Upconversion Fluorescence Research Articles

One-pot hydrothermal synthesis of Si-doped carbon quantum dots with up-conversion fluorescence as fluorescent probes for dual-readout detection of berberine hydrochloride

Here, the high fluorescent silicon-doped carbon quantum dots (Si-CQDs) were prepared by a facile and one-pot hydrothermal assay using 3-aminopropyltrimethoxysilane as the carbon and silicon source. The prepared Si-CQDs exhibit favorable water-soluble, high-temperature resistance, acid resistance, alkali resistance, high ionic strength resistance, high photostability, film-forming ability and solid-state fluorescence. Compared to other Si-CQDs that have been reported, the prepared Si-CQDs show unique up-conversion fluorescence. Furthermore, it is found that berberine hydrochloride (BH) can effectively quench the down- and up-conversion fluorescence of the Si-CQDs, making it can be used as a highly sensitive and specific probe for BH dual-mode sensing. Meanwhile, the linear range of down-conversion fluorescence detection for BH is 0.5-30.0 µmol/L with a limit of detection (LOD) of 50 nmol/L, and the linear range of up-conversion fluorescence assay for BH is 0-25.0 µmol/L. The mechanism of down-conversion fluorescence quenching by BH was investigated through a series of studies. The results show the quenching mechanism is the inner filter effect (IFE). Moreover, this proposed strategy has been well used to analyze BH in urine samples with satisfactory results.

Facile Synthesis of NaYF4:Yb Up-Conversion Nanoparticles Modified with Photosensitizer and Targeting Antibody for In Vitro Photodynamic Therapy of Hepatocellular Carcinoma.

Rare Earth up-conversion nanoparticles NaYF4:20%Yb,2%Er@PEI (UCNPs) were generated via a one-step hydrothermal technique at relatively reduced temperatures. Photosensitizer Ce6 and anti-EpCAM, a highly expressed monoclonal antibody in cancer stem cells of hepatocellular carcinoma, were linked to UCNP surfaces via the formation of amide linkage between carboxyl from Ce6 or anti-EpCAM and abundant amino from PEI, leading to the formation of Ps-Ce6 and anti-EpCAM-UCNPs-Ce6 nanoparticles. The synthesized nanoparticles characterized by XRD, TEM, and IR, and their zeta potential, ROS generation ability, Ce6 loading rate, and up-conversion fluorescence properties were investigated. It has been revealed that all the products were uniformly dispersed nanoparticles (25–32 nm), which crystallized primarily as hexagonal structures, and their up-conversion fluorescence spectra were similar to that of NaYF4:20%Yb,2%Er. The Ce6 loading rate in the anti-EpCAM-UCNPs-Ce6 nanoparticles was about 2.9%, thereby resulting in good ROS generation ability. For anti-EpCAM-UCNPs-Ce6, the biosafety, targeting effect, and PDT effect exposed under near-infrared (NIR) laser (980 nm) were evaluated using human liver cancer cells (BEL-7404). The results showed that it has good biocompatibility and biosafety as well as high targeting and PDT treatment efficiencies, which renders it a potential experimental material for the near-infrared PDT study.

Photonic crystal films with upconversion luminescence based on the self-assembly of polystyrene encapsulated NaYF4:Ln3+ composite microspheres for dual-mode optical code

The design and fabrication of advanced materials with multiple optical states for constructing security code are of great value in anti-counterfeiting. Herein, novel upconversion photonic crystal (UCPC) films with tunable luminescence and structural color were prepared by vertical deposition of polystyrene encapsulated NaYF4:Ln3+ (CSNPs@SiO2/PS) composite microspheres. The composite microspheres were synthesized by sequential coating technology. Firstly, NaYF4:Ln3+@NaYF4 core/shell nanoparticles (CSNPs) were synthesized and served as upconversion luminescent emission centers. Then, the CSNPs were further coated by a SiO2 shell with pendant double bond to form CSNPs@SiO2-MPS. Afterward, mono-dispersed CSNPs@SiO2/PS composite microspheres were synthesized by emulsion polymerization of styrene in the presence of CSNPs@SiO2-MPS. By tailoring the doped lanthanide ions in CSNPs and adjusting the diameter of the composite microspheres, UCPC films with diverse upconversion fluorescence and structural color can be obtained. As a proof of concept, these different kinds of UCPC films were employed as information coding units to construct dual-mode anti-counterfeiting code. Our protocol provided a new security strategy for information storage.

