Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications

Upconversion nanoparticles (UCNPs) convert low‐energy infrared (IR) or near‐infrared (NIR) photons into high‐energy emission radiation ranging from ultraviolet to visible through a photon upconversion process. In comparison to conventional fluorophores, such as organic dyes or semiconductor quantum dots, lanthanide‐ion‐doped UCNPs exhibit high photostability, no photoblinking, no photobleaching, low cytotoxicity, sharp emission lines, and long luminescent lifetimes. Additionally, the use of IR or NIR for excitation in such UCNPs reduces the autofluorescence background and enables deeper penetration into biological samples due to reduced light scattering with negligible damage to the samples. Because of these attributes, UCNPs have found numerous potential applications in biological and medicinal fields as novel fluorescent materials. Different upconversion mechanisms commonly observed in UCNPs, various methods that are used in their synthesis, and surface modification processes are discussed. Recent applications of Ln‐UCNPs in the biological and medicinal fields, including in vivo and in vitro biological imaging, multimodal imaging, photodynamic therapy, drug delivery, and antibacterial activity, are also presented.     

Thiol-Capped CdTe Quantum Dots with Two-Photon Excitation for Imaging High Autofluorescence Background Living Cells

To effectively image living cells with quantum dots (QDs), particularly for those cells containing high content of native fluorophores, the two-photon excitation (TPE) with a femto-second 800 nm laser was employed and compared with the single-photon excitations (SPE) of 405 nm and 488 nm in BY-2 Tobacco (BY-2-T) and human hepatocellular carcinoma (QGY) cells, respectively. The 405 nm SPE produced the bright photoluminescence (PL) signals of cellular QDs but also induced a strong autofluorescence(AF) from the native fluorophores like flavins in cells. The AF occupied about 30% and 13% of the total signals detected in QD imaging channel in the BY-2-T and QGY cells, respectively. With the excitation of 488 nm SPE, the PL signals were lower than those excited with the 405 nm SPE, although the AF signals were also reduced. The 800 nm TPE generated the best PL images of intracellular QDs with the highest signal ratio of PL to AF, because the two-photon absorption cross section of QDs is much higher than that of the native fluorophores. By means of the TPE, the reliable cellular imaging with QDs, even for the cells having the high AF background, can be achieved.     

Photostability comparison of CdTe and CdSe/CdS/ZnS quantum dots in living cells under single and two-photon excitations

The photostability is an outstanding feature of quantum dots (QDs) used as fluorescence probes in biological staining and cell imaging. To find out the related factors in the QD photostability, the photobleaching of naked CdTe QDs and BSA coated CdSe/CdS/ZnS QDs in human hepatocellular carcinoma (QGY) cells and human nasopharynx carcinoma (KB) cells were studied under single photon excitation (SPE) and two-photon excitation (TPE). In these two cell lines the cellular QDs were irradiated by a 405 nm continuous wave laser for SPE or an 800 nm femto-second (fs) laser for TPE. The QD photobleaching with the irradiation time was found to fit a biexponential decay. The fast decay plays a dominant role in the bleaching course and thus can be used as the parameter to quantitatively evaluate the QD photostability. The TPE decreased the QD photobleaching as compared to SPE. The BSA coated core/shell QDs had improved the photostability up to 4-5 times than the naked QDs due to the shielding effect of the QD shell. Therefore, it is better to use core/shell structured QDs as the fluorescence probe combining with a TPE manner for those long-term monitoring studies.     

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS₂+Ga₂O₃ (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics.     

