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Cell-cell communication is important for cellular differentiation, organ function, and immune responses. In intercellular communication, the extracellular vesicles (EVs) play a significant role in delivering the cargo molecules such as genes, proteins, and enzymes, to regulate and control the ability of the recipient cells. In this study, the observation of intercellular cargo transfer

Upconverting nanoparticles (UCNPs) have been extensively investigated for nanophotonics and biomedical applications. However, establishing a unified view of their emission characteristics to elucidate the underlying photophysics and expand the application fields of these materials is a great challenge due to their sophisticated internal energy transfer and lack of standardized single-particle spectroscopy (SPS) platform. Here, we present an SPS technique called multiband single-particle irradiance-dependent imaging (multiband SPIDI). We demonstrate that the emission characteristics of Yb

Materials whose luminescence can be switched by optical stimulation drive technologies ranging from superresolution imaging1-4, nanophotonics5, and optical data storage6-8, to targeted pharmacology, optogenetics, and chemical reactivity9. These photoswitchable probes, including organic fluorophores and proteins, are prone to photodegradation, and often require phototoxic doses of ultraviolet (UV) or visible light. Colloidal inorganic nanoparticles have significant stability advantages over existing photoswitchable materials, but the ability to switch emission bidirectionally, particularly with NIR light, has not been reported with nanoparticles. Here, we present 2-way, near-infrared (NIR) photoswitching of avalanching nanoparticles (ANPs), showing full optical control of upconverted emission using phototriggers in the NIR-I and NIR-II spectral regions useful for subsurface imaging. Employing single-step photodarkening10-13 and photobrightening12,14-18, we demonstrate indefinite photoswitching of individual nanoparticles (>1000 cycles over 7 h) in ambient or aqueous conditions without measurable photodegradation. Critical steps of the photoswitching mechanism are elucidated by modeling and by measuring the photon avalanche properties of single ANPs in both bright and dark states. Unlimited, reversible photoswitching of ANPs enables indefinitely rewritable 2D and 3D multi-level optical patterning of ANPs, as well as optical nanoscopy with sub-{\AA} localization superresolution that allows us to distinguish individual ANPs within tightly packed clusters., Comment: 15 pages, 5 figures

Plasmonic coupling of metallic nanostructures with two-dimensional molybdenum disulfide (MoS2) atomic layers is an important topic because it provides a pathway to manipulate the optoelectronic properties and to overcome the limited optical cross-section of the materials. Plasmonic enhanced light-matter interaction of a MoS2 layer is known to be mainly governed by optical field enhancement and the Purcell effect, while the discrimination of the contribution from each mechanism to the plasmonic enhancement is challenging. Here, we investigate photoluminescence (PL) enhancement from few-layer MoS2 transferred on Au nanostructure arrays with controlled localized surface plasmon resonance (LSPR) spectral positions that were detuned from the excitation wavelengths. Two distinctive regimes in LSPR mode-dependent PL enhancement were revealed showing a maximum enhancement (∼40-fold) with zero detuning and a modest enhancement (∼10-fold) with the red-shift detuned LSPR from the excitation wavelength, which were attributed to LSPR-induced optical field enhancement and the Purcell effect, respectively. By applying the experimental parameters into the Purcell effect formalism, an effective mode volume of ∼0.016λ03 was estimated. Our work provides an insight into how to utilize few-layer MoS2 as a base material for optoelectronics by harnessing Purcell-enhanced optical responsivity.

In this study, a three-stage bio-aerosol sampler with a sampling flow rate of 170 L/min was designed and fabricated for sampling the bio-aerosols released during human breathing and coughing, and its performance was evaluated. The sampler was constructed using a cyclone separator with a cutoff size of 2.5 μm as a preseparator, a multinozzle virtual impactor with a cutoff size of 0.34 μm as an aerosol concentrator, and a Bio-Sampler, which is a commercial product, for collecting bio-aerosols in a collection fluid. The collection efficiency of the sampler was evaluated through simulations and experiments. Only particles with sizes of 0.1–4 μm were selectively collected in the collection fluid. Bacteriophage bio-aerosols were sampled using the developed sampler and ACD-200 Bobcat sampler, which is a commercial product. The amounts of collected bacteriophages were compared using the polymerase chain reaction (PCR) technique. The sampling performance of the developed sampler was similar to that of the ACD-200 Bobcat sampler. Moreover, the developed sampler showed its ability to sample bio-aerosols of a specific size range and collect them directly in a collection fluid for the PCR analysis. Therefore, the developed sampler is expected to be useful for indoor environmental monitoring by effectively sampling the bio-aerosols released indoors during human breathing and coughing.

