PARKINSON’S DISEASE (PD) IS A NEURODEGENERATIVE DISEASE WHICH CAUSES PROGRESSIVE DISORDERS IN THE EXTRAPYRAMIDAL SYSTEM THAT REGULATES THE COMMUNICATION BETWEEN THE NEURONS IN THE BRAIN AND MUSCLES IN THE HUMAN BODY. PD IS BELIEVED TO BE RELATED TO LOW LEVELS OF DOPAMINE IN CERTAIN PARTS OF THE BRAIN.3, 4-DIHYDROXYPHENYLALANINE (L-DOPA), WHICH IS A CATECHOLAMINE, IS A FASCINATING MOLECULE THAT PLAYS IMPORTANT ROLES IN BIOCHEMISTRY AND MEDICINAL CHEMISTRY AND IT IS CONSIDERED AS THE MOST EFFECTIVE TREATMENT FOR PD. SEVERAL TECHNIQUES HAVE BEEN REPORTED FOR ANALYSIS OF L-DOPA IN PHARMACEUTICAL FORMULATIONS AND BIOLOGICAL FLUIDS, ESPECIALLY SPECTROPHOTOMETRY, HIGH PERFORMANCE LIQUID CHROMATOGRAPHY AND CAPILLARY ZONE ELECTROPHORESIS. L-DOPA IS AN ELECTRO ACTIVE COMPOUND SO IT CAN ALSO BE STUDIED VIA ELECTROCHEMICAL METHODS WHICH ARE POWERFUL TECHNIQUES TO FOLLOW THE OXIDATION OF CATECHOLAMINES [1, 2]. IN THIS WORK, SENSITIVE DETECTION OF L-DOPA USING A GLASSY CARBON ELECTRODE MODIFIED WITH FE3O4 MAGNETIC NANOPARTICLES@ GRAPHENE QUANTUM DOTS (FE3O4MNPS@GQDS) AND MULTI WALLED CARBON NANOTUBES (MWCNTS). THE PREPARED ELECTRODE SHOWED GOOD ELECTROCHEMICAL RESPONSES FOR DIRECT ELECTROCHEMICAL OXIDATION OF LDOPA IN PHOSPHATE BUFFER SOLUTION (PH 5.5). THE ELECTRODE EXHIBITED GOOD ELECTROCATALYTIC ACTIVITY FOR OXIDATION OF L-DOPA IN CONCENTRATION RANGE OF 1-100 MM AND THE DETECTION LIMIT WAS COMPUTED TO BE 14 NM. THE PROPOSED METHOD WAS SUCCESSFULLY APPLIED TO QUANTIFY THE AMOUNT OF L-DOPA IN HUMAN BLOOD SERUM.

A NOVEL MODIFIED CARBON IONIC LIQUID ELECTRODE IS PREPARED AS AN ELECTROCHEMICAL SENSOR FOR SIMULTANEOUS DETERMINATION OF LEVODOPA (L-DOPA) AND SEROTONIN (5-HT). THE FABRICATED SENSOR REVEALED SOME ADVANTAGES SUCH AS CONVENIENT PREPARATION, GOOD STABILITY AND HIGH SENSITIVITY TOWARD 5-HT AND L -DOPA DETERMINATION. THE DPV DATA SHOWED THAT THE OBTAINED ANODIC PEAK CURRENTS WERE LINEARLY DEPENDENT ON THE L-DOPA AND 5-HT CONCENTRATIONS IN THE RANGE OF 0.25-225 AND 0.05-75 MM, RESPECTIVELY. THE APPLICABILITY OF THE MODIFIED ELECTRODE WAS DEMONSTRATED BY SIMULTANEOUS DETERMINATION OF 5-HT AND L-DOPA IN HUMAN SERUM. NEUROTRANSMITTERS PLAY A SIGNIFICANT ROLE IN THE RESEARCH OF PARKINSON’S DISEASE [1].L-DOPA IS CURRENTLY THE THERAPEUTIC DRUG IN THE TREATMENT OF PARKINSON’S DISEASE AND REQUIRED BY THE BRAIN TO PRODUCE DOPAMINE. LOW LEVELS OF 5-HT HAVE BEEN ASSOCIATED WITH SEVERAL DISORDERS, NOTABLY DEPRESSION, MIGRAINE, BIPOLAR DISORDER AND ANXIETY [2]. AS AN ION-EXCHANGE POLYMER, NAFION FILMS ARE HIGHLY PERMEABLE TO CATIONS BUT ALMOST IMPERMEABLE TO ANIONS [3]. THE CARBON IONIC LIQUID ELECTRODE WAS PREPARED BY MIXING GRAPHITE POWDER AND BMIMPF6 THOROUGHLY IN A MORTAR TO FORM A CARBON PASTE. A PORTION OF THE CARBON PASTE WAS