Low Concentration Region Research Articles

Cathodoluminescence Study of m‐Plane α‐Ga2O3 Grown by Mist Chemical Vapor Deposition

The cathodoluminescence (CL) properties of m‐plane α‐Ga2O3 grown by mist chemical vapor deposition are investigated. The m‐plane α‐Ga2O3 is found to have two types of characteristic luminescence bands: blue luminescence (BL) band (centered at 2.8 eV) and UV luminescence (UVL) band (centered at 3.7 eV). To characterize these bands, the Sn concentration and temperature dependences of the CL spectra are investigated using samples with varying Sn concentrations from 1 × 1017 to 1 × 1019 cm−3. The Sn concentration‐dependent CL spectra show that the luminescence from the UVL band is dominant in the low Sn concentration region, while that from the BL band is dominant in the high Sn concentration region. The temperature‐dependent CL spectra indicate that the peak intensity of the UVL band depending on temperature is larger than that of the BL band. The activation energies in the UVL band of the undoped and lightly Sn‐doped samples are determined as 110 meV. In addition, the parameters of the Huang–Rhys factor in the UVL band are obtained as 28.6 and 18.8, respectively. These results strongly suggest that the UVL band is derived from self‐trapped excitons, which is the recombination of free electrons and self‐trapped holes.

Pilot groundwater radon mapping and the assessment of health risk from heavy metals in drinking water of southwest, Nigeria

Radon and heavy metals are sources of groundwater pollution and are identified as potential carcinogens. Southwest Nigeria's populace mostly relies on groundwater source for drinking. This study aims to map radon distribution in groundwater of southwest Nigeria and to determine the health risk of radon and heavy metal in drinking water. Radon concentrations of 145 groundwater samples were measured using RAD7 electronic radon detector and heavy metal concentrations of 52 groundwater samples were measured using atomic absorption spectrophotometer. Radon concentration distributions were delineated using geographical information system. Radon concentration of water samples ranges between 1.6 Bq l−1 and 271 Bq l−1 with an average value of 35.9 ± 38.4 Bq l−1. The average groundwater radon concentration is higher than US-EPA recommended level of 11.1 Bq l−1 but lower than the WHO recommended limit of 100 Bq l−1. The estimated average annual effective radiation doses to infants, children, and adults are 29 μSvy−1, 41 μSvy−1 and 92 μSvy−1 respectively. The radon distribution map of the study area reveals regions of high, medium, and low groundwater radon concentrations. The average concentration values of heavy metals in groundwater samples are of the order Mn > Zn > Pb > Cu > Cr > Ni > Cd. 84% of groundwater exhibits good to excellent quality in terms of heavy metal pollution. However, about 16% of the samples which lie in the sedimentary regions of Ogun and Lagos States exhibit poor to very poor quality. Overall, ingestion of groundwater in the study area may not pose a serious health hazards from radon ingestion and heavy metal toxicity.

Study on impinging ignition and wall-attached fuel film combustion characteristics of light- to heavy-duty diesel engines at low temperatures

The difference in impinging ignition characteristics of light- to heavy-duty diesel engines at low temperatures and the heating effect of fuel film combustion on the wall are still not well understood. Thus, visualization experiments are conducted in a constant volume combustion chamber using Mie-scattering and direct photography methods, and 3-D simulation is used to supplement and explain the experimental phenomena. The results show that the autoignition initiates in the free spray and then hits the wall for the 0.12 mm nozzle. However, 30% of the liquid fuel under the 0.32 mm nozzle adheres to the wall, and the cooling effect causes the evaporation rate to decrease by orders of magnitude. The mixture at the initial flame is mainly distributed in the low-temperature and low-concentration region, and coupled with the excessive fuel diffusion caused by spray-wall interaction, the transition from the cool flame to hot flame is severely slowed down. With the increase of nozzle diameter from 0.12 mm to 0.32 mm, the hot flame position shifts from the fuel-rich side to the fuel-lean side, the flame fluctuates greatly and the area decreases, and the critical ignition temperature increases from 753 K to 793 K. When the wall-attached fuel accumulated in a misfire or an unstable ignition condition is ignited again, the combustion lasts for nearly 100 ms. As the nozzle diameter increases from 0.12 mm to 0.32 mm, the peak wall temperature rises from 487 K to 556 K, and the heat flux increases nearly twice, which inevitably increases the heat load of the wall.

