Experimental

Apparatus and chemicals

The general-purpose electrochemical system software operated the Autolab potentiostat/galvanostat, which conducted electrochemical experiments through its PGSTAT 302N instrument. The screen-printed electrode (DropSens, DRP-110, Spain) consists of an unmodified carbon working electrode, a silver pseudo-reference electrode and a carbon counter electrode. The Metrohm 710 pH meter was used to measure the pH.

All reagents and solvents met analytical quality standards. Tyrosine and dopamine were supplied by Merck (Darmstadt, Germany) without alteration. Phosphate buffer solutions (PBS) were prepared using orthophosphoric acid over the pH range 2.0 to 9.0.

Synthesis of Co/Ni-MOF

Co(NO3)2·6H2O (1.2 mmol), NiCl2·6H2O (4 mmol), and terephthalic acid (1 mmol) were dissolved in dimethyl formamide (DMF) during a 10-minute period at room temperature while magnetic stirring. The autoclave contained the mixture during its operation. The system was heated to 120 °C for 16 hours, then allowed to cool naturally to ambient temperature. The centrifuge operation separated the products after five minutes at 9000 rpm and the materials were cleaned through multiple ethanol and DMF washings. The samples were dried under vacuum for 12 hours at 80 °C. Figure 1 displays the Co/Ni-MOF FE-SEM image.

Figure 1.: FE-SEM image of Co/Ni-MOF

Co/Ni-MOF modified-SPCE

Co/Ni-MOF was applied to the modification of the SPCE in the following manner: a 4 μL aliquot of the Co/Ni-MOF/H2O suspension was cast onto the carbon working electrodes and allowed to evaporate at room temperature after a stock solution of Co/Ni-MOF in 1 mL of aqueous solution was prepared by dispersing 1 mg of Co/Ni-MOF with ultrasonication for 45 minutes. Ultimately, a modified electrode, Co/Ni-MOF/SPCE, was created. The surface area of the modified electrode was calculated to be 0.091 cm2 compared to 0.0318 cm2 for bare SPE, using the Randles-Ševčík equation.