Near-infrared Light Excitation Research Articles

Light-Harvesting Photosensitizers for Photodynamic Inactivation of Bacteria under Both Visible and Near-Infrared Excitations.

We report a hybrid singlet oxygen production system, where strong resonance coupling between plasmonic nanoparticles and photosensitizing molecules results in exceptionally high singlet oxygen production under both visible light and near-infrared light excitation, even for the photosensitizing molecules without near-infrared absorption. The light-harvesting property of the plasmon-photosensitizer hybrids leads to an enhanced, broad-spectrum photodynamic inactivation of bacteria under a wide range of excitations, including that with near-infrared light.

Quasi-Continuous Wave Near-Infrared Excitation of Upconversion Nanoparticles for Optogenetic Manipulation of C. elegans.

Optogenetics is an emerging powerful tool to investigate workings of the nervous system. However, the use of low tissue penetrating visible light limits its therapeutic potential. Employing deep penetrating near-infrared (NIR) light for optogenetics would be beneficial but it cannot be used directly. This issue can be tackled with upconversion nanoparticles (UCNs) acting as nanotransducers emitting at shorter wavelengths extending to the UV range upon NIR light excitation. Although attractive, implementation of such NIR-optogenetics is hindered by the low UCN emission intensity that necessitates high NIR excitation intensities, resulting in overheating issues. A novel quasi-continuous wave (quasi-CW) excitation approach is developed that significantly enhances multiphoton emissions from UCNs, and for the first time NIR light-triggered optogenetic manipulations are implemented in vitro and in C. elegans. The approach developed here enables the activation of channelrhodopsin-2 with a significantly lower excitation power and UCN concentration along with negligible phototoxicity as seen with CW excitation, paving the way for therapeutic optogenetics.

Hydrothermal-assisted crystallization for the synthesis of upconversion nanoparticles/CdS/TiO2composite nanofibers by electrospinning

Upconversion nanoparticles/semiconductor nanocomposites have received intense interest in the past two decades. In this work, we demonstrated a facile electrospinning technique and a hydrothermal-assisted crystallization process to fabricate upconversion nanoparticles (UCNPs)/CdS/TiO2 nanofibers successfully. Polyvinylpyrrolidone (PVP, Mw ≈ 1 300 000) has been selected as the polymer matrix and tetrabutyl titanate (TBT, 99.0%) was used as the titanium source. The morphologies and phase of the as-prepared samples have been studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Experimental results revealed that the polymer matrix (PVP) can be dissolved and removed completely under hydrothermal conditions. In addition, the crystalline phase of TiO2 was also achieved under hydrothermal conditions. The as-prepared composite nanofibers are hundreds of micrometers in length and 650 nm in diameter and show weak upconversion fluorescence under the excitation of near-infrared light (980 nm), indicating the high energy transfer efficiency between upconversion nanoparticles and semiconductors. As expected, the UCNPs/CdS/TiO2 nanofibers may have enhanced photocatalytic performance as they make full use of solar energy using UCNPs as nanotransducers for infrared (IR) light.

Rational design of Nd(3+)-sensitized multifunctional nanoparticles with highly dominant red emission.

Controlling excitation and emission wavelengths on demand is very significant in bioimaging. Up-conversion nanoparticles (UCNPs) emit visible light upon near-infrared (NIR) light excitation and are well studied in bioimaging. Red emission is usually preferred to green due to its higher tissue penetration depth in bioimaging. Herein, dominant red emission has been achieved under 808 nm excitation based on the designed α-NaYbF4:Mn(2+)/Er(3+)@NaLuF4:Mn(2+)/Yb(3+)@NaNdF4:Yb(3+)@NaGdF4 (C@S1@S2@S3) nanostructure. The rationally designed interlayer shell NaLuF4:Mn(2+)/Yb(3+) could efficiently filter unwanted energy back-transfer from Er(3+) to Nd(3+) and the outmost shell NaGdF4 could prevent excitation energy from surface-related quenching. The lifetime of (4)F9/2→(4)I15/2 transition of Er(3+) could be as high as 0.7 ms. Moreover, C@S1@S2@S3 UCNPs also possess effective contrast efficiency for both X-ray computed tomography (CT) and magnetic resonance (MR) imaging. The designed multifunctional UCNPs could be used as a potential multimodal bioprobe in bioimaging applications.