Ultrathin nanomaterials are very significant members of the nanocrystalline material family because of their unique properties of broad significance. In the present study, highly uniform atomically thick YF3 nanobelts and nanowires are fabricated by using an oleylamine assisted colloidal chemical strategy. Reaction monitoring demonstrates that two-dimensional lamellar assemblies of YF3 clusters are vital intermediates in the growth process, which transform to ultrathin nanobelts and nanowires depending on the heating temperature. This approach can be readily extended to produce ultrathin structures of other lanthanide fluoride (ErF3, YbF3, TmF3, NdF3, and LaF3) systems. The polarized upconversion emission of Yb3+/Er3+ co-doped YF3 is demonstrated for a domain of a perfectly aligned assembly of parallel ultrathin nanowires. The polarization degree of green, red and infrared emission peaks are 0.32, 0.28 and 0.50, respectively.

Plasmonic coupling of metallic nanostructures with two-dimensional molybdenum disulfide (MoS2) atomic layers is an important topic because it provides a pathway to manipulate the optoelectronic properties and to overcome the limited optical cross-section of the materials. Plasmonic enhanced light-matter interaction of a MoS2 layer is known to be mainly governed by optical field enhancement and the Purcell effect, while the discrimination of the contribution from each mechanism to the plasmonic enhancement is challenging. Here, we investigate photoluminescence (PL) enhancement from few-layer MoS2 transferred on Au nanostructure arrays with controlled localized surface plasmon resonance (LSPR) spectral positions that were detuned from the excitation wavelengths. Two distinctive regimes in LSPR mode-dependent PL enhancement were revealed showing a maximum enhancement (∼40-fold) with zero detuning and a modest enhancement (∼10-fold) with the red-shift detuned LSPR from the excitation wavelength, which were attributed to LSPR-induced optical field enhancement and the Purcell effect, respectively. By applying the experimental parameters into the Purcell effect formalism, an effective mode volume of ∼0.016λ03 was estimated. Our work provides an insight into how to utilize few-layer MoS2 as a base material for optoelectronics by harnessing Purcell-enhanced optical responsivity.

Fabrication of plasmonic nanostructures in a precise and reliable manner is a topic of huge interest because their structural details significantly affect their plasmonic properties. Herein, we present nanotip indentation lithography (NTIL) based on atomic force microscopy (AFM) indentation for the patterning of plasmonic nanostructures with precisely controlled size and shape. The size of the nanostructures is controlled by varying the indentation force of AFM tips into the mask polymer; while their shapes are determined to be nanodisks (NDs) or nanotriangles (NTs) depending on the shapes of the AFM tip apex. The localized surface plasmon resonance of the NDs is tailored to cover most of the visible-wavelength regime by controlling their size. The NTs show distinct polarization-dependent plasmon modes consistent with full-wave optical simulations. For the demonstration of the light–matter interaction control capability of NTIL nanostructures, we show that photoluminescence enhancement from MoS2 layers can be deliberately controlled by tuning the size of the nanostructures. Our results pave the way for the AFM-indentation-based fabrication of plasmonic nanostructures with a highly precise size and shape controllability and reproducibility.

Natural killer (NK) cells, which are cytotoxic lymphocytes of the innate immune system and recognize cancer cells via various immune receptors, are promising agents in cell immunotherapy. To utilize NK cells as a therapeutic agent, their biodistribution and pharmacokinetics need to be evaluated following systemic administration. Therefore, in vivo imaging and tracking with efficient labeling and quantitative analysis of NK cells are required. However, the lack of the phagocytic capacity of NK cells makes it difficult to establish breakthroughs in cell labeling and subsequent in vivo studies. Herein, an effective labeling of upconverting nanoparticles (UCNPs) in NK cells is proposed using electroporation with high sensitivity and stability. The labeling performance of UCNPs functionalized with carboxy-polyethylene glycol (PEG) is better than with methoxy-PEG or with amine-PEG. The labeling efficiency becomes higher, but cell damage is greater as electric field increases; thus, there is an optimum electroporation condition for internalization of UCNPs into NK cells. The tracking and biodistribution imaging analyses of intravenously injected NK cells show that the labeled NK cells are initially distributed primarily in lungs and then spread to the liver and spleen. These advances will accelerate the application of NK cells as key components of immunotherapy against cancer.

