A Novel Label-free Chronoamperometric Immunosensor Based on a Biocomposite Material for Rapid Detection of Carcinoembryonic Antigen

In this research, poly(diallyldimethylammonium chloride)-capped gold nanoparticles, nickel ferrite particles, and carbon nanotubes were combined to form a PANC metal composite. The prepared metal composite modified onto a glassy carbon electrode was electropolymerized with poly(o-phenylenediamine) and immobilized with horseradish peroxidase, anti-carcinoembryonic antigen antibody, and bovine serum albumin to create the label-free immunosensors for rapid detection of carcinoembryonic antigen (CEA) using chronoamperometry. This developed biocomposite material modified onto a glassy carbon electrode presented an excellent electrocatalytic response to the redox reaction of hydrogen peroxide as a sensing probe, from which the kinetic parameters including of a charge transfer rate constant, a diffusion coefficient value, an electroactive surface area, and a surface concentration were calculated to be 1.85 s⁻¹, 4.28×10⁻⁶ cm² s⁻¹, 0.14 cm² and 1.87×10⁻⁸ mol cm⁻², respectively. The developed immunosensors also exhibited a wide linear range of CEA concentration from 0.01 to 25 ng mL⁻¹ with high sensitivity (96.21 μA cm⁻² ng⁻¹ mL) and low detection limit (0.72 pg mL⁻¹), excellent selectivity without interfering effects from possible species (amoxicillin, ascorbic acid, aspirin, caffeine, cholesterol, dopamine, glucose, and uric acid), outstanding stability (n=100, %I>50 %), repeatability (%RSD=0.34, n=10), reproducibility (%RSD=4.06, n=10), and rapid analysis (25 s each operation time). This proposed method was successfully applied for CEA detection in whole blood samples with satisfactory results, suggesting that this developed sensing platform may be considered to be exploited for fabrication of other label-free electrochemical immunosensors for the real sample analysis.     

Electroanalysis of sulfonamides by flow injection system/high-performance liquid chromatography coupled with amperometric detection using boron-doped diamond electrode

Sulfonamides (SAs) were electrochemically investigated using cyclic voltammetry at a boron-doped diamond (BDD) electrode. Comparison experiments were carried out using a glassy carbon electrode. The BDD electrode provided well-resolved oxidation, irreversible cyclic voltammograms and higher current signals when compared to the glassy carbon electrode. Results obtained from using the BDD electrode in a flow injection system coupled with amperometric detection were illustrated. The optimum potential from a hydrodynamic voltammogram was found to be 1100 mV versus Ag/AgCl, which was chosen for the HPLC-amperometric system. Excellent results of linear range and detection limit were obtained. This method was also used for determination of sulfonamides in egg samples. The standard solutions of 5, 10, and 15 ppm were spiked in a real sample, and percentage of recoveries was found to be between 90.0 and 107.7.     

Use of nickel implanted boron-doped diamond thin film electrode coupled to HPLC system for the determination of tetracyclines

The electrochemical analysis of tetracyclines was investigated using nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) by cyclic voltammetry and high performance liquid chromatographic with amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. Comparison experiments were carried out utilizing as-deposited BDD and glassy carbon electrodes. Ni-DIA electrode provided well-resolved oxidative irreversible cyclic voltammograms and the highest current signals among the electrode studied. High performance liquid chromatography (HPLC) with amperometric detection was also studied. The chromatography was performed using a commercially available Inertsil C18 column, with the mobile phase being: 80% phosphate buffer (pH 2.5)-20% acetonitrile and detected at 1.55 V. The methods were validated over the concentration range 0.05-100 ppm with the overall average recoveries from 83.3 to 102.5% and R.S.D. of less than 10%. The proposed method was further applied to analyse shrimp samples.     

Enhancing a Novel Robust Multicomposite Materials Platform for Glucose Biosensors