Near-infrared triggered generation of reactive oxygen species from upconverting nanoparticles decorated with an organoiridium complex.

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.

Correlative cathodoluminescence and near-infrared fluorescence imaging for bridging from nanometer to millimeter scale bioimaging.

Correlative light and electron microscopy (CLEM) is one attractive method of observing biological specimens because it combines the advantages of both light microscopy (LM) and electron microscopy (EM). In LM, specimens are fully hydrated, and molecular species are distinguished based on the fluorescence colors of probes. EM provides both high-spatial-resolution images superior to those obtained with LM and ultrastructural information of cellular components. The combination of LM and EM gives much more information than either method alone, which helps us to analyze cellular function in more detail.We propose a Y2O3:Tm,Yb phosphor nanoparticle which allows upconversion luminescence (UCL) imaging with near-infrared (NIR) light excitation and cathodoluminescence (CL) imaging [1], where the light emission induced by an electron beam is called cathodoluminescence (CL). Due to electron beam excitation, the spatial resolution of CL microscopy is on the order of nanometers [2,3]. Upconversion is a process in which lower energy, longer wavelength excitation light is transduced to higher energy, shorter wavelength emission light. So far, in LM observation for CLEM, ultraviolet (UV) or visible light has been used for excitation. However, UV and visible light have limited ability to observe deep tissue regions due to absorption, scattering, and autofluorescence. On the other hand, NIR light does not suffer from these problems. Rare-earth-doped upconversion nanophosphors have been applied to biological imaging because of the advantages of NIR excitation [4].We investigated the UCL and CL spectra of Y2O3:Tm,Yb nanophosphors. Y2O3:Tm,Yb nanophosphors that emit visible and near-infrared UCL under 980nm irradiation and blue CL via electron beam excitation. To confirm bimodality of our nanophosphors, correlative UCL/CL images of the nanophosphors were obtained for the same region. The nanophosphors were poured onto a P doped Si substrate (Fig.1(a)) and were irradiated with 980 nm NIR CW laser light or an electron beam. Fig.1(b) shows the UCL image of the nanophosphors under 980 nm NIR CW laser irradiation, UCL spots were observed, but the individual nanophosphors in each spot were difficult to distinguish in the UCL image. On the other hand, the edges and the gap between the nanophosphors were clearly distinguished in the CL image (Fig.1(c)), showing that the spatial-resolution of CL imaging was enough higher than that of UCL image. We believe that upconversion phosphors of the type described here will allow the realization of new CLEM imaging techniques covering the nanometer to millimeter scale, i.e., the molecular to in vivo scale.jmicro;63/suppl_1/i29/DFU073F1F1DFU073F1Fig. 1.(a) SEM and correlative (b) UCL (intensity of 980 nm NIR CW laser 8 mW) and (c) CL images of Y2O3:Tm,Yb nanophosphors in same region (accelerating voltage 3 kV, exposure time 100 ms/pixel).

Near‐Infrared Light‐Induced Photocurrent from a (NaYF4:Yb‐Tm)/(Cu2O) Composite Thin Film

Utilization of photons of sub‐bandgap energy, mostly near‐infrared (NIR) photo­ns, is highly desirable for photovoltaic devices. We show that (NaYF4:Yb‐Tm)/(Cu2O) composite films formed by electrodeposition exhibit robust photoactive current generation under NIR light excitation. The composite films consist of homogeneous crystalline particles of the fluoride and Cu2O in sub‐micrometer size. From spectroscopic characterization, it is found that the NaYF4:Yb‐Tm layer in the composite film converts NIR radiation by up‐conversion into visible emission, which is efficiently absorbed by the covering semiconducting Cu2O film, producing photoelectrons. Accordingly, the composite films exhibit highly photoactive current generation by means of a photoelectrochemical process driven by NIR irradiation. The methodology demonstrated here may have certain implications for the utilization of NIR radiation in solar cells, photocatalysts, and infrared photodetectors.

