An innovative electrochemical approach for voltammetric determination of levodopa using gold nanoparticles doped on titanium dioxide nanotubes

Electroanalytical Overview: The Determination of Levodopa (L-DOPA)

L-DOPA (levodopa) is a therapeutic agent which is the most effective medication for treating Parkinson's disease, but it needs dose optimization, and therefore its analytical determination is required. Laboratory analytical instruments can be routinely used to measure L-DOPA but are not always available in clinical settings and traditional research laboratories, and they also have slow result delivery times and high costs. The use of electroanalytical sensing overcomes these problems providing a highly sensitivity, low-cost, and readily portable solution. Consequently, we overview the electroanalytical determination of L-DOPA reported throughout the literature summarizing the endeavors toward sensing L-DOPA, and we offer insights into future research opportunities.

Malachite Green Dye Decoloration over Au/TiO2-Nanotubes Photocatalyst under Simulate Visible-Light Irradiation

Au nanoparticles were supported on TiO₂ nanotubes by a novel vapor phase impregnation approach (VPI) using gold dimethyl-acetylacetonate as a precursor. This study aimed to evaluate the capacity of these materials in the photodecoloration of malachite green dye, with the vision to correlate the chemical, structural, morphological, and optical properties with its photocatalytic performance. The photocatalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectronic spectroscopy (XPS), electronic microscopy (HAADF-STEM and HRTEM), and UV-vis spectroscopy. The techniques mentioned above made it possible to detect the presence of small gold nanoparticles (around 3.1 nm), with a high apparent dispersion even at high metal loading for all analyzed systems. According to the XPS results, the Au nanoparticles remain reduced (Au°), and they have a high electronic interaction with TiO₂, which eventually originates an electronic exchange between them and consequently a decrease in the band gap energy. In addition, the surface plasmonic resonance observed through UV-vis spectroscopy of the Au nanoparticles are factors that can be related to the high decoloration observed in these photocatalysts, specifically in the 15 wt% Au material, which achieves maximum photodecoloration of malachite green dye at 93%.

Comparison of Gold Nanoparticles Deposition Methods and Their Influence on Electrochemical and Adsorption Properties of Titanium Dioxide Nanotubes

The increasing interest of attachment of gold nanoparticles (AuNPs) on titanium dioxide nanotubes (TNTs) has been devoted to obtaining tremendous properties suitable for biosensor applications. Achieving precise control of the attachment and shape of AuNPs by methods described in the literature are far from satisfactory. This work shows the comparison of physical adsorption (PA), cyclic voltammetry (CV) and chronoamperometry (CA) methods and the parameters of these methods on TNTs properties. The structural, chemical, phase and electrochemical characterizations of TNTs, Au/TNTs, AuNPs/TNTs are carried out using scanning electron microscopy (SEM), electrochemical impedance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy. The use of PA methods does not allow the deposition of AuNPs on TNTs. CV allows easily obtaining spherical nanoparticles, for which the diameter increases from 20.3 ± 2.9 nm to 182.3 ± 51.7 nm as a concentration of tetrachloroauric acid solution increase from 0.1 mM to 10 mM. Increasing the AuNPs deposition time in the CA method increases the amount of gold, but the AuNPs diameter does not change (35.0 ± 5 nm). Importantly, the CA method also causes the dissolution of the nanotubes layer from 1000 ± 10.0 nm to 823 ± 15.3 nm. Modification of titanium dioxide nanotubes with gold nanoparticles improved the electron transfer and increased the corrosion resistance, as well as promoted the protein adsorption. Importantly, after the deposition of bovine serum albumin, an almost 5.5-fold (324%) increase in real impedance, compared to TNTs (59%) was observed. We found that the Au nanoparticles-especially those with smaller diameter-promoted the stability of bovine serum albumin binding to the TNTs platform. It confirms that the modification of TNTs with gold nanoparticles allows the development of the best platform for biosensing applications.

