Validated electrochemical immunosensor for ultra-sensitive procalcitonin detection: Carbon electrode modified with gold nanoparticles functionalized sulfur doped MXene as sensor platform and carboxylated graphitic carbon nitride as signal amplification

•Ultra-sensitive sandwich type electrochemical immunosensor is developed for procalcitonin recognition.•The prepared immunosensor is characterized by several methods.•The prepared immunosensor shows high stability, repeatability, reproducibility and reusability.•The prepared immunosensor is preferred in comparison with the other analytical methods. Septicemia, also known as sepsis, refers to a systemic inflammatory response syndrome and becomes the dominant reason of mortality for seriously diseases. Procalcitonin (PCT), the peptide precursor of the hormones, is a key biomarker of septicemia in the diagnosis and detection of bacterial inflammation. In this study, an ultra-sensitive sandwich type electrochemical immunosensor for PCT detection was constructed. Firstly, delaminated sulfur-doped MXene (d-S-Ti3C2TX MXene) modified glassy carbon electrode (GCE) including gold nanoparticles (AuNPs) was utilized as immunosensor platform to increase the amount of PCT antibody1 (Ab1). After that, carboxylated graphitic carbon nitride (c-g-C3N4) was used to label PCT Ab2 as signal amplification. The structure of electrochemical immunosensor was highlighted by x-ray diffraction (XRD) method, scanning electron microscope (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Herein, c-g-C3N4 not only has excellent catalytic activity toward H2O2 for signal amplification, but also can be directly utilized as redox probe. The analytical results have revealed that 0.01 - 1.0 pg mL-1 and 2.0 fg mL-1 were found as linearity range and limit of detection (LOD). Furthermore, the validated electrochemical immunosensor was examined in terms of stability, repeatability, reproducibility and reusability. Finally, the immunosensor was applied to plasma samples having high recovery.