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Rare-earth doped multi-shell nanoparticles slated for theranostic applications produce a variety of emission bands upon near-infrared (NIR) excitation. Their downshifting emission is useful for high-contrast NIR imaging, while the upconversion light can induce photodynamic therapy (PDT). Unfortunately, integration of imaging and therapy is challenging. These modalities are better to be controlled independently so that, with the help of imaging, selective delivery of a theranostic agent at the site of interest could be ensured prior to on-demand PDT initiation. We introduce here multi-shell rare-earth doped nanoparticles (RENPs) arranged in a manner to produce only downshifting emission for NIR imaging when excited at one NIR wavelength and upconversion emission for therapeutic action by using a different excitation wavelength. In this work, multi-shell RENPs with a surface-bound sensitizer have been synthesized for decoupled 1550 nm downshifting emission upon 800 nm excitation and 550 nm upconversion emission caused by 980 nm irradiation. The independently controlled emission bands allow for high-contrast NIR imaging in NIR-IIb of optical transparency that gives high-contrast images due to significantly reduced light scattering. This can be conducted prior to PDT using 980 nm to produce upconverted light at 550 nm that excites the RENP surface-bound photosensitizer, Rose Bengal (RB), to effect photodynamic therapy with high specificity and safer theranostics.

Upconverting nanoparticles (UCNPs) are well-known for their capacity to convert near-infrared light into UV/visible light, benefitting various applications where light triggering is required. At the nanoscale, loss of luminescence intensity is observed and thus, a decrease in photoluminescence quantum yield (PLQY), usually ascribed to surface quenching. We evaluate this by measuring the PLQY of NaGdF4:Er3+,Yb3+ UCNPs as a function of size (ca. 15 to 100 nm) and shape (spheres, cubes, hexagons). Our results show that the PLQY of α-phase NaGdF4 Er3+,Yb3+ surpasses that of β-NaGdF4 for sizes below 20 nm, an observation related to distortion of the crystal lattice when the UCNPs become smaller. The present study also underlines that particle shape must not be neglected as a relevant parameter for PLQY. In fact, based on a mathematical nucleus/hull volumetric model, shape was found to be particularly relevant in the 20 to 60 nm size range of the investigated UCNPs.

Among luminescent nanostructures actively investigated in the last couple of decades, rare earth (RE

Temperature touches all aspects of our daily life, including climate, production plants, food storage, transportation, metrology, microelectronics, and medicine, and is a major factor dictating performance of nanotechnologies.1-4 However, while the heat transfer is well understood in bulk, neither experimental nor theoretical models provide a complete picture of the thermal dynamics at the nanoscale.5-7 Here, in situ luminescence thermometry is used to probe the heat propagation taking place within lanthanide (Ln3+)-doped upconverting nanoparticles (UCNPs). We have designed UCNPs with Er3+ and Tm3+ thermometric layers positioned at different locations relative to their surface, varying the distance a heat wave travels before encountering the layers. Despite being separated only by a few tens of nanometers, the thermometric layer closer to the surface of UCNPs detects temperature increase much earlier than the one located at the center – yielding the heat propagation speed in UCNPs ~1.3 nm/s. The UCNPs featuring the two thermometric layers in a single nanostructure confirmed the above result and allowed us to uncover diffusive and non-diffusive (ballistic) heat transport regimes, as well as their interplay and complex heat exchange dynamics taking place in colloidal nanoparticles (nanofluids) at a room temperature.

In this work, we have established a one-pot synthesis strategy to develop a new theranostic nanoplatform by simultaneously encapsulating Er3+, Yb3+ doped NaGdF4 upconverting nanoparticles (UCNPs) and photosensitizer zinc phthalocyanine (ZnPc) into polymeric micelle/silica nanocapsules. This approach consisted of interfacial templating condensation, using triblock copolymers, ethylene oxide)106(propylene oxide)70(ethylene oxide)106 (PEO-PPO-PEO), as the templating and protecting agent. The encapsulation followed a straightforward microemulsion mechanism in an aqueous environment of a near neutral pH. The surface hydrophobic nature of UCNPs is crucial for the success of encapsulation. To prevent the interaction between the hydrophobic OA ligands of UCNPs and the silanol groups of hydrated tetramethoxysilane (TMOS), we modified the previous procedure by tuning the addition sequence of TMOS. It allowed first to encapsulate UCNPs in PEO-PPO-PEO micelles, and then grow the silica shell within the micellar PPO core and PEO corona interface. The silica shell is incorporated for its chemical and mechanical stability, while the PEO corona confers additional steric stability to the nanocapsule. Using the modified strategy we successfully co-encapsulated UCNPs and ZnPc in one-pot, and minimized the distance between the two payloads to facilitate the energy transfer from UCNPs to ZnPc, as compared to conventional PS loading in the mesoporous silica coating. The integrated nanocapsule has an average hydrodynamic size of 85 nm with a low polydispersity index of 0.1, and demonstrates excellent colloidal stability, biocompatibility, as well as enhanced negative contrast for T2-weighted imaging and photodynamic therapy. The latter is obtained through indirect excitation of co-encapsulated ZnPc by UCNPs, resulting in singlet oxygen generation and in vitro eradication of BT474 breast cancer cells. Overall, the presented one-pot approach shined light on the co-encapsulation of OA capped inorganic UCNPs with hydrophobic photosensitizers, constituting an important step forward in the surface engineering of UCNPs, as well as upconversion based photodynamic therapy delivery systems.

