Extremely High Brightness from Polymer-Encapsulated Quantum Dots for Two-photon Cellular and Deep-tissue Imaging

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.

Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy

“…102 The resultant QDs exhibited a notable penetration depth of 2.2 cm in two-photon imaging of cells underneath a tissue phantom, suggesting the feasibility of utilizing QDs as two-photon mediated deep tissue PDT probes. Plasmonic metal NPs (e.g., Au, Ag) are known to have unique optical properties arising from collective oscillation of conduction band electrons on surfaces, which can induce local electromagnetic fields and modulate optical properties of nearby chromophores.…”

“…97, 101 Despite the extensive research interest, these molecular TPA materials often suffer from severely decreased quantum yield after transferring into water through molecular engineering or nanoparticle formulation. 102 …”

Revisiting the classification of NIR-absorbing/emitting nanomaterials for in vivo bioapplications

“…Another example is the use of multi-QDs embedded in PMMA-co-MAA nanospheres, which showed extremely high brightness (TPA cross-section up to 6.23 × 10 6 GM). 140 In vitro and in vivo experiments provided evidence of a superior signal-to-background ratio (4100) in cellular imaging as well as a deeper penetration depth for tissue imaging.…”

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

“…In this context, semiconductor quantum dots (QDs) have recently emerged as an interesting alternative to organic dyes for nonlinear biophotonic applications. [1][2][3][4] However, the optimization of their use is hampered by the scarcity of the relevant data that depend strongly on the chemical composition, size, and shape of the nanoparticles. Indeed, measurements of TPA cross sections of various QDs are often performed for a single wavelength only that does not necessarily correspond to the maximum of the TPA band, and the reports lack the confrontation of the obtained values with the quantum yield (QY) of the TPEE, which is a crucial parameter in microscopy imaging applications.…”