Previous illumination of a water soluble chlorine photosensitizer increases its cytotoxicity

Photodithazine (PDZ) is an N-methyl-D-glucosamine derivative of chlorine e6 that is water soluble and has an intense absorption in the range of 650?C680 nm. PDZ photobleaching and photoproduct formation were induced by illumination with laser at two wavelengths: 514 nm (ion argon laser) as well as in 630 nm (dye laser). The time constants of PDZ photobleaching were: 18 min for 630 nm irradiation and 50 min for 514 nm irradiation, suggesting that degradation after irradiation with red light is faster than with green light. Photoproducts formation was evidenced by the appearance of a new absorption band at 668 nm with slight broaden of the Soret band, suggesting that there was no break of the macrocycle. The cytotoxicity of the photodegradated PDZ was investigated and showed to be lower in the dark and higher than non irradiated PDZ. These results may have important clinical implications for PDT such as the possibility to use the previously irradiated PDZ just before clinical application in order to get increased efficiency.     

Detection of biotin–avidin affinity binding by exploiting a self-referenced system composed of upconverting luminescent nanoparticles and gold nanoparticles

We demonstrate an affinity system based on the interaction of two types of nanoparticles. The first consists of upconverting luminescent NaYF₄:Yb,Er nanoparticles (UCNPs) with a size of 40–100 nm, absorbing light in the infrared and showing luminescence at 521, 543 and at 657 nm. The second consists of (red) gold nanoparticles (Au-NPs) with a size of about 50 nm and capable of absorbing the green luminescence of the UCNPs. By labeling the UCNPs with avidin and the AuNPs with biotin we have established a model system for a self referenced affinity system applicable to sensing in biological samples. In the presence of avidin-modified UCNPs, the biotinylated Au-NPs can be detected in the range from 12 to 250 μg mL⁻¹ by ratioing the intensity of the red (analyte-independent) emission to that of the green (analyte-dependent) emission band. The nanoparticles were characterized in terms of size and composition using transmission electron microscopy, thermogravimetry, and FTIR spectroscopy.     

FITC Labeled Silica Nanoparticles as Efficient Cell Tags: Uptake and Photostability Study in Endothelial Cells

The use of fluorescent nanomaterials has gained great importance in the field of medical imaging. Many traditional imaging technologies have been reported utilizing dyes in the past. These methods face drawbacks due to non-specific accumulation and photobleaching of dyes. We studied the uptake and internalization of two different sized (30 nm and 100 nm) FITC labeled silica nanoparticles in Human umbilical vein endothelial cell line. These nanomaterials show high biocompatability and are highly photostable inside live cells for increased period of time in comparison to the dye alone. To our knowledge, we report for the first time the use of 30 nm fluorescent silica nanoparticles as efficient endothelial tags along with the well studied 100 nm particles. We also have emphasized the good photostability of these materials in live cells.     

Photostability of Cy3 and Cy5-Labeled DNA in the Presence of Metallic Silver Particles

We examined the photostability of a double-stranded DNA oligomer, covalently labeled with Cy3 or Cy5 on one strand, in the presence of metallic silver island films. In our experimental configuration a minor fraction of the labeled DNA was close to the silver particles and the remainder was distant from the particles. Proximity of the fluorophores to silver island films resulted in increased intensity. Upon continuous illumination we found a fraction of the emission that was resistant to the photobleaching. The emission spectra of the residual fractions were identical to the initial spectra. The frequency-domain lifetime measurements of this fraction revealed greatly shortened decay times. These results are consistent with the photostable fraction being close to the silver particles. This results suggest that the number of photons detected per fluorophore, prior to photobleaching, can be increased 5-fold or more by proximity to silver particles. Localization at an optimal distance from the silver surface may result in larger enhancements.     

