Protein–Conjugated Quantum Dots Interface: Binding Kinetics and Label-Free Lipid Detection

We propose a label-free biosensor platform to investigate the binding kinetics using antigen–antibody interaction via electrochemical and surface plasmon resonance (SPR) techniques. The l-cysteine in situ capped cadmium sulfide (CdS; size < 7 nm) quantum dots (QDs) self-assembled on gold (Au) coated glass electrode have been covalently functionalized with apolipoprotein B-100 antibodies (AAB). This protein conjugated QDs-based electrode (AAB/CysCdS/Au) has been used to detect lipid (low density lipoprotein, LDL) biomolecules. The electrochemical impedimetric response of the AAB/CysCdS/Au biosensor shows higher sensitivity (32.8 kΩ μM^–1/cm²) in the detection range, 5–120 mg/dL. Besides this, efforts have been made to investigate the kinetics of antigen–antibody interactions at the CysCdS surface. The label-free SPR response of AAB/CysCdS/Au biosensor exhibits highly specific interaction to protein (LDL) with association constant of 33.4 kM^–1 s^–1 indicating higher affinity toward LDL biomolecules and a dissociation constant of 0.896 ms^–1. The results of these studies prove the efficacy of the CysCdS-Au platform as a high throughput compact biosensing device for investigating biomolecular interactions