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Targeted imaging is playing an increasingly important role in the early detection and precise diagnosis of cancer. This need has motivated research into sensory nanomaterials that can be constructed into imaging agents to serve as biosensors. Graphene quantum dots (GQDs) as a valuable nanoprobe show great potential for use in two-photon biological imaging. However, most as-prepared GQDs exhibit a low two-photon absorption cross-section, narrow spectral coverage, and "one-to-one" signal conversion mode, which greatly hamper their wide application in sensitive early-stage cancer detection. Herein, a versatile strategy has been employed to fabricate an aptamer Sgc8c-functionalized hybrid as a proof-of-concept of the signal amplification strategy for targeted cancer imaging. In this study, GQDs with two-photon imaging performance, and silica nanoparticles (SiO2 NPs) as nanocarriers to provide amplified recognition events by high loading of GQD signal tags, were adopted to construct a two-photon hybrid-based signal amplification strategy. Thus, the obtained hybrid (denoted SiO2@GQDs) enabled extremely strong fluorescence with a quantum yield up to 0.49, excellent photostability and biocompatibility, and enhanced bright two-photon fluorescence up to 2.7 times that of bare GQDs (excitation at 760 nm; emission at 512 nm). Moreover, further modification with aptamer Sgc8c showed little disruption to the structure of the SiO2@GQDs-hybrid and the corresponding two-photon emission. Hence, SiO2@GQDs–Sgc8c showed specific responses to target cells. Moreover, it could be used as a signal-amplifying two-photon nanoprobe for targeted cancer imaging with high specificity and great efficiency, which exhibits a distinct green fluorescence compared to that of GQDs–Sgc8c or SiO2@GQDs. This signal amplification strategy holds great potential for the accurate early diagnosis of tumors and offers new tools for the detection a wide variety of analytes in clinical application. [ABSTRACT FROM AUTHOR]

In this paper, one-dimensional ZnS:Mn2+ nanowires (NWs)/Fe3O4 quantum dots (QDs)/SiO2 heterostructures were successfully synthesized by the Stöber method to form the water-soluble fluorescent/superparamagnetic nanocomposites. The average diameter of the ZnS:Mn2+ NWs, Fe3O4 QDs and ZnS:Mn2+ NWs/Fe3O4 QDs/SiO2 heterostructures was about 6–8 nm, 4–5 nm and 18 nm, respectively. The Fe3O4 QDs were covalently linked to the ZnS:Mn2+ NWs by the conjugation of the hydroxyl groups on the surface of the QDs and the carboxyl groups modified on the surface of the NWs. It was found that the covalent bonds between the NWs and QDs could effectively suppress the energy transfer from the ZnS:Mn2+ NWs to the Fe3O4 QDs. As the SiO2 shell thickness increased, the fluorescence intensity reached the highest value when the hydrolysis time of tetraethyl orthosilicate was 5 hours, which was comparable to that of the ZnS:Mn2+ NWs. The superparamagnetic properties of the heterostructures were observed at room temperature, which decreased as the SiO2 thickness increased. [ABSTRACT FROM AUTHOR]