Abstract
Materials possessing high two photon absorption (TPA) are highly desirable for a range of fields, such as three-dimensional data storage, TP microscopy (TPM) and photodynamic therapy (PDT). Specifically, for TPM, high TP excitation (TPE) brightness (σ × ϕ, where σ is TPA cross-sections and ϕ is fluorescence quantum yield), excellent photostability and minimal cytotoxicity are highly desirable. However, when TPA materials are transferred to aqueous media through molecule engineering or nanoparticle formulation, they usually suffer from the severely decrease of quantum yield (QY). Here, we report a convenient and efficient method for preparing polymer-encapsulated quantum dots (P-QD). Interestingly, the QY was considerably enhanced from original 0.33 (QDs in THF) to 0.84 (P-QD in water). This dramatic enhancement in QY is mainly from the efficiently blocking nonradiative decay pathway from the surface trap states, according to the fluorescence decay lifetimes analysis. The P-QD exhibits extremely high brightness (σ × ϕ up to 6.2 × 106 GM), high photostability, excellent colloidal stability and minimal cytotoxicity. High quality cellular TP imaging with high signal-to-background ratio (> 100) and tissue imaging with a penetration depth of 2200 μm have been achieved with P-QD as probe.
Highlights
Materials possessing high two photon absorption (TPA) are highly desirable for a range of fields, such as three-dimensional data storage, TP microscopy (TPM) and photodynamic therapy (PDT)
The zeta potential of the polymer-encapsulated quantum dots (P-Quantum dots (QDs)) dispersed in deionized water was measured to be 224.4 6 0.7 mV, which can be ascribed to the ionization of the surface carboxyl groups
To conclude, we have introduced a new class of polymer-encapsulated QDs with high TP excitation (TPE) brightness s 3 w as high as 6.2 3 106 GM (1 GM 5 10250 cm[4] sphoton[21] particle21)
Summary
Materials possessing high two photon absorption (TPA) are highly desirable for a range of fields, such as three-dimensional data storage, TP microscopy (TPM) and photodynamic therapy (PDT). For TPM, high TP excitation (TPE) brightness (s 3 w, where s is TPA cross-sections and w is fluorescence quantum yield), excellent photostability and minimal cytotoxicity are highly desirable. Different kinds of TPA materials have been developed toward the creation of TP bioprobes and some of them have been successfully used for TP biomedical imaging[5,6] Despite these previous achievements, a major limitation of TPM is the lack of available probes with high TPE brightness because most of them have very small TPA crosssections (s), typically s , 50 GM (1 GM 5 10250 cm[4] s photon21)[7], and/or low quantum yield (QY, w). The development of QDs-based TP probes without degrading the original superior optical properties, and with excellent photostability and minimal cytotoxicity, is techinally challenging, but highly desirable for pratical TPM
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