Cationic and anionic phenothiazine derivatives: electrochemical behavior and application in DNA sensor development

The global shift toward personalized medicine and point-of-care testing drives the need for improved analytical performance in sensor technologies. A critical aspect of developing voltammetric sensors lies in identifying novel materials for electrode modification. This study focuses on the electrochemical investigation of two phenothiazine derivatives with distinct terminal functional groups: a cationic compound, 3,7-bis(4-aminophenylamino)phenothiazin-5-ium chloride, and an anionic compound, 3,7-bis(4-carboxyphenylamino)phenothiazin-5-ium chloride. Cyclic voltammetry, electrochemical impedance spectroscopy, quartz crystal microbalance, and scanning electron microscopy were employed to characterize these novel materials. The mutual influence of phenothiazines on voltammetric signals in solutions was analyzed, revealing changes in the number of hydrogen ions transferred when transitioning from an individual cationic derivative solution to a mixed solution with the anionic derivative. Two approaches for modifying glassy carbon electrodes were studied: electropolymerization from a mixture of phenothiazines and consecutive electrodeposition of polymeric films from individual solutions. Morphological and quantitative differences in the resulting electrode films were observed, with the latter method yielding a more uniform and thicker layer of redox-active material. A DNA sensor based on the consecutive electrodeposited films for the detection of doxorubicin was developed. The redox peak currents of the electropolymerized phenothiazine products exhibited a linear response to the logarithm of doxorubicin concentration. The sensor displayed two distinct linear ranges from 0.1 fM to 1 nM and from 1 nM to 1 μM, with a limit of detection calculated from the first range at 0.6 fM. This DNA sensor offers promising applications for advancing point-of-care diagnostics.