Facile fabrication of dual-ratiometric electrochemical sensors based on a bare electrode for dual-signal sensing of analytes in electrolyte solution

In this work, a general strategy to facilely fabricate novel dual-ratiometric (DR) electrochemical sensors (ECSs) was developed. This strategy referred to three types of substances with respective oxidation current peaks at different electric potentials, such as ferrocene (Fc) at 0.15 V, methylene blue (MB) at −0.26 V, and doxorubicin (DOX) at −0.62 V. In a conventional electrolyte solution of phosphate buffered saline (0.01 M, pH 6.5, containing 0.15 M of NaCl), Fc and MB as reference electroactive substances were added and their concentrations in electrolyte solution were fixed to 30 and 4 μM, respectively. Then, DOX as the analyte was also added into the electrolyte solution to form a homogeneous electrolyte solution. Through directly using a bare glassy carbon electrode as dual-signal sensing platform, square wave voltammetry curves of various electrolyte solutions containing three components of different concentrations were measured, with the each increment of DOX concentration [DOX] from 0.01 to 6 μM. Ratiometric oxidation current peak intensities (IDOX/IFc or IDOX/IMB) nearly linearly enhanced with the increase of [DOX], together with good linear coefficients and low limits of detection (3 nM). The DR-ECSs enabled highly selective and sensitive DOX detection in real human serum and saliva samples with high detection recoveries. These results revealed that this strategy to fabricate novel DR-ECSs was facile and flexible, which would facilitate a further development in the field of electrochemical sensing.