Search

Dye‐sensitized down‐conversion nanoparticles (DCNPs) can significantly enhance photon absorption, bridging the gap of narrow and weak absorption cross‐section of lanthanide (Ln) ions, thus fundamentally prompting their near‐infrared (NIR) emission. However, the ideal strategy for utilization of both the singlet and triplet energy of the dyes is hindered by the nanostructures and the dependence on the heavy atom effect. Herein, thermally activated delayed fluorescence (TADF) dye is utilized with a small singlet‐triplet energy gap as the absorption antenna, achieving a 733 fold emission enhancement. This strategy facilitates efficient intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, enabling effective energy transfer from singlet (S1) and triplet (T1) excitons to emitted energy levels of Er3+. Combining highly Erbium‐doped nanoparticles, the water‐dispersed AD‐sensitized system shows excellent hydrodynamic stability and photostability. This innovative approach marks the first report of TADF dye‐sensitized Ln nanosystems, offering a new direction for photo conversion technology. [ABSTRACT FROM AUTHOR]

Recent advances reveal that due to the cross‐relaxation restriction, impressive upconversion (UC) enhancement (≈100‐folds) can be achieved in cryogenic Er3+‐rich core‐inert shell nanostructures (e.g., NaErF4@NaYF4), which opens up exciting opportunities in diverse frontier applications. However, further promotion of UC intensity is still highly desired, in which the rational design of nanostructures can play a key role. Herein, it is demonstrated that adopting an active shell design will constantly benefit the UC within a wide temperature range (40–300 K). Specifically, through constructing the luminescent core@active shell@inert shell sandwich nanostructure (e.g., NaErF4@NaYbF4@NaYF4), 8.3–73‐folds UC enhancement will be achieved (taking the corresponding core@inert shell structures as competitors). Moreover, from spectral‐domain and time‐domain spectroscopic experiments, the relevant UC enhancement is convincingly attributed to a temperature‐dependent energy injection process (from the active shell to the luminescent core). More interestingly, the unique property of the material makes a temperature‐induced high‐level encryption application possible, which is obtained by employing the nanomaterials on a quick response (QR) code. These results not only deepen the UC mechanism in multi‐layer nanostructures, but also introduce an expanded dimension (via low temperatures) in information security. [ABSTRACT FROM AUTHOR]

Recently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er3+‐rich UC nanosystem as an example, we confirm unambiguously that the phonon‐assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er3+‐rich core/multi‐shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra‐sensitive temperature sensing. [ABSTRACT FROM AUTHOR]

Relatively low efficiency is the bottleneck for the application of lanthanide‐doped upconversion nanoparticles (UCNPs). The high‐level doping strategy realized in recent years has not improved the efficiency as much as expected. It is argued that cross relaxation (CR) is not detrimental to upconversion. Here we combine theoretical simulation and spectroscopy to elucidate the role of CR in upconversion process of Er3+ highly doped (HD) UCNPs. It is found that if CR is purposively suppressed, upconversion efficiency can be significantly improved. Specifically, we demonstrate experimentally that inhibition of CR by introducing cryogenic environment (40 K) enhances upconversion emission by more than two orders of magnitude. This work not only elucidates the nature of CR and its non‐negligible adverse effects, but also provides a new perspective for improving upconversion efficiency. The result can be directly applied to cryogenic imaging and wide range temperature sensing. [ABSTRACT FROM AUTHOR]

Collaborative therapy is regarded as an effective approach in increasing the therapeutic efficacy of cancer. In this work, we have proposed and validated the concept of upconversion lumienscence image guided synergy of photodynamic therapy (PDT) and radiotherapy (RT) for deep cancer, via a specially designed nanoplatform integrating near infrared (NIR) light activated luminescence upconversion and X-ray induced scintillation. Upon NIR light irradiation, the nanoplatform emits highly monochromatic red light solely for imaging the targeted cancer cells without triggering therapy; however, when the irradiation turns to a low dose of X-rays, scintillation will occur which induces effectively the PDT destroying the cancer cells together with X-ray induced RT. The novel theranostic nanoplatform is constructed in such a way that the interactions between the upconversion core and the outmost scintillating shell are blocked effectively by an inert layer between them. This structural design not only enables a nearly perfect excitation energy delivery (∼100% at a spectral overlapping wavelength of ∼540 nm) from the outermost scintellating layer to the surface-anchored photosensitizers and so a maximum yield of radical oxygen species, but also achieves a strong NIR induced upconversion luminescence for imaging. Since PDT and RT attack different parts of a cancer cell, this synergy is more effective in destroying cancer than a single therapy, resulting in the reduction of the X-ray irradiation dosage. As a proof of principle, the theranostic effect is validated by in vitro and in vivo experiments, exhibiting the great potential of this sort of nanoplatform in deep cancer treatment. [ABSTRACT FROM AUTHOR]

