Frequency Upconversion Luminescence Research Articles

Biothiols-activated near-infrared frequency up-conversion luminescence probe for early evaluation of drug-induced hepatotoxicity

A novel biothiols-sensitive near-infrared (NIR) fluorescent probe RhDN based on a rhodamine skeleton was developed for early detection of drug-induced hepatotoxicity in living mice. RhDN can be used not only as a conventional large stokes shift fluorescent (FL) probe, but also as a kind of anti-Stokes frequency upconversion luminescence (FUCL) molecular probe, which represents a long wavelength excitation (808 nm) to short wavelength emission (760 nm), and response to Cys/Hcy/GSH with high sensitivity. Compared with traditional FL methods, the FUCL method exhibited a lower detection limit of Cys, Hcy, and GSH in 75.1 nM, 101.8 nM, and 84.9 nM, respectively. We exemplify RhDN for tracking endogenously biothiols distribution in living cells and further realize real-time in vivo bioimaging of biothiols activity in mice with dual-mode luminescence system. Moreover, RhDN has been successfully applied to visualize the detection of drug-induced hepatotoxicity in living mice. Overall, this report presents a unique approach to the development of large stokes shift NIR FUCL molecular probes for in vitro and in vivo biothiols biosensing.

Mitochondria-specific near-infrared photoactivation of peroxynitrite upconversion luminescent nanogenerator for precision cancer gas therapy

Gas therapy is emerging as a highly promising therapeutic strategy for cancer treatment. However, there are limitations, including the lack of targeted subcellular organelle accuracy and spatiotemporal release precision, associated with gas therapy. In this study, we developed a series of photoactivatable nitric oxide (NO) donors NRh-R-NO (R = Me, Et, Bn, iPr, and Ph) based on an N-nitrosated upconversion luminescent rhodamine scaffold. Under the irradiation of 808 nm light, only NRh-Ph-NO could effectively release NO and NRh-Ph with a significant turn-on frequency upconversion luminescence (FUCL) signal at 740 nm, ascribed to lower N–N bond dissociation energy. We also investigated the involved multistage near-infrared-controlled cascade release of gas therapy, including the NO released from NRh-Ph-NO along with one NRh-Ph molecule generation, the superoxide anion O2⋅− produced by the photodynamic therapy (PDT) effect of NRh-Ph, and highly toxic peroxynitrite anion (ONOO‒) generated from the co-existence of NO and O2⋅−. After mild nano-modification, the nanogenerator (NRh-Ph-NO NPs) empowered with superior biocompatibility could target mitochondria. Under an 808 nm laser irradiation, NRh-Ph-NO NPs could induce NO/ROS to generate RNS, causing a decrease in the mitochondrial membrane potential and initiating apoptosis by caspase-3 activation, which further induced tumor immunogenic cell death (ICD). In vivo therapeutic results of NRh-Ph-NO NPs showed augmented RNS-potentiated gas therapy, demonstrating excellent biocompatibility and effective tumor inhibition guided by real-time FUCL imaging. Collectively, this versatile strategy defines the targeted RNS-mediated cancer therapy.

Activatable organic upconversion nanoprobe for bioimaging of monoamine oxidase B in Parkinson’s disease

Monoamine oxidase B (MAO-B) activity has been observed abnormally elevated in Parkinson’s disease patients and can be used as a potential biomarker. Herein, we report an activatable frequency upconversion luminescence (FUCL) MAO-B nano-probe (NIR-MNP) capable of highly specific and real-time MAO-B imaging in biological samples. The turn-on FUCL effect is beneficial to obtaining high-quality imaging and penetrating tissue to achieve in vivo imaging, making it stand out from the existing probes. Moreover, we used NIR-MNP to confirm the role of MAO-B inhibitor in delaying Parkinson’s disease (PD) progression in mouse PD models through bio-imaging technique in vivo. Finally, our study may offer a visual way help researchers to gain further insight into the involvement of MAO-B in PD onset and progression in animals.

