Research Article Acetic acid-mediated rapid cubic-to-hexagonal(α-β)phase transformation for ultra-bright lanthanide-dopedβ-NaYF_(4)nanobioprobes

Hexagonal-phase NaYF_(4)(β-NaYF_(4))has been acknowledged to be one of the most efficient doping hosts to prepare bright lanthanide-doped luminescent nano-bioprobes for various biomedical applications.However,to date,it remains a great challenge to synthesize ultra-bright lanthanide-dopedβ-NaYF_(4)nano-bioprobes under a low reaction temperature by using conventional synthetic methods.Herein,we first develop an acetic acid(HAc)-mediated coprecipitation method for the preparation of ultrabright lanthanide-dopedβ-NaYF_(4)nanoprobes under a low reaction temperature at 200℃.Based on a series of comparative spectroscopic investigations,we show that the use of HAc in the reaction environment can not only promote the rapidα-βphase transformation of NaYF_(4)host at 200℃ within 1 h but also boost the absolute photoluminescence quantum yield(PLQY)of NaYF_(4)nanocrystals to 30.68%for near-infrared emission and to 3.79%for upconversion luminescence,both of which are amongst the highest values for diverse lanthanide-doped luminescent nanocrystals ever reported.By virtue of their superior nearinfrared luminescence,we achieve optical-guided dynamic vasculature imaging in vivo of the whole body at a high spatial resolution(23.8μm)under 980 nm excitation,indicating its potential for the diagnosis and treatment evaluation of vasculaturerelated diseases.

Multiplexed intracellular detection based on dual-excitation/dualemission upconversion nanoprobes

Multiplexed intracellular detection is desirable in biomedical sciences for its higher eficiency and accuracy compared to the single-analyte detection.However,it is very challenging to construct nanoprobes that possess multiple fluorescent signals to recognize the different intracellular species synchronously.Herein,we proposed a novel dual-excitation/dual-emission upconversion strategy for multiplexed detection through the design of upconversion nanoparticles(UCNP)loaded with two dyes for sensitization and quenching of the upconversion luminescence(UCL),respectively.Based on the two independent energy transfer processes of near-infrared(NIR)dye IR845 to UCNP and UCNP to visible dye PAPS-Zn,CIO-and Zn2+were simultaneously detected with a limit of detection(LOD)of41.4 and 10.5 nM,respectively.By tilizing a purpose built 830/980 nm dual-laser confocal microscope,both intrinsic and exogenous CIO and Zn2+in live MCF-7 cells have been accurately quantified.Such dual-excitation/dual-emission ratiometric UCL detection mode enables not only monitoring multiple intracellular analytes but also eliminating the detection deviation caused by inhomogeneous probe distribution in cells.Through modulation of NIR dye and visible dye with other reactive groups,the nanoprobes can be extended to analyze various intraellular species,which provides a promising tool to study the biological activities in live cells and diagnose diseases.

Fabricating ultralow-power-excitable lanthanide-doped inorganic nanoparticles with anomalous thermo-enhanced photoluminescence behavior

Trivalent lanthanide(Ln^(3+))-doped luminescent nanoparticles(NPs)have been extensively investigated as deep-tissue-penetration visual bioimaging agents owing to their exceptional upconversion and near-infrared(NIR)luminescence upon irradiation of NIR light.However,in most cases,the power density of irradiation used for in vivo biological imaging is much higher than that of the reported maximum permissible exposure(MPE)value of NIR light,which inevitably does great damage to the living organisms under study and thus impedes the plausible clinical applications.Herein,by using a facile syringe pump-aided shell epitaxial growth method,we construct for the first time a new class of Ln^(3+)-doped KMgF_(3):Yb/Er@KMgF_(3)core-shell NPs that can be activated by utilizing a 980-nm xenon lamp or diode laser with an ultralow excitation power density down to 0.08 mW cm^(−2),a value that is approximately 4 orders of magnitude lower than the MPE value set by the American National Standards Institute(ANSI)for safe bioimaging in vivo.By combining the comparative spectroscopic investigations with atomic-resolved spherical aberration corrected transmission electron microscopy(AC-TEM)characterization,we find that the reduced crystallographic defects are the primary cause underlying such an ultralow-power-excitable feature of the KMgF_(3):Yb/Er@KMgF_(3)core-shell NPs.And,by the same token,the resultant KMgF_(3):Yb/Er@KMgF_(3)core-shell NPs also exhibit an anomalous thermo-enhanced photoluminescence(PL)behavior coupled with an excellent photothermal stability that cannot occur in other Ln^(3+)-doped core-shell NPs.These findings described here unambiguously pave a new way to prepare high-quality Ln^(3+)-doped luminescent NPs with desirable ultralow-power-excitable capability and photothermal stability for future biomedical applications.

Luminescent nano-bioprobes based on NIR dye/lanthanide nanoparticle composites

Near-infrared(NIR)light,which has ignorable tissue scattering/absorption,minimal photodamage,and no autofluorescence interference,is highly favorable for bioapplications.NIR dye and lanthanide-doped nanoparticle(LnNP),as representative NIR-excited luminescence probes,have attracted increasing interest due to their unique optical property and low biological toxicity.Design of luminescence probes based on NIR dye/LnNP nanocomposites cannot only integrate the advantages but also achieve additional functions via regulating internal energy transfer pathways.In this review,we focus on the most recent advances in the development of NIR dye/LnNP nanocomposites as potential bioprobes,which cover from their fundamental photophysics to bioapplications,including energy transfer mechanisms,interface engineering(involving binding interaction,distance,and aggregation as key factors),and their applications for dye-sensitized upconversion/downshifting luminescent bioimaging,detection of biomolecules,and NIR-triggered diagnosis and therapy.Some future prospects and efforts toward this active research field are also envisioned.