Color-modulated upconversion nanoparticles (UCNPs) have garnered widespread optical applications owing to their superior properties, including low auto-fluorescence background noise, large anti-Stokes shift, and distinguishable sharp emission bands. Recent success in multicolor alteration of UCNPs has mostly relied on the cross-relaxation between activators and other elements, which allows them to perform excellently in optical encoding and bioimaging. However, the color modulation is subject to the cross-relaxation strategy, which heavily weakens the original emission intensity of the activators. Herein, we report a dye-sensitization strategy of conjugating strong near-infrared absorptive dyes on the surface of UCNPs. It was proven that dye sensitization can manipulate the red to green (R/G) emission ratio of NaYF4:Yb/Er@NaYF4:Nd UCNPs and simultaneously enhance their luminescence intensity. The R/G emission ratio can be tuned to increase or decrease, benefiting from the dye sensitization strategy. Proof of concept was demonstrated for anti-counterfeiting application under orthogonal excitation of 808 nm and 980 nm. [ABSTRACT FROM AUTHOR]

Abstract: Upconversion emission dynamics have long been believed to be determined by the activator and its interaction with neighboring sensitizers. Herein this assumption is, however, shown to be invalid for nanostructures. We demonstrate that excitation energy migration greatly affects upconversion emission dynamics. “Dopant ions’ spatial separation” nanostructures are designed as model systems and the intimate link between the random nature of energy migration and upconversion emission time behavior is unraveled by theoretical modelling and confirmed spectroscopically. Based on this new fundamental insight, we have successfully realized fine control of upconversion emission time behavior (either rise or decay process) by tuning the energy migration paths in various specifically designed nanostructures. This result is significant for applications of this type of materials in super resolution spectroscopy, high‐density data storage, anti‐counterfeiting, and biological imaging. [ABSTRACT FROM AUTHOR]

To enhance the treatment efficiency of photothermal therapy (PTT) with very little light-associated side effect, we have constructed a highly effective PTT nanoplatform for fluorescence and MRI dual imaging-guided PTT of cancer, based on IR806 dye and iron oxide complex functionalized with mPEG-PCL-G2.0PAMAM-Cit, which can be for charge-conversion for targeted accumulation in tumor. Combination of iron oxide nanoparticles and IR806 improve light to thermal conversion efficiency and lower light irradiation dose. In vitro and in vivo tests demonstrated that an effective dual imaging-guided PTT as low as 0.25 W cm−2 could be realized under a light irradiation of 808 nm. These efforts highlight the potential of this PTT nanoplatform in “precision medicine”. [ABSTRACT FROM AUTHOR]

We provide the first demonstration of a near infrared light driven water oxidation reaction in a molecule-based artificial photosynthetic device using an upconversion nano-photosensitizer. One very attractive advantage of this system is that using NIR light irradiation does not cause significant photodamage, a serious problem in molecular based artificial photosynthesis under visible light irradiation. [ABSTRACT FROM AUTHOR]

Recent efforts and progress in unraveling the fundamental mechanism of excitation energy migration dynamics in upconversion nanomaterials are covered in this review, including short- and long-term interactions and other interactions in homogeneous and heterogeneous nanostructures. Comprehension of the role of spatial confinement in excitation energy migration processes is updated. Problems and challenges are also addressed. [ABSTRACT FROM AUTHOR]

Applying the Stöber method to directly coat noble metal nanoparticles (NPs) such as gold (Au) and silver (Ag) NPs with silica shells presents challenges, since the noble metal NPs are not stable in alcoholic solution and have low chemical affinity for silica. This paper describes a method which uses 11-mercaptoundecanoic acid (MUA) as a linker molecule between the silica shell and the noble metal NPs. MUA binds strongly to the surface of the NPs via a metal–S bond by replacing the standard capping agents on the surface of the NPs. Upon MUA stabilization, the NPs can be transferred into alcohol solution and show chemical affinity for silica. The MUA-modified NPs can be directly coated with thickness controlled, smooth and homogeneous silica shells via the standard Stöber method by varying the amount of tetraethoxysilane (TEOS). Compared with methods reported in the literature for the coating of such particles, this method can not only be used to successfully coat citrated-stabilized Au or Ag NPs, but can also be extended to encapsulate oleylamine (OA)-stabilized Au NPs and cetyltrimethylammonium bromide (CTAB)-stabilized Au nanorods (NRs) by using MUA to displace the original ligand on the surface of the NPs. Additionally, the obtained metal@SiO2 core–shell NPs have been successfully applied as plasmonic nanoantennas for fluorescence enhancement in metal@SiO2@fluorophore NPs. [ABSTRACT FROM AUTHOR]