Magnetite (Fe3O4)-gold (Au) core-shell nanoparticles (NPs) have unique magnetic and optical properties. When combined with biological moieties, these NPs can offer new strategies for biomedical applications, such as drug delivery and cancer targeting. Here, we present an effective method for the controllable cellular uptake of magnetic core-shell NP systems combined with biological moieties. Vimentin, which is the structural protein, has been biochemically confirmed to affect phagocytosis potently. In addition, vimentin affects exogenic materials internalization into cells even though under multiple inhibitions of biological moieties. In this study, we demonstrate the cellular internalization performance of Fe3O4-Au core-shell NPs with surface modification using a combination of biological moieties. The photofluorescence of vimentin-tagged NPs remained unaffected under multiple inhibition tests, indicating that the NPs were minimally influenced by nystatin, dynasore, cytochalasin D, and even the Muc1 antibody (Ab). Consequently, this result indicates that the Muc1 Ab can target specific molecules and can control specific endocytosis. Besides, we show the possibility of controlling specific endocytosis in colorectal cancer cells.

Avalanche phenomena leverage steeply nonlinear dynamics to generate disproportionately high responses from small perturbations and are found in a multitude of events and materials, enabling technologies including optical phase-conjugate imaging, infrared quantum counting, and efficient upconverted lasing. However, the photon avalanching (PA) mechanism underlying these optical innovations has been observed only in bulk materials and aggregates, and typically at cryogenic temperatures, limiting its utility and impact. Here, we report the realization of PA at room temperature in single nanostructures--small, Tm-doped upconverting nanocrystals--and demonstrate their use in superresolution imaging at near-infrared (NIR) wavelengths within spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by continuous-wave or pulsed lasers and exhibit all of the defining features of PA. These hallmarks include excitation power thresholds, long rise time at threshold, and a dominant excited-state absorption that is >13,000x larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales nonlinearly with the 26th power of pump intensity. This enables the realization of photon-avalanche single-beam superresolution imaging (PASSI), achieving sub-70 nm spatial resolution using only simple scanning confocal microscopy and before any computational analysis. Pairing their steep nonlinearity with existing superresolution techniques and computational methods, ANPs allow for imaging with higher resolution and at ca. 100-fold lower excitation intensities than is possible with other probes. The low PA threshold and exceptional photostability of ANPs also suggest their utility in a diverse array of applications including sub-wavelength bioimaging, IR detection, temperature and pressure transduction, neuromorphic computing, and quantum optics., 14 pages, 4 figures

Correction for ‘Visualization of intercellular cargo transfer using upconverting nanoparticles’ by Yeongchang Goh et al., Nanoscale, 2022, https://doi.org/10.1039/d2nr01999j.

Developing a sensor that identifies and quantifies trace amounts of analyte molecules is crucially important for widespread applications, especially in the areas of chemical and biological detection. By non-invasively identifying the vibrational signatures of the target molecules, surface-enhanced Raman scattering (SERS) has been widely employed as a tool for molecular detection. Here, we report on the reproducible fabrication of wafer-scale dense SERS arrays and single-nanogap level near-field imaging of these dense arrays under ambient conditions. Plasmonic nanogaps densely populated the spaces among globular Ag nanoparticles with an areal density of 120 particles per μm2 upon application of a nanolithography-free simple process consisting of the Ar plasma treatment of a polyethylene terephthalate substrate and subsequent Ag sputter deposition. The compact nanogaps produced a high SERS enhancement factor of 3.3 × 107 and homogeneous (coefficient of variation of 8.1%) SERS response. The local near fields at these nanogaps were visualized using photo-induced force microscopy that simultaneously enabled near-field excitation and near-field force detection under ambient conditions. A high spatial resolution of 3.1 nm was achieved. Taken together, the generation of a large-area SERS array with dense plasmonic nanogaps and the subsequent single-nanogap level characterization of the local near field have profound implications in the nanoplasmonic imaging and sensing applications.