Novel near-infrared frequency up-conversion luminescence probe for monitoring biothiols in vitro and in vivo

Biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play important roles in the antioxidant activity of cells, and a variety of diseases could be linked to their abnormal levels. Frequency up-conversion luminescence (FUCL) probes have low background fluorescence and cause low tissue damage; thus it is less harmful than Stokes shift luminescence probes, the traditional fluorescence probes. However, the utilization of FUCL probes for detection of biothiols has rarely been reported. In this work, we designed and synthesized a near-infrared (NIR) xanthene derivative IFU-1 and used as a frequency up-conversion luminescence probe to detect biothiols. The probe IFU-1 had high selectivity for biothiols and exhibited enhanced FUCL signals in response to them. In addition, it has extremely low limit of detection with regards to different biothiols: 4.8 nM for Cys; 6.2 nM for Hcy, and 9.5 nM for GSH, which are about 10 times lower than the detection limit of traditional excitation methods (63 nM for Cys, 31 nM for Hcy, and 76 nM for GSH). This work presents a novel approach for constructing FUCL biosensors.

Anti-stokes luminescent organic nanoparticles for frequency upconversion biomedical imaging

Frequency upconversion optical imaging has attracted great attention due to its remarkable advantages over traditional down-conversion optical imaging. However, the development of frequency upconversion optical imaging is extremely limited. Herein, five derivatives with BODIPY structure (B1–B5) were developed to investigate its frequency upconversion luminescence (FUCL) performance by introducing electron-donating and electron-withdrawing groups. Except for the nitro group decorated derivative, the other derivatives have strong and stable FUCL around 520 nm under 635 nm light excitation. More importantly, B5 retains FUCL ability after self-assembly. When applied to FUCL imaging of cells, B5 nanoparticles can be enriched in the cytoplasm and show a good signal-to-noise ratio. Meanwhile, FUCL tumor imaging can be achieved after 1 h of injection. This study not only provides a potential agent for FUCL biomedical imaging but also develops a new strategy for designing FUCL agents that exhibit excellent performance.

Albumin-based near-infrared phototheranostics for frequency upconversion luminescence/photoacoustic dual-modal imaging-guided photothermal therapy.

Engineering versatile phototheranostics for multimodal diagnostic imaging and effective therapy has great potential in cancer treatment. However, developing an inherently versatile molecule is a huge challenge. In this work, a near-infrared organic dye (NRh) was synthesized and further bound with bovine serum albumin (BSA) to construct facile "one-for-all" phototheranostics (NRh-BSA NPs), which exhibited enhanced frequency upconversion luminescence (FUCL, λex/em = 850/825 nm) and excellent photoacoustic (PA) and photothermal properties (λ'ex = 808 nm). Additionally, the BSA-modified phototheranostics NRh-BSA NPs showed specific accumulation in the tumor region through passive targeting. Based on the FUCL/PA dual modal imaging-guidance, the NRh-BSA NPs not only can guarantee the accuracy of imaging of the U87MG tumor sites, but also can improve the therapeutic effect on ablating tumors without recurrence by photothermal therapy (PTT). Collectively, our work proposed a novel strategy to construct versatile phototheranostics with the unique FUCL/PA imaging-guided technique for accurate cancer theranostics.

Mitochondria targeted upconversion molecular platform for photodynamic therapy of cancer cells

Increasing interest has been noted in photosensitizer design. Currently, most small molecular photosensitizers have several drawbacks, including limited penetration depth and unsatisfying photostability. For addressing these limitations, Frequency upconversion luminescence (FUCL) small molecule was adopted as a photosensitizer design strategy for its deeper penetration, sensitive imaging, and better photostability. We developed a series of FUCL (NIR-NH2, NIR-NHEt, NIR-NEt2) molecules with rigid structures. Equipped with the most powerful electron donor, NIR-NEt2 exhibits the highest singlet oxygen generation, the strongest upconversion luminescence intensity under 808 nm irradiation and mitochondria-targeted ability. FUCL can be a superior molecular platform for image-guided photodynamic therapy of cancer cells.

Near-Infrared Frequency Upconversion Luminescence Bioimaging Based on Cyanine Nanomicelles

Upconversion optical imaging has great application prospects in biomedical imaging. However, research on molecular upconversion luminescence materials is very limited. In this study, a cyanine dye modified using polyethylene glycol is reported, which has frequency upconversion luminescence (FUCL) capability and can be applied for in vivo FUCL imaging after forming nanomicelles. The optical properties of PEGylated cyanine dye show that the light absorption property of cyanine does not be influenced and can still emit near-infrared fluorescence. However, under the condition that the illumination wavelength is larger than the maximal fluorescence wavelength, the FUCL of cyanine dye is generated at the same position as the down-converted luminescence. The nanomicelles exhibit good biocompatibility. When applied to in vivo imaging, the cyanine-based nanomicelles not only qualify for high-resolution subcutaneous blood vessel imaging but also exhibit good imaging ability for various organs and tumors. These results point out that cyanine-based nanomicelles with FUCL characteristics are expected to be further applied in the field of biomedicine, providing a basis for the construction of FUCL molecules.

