A novel QCM immunosensor development based on gold nanoparticles functionalized sulfur-doped graphene quantum dot and h-ZnS-CdS NC for Interleukin-6 detection

Interleukin 6 (IL-6) acts as both a proinflammatory and anti-inflammatory cytokine and is generally utilized as an important diagnostic biomarker for sepsis. In addition, the high levels of IL-6 measured in plasma have been associated with pathological inflammation. A novel quartz crystal microbalance (QCM) immunoassay method was presented for high sensitivity and selectivity detection of interleukin-6 (IL-6) based on gold nanoparticles functionalized sulfur-doped graphene quantum dot (AuNPs/S-GQD) and hollow ZnS–CdS nanocage (h-ZnS-CdS NC). Firstly, AuNPs/S-GQD nanocomposite was synthesized in the presence of tetrachloroauric acid and then conjugated onto anti-IL-6 antibodies by amino-gold affinity. The sandwich-type QCM immunoassay probe was prepared by immune-reaction between AuNPs/S-GQD/QCM immobilized with anti-IL-6 capture antibodies and h-ZnS-CdS NC including detection anti-IL-6 antibodies in the presence of target IL-6. The prepared QCM immunoassay probe was characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The QCM immunosensor showed a linearity range (0.01–2.0 pg mL−1) and a low detection limit (3.33 fg mL−1). Lastly, high stable and selective QCM immunosensor was applied to prepared plasma samples with good recovery.