A portable smartphone-compatible ratiometric electrochemical sensor with ultrahigh sensitivity for anticancer drug mitoxantrone sensing

The development of reliable, sensitive, and highly stable electrochemical sensors with minimal extrinsic or intrinsic factors such as background noises, content of sensing materials, morphologies, and environmental changes is a difficult task. Here, a new sensitive nanocomposite (Ti3C2Tx-MXene) modified glassy carbon electrode (GCE) ratiometric electrochemical sensor coupled with an intrinsic built-in-correction has been developed through incorporating multi-walled carbon nanotubes (MWCNTs) to enhance conduction and methylene blue (MB) as an internal reference. Analysis of the electrochemical properties by cyclic voltammetry (CV) and adsorptive stripping differential pulse voltammetry (AdSDPV) showed an excellent electrocatalytic response for the anticancer agent mitoxantrone (MIT), even in serum and urine samples, in the linear range between 3.0 nM and 11.0 µM with a limit of detection as low as 79.15 pM, a rapid response of less than 120 s, and good anti-interference ability against multiple co-existing compounds. Additionally, no deterioration in sensitivity was observed in one month due to the strong adsorption capability of MXene towards the inner reference MB. However, GCE-modified electrodes have certain limitations, such as complicated setup and handling, electroactive material fouling, and extensive requirements for electrode washings, which cause these studies to be confined to laboratories and are not suitable for in-field use. To assist in point-of-care testing, we developed a portable, smartphone-compatible ratiometric sensor by depositing MB/Ti3C2Tx/MWCNTs on a paper substrate, which allowed the sensitive detection of MIT in serum and urine samples. The performances of GCE-modified and paper-based sensors were compared, and the advantages and disadvantages of each were discussed.