Reproducible Single-Droplet multiplexed detection through Excitation-Encoded Tri-mode upconversion solid sensors

The article reports a reproducible and resuable sensor for upconversion fluorescence multiplexed detection constructed by excitation-encoded core-multishell upconversion nanoparticles with a thin superhydrophobic SiO 2 layer, which outperforms the sensors with co-doped upconversion nanoparticles and multi-channel upconversion nanoparticle mixtures. Such solid-multi-mode sensor can achieve visual colorimetric and reproducible multiplexed simultaneous detection of multi-analytes. Upconversion multiplexed optical sensors are promising in clinical diagnostics, molecular mapping and environmental monitoring. However, traditional co-doped emitter sensors and mixture sensors show poor sensitivity and reproducibility due to the strong cross-relaxation quenching and instability. Herein, upconversion multi-shell nanoparticles are, for the first time, applied as excitation-controlled nanosensors for reproducible and channel-independent multiplexed detection. The multi-shell structure favors the excitation-encoded reproducible blue/green/red fluorescence signals from different upconversion shells in a single upconversion nanosensor, avoiding using instable upconversion nanoparticle mixtures for multiplexed detection. A reproducible and self-cleaning solid tri-mode sensor is constructed by the upconversion multi-shell nanoparticles coated with a thin superhydrophobic SiO 2 layer. The solid sensor shows superior single-droplet (≈10 µL) multiplexed detection capability with a low detection limit for dye molecules (∼0.1 μg/mL), high stability and excellent recyclability (more than 100 cycles). This work provides an intriguing strategy to achieve channel-independent, reproducible UC multiplexed sensors for simultaneous detection of multi-analytes.

Upconversion-luminescent optical fiber probe for in situ tyrosinase monitoring

Tyrosinase (TYR) is related to a variety of skin diseases, melanoma and Parkinson's disease, and it is essential for the quantitative detection of TYR. Although the traditional TYR sensors in solution have extremely high sensitivity, and it is expected to develop a biosensor for point of care (POC) detection due to its poor portability, nanoparticle aggregation, reusability, and complexity of use. Here, we report a simple and compact interrogation setup of an optical fiber sensor that facilitates signal transmission and can identify and quantify TYR. The sensor consists of multimode optical fibers (MOF) modified by up-conversion nanoparticles (UCNPs) based on chemical bonds, and the photoconductive MOF can both excite UCNPs and collect the upconversion fluorescence of UCNPs. TYR is detected based on photo-induced electron transfer (PET) between UCNPs and dopaquinone (DQ). The fiber optic sensor has an optical reading, a linear response of up to 0.6 U mL−1, and a detection limit as low as 0.028 U mL−1. Our optical microsensor has great potential to be used as a portable and in situ detection probe to monitor TYR.

Quantum optical immunoassay: upconversion nanoparticle-based neutralizing assay for COVID-19

In a viral pandemic, a few important tests are required for successful containment of the virus and reduction in severity of the infection. Among those tests, a test for the neutralizing ability of an antibody is crucial for assessment of population immunity gained through vaccination, and to test therapeutic value of antibodies made to counter the infections. Here, we report a sensitive technique to detect the relative neutralizing strength of various antibodies against the SARS-CoV-2 virus. We used bright, photostable, background-free, fluorescent upconversion nanoparticles conjugated with SARS-CoV-2 receptor binding domain as a phantom virion. A glass bottom plate coated with angiotensin-converting enzyme 2 (ACE-2) protein imitates the target cells. When no neutralizing IgG antibody was present in the sample, the particles would bind to the ACE-2 with high affinity. In contrast, a neutralizing antibody can prevent particle attachment to the ACE-2-coated substrate. A prototype system consisting of a custom-made confocal microscope was used to quantify particle attachment to the substrate. The sensitivity of this assay can reach 4.0 ng/ml and the dynamic range is from 1.0 ng/ml to 3.2 upmug/ml. This is to be compared to 19 ng/ml sensitivity of commercially available kits.

“Off-On” typed upconversion fluorescence resonance energy transfer probe for the determination of Cu2+ in tap water

Detection of copper plays a prominent role in the environmental protection and human health. Herein, we firstly design and construct an “off–on” upconversion fluorescence resonance energy transfer (UFRET) probe with low toxicity for the Cu2+ determination by using NaYF4: Yb3+, Er3+ upconversion nanoparticles (UCNPs) and Au NPs. UCNPs with positive charge and Au NPs with negative charge are respectively employed as the donor and acceptor, and bound together to form UFRET probe. The upconversion fluorescence quenching of UCNPs occurs by Au NPs through FRET (defined as “off” state). When Cu2+ exists in samples, Cu2+ reacts with 4-mercaptobenzoic acid (4-MBA) capped on the surface of Au NPs to make Au NPs detach from UCNPs, leading to the termination of FRET and the recovery of upconversion fluorescence (defined as “on” state). “Off-on” typed UFRET probe has excellent sensing performances, including linear range of 0.02–1 μM Cu2+ concentration, the limit of detection of 18.2 nM, high selectivity to Cu2+ and good recovery. The probe has been successfully used to determine Cu2+ in spiked tap water with satisfactory results. The probe will provide theoretical and technical support for the design of new sensitive heavy metal ion detection probe.

