With the development of nonlinear optics and new imaging methods, near-infrared (NIR) light can excite contrast agents to probe biological specimens both functionally and structurally with a deeper imaging depth and a higher spatial resolution than linear optical approaches. There is considerable and growing interest in how biological specimens respond to NIR light. Moreover, the visible absorption band of most functional nanomaterials becomes NIR-excitable through multiphoton processes, thus allowing multifunctional imaging and combined therapy with noble metal and magnetic nanoparticles both in vitro and in vivo. A groundbreaking example is the use of different laser techniques to excite single-type NIR-absorbing/emitting nanomaterials to produce multiphoton emission by femtosecond lasers using either a remote control system for photodynamic therapy or photo-induced chemical bond dissociation. These techniques provided superior anatomical resolution and detection sensitivity for in vivo tumor-targeted imaging than those offered by conventional methods. Here we summarize the most recent progress in the development of smart NIR-absorbing/emitting nanomaterials for in vivo bioapplications.
The unique photoluminescent properties of upconversion nanoparticles (UCNPs) have attracted worldwide research interest and inspired many bioanalytical applications. The anti‐Stokes emission with long luminescence lifetimes, narrow and multiple absorption and emission bands, and excellent photostability enable background‐free and multiplexed detection in deep tissues. So far, however, in vitro and in vivo applications of UCNPs are restricted to the laboratory use due to safety concerns. Possible harmful effects may originate from the chemical composition but also from the small size of UCNPs. Potential end users must rely on well‐founded safety data. Thus, a risk to benefit assessment of the envisioned combined therapeutic and diagnostic (“theranostic”) applications is fundamentally important to bridge the translational gap between laboratory and clinics. The COST Action CM1403 “The European Upconversion Network—From the Design of Photon‐Upconverting Nanomaterials to Biomedical Applications” integrates research on UCNPs ranging from fundamental materials synthesis and research, detection instrumentation, biofunctionalization, and bioassay development to toxicity testing. Such an interdisciplinary approach is necessary for a better and safer theranostic use of UCNPs. Here, the status of nanotoxicity research on UCNPs is compared to other nanomaterials, and routes for the translation of UCNPs into clinical applications are delineated.
Laser induced white light emission was observed from porous graphene foam irradiated with a focused continuous wave beam of the infrared laser diode. It was found that the intensity of the emission increases exponentially with increasing laser power density, having a saturation level at ca. 1.5 W and being characterized by stable emission conditions. It was also observed that the white light emission is spatially confined to the focal point dimensions of the illuminating laser light. Several other features of the laser induced white light emission were also discussed. It was observed that the white light emission is highly dependent on the electric field intensity, allowing one to modulate the emission intensity. The electric field intensity ca. 0.5 V/μm was able to decrease the white light intensity by half. Origins of the laser-induced white light emission along with its characteristic features were discussed in terms of avalanche multiphoton ionization, inter-valence charge transfer and possible plasma build-up processes. It is shown that the laser-induced white light emission may be well utilized in new types of white light sources.
Two figures of merit are typically taken into account studying rareearth-doped materials and processes suitable for optical nanothermometry, namely, temperature sensing range and the sensitivity. To optimize the composition of such phosphors and make quantitative comparison between different materials, other factors, such as excitation density and pulse duration, have to been included. Owing to the metastable character of lanthanide excited states, the excitation intensity has a critical importance but has been disregarded so far. Our studies show, based on a new nanocrystalline Er:LiYbP 4 O 12 luminescent thermometer, the influence of the excitation power density on its suitability for temperature sensing. The highest sensitivity was reached for LiYbP 4 O 12 :0.1% Er nanocrystals upon pulsed excitation: 2.88%/K at average power below 25 mW/cm 2 , while the same material displayed lower ∼0.5%/K sensitivity at higher 50−300 mW/cm 2 excitation intensities. The mechanism responsible for the observed sensitivity changes was discussed in terms of competition between thermalization and nonradiative depopulation processes.
An innovative approach for up-converting nanoparticles adaptation for bio-related and theranostic applications is presented. We have successfully encapsulated multiple, ~8 nm in size NaYF4 nanoparticles inside the polymeric nanocarriers with average size of ~150 nm. The initial coating of nanoparticles surfaces was preserved due to the hydrophobic environment inside the nanocapsules, and thus no single nanoparticle surface functionalization was necessary. The selection of biodegradable and sugar-based polyelectrolyte shells ensured biocompatibility of the nanostructures, while the choice of Tm3+ and Yb3+ NaYF4 nanoparticles co-doping allowed for near-infrared to near-infrared bioimaging of healthy and cancerous cell lines. The protective role of organic shell resulted in not only preserved high up-converted emission intensity and long luminescence lifetimes, without quenching from water environment, but also ensured low cytotoxicity and high cellular uptake of the engineered nanocapsules. The multifunctionality of the proposed nanocarriers is a consequence of both the organic exterior part that is accessible for conjugation with biologically important molecules, and the hydrophobic interior, which in future application may be used as a container for co-encapsulation of inorganic nanoparticles and anticancer drug cargo.
The intentional design of chemical architecture of lanthanide doped luminescent nanoparticles through the proper selection of dopants in core−shell and core−shell−shell structures enables optimization of their optical properties. Such an approach allows one to achieve energy transfer upconversion (ETU) and energy migration mediated upconversion (EMU) and green emission from Tb 3+ ions with the Yb 3+ and Nd 3+ sensitizers at 980 and 808 nm photoexcitation, respectively. The [Nd 3+ → Yb 3+ ]→ [Yb 3+ → Tb 3+ ] EMU phenomenon was significantly enhanced by spatial displacement of the sensitizing Nd 3+ ions from the activator Tb 3+ ions by intentionally introducing an intermediate Yb 3+ sensitizer layer forming a [Nd 3+ → Yb 3+ ] → [Yb 3+ ] → [Yb 3+ → Tb 3+ ] system. Otherwise Tb 3+ emission was considerably quenched by Nd 3+ ions even though they were spitted between the core and shell, respectively. Moreover, (Tb 3+ ,Yb 3+ ) → (Tb 4+ ,Yb 2+ ) valence change has been discovered to limit the Tb 3+ upconversion emission. The studies explain how the chemical architecture of the smartly designed
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.