Highly Bright and Photostable Li(Gd,Y)F4:Yb,Er/LiGdF4 Core/Shell Upconversion Nanophosphors for Bioimaging Applications

Intense green‐emitting Li(Gd,Y)F₄:Yb,Er/LiGdF₄ core/shell (C/S) upconversion nanophosphors (UCNPs) with a tetragonal bipyramidal morphology are synthesized. The morphology and UC luminescence of the Li(Gd,Y)F₄:Yb,Er UCNPs are significantly affected by the Li precursors, and bright UC green‐emitting Li(Gd,Y)F₄:Yb,Er UCNPs with a tetragonal bipyramidal shape, i.e., UC tetragonal bipyramids (UCTBs), are synthesized using LiOH·H₂O as a Li precursor. A LiGdF₄ shell is grown on the Li(Gd,Y)F₄:Yb,Er UCTBs, and the C/S UCNPs exhibit 4.7 times higher luminescence intensity than core UCTBs. The C/S UCNPs show a high absolute UC quantum yield of 4.6% under excitation with 980 nm near infrared (NIR) light, and the UC luminescence from the C/S UCNPs is stable under continuous irradiation with the 980 nm NIR laser for 1 h. The hydrophobic surfaces of the as‐synthesized C/S UCNPs are modified to hydrophilic surfaces by using poly(acrylic acid) (PAA) for bioimaging applications. They are applied to human cervical adenocarcinoma (HeLa) cell imaging and SK‐MEL‐2 melanoma cell imaging and in vivo imaging, including subcutaneous and intramuscular imaging, and UC luminescence images with high signal‐to‐noise ratio are obtained. Furthermore, sentinel‐lymph‐node imaging is successfully conducted with the PAA‐capped Li(Gd,Y)F₄:Yb,Er/LiGdF₄ C/S UCNPs under illumination with NIR light.     

基于近红外上转换荧光共振能量传递体系的均相免疫分析

在上转换纳米晶(UCNPs)为供体的荧光共振能量传递(FRET)生物均相检测体系中,弱的供体光强度使FRET信号难于检测,同时还有来自生物基质的自发荧光干扰。这使得UCNPs不产生背景荧光和散射光的优点不能够充分地体现。针对这个问题,作者利用在800nm处有强近红外光的NaYF4:Yb3+,Tm3+UCNPs作为供体,在784nm处有表面等离子共振吸收带的金纳米粒子(GNPs)作为受体构建了新型的FRET体系。UCNPs偶联抗体(goat antihumanIgG)及GNPs偶联抗原(humanIgG),在抗原抗体免疫亲和作用下两者距离靠近;UCNPs荧光光谱和GNPs吸收光谱有效交叠,使FRET发生。当体系中加入单纯humanIgG,竞争性地争夺与goatantihumanIgG结合位点,破坏FRET构建,供体近红外光增强。根据此对应关系,确定humanIgG检测限为5μg·mL-1。这种方法可适用于更广泛的荧光分析。     

In situ optical measurements of bacterial endospore breakdown in a shock tube

The interaction of endospore-laden bioaerosols and shock waves is monitored with a combination of laser absorption and scattering. Tests are performed in the Stanford aerosol shock tube for post-shock temperatures ranging from 400–1100 K. In situ laser measurements at 266 and 665 nm provide a real-time monitor of endospore morphology. Scatter of visible light measures the integrity of endospore structure, while absorption of UV light provides a monitor of biochemicals released by endospore rupture. For post-shock temperatures greater than 750 K endospore morphological breakdown is observed. A simple theoretical model is employed to quantify the optical measurements, and mechanisms leading to the observed data are discussed.     

Influence of the nanoparticle sizes on the photo-induced absorption of La–Ga–S–O–Dy glass nanocomposites

We have established that the illumination by two coherent beams originating from nanosecond Nd:YAG laser at wavelengths 1064 nm and 532 nm in the La–Ga–S–O–Gd:PVA La-Ga-S-O-Dy polymer glass nanocomposites leads to substantial changes in the absorption. The effect is completely reversible and disappears after interruption of the optical treatment. The illumination power density was varied up to 0.6 GW/cm². All the samples show destruction less than 0.2% changes after more than 300,000 laser pulses. The beams were incident with the angles varying between 45° and 50° with respect to the nanocomposite surface. Moreover, the additional analysis of TEM did not demonstrate any additional aggregations. The role of light polarizations, beam stability, and light scattering is discussed.     