Raman investigation and glass-compositional dependence on blue up-conversion photoluminescence for Tm^3+/Yb^3+ co-doped TeO_2-TlO_05-ZnO glasses

In this study, glass-compositional dependence of Tm3+ blue up-conversion photoluminescence (UCPL), which is known to be obtained via three-steps’ energy transfers from Yb3+ to Tm3+ ions under near-infrared light excitation at ~980 nm, is investigated for Tm3+/Yb3+ co-doped TeO2-TlO0.5-ZnO glasses. The third step of energy transfer from Yb3+ to Tm3+ ions is particularly important ((Yb3+, Tm3+); (2F5/2, 3H4)→(2F7/2, 1G4)) since it determines the final blue UCPL intensity from 1G4 level compared to red and near-infrared UCPLs, and so then estimated with varied TlO0.5 and ZnO contents at the expense of TeO2 in the fixed Tm3+ and Yb3+ contents ([Yb3+]/[Tm3+] = 5). The substantial energy transfer rate (ETR) in the third step is evaluated from excitation power dependence of the blue UCPL intensity in comparison with near-infrared UCPL of Tm3+ ions with an aid of analytical method of PL lifetime and Judd-Ofelt theory. It is here revealed that the highest ETR is achieved to be 3.54 × 10−17 cm3/s for the glass composition of 70TeO2-10TlO0.5-19.4ZnO-0.1Tm2O3-0.5Yb2O3, and that the transfer rate is possibly related with the length of TeO2 glass network because a long tellurite glass network can cause segregation of rare-earth elements inducing effective Yb3+-Yb3+ energy migration and less quenching centers like dangling bonds of isolated TeO32-, resulted in the enhancement of the energy transfer for blue UCPL.

Nd2O3/Au nanocomposites: upconversion broadband emission and enhancement under near-infrared light excitation

In the present work, the novel Nd2O3/Au nanocomposites were successfully prepared by a co-precipitation process, which realized the upconversion broadband emission and enhancement under near infrared light excitation.

Synthesis and upconversion luminescent properties of BaMgF4：Er3+, Yb3+ nanocrystals

BaMgF4:Er3+, Yb3+ nanocrystals in rod-shape are synthesized by means of the reverse co-precipitation. They emit green and red light under excitation of near-infrared light (980 nm). The green and red emissions may be attributed to the 2H11/24I15/2, 4S3/24I15/2 and 4F9/24I15/2 transitions of Er3+. Dopant ions Yb3+ as sensibilizers can improve the upconversion transformation efficiency. The emission intensity is the strongest when the contents of Er3+ and Yb3+ are 3% and 10%, respectively. With increasing concentration of Yb3+, the red emission intensity increases while the green emission reduces. And the conversion fitting curve between the luminous intensity and pump current indicates that the upconversion process of the green and red light of BaMgF4: Er3+, Yb3+ is due to two-photon absorption.

Long persistent and photo-stimulated luminescence in Cr3+-doped Zn–Ga–Sn–O phosphors for deep and reproducible tissue imaging

A phosphor with remarkable long persistent luminescence features, Zn3Ga2Sn1O8:0.5 Cr3+, suitable for deep and reproducible tissue imaging has been rationally designed and successfully fabricated. This phosphor shows bright and long persistent luminescence over 300 h in the near-infrared region, and permits an enabling long-term, reproducible, real-time and reliable structural imaging of deep tissues. Moreover, the revived luminescence and persistent luminescence under the excitation of near-infrared incoherent light are also demonstrated to reveal an optional multiplexed detection. This new luminescent indicator will allow repeatable visualization of the structural and functional processes in cells, tissues and other complex systems. In addition, multifarious and systematic investigations are successfully carried out to unravel the nature of traps and also to verify the rationality of the material design.

