Microcavity-based SERS chip for ultrasensitive immune detection of cardiac biomarkers

The detection of cardiac markers with high sensitivity and specificity is exceedingly essential for the early diagnosis and warning of cardiovascular disease. In this work, we developed a microcavity-based sandwich immune chip to realize the ultrasensitive detection of cardiac troponin I (cTnI) and creatine kinase isoenzyme MB (CK-MB) by surface-enhanced Raman spectroscopy (SERS) method. Herein, polystyrene microspheres modified with gold nanoparticles (Au NPs) were fixed on the substrate via polydopamine, which was used as an immune capture chip. 5,5′-Dithio bis-(2-nitrobenzoic acid) (DTNB) and 4-mercaptobenzoic acid (4MBA) labelled Au NPs served as immune signal probes for cTnI and CK-MB, respectively. Light confinement effect of polystyrene (PS) microcavities and localized surface plasmon resonance (LSPR) near the Au NPs synergistically strengthened the electromagnetic field and promoted the interaction between light and matter, which enhanced SERS performance with an enhancement factor of 1.95×1012 for SERS sensing. The immunoassay results demonstrated the sensitive quantitative detection with the limit of detection (LOD) of 3.16 pg/mL and 4.27 pg/mL for cTnI and CK-MB, separately. The method also had good specificity, reproducibility and stability. It could be expected that our proposed microcavity-based SERS chip immunoassay technique would be considered as an effective diagnostic tool for ultrasensitive detection of cardiac biomarkers.