Voltammetric determination of L-dopa using an electrode modified with trinuclear ruthenium ammine complex (Ru-red) supported on Y-type zeolite

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.

Targeting Underlying Inflammation in Carcinoma Is Essential for the Resolution of Depressiveness

In modern clinical practice and research on behavioral changes in patients with oncological problems, there are several one-sided approaches to these problems. Strategies for early detection of behavioral changes are considered, but they must take into account the specifics of the localization and phase in the course and treatment of somatic oncological disease. Behavioral changes, in particular, may correlate with systemic proinflammatory changes. In the up-to-date literature, there are a lot of useful pointers on the relationship between carcinoma and inflammation and between depression and inflammation. This review is intended to provide an overview of these similar underlying inflammatory disturbances in both oncological disease and depression. The specificities of acute and chronic inflammation are considered as a basis for causal current and future therapies. Modern therapeutic oncology protocols may also cause transient behavioral changes, so assessment of the quality, quantity, and duration of behavioral symptoms is necessary to prescribe adequate therapy. Conversely, antidepressant properties could be used to ameliorate inflammation. We will attempt to provide some impetus and present some unconventional potential treatment targets related to inflammation. It is certain that only an integrative oncology approach is justifiable in modern patient treatment.

Trypsin mediated one-pot reaction for the synthesis of red fluorescent gold nanoclusters: Sensing of multiple analytes (carbidopa, dopamine, Cu2+, Co2+ and Hg2+ ions)

Herein, we fabricated fluorescent gold nanoclusters (Au NCs) by using trypsin as a ligand. The fabricated trypsin-Au NCs emit bright red color fluorescence upon the exposure of 365 nm UV light. The trypsin-Au NCs are stable and well dispersed in water, which exhibited strong red emission peak at 665 nm upon excitation wavelength of 520 nm. The red fluorescence of trypsin-Au NCs was greatly quenched by the addition of multiple analytes such as drugs (carbidopa and dopamine) and three divalent metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion). As a result, a novel fluorescence "turn-off" probe was developed for the detection of the above analytes with good selectivity and sensitivity. This method exhibits the detection limits for carbidopa, dopamine, Cu²⁺, Co²⁺ and Hg²⁺ ions are 6.5, 0.14, 5.2, 0.0078, and 0.005 nM, respectively. The trypsin-Au NCs were successfully applied to detect drugs (carbidopa, and dopamine) in pharmaceutical samples and metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion) in biofluids and water samples, exhibiting good precision and accuracy, which offers a facile analytical strategy for assaying of the above analytes in pharmaceutical and biological samples.

Impedimetric sensor for tyramine based on gold nanoparticle doped-poly(8-anilino-1-naphthalene sulphonic acid) modified gold electrodes

A novel impedimetric sensor for the determination of tyramine (Tyr), a biogenic amine, on the surface of gold nanoparticle-poly-(8-anilino-1-napthalene sulphonic acid), AuNP-PANSA modified gold electrode (AuE) is presented for the first time. The AuNP were successfully synthesized by a green synthesis method. Their characterization and optimization were conducted using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Under optimal conditions, the impedimetric sensor revealed a relatively broad linear range from 0.8 to 80 µM similar to more complex architectures found in the literature and the limit of detection of 0.04 µM was the lowest achieved until now. In order to test the reliability of the proposed method, real sample application studies were conducted using dairy products and fermented drinks. It was found that the sensor presented a good selectivity and recovery. Furthermore, the impedimetric sensor shows good reproducibility, stability, selectivity and very small interferences which augur well for its application in food safety control processes.

Selective Determination of Levodopa in the Presence of Vitamin B6, Theophylline and Guaifenesin Using a Glassy Carbon Electrode Modified with a Composite of Hematoxylin and Graphene/ZnO

An electrode has been developed based on using a composite of hematoxylin/graphene/ZnO nanocomposite to modify a glassy carbon electrode (GCE). The electrode (HGGCE) was tested and found to be applicable for the voltammetric analysis of levodopa in the presence of vitamin B₆, theophylline and guaifenesin using a 0.1 M phosphate buffer solution (PBS) pH 7 as the solvent. The HGGCE was used as the working electrode in cyclic voltammetry (CV) and square wave voltammetry (SWV) studies on the electrochemical behavior of levodopa at its surface. The results showed a dramatic enhancement in the oxidation current of levodopa and a shift in its oxidation potential towards more negative potentials as opposed to identical tests using bare GCE as the working electrode. The studies showed that the increase in the oxidation current has two linear profiles in two concentration ranges of 0.05 - 90.0 and 90.0 - 1000.0 μM. The detection limit of SWV analysis using the modified electrode was determined to be 0.03 μM (S/N = 3). Further advantages of the methods based on HGGCE include the simple modification procedure of the electrode, as well as its excellent sensitivity and reproducibility. The modified electrode was eventually found to be applicable to the determination of mixtures of levodopa, vitamin B₆, theophylline and guaifenesin in real samples.