Carbon nanodots (CNDs) have attracted substantial scientific curiosity because of their intriguing stimuli-responsive optical properties. However, one obstacle to the more widespread use of CNDs as transducers for e.g., biodetection systems is incomplete knowledge regarding the underlying chemical changes responsible for this responsiveness, and how these chemical features can be engineered via the precursors chosen for CND synthesis. This study demonstrates that the precursor's functional groups play a key role in directing N/S/Se heteroatom dopants either towards the surface of the CNDs, towards the aromatic core, or towards small organic fluorophores in the core. Divergent optical properties, which were consistent amongst groups of CNDs prepared with similar precursors, were obtained including either a decrease or increase of fluorescence intensity in the presence of hydrogen peroxide. Moreover, CNDs were identified with orthogonal responsiveness to radical (hydroxyl radicals, ˙OH; down to 2.5 μM) vs. non-radical oxidants (H2O2; down to 50 μM), which suggests that control of the chemistry of CNDs via the choice of precursor could yield probes that are specific to certain sub-species of reactive oxygen species or entirely different molecules altogether, based on the way they chemically-modify the surface (respond faster) and core functional groups (respond slower) associated with chromophores/fluorophores of which the CNDs are composed.

Upconverting nanoparticles (UCNPs) are well-known for their capacity to convert near-infrared light into UV/visible light, benefitting various applications where light triggering is required. At the nanoscale, loss of luminescence intensity is observed and thus, a decrease in photoluminescence quantum yield (PLQY), usually ascribed to surface quenching. We evaluate this by measuring the PLQY of NaGdF

Chronic wounds present a high risk of infection due to delayed and incomplete healing, leading to increased health risks and financial burden to health-care systems. Numerous approaches to promote wound healing have been extensively explored, especially the development of effective wound dressing materials embedded with therapeutic drug molecules. Despite advances made in this area, a remaining challenge to be addressed is the controlled, on-demand release of therapeutic molecules using noncytotoxic stimulus, for example, near-infrared (NIR) excitation. Here, we report a platform that allows for the development of electrospun poly(vinyl alcohol) (PVA) fibrous hybrids embedded with upconverting nanoparticles (UCNPs) and UV-cleavable levofloxacin conjugates for wound dressings. Upon irradiation with NIR light, the excited UCNPs emit UV light around 365 nm, which can cleave the

Luminescent nanomaterials that can be excited, as well as emit, in the near-infrared (NIR) have been investigated for use in a plethora of applications including nanomedicine, nanoelectronics, biosensing, bioimaging, photovoltaics, photocatalysis, etc. The use of NIR light for excitation mitigates some of the drawbacks associated with high-energy (UV or blue) excitation, for example, little to no background autofluorescence from the specimen under investigation as well as no incurred photodamage. Moreover, one of the biggest limitations is of course, that of penetration. As such, NIR light can penetrate tissues much better than high-energy light especially when these wavelengths lie within the three biological windows (BW-I: 700-950, BW-II: 1000-1350, BW-III: 1550-1870 nm) where tissues are optically transparent. At the forefront of NIR excited nanomaterials are rare earth doped nanoparticles, which due to their 4f electronic energy states can undergo conventional (Stokes) luminescence and emit in the three NIR biological windows. However, unlike other classes of nanoparticles, they can also undergo a multiphoton process (known as upconversion) where the NIR excitation light is converted to higher energies resulting in anti-Stokes luminescence spanning the UV-visible-NIR regions. Perhaps the biggest impact of such materials would be in the field of disease diagnostics and therapeutics, now commonly referred to as theranostics. Due to the versatility of their optical properties, it now becomes possible to generate high-energy light (UV or blue) in situ to trigger other light activated therapeutic modalities (i.e. drug release) while using the NIR emission for diagnostics (i.e. bioimaging, nanothermometry). Here, we present the synthesis of various NIR excited (and emitting) rare earth doped core/shell (and multishell) nanoparticles and demonstrate how their luminescence properties can be exploited for potential use in diverse biomedical applications.

Fluorophores with multifunctional properties known as rare-earth-doped nanoparticles (RENPs) are promising candidates for bioimaging, therapy, and drug delivery. When applied in vivo, these nanoparticles (NPs) have to retain long blood-circulation time, bypass elimination by phagocytic cells, and successfully arrive at the target area. Usually, NPs in a biological medium are exposed to proteins, which form the so-called "protein corona" (PC) around the NPs and influence their targeted delivery and accumulation in cells and tissues. Different surface coatings change the PC size and composition, subsequently deciding the fate of the NPs. Thus, detailed studies on the PC are of utmost importance to determine the most suitable NP surface modification for biomedical use. When it comes to RENPs, these studies are particularly scarce. Here, we investigate the PC composition and its impact on the cellular uptake of citrate-, SiO2-, and phospholipid micelle-coated RENPs (LiYF4:Yb3+,Tm3+). We observed that the PC of citrate- and phospholipid-coated RENPs is relatively stable and similar in the adsorbed protein composition, while the PC of SiO2-coated RENPs is larger and highly dynamic. Moreover, biocompatibility, accumulation, and cytotoxicity of various RENPs in cancer cells have been evaluated. On the basis of the cellular imaging, supported by the inhibition studies, it was revealed that RENPs are internalized by endocytosis and that specific endocytic routes are PC composition dependent. Overall, these results are essential to fill the gaps in the fundamental understanding of the nano-biointeractions of RENPs, pertinent for their envisioned application in biomedicine.

β-phase NaGdF4 nanocrystals doped with Er3+ and Yb3+ possessing diverse morphologies were synthesized from the thermolysis of trifluoroacetate precursors in 1-octadecene and oleic acid by modifying the hot-injection strategy. Modulation of the injection temperature during the hot-injection step was an effective approach to control the size and shape of the prepared nanocrystals and allowed for the direct synthesis of nanorods. Here, we report for the first time the fabrication of monodispersed uniform nanorods through a one-step thermolysis approach. The different supersaturation caused by the different temperatures could directly manipulate the nucleation and growth of α-phase nanoparticles before the α → β phase transition, subsequently influences the Ostwald ripening mode during the α → β phase transition, and consequently affects their morphology (i.e., nanorods, nanospheres, nanoprisms, nanoplates, and nanodisks), uniformity, and monodispersity. The upconversion luminescence intensity decreased with ...

