Quantum Dot Fullerene-Based Molecular Beacon Nanosensors for Rapid, Highly Sensitive Nucleic Acid Detection

Spherical fullerene (C₆₀) can quench the fluorescence of a quantum dot (QD) through energy-transfer and charge-transfer processes, with the quenching efficiency regulated by the number of proximate C₆₀ on each QD. With the quenching property and its small size compared with other nanoparticle-based quenchers, it is advantageous to group a QD reporter and multiple C₆₀-labeled oligonucleotide probes to construct a molecular beacon (MB) probe for sensitive, robust nucleic acid detection. We demonstrated a rapid, high-sensitivity DNA detection method using the nanosensors composed of QD-C₆₀-based MBs carried by magnetic nanoparticles. The assay was accelerated by first dispersing the nanosensors in analytes for highly efficient DNA capture resulting from short-distance three-dimensional diffusion of targets to the sensor surface and then concentrating the nanosensors to a substrate by magnetic force to amplify the fluorescence signal for target quantification. The enhanced mass transport enabled a rapid detection (<10 min) with a small sample volume (1-10 μL). The high signal-to-noise ratio produced by the QD-C₆₀ pairs and magnetic concentration yielded a detection limit of 100 fM (∼10⁶ target DNA copies for a 10 μL analyte). The rapid, sensitive, label-free detection method will benefit the applications in point-of-care molecular diagnostic technologies.