Bright luminescent optically engineered core/alloyed shell quantum dots: an ultrasensitive signal transducer for dengue virus RNA via localized surface plasmon resonance-induced hairpin hybridization.

Novel probes that can accurately (with sensitivity and specificity) detect and discriminate between the various serotypes of dengue virus (DENV) are needed for point-of-care treatment. The efficacy of a fluorophore reporter at optically transducing an ultrasensitive fluorescence intensity signal for a target nucleic acid within a molecular beacon (MB) biosensor system depends primarily on its optical properties. A new class of bright luminescent and size-dependent glutathione (GSH)-functionalized CdSe/ZnSeS core/alloyed shell quantum dots (Qdots) have been synthesized and characterized. Shell alloying tuned the photoluminescence (PL) quantum yield within the range of 23-99%, representing an approximately 2-8-fold increase over that of the binary CdSe core. In the first step of the biosensor design, gold nanoparticles (AuNPs) were conjugated to the Qdots to form AuNP-Qdot nanohybrids. In the second step, the AuNP-Qdot nanohybrids were conjugated to the 5' end of the MB. Despite the strong binding of the entities, both the AuNP-Qdot and AuNP-Qdot-MB conjugates maintained high colloidal stability. Nucleic acids of DENV1-4 were detected by the AuNP-Qdot-MB biosensors with high sensitivity, with the detection limits of the serotypes ranging from 31-260 copies per mL. The biosensor specifically discriminated between each serotype of the virus. A sensitivity comparison of a Qdot-MB with the AuNP-Qdot-MB showed that the localized surface plasmon resonance-induced signal from the AuNPs to the fluorescence intensity of the Qdots enhanced the performance of the biosensor. We have developed a new AuNP-Qdot-MB biosensor for DENV possessing high sensitivity and specificity. The new ultrasensitive assay holds great promise for the specific diagnosis of DENV, while the versatile biosensor concept is applicable to any type of RNA virus.