Integrating multiple components to realize cancer diagnosis and therapy in a single theranostic nanoplatform has drawn considerable attention. Herein, a multifunctional theranostic nanoplatform (mSiO2@PbS/CdS-Fe3O4) was successfully fabricated by carefully designing thiol-modified large-pore mesoporous silica nanospheres (mSiO2), followed by coordination-driven embedding of Fe3O4 nanoparticles (NPs) and PbS/CdS quantum dots (QDs) inside. The excellent feature of near-infrared (NIR) excitation and NIR emission of PbS/CdS QDs enables deep-tissue photoluminescence imaging, which was demonstrated ex vivo with tissue as thick as 14 mm. Meanwhile, owing to the presence of superparamagnetic Fe3O4 NPs, mSiO2@PbS/CdS-Fe3O4 can be rapidly confined under an external magnetic field (MF), and exhibit a significantly high T2 relaxivity in T2-weighted magnetic resonance (MR) images in vivo. When mSiO2@PbS/CdS-Fe3O4 was exposed to external physical stimuli of MF and/or NIR laser, they produced strong local heating throug...

Bright and nontoxic quantum dots (QDs) are highly desirable in a variety of applications, from solid-state devices to luminescent probes in assays. However, the processability of these species is often curbed by their surface chemistry, which limits their dispersibility in selected solvents. This renders a surface modification step often mandatory to make the QDs compatible with the solvent of interest. Here, we present a new synthetic approach to produce CuInS2 QDs compatible with organic polar solvents and readily usable for the preparation of composite materials. 3-Mercaptopropyl trimethoxysilane (MPTS) was used simultaneously as solvent, sulfur source, and capping agent for the QD synthesis. The synthesized QDs possessed a maximum photoluminescence quantum yield around 6%, reaching approximately 55% after growing a ZnS shell. The partial condensation of MPTS molecules on the surface of QDs was probed by solid-state nuclear magnetic resonance, whose results were used to interpret the interaction of the QDs with different solvents. To prove the versatility of the developed QDs, imparted by the thiolated silane molecules, we prepared via straightforward procedures two nanocomposites of practical interest: (i) silica nanoparticles decorated with QDs and (ii) an inexpensive polymeric film with embedded QDs. We further demonstrate the potential of this composite film as a luminescence thermometer operational over a broad temperature interval, with relative thermal sensitivity above 1% K-1 in the range of biological interest. ©

Developing multifunctional therapeutic and diagnostic (theranostic) nanoplatforms is critical for addressing challenging issues associated with cancers. Here, self-assembled supernanoparticles consisting of superparamagnetic Fe3O4 nanoparticles and photoluminescent PbS/CdS quantum dots whose emission lies within the second biological window (II-BW) are developed. The proposed self-assembled Fe3O4 and PbS/CdS (II-BW) supernanoparticles [SASNs (II-BW)] exhibit outstanding photoluminescence detectable through a tissue as thick as 14 mm, by overcoming severe light extinction and concomitant autofluorescence in II-BW, and significantly enhanced T2 relaxivity (282 mM–1 s–1, ca. 4 times higher than free Fe3O4 nanoparticles) due to largely enhanced magnetic field inhomogeneity. On the other hand, SASNs (II-BW) possess the dual capacity to act as both magnetothermal and photothermal agents, overcoming the main drawbacks of each type of heating separately. When SASNs (II-BW) are exposed to the dual-mode (magnetothe...

Near-infrared (NIR) emitting contrast agents with integrated optical temperature sensing are highly desirable for a variety of biomedical applications, particularly when subcutaneous target visualization and measurement of its thermodynamic properties are required. To that end, the possibility of using Nd3+ doped LiLuF4 rare-earth nanoparticles (RENPs) as NIR photoluminescent nanothermometers is explored. These RENPs are relatively small, have narrow size distribution, and can easily be core/shell engineered – all combined, these features meet the requirements of biologically relevant and multifunctional nanoprobes. The LiLuF4 host allows to observe the fine Stark structure of the 4F3/2 → 4I9/2, 4I11/2, and 4I13/2 optical transitions, each of which can then be used for single-band NIR nanothermometry. The thermometric parameter defined for the most intense Nd3+ emission around 1050 nm, shows high temperature sensitivity (∼0.49% °C−1), and low temperature uncertainty (0.3 °C) as compared to the thermometric parameters defined for the 880 and 1320 nm Nd3+ emissions. Additionally, transient temperature measurements through tissue show that these RENPs can be used to assess fast temperature changes at a tissue depth of 3 mm, while slower temperature changes can be measured at even greater depths. Nd3+ doped LiLuF4 RENPs represent a significant improvement for Nd3+ based single-band photoluminescence nanothermometry, with the possibility of its integration within more sophisticated multifunctional theranostic nanostructures.

With the rise of stereolithographic processes and advanced fabrication processes, photo-induced polymerization is becoming increasingly popular. The development of panchromatic radical initiators, that is to say initiators which are activated by a wide spectrum, is still in its infancy, with the near-infrared range remaining a challenge. We have reported a rationally-designed nanohybrid which can initiate photo-polymerization from ultraviolet to near-infrared wavelengths. Integration of Ag and Au plasmonic nanoparticles (NPs), upconverting (UC) materials and BiFeO3 (BFO) semiconductors with a rational architecture design results in the formation of an Ag@SiO2@UC@BFO–Au core@triple-shell structure. Compared to the conventional thermal radical polymerization method, this material can initiate polymerization under visible or near-infrared light at room temperature, and the initiator can easily be recycled and reused. The excellent activity of the nanohybrid photoinitiator is attributed to the combination of the optical properties of the UC material and BFO semiconductor and the surface plasmon resonance (SPR) in the core@shell configuration, where the Ag NP core demonstrates dual roles of increasing resonant VIS photon scattering as a “mirror” and improving the upconverting efficiency of the NIR-to-VIS photons as a “resonator”; the Au NPs anchored on the BFO shell further enable an efficient energy transfer of absorbed VIS photon energy from Au to BFO via a plasmon-induced resonance energy transfer (PIRET) process.

