Increased electrocatalyzed performance through hairpin oligonucleotide aptamer-functionalized gold nanorods labels and graphene-streptavidin nanomatrix: Highly selective and sensitive electrochemical biosensor of carcinoembryonic antigen.

We report a triplex signal amplification strategy for sensitive biosensing of cancer biomarker by taking advantage of hairpin-shaped oligonucleotide-functionalized gold nanorods (HO-GNRs), graphene and the avidin-biotin reation. The strategy expands electrochemical detection of carcinoembryonic antigen (CEA) by using an aptamer as biosensor's recognition element and HO-GNRs as signal enhancer. To construct this biosensor, the GNR was used as a carrier of horseradish peroxidase (HRP) and HO aptamer with a biotin at the 3'-end and a thiol at the 5'-end, which amplified the electrochemical response because of a large molar ratio of HRP to HO. In the presence of target CEA, the binding reactions of CEA with the loop portions of the HOs caused HOs' loop-stem structure opened and exposed the biotins, and then HRP-GNRs-HO conjugates were captured on graphene and streptavidin modified electrodes via the reaction between the exposed biotins and preimmobilized streptavidins. The accumulation of HRP effectively catalyzed the hydrogen peroxide-mediated oxidation of o-phenylenediamine to generate an electrochemical reduction current for CEA detection. Under optimal conditions, the electrochemical biosensor exhibited a wide dynamic range of 5pgmL(-1) and 50ngmL(-1) toward CEA standards with a low detection limit of 1.5pgmL(-1) (signal-to-noise ratio of 3). The proposed biosensor accurately detected CEA concentration in 8 human serum samples from patients with lung diseases, showing excellent correlations with standard chemiluminescence immunoassay. Furthermore, these results of target DNA detection made it abundantly clear that the proposed strategy can also be extended for detection of other relative biomarkers using different functional DNA structures, which shows great prospects in single-nucleotide polymorphisms analysis, biomedical sensing and application for accurate clinical diseases diagnostic.

Folic acid-conjugated silica-coated gold nanorods and quantum dots for dual-modality CT and fluorescence imaging and photothermal therapy.

Multifunctional nanoparticles (NPs) have great potential for multimodal cancer imaging and effective therapy. We have developed multifunctional NPs (GNR@SiO2@QDs) by incorporating gold nanorods (GNRs) and CdSe/ZnS quantum dots (QDs) into silica. Folic acid (FA) as a targeting ligand was covalently conjugated on the surfaces of GNR@SiO2@QDs with a silane coupling agent. Cell viability assay showed that these NPs had low cytotoxicity. And confocal fluorescence images illustrated that they could selectively target HeLa cells overexpressing folate receptors (FRs) rather than FR-deficient A549 cells. In vitro cell imaging experiments revealed that these NPs exhibited strong X-ray attenuation for X-ray computed tomography (CT) imaging and strong fluorescence for fluorescence imaging. They also showed an enhanced photothermal therapy (PTT) effect for cancer cells due to GNRs' high absorption coefficient in the near infrared (NIR) region and a better heat generation rate. All results show that they have great potential in theranostic applications such as for targeted tumor imaging and therapy.