A Novel Platform Based on Au−CeO₂@MWCNT Functionalized Glassy Carbon Microspheres for Voltammetric Sensing of Valrubicin as Bladder Anticancer Drug and its Interaction with DNA

In this work, a sensitive and simple electrochemical sensor was constructed for the quantitative analysis of valrubicin (VLB), as a chemotherapy drug, in biological samples based on MWCNTs-OH, CeO₂NPs, AuNPs and functionalized glassy carbon microspheres (FGCM) modified electrode (Au−CeO₂@MWCNT-OH/FGCME). The new nanocomposite Au−CeO₂@MWCNT-OH/FGCM produced an electrocatalytic effect towards the electrochemical oxidation of VLB. The electrochemical behavior of the Au−CeO₂@MWCNT-OH/FGCME was also investigated using EIS and CV. The experimental and operation parameters that affect the sensitivity of the sensor were optimized. SWV was utilized for the electrochemical analysis of VLB. The oxidation peak currents were linearly dependent on the concentration of VLB in the range of 7.10×10⁻⁸ M to 5.8×10⁻⁷ M. The detection limit of VLB was found to be 1.56×10⁻⁹ M which was more sensitive than the reported method. The possible coexistence biological matrix had no interference effect on the determination of VLB. The fabricated sensor was also effectively employed to the sensitive detection of VLB in human body fluids. The interaction of VLB with salmon testes and calf thymus double-stranded DNA (st-DNA and ct-DNA) on Au−CeO₂@MWCNT-OH/FGCME has been further studied by cyclic voltammetry. The corresponding binding constant (K), surface concentration (Γ) and Gibbs free energy (ΔG°) were computed for the free VLB and the bound VLB-dsDNA complex. The obtained results revealed that VLB binds to DNA with a high binding constant as well as the K value for VLB-st-DNA (K=1.81×10⁵ M⁻¹) is higher than that of VLB-ct-DNA (K=4.99×10⁴ M⁻¹).