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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. [ABSTRACT FROM AUTHOR]

Luminescence thermometry usually suffer from cellular complexity of the biochemical environment (such as pH and ionic strength), and thus the accuracy and reliability of the determined intracellular temperature are directly affected. Herein, a photoluminescent nanothermometer composed of polymer encapsulated quantum dots (P-QD) has been developed. And the prepared nanothermometer exhibits some advantages: such as non-sensitivity to pH and ionic strength, as well as high detection sensitivity and ultrahigh reversibility. The intracellular temperature was accurately determined under physiological conditions with different pH and ionic strength, and direct measurement of thermogenesis in individual cells has been achieved.