Although it is widely recognized that doping sensitizers in the shell can improve significantly the luminescence of lanthanides doped nanocrystals, lack of an unambiguous picture of relevant luminescence enhancement mechanism seriously hinders the optimization of this approach. In this work, the complete processes of excitation energy migration, from photon absorption to emission, was dissected to unravel the role of sensitizers doped in shell in every individual stage. We revealed that the essence of doping sensitizers in the shell is just to increase the absorption efficiency whereas the quantum yield is lessened simultaneously. The optimal sensitizer doping concentration is also fixed to achieve the best luminescence performance. [ABSTRACT FROM AUTHOR]

To design more effective CIEEL (chemically initiated electron exchange luminescence) systems demands a complete picture of the dynamics of the chemiluminescence, which is often a challenge. In this work, photoluminescence of the methyl m-oxybenzoate anion – the authentic emitter of AMPPD (3-[2-spiroadamantane]-4-methoxy-4-[3-phosphoryloxy]-phenyl-1,2-dioxetane) in aqueous solvent has been studied. Combining the effect of solvent properties, e.g.pH value, and spectroscopic studies employing steady-state and ultrafast time-resolved emission and absorption and 1H NMR techniques, a novel mechanism is proposed. We conclude that the deviation of emission peaks between chemiluminescence and photoluminescence of the authentic emitter of AMPPD i.e.the methyl m-oxybenzoate anion, in alkaline aqueous solvents is due to its hydrolysis, rather than the hydrogen-bonding effect as has been assumed so far. Besides, the hydrogen-bonding is suggested to play a key role in significantly decreasing the chemiluminescence yield of AMPPD in aqueous solution by shortening the lifetime of the excited authentic emitter to 10 ps order of magnitude – three orders of magnitude shorter than the previously reported value (∼10 ns). These results shed light on the chemiluminescence dynamics of AMPPD and facilitate the design of more effective CIEEL systems. [ABSTRACT FROM AUTHOR]

Tailor-designed Au/SiO2core/shell nanoparticles are employed to enhance the efficiency of fluorescence resonance energy transfer based on quantum dots and R-phycoerythrin in solution. [ABSTRACT FROM AUTHOR]

Tailor-designed Au/SiO2core/shell nanoparticles are employed to enhance the efficiency of fluorescence resonance energy transfer based on quantum dots and R-phycoerythrin in solution. [ABSTRACT FROM AUTHOR]

Recent advances in upconversion nanophotosensitizers (UCNPs-PS) excited by near-infrared (NIR) light have led to substantial progress in improving photodynamic therapy (PDT) of cancer. For a successful PDT, subcellular organelles are promising therapeutic targets for reaching a satisfactory efficacy. It is of vital importance for these nanophotosensitizers to reach specifically the organelles and to perform PDT with precise time control. To do so, we have in this work traced the dynamic subcellular distribution, especially in organelles such as lysosomes and mitochondria, of the poly(allylamine)-modified and dual-loaded nanophotosensitizers. The apoptosis of the cancer cells induced by PDT with the dependence of the distribution status of the nanophotosensitizers in organelles was obtained, which has provided an in-depth picture of intracellular trafficking of organelle-targeted nanophotosensitizers. Our results shall facilitate the improvement of nanotechnology assisted photodynamic therapy of cancers. [ABSTRACT FROM AUTHOR]

Accurate quantitation of intracellular pH (pHi) is of great importance in revealing the cellular activities and early warning of diseases. A series of fluorescence-based nano-bioprobes composed of different nanoparticles or/and dye pairs have already been developed for pHi sensing. Till now, biological auto-fluorescence background upon UV-Vis excitation and severe photo-bleaching of dyes are the two main factors impeding the accurate quantitative detection of pHi. Herein, we have developed a self-ratiometric luminescence nanoprobe based on förster resonant energy transfer (FRET) for probing pHi, in which pH-sensitive fluorescein isothiocyanate (FITC) and upconversion nanoparticles (UCNPs) were served as energy acceptor and donor, respectively. Under 980 nm excitation, upconversion emission bands at 475 nm and 645 nm of NaYF4:Yb3+, Tm3+ UCNPs were used as pHi response and self-ratiometric reference signal, respectively. This direct quantitative sensing approach has circumvented the traditional software-based subsequent processing of images which may lead to relatively large uncertainty of the results. Due to efficient FRET and fluorescence background free, a highly-sensitive and accurate sensing has been achieved, featured by 3.56 per unit change in pHi value 3.0-7.0 with deviation less than 0.43. This approach shall facilitate the researches in pHi related areas and development of the intracellular drug delivery systems. [ABSTRACT FROM AUTHOR]

