Abstract
BackgroundQuantum dots (QDs) have been used as fluorophores in various imaging fields owing to their strong fluorescent intensity, high quantum yield (QY), and narrow emission bandwidth. However, the application of QDs to bio-imaging is limited because the QY of QDs decreases substantially during the surface modification step for bio-application.ResultsIn this study, we fabricated alloy-typed core/shell CdSeZnS/ZnS quantum dots (alloy QDs) that showed higher quantum yield and stability during the surface modification for hydrophilization compared with conventional CdSe/CdS/ZnS multilayer quantum dots (MQDs). The structure of the alloy QDs was confirmed using time-of-flight medium-energy ion scattering spectroscopy. The alloy QDs exhibited strong fluorescence and a high QY of 98.0%. After hydrophilic surface modification, the alloy QDs exhibited a QY of 84.7%, which is 1.5 times higher than that of MQDs. The QY was 77.8% after the alloy QDs were conjugated with folic acid (FA). Alloy QDs and MQDs, after conjugation with FA, were successfully used for targeting human KB cells. The alloy QDs exhibited a stronger fluorescence signal than MQD; these signals were retained in the popliteal lymph node area for 24 h.ConclusionThe alloy QDs maintained a higher QY in hydrophilization for biological applications than MQDs. And also, alloy QDs showed the potential as nanoprobes for highly sensitive bioimaging analysis.Graphical
Highlights
Quantum dots (QDs) have been used as fluorophores in various imaging fields owing to their strong fluorescent intensity, high quantum yield (QY), and narrow emission bandwidth
We previously reported on the fabrication of alloytyped CdSeZnS/ZnS QDs with high QY and their applications for immunoassay [16]
Characterization of multilayer quantum dots (MQDs) and alloy QDs According to previous reports, the diffusion of Zn ions into the surface of the CdSeZnS core occurs under a high reaction temperature during ZnS shell formation reaction; this phenomenon reduces the formation of structural defects and enhances the QY of the QDs [13, 14]
Summary
Quantum dots (QDs) have been used as fluorophores in various imaging fields owing to their strong fluorescent intensity, high quantum yield (QY), and narrow emission bandwidth. QDs have been used as an alternative to fluorophores in various fields, in bio-imaging [1,2,3,4]. During QD fabrication, their surface is surrounded with ligands such as trioctylphosphine (TOP) or trioctylphosphine oxide (TOPO) These ligands enhance the stability of QDs in hydrophobic environments such as toluene or n-hexane, QDs with these ligands cannot be used for bio-imaging because they aggregate in such physiological conditions due to the hydrophobicity of the ligands. The quantum yield (QY), an important performance index, of QDs has been reported to decrease during the surface modification step. Low QY has been a major drawback of QDs, which limits their bio-application [9,10,11]
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