A novel selective ternary platform fabricated with MgAl-layered double hydroxide/NiMn2O4 functionalized polyaniline nanocomposite deposited on a glassy carbon electrode for electrochemical sensing of levodopa

In this study, a novel selective electrochemical sensor was fabricated for determination of levodopa (LD) using a glassy carbon electrode modified with MgAl-layered double hydroxide/NiMn₂O₄ functionalized polyaniline nanocomposite (LDH/NMO/PANI) and its successful formation was confirmed by various techniques. Owing to the high surface area and outstanding conductivity features provided by the combination of MgAl-LDH, NiMn₂O₄ and PANI nanoparticles, this ternary nanocomposite exhibited excellent electrochemical activity towards the detection of LD compared with the electrode modified by the pristine MgAl-LDH and MgAl-LDH/NiMn₂O₄ binary nanocomposite. In addition, enormous quantities of amine and imine functional groups on the surface of PANI lead to a strong affinity for attachment to organic molecules such as LD. The ternary nanocomposite modified electrode exhibited excellent analytical parameters such as wide linear response from 0.1 to 100 μM with very low detection limit of 0.005 μM, good reproducibility and long-term stability which are superior among the LD electrochemical sensors. Besides, the constructive sensor possessed acceptable selectivity for recognition of LD in the presence of a variety of potentially interfering species and can also effectively avoid the interference of dopamine (DA) and ascorbic acid (AA). Consequently, the LDH/NMO/PANI/GC electrode was effectively applied to detect LD in human plasma and urine samples with good recoveries, ranging from 98.0-100.1% and it shows potential usage in clinical researches.

Simultaneous electrochemical detection of levodapa, paracetamol and l-tyrosine based on multi-walled carbon nanotubes

A novel electrochemical sensor for the simultaneous detection of levodopa, paracetamol and l-tyrosine was developed based on multi-walled carbon nanotubes. The sensor has the merits of wide linear range, good selectivity and good reproducibility.

The Influence of the Parameters of a Gold Nanoparticle Deposition Method on Titanium Dioxide Nanotubes, Their Electrochemical Response, and Protein Adsorption

The goal of this research was to find the best conditions to prepare titanium dioxide nanotubes (TNTs) modified with gold nanoparticles (AuNPs). This paper, for the first time, reports on the influence of the parameters of cyclic voltammetry process (CV) -based AuNP deposition, i.e., the number of cycles and the concentration of gold salt solution, on corrosion resistance and the capacitance of TNTs. Another innovation was to fabricate AuNPs with well-formed spherical geometry and uniform distribution on TNTs. The AuNPs/TNTs were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and open-circuit potential measurement. From the obtained results, the correlation between the deposition process parameters, the AuNP diameters, and the electrical conductivity of the TNTs was found in a range from 14.3 ± 1.8 to 182.3 ± 51.7 nm. The size and amount of the AuNPs could be controlled by the number of deposition cycles and the concentration of the gold salt solution. The modification of TNTs using AuNPs facilitated electron transfer, increased the corrosion resistance, and caused better adsorption properties for bovine serum albumin.

3-Dimensional hollow graphene balls for voltammetric sensing of levodopa in the presence of uric acid

The development of novel nanomaterials brings new opportunity and challenge for high sensing detection of biomolecules. The authors describe the preparation of 3-dimentional hollow graphene balls (3D HGBs) using nickel nanoparticles (Ni-NPs) as the template. The Ni-NPs were synthesized by chemical reduction of nickel chloride and then graphene was coated onto their surface via carburization and carbonization. After etching Ni-NPs, 3D HGBs with few layers and a typical size of 100 nm were obtained. They were sprayed onto indium tin oxide glass to obtain a working electrode for electrochemical determination of levodopa in the presence of uric acid. Due to the unique hollow porous structure of the 3D HGBs, the electrode exhibits a sensitivity of 0.69 μA·μM^-1·cm^-2 and a 1 μM limit of detection. It is selective, reproducible and stable. It was applied to the determination of levodopa in spiked human plasma samples and it is of potential use in clinical research. Graphical abstract Schematic presentation of the preparation of 3-dimensional hollow graphene balls (HGBs) by using nickel nanoparticles as a template that can be removed by etching. The HGBs were sprayed onto indium tin oxide (ITO) glass to obtain a working electrode that has a sensitivity of 0.69 μA⋅μM^-1·cm^-2 and a 1 μM limit of detection for the determination of levodopa.

One-pot in situ synthesis of a CoFe2O4nanoparticle-reduced graphene oxide nanocomposite with high performance for levodopa sensing

We demonstrate that a new nanocomposite of CoFe₂O₄-reduced graphene oxide can be used as an enhanced electrochemical sensing platform for levodopa.