Understanding the Adsorption of Rare-Earth Elements in Oligo-Grafted Mesoporous Carbon.

Rare-earth elements (REEs) are 17 elements of the periodic table primarily consisting of lanthanides. In modern society, the usage of REEs is ubiquitous in almost all modern gadgets and therefore efficient recovery and separation of REEs are of high importance. Selective adsorption and chelation of REEs in solid sorbents is a unique and sustainable process for their recovery. In this work, single-stranded oligos with 100 units of thymine were grafted onto carboxylated mesoporous carbon to synthesize a sorbent with phosphorus and oxygen functionalities. The sorbent was characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Three different REEs with varying atomic radii and densities, Lu, Dy, and La, were adsorbed onto the carbon from aqueous solutions. It was observed that the adsorbed amounts increased with the increase in the atomic radius or decrease in the atomic density. Calculation of the distribution coefficients for all the equilibrium adsorption amounts suggested that adsorption is more effective in the lower concentration region. The L3-edge X-ray absorption near-edge structure confirmed a 3+ oxidation state of REEs in the adsorbed phase. Extended X-ray absorption fine structure (EXAFS) confirmed the binding of REEs with oxygen functionalities in the adsorbed phase. The radial distribution functions calculated from the EXAFS data suggest a longer RE-O distance for La compared to those for Lu and Dy. The coordination numbers and Debye-Waller factors have typical values of about 8-9 atoms and 0.01-0.02 Å2, respectively.

Quantum Hall Effect across Graphene Grain Boundary.

Charge carrier scattering at grain boundaries (GBs) in a chemical vapor deposition (CVD) graphene reduces the carrier mobility and degrades the performance of the graphene device, which is expected to affect the quantum Hall effect (QHE). This study investigated the influence of individual GBs on the QH state at different stitching angles of the GB in a monolayer CVD graphene. The measured voltage probes of the equipotential line in the QH state showed that the longitudinal resistance (Rxx) was affected by the scattering of the GB only in the low carrier concentration region, and the standard QHE of a monolayer graphene was observed regardless of the stitching angle of the GB. In addition, a controlled device with an added metal bar placed in the middle of the Hall bar configuration was introduced. Despite the fact that the equipotential lines in the controlled device were broken by the additional metal bar, only the Rxx was affected by nonzero resistance, whereas the Hall resistance (Rxy) revealed the well-quantized plateaus in the QH state. Thus, our study clarifies the effect of individual GBs on the QH states of graphenes.

Ultrafast Deep-Ultraviolet Laser-Induced Voltage Response of Pyrite.

Ultrafast, high-sensitivity deep-ultraviolet (UV) photodetectors are crucial for practical applications, including optical communication, ozone layer monitoring, flame detection, etc. However, fast-response UV photodetectors based on traditional materials suffer from issues of expensive production processes. Here, we focused on pyrite with simultaneously cheap production processes and ultrafast response speed. Nanoseconds photovoltaic response was observed under UV pulsed laser irradiation without an applied bias at room temperature. In addition, the response time of the laser-induced voltage (LIV) signals was ~20 ns, which was the same as the UV laser pulse width. The maximum value of the responsivity is 0.52 V/mJ and the minimum value of detectivity was about to ~1.4 × 1013 Jones. When there exists nonuniform illumination, a process of diffusion occurs by which the carriers migrate from the region of high concentration toward the region of low concentration. The response speed is limited by a factor of the diffusion of the carriers. With an increment in laser energy, the response speed of LIV is greatly improved. The high response speed combined with low-cost fabrication makes these UV photodetectors highly attractive for applications in ultrafast detection.