Upconversion nanothermometry combines the possibility of optically sensing temperatures in very small areas, such as microfluidic channels or on microelectronic chips, with a simple detection setup in the visible spectral range and reduced heat transfer after near-infrared (NIR) excitation. We propose a ratiometric strategy based on Eu3+ ion luminescence activated through upconversion processes. Yb3+ ions act as a sensitizer in the NIR region (980 nm), and energy is transferred to Tm3+ ions that in turn excite Eu3+ ions whose luminescence is shown to be thermally sensitive. Tridoped SrF2:Yb3+,Tm3+,Eu3+ nanoparticles (average size of 17 nm) show a relative thermal sensitivity of 1.1% K−1 at 25.0 °C, in the range of the best ones reported to date for Ln3+-based nanothermometers based on upconversion emission. The present nanoparticle design allows us to exploit upconversion of lanthanide ions that otherwise cannot be directly excited upon NIR excitation and that may provide operational wavelengths with a highly stable read out to fill the spectral gaps currently existing in upconversion-based nanothermometry.

International audience; Development of contactless temperature-probing nanoplatforms based on thermosensitive near-infrared (NIR) light-emitting nanoparticles opens up new horizons for biomedical theranostics at a deep tissue level. Here, we report on the crystallinity and relative thermal sensitivity of NIR emitting Nd3+ doped Gd3Sc2Al3O12 (GSAG:Nd3+) nanoparticles synthesized by a solvothermal method. The obtained nanoparticles are well-crystallized, with sizes less than 100 nm, and can be dispersed in water without any additional functionalization. Upon excitation at 806 nm, the nanoparticles exhibit emission in the first and second biological optical transparency windows. The temperature sensing properties were evaluated from the luminescence intensity ratio of the thermally coupled emission lines corresponding to the R1, R2 Z5 transitions between the Stark sublevels of the 4F3/2 and 4I9/2 electronic states of Nd3+ in the physiological temperature range of 20-50 °C. GSAG:Nd3+ nanoparticles exhibit a maximal relative thermal sensitivity of 0.20% °C-1, higher than that of YAG:Nd3+ nanoparticles used as a control, due to the difference in the crystal field of the host matrices. A higher synthesis temperature in the range of 300-400 °C was also provided to improve the crystallinity of the GSAG:Nd3+ nanoparticles which results in a higher relative thermal sensitivity. Our results demonstrate the potential of GSAG:Nd3+ nanoparticles as luminescence nanothermometers and emphasize the interest of the GSAG matrix itself, which with the presence of Gd, could lead to multimodal diagnostic applications in nanothermometry and magnetic resonance imaging (MRI).

Light triggered theranostic (therapy and diagnostic) nanoplatforms have gained a considerable attention in recent years. In theranostics, light as an external trigger stands out due to its non-invasiveness, high local precision and temporal resolution. Many such nanoplatforms employ high-energy (visible or UV) light to initiate the individual therapeutic and diagnostic modalities. However, light at these wavelengths suffers from inherent drawbacks such as having little to no penetration in living tissue, inducing autofluorescence from inherent fluorophores or chromophores in tissues and causing photodamage. The use of near-infrared (NIR) light for excitation mitigates such drawbacks associated with high-energy excitation, for example, little to no background autofluorescence from the specimen under investigation as well as no incurred photodamage. Moreover, one of the biggest limitations is that of penetration and NIR light can penetrate tissues much better than high-energy light especially when these wavelengths lie within the three biological windows where tissues are optically transparent. At the forefront of NIR excited nanomaterials are lanthanide doped nanoparticles, which can undergo conventional (Stokes) luminescence and emit in the NIR biological windows. However, unlike other classes of nanoparticles, they can also undergo a multiphoton excitation process where the NIR excitation light is converted to higher energies resulting in anti-Stokes luminescence spanning the UV-visible-NIR regions (known as upconversion). Thus, it now becomes possible to generate upconverted high-energy light (UV or visible) in situ to trigger other light activated therapeutic modalities (i.e. drug release) while using the NIR emission for diagnostics (i.e. bioimaging, nanothermometry). Here, we demonstrate how the luminescence properties (upconversion and NIR) of various lanthanide doped core/shell (and multishell) nanoparticles can be exploited for potential use in theranostics.

We develop a compressed-sensing two-dimensional rotating-mirror streak camera that enables single-shot ultrahigh-speed optical imaging with a speed of up to 1.5 million frames per second. Using this technique, we have imaged a single laser pulse illuminating through a transmissive target.

Single-shot real-time ultra-high-speed imaging is of significance in capturing transient phenomena. Existing techniques fall short in possessing satisfying specifications in the imaging speed, sequence depth, and pixel count. To overcome these limitations, we have developed compressed optical-streaking ultra-high-speed photography (COSUP) that records a scene (x, y, t) by applying the operations of spatial encoding, temporal shearing, and spatiotemporal integrating. The COSUP system possesses an imaging speed of 1.5 million frames per second (fps), a sequence depth of 500 frames, and a pixel count of 0.5 megapixels per frame. COSUP is demonstrated by imaging single laser pulses illuminating through transmissive targets and by tracking a fast-moving object. We envision COSUP to be applied in widespread applications in biomedicine and materials science.