Use of DNA nanosensors based on upconverting nanoparticles for detection of Nosema bombycis by fluorescence resonance energy transfer

In this study, NaYF4:20%Yb, 2%Er upconverting nanoparticles (UCNPs) were synthesized by solvothermal method and characterized by transmission electron microscopy and upconversion fluorescence spectrometry. The results showed that the UCNP particles present good dispersion and uniform spherical shape with a size of 29 ~ 42nm. Hydroxyl UCNPs were converted to hydrophilic carboxylic acid-functionalized ones by ligand exchange, and the streptavidin was attached on the surface of carboxylic acid-functionalized UCNPs via amide bond. The DNA nanosensors based on UCNPs with DNA probes have been successfully developed. Only the genomic DNA of Nosema bombycis can be specifically detected by the DNA nanosensors when the DNA of Bombyx mori and its pathogens was used as target DNA. When the DNA nanosensors were used to detect the DNA of N. bombycis, a broad emission peak signal appeared at 580nm. There is linear relationship between the signal intensity and DNA concentration of N. bombycis, I580/I545 (R2 = 0.820) and I545/I654 (R2 = 0.901). The detectable minimum concentration of genomic DNA of N. bombycis was 100ng/μL while the tested concentrations of N. bombycis genomic DNA were 3000ng/μL, 1500ng/μL, 1000ng/μL, 500ng/μL, 250ng/μL, and 100ng/μL, respectively. The whole detection process for target DNA takes less than 60min.

Triplet‐Triplet Annihilation Upconversion from Ru(II) Phenanthroline Complexes and 2‐Substituted Anthracene Derivatives

AbstractTwo Ru(II) phenanthroline complexes (Ru‐ph and Ru‐py) were synthesized and their photophysical properties were systematically investigated. For Ru‐py, the conjugation of pyrene at 3‐ and 8‐positions of auxiliary ligand 1,10‐phenanthroline can increase the phosphorescence quantum yield, prolong the triplet lifetime and reduce the triplet energy level. The extended triplet lifetime of Ru‐py was revealed by using the density function theory calculations, which is originated from the triplet state equilibrium between the metal‐to‐ligand charge‐transfer (3MLCT) state and the intraligand (3IL) state. The upconversion fluorescence of 2‐substituted anthracene derivatives (DTACl, DTACN and DNACN) sensitized by Ru‐ph and Ru‐py in DMF was investigated under monochromatic 488 nm excitation with an ultralow power density of 40 mW/cm2. Among them, Ru‐py/DTACl presents the highest upconversion quantum yield (7.4 %). It is found that a small energy gap between the triplet states of sensitizer and emitter helps to increase upconversion quantum yield besides the high triplet‐triplet annihilation efficiency and fluorescence radiation of emitter and the long triplet lifetime of sensitizer.

Subwavelength-resolution imaging of surface plasmon polaritons with up-conversion fluorescence microscopy.

Imaging and characterization of surface plasmon polaritons (SPPs) are crucial for the research and development of the plasmonic devices and circuits. Here, we report on direct imaging of SPPs propagation on SiO2/metal interface with subwavelength spatial resolution using up-conversion fluorescence microscopy, that exploits rare-earth ions, such as Er3+, Yb3+, and Nd3+, doped nanoparticles as the fluorophores. We demonstrated that by further taking the intensity ratio of the image obtained with fluorescent emission at different wavelengths, we are able to substantially enhance the features associated to the SPP wavefronts in the image for quantitative analysis, such as the wavevector and propagation direction of the SPPs. Our results agree with the theoretic prediction of the SPP wavelengths quantitatively. We further demonstrate the evolution of the SPP wavefronts due to refraction SPPs, and reproduced the experiment with finite difference time domain (FDTD) method simulations. The relative refractive index of SPP estimated from the experiment also agrees quantitatively with those extracted from the theory and the simulation.

Integration of Au Nanosheets and GdOF:Yb,Er for NIR-I and NIR-II Light-Activated Synergistic Theranostics.

