Site specific biotinylated antibody functionalized Ag@AuNIs LSPR biosensor for the ultrasensitive detection of exosomal MCT4, a glioblastoma progression biomarker

Glioblastoma (GBM) is an incurable brain tumor in which hypoxic GBM cells (GMs) increase the production and release of exosomes, which are 30–200 nm vesicles crossing the blood–brain-barrier, enabling exosomal biomarkers to be promising targets for the tracking of GBM malignancy. Here, a localized surface plasmon resonance (LSPR) sensor chip was developed to detect an infinitesimal amount of exosomal biomarkers. Self-assembly silver nanoparticles decorated on gold nano-islands (Ag@AuNIs) sensor chip was used to provide site-specific bio-conjunction of biotinylated antibodies for detection of exosomal surface biomarkers. The biotinylated antibody functionalized (BAF) Ag@AuNIs LSPR biosensor sensitively detected cluster of differentiation 63, an exosome marker, and monocarboxylate transporter 4 (MCT4), a GBM progression biomarker, in malignant GMs-derived exosomes in the dynamic range of 3.8 × 10⁻⁴ to 50 μg/ml with limit of detection (LOD) of 0.38 ng/ml and 1.4 × 10⁻³ to 500 μg/ml with LOD of 1.4 ng/ml, respectively. Furthermore, it detected the enhanced level of MCT4 in malignant hypoxic GMs-derived exosomes as well as increased MCT4 in the blood serum-derived exosomes of GBM mice in the dynamic range of 4 × 10⁻⁴ to 50 μg/ml with LOD of 0.4 ng/ml. Finally, it could quantify MCT4 in the isolated GMs-derived exosomes from the blood of GBM mice by epidermal growth factor receptor variant III-based immunocapture, suggesting its utility for minimally-invasive monitoring of GBM progression as liquid biopsy. With excellent attributes of high sensitivity and selectivity in label-free sensing for exosomal biomarkers, the BAF Ag@AuNIs LSPR biosensor has great potential for early detection of GBM formation and progression.