Surface-enhanced Raman scattering (SERS) has been investigated as a promising spectroscopic tool for various assay platforms. However, key challenges, such as the reproducibility and sensitivity of this tool should be addressed to enable it to become a reliable and practical method for future clinical applications. Although the single-molecule sensitivity of SERS has already been proven in dry state analysis, its signal reproducibility remains a key challenge in developing a real assay platform. The signal reproducibility of SERS can be significantly improved by obtaining the Raman signal from the solution state; however, the sensitivity of this method is not satisfactory. In this study, we demonstrate a method to overcome both key challenges by using a solution-state formation of gold-silver core-shell nanodumbbells (GSNDs) with target nucleic acid and nanoscale Ag shell formation, which was proven to exhibit single-molecule sensitivity in dry state analysis. To utilize the concept of a reliable assay platform in solution, diverse parameters such as the length of the target sequences, hybridization conditions, number density of probe sequences, and the Ag shell thickness are investigated. The hybridization yield of Au dimer reaches up to 79.36% for E. faecalis, indicating that the hybridization yields are target sequence dependent. It is strongly correlated with detection limit for the target bacteria. The solution-state GSND-based assay shows a highly sensitive results for bacterial target DNA with no mutual interference and excellent reproducibility. The method can identify extremely low concentrations of bacteria (4.5 cfu mL−1), which is much superior to the conventional PCR (4500 cfu mL−1) and culture-based assays (45 cfu mL−1). The results envision the current GSND-based assay as a promising assay platform for future clinical applications.

Owing to the recent global spread of the new coronavirus SARS-CoV-2, the development of technology to effectively detect viruses in crowded public places is urgently needed. In this study, a three-stage high-volume bioaerosol sampler was developed for the size-selective sampling of bioaerosols through the suction of air at a high flow rate of 1000 L/min. In stage 1, an omnidirectional inlet cyclone separator that can draw air from all directions was applied to collect bioaerosols larger than 10 μm in the collection fluid. In stage 2, an axial flow cyclone separator was used to collect bioaerosols sized between 2.5 and 10 μm in the collection fluid. In stage 3, bioaerosols smaller than 2.5 μm were collected on a filter and extracted in a solution through an elution process using a sodium phosphate buffer. To simulate the suspension of bioparticles including viruses that are attached to other particles in the atmosphere, the aerosol samples were prepared by coagulating aerosolized bacteriophages with Arizona test dust. Then, the coagulated particles were collected for 30 min using the developed bioaerosol sampler, and the samples collected in each stage were analyzed via polymerase chain reaction (PCR) method. The PCR analysis results confirmed that the high-volume bioaerosol sampler enables size-selective bioaerosol sampling even at a high airflow rate of 1000 L/min. The developed high-volume bioaerosol sampler will be useful in detecting viruses through PCR analysis because it can collect bioaerosols within a specific size range.

Although diverse endogenous biomolecules involved in life processes are of major interest in cell biology, there is still a lack of suitable methods for studying biomolecules within live cells without labelling. Herein, we describe a near-infrared (NIR) surface-enhanced Raman scattering (SERS)-based particle tracking technique gathering chemical information inside live cells for monitoring their intracellular dynamics. The wide-field SERS imaging spectroscopy system facilitates high temporal resolution (200 ms) under high spatial resolution (512 × 512 pixels) for one live cell. With high spatiotemporal resolution and signal-to-background ratio, we show that the Raman signal from intracellular cargoes in live cells is sporadically observed and localized to a vesicular level.

Particulate matters (PMs), which are condensed from air pollutants, pose severe health threats in many industrialized countries. Various chemical analyses of the particulate matters are crucial to specify their air pollutant sources and reduce PMs. Here, we report a chemical analysis technique for the PMs based on Surface Enhanced Raman Spectroscopy (SERS). Distinctive Raman spectroscopic signals are detected from PMs whose surface are dispersed with gold nanoparticle aggregates. By exploiting the molecular specific sensitivity of SERS, we distinguish between the PMs according to their sources. To be specific, artificially generated PM materials as a reference are successfully distinguished from soil dusts collected from on-site. This work would pave a way towards identifying the PMs according to their sources and developing an on-site chemical analysis of PMs.

