Sandwich-structured PEDOT:PSS/MXene-PdAu/PEDOT:PSS film for highly sensitive detection of shikonin in lithospermum erythrorhizon.

Promising electrochemical sensing platforms can be constructed by two-dimensional (2D) inorganic materials, metal nanoparticles and conducting polymers (CPs) via suitable and effective composite-structural fabrication. Herein, a sandwich-structured composite film was fabricated with MXene (Ti3C2Tx), PdAu nanoparticles and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). In the fabrication, PdAu nanoparticles were first loaded on the surface of MXene nanosheets by one-pot method, preventing self-stacking and improving the dispersion of MXene nanosheets. And then, the PEDOT:PSS/MXene-PdAu/PEDOT:PSS sandwich structure was obtained with PEDOT:PSS as the upper and lower layers and MXene-PdAu as the interlayer. Indeed, the upper PEDOT:PSS film can permeate between MXene-PdAu particles and contribute to the continuity of MXene nanosheets, forming a complete conducting three-dimensional framework. The formed PEDOT:PSS/MXene-PdAu/PEDOT:PSS framework exhibits promising electrochemical sensing properties towards shikonin detection with a wide range of 0.001-35 μM, a low detection limit of 0.33 nM and a high sensitivity of 5.685 μA μM-1 cm-2. Furthermore, this sensing platform performs favorable selectivity and stability. In the actual sample testing, the sensing platform was used for shikonin detection in Lithospermum erythrorhizon and performed comparable results with high-performance liquid chromatography (HPLC), indicating the promising application prospect of PEDOT:PSS/MXene-PdAu/PEDOT:PSS film for the qualitative and quantitative analysis of shikonin.