Recent advances in the optimization and functionalization of upconversion nanomaterials for in vivo bioapplications

Upconversion nanophosphors are considered to be important components in advanced materials designed for in vivo bioapplications and benefit from their unique anti-Stokes upconversion luminescence properties. The near-infrared light excitation allows for a large penetration depth in biotissues during in vivo applications. This review presents recent advances in the optimization and functionalization of upconversion nanomaterials for bioimaging and in vivo therapy. The most effective protocols are introduced in detail. Current limitations and future prospects are also included to provide a general summary and suggest future research directions. Upconversion nanophosphors have unique ability to generate anti-Stokes luminescence. The rapid developments of nanotechnology in recent years have demonstrated the successful synthesis and optimization of such upconversion nanophosphors. This review summarizes the recent advances using upconversion nanophosphors as bioprobe for in vivo applications. Upconversion nanoparticles emit photons at shorter wavelengths than the wavelengths of the photons they absorb under excitation, and thus convert low-energy light into higher-energy light. With obvious potential for solar cells, these nanoparticles also show promise in bioimaging and therapeutic applications: they can be excited by near-infrared radiation and emit shorter near-infrared or visible light, leading to minimal scattering by biological tissues and good penetration depth. Fuyou Li and colleagues from Fudan University, China, review recent progress toward optimizing and functionalizing these nanoparticles for in vivo applications such as multi-modality imaging and near-infrared light-driven therapy. Challenges include insufficient luminescent efficiencies, which can be improved through core-shell structures, as well as the alleviation of overheating effects—achieved, for example, through incorporating additional ions that act as antennas and result in more efficient wavelength conversion. Additionally, the potential toxicity of these inorganic particles—including their distribution and effects in the body—needs to be investigated further.

Neodymium doped lanthanum oxysulfide as optical temperature sensors

The fluorescence intensity ratio (FIR) technique for temperature sensing has been demonstrated in La2O2S:Nd3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffraction, photoluminescence excitation, and photoluminescence spectra. Upon ultraviolet–visible (UV–vis) or near-infrared (NIR) light excitation, two intense NIR emissions of Nd3+ peaking at 897nm and 1074nm corresponding to transitions of 4F3/2→4I9/2 and 4F3/2→4I11/2 were generated at room temperature. NIR emission of Nd3+ in a wide temperature range from 30K to 600K was investigated. Experimental results show that the temperature evaluation can be realized by monitoring the emission peak position, measuring the fluorescence intensity ratio of 4F5/2 and 4F3/2 or that of the two Stark components of the 4F3/2 level in the bulk La2O2S:Nd3+. Furthermore, the effective energy difference of the thermalized levels 4F5/2 and 4F3/2, and 4F3/2 two Stark components were 987cm−1 and 110cm−1, respectively. Those results imply that La2O2S:Nd3+ phosphor is a potential candidate for the optical temperature sensor.

Micromolding in Capillaries for Calcination-Free Fabrication of Flexible Inorganic Phosphor Films Consisting of Rare-Earth-Ion-Doped Nanoparticles

We discuss the micromolding in capillaries technique for the direct fabrication of calcination-free rare earth ion-doped (RE) phosphor films consisting of RE nanoparticles on plastic sheets. We synthesized two types of RE nanoparticles consisting of Y2O3 matrix doped with Er and Yb ions. Green upconversion luminescence, red upconversion luminescence, and near-infrared fluorescence appeared from the RE nanoparticles under excitation of near-infrared light. Adjusting the channel width and depth of polydimethylsiloxane molds led to control of the density of nanoparticles in the patterned RE nanoparticle films. Adjusting concentration of the RE nanoparticle dispersion and size of the RE nanoparticles allowed for the control of the density of nanoparticles in the patterned RE nanoparticle films. The density of nanoparticles in the patterned RE films on plastic sheets increased with an increase in the number of injection and drying of the RE nanoparticle dispersion. These results demonstrate that this technique enables us to directly fabricate the patterned RE phosphor films on plastic sheets, leading to the fabrication of inorganic flexible devices with small fabrication steps and material consumptions.