The molecular structure of aniline dimer cation, (PhNH 2 ) 2 + , was investigated by photodissociation spectroscopy coupled with tandem time of flight mass spectrometry. Mass-selected (PhNH 2 ) 2 + was dissociated by the irradiation of photons ranging from visible to near infrared region (420–1500 and 2600–3600 nm). An intense absorption band was observed at ∼1.12 eV (1110 nm) in the photodissociation action spectrum and was assigned as the charge resonance (CR) interaction band of (PhNH 2 ) 2 + cation. Two other bands observed at ∼1.9 eV (650 nm) and >3.0 eV ( 2 A 2 ← X 2 B 1 and B 2 B 1 ← X 2 B 1 of PhNH 2 + in (PhNH 2 ) 2 + , respectively (Honda et al., 2002). In the infrared spectrum, two broad and intense absorption bands were observed at ∼3190 and 3420 cm −1 and were assigned as the symmetric and antisymmetric NH 2 stretching of PhNH 2 + , respectively. The density functional theory calculations at the level of M06-2X/6-311++G(2d) and B3LYP/cc-pVTZ suggest a “head to tail” type stacked CR structure for (PhNH 2 ) 2 + , stabilized by at least 800 and 250 cm −1 compared to other possible isomers in the two theory levels, respectively. Besides, the basis set superposition error corrected binding energy derived from counterpoise calculation also indicated that the interaction energy was peaked in the CR structure.

Plasmonic nanostructures are widely studied and used because of their useful size, shape, composition and assembled structure-based plasmonic properties. It is, however, highly challenging to precisely design, reproducibly synthesize and reliably utilize plasmonic nanostructures with enhanced optical properties. Here, we devise a facile synthetic method to generate Au surface roughness-controlled nanobridged nanogap particles (Au-RNNPs) with ultrasmall (≈1 nm) interior gap and tunable surface roughness in a highly controllable manner. Importantly, we found that particle surface roughness can be associated with and enhance the electromagnetic field inside the interior gap, and stronger nanogap-enhanced Raman scattering (NERS) signals can be generated from particles by increasing particle surface roughness. The finite-element method-based calculation results support and are matched well with the experimental results and suggest one needs to consider particle shape, nanogap and nanobridges simultaneously to understand and control the optical properties of this type of nanostructures. Finally, the potential of multiplexed Raman detection and imaging with RNNPs and the high-speed, high-resolution Raman bio-imaging of Au-RNNPs inside cells with a wide-field Raman imaging setup with liquid crystal tunable filter are demonstrated. Our results provide strategies and principles in designing and synthesizing plasmonically enhanced nanostructures and show potential for detecting and imaging Raman nanoprobes in a highly specific, sensitive and multiplexed manner.

In the present study, an enhanced solar light harvesting strategy based on the wavelength conversion effect is suggested for dye-sensitized solar cells (DSSCs). Incorporating β-NaYF4:Yb3+,Er3+ phosphor microcrystals as a component of the DSSCs enables wavelength conversion from infrared to visible light, which maximizes the absorption of visible light by the C106 organometallic dye and produces excess current, thus enhancing the quantum efficiency. It is demonstrated that the photocurrent density generated is increased by the wavelength conversion effect of the phosphor material. The introduction of up-converting β-NaYF4:Yb3+,Er3+ phosphor microcrystals dispersed in an iodide electrolyte and the use of an additional phosphor reflecting film increases the overall solar-to-electrical energy conversion efficiency (η) from 9.02% of reference DSSCs to 9.48 and 10.76%, respectively. DSSCs with phosphors contained in both the iodide electrolyte solution as well as an additional phosphor reflecting film show a highly enhanced overall efficiency of 10.90%. Herein, a strategy for effective wavelength conversion is investigated for enhanced solar light harvesting, and the results of the study contribute the most viable strategy for achieving maximum utilization of the solar spectrum.

Lanthanide-doped upconversion nanoparticles enable anti-Stokes emission via nonlinear processes, where low-energy excitation photons in the near-infrared window can be upconverted into high-energy emission ones in the visible or ultraviolet regions. The past decade has seen great success in the high-quality synthesis of upconversion nanoparticles with controlled structure, crystalline phase, size, and shape. The unique capacity of upconversion nanocrystals to undertake near-infrared excitation, amalgamated with their excellent luminescent characteristics, such as massive anti-Stokes spectral shift, sharp emission band, multicolor emission, and long luminescence lifetime, makes these nanomaterials prime candidates for a plethora of applications. Herein, we review the field of upconversion nanoparticles from the perspectives of fundamental luminescence mechanisms, new synthetic routes, and current practical approaches to tuning emission color and enhancing upconversion efficiency. In particular, we highlight the recent advances in utilizing upconversion nanocrystals for bioimaging, therapy, biosensing, neuroscience, super-resolution imaging, photoswitching, and lasing applications. We also discuss the key challenges and issues that are critical for the further implementation of upconversion nanoparticles in diverse settings.