A Stable 1550nm WGM Laser Generated by Yb3+/Er3+ Co-doped Silica Microspheres under μm ASE Source Pumping

The amplified spontaneous emission (ASE) light source at 1 μm was used to excite Yb3+/Er3+ co-doped silica (YEDS) microspheres by evanescent-wave coupling through a taper optical fiber (TOF) to generate a stable 1550 nm laser. Inevitably, the experimental process was accompanied by a frequency up-conversion luminescence whose fluorescence spectrum was collected and analyzed. Pumped by the ASE light source with different power, the system of YEDS microsphere and TOF also generated single-mode laser and multi-longitudinal mode laser. Their peak wavelength, output power of the peak laser, full width at half maximum (FWHM), and side mode suppression ratio (SMSR) were respectively measured. Moreover, the characteristics of a 1550 nm whispering gallery mode (WGM) laser excited by a 1 μm ASE pumping and a tunable laser (TLS) pumping were compared under different variable conditions. It was demonstrated that the ASE pump source has polarization in all directions to excite WGMs in the microsphere cavity, which was different from and superior to the TLS. Therefore, the laser generated by the ASE pump source as an excitation source was not affected by vibration and temperature change. The results show that the 1550 nm laser pumped by ASE can stably output the microsphere WGM mode laser under the interference of vibration and temperature change, which is more suitable for the actual application environment.

Nitroso-caged upconversion luminescent prodrug: Near infrared light-activatable NO nano-donor for gas therapy

Gas therapy has emerged as an effective cancer treatment for minimal tissue invasiveness and little drug resistance. Particularly, Nitric oxide (NO) gas transmitter has drawn extensive attention for direct cancer-killing efficiency at high concentrations. However, the major drawbacks of the current NO prodrugs are insufficient NO delivery to the target tissues and lack the ability of spatiotemporal release precision. Meanwhile, it is also underestimated for NO prodrugs to achieve real-time deep-tissue drug monitoring visualization with high sensitivity for reliable delivery confirmation. Herein, two near infrared (NIR) light-triggered NO-releasing donors (NRh-Bn-NO and NRh-Et-NO) are synthesized for NO delivery with superb spatiotemporal controllability while tracing drug release mediated by frequency upconversion luminescence (FUCL) readout. FUCL is a unique anti-Stokes luminescence imaging modality that provides superior imaging sensitivity and increased signal-to-noise ratio for high resolution, which takes precedence in deep-seated tumor imaging. Furthermore, a nano-system (PEG-Bn-NO) is constructed with NRh-Bn-NO to guarantee efficient NO generation by direct NIR activation while allowing high-resolution drug monitoring in depth. Following intravenous administration, PEG-Bn-NO is specifically targeted to the tumor site and selectively controlled tumor growth induced by NIR light. The NO nano-prodrug should be inspirational to highly efficient gas therapy integrated with real-time drug delivery monitoring.

Near-infrared frequency upconversion probe for revealing the relationship between glutathione S-transferase and drug-resistance

Drug resistance poses an enormous challenge for successful chemotherapy. Glutathione S-transferase (GST) has been confirmed to be involved in the progression of drug resistance to some anticancer drugs, thus revealing that the role of GST in anticancer drug resistance is necessary. Herein, by taking advantage of frequency upconversion luminescence (FUCL) technology, we reported an FUCL probe (NRh-NDs) that can detect GST based on a rhodamine derivative structure decorated with a 2,4-dinitrobenzenesulfonyl group (NDs). The NRh-NDs showed excellent sensitivity and high selectivity for GST and released the emissive dye NRh–NH2, which showed emission and excitation wavelengths in vitro of 820 nm and 850 nm, respectively. The NRh-NDs probe successfully tested endogenic GST in U87, MCF-7 and A549 cells. The cell data showed that the increased levels of GST were positively related to cisplatin resistance but not to 5-fluorouracil resistance. These results suggested that the probe could be used as a visual tool to reveal the cause of drug resistance for cisplatin resistance in cancer treatment. Furthermore, it may serve as an effective tool to confirm the mechanism of antitumor drug resistance.

Mitochondria targeted near-infrared chemodosimeter for upconversion luminescence bioimaging of hypoxia.