An effective, stable enzymatic glucose biosensor was fabricated on a glassy carbon electrode (GCE) surface using simple multicomposite materials (MCM): a solution of prepared poly(diallyldimethylammonium chloride)‐capped gold nanoparticles‐nickel ferrite particles‐carbon nanotubes‐chitosan (PDDA‐AuNPs‐NiFe₂O₄‐CNTs‐CHIT), electropolymerization of poly(o‐phenylenediamine) (PoPD) and immobilization of glucose oxidase (GOx). Biocompatibility and synergy of the MCM enhanced the immobilization and the reaction of GOx and as well as the electron transfer from an oxidation reaction of hydrogen peroxide in the system. The NiFe₂O₄ was synthesized by co‐precipitation and calcined at 700 °C. Characterization was carried out by field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) which presented both tetrahedral and octahedral metal stretching with a cubic NiFe₂O₄ crystal phase. The GOx/PoPD/MCM/GCE yielded a 0.77 s^?1 charge transfer rate constant (K_s), a 2.28×10^?6 cm² s^?1 diffusion coefficient value (D), a 0.21 mm² electroactive surface area (A_e) and a 1.93×10^?8 mol cm^?2 surface concentration ( ) as determined by cyclic voltammetry. The modified electrode showed a durable operation time (n=97, more than 50 % I), repeatability (%RSD=0.38, n=10), reproducibility (%RSD=1.60, n=10), high sensitivity (853.07 μA mM^?1 cm^?2), selectivity without effects of electroactive species (aspirin, uric acid, caffeine, cholesterol, ascorbic acid and dopamine) and two linear ranges from 0.5 to 10 μM (R²=0.998) and 10 to 15,000 μM (R²=0.991) with a low detection limit (0.35 μM, S/N=3). Its Michaelis‐Menten constant (K_m) was calculated as 93.51 μM with 46.30 μA maximum current (I_max). This proposed simple method was successfully applied for glucose determination in human blood samples.     

Enzyme‐free Cu2O@MnO2/GCE for Hydrogen Peroxide Sensing

A novel composite material of copper (I) oxide at manganese (IV) oxide (Cu₂O@MnO₂), was synthesized and applied for modification on the glassy carbon electrode (GCE) surface (Cu₂O@MnO₂/GCE) as a hydrogen peroxide (H₂O₂) sensor. The composite material was characterized regarding its structural and morphological properties, using field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The Cu₂O@MnO₂/GCE showed an excellent electrocatalytic response to the oxidation of H₂O₂ which provided a 0.56 s^?1 charge transfer rate constant (K_s), 1.65×10^?5 cm² s^?1 diffusion coefficient value (D), 0.12 mm² electroactive surface area (A_e) and 1.04×10^?8 mol cm^?2 surface concentration ( ). At the optimal condition, the constructed sensor exhibited a wide linear range from 0.5 μM to 20 mM with a low limit of detection (63 nM, (S/N=3) and a good sensitivity of 256.33 μA mM^?1 cm^?2. It also presented high stability (ΔI_response±15 %, n=100), repeatability (1.25 %RSD, n=10) and reproducibility (3.55 %RSD, n=10). The results indicated that the synthesized Cu₂O@MnO₂ was successfully used as a new platform for H₂O₂ sensing.     

Choline Oxidase Based Composite ZrO2@AuNPs with Cu2O@MnO2 Platform for Signal Enhancing the Choline Biosensors

A novel metal composite material based on zirconium dioxide decorated gold nanoparticles (ZrO₂@AuNPs), copper (I) oxide at manganese (IV) oxide (Cu₂O@MnO₂) and immobilized choline oxidase (ChOx) onto a glassy carbon electrode (GCE) (ChOx/Cu₂O@MnO₂-ZrO₂@AuNPs/GCE) has been developed for enhancing the electro-catalytic property, sensitivity and stability of the amperometric choline biosensor. The ChOx/Cu₂O@MnO₂-ZrO₂@AuNPs/GCE displayed an excellent electrocatalytic response to the oxidation of the byproduct H₂O₂ from the choline catalyzed reaction, which exhibited a charge transfer rate constant (K_s) of 0.97 s⁻¹, a diffusion coefficient value (D) of 4.50×10⁻⁶ cm² s⁻¹, an electroactive surface area (A_e) of 0.97 cm² and a surface concentration (γ) of 0.54×10⁻⁸ mol cm⁻². The modified electrode also provided a wide linear range of choline concentration from 0.5 to 1,000.0 μM with good sensitivity (97.4 μA cm⁻² mM⁻¹) and low detection limit (0.3 μM). The apparent Michaelis-Menten constant was found to be 0.08 mM with I_max of 0.67 μA. This choline biosensor presented high repeatability (%RSD=2.9, n=5), excellent reproducibility (%RSD=2.9, n=5), long time of use (n=28 with %I>50.0 %) and good selectivity without interfering effects from possible electroactive species such as ascorbic acid, aspirin, amoxicillin, caffeine, dopamine, glucose, sucrose and uric acid. This optimal method was successfully applied for choline measurement in prepared human blood samples which demonstrated accurate and excellent reliability in the recovery range from 96.7 to 102.0 %.