Spatial and temporal multivariate statistical analysis to assess drinking water quality in medical services

Drinking water quality supplied to medical services presents significant role regarding the health aspect of the society. Multivariate statistical techniques were applied for the interpretation of data obtained, i.e., cluster analysis (CA), principal component analysis (PCA), factor analysis (FA), and discriminant analysis (DA) to analyze and assess the spatial and temporal variations of drinking water quality in different medical services in Kuwait. This study was generated over a period of 11 years (2007–2017), including 19 parameters at fourteen different sites. Hierarchical CA obtained two groups regarding both spatial and temporal variations. For spatial variations, 14 sampling sites were grouped into Low Concentration (LC) and High Concentration (HC). For temporal variations, 12 months were grouped into Summer and Winter. DA provided better results by data reduction for the large data set with great discriminatory ability for both spatial and temporal variations, as only five parameters were used concerning the spatial variations to afford 68.4% of the cases being assigned correctly, and seven parameters were interpreted for the temporal variations affording 76.1% of correctly classified cases. The applied PCA/FA on the spatial variations resulted in five principle components (PCs) for the LC region, and the total variance is 74.84% and three PCs for the HC region explaining a total variance of 64.86%. For the temporal variations, summer yielded into five PCs with a total variance of 70.6%, whereas the winter resulted in three PCs describing 67.1% total variance. Thus, multivariate analysis provides better spatial and temporal variations assessment in contemplation of effective drinking water quality management and control.

Shape memory alloy based NiTi reinforced functionally graded material for vibration damping

Shape memory based high performance nickel-titanium alloy particles were embedded by friction stir processing in graded concentration on the surface of light weight commercially pure magnesium cast plates. The novel functionally graded material so developed was analyzed for microhardness evolution and vibration damping effect. The nickel-titanium alloy particles were filled in a 2.5 wide × 3 mm deep slot and embedded on the surface by friction stir processing. A shallower slot 2.5 wide × 1.5 mm deep was milled over the previously embedded surface in which nickel-titanium alloy powder was again filled and embedded on the surface by second pass friction stir processing. This sequence of pass created the graded variation in nickel-titanium alloy concentration. The so fabricated functionally graded material was cut out from the plate and it was hot-forged to 2/3 thickness and subsequently quenched. The microstructural examination confirmed homogeneous dispersion of nickel-titanium alloy particles and clear interface between high and low concentration regions. The microhardness confirmed a uniform graded variation in hardness. The vibration damping tests confirm considerable improvement in the damping capacity of the fabricated functionally graded material.

Optimization of reconstruction parameters in [18F]FDG PET brain images aiming scan time reduction

Iterative image reconstruction methods are widely used in PET due to their better image quality when compared to analytical methods. However, inaccurate quantification occurs in low activity concentration regions, which leads to biased quantification of PET images. The diagnosis of some neurodegenerative diseases, such as Alzheimer’s disease, is based on identifying such low-uptake regions. Furthermore, PET imaging in these populations should be as short as possible to limit head movements and improve patient comfort. This work aims to identify optimized reconstruction parameters of [18F]FDG PET brain images aiming to reduce image acquisition time with minimal impact on quantification. For this, [18F]FDG PET images of a Hoffman 3-D brain phantom were acquired. Analytical and iterative reconstruction methods were compared utilizing image quality and quantitative accuracy metrics. OSEM reconstruction algorithm was optimized (4 iterations and 32 subsets). It resulted in remarkably similar images compared to the current clinical settings, with a 50% reduction in scan time (5 min with a post-reconstruction filter of 4 mm). Future clinical studies are needed to confirm the results presented here.