Made available in DSpace on 2021-06-25T11:05:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-12-01 Near-infrared (NIR) nanothermometers are sought after in biomedicine when it comes to measuring temperatures subcutaneously. Yet, temperature sensing within the third biological imaging window (BW-III), where the highest contrast images can be obtained, remains relatively unexplored. Here, LiErF4/LiYF4 rare-earth nanoparticles (RENPs) are studied as NIR nanothermometers in the BW-III. Under 793 nm excitation, LiErF4/LiYF4RENPs emit around 1540 nm, corresponding to the 4I13/2 → 4I15/2radiative transition of Er3+. The fine Stark structure of this transition allows to delineate intensity regions within the emission band that can be used for single-band ratiometric nanothermometry. These nanothermometers have a relative temperature sensitivity of ≈0.40% °C−1. The temperature-dependent energy transfer to the surrounding solvent molecules plays a significant role in the thermometric properties of the RENPs. In addition, Ce3+ions are doped in the core of the RENPs to examine whether it affects the NIR emission and temperature sensitivity. Ce3+ at 1 mol% marginally influences the downshifting emission intensity of the RENPs, yet increases the relative thermal sensitivity to ≈0.45% °C−1. Furthermore, Ce3+ quenches the visible upconversion emission of the RENPs. Together, LiErF4:Ce3+/LiYF4RENPs enable single-band photoluminescence nanothermometry in the BW-III, with the future possibility of its integration within multifunctional decoupled theranostic nanostructures. Institut National de la Recherche Scientifique Centre Énergie Matériaux et Télécommunications Université du Québec, 1650 Boul. Lionel-Boulet Institute of Chemistry São Paulo State University—UNESP Institute of Chemistry São Paulo State University—UNESP

In this work, we capitalize on the unique properties of terahertz radiation to investigate nanoparticle-assisted laser-tissue interaction. We demonstrate the promising capability of the proposed technique to perform the simultaneous monitoring of laser-tissue interaction and the three-dimensional visualization of the induced photothermal damage in a non-invasive and noncontact manner.

In light of the recent developments on Yb

In this work, rare-earth-based nanoparticles based on LiYbF4 and doped with Er3+, Tm3+ and Ho3+ were investigated. The effect of the concentration of the dopant ions was thoroughly studiedfrom a spectroscopic standpoint under 980 nm excitation. The upconversion emission that originates from the absorption of the optical energy from the Yb3+ ions in the crystal lattice and the subsequent energy transfer to the other rare earth in the lattice (i.e., Er3+, Tm3+ or Ho3+) highly depends on the concentration of the latter ion. Overall, the findings in this manuscripts provide important insights into the properties and rational design of upconverting nanoparticles.

With the goal of developing more accurate, efficient, non-invasive and fast diagnostic tools, the use of near-infrared (NIR) light in the range of the second and third biological windows (NIR-II: 1000–1350 nm, NIR-III: 1550–1870 nm) is growing remarkably as it provides the advantages of deeper penetration depth into biological tissues, better image contrast, reduced phototoxicity and photobleaching. Consequently, NIR-based bioimaging has become a quickly emerging field and manifold new NIR-emitting bioprobes have been reported. Classes of materials suggested as potential probes for NIR-to-NIR bioimaging (using NIR light for the excitation and emission) are quite diverse. These include rare-earth based nanoparticles, Group-IV nanostructures (single-walled carbon nanotubes, carbon nanoparticles and more recently Si- or Ge-based nanostructures) as well as Ag, In and Pb chalcogenide quantum dots. This review summarizes and discusses current trends, material merits, and latest developments in NIR-to-NIR bioimaging taking advantage of the region above 1000 nm (i.e. the second and third biological windows). Further consideration will be given to upcoming probe materials emitting in the NIR-I region (700–950 nm), thus do not possess emissions in these two windows, but have high expectations. Overall, the focus is placed on recent discussions concerning the optimal choice of excitation and emission wavelengths for deep-tissue high-resolution optical bioimaging and on fluorescent bioprobes that have successfully been implemented in in vitro and in vivo applications.

In view of minimally-invasive clinical interventions, laser tissue soldering assisted by plasmonic nanoparticles is emerging as an appealing concept in surgical medicine, holding the promise of surgeries without sutures. Rigorous monitoring of the plasmonically-heated solder and the underlying tissue is crucial for optimizing the soldering bonding strength and minimizing the photothermal damage. To this end, we propose a non-invasive, non-contact, and non-ionizing modality for monitoring nanoparticle-assisted laser-tissue interaction and visualizing the localized photothermal damage, by taking advantage of the unique sensitivity of terahertz radiation to the hydration level of biological tissue. We demonstrate that terahertz radiation can be employed as a versatile tool to reveal the thermally-affected evolution in tissue, and to quantitatively characterize the photothermal damage induced by nanoparticle-assisted laser tissue soldering in three dimensions. Our approach can be easily extended and applied across a broad range of clinical applications involving laser-tissue interaction, such as laser ablation and photothermal therapies.

In the synthesis of CuInS2 quantum dots (QDs), the halide ions present in the copper salts influence the QD growth and optical properties. X-ray absorption spectroscopy allowed rationalizing the halide incorporation in the lattice and the dependence of electronic properties of the material on the ion's polarizability and interaction with hydrophobic moieties.