Acoustically induced light gyration in nickel nanoparticles

Circularly polarized acoustically induced light gyration (AILG) in nickel nanoparticles (NiNPs) attached to indium tin oxide (ITO) substrates was observed to be enhanced by nanosecond UV laser excitation at a wavelength in the surface plasmon resonance region. The AILG was observed during exposure to two acoustical waves with frequencies of 2 and 4 MHz and power densities of up to 5 W/cm². The maximum value of the AILG observed for NiNPs of average size ca. 8.7 nm, attached to an ITO substrate was about 2.8°/mm without UV-light illumination. Additional irradiation by 5 ns pulse UV laser light (λ: 337 nm) at the surface plasmon resonance region was found to favour the additional enhancement of the AILG up to 11°/mm. The effect was optimized at a temperature of 120 K. This increase was not observed when the size of NiNPs was 16.8 nm.     

Monitor for detecting and assessing exposure to airborne nanoparticles

An important safety aspect of the workplace environment concerns the severity of its air pollution with nanoparticles (NP; <100 nm) and ultrafine particles (UFP; <300 nm). Depending on their size and chemical nature, exposure to these particles through inhalation can be hazardous because of their intrinsic ability to deposit in the deep lung regions and the possibility to subsequently pass into the blood stream. Recommended safety measures in the nanomaterials industry are pragmatic, aiming at exposure minimization in general, and advocating continuous control by monitoring both the workplace air pollution level and the personal exposure to airborne NPs. This article describes the design and operation of the Aerasense NP monitor that enables intelligence gathering in particular with respect to airborne particles in the 10–300 nm size range. The NP monitor provides real time information about their number concentration, average size, and surface areas per unit volume of inhaled air that deposit in the various compartments of the respiratory tract. The monitor’s functionality relies on electrical charging of airborne particles and subsequent measurements of the total particle charge concentration under various conditions. Information obtained with the NP monitor in a typical workplace environment has been compared with simultaneously recorded data from a Scanning Mobility Particle Sizer (SMPS) capable of measuring the particle size distribution in the 11–1086 nm size range. When the toxicological properties of the engineered and/or released particles in the workplace are known, personal exposure monitoring allows a risk assessment to be made for a worker during each workday, when the workplace-produced particles can be distinguished from other (ambient) particles.     

Self-grown fiber fabrication by two-photon photopolymerization

We demonstrate a new fiber growth mechanism in a photocurable resin by ultrafast laser illumination. A high-repetition rate (∼1 MHz) ultrafast laser beam at the wavelength of ∼523 nm was focused into an ultraviolet photocurable resin to trigger two-photon photopolymerization process. Time-resolved shadowgraphs and scattered light imaging revealed that the curing commenced in the neighborhood of the geometric focal point of the laser beam and that the fiber growth progressed mostly towards the laser source. The cured fiber was thinner and longer than the profile of the focused laser beam, facilitated by nonlinear propagation and absorption of the ultra-fast laser beam. The achieved aspect ratio of the fiber was higher than 180 with ∼10 μm mean diameter, and the average growth rate was up to ∼2 mm/s.     

A high-sensitivity in situ optical diagnostic technique for laser cleaning of transparent substrates

A differential optical transmission technique has been used to monitor in situ the efficiency of laser cleaning for the removal of sub-micrometer-sized particles on substrates transparent at the monitoring wavelength. This technique has been applied to the removal of sub-micrometer polystyrene particles on polyimide substrates using laser pulses of 30 ps duration at 292 nm while probing the material transmission at 633 nm. The sensitivity achieved -1/10⁴ for the transmission changes induced upon single-pulse laser exposure – allows us to monitor the removal of just a few sub-micron-sized particles from the probed region inside the irradiated area. Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +33-3/87844082, E-mail: nchaoui@iut.univ-metz.fr RID="**" ID="**"Present address: Laboratoire de Chimie et Applications, Institut Universitaire de Technologie de Metz, Département Chimie, Rue Victor Demange, 57500 Saint-Avold, France     