Coupled effects of circular and elliptical feed spacers under forced-slip on viscous dissipation and mass transfer enhancement based on CFD

Combining unsteady state shear strategies and a novel spacer geometry for spirally wound membrane modules may lead to greater flux enhancement than only optimising the spacer geometry. In this paper, CFD is employed to simulate the effect of different spacer profiles (circular and elliptical) and configurations (2- and 3-layer) on flux enhancement generated by unsteady forced-slip. Data analysis shows that a similar Strouhal number is observed for all spacer filaments under consideration, regardless of profile shape. Although a submerged spacer leads to relatively larger pressure losses, implementing forced-slip with that geometry results in the largest flux increase (40%) compared to other configurations under consideration. This is associated with the shedding of vortices near the membrane surface, coupled with vortex flow cross-over from regions of high concentration (near the membrane) to low concentration regions in the bulk. However, the flow instabilities that improve mass transfer are weakened in channels with smaller void fraction, leading to smaller flux enhancement. The results therefore suggest that the simple circular profile is preferred for maximising vortex-shedding-induced permeate flux enhancement.

Quantitative evaluation of effects of coupled temperature elevation, thermal damage, and enlarged porosity on nanoparticle migration in tumors during magnetic nanoparticle hyperthermia

Using simulation to accurately design a heating protocol in magnetic nanoparticle hyperthermia relies on not only the initial nanoparticle distribution, but also the dynamic particle migration during heating. A coupled theoretical framework consisting of nanoparticle migration in a porous medium model and temperature elevation in a heat transfer model was developed to evaluate possible nanoparticle redistribution during local heating. Five generated tumor models from microcomputed tomography (microCT) with nanoparticle deposition were used to predict temperature elevations and assess local thermal damage when each tumor was subject to an alternating magnetic field. Local thermal damage further changed the interstitial structure in the tumor, resulting in enhancements in porosity and diffusion coefficient to promote nanoparticle diffusion to low concentration regions. The distribution volumes of nanoparticles in the highest concentration range reduced after heating, while those in the lower concentration ranges increased. After heating, the total nanoparticle distribution volume defined as the tumor volume occupied by nanoparticles was 21% bigger than that before the heating. The theoretical predictions of nanoparticle migration trend agree well with experimental results of microCT scan analyses. It is concluded that thermal damage induced enhancement in nanoparticle diffusion may be one of the mechanisms to explain nanoparticle migration during magnetic nanoparticle hyperthermia. Results from this study may suggest a feasibility of enhancing nanoparticle dispersion from injection sites using deliberate thermal damage.

Coherent structure characteristics of the swirling flow during turbulent mixing in a multi-inlet vortex reactor

Improving the efficiency of the production of uniformly sized functional nanoparticles for pharmaceutical and agricultural applications has been a problem of great interest. The macroscale multi-inlet vortex Reactor (macro-MIVR) could potentially be used for this purpose due to its ability to achieve the rapid mixing necessary for the flash nanoprecipitation nanoparticle fabrication technique. In the presented work, the coherent structures, a key contributor to the turbulent mixing, were investigated for the turbulent swirling flow within the MIVR. The two-point spatial correlations of velocity and concentration fluctuations at various basepoints were measured from instantaneous velocity and concentration fields obtained using simultaneous stereoscopic particle image velocimetry and planar laser-induced fluorescence. The basepoint locations were chosen as the middle and at the edge of the partially mixed concentration spiral arms. The correlations were found to be elliptical in shape, inclined, and peaked at the basepoints. A region near the basepoint was positively correlated and was surrounded by negatively correlated regions. Autocorrelations of concentration were also elliptical and curved toward the center of the reactor. The linear stochastic estimation was used to interpret the coherent structure features that would result in the observed spatial correlations. The linear stochastic estimates of the velocity fields were computed directly from the cross correlations of the tangential velocity fluctuations with the concentration fluctuations. The estimated conditional velocity fields revealed obliquely oriented counter-rotating vortical structures that stir the fluid from high-concentration regions to low-concentration regions, and the orientation of these vortical structures depended on the local concentration gradient.