Anisotropically structured upconversion nanocrystals capable of exhibiting bright upconversion emission properties are a promising new class of high performance optical materials. In this study, we investigate a facile synthetic method for the new nanoplate structure of YF3:Yb3+/Er3+ with enhanced luminescence intensity. The shape of YF3:Yb3+/Er3+ nanocrystals can be controlled by changing the synthesis conditions of the NaOH concentration, reaction time, and surfactant. The concentration of NaOH determines the final structure of YF3:Yb3+/Er3+. By increasing the NaOH concentration from 0.25 mmol to 2.5 mmol, YF3:Yb3+/Er3+ nanoplates transform into NaYF4:Yb3+/Er3+ nanoparticles; in the absence of NaOH, the nanoplate structure of YF3:Yb3+/Er3+ changes to particles. The YF3:Yb3+/Er3+ nanoplates show luminescence efficiency much greater than that of the spherical YF3:Yb3+/Er3+ nanocrystals.

We report DNA-mediated simple synthetic methods to obtain anisotropic plasmonic nanostructures with a tailorable intra-nanogap distance ranging from 0.9 to 4.0 nm. Anisotropic half-shell structures with sub-1.0 nm intra-nanogaps showed a wavelength-independent surface-enhanced Raman scattering (SERS) intensity and a highly sensitive SERS response to NIR light. We found that the reaction conditions such as pH and NaCl concentration are responsible for the resulting shell structures and intra-nanogap distances. Three noticeable plasmonic nanostructures [i.e., half-shell with sub-1.0 nm nanogaps, closed-shell with a wide nanogap (2.1 nm) and star-shaped with an irregular nanogap (1.5–4.0 nm)] were synthesized, and solution-based and single particle-based Raman measurements showed a strong relationship between the plasmonic structures and the SERS intensity. An understanding of DNA-mediated control for nanogap-engineered plasmonic nanostructures and studies of SERS-activity relationships using single particle-correlated measurements can provide new insights into the design of new plasmonic nanostructures and SERS-based biosensing applications.

Nanoprobes used for biomedical applications usually require surface modifications with amphiphilic surfactants or inorganic coating materials to enhance their biocompatibility. We proposed a facile synthetic approach for the phase transfer of hydrophobic magnetic nanoparticles by the direct adherence of fluorescent probes, without any chemical modifications, for use as a magnetic resonance (MR)/near-infrared (NIR) fluorescence bimodal imaging contrast agent. Indocyanine green (ICG) was used not only as an optical component for NIR imaging, but also as a surfactant for phase transfer with no superfluous moiety: we therefore called the process “ICGylation”. Cell labeling and tracking in vivo with ICGylated magnetic nanoparticles were successfully performed by MR/NIR dual-mode imaging for three days, which showed remarkable biostability without any additional surface functionalization. We expect that this novel MR/NIR contrast agent demonstrating sensitive detection and simultaneous imaging capability can be used in diverse fields, such as the imaging and tracking of immune cells to confirm immunotherapeutic efficacy. The approach used could also be applied to other kinds of nanoparticles, and it would promote the development of advanced functional multimodal nanobioprobes.

Upconverting nanoparticles (UCNPs) have been studied as novel bioimaging probes owing to the absence of autofluorescence and excellent photostability. For practical applications, biocompatible UCNPs with high upconversion efficiency, bright luminescence, and good colloidal stability are desirable. Herein, we report a quantitative and systematic study on the upconversion luminescence from a set of NaYF4:Yb3+,Er3+-based nanoparticles by varying crystal structures, core/shell structures, and surface ligands. Upconversion luminescent properties in colloidal solution and at the single-particle level were examined. Hexagonal-phase core/shell UCNPs exhibited the most intense luminescence among various structures, while the excellent photostability was observed in all different types of UCNPs. To optimize the biomedical imaging capability of UCNPs, various surface coating strategies were tested. By quantitative spectroscopic measurements of surface-modified UCNPs in water, it was suggested that encapsulation with...

Lanthanide-doped upconverting nanoparticles (UCNPs) have recently attracted enormous attention in the field of biological imaging owing to their unique optical properties (near-infrared excitation followed by photoluminescence in the visible spectral range). For biological applications, it is critical to understand the interaction between these nanoparticles and biological systems at the cellular level. In this paper, using epi-fluorescence microscopy with 980-nm excitation, a full intracellular pathway composed of endocytosis, active transport, and exocytosis was clearly visualized for PEG-phospholipid-coated UCNPs in single HeLa cells, which was experimentally feasible mostly thanks to the excellent photostability and low cytotoxicity thereof. Each step in the pathway was characterized and identified by various chemical inhibition studies and spectroscopic measurements.