We report a mitochondria-targeted near-infrared probe (NRh-O) for frequency upconversion luminescence (FUCL) imaging of hypoxia. Under hypoxic conditions, NRh-O rapidly responds to release the FUCL product NRh (λex/em = 850/825 nm) with high sensitivity and selectivity in mitochondria. This highlights the potential application of a hypoxia-responsive probe in early clinical diagnosis.

Upconversion NIR-II fluorophores for mitochondria-targeted cancer imaging and photothermal therapy

NIR-II fluorophores have shown great promise for biomedical applications with superior in vivo optical properties. To date, few small-molecule NIR-II fluorophores have been discovered with donor-acceptor-donor (D-A-D) or symmetrical structures, and upconversion-mitochondria-targeted NIR-II dyes have not been reported. Herein, we report development of D-A type thiopyrylium-based NIR-II fluorophores with frequency upconversion luminescence (FUCL) at ~580 nm upon excitation at ~850 nm. H4-PEG-PT can not only quickly and effectively image mitochondria in live or fixed osteosarcoma cells with subcellular resolution at 1 nM, but also efficiently convert optical energy into heat, achieving mitochondria-targeted photothermal cancer therapy without ROS effects. H4-PEG-PT has been further evaluated in vivo and exhibited strong tumor uptake, specific NIR-II signals with high spatial and temporal resolution, and remarkable NIR-II image-guided photothermal therapy. This report presents the first D-A type thiopyrylium NIR-II theranostics for synchronous upconversion-mitochondria-targeted cell imaging, in vivo NIR-II osteosarcoma imaging and excellent photothermal efficiency.

Hybrid excitation mechanism of upconversion fluorescence in hollow La2Ti2O7: Tm3+/Yb3+ submicron fibers

High-crystalline, hollow-mesh-like Tm3+/Yb3+-co-doped La2Ti2O7 (LTO) submicron fibers are prepared by electrospinning technique and identified as monoclinic structure. The LTO matrix fibers and the Tm3+/Yb3+-co-doped fibers exhibit different frequency upconversion luminescence. The fluorescence of the matrix at the 487 and 542 nm is ascribed to the two-photon absorption and the cross-relaxation processes caused by the defect center at 977 nm excitation, respectively. The upconversion luminescence intensity enhances when the rare-earth ions are incorporated into LTO fibers. The emissions of Tm3+ in co-doped LTO membranes at 479 and 789 nm under the excitation of 977 nm indicate the effectiveness of the three- and two-photon absorption processes, respectively. The pristine LTO fibers have the potential to be employed for water purification as a laser-excited photocatalytic material because the LTO materials are conducive to absorbing the highly penetrating NIR laser. Furthermore, the Tm3+/Yb3+ ions play a positive role in further promoting the laser-absorption capacity, and the hybrid excitation mechanism in the Tm3+/Yb3+-co-doped LTO composite fibers provides a new perspective for the development of anti-laser inorganic materials.

Upconversion luminescence in europium doped Y2O3 powder excited by absorption of three, four, and five infrared photons

Frequency upconversion (UC) luminescence was observed in yttrium oxide (Y2O3) powders doped with trivalent europium ions (Eu3+) when the samples were irradiated with a femtosecond laser system operating either at 1275 nm or 1500 nm. The samples, prepared by low temperature combustion synthesis, were characterized by X-ray diffraction, scanning electronic microscopy, spontaneous Raman scattering and photoluminescence. The UC luminescence, corresponding to the 5D0 → 7FJ (J = 1, 2, 3, 4) transitions of Eu3+, characterized by measuring the amplitude of the UC signal versus the laser intensity, is attributed to the simultaneous absorption of three, four and five infrared photons. The results indicate that Eu3+ doped Y2O3 powder is an efficient upconverter for excitation using femtosecond near-infrared lasers.

