Experimental

Chemicals and apparatus

All analytical-grade reagents were used exactly as provided, requiring no additional purification. Orthophosphoric acid was used to prepare phosphate buffer solutions (PBS), which served as the electrolyte supporting the electrochemical measurement of DOX over the pH range 2.0 to 9.0. The researchers used a NaOH solution to adjust the pH.

The electrochemical tests were conducted on an Autolab potentiostat/galvanostat system (PGSTAT-302 N, Netherlands). The GPES software functioned as the control system for all experimental parameters. The screen-printed three-electrode configuration (DropSens, DRP-110, Spain) consisted of a Zn-Ni MOF NSs@GO/SPCE working electrode, a carbon auxiliary electrode and a silver pseudo-reference electrode. The pH was determined using a Metrohm 710 pH meter. The Zn-Ni MOF NSs@GO nanocomposites were synthesized based on their previous work [41].

Zn-Ni MOF NSs@GO modified-screen-printed carbon electrode

The Zn-Ni MOF NSs@GO/SPCE was initially prepared by dispersing 1.0 mg of the Zn-Ni MOF NSs@GO nanocomposite in 1.0 mL of deionized water using ultrasonic agitation to create a homogeneous suspension. After casting 2.0 μL of the homogeneous suspension onto the SPCE surface, the solvent was allowed to evaporate at room temperature. The Zn-Ni MOF NSs@GO/SPCE was used as the working electrode. The electrochemical surface areas of Zn-Ni MOF NSs@GO/SPCE and bare SPCE was calculated to be 0.060 and 0.0134 cm2, respectively.

Preparation of injection sample of doxorubicin

For investigating the ability of the Zn-Ni MOF NSs@GO/SPCE sensor in the analysis of pharmaceutical formulations, 1.0 ml of DOX HCl injection solution (vial 25 ml contains 50 mg DOX·HCl) was diluted 10 times using PBS without any other pretreatment. Then, a certain volume of the diluted sample was transferred to a 25 ml volumetric flask, which was filled to the mark with PBS. This sample was analysed using differential pulse voltammetry (DPV) to determine the DOX concentration in the diluted sample. Subsequently, the diluted samples were separately spiked with various concentrations of DOX solution. The DPVs of these samples were then recorded.