Water-Dispersible Silica-Coated Upconverting Liposomes: Can a Thin Silica Layer Protect TTA-UC against Oxygen Quenching?

Abstract

Light upconversion by triplet–triplet annihilation (TTA-UC) in nanoparticles has received considerable attention for bioimaging and light activation of prodrugs. However, the mechanism of TTA-UC is inherently sensitive for quenching by molecular oxygen. A potential oxygen protection strategy is the coating of TTA-UC nanoparticles with a layer of oxygen-impermeable material. In this work, we explore if (organo)silica can fulfill this protecting role. Three synthesis routes are described for preparing water-dispersible (organo)silica-coated red-to-blue upconverting liposomes. Their upconversion properties are investigated in solution and in A549 lung carcinoma cells. Although it was found that the silica offered no protection from oxygen in solution and after uptake in A549 cancer cells, upon drying of the silica-coated liposome dispersion in an excess of (organo)silica precursor, interesting liposome–silica nanocomposite materials were obtained that were capable of generating blue light upon red light excitation in air.

Recent progress in upconversion luminescence nanomaterials for biomedical applications

“…Three dyes, BODIPY-FL, Cy3.5, and IR-806 with different absorption capacity were employed as sensitizer I, II, and III, respectively. 142 The energy harvested by sensitizer I can transfer to sensitizer II, followed by the sequential energy transfer to sensitizer II, sensitizer III, Yb 3+ , and then Tm 3+ activator of NaYF4:Yb 3+ ,Tm 3+ . In addition, irradiation of anyone of three sensitizers can trigger the multi-step cascade energy transfer, extending the absorption band of upconversion with the energy transfer mechanism.…”

“…161 In these dual color Recently, silica coated upconversion liposome has been reported by Askes and colleagues. 142 In this work, the sensitizer and annihilator molecules (PdTPDBP-perylene/TBP pair) were firstly loaded into the liposome nanoencapulator, followed by the silica coating with three different methods. In solution and live A549 cells, no protection from oxygen quenching for silica coating was observed.…”

Robust triplet–triplet annihilation photon upconversion by efficient oxygen scavenging

“…[5][6][7][8] Similarly, protective coating has been applied to rubbery matrices to isolate the TTA-UC system from oxygen as well as (organic) silica-coating to semi-fluid systems in liposomes. 9,10 So far, the highest robustness has been found in a system without solvent where the annihilator has been modified to act as a viscous solvent itself. 11 This benefits the contact between the interacting species and allows the TTA-UC process to proceed with rates that exceed the diffusion limit, thus lowering the sensitivity of the diffusion limited O 2 quenching.…”

Hot-band absorption of indocyanine green for advanced anti-stokes fluorescence bioimaging

“…Triplet-triplet annihilation-based metal complex-organic compound systems have stronger absorption and higher quantum efficiency to be more efficient upconverters than rare-earth ion doped materials 8 , 9 . Unfortunately, the photostability of triplet-triplet annihilation-based upconverters is relatively low due to strong quenching processes caused by molecular oxygen 10 . TADF and HBA processes in organic molecules also excited by the CW laser are attractive anti-Stokes processes.…”