Nd3+-Sensitized Upconversion Nanophosphors: EfficientIn VivoBioimaging Probes with Minimized Heating Effect

Upconversion (UC) process in lanthanide-doped nanomaterials has attracted great research interest for its extensive biological applications in vitro and in vivo, benefiting from the high tissue penetration depth of near-infrared excitation light and low autofluorescence background. However, the 980 nm laser, typically used to trigger the Yb(3+)-sensitized UC process, is strongly absorbed by water in biological structures and could cause severe overheating effect. In this article, we report the extension of the UC excitation spectrum to shorter wavelengths, where water has lower absorption. This is realized by further introducing Nd(3+) as the sensitizer and by building a core/shell structure to ensure successive Nd(3+) → Yb(3+) → activator energy transfer. The efficacy of this Nd(3+)-sensitized UC process is demonstrated in in vivo imaging, and the results confirmed that the laser-induced local overheating effect is greatly minimized.

Upconversion Nanoparticles for Photodynamic Therapy and Other Cancer Therapeutics

Photodynamic therapy (PDT) is a non-invasive treatment modality for a variety of diseases including cancer. PDT based on upconversion nanoparticles (UCNPs) has received much attention in recent years. Under near-infrared (NIR) light excitation, UCNPs are able to emit high-energy visible light, which can activate surrounding photosensitizer (PS) molecules to produce singlet oxygen and kill cancer cells. Owing to the high tissue penetration ability of NIR light, NIR-excited UCNPs can be used to activate PS molecules in much deeper tissues compared to traditional PDT induced by visible or ultraviolet (UV) light. In addition to the application of UCNPs as an energy donor in PDT, via similar mechanisms, they could also be used for the NIR light-triggered drug release or activation of 'caged' imaging or therapeutic molecules. In this review, we will summarize the latest progresses regarding the applications of UCNPs for photodynamic therapy, NIR triggered drug and gene delivery, as well as several other UCNP-based cancer therapeutic approaches. The future prospects and challenges in this emerging field will be also discussed.

Indocyanine green fluorescence endoscopy for visual differentiation of pituitary tumor from surrounding structures

As demonstrated by histological and neuroimaging studies, pituitary adenomas have a capillary vascular density that differs significantly from that of surrounding structures. The authors hypothesized that intraoperative indocyanine green (ICG) fluorescence endoscopy could be used to visually differentiate tumor from surrounding tissues, including normal pituitary gland and dura. After institutional review board approval, 16 patients undergoing endoscopic transsphenoidal surgery for benign pituitary lesions were prospectively enrolled in the study. A standard endoscopic endonasal approach to the sella was completed. Each patient then underwent endoscopic examination of the sellar dura and then the exposed pituitary adenoma after ICG bolus injection (12.5-25 mg). This examination was performed using a custom endoscope with a near-infrared light source and excitation wavelength filter. The authors successfully recorded ICG fluorescence from sellar dura, pituitary, and surrounding structures in 12 of 16 patients enrolled. There were 3 technical failures of intraoperative ICG endoscopy, and 1 patient was excluded following discovery of a dye cross-allergy. A standard dose of 25 mg of ICG in 10 ml of aqueous solution optimized visualization of sellar region microvasculature within 45 seconds of peripheral bolus injection. Adenoma was less fluorescent than normal pituitary gland. Dural invasion by tumor was identifiable by a marked increase in fluorescence compared with native dura. The ICG endoscopic examination added 15-20 minutes of operative time under general anesthesia. There were no complications that resulted from use of ICG or the fluorescent light source. Indocyanine green fluorescence endoscopy shows promise as an intraoperative modality to visually distinguish pituitary tumors from normal tissue and to visually identify areas of dural invasion, thereby facilitating complete tumor resection and minimizing injury to surrounding structures. These results support the continued development of fluorescence endoscopic resection techniques.