The significance of lymphatic system has gathered great attention for immunotechnology related to cancer metastasis and immunotherapy. To develop innovative immunodiagnostics and immunotherapy in in vivo environments, it is very important to understand excretion pathways and clearance of injected cargoes. Herein, we employed Tm3+-doped upconverting nanoparticles (UCNPs) with versatile advantages suitable for long-term non-invasive in vivo optical imaging and tracking. Transport and retention of the UCNPs in the lymphatic system were evaluated with high-quality NIR-to-NIR upconversion luminescence (UCL) imaging. We obtained their kinetic luminescence profiles for the injection site and sentinel lymph node (SLN) and observed luminescence signals for one month; we also examined UCL images in SLN tissues, organs, and faeces at each time point. We speculate that the injected UCNPs in a footpad of a small mouse are transported rapidly from the lymphatic system to the blood system and then eventually result in an efficient excretion by the hepatobiliary route. These results will support development of novel techniques for SLN biopsy as well as immunotechnology.

Photodissociation of nitrous oxide near 203 nm has been studied by a combination of high resolution slice ion imaging technique and (2+1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy of N 2 (X 1 Σ g + ) via the (a" 1 Σ g + ) state. We have measured the recoil velocity and angular distributions of N 2 fragments by ion images of the state-resolved photofragments. The N 2 fragments were highly rotationally excited and the NN-O bond dissociation energy was determined to be 3.635 eV Also, we investigated the photo fragment images from the photodissociation of N 2 O clusters with various stagnation pressures.

The photodissociation dynamics of 4-aminobenzonitrile+(water)n (4ABN +Wn) (n = 1-18) clusters was investigated using a home-built linear-tandem time-of-flight (TOF) mass spectrometer consisting of two stages. Massselected cluster cations (n = 8-18) were irradiated by photons with energies ranging from 2.15 to 2.95 eV in the field-free region at the second stage. The average numbers of ejected water molecules were obtained at various photon energies from the photofragmentation mass spectra, from which the average binding energies of water molecules were estimated. Also, the optimum structures of the clusters and binding energies of the water molecules were suggested via theoretical calculations. The local excitation (LE) band observed in the photodissociation spectra of the 4ABN+Wn (n = 1-3) clusters and 4ABN2 + shifted to blue with increase in the number of solvated water molecules.

Structures of mono- and dihydrated adenine dimers and their cations were calculated using B3LYP density functional theory with the 6-31+G(d,p) basis set, in order to help understand photofragmentation experiments of hydrated adenine dimers from the energetics point of view. Several important pathways leading to the major fragmentation product, protonated adenine ion (AH(+)), thermodynamically at minimum costs were investigated at the ground-state electronic potential surface of hydrated adenine dimer cations. Our calculations suggest that the proton transfer from one adenine moiety to the other in hydrated dimer ions readily occurs with negligible barriers in normal hydration conditions. In asymmetrically hydrated ions, however, the proton transfer to more hydrated adenine moieties is kinetically hindered due to heightened transition-state barriers, while the other way is still barrierless. Such directional preference in proton transfer may be characterized as a unique dimer ion property, stemming from the difference in basicity of the two nitrogen atoms involved in the double hydrogen bond that would be equivalent without hydration. We also found that dimer cleavage requires about 4 times larger energy than evaporation of individual water molecules, so it is likely that most solvent molecules evaporate before the eventual dimer cleavage when available internal energy is limited.

We studied photodissociation dynamics of adenine dimer radical ions, A 2 + , and hydrated adenine dimer ions, A 2 + ( H 2 O ) n (n = 1–6), at three wavelengths. The most abundant daughter ion is found to be protonated adenines, (AH)+, which implies that proton transfer is followed by dissociation in A 2 + and A 2 + ( H 2 O ) n . Theoretical calculations support that the most stable structures of A 2 + and A 2 + ( H 2 O ) 1 are formed by proton transfer. As cluster size of A 2 + ( H 2 O ) n becomes larger, the intensity of A 2 + as a daughter ion increases with the decrease in the intensity of (AH)+. Upon photoexcitation of A 2 + by 266 nm, adenine monomer ion (A+) is also observed along with (AH)+, which suggests that electronically excited states of (AH)+ moiety in A 2 + promotes the hydrogen abstraction from (AH)+.