Two-pass amplification of CW laser by Nd/Cr:YAG ceramic Active mirror under lamp light pumping

The concept of an Active mirror with transparent Nd/Cr:YAG ceramics is proposed. A new ceramic material pumped by an arc-metal-halide lamp has been experimentally implemented. CW-laser light generated in a 1064 nm Nd:YAG micro-tip oscillator was amplified by an Active mirror made of Nd/Cr:YAG ceramic and pumped by CW arc-lamp light. The saturation power density of the Nd/Cr:YAG ceramic was lower than that of Nd:YAG because the stimulated-cross-section and lifetime were effectively enhanced by the sensitization of Cr ions. The maximum output laser power while keeping spatial beam quality was up to 3 W with an input lamp power of 9 W; the resulting optical-optical conversion efficiency of 33% was close to the theoretical prediction of nearly 50%.     

Optical properties of pulsed laser heated soot

To investigate the transient change of soot optical properties resulting from pulsed laser heating of soot in a cooled exhaust plume we have simultaneously performed cw light extinction at 405 and 830 nm and elastic light scattering at 1064 nm. A reversible increase to the 830-nm light extinction of up to 7%, observed during the time period where the soot was hot, suggests a temperature-dependent light absorption refractive index function, E(m _λ ). At low fluence, small permanent increases of E(m _λ ) of <2% were also observed. 405-nm extinction measurements revealed that the soot likely contained material which continued to absorb 405-nm radiation when desorbed, thus complicating measurement interpretation. 1064-nm light scattering measurements showed a gradual decrease of scattering propensity with increasing laser fluence up to the point of material loss, which is consistent with the expected decrease of the structure factor of the soot aggregates as they expand. It is concluded that variations of the optical properties are occurring at the time of laser-induced incandescence (LII) emission, which should be accounted for in time-resolved LII measurement interpretation.     

Light quenching of tetraphenylbutadiene fluorescence observed during two-photon excitation

We observed the steady-state and time-resolved emission of tetraphenylbutadiene (TPB) whea excited by simultaneous absorption of two photons (514 to 610 nm). The intensity initially increased quadratically with laser power, as expected for a two-photon process. At higher laser powers the intensity increases in TPB were subquadratic. The intensity and anisotropy decay times of TPB were unchanged under the locally intense illumination. Importantly, the time zero anisotropy of TPB was decreased under conditions where the intensity was subquadratic. Furthermore, the subquadratic dependence on incident power was not observed for two-photon excitation of 2,5-diphenyloxazole (PPO), for which the incident wavelength does not overlap with the emission spectrum. These results are consistent with stimulated emission (light quenching) of TPB at high laser intensities. The phenomenon of light quenching may be important for other fluorophores used in biochemical research, particularly for the high local intensities used for two-photon excitation.     

The fabrication and photo-induced melting of networked gold nanostructures and twisted gold nanorods

Fabrications of both networked Au nanostructured particles and twisted gold nanorods (TGNRs) suspended in water were accomplished via a laser ablation technique. They can be further purified by simple filtration. We conducted the photo-induced melting studies on these two types of nanostructures under both 532 and 1064 nm laser irradiation wavelengths. Both structural changes and their absorption spectral responses are reported. The TGNR sample contains particles with a wide distribution of aspect ratios. Its typical absorption spectrum shows a flat and continuously rising feature to the red of ca. 520 nm, which show a similarity with that of the suspended Au networks. The photo-induced melting processes corresponding to these two types of Au nanostructures demonstrate quite different spectral responses associated with their structural variations. Various observations on the wavelength- and laser power-dependence are presented. Generally, this type of photoannealing results in a formation of spherical shaped particles. Among them, we demonstrate that a spectral ‘hole’ burning can be uniquely achieved in the case of TGNRs suspension after 1064 nm low-fluence laser beam irradiation. Its contribution based on a selective melting will be addressed.