A near-infrared frequency upconversion probe for nitroreductase detection and hypoxia tumor in vivo imaging

Nitroreductase (NTR) acts as a detective enzyme that can be used to judge the hypoxic level of solid tumors. To date, only a few optical probes can effectively and selectively monitor NTR in vivo. Therefore, it is important to develop an ideal probe with near-infrared (NIR) excitation and emission for NTR detection and imaging. In this study, we report a NIR frequency upconversion luminescence (FUCL) probe (Cy7-NO2) based on a cyanine structure decorated with an aromatic nitro group to detect NTR in vivo. Cy7-NO2 not only was excited at 850 nm and emitted at 790 nm, but also showed a fast and selective response to NTR. Docking calculations revealed that NTR was able to form hydrogen bonds with Cy7-NO2 and underwent an enzyme-catalyzed reduction reaction. Compared with absorption and the Stokes emission methods, FUCL method exhibited a lower detection limit (3.4 ng mL−1). In addition, Cy7-NO2 was used for FUCL bioimaging of NTR in living cells and mice. All of these results proved that Cy7-NO2 as a FUCL probe supplies a new method for biodetection and bioimaging of NTR in vitro and in vivo.

A reversible frequency upconversion probe for real-time intracellular lysosome-pH detection and subcellular imaging.

Lysosomal pH is known to be acidic, which plays a vital role in various processes in living organisms. Frequency upconversion luminescence exhibits the unique ability to convert low energy photons into high energy photons, which can be used in live samples due to its deep penetration, low tissue damage, etc. The development of sensitive frequency upconversion probes with a low pKa, high sensitivity, and specific selectivity for lysosomal pH detection is of great importance. Herein, we report a novel frequency upconversion luminescence probe, NRH-Lyso, by conjugating the rhodamine derivative NRH and the lysosome targeting functional group 4-(2-aminoethyl)morpholine. NRH-Lyso shows a sensitive response to acidic pH and excellent selectivity in the presence of metal ions, anions, and small molecules. Due to the structural transformation of lactam ring opening and closing of NRH-Lyso, the probe shows an almost 80-fold enhancement in emission intensity when the pH changes from 7.0 to 4.0 under 808 nm laser excitation. The living cell imaging data reveals that NRH-Lyso can selectively detect lysosomal pH changes with excellent photostability and low cytotoxicity. All these features make NRH-Lyso a good candidate to investigate the lysosomal pH-associated physiological and pathological processes.

IR-to-visible frequency upconversion in Yb3+/Tm3+ co-doped phosphate glass

Frequency upconversion luminescence in Yb3+/Tm3+ co-doped 60P2O5·15ZnO·5Al2O3·10BaO·10PbO glass (PZABP) excited at 980 nm is reported. Pump power dependence, lifetime measurements, and the absorption spectra of the Tm3+ ions in the visible to IR region are investigated as a function of sensitizer (Yb3+) concentration. Blue light at 475 nm and red light at 660 nm generation was observed. Intensity saturation behavior is observed for the 475 nm (1G4 – 3H6), 650–664 nm (1G4 – 3F4 and/or 3F2,3 – 3H6) and 793 nm (3H4 – 3H6) upconversion emissions, when laser power was above ∼ 75 mW (∼1.9 kW/cm2). The radiative lifetimes measured for the observed emissions were 270 μs (475 nm), 195 μs (650 nm), 177 μs (664 nm), 184 μs (793 nm) and 335 μs (1211 nm). The application of the Davis-Mott model detected a slight change of 6.6% in the value of the energy bandgap for the highest doping concentration in comparison with the undoped sample. Results indicate that the PZABP glass matrix herein reported is a promising contender as host for rare-earth doped based photonic devices.

Luminescent Probes for Sensitive Detection of pH Changes in Live Cells through Two Near-Infrared Luminescence Channels.

Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2'-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.

High temperature-sensing performance of Er- and Yb-codoped tungsten bronze oxides based on frequency up-conversion luminescence

Novel tungsten bronze Ba4Gd0.65-xEr0.02YbxNb10O30 (0≤x≤0.1) phosphors were synthesized. Their phase and structure were characterized and analyzed by X-ray diffraction (XRD) and Rietveld structural refinements. Under 980nm excitation, bright frequency up-conversion (FUC) green and weak red emissions were observed. The concentration of Yb3+ had an important influence on the FUC luminescence properties and a possible UC mechanism was proposed. Temperature sensing properties of the Ba4Gd0.55Er0.02Yb0.1Nb10O30 phosphor in the range from 303 to 573K were obtained by measuring the temperature dependent fluorescence intensity ratio (FIR) of the FUC green emissions at 531 and 554nm originated from two thermally coupled 2H11/2 and 4S3/2 emitting energy levels. A temperature-sensing sensitivity of 0.013K−1 at 573K was obtained experimentally and the obtained energy difference ΔE was 971cm−1, indicating that this material can be utilized as a promising candidate for the future optical temperature sensors of high accuracy and resolution.