The local hyperthermia (>41 °C) effect of photothermal therapy (PTT) is significantly limited by the efficiency of PTT agents to convert laser energy to heat, and such oncotherapy, similar to conventional chemotherapy, invariably encounters the challenge of nonspecific application. Undue reliance on oxygen sources still poses particular difficulties in photodynamic therapy (PDT) for deep-level clinical applications. Considering these therapeutic issues, in this study, we constructed a versatile but unique nanosystem by encapsulating Au nanosheets in codoped gadolinium oxyfluoride (GdOF):Yb,Er spheres, followed by decoration of a chemotherapeutic drug (doxorubicin), photosensitizer (rose Bengal, RB), and targeted agent (folic acid). This allowed the incorporation of cancer treatment and real-time curative efficacy monitoring into one single theranostic nanoplatform. Benefiting from the dual contribution of the strong absorptions in the NIR-I and NIR-II regions, relevant photothermal-conversion efficiency (η) values pertaining to that final product were 39.2% at 1064 nm irradiation and 35.7% at 980 nm illumination. The fluorescence resonance energy transfer that occurred in the up-converted GdOF:Yb,Er to RB contributed to the high PDT efficacy. Combined with a micromeric acid-responsive drug release in a targeted tumor microenvironment, high-performance synergistic therapy was realized. In addition, up-conversion fluorescence imaging and computed tomography imaging accompanied by multimodal magnetic resonance imaging were simultaneously achieved owing to the doped lanthanide ions and the encapsulated Au nanosheets. Our designed oncotherapy nanosystem provides an alternative strategy to acquire ideal theranostic effects.

Amino‐Modified Poly (l–lactic Acid) Nanofibers Enable pH‐Stimulated Drug Release and NIR Real‐Time Detection

AbstractStimulus‐responsive nanofibers can adjust the speed of drug delivery, and real‐time monitoring elucidates the relationship between drug release and therapeutic efficacy. Both of these advantages have great potential in clinical therapy. However, the complex preparation of current stimulus‐responsive drug‐loaded nanofibers leads to low drug‐loading levels, limiting their widespread applications. In this study, we prepared pH‐responsive drug‐loaded nanofibers with fluorescence monitoring properties using the electrospinning method. A representative drug of DOX was loaded onto the nanofibers. The degradable flexible nanofibers modified by amino groups attained higher drug loading and controlled drug release. Precisely, the rate of drug release varies with different pH. Faster release speed occurs in the tumor microenvironment with faintly acidic conditions than in healthy tissues with neutral conditions. The pH‐responsive mechanism was due to hydrazone bonds between the amino groups and DOX molecules, which FTIR confirmed. In addition, these pH‐responsive nanofibers with intense upconversion fluorescence enable more sensitive monitoring, whereas weak luminescence cannot achieve.

Upconversion fluorescence of MXene nanosheets and the sensitive detection of l-tryptophan

The unique up-conversion fluorescence behavior of Ti3C2 MXene nanosheets was reported for the first time and was applied in the highly sensitive and selective analysis of l-tryptophan.

Materials for thermally activated delayed fluorescence and/or triplet fusion upconversion

Guest editors Malika Jeffries-EL, Nobuhiro Yanai and Eli Zysman-Colman introduce this themed issue on thermally activated delayed fluorescence, and triplet–triplet annihilation-based photon upconversion, materials.

Inner filter effect-based upconversion fluorescence sensing of sulfide ions.

Upconversion nanocrystals (UCNCs) have emerged as a new type of fluorescent probe for sensing applications. Herein, we designed a 980 nm excited upconversion luminescence system, composed of core-shell-structured NaYF4 : Yb,Er@NaYF4 : Yb nanocrystals (csUCNCs) and the triethylenetetramine-Cu complex (complex-I), for quantitative detection of sulfide ions. Taking advantage of the specific recognition of complex-I toward S2-, the as-formed compound (complex-II) exhibits excellent spectral overlap not only in the range of fluorescence emissions of UCNCs but also in the excitation wavelength for UCNCs; fluorescence quenching of UCNCs occurs where the complex-II acts as the energy acceptor. Due to the electrostatic repulsion between positively charged ligand-free csUCNCs and complex-I, the fluorescence quenching is based on the primary and secondary inner filter effect rather than the fluorescence resonance energy transfer process. The detection limit of S2- for the upconversion-based system is calculated to be 2.7 μM, exhibiting higher detection sensitivity over the single complex-I compound measured by the spectrophotometric method. Moreover, no significant variation in upconversion luminescence is observed upon the addition of other interfering ions, showing the excellent selectivity of this nanoprobe toward S2-.

Photobase-catalysed anionic thiol-epoxy click photopolymerization under NIR irradiation: from deep curing to shape memory

A photobase generator absorbing upconversion fluorescence can efficiently catalyze anionic thiol-epoxy click photopolymerization under 980 nm NIR light irradiation.

