensitivities of 4135 and 2972 μA mM⁻¹ cm⁻², respectively. The lower detection limit was 0.1 μM with a signal-to-noise ratio of 3. Additionally, the sensor features excellent selectivity and stability. These satisfactory results indicate that Cu/Ni/Au film is a promising platform for the development of non-enzymatic glucose sensors.

Ordered nanoporous Cu/Ni/Au film prepared by template method could be transferred and used as an effective glucose sensor.