Voltammetric studies of topotecan transfer across liquid/liquid interfaces and sensing applications

An amperometric ion sensor featuring a microhole supported water/organic gel interface was developed for the quantitative analysis of a water-soluble anticancer drug species, namely, topotecan, which has been used for ovarian and lung cancer treatments. Voltammetric responses associated with topotecan transfer across a polarized water/1,2-dichloroethane (1,2-DCE) interface were first investigated at different aqueous pH values to provide information on a topotecan partition diagram for understanding the lipophilicity of the topotecan drug species. The well-defined voltammetric characteristics for topotecan transfer in pH 4.0 buffer was then employed in conjunction with a microhole supported water/polyvinyl chloride-2-nitrophenyloctyl ether (PVC-NPOE) gel interface to develop a topotecan sensor. Current responses due to the direct transfer of topotecan molecules across the microhole interface increased linearly with respect to topotecan concentration when using cyclic voltammetry and differential pulse stripping voltammetry (DPSV). Improvements in sensitivity were obtained using DPSV and preconcentrating topotecan in the gel layer by holding the transferring potential at 1 V (vs Ag/AgCl) for 30 s followed by stripping of the drug. The topotecan drug sensor shows a low detectable concentration of 0.1 μM with a good selectivity over other anticancer drug molecules and interfering reagents. As a practical demonstration, the sensing platform was applied for the analysis of topotecan in a diluted serum sample. The results were also compared to those using high performance liquid chromatography (HPLC).