Direct observation of singlet ππ∗ and nπ* equilibrium state in 2-amino-1,3,5-triazine solution

1,3,5-Triazine molecules represent a class of molecules that may have been prebiotic information carriers in a primordial soup in early Earth and their excited state dynamics has received attention in recent years. In our previous study, one component with lifetime longer than 100 ps was discovered in 2-amino-1,3,5-trainzine (2-AT), but its nature has not been revealed. In this study, excited state dynamics of 2-AT is studied in different solvents by using femtosecond time-resolved transient absorption and fluorescence up-conversion spectroscopy. Interestingly, an equilibrium state consisting of the bright ππ∗ and dark nπ∗ states in 2-AT is directly observed in aqueous solution and its dynamics is solvent sensitive. The whole picture of the excited state deactivation mechanism of 2-AT is proposed based on our spectroscopy results.

The Excited State Dynamics of a Mutagenic Cytidine Etheno Adduct Investigated by Combining Time-Resolved Spectroscopy and Quantum Mechanical Calculations.

Joint femtosecond fluorescence upconversion experiments and theoretical calculations provide a hitherto unattained degree of characterization and understanding of the mutagenic etheno adduct 3,N4-etheno-2′-deoxycytidine (εdC) excited state relaxation. This endogenously formed lesion is attracting great interest because of its ubiquity in human tissues and its highly mutagenic properties. The εdC fluorescence is modified with respect to that of the canonical base dC, with a 3-fold increased lifetime and quantum yield at neutral pH. This behavior is amplified upon protonation of the etheno ring (εdCH+). Quantum mechanical calculations show that the lowest energy state ππ*1 is responsible for the fluorescence and that the main nonradiative decay pathway to the ground state goes through an ethene-like conical intersection, involving the out-of-plane motion of the C5 and C6 substituents. This conical intersection is lower in energy than the ππ* state (ππ*1) minimum, but a sizable energy barrier explains the increase of εdC and εdCH+ fluorescence lifetimes with respect to that of dC.

Tm3+,Yb3+: Y2SiO5 up-conversion phosphors: Exploration of temperature sensing performance by monitoring the luminescence emission

Tm3+,Yb3+:Y2SiO5 ceramic powders synthesized via combustion route exhibited up-conversion (UC) fluorescence when were submitted to CW-laser radiation at 980 nm. Four emission bands at 478 nm, 650 nm 690 nm and 798 nm, corresponding to transitions 1G4→3H6, 1G4→3F4, 3F2,3 → 3H6 and 3H4→3H6 were observed. The properties of the UC emission bands are influenced by temperature. Thermal coupling levels (TCL) cause a noticeable change in the relative intensities between the excited states 3F2,3 → 3H6 and 3H4→3H6 in the temperature range of 298–473 K. The maximum absolute sensitivity (1.25 × 10−3 K-1, 473 K) and relative sensitivity (1.83% K−1, 298 K) were obtained using the fluorescence intensity ratio (FIR) technique. Thermal sensing performance has been explored by utilizing the FIR technique between non-thermally coupled levels (NTCL). Through the calculation of FIR of NTCL1G4→3H6 and 3H4→3H6, the value of the relative sensitivity was acquired (1.5% K−1, 298 K). The comparison of TCL and NTCL FIR-method performances shows that this ceramic powder has the potential to be used as a ratiometric thermal sensor for remote temperature measurements.

Defect-Interceded Cascading Energy Transfer and Underlying Charge Transfer in Europium-Doped CsPbCl3 Nanocrystals.

Rare-earth ion (RE3+) doping in cesium lead chloride (CsPbCl3) has unlocked novel prospects to explore changes in optical, magnetic, and charge carrier transport properties. This leads to a huge advancement in optoelectronic applications, yet deep understanding of the photophysics governing the energy transfer processes is lacking and demands vital attention. Herein, we probe into the mechanistic transfer processes from the band edge of the host (CsPbCl3) to the dopant europium ion (Eu3+) with the aid of femtosecond fluorescence upconversion and transient absorption (TA) spectroscopy. The upconversion measurement portrays a defect-mediated cascading energy transfer from CsPbCl3 to Eu3+ and further cross-relaxation among Eu3+ states. Moreover, TA studies reveal that there is charge transfer from the band edge of CsPbCl3 to doping-induced shallow defect states. Furthermore, two-photon absorption study establishes no compromise in the transfer mechanism even upon bandgap excitation. This work validates that Eu-CsPbCl3 is an apt entrant for optoelectronic applications.