Synthesis of Samarium Molybdate Nanoplates and its application in construction of Electrochemical Sensors based Graphene Quantum Dots for Catecholamine drugs determination

Levodopa (LD) is one of the commonly prescribed medications used in combination with other medications in Parkinson disease. Carbidopa (CD) and Entacapone ( EN) together with levodopa causes a longer effect of levodopa in the brain [1]. LD, as one of the catecholamines is the intermediate precursor of the neurotransmitter dopamine. Unlike dopamine, LD easily enters the central nervous system [2]. In this work, due to the importance of these drugs, a novel modified nanocomposite electrode based on Sm2(MoO4)3 nanoplates and Graphene Quantum Dots (GQDs) was introduced for determination of LD and CD. A facile one pot precipitation method was used for the preparation of the used nanomaterials. The synthesized nanoplates were characterized through FT-IR, XRD, EDX, FESEM and Zeta potential technique, also the highly conductive synthesized GQDs were characterized through TEM. Next, Sm2(MoO4)3 nanoplates was used as modifier in a carbon paste electrode (CPE). The characterization of modified electrodes accomplished by FESEM, EDX and EIS. Then the surface of the modified CPE was coated by GQDs in a drop wise manner. Finally, the electrode was used as an electrochemical sensor in determination of LD and CD by Differential pulse voltammetry technique. The possibility of analyzing LD and CD, separately and simultaneously is investigated. Electrochemical tests showed that because of unique properties of GQDs, such as large surface area, facile electronic transport and high electrocatalytic activity and synergic effect between GQDs and Sm2(MoO4)3 nanoplates, the final modified electrode exhibited highly enhanced electrochemical performance of LD electrooxidation in comparison with the modified electrode just by Sm2(MoO4)3 nanoplates. It showed an excellent electrocatalytic activity toward LD with a lower overvoltage. This sensor is sensitive for the determination of LD through electrooxidation of phenolic functional group in a supporting electrolyte 0.1 M PBS solution (pH 6.5) while has no sensitivity to determine the amount of CD. The primary fabricated electrode modified with Sm2(MoO4)3 nanoplates was also evaluated for the simultaneous determination of LD and CD in a supporting electrolyte 0.1 M PBS solution (pH 9.0 and pH 3.0 respectively). Under the selective conditions, the detection limit of proposed modified electrode was 0.02 nM for LD (LOQ = 0.08 nM) and detection limit of primary modified electrode was 0.05 nM for CD (LOQ =0.15 nM) based on S/N = 3. The linear dynamic range of determinations were as follows: 1 × 10-4–1 × 103 µM for LD and 1 × 10-4–1 × 102 µM for CD. Also in determination of CD, EN does not interfere. For evaluating the validity of the suggested method, human plasma samples were analyzed and it is potential for use in clinical research. Reproducibility, stability, low detection limits, wide dynamic linear ranges and long life-time are some of the advantages of the recommended sensor in this investigation.