Controllable functionalization of carbon dots as fluorescent sensors for independent Cr(Ⅵ), Fe(Ⅲ) and Cu(Ⅱ) ions detection

Carbon-dots (CDs)-based fluorescent sensors have been successfully used for heavy metal ion detection in drinking water, but the following two points hinder their large scale applications: (1) CDs usually exhibit poor response selectivity for specific ions; (2) there is a lack of multifunctional CDs probes with independent detection of multiple ions. So it’s very urgent to develop multifunctional CDs fluorescent probes for their independent and highly selective detection of multiple ions in water. In this work, carbon nanosheets (CNs) were first stripped from carbon rods by the electrochemical method, and then polymerized into CDs less than 10 nm in size and simultaneously functionalized with ammonia, N,N-Dimethylformamide or polyethylene glycol in the hydrothermal/solvothermal process, respectively. These functionalization can selectively introduce CN bonds, NH2 and OH groups on CDs surface, respectively. These three functionalized CDs exhibit evidently enhanced fluorescence response to Cr6+, Cu2+ and Fe3+ ions, respectively. Compared with the bare CNs, their sensitivity and selectivity can be enhanced by more than 12 and 7 times, respectively. Their limit of detection is reduced by at least one order of magnitude, and the linear response intervals are significantly broadened to low-concentration region (i.e., 0.8–20.0 μM).

Structural and Dynamic Insights into the Conduction of Lithium-Ionic-Liquid Mixtures in Nanoporous Metal-Organic Frameworks as Solid-State Electrolytes.

Metal-organic framework (MOF)-based separators in Li-ion batteries (LIBs) have the potential to improve the battery performance. The mobility and conduction of lithium and organic ionic liquids (ILs) in these materials acting as (quasi) solid-state electrolytes are crucial for the battery power output. Here, we investigate the mobility of a Li-based IL in MOF nanopores and unveil the details of the conduction mechanism by molecular dynamics (MD) simulations. A complex conductivity depending on the Li-IL loading and on the IL composition is observed. Most importantly, the presence of Li prevents the collapse of the conductivity at high IL loadings. The fully atomistic MD simulations including guest-guest and guest-host interactions elucidate the competing mechanisms: Li follows a Grotthuss-like conduction mechanism with large mobility. While at small pore fillings, the Li conduction is limited by the large distance between the anions facilitating the Grotthuss-like conduction; the conduction at high pore fillings is governed by field-induced concentration inhomogeneities. Because of the small MOF pore windows, which hinders the simultaneous passage of the large IL cations and anions in opposite directions, the IL shows field-induced MOF pore blocking and ion bunching. The regions of low anion concentration and high cation concentration represent barriers for Li, decreasing its mobility. In comparison to Li-free IL, the IL bunching effect is attenuated by the formation of charge-neutral Li-anion complexes, resulting in a tremendously increased conductivity at maximum pore filling. The exploitation of this mechanism may enhance the development of advanced batteries based on IL and nanoporous separators.

Image-derived modeling of nucleus strain amplification associated with chromatin heterogeneity