By adopting a fast photography and time-resolved optical emission spectrometry, we have investigated the effects of transverse magnetic field on the expansion dynamics and enrichment of Zn atoms and Zn + ions in a plume produced by laser ablation of a Zn target in oxygen atmosphere. Plume splitting due to the magnetic field was apparent but the splitting patterns of Zn and Zn + were totally different. The surface morphology and photoluminescence characteristics also changed significantly. In particular, the growth rate increased by as much as 2.4–4.3 times compared to the conventional PLD method.

By adopting a time-resolved optical emission spectrometry, we have investigated the effects of transverse magnetic field on C2 and CN molecules produced by laser ablation of a graphite target in nitrogen atmosphere. We found that the spectroscopic temperatures of both species, obtained via simulation of the optical emission spectra, as well as their emission intensities from the electronically excited states increased significantly in the presence of a magnetic field. The cyclotron radii and frequencies for electrons and ions were estimated to explain the increase in the number of collisions in the laser-produced carbon plasma plume under a magnetic field.

The average kinetic energy of Zn+ ions and optical emission intensities from Zn* and Zn+* produced by laser ablation of a Zn target were measured as a function of bias voltage applied to a grid mounted facing the target to elucidate the effects of the external electric field on the laser-produced plasma plume. It turned out that the relative concentration of the ionic species in the plume increased and the crystallinity of the deposited ZnO film improved with increasing the bias voltage.

A linear tandem-type time-of-flight mass spectrometer was employed to study unimolecular dissociation of metastable aniline+-(methanol)n (An+-(CH3OH)n, n = 2–9) cluster cations formed by two-photon ionization of neutral clusters. The dominant dissociation channel was to liberate a single methanol molecule, namely, An+-(CH3OH)n → An+-(CH3OH)n−1 + CH3OH. The decay time constant of the ions ranged from 65 to 460 μs and turned out to be highly dependent on the cluster size. Also, hydrogen transfer mechanism in the formation of An+-(CH3OH)nH was examined by analyzing experimental results from isotopomers, such as deuterated An-d7+-(CH3OD) and An-d7+-(CD3OD) cluster ions. Density functional theory calculations were carried out to obtain optimized structures for neutral and ionic clusters and to support mechanisms related to the hydrogen transfer and unimolecular dissociation reaction.

Lanthanide-doped upconverting nanoparticles (UCNPs, NaYF4:Yb(3+),Er(3+)) are well known for emitting visible photons upon absorption of two or more near-infrared (NIR) photons through energy transfer from the sensitizer (Yb(3+)) to the activator (Er(3+)). Of the visible emission bands (two green and one red band), it has been suggested that the red emission results from two competing upconversion pathways where the non-radiative relaxation occurs after the second energy transfer (pathway A, (4)I15/2 → (4)I11/2 → (4)F7/2 → (2)H11/2 → (4)S3/2 → (4)F9/2 → (4)I15/2) or between the first and the second energy transfer (pathway B, (4)I15/2 → (4)I11/2 → (4)I13/2 → (4)F9/2 → (4)I15/2). However, there has been no clear evidence or thorough analysis of the partitioning between the two pathways. We examined the spectra, power dependence, and time profiles of UCNP emission at either 980 nm or 488 nm excitation, to address which pathway is preferred. It turned out that the pathway B is predominant for the red emission over a wide range of excitation powers.

In the field of nanomedicine, long term accumulation of nanoparticles (NPs) in the mononuclear phagocyte system (MPS) such as liver is the major hurdle in clinical translation. On the other hand, NPs could be excreted via hepatobiliary excretion pathway without overt tissue toxicity. Therefore, it is critical to develop NPs that show favorable excretion property. Herein, we demonstrated that micelle encapsulated 64Cu-labeled upconverting nanoparticles (micelle encapsulated 64Cu-NOTA-UCNPs) showed substantial hepatobiliary excretion by in vivo positron emission tomography (PET) and also upconversion luminescence imaging (ULI). Ex vivo biodistribution study reinforced the imaging results by showing clearance of 84% of initial hepatic uptake in 72 hours. Hepatobiliary excretion of the UCNPs was also verified by transmission electron microscopy (TEM) examination. Micelle encapsulated 64Cu-NOTA-UCNPs could be an optimal bimodal imaging agent owing to quantifiability of 64Cu, ability of in vivo/ex vivo ULI and good hepatobiliary excretion property.