Development of glassy carbon electrode modified with ruthenium red-multiwalled carbon nanotubes for simultaneous determination of epinephrine and acetaminophen

A glassy carbon electrode modified with ruthenium red and functionalized multi-walled carbon nanotube has been developed. The electrochemical response characteristics of the modified electrode toward epinephrine (EP) and acetaminophen (AC) was investigated by differential pulse voltammetry (DPV). Linear calibration plots were obtained over the range of 0.3 - 333.3 μM for both EP and AC with sensitivities of 0.221 and 0.174 μA μM(-1) for EP and AC, respectively. The detection limits for EP and AC were 0.04 and 0.06 μM, respectively. The diffusion coefficients for the oxidation of EP and AC at the modified electrode were calculated as 2.74 ± 0.05 × 10(-5) and 1.75 ± 0.07 × 10(-5) cm(2) s(-1), respectively. The practical analytical utilities of the modified electrode were demonstrated by the determination of EP and AC in human urine and serum as well as AC tablet samples.

Detection of the neurotransmitter dopamine by a glassy carbon electrode modified with self-assembled perovskite LaFeO3 microspheres made up of nanospheres

Glassy carbon electrode modified with LaFeO₃ microspheres made up of nanospheres and having high electrocatalytic ability to detect the neurotransmitter dopamine.

Synthesis of γ-Fe2O3/TiO2 nanocomposite and its application in removal of dyes from water samples by adsorption and degradation processes

A new facile route is proposed for synthesis of γ-Fe₂O₃/TiO₂ nanocomposite.

Thermodynamic parameters of electrochemical oxidation of L-DOPA: experimental and theoretical studies

Electrode potential and thermodynamic parameters of the electrochemical reaction of L-DOPA in aqueous solution are obtained experimentally by cyclic voltammetry method and also calculated theoretically using accurate ab initio calculations (G3MP2//B3LYP) along with the available solvation model of CPCM. The pH dependence of the redox activity of L-DOPA in aqueous solution at temperatures in the range of 10-30 °C was used for the experimental determination of the standard reduction potential, changes of entropy, enthalpy, and Gibbs free energy for the studied reaction. The experimental formal redox potential of the two-proton-two-electron reduction process was obtained to be 0.745 V versus standard hydrogen electrode (SHE). The theoretical and experimental values (0.728 and 0.745 V) for the standard electrode potential of L-DOPA are in agreement with each other. The difference between the peak potential of the L-DOPA and the products, which are produced by chemical reactions, has been measured experimentally and also calculated theoretically. There is also an agreement between experimental and theoretical potential difference. Also in this work, the changes of thermodynamic functions of solvation are calculated from the differences between the solution-phase experimental values and the gas-phase theoretical values.

Determination of l-dopa using electropolymerized 3,3′,3″,3‴-tetraaminophthalocyanatonickel(II) film on glassy carbon electrode

Electropolymerized film of 3,3',3'',3'''-tetraaminophthalocyanatonickel(II) (p-Ni(II)TAPc) on glassy carbon (GC) electrode was used for the selective and stable determination of 3,4-dihydroxy-L-phenylalanine (L-dopa) in acetate buffer (pH 4.0) solution. Bare GC electrode fails to determine the concentration of L-dopa accurately in acetate buffer solution due to the cyclization reaction of dopaquinone to cyclodopa in solution. On the other hand, p-Ni(II)TAPc electrode successfully determines the concentration of L-dopa accurately because the cyclization reaction was prevented at this electrode. It was found that the electrochemical reaction of L-dopa at the modified electrode is faster than that at the bare GC electrode. This was confirmed from the higher heterogeneous electron transfer rate constant (k(0)) of L-dopa at p-Ni(II)TAPc electrode (3.35 x 10(-2) cms(-1)) when compared to that at the bare GC electrode (5.18 x 10(-3) cms(-1)). Further, it was found that p-Ni(II)TAPc electrode separates the signals of ascorbic acid (AA) and L-dopa in a mixture with a peak separation of 220 mV. Lowest detection limit of 100 nM was achieved at the modified electrode using amperometric method. Common physiological interferents like uric acid, glucose and urea does not show any interference within the potential window of L-dopa oxidation. The present electrode system was also successfully applied to estimate the concentration of L-dopa in the commercially available tablets.

Simultaneous kinetic determination of levodopa and carbidopa by H-point standard addition method

The kinetic H-point standard addition method (HPSAM) was applied to the simultaneous determination of levodopa and carbidopa. The method was based on the difference in the rate of oxidation of these compounds with Cu(II)-neocuproine system and formation of Cu(I)-neocuproine complex at pH 5.5. The absorbance of the Cu(I)-neocuproine complex was monitored at 453 nm. Experimental conditions such as pH, reagent concentrations, ionic strength and temperature were optimized. Simultaneous determination of levodopa and carbidopa was performed in the range of 0.8-4 and 0.2-1.5 microg ml(-1), respectively. The proposed method was applied to the simultaneous determination of levodopa and carbidopa in pharmaceutical samples, and satisfactory results were obtained.