Beyond the critical role of cell nuclei in gene expression and DNA replication, they also have a significant influence on cell mechanosensation and migration. Nuclear stiffness can impact force transmission and, furthermore, act as a physical barrier to translocation across tight spaces. As such, it is of wide interest to accurately characterize nucleus mechanical behavior. In this study, we present a computational investigation of the in situ deformation of a heterogeneous chondrocyte nucleus. A methodology is developed to accurately reconstruct a three-dimensional finite-element model of a cell nucleus from confocal microscopy. By incorporating the reconstructed nucleus into a chondrocyte model embedded in pericellular and extracellular matrix, we explore the relationship between spatially heterogeneous nuclear DNA content, shear stiffness, and resultant shear strain. We simulate an externally applied extracellular matrix shear deformation and compute intranuclear strain distributions, which are directly compared with corresponding experimentally measured distributions. Simulations suggest that the mechanical behavior of the nucleus is highly heterogeneous, with a nonlinear relationship between experimentally measured grayscale values and corresponding local shear moduli (μn). Three distinct phases are identified within the nucleus: a low-stiffness mRNA-rich interchromatin phase (0.17 kPa ≤ μn ≤ 0.63 kPa), an intermediate-stiffness euchromatin phase (1.48 kPa ≤ μn ≤ 2.7 kPa), and a high-stiffness heterochromatin phase (3.58 kPa ≤ μn ≤ 4.0 kPa). Our simulations also indicate that disruption of the nuclear envelope associated with lamin A/C depletion significantly increases nuclear strain in regions of low DNA concentration. We further investigate a phenotypic shift of chondrocytes to fibroblast-like cells, a signature for osteoarthritic cartilage, by increasing the contractility of the actin cytoskeleton to a level associated with fibroblasts. Peak nucleus strains increase by 35% compared to control, with the nucleus becoming more ellipsoidal. Our findings may have broad implications for current understanding of how local DNA concentrations and associated strain amplification can impact cell mechanotransduction and drive cell behavior in development, migration, and tumorigenesis.

Trapping nitrous gases during nitric acid leaching of sulfide concentrates

Gas-air mixtures that form in nitric acid leaching of sulfide raw materials possess the following peculiarities making a negative impact on trapping of nitrogen oxides: elevated temperature, different oxidation level of nitrogen oxides, slow oxidation of NO in region of low concentrations, and instability of the resulting gas-air mixture flow. Therefore, well-known methods of trapping nitrous gases shall be adapted to specific sulfide raw material. We propose a process flow diagram for trapping nitrous gases formed during nitric acid leaching of sulfide concentrates at atmospheric pressure on the example of Zhezkazgan concentrate. The paper addresses theoretical aspects of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases, and typical reactions of interaction of the proposed absorbents with nitrogen oxides. The choice of water-ore pulp as an absorber was made because of similarity between the mechanism of absorption of nitrogen oxides for neutral and alkali ore suspensions and the one for alkali solutions: nitrogen dioxide and nitrous anhydride are absorbed with formation of a solution of nitrates and nitrites. Due to availability in a liquid phase of ferrous iron along with NO2 and N2O3, acidic suspensions are also capable to absorb nitric oxide, to some extent, with formation of Fe(NO)SО4 complex. Process water absorbs only nitrogen dioxide, with formation of nitric and nitrous acids. Nitrous acid is an unstable compound in acidic environments and decomposes with formation of water and nitrogen oxide. At the stages of trapping nitrogen oxides with water-ore pulp and process water (circulating solution), it is recommended conditioning of gas-air mixtures by choosing the volume of additionally introduced air, in an amount to provide the highest rate of nitrogen oxide oxidation. At the stages of sulfuric acid and alkaline trapping of nitrogen oxides, it is recommended conditioning of gas-air mixtures by selecting the volume of additionally introduced air and the oxidation time of nitrogen oxide that provide an equimolecular mixture of NO and NO2. A distinctive feature of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases is possibility to use the products of absorption at the stage of sulfide concentrate leaching. The extended tests of trapping nitrous gases have been conducted. The plant capacity by the gas-air mixture ranged 17–21 m3/h, and by leached concentrate — 12–15 kg/h. In this case, the degree of capturing nitrous gases reached 96.8%. Return of the products of absorption of nitrous gases in the form of condensate, water-ore pulp, nitrosyl sulfuric acid, nitric acid solution, nitritenitrate lye allows to reduce the nitric acid consumption by 7–10 times relative the values obtained without using the trapping system. In this case, the degree of copper extraction into the leaching solution was 97.7%. The extraction degree of silver, rhenium, zinc was respectively 98.0%, 99.0%; 98.5%.

