One-pot synthesized DNA-CdTe quantum dots applied in a biosensor for the detection of sequence-specific oligonucleotides.

In the past decade, as a new class of fluorescent probes, semiconductor quantum dots (QDs) have been widely applied in the area of biosensing, immunoassays, and biological imaging because of their unique optical characteristics and biocompatibility. In these applications, a number of biomolecule-labeled QDs were devoted to biospecific interactions, such as DNA-labeled QDs. These QDs can be usually used as a donor for molecular recognition mainly in fluorescence resonance energy transfer (FRET). The coupling reaction between streptavidin QDs and biotin–DNA is a common approach for DNA-labeled QDs for the streptavidin–biotin specific reaction. The method is convenient, but it has no advantage in FRET application, due to increasing the distance between the donor (the large size of the QD) and the acceptor. Furthermore, streptavidin QDs are expensive. DNA covalent bonding to QDs by reaction between the carboxy/amino group of QDs and amino/carboxy group modified DNA could overcome these flaws; however; the acidic coupling conditions may lead to the breakdown of the QDs, which limits its application. Zhou et al. directly coupled a dye-labeled DNA acceptor to a QD donor through a thiol linker. This method costs less, significantly reduces the donor–acceptor distance to increase the FRET efficiency, and at the same time retains the stability of the QDs . However, the process is multistep and complicated. A one-step synthesis of DNA-labeled QDs has been established in such an environment. Phosphorothiolate phosphate (ps–po) DNA compounds were used as ligands to obtain DNA-labeled QDs. Herein, we have synthesized nucleic acid functionalized CdTe nanocrystals with different emission wavelengths by a one-step synthesis. Recently, new emerging zero-bandgap carbon nanomaterials, graphene, and graphene oxide (GO) have attracted great interest in the fields of biology, chemistry, physics, and materials. Graphene and GO have p-systems, which allows them very easily to accept electrons. Inspired by the property, researchers have used graphene and GO as energy acceptors to develop many biosensors based on the FRET system. Importantly, graphene and GO possess a superquenching ability that is critical for the sensitivity of assays. In addition, graphene displays better conductivity than GO, because GO has many oxygen-containing groups, which destroy the conjugate structure. Thus, graphene was chosen as the energy acceptor in this paper. A biosensor, which is based on FRET from the DNA-functionalized CdTe nanocrystals to graphene, has been developed, that is, DNA–CdTe QDs prepared by a one-pot method, and its successful application in the analytical detection of the hepatitis B virus (HBV) surface–antigen gene is described for the first time. Scheme 1 shows the preparation of DNA–CdTe QDs by a one-pot method. Glutathione (GSH) and a specific-sequence DNA were used as a co-ligands to stabilize the QDs. The DNA ligand consisted of two domains: phosphorothio-