Dual-mode electrochemical–colorimetric immunosensor based on an integrated FeOOH–Au–MB probe for sensitive procalcitonin detection

The integration of a dual-mode detection mechanism into immunosensing analysis technology can significantly enhance detection accuracy. However, the construction process is complex due to the differences in analysis principles, posing substantial technical challenges in the coordinated adaptation of multiple principles. We developed a novel dual-mode immunosensor based on ferric oxyhydroxide (FeOOH) microboxes modified with gold nanoparticles and loaded with methylene blue into a multifunctional FeOOH-Au-MB probe which does not require any additional reagents. In the electrochemical detection mode, the abundant hydroxyl groups on the surface of the FeOOH microboxes prepared at room temperature can efficiently bind to the electron mediator methylene blue, achieving significant amplification of the electrochemical signal. In the colorimetric detection mode, the Fe³⁺ ions released from the FeOOH microboxes react with ferrocyanide ([Fe(CN)₆]^4-) to form Prussian blue, resulting in a visible color change. The dual-mode self-calibration function can enhance the reliability and sensitivity of detection. Under optimal detection conditions, it exhibits a wide detection range from 1.0 pg mL^-1 to 50 ng mL^-1 for the sepsis biomarker procalcitonin (PCT), with detection limits of 0.28 pg mL^-1 (electrochemical mode) and 0.42 pg mL^-1 (colorimetric mode). The dual-mode immunosensor based on FeOOH-Au-MB could be used for clinical diagnosis, providing a potential tool for medical professionals.