Neodymium-doped yttrium aluminum garnet (YAG:Nd3+) has been widely developed during roughly the last sixty years and has been an outstanding fluorescent material. It has been considered as the gold standard among multipurpose solid-state lasers. Yet, the successful downsizing of this system into the nano regimen has been elusive, so far. Indeed, the synthesis of a garnet structure at the nanoscale, with enough crystalline quality for optical applications was found to be quite challenging. Here, we present an improved solvothermal synthesis method producing YAG:Nd3+ nanocrystals of remarkably good structural quality. Adequate surface functionalization using asymmetric double-hydrophilic block copolymers, constituted of a metal-binding block and a neutral water soluble block, provides stabilized YAG:Nd3+ nanocrystals with a long term colloidal stability in aqueous suspensions. These newly stabilized nanoprobes keep the spectroscopic quality (long lifetimes, narrow emission lines, and large Stokes shift) characteristic of bulk YAG:Nd3+. The narrow emission lines of YAG:Nd3+ nanocrystals are exploited by differential infrared fluorescence imaging, thus achieving an autofluorescence-free in vivo readout. In addition, nanothermometry measurements, based on the ratiometric fluorescence of the stabilized YAG:Nd3+ nanocrystals, are demonstrated. The progress here reported paves the way for the implementation of this new stabilized YAG:Nd3+ system in the preclinical arena.

Efficient control over drug release is critical to increasing drug efficacy and avoiding side effects. An ideal drug delivery system would deliver drugs in the right amount, at the right location and at the right time noninvasively. This can be achieved using light-triggered delivery: light is noninvasive, spatially precise and safe if appropriate wavelengths are chosen. However, the use of light-controlled delivery systems has been limited to areas that are not too deep inside the body because ultraviolet (UV) or visible (Vis) light, the typical wavelengths used for photoreactions, have limited penetration and are toxic to biological tissues. The advent of upconverting nanoparticles (UCNPs) has made it possible to overcome this crucial challenge. UCNPs can convert near-infrared (NIR) radiation, which can penetrate deeper inside the body, to shorter wavelength NIR, Vis and UV radiation. UCNPs have been used as bright, in situ sources of light for on-demand drug release and bioimaging applications. These remote-controlled, NIR-triggered drug delivery systems are especially attractive in applications where a drug is required at a specific location and time such as in anesthetics, postwound healing, cardiothoracic surgery and cancer treatment. In this Perspective, we discuss recent progress and challenges as well as propose potential solutions and future directions, especially with regard to their translation to the clinic.

We propose two effective approaches to enhance the Förster resonance energy transfer (FRET) efficiency from near-infrared excited upconverting nanoparticles (UCNPs, namely, LiYF4:Yb3+,Tm3+) to CuInS2 quantum dots (QDs) upon engineering of the donor’s architecture. The study of the particles’ interaction highlighted a radiative nature of the energy transfer among the moieties under investigation when in solution. However, analyses performed on dry powders allowed observing clear evidence of a FRET mechanism. In particular, photoluminescence lifetime measurements showed that FRET efficiency could be effectively increased by both reducing the size of the UCNPs and directly controlling the distribution of the active ions throughout the donor’s volume, i.e., doping them only in the outer shell of a core/shell system. Both strategies resulted at least in a more than doubled FRET efficiency compared to larger core-only UCNPs. Obtained experimental values were compatible with those predicted from geometrical considerations on the active ions’ distribution over the UCNP volume. These results provide a concrete proof of the potential of a UCNP–QD FRET pair when the system is properly designed, hence setting a solid base for the development of robust and efficient all-inorganic probes for FRET-based assays.

Lanthanide-activated SrF2 nanoparticles with a multishell architecture were investigated as optical thermometers in the biological windows. A ratiometric approach based on the relative changes in the intensities of different lanthanide (Nd3+ and Yb3+) NIR emissions was applied to investigate the thermometric properties of the nanoparticles. It was found that an appropriate doping with Er3+ ions can increase the thermometric properties of the Nd3+-Yb3+ coupled systems. In addition, a core containing Yb3+ and Tm3+ can generate light in the visible and UV regions upon near-infrared (NIR) laser excitation at 980 nm. The multishell structure combined with the rational choice of dopants proves to be particularly important to control and enhance the performance of nanoparticles as NIR nanothermometers.

Photoelectrochemical (PEC) water splitting implementing colloidal quantum dots (QDs) as sensitizers is a promising approach for hydrogen (H2) generation, due to the QD's size-tunable optical properties. However, the challenge of long-term stability of the QDs is still unresolved. Here, we introduce a highly stable QD-based PEC device for H2 generation using a photoanode based on a SnO2-TiO2 heterostructure, sensitized by CdSe/CdS core/thick-shell "giant" QDs. This hybrid photoanode architecture leads to an appreciable saturated photocurrent density of ∼4.7 mA cm-2, retaining an unprecedented ∼96% of its initial current density after two hours, and sustaining ∼93% after five hours of continuous irradiation under an AM 1.5G (100 mW cm-2) simulated solar spectrum. Transient photoluminescence (PL) measurements demonstrate that the heterostructured SnO2-TiO2 photoanode exhibits faster electron transfer compared with the bare TiO2 photoanode. The lower electron transfer rate in the TiO2 photoanode can be attributed to slow electron kinetics in the ultraviolet regime, revealed by ultrafast transient absorption spectroscopy. Graphene microplatelets were further introduced into the heterostructured photoanode, which boosted the photocurrent density to ∼5.6 mA cm-2. Our results demonstrate that the SnO2-TiO2 heterostructured photoanode holds significant potential for developing highly stable PEC cells.

The long term stability of photoelectrochemical (PEC) devices based on colloidal quantum dots (QDs) for hydrogen production is a major challenge. The degradation is often caused by the self-oxidation of QDs induced by the excess accumulation of holes in the valance band. Here, we use heterostructured “giant” core/alloyed-shell CdSe/PbxCd1−xS/CdS QDs to sensitize TiO2 mesoporous films for PEC hydrogen production. Transient fluorescence analysis results show that the use of a PbxCd1−xS gradient layer leads to a three-fold increase in the hole transfer rate compared to a pure CdS shell with similar shell thickness. The as-prepared PEC cell using alloyed shell “giant” QDs exhibits an enhanced photocurrent density of 10.2 mA cm−2 (97 mL per cm2 per day) under one sun illumination (100 mW cm−2). The PEC cell based on alloyed shell “giant” QDs shows an enhanced PEC device stability, with retention of ∼94.9% of its initial photocurrent after 2 h under one sun illumination. This finding provides unique insights to improve the stability and functional performance of PEC devices in which the photoanode is sensitized using colloidal “giant” QDs.