The advances in surface-enhanced Raman scattering (SERS) have resulted in significant improvements for sensing glucose, achieving a highly detecting sensitivity of the order of μM. Highly sensitive glucose detection, however, is still a challenge due to extremely small Raman scattering cross section of glucose molecules and weak interaction between the molecules and the metal nanoparticles. Here, we designed a novel homogeneous SERS-based nanoplatform composing of the SERS tags and glucose oxidase in aqueous solution for a highly sensitive glucose detection. Adding glucose caused enzymatic oxidation reaction to etch the tip electric field (E) of silver nanotriangle. Thus, the decreased intensity of E was greatly amplified by the change of SERS signal (E 4 dependent), which resulted in an excellent glucose detection limit of 0.4 nM was firstly achieved. Furthermore, the nonlinear relationship between the decreased SERS intensity and the glucose concentrations was reasonably revealed based on theoretical calculations and deeply understanding of the enhancement mechanism, which is very useful in improving the sensitivity and accuracy of trace glucose detection. The as-prepared nanoplatform showed good sensitivity and high selectivity only through observing the SERS intensity change, which is potential for highly sensitive and practical glucose detection for clinical trace analyses. Unlabelled Image • SNTs/ p -ATP-GOx homogeneous nanoplatform showed perfect SERS sensing behaviors of glucose. • The huge decay degree of the SERS signal caused by etching the tips of SNTs • Good selectivity to glucose and high sensitivity to 0.1 nM [ABSTRACT FROM AUTHOR]

Combating the concentration quenching effect by increasing the concentration of sensitized rare-earth ions in rational design upconversion nanostructure will make it easier to utilize injection energy flux and transfer it to emitters, resulting in improved upconversion luminescence (UCL). We proposed a host-sensitized nanostructure (active core@luminescent shell@inert shell) to improve multiphoton UCL of Tm 3+ based on the LiLnF 4 host. Yb 3+ ions were isolated in the core as energy absorbents, and Tm 3+ was doped in the interior LiYbF 4 host shell. Compared with sandwich structured nanocrystals (Y@Y:Yb/Tm@Y), reverse structure (YbTm@Yb@Y), and fully doped structure (YbTm@YbTm@Y), the proposed structure achieved the highest efficiency of multiphoton UCL and favored a better FRET-based application performance as the Tm 3+ located at an optimized spatial distribution. Furthermore, steady-state and dynamic analysis results demonstrate that by manipulating the spatial distribution of the active ions, excited energy can be tuned to enable multiphoton upconversion enhancement, overcoming the conventional limitations.

Photodynamic therapy (PDT) has been widely used in tumor therapy due to its high spatial-temporal control and noninvasiveness. However, its clinical application is limited by weak efficacy, shallow tissue penetration, and phototoxicity. Herein, a facile theranostic nanoplatform based on photoswitchable lanthanide-doped nanoparticles was designed. Typically, these nanoparticles had UV-blue and 1525 nm emission upon 980 nm excitation and 1525 nm emission upon 800 nm excitation. We further used these nanoparticles for achieving real-time near-infrared (NIR)-IIb imaging (800 nm) with a high signal-to-noise ratio and imaging-guided PDT (980 nm). Moreover, such a photoswitchable nanoplatform capping with pH-sensitive calcium phosphate for coloading doxorubicin (a chemotherapeutic immunogenic cell death [ICD] inducer) and paramagnetic Mn 2+ ions enhances T 1 -magnetic resonance imaging in the tumor microenvironment. Our results suggest that this theranostic nanoplatform could not only kill tumor cells directly through dual-modal image-guided PDT/chemotherapy but also inhibit distant tumor and lung metastasis through ICD. Therefore, it has great potential for clinical application .