FIRMLY FILLED INTO ONE END OF A GLASS TUBE AND A COPPER WIRE WAS INSERTED THROUGH THE OPPOSITE END. THE RESPONSE OF A SENSOR IS RELATED TO ITS PHYSICAL MORPHOLOGY. SCANNING ELECTRON MICROSCOPY WAS PERFORMED TO THE COHNPS SYNTHESIZED THROUGH THE PRECIPITATION METHOD. THE AMOUNT RATIO OF COHNPS WAS INCREASED FROM 0 TO 6%, THE RESPONSE OF THE ELECTRODE IMPROVED AND WHEN THE RATIO WAS MORE THAN 6%, THE RESPONSE DECREASED WITH LARGER BACKGROUND CURRENT. THEREFORE 20 ML OF 6% COHNPS NANOSCALE (94% MWCNTS) WAS CHOSEN FOR THE FABRICATION OF THE SENSOR. AT OPTIMUM PH OF 7.5, THE NEGATIVELY CHARGED NAFION MEMBRANE ELECTROSTATICALLY ATTRACTS L-DOPA AND 5-HT CATIONS BUT REJECTS AA AND UA ANIONS. BUT ON THE OTHER HAND NAFION HAS WEAK ELECT RICAL CONDUCTIVITY, CONSEQUENTLY APPLICATION OF LARGE AMOUNT OF NAFION WOULD DECREASE THE MASS TRANSFER RATE. THE ANODIC CURRENT COULD REACH THE HIGHEST VALUE WHEN 10.0 ML OF NAFION WAS USED. HOWEVER BY FURTHER INCREASING THE AMOUNT OF NAFION THE CURRENT DECREASES. THE OXIDATION PEAK CURRENTS OF L-DOPA AND 5-HT AFTER 60 S ACCUMULATION AT DIFFERENT POTENTIALS FROM 0.50 TO 0.10 V REMAINED ALMOST STABLE, REVEALING THAT POTENTIAL DOES NOT AFFECT THE OXIDATION PEAK CURRENTS OF LDOPA AND 5-HT. THE BEST PEAK SEPARATION CAN BE SEEN IN PH 6.5. HOWEVER IN THE SOLUTION WITH PH 7.5, HIGHER ANODIC PEAK CURRENTS FOR BOTH COMPOUNDS WERE OBTAINED. IN ORDER TO INVESTIGATE THE EFFECT OF SCAN RATE, CYCLIC VOLTAMMETRY OF SOLUTIONS OF 50 MM L-DOPA AND 25 MM 5-HT WERE OBTAINED IN THE RANGE 0.01-0.8 V S-1. THE RESULTS SHOWED THAT THE PEAK CURRENTS VARY LINEARLY WITH THE SCAN RATE OVER THE RANGE 10-150 MV S-1 FOR BOTH DRUGS WHICH CONFIRM THE ADSORPTION-CONTROLLED PROCESS FOR ELECTRO-OXIDATION OF L-DOPA AND 5-HT ON THE SURFACE OF THE ELECTRODE THE PLOT OF EP VERSUS THE LOGARITHM OF SCAN RATE (LOG(N)) WAS NOT LINEAR FOR L-DOPA, BUT SHOWED A LINEAR BEHAVIOR FOR 5-HT ACCORDING TO LAVIRON THEORY. THE CHARGE TRANSFER COEFFICIENT (A) CAN BE DETERMINED BY MEASURING THE VARIATION OF EP VS. LOG(N). THE SLOPE OF THE EP VS. LOG(N), WAS ABOUT, 0.0541 V. BY APPLICATION OF THE DPV METHOD TWO LINEAR RANGES WERE OBTAINED. THE FIRST LINEAR DYNAMIC RANGE WAS FROM 0.25 TO 10 MM AND THE SECOND LINEAR DYNAMIC RANGE WAS BETWEEN 15 AND 225 MM. A DETECTION LIMIT OF 0.12 MM WAS OBTAINED. THE ELECTRODE IS PRACTICALLY IMPERMEABLE TO AA AND UA AND OTHER ANIONIC SPECIES AND ONLY SLIGHTLY RESPONSIVE TO NEUTRAL METABOLITES. THUS IT BECOMES SELECTIVE FOR THE CATIONIC NEUROTRANSMITTERS, L-DOPA AND 5-HT WITH HIGH SENSITIVITY IN REAL BIOLOGICAL SAMPLES. DUE TO THE COCONTRIBUTION OF CILE AND MODIFIERS ON THE ELECTRODE SURFACE, THE RESULTING ELECTRODE EXHIBITED A GOOD ELECTROCATALYTIC PERFORMANCE TO SIMULTANEOUS TRACE DETERMINATION OF L-DOPA AND 5-HT.