Owing to the alluring possibility of contactless temperature probing with microscopic spatial resolution, photoluminescence nanothermometry at the nanoscale is rapidly advancing towards its successful application in biomedical sciences. The emergence of near-infrared nanothermometers has paved the way for temperature sensing at the deep tissue level. However, water dispersibility, adequate size at the nanoscale, and the capability to efficiently operate in the second and third biological optical transparency windows are the requirements that still have to be fulfilled in a single nanoprobe. In this work, these requirements are addressed by rare-earth doped nanoparticles with core/shell-architecture, dispersed in water, whose excitation and emission wavelengths conveniently fall within the biological optical transparency windows. Under heating-free 800 nm excitation, double nanothermometry is realized either with Ho3+–Nd3+ (1.18–1.34 μm) or Er3+–Nd3+ (1.55–1.34 μm) NIR emission band ratios, both displaying equal thermal sensitivities around 1.1% °C−1. It is further demonstrated that, along with the interionic energy transfer processes, the thermometric properties of these nanoparticles are also governed by the temperature dependent energy transfer to the surrounding solvent (water) molecules. Overall, this work presents a novel water dispersible double ratiometric nanothermometer operating in the second and third biological optical transparency windows. The temperature dependent particle–solvent interaction is also presented, which is critical for e.g. future in vivo applications.

Development of contactless temperature-probing nanoplatforms based on thermosensitive near-infrared (NIR) light-emitting nanoparticles opens up new horizons for biomedical theranostics at a deep tissue level. Here, we report on the crystallinity and relative thermal sensitivity of NIR emitting Nd

Lanthanide-doped upconverting nanoparticles (UCNPs) are well-known for their inherent ability to convert low energy near-infrared (NIR) excitation wavelengths into higher energy emission wavelengths covering the ultraviolet (UV) to NIR regions. This optical feature makes UCNPs highly attractive for a broad range of applications including (bio)imaging and the biomedical use of light-triggered processes such as drug release. In the quest for novel theranostic approaches, the combination of multiple modalities on a single nanoscale platform, for example, combining optical imaging and drug delivery, is very desirable. In this context, liposomes, artificially prepared constructs composed of a lamellar phase lipid bilayer, have been introduced as suitable nanocarriers for UCNPs. Here, we developed a hybrid nanocarrier consisting of Er(3+) and Yb(3+) co-doped NaGdF4 UCNPs that were encapsulated in the aqueous core of the liposomes and the potential of the obtained nanocarriers for drug delivery was shown by co-loading the model anticancer drug doxorubicin (DOX). Under 980 nm excitation, a decrease of the green upconversion emission of the NaGdF4:Er(3+), Yb(3+) UCNPs was observed when DOX was co-loaded with the UCNPs in the liposome nanocarrier. This quenching effect is assigned to the energy transfer between the donor UCNP and the acceptor DOX and is most significant, since it allows for the spectral monitoring of the DOX loading and release from the liposome nanocarriers. Thus, the drug loading, release, and spectral monitoring properties of the obtained liposome nanocarriers were thoroughly characterized allowing us to assess their future potential as theranostic nanocarriers.

Lanthanide-doped upconverting nanoparticles (UCNPs) have emerged as excellent nanotransducers for converting longer wavelength near-infrared (NIR) light to shorter wavelengths spanning the ultraviolet (UV) to the visible (Vis) regions of the spectrum via a multiphoton absorption process, known as upconversion. Here, we report the development of NIR to UV-Vis-NIR UCNPs consisting of LiYF4:Yb(3+)/Tm(3+)@SiO2 individually coated with a 10 ± 2 nm layer of chitosan (CH) hydrogel cross-linked with a photocleavable cross-linker (PhL). We encapsulated fluorescent-bovine serum albumin (FITC-BSA) inside the gel. Under 980 nm excitation, the upconverted UV emission cleaves the PhL cross-links and instantaneously liberates the FITC-BSA under 2 cm thick tissue. The release is immediately arrested if the excitation source is switched off. The upconverted NIR light allows for the tracking of particles under the tissue. Nucleus pulposus (NP) cells cultured with UCNPs are viable both in the presence and in the absence of laser irradiation. Controlled drug delivery of large biomolecules and deep tissue imaging make this system an excellent theranostic platform for tissue engineering, biomapping, and cellular imaging applications.

Recently, research efforts have been focused on developing near-infrared perturbable nanoparticles to sensitize photostimulable molecules for the production of reactive oxygen species. Research in this direction is looking to broaden the use of photodynamic therapy, an indispensable clinical tool for cancer therapeutics, which relies on the photoexcitation of a suitable photosensitizer, to convert light into reactive oxygen species that are toxic to cells. To date most commercially available photosensitizers are excited with high energy light (UV or visible) presenting disadvantages that limit the clinical use of this technique to cancers that are on or near the surface of the skin. Here, we develop a hybrid platform capable of near-infrared triggered generation of reactive oxygen species. This hybrid nanostructure is based on LiYF4:Tm3+,Yb3+ nanoparticles, which are capable of producing strong UV emissions, following excitation at 980 nm, through a multiphoton process known as upconversion. When appropriately surface functionalized with an organoiridium complex, excitation at 980 nm produces a strong UV emission, which is absorbed by the organoiridium molecules on the surface, in turn generating reactive oxygen species. Moreover, the effect of the organoiridium concentration on the surface of the upconverting nanoparticles as well as the nature of the sensitization process is discussed.

