Sandpaper-templated Stretchable Immunosensing Electrodes for Sub-picomolar Progesterone Detection

Female hormone detection, particularly non-invasive monitoring progesterone (P4) levels in body fluids, plays a critical role in female health management and disease diagnosis. However, the challenge still exists because of the ultralow abundance of P4 (<100 pmol/L) in sweat and saliva, necessitating highly sensitive methods for wearable detection. Herein, we present a simple sandpaper-templated stretchable immunosensing electrode designed for ultra-sensitive detection of P4 at sub-picomolar level. A molding technique is employed to replicate the sandpaper textures to provide a microstructured elastomeric substrate for electrode preparation. Such microstructured surface coated with poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/LiTFSI [LiTFSI=lithium bis(trifluoromethanesulfonyl) imide] provided a stretchable polymer electrode with high conductivity, and further decoration with gold nanoparticles (AuNPs) enabled the immunosensing for P4 by electrochemical impedance spectroscopy (EIS) measurements. Through adjusting the AuNPs deposition conditions, ultrasensitive detection of P4 is realized with a low limit of detection (LOD) of ca. 10 fmol/L and a tunable dynamic range up to µmol/L. Notably, the stretchable electrode exhibits stable electrochemical performance, enabling the detection of P4 at sub-picomolar levels even under mechanical strain of 30%. This innovative electrochemical sensor holds significant promise for non-invasive, on-site monitoring of P4 levels in healthcare, as well as hormone detection in food safety and environment surveillance.