Collaborative therapy is regarded as an effective approach in increasing the therapeutic efficacy of cancer. In this work, we have proposed and validated the concept of upconversion lumienscence image guided synergy of photodynamic therapy (PDT) and radiotherapy (RT) for deep cancer, via a specially designed nanoplatform integrating near infrared (NIR) light activated luminescence upconversion and X-ray induced scintillation. Upon NIR light irradiation, the nanoplatform emits highly monochromatic red light solely for imaging the targeted cancer cells without triggering therapy; however, when the irradiation turns to a low dose of X-rays, scintillation will occur which induces effectively the PDT destroying the cancer cells together with X-ray induced RT. The novel theranostic nanoplatform is constructed in such a way that the interactions between the upconversion core and the outmost scintillating shell are blocked effectively by an inert layer between them. This structural design not only enables a nearly perfect excitation energy delivery (∼100% at a spectral overlapping wavelength of ∼540 nm) from the outermost scintellating layer to the surface-anchored photosensitizers and so a maximum yield of radical oxygen species, but also achieves a strong NIR induced upconversion luminescence for imaging. Since PDT and RT attack different parts of a cancer cell, this synergy is more effective in destroying cancer than a single therapy, resulting in the reduction of the X-ray irradiation dosage. As a proof of principle, the theranostic effect is validated by in vitro and in vivo experiments, exhibiting the great potential of this sort of nanoplatform in deep cancer treatment., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dye sensitization is becoming a new dimension to highly improve the upconversion luminescence (UCL) of lanthanide-doped upconversion nanoparticles (UCNPs). However, there is still a lack of general understanding of the dye-UCNPs interactions, especially the confused large mismatch between the inputs and outputs. By taking dye-sensitized NaYF 4 :Yb/Er@NaYF 4 :Nd UCNPs as a model system, we not only revealed the in-depth energy-dissipative process for dye-sensitized UCL but also confirmed the first ever experimental observation of the energy back transfer (EBT) in the dye-sensitized UCL. Furthermore, this energy-dissipative EBT restricted the optimal ratio of dyes to UCNP. By unearthing all of the energy loss behind the EBT, energy transfer, and energy migration processes, this paper sheds light on the further design of effective dye-sensitized nanosystems for UCL or even downconversion luminescence.

Multimodality imaging-guided therapy based on lanthanide-doped upconversion nanoparticles (UCNPs) has become a trend in cancer theranostics. However, the overheating effect of 980 nm excitation in photodynamic therapy (PDT) and the difficulties in optimizing multimodality imaging integration within a single particle are still challenges. Herein, 800 nm driven NaErF4@NaLuF4 UCNPs have been explored for optimized multimodality imaging and near-infrared (NIR) triggered PDT. Our results confirmed that the optimal ∼5 nm shell thickness can well balance the enhancement of upconversion luminescence and the attenuation of energy transfer efficiency from Er3+ towards a photosensitizer, to achieve efficient production of singlet oxygen (1O2) for PDT under 800 nm excitation. Furthermore, the as-obtained NaErF4@NaLuF4 UCNPs showed effective and applicable performance for upconversion luminescence (UCL) imaging, X-ray computed tomography (CT), and high-field T2 magnetic resonance imaging (MRI). This nanomaterial can serve as an excellent theranostic agent for multimodality imaging and image-guided therapy.

Photoswitchable materials are important in broad applications. Recently appeared inorganic photoswitchable upconversion nanoparticles (PUCNPs) become a competitive candidate to surmount the widespread issue of the organic counterparts -photobleaching. However, current PUCNPs follow solely Yb 3+ /Nd 3+ cosensitizing mode, which results in complex multilayer doping patterns and imperfectness of switching in UV-blue region. In this work, we have adopted a new strategy to construct Nd 3+ free PUCNPs-NaErF 4 @NaYF 4 @NaYbF 4 :0.5%Tm@NaYF 4 . These PUCNPs demonstrate the superior property of photoswitching. A prominent UV-blue emission from Tm 3+ is turned on upon 980 nm excitation, which can be completely turned off by 800 nm light. The quasi-monochromatic red upconversion emission upon 800 nm excitation-a distinct feature of undoping NaErF 4 upconversion system-endows the PUCNPs with promising image-guided photoinduced "off-on" therapy in biomedicine. As a proof-of-concept we have demonstrated the imaging-guided photodynamic therapy (PDT) of cancer, where 800 nm excitation turns off the UV-blue emission and leaves the emission at 660 nm for imaging. Once the tumor site is targeted, excitation switching to 980 nm results in UV-blue emission and the red emission. The former is used to induce PDT, whereas the latter is to monitor the therapeutic process. Our study implies that this upconversion photoswitching material is suitable for real-time imaging and image-guided therapy under temporal and spatial control.