Single-Sweep Voltammetric Determination of Tamoxifen at Carbon Paste Electrode

Cyclic and Linear Sweep Voltammetric Studies of a Modified Carbon Paste Electrode with Nickel Oxide Nanoparticles toward Tamoxifen: Effects of Surface Modification on Electrode Response Kinetics

Due to the serious adverse futures of some anticancer drugs, the determination of trace amounts of these drugs by simple analytical techniques is of great interest. In this regard, knowing about the mechanism of the analyte with the sensing material plays an important role. Nickel oxide nanoparticles (NiO NPs) modified by a carbon paste electrode (NiO-CPE) showed an irreversible cyclic voltammetric (CV) behavior in the NaOH (pH 13) supporting electrolyte based on the peak separation of 311 mV. Its peak current was decreased by adding tamoxifen (TAM), confirming that TAM molecules can consume NiO before participating in the electrode reaction. For this goal, TAM can be oxidized or reduced, and the corresponding mechanisms are schematically illustrated in the text. This study focused on the kinetic aspects of the process. Based on the CV results, a surface coverage (Γ) value of 2.72 × 10^-5 mol NiO per cm² was obtained with charge transfer coefficients α_a and α_c of 0.317 and 0.563, respectively. α_a and α_c values were changed to 0.08 and 0.72 in the presence of TAM. Further, the rate constant (k _s) value was 0.021 ± 0.01 s^-1 in the presence of TAM. In linear sweep voltammetry (LSV), an α value of about 0.636 ± 0.023 and an exchange rate constant (k _o) value of about 0.097 ± 0.031 s^-1 were obtained in the absence of TAM, which changed to 0.62 ± 0.081 and 0.089 ± 0.021 s^-1 in the presence of TAM, respectively. Despite more published papers, when the TAM analyte was added to the NaOH supporting electrolyte, both anodic and cathodic peak currents of the modified NiO-CPE decreased. We suggested some reasons for this decreased peak current, and four mechanisms were illustrated for the electrode response in the presence of TAM.

The first electrochemical MIP sensor for tamoxifen

We present an electrochemical MIP sensor for tamoxifen (TAM)—a nonsteroidal anti-estrogen—which is based on the electropolymerisation of an O-phenylenediamine–resorcinol mixture directly on the electrode surface in the presence of the template molecule. Up to now only “bulk” MIPs for TAM have been described in literature, which are applied for separation in chromatography columns. Electro-polymerisation of the monomers in the presence of TAM generated a film which completely suppressed the reduction of ferricyanide. Removal of the template gave a markedly increased ferricyanide signal, which was again suppressed after rebinding as expected for filling of the cavities by target binding. The decrease of the ferricyanide peak of the MIP electrode depended linearly on the TAM concentration between 1 and 100 nM. The TAM-imprinted electrode showed a 2.3 times higher recognition of the template molecule itself as compared to its metabolite 4-hydroxytamoxifen and no cross-reactivity with the anticancer drug doxorubucin was found. Measurements at +1.1 V caused a fouling of the electrode surface, whilst pretreatment of TAM with peroxide in presence of HRP generated an oxidation product which was reducible at 0 mV, thus circumventing the polymer formation and electrochemical interferences.