Use of thermally modified waste concrete powder for removal of Pb (II) from wastewater: Effects and mechanism.

Exploring effective uses of waste concrete powder (WCP), produced from recycling of construction & demolition waste is beneficial to the environment and sustainable development. In this study, WCP was first treated thermally to enhance the ability to remove Pb (II) from aqueous solutions. The experimental results revealed that the thermal treatment could enhance adsorption capacity due to modification of calcium bonding and pore structure of WCP. Preparation parameters such as temperature, particle size, and water-cement ratio were investigated to obtain the optimal operational conditions. Batch adsorption experiments were performed to explore influence factors of pH (1.00-6.00), ionic strength (0.05-2mol/L), dosage (2-50 g/L), and temperature (25-45°C). The pseudo-second-order kinetics model could adequately describe the adsorption process, and the Langmuir model was capable to predict the isotherm data well in the low concentration region (C0<500mg/L). The maximum uptake capacity for Pb (II) calculated by Langmuir model at 25, 35 and 45°C were 46.02, 38.58 and 30.01mg/g respectively, and the removal rate of Pb (II) was 92.96% at a dosage of 50 g/L (C0=1000mg/L). Precipitation, ion exchange, and surface complexation were identified to be the main mechanisms of Pb (II) adsorption through microscopic investigation by SEM-EDX, XRD, FTIR, XPS, and BET inspections. The study confirms that the WCP after thermal modification, can be selected as a promising adsorbent for the high performance and eco-friendliness.

Dynamics of a surfactant-laden bubble bursting through an interface

Abstract

Concentration‐Dependent Subcellular Distribution of Ultrasmall Near‐Infrared‐Emitting Gold Nanoparticles

AbstractThe ability to accurately control the subcellular distribution of nanomedicines provides unique advantages on understanding of cellular biology and disease theranostics. The nanomedicine concentration is a key factor to affect the theranostic efficiency and systematic toxicity. Herein, we unravel a concentration‐dependent subcellular distribution of near‐infrared‐emitting gold nanoparticles (AuNPs) co‐coated with glutathione and a cell‐penetrating peptide CR8 (CR‐AuNPs), which shows a strong membrane‐binding at high concentration but more endocytosis for mitochondria targeting at the low concentration region. Attributing to high content of AuI and microsecond luminescent lifetimes, these AuNPs can catalyze dissolved oxygen to generate singlet oxygen (1O2) efficiently. Combining with the concentration‐dependent subcellular distribution, the luminescent AuNPs show photocytotoxicity in the relative low concentration region. These findings facilitate the fundamental understanding of the biological behaviors and potential cytotoxicity of ultrasmall luminescent AuNPs toward future theranostics.

Concentration-Dependent Subcellular Distribution of Ultrasmall Near-Infrared-Emitting Gold Nanoparticles.

The ability to accurately control the subcellular distribution of nanomedicines provides unique advantages on understanding of cellular biology and disease theranostics. The nanomedicine concentration is a key factor to affect the theranostic efficiency and systematic toxicity. Herein, we unravel a concentration-dependent subcellular distribution of near-infrared-emitting gold nanoparticles (AuNPs) co-coated with glutathione and a cell-penetrating peptide CR8 (CR-AuNPs), which shows a strong membrane-binding at high concentration but more endocytosis for mitochondria targeting at the low concentration region. Attributing to high content of AuI and microsecond luminescent lifetimes, these AuNPs can catalyze dissolved oxygen to generate singlet oxygen (1 O2 ) efficiently. Combining with the concentration-dependent subcellular distribution, the luminescent AuNPs show photocytotoxicity in the relative low concentration region. These findings facilitate the fundamental understanding of the biological behaviors and potential cytotoxicity of ultrasmall luminescent AuNPs toward future theranostics.