In this study, we report anomalous size-dependent photoluminescence (PL) intensity variation of PbS quantum dots (QDs) with the formation of a thin CdS shell via a microwave-assisted cation exchange approach. Thin shell formation has been established as an effective strategy for increasing the PL of QDs. Nonetheless, herein we observed an unusual PL decrease in ultrasmall QDs upon shell formation. We attempted to understand this abnormal phenomenon from the perspective of trap density variation and the probability of electrons and holes reaching surface defects. To this end, the quantum yield (QY) and PL lifetime (on the ns-μs time scales) of pristine PbS QDs and PbS/CdS core/shell QDs were measured and the radiative and non-radiative recombination rates were derived and compared. Moreover, transient absorption (TA) analysis (on the fs-ns time scale) was performed to better understand exciton dynamics at early times that lead to and affect longer time dynamics and optical properties such as PL. These experimental results, in conjunction with theoretical calculations of electron and hole wave functions, provide a complete picture of the photophysics governing the core/shell system. A model was proposed to explain the size-dependent optical and dynamic properties observed.

In the biomedical field, research has recently focused on nanoparticle-based “theranostic” agents for the treatment of diverse diseases, including cancer. This new paradigm in personalized medicine intends to exploit nanoplatforms that carry both therapeutic and diagnostic (theranostic) modalities. Compared with delivering drugs or imaging agents separately, theranostic agents can simultaneously deliver them to specific sites, enabling detection and treatment of disease in a single procedure. Many theranostic nanoplatforms are triggered by light, however, the vast majority of these are limited in that the ultraviolet or visible excitation light used has minimal applicability in biological applications. Rare earth doped nanoparticles, on the other can be excited with biologically friendly near-infrared light (in the biological windows) and can emit in the ultraviolet, visible or near-infrared regions through a multiphoton upconversion process while simultaneously emitting in the near-infrared region (also in the 3 biological windows) through a Stokes or downshifted process. Hence, the upconversion luminescence can be used to trigger the therapeutic application (drug delivery, photodynamic therapy, etc.) while the near-infrared luminescence can be used for the diagnostic modality (bioimaging, nanothermometry/temperature sensing, etc). In this presentation, we will introduce rare earth doped nanoparticles and demonstrate their usefulness in theranostics. In particular, we will show that complex nanoparticle architectures can endow further functionality to these nanoparticles and discuss how they can be used for temperature sensing (nanothermometry) in biological systems.

Scattering affects excitation power density, penetration depth and upconversion emission self-absorption, resulting in particle size –dependent modifications of the external photoluminescence quantum yield (ePLQY) and net emission. Micron-size NaYF4:Yb3+, Er3+ encapsulated phosphors (∼4.2 µm) showed ePLQY enhancements of >402%, with particle-media refractive index disparity (Δn): 0.4969, and net emission increases of >70%. In sub-micron phosphor encapsulants (∼406 nm), self-absorption limited ePLQY and emission as particle concentration increases, while appearing negligible in nanoparticle dispersions (∼31.8 nm). These dependencies are important for standardising PLQY measurements and optimising UC devices, since the encapsulant can drastically enhance UC emission.

We report the effect of incorporating graphene microplatelets into a SnO2–TiO2 mesoporous heterostructured anode, to enhance the efficiency and long-term stability of dye-sensitized solar cells (DSSCs). DSSCs were fabricated by introducing different concentrations of graphene microplatelets (up to 0.50 wt%.) into the SnO2–TiO2 mesoporous network. At an optimized concentration of 0.03 wt% of graphene microplatelets, the highest photoconversion efficiency (PCE) of 3.37% was achieved, which is ∼16% higher than the one measured for control devices made with standard SnO2–TiO2 anodes. This improvement of PCE can be attributed to enhanced electron lifetime and reduced charge recombination in the hybrid SnO2–TiO2/graphene heterostructure anodes, confirmed by transient photovoltage decay and electrochemical impedance spectroscopy. Improved dye loading in the SnO2–TiO2/graphene anode was confirmed with UV–Vis–NIR spectrophotometry. In addition, we recorded the long-term stability of the DSSCs for 200 h of continuous illumination under one sun simulated sunlight (AM 1.5G). Our investigation demonstrated that the addition of graphene microplatelets (0.03 wt%) in the anode, shows superior long-term stability exhibiting a mere 8% PCE drop, while a sharp plummet of ∼30% in PCE was observed in control devices. These findings signify that the SnO2–TiO2/graphene heterostructure architecture is a promising anode towards efficient and stable DSSCs.

In recent years, a significant amount of research has focused on nanoparticle-based “theranostic” agents for the treatment of a wide array of diseases, including cancer. This new paradigm in personalized medicine intends to exploit nanoplatforms that carry both therapeutic and diagnostic (theranostic) modalities. Compared with delivering drugs or imaging agents separately, theranostic agents can simultaneously deliver them to specific sites, enabling detection and treatment of disease in a single procedure. Many theranostic nanoplatforms are triggered by light, however, the vast majority of these are limited in that the ultraviolet or visible excitation light used has minimal applicability in biological applications. Lanthanide doped nanoparticles, on the other can be excited with biologically friendly near-infrared light (in the biological windows) and can emit in the ultraviolet, visible or near-infrared regions through a multiphoton upconversion process while simultaneously emitting in the near-infrared region through a Stokes or downshifted process. Hence, the upconversion luminescence can be used to trigger the therapeutic application (drug delivery, photodynamic therapy, etc.) while the near-infrared luminescence can be used for the diagnostic modality (bioimaging, nanothermometry, etc). In this presentation, we will introduce lanthanide doped nanoparticles and demonstrate their usefulness in theranostics. In particular, we will show complex nanoparticle architectures can endow further functionality to these nanoparticles including the ability to decouple the theranostic processes that are conventionally delivered simultaneously.