Near-infrared light sensitive polypeptide block copolymer micelles for drug delivery

A new biocompatible block copolymer (BCP) composed of poly(ethylene oxide) (PEO) and poly(L-glutamic acid) bearing a number of 6-bromo-7-hydroxycoumarin-4-ylmethyl groups, PEO114-b-P(LGA0.62-co-COU0.38)34, was prepared for near-infrared (NIR) light-induced drug delivery. We demonstrate that micelles of PEO114-b-P(LGA0.62-co-COU0.38)34 could be disrupted by 794 nm NIR light excitation via two-photon absorption. This was linked to the high two-photon absorption cross-section of the coumarin moiety. Disruption followed from the NIR light-induced removal of coumarin groups from the polypeptide block that shifted the hydrophilic–hydrophobic balance toward the destabilization of the micelles in aqueous solution. Using NIR light-triggered disruption of BCP micelles, we investigated the release of an antibacterial drug (Rifampicin) and an anticancer drug (Paclitaxel) loaded into the photosensitive BCP micelles. We found that the two drugs could be released effectively upon NIR light exposure of the micellar solution. To our knowledge, this is the first study of NIR light-triggered disruption of biocompatible polypeptide BCP micelles and its use for drug release. This is a step forward towards light-controllable drug delivery applications.

Near-Infrared Light-Triggered Dissociation of Block Copolymer Micelles Using Upconverting Nanoparticles

We demonstrate a novel strategy enabling the use of a continuous-wave diode near-infrared (NIR) laser to disrupt block copolymer (BCP) micelles and trigger the release of their "payloads". By encapsulating NaYF(4):TmYb upconverting nanoparticles (UCNPs) inside micelles of poly(ethylene oxide)-block-poly(4,5-dimethoxy-2-nitrobenzyl methacrylate) and exposing the micellar solution to 980 nm light, photons in the UV region are emitted by the UCNPs, which in turn are absorbed by o-nitrobenzyl groups on the micelle core-forming block, activating the photocleavage reaction and leading to the dissociation of BCP micelles and release of co-loaded hydrophobic species. Our strategy of using UCNPs as an internal UV or visible light source upon NIR light excitation represents a general and efficient method to circumvent the need for UV or visible light excitation that is a common drawback for light-responsive polymeric systems developed for potential biomedical applications.

Strong dependence of upconversion luminescence on doping concentration in holmium and ytterbium co-doped Y 2O 3 phosphor

Under the excitation of 980 nm diode laser, intense green emission ( 5F 4+ 5S 2- 5I 8) of Ho 3+ was observed in Ho 3+ and Yb 3+ co-doped cubic Y 2O 3. The doping concentration and laser power dependence of the upconverted emission were studied. The decay curves of 5F 4+ 5S 2 emission of Ho 3+ under the excitation of 355 nm pulse laser were measured to investigate the energy transfer process between Ho 3+ and Yb 3+. The results indicated that two-photon process was responsible for the upconversion (UC) emission. The Ho 3+ concentration of 0.04 mol.% and the Yb 3+ concentration of 5 mol.% were determined to be the best value for the strongest Ho 3+ emission under the excitation of 980 nm light. The cross-relaxation between two neighboring Ho 3+ ions and the back energy transfer from Ho 3+ to Yb 3+ were important factors for determining the optimal doping concentration. This material was a promising candidate for the application in biomedical fluorescent labels for the intense green emission upon excitation of near-infrared (NIR) light.