Diblock copolymer membranes investigated by single-particle tracking

We report a study on particle diffusion in membranes formed from polystyrene-block-poly(2-(dimethylamino)ethyl methacrylate) (PS-b-PDMAEMA) diblock copolymers. The membranes were investigated by scanning electron microscopy and by single-particle tracking employing carboxy-functionalized polystyrene beads loaded with a fluorophore as spectroscopic probes. From the diffusion trajectories we extracted the domain size distribution of the membranes and the local diffusion coefficient of the beads as a function of the size of the beads. The single-particle tracking data revealed that the effective domain sizes of the membranes are reduced with respect to the domain sizes obtained from scanning electron microscopy, reflecting the confined diffusion of the probe particles due to interactions with the domain walls. This is corroborated by a clear correlation between the diffusion coefficient of an individual polystyrene bead and the size of the actual domain to which it is confined.     

Apparent microrheology of oil-water interfaces by single-particle tracking

We investigate the dynamics of charged microparticles at polydimethylsiloxane (oil)-water interfaces using Pickering emulsions as an experimental template. The mobility of the charged particles depends largely on the viscoelastic properties of the oil phase and the wettability of the solid particles. In addition, we have explored the potential of developing microrheology at liquid-liquid interfaces from the single-particle tracking technique. The apparent loss modulus, storage modulus, and