A General Strategy for Biocompatible, High-Effective Upconversion Nanocapsules Based on Triplet–Triplet Annihilation

Abstract

A general strategy for constructing high-effective upconversion nanocapsules based on triplet-triplet annihilation (TTA) was developed by loading both sensitizer and annihilator into BSA-dextran stabilized oil droplets. This strategy can maintain high translational mobility of the chromophores, avoid luminescence quenching of chromophore by aggregation, and decrease the O2-induced quenching of TTA-based upconversion emission. Pt(II)-tetraphenyl-tetrabenzoporphyrin (PtTPBP) and BODIPY dyes (BDP-G and BDP-Y with the maximal fluorescence emission at 528 and 546 nm, respectively) were chosen as sensitizer/annihilator couples to fabricate green and yellow upconversion luminescent emissive nanocapsules, named UCNC-G and UCNC-Y, respectively. In water under the atmospheric environment, interestingly, UCNC-G and UCNC-Y exhibit intense upconversion luminescence (UCL) emission (λex = 635 nm) with the quantum efficiencies (ΦUCL) of 1.7% and 4.8%, respectively, whereas very weak UCL emission (ΦUCL < 0.1%) was observed for the corresponding previous reported SiO2-coating nanosystems because of aggregation-induced fluorescence quenching of annihilators. Furthermore, application of theses upconversion nanocapsules for high-contrast UCL bioimaging in vivo of living mice without removing the skin was demonstrated under 635-nm excitation with low power density of 12.5 mW cm(-2).

Photochemical upconversion: present status and prospects for its application to solar energy conversion

“…Polymeric micro-or nano-capsules filled with a liquid TTA system have been presented in a number of studies and allow stable operation in water, 129,[146][147][148][149] as do polymeric nanofibers containing nano-capsules filled with a liquid TTA system. 150 Self-organized micellar carriers based on non-ionic surfactants have been presented and likewise allow transference of the system into water.…”

Red Light Activation of Ru(II) Polypyridyl Prodrugs via Triplet-Triplet Annihilation Upconversion: Feasibility in Air and through Meat

“…TTA-UC has been demonstrated in various organic, inorganic, and/or supramolecular materials [15,[18][19][20][21][22], as well as in nano-or micro-sized particles [23][24][25]. For biological applications, i.e., for drug delivery and activation [26,27] or bio-imaging [13,[28][29][30][31][32][33], one of the main problems of TTA-UC is its sensitivity to molecular oxygen, which readily quenches the triplet state chromophores involved in the TTA-UC mechanism.…”

Recent advances in the optimization and functionalization of upconversion nanomaterials for in vivo bioapplications

“…54 The nanocapsules were composed of an oil droplet and a surface bovine serum albumindextran layer to protect the oil phase. The TTA sensitizer and emitter molecules were easily loaded into the oil droplets without significantly affecting their mobility and luminescence properties.…”

“…If another TTA-based UCNP composed of PtTPBP and BDP, oil and bovine serum albumindextran possessing a green (or yellow) upconversion emission (excited at 635 nm) is used as the probe, then lymphatic images can be easily obtained in vivo and without removal of the skin. 54 UCNPs DESIGNED FOR TUMOR-TARGETED IMAGING In addition to basic imaging of the liver or spleen by simply injecting the hydrophilic UCNPs into the mouse via the tail vein, researchers also want to utilize UCNPs for functional imaging experiments. Tumor targeting is one of the most attractive functional imaging applications because of the importance of tumor detection and inclinic therapy.…”

“…53,54 Because of their relatively high absorption coefficient and upconversion efficiency, these TTA-based upconversion materials can be excited by low-power density radiation. However, the synthesis of such TTA-based upconversion nanomaterials through NIR emissions, as well as related issues such as long-term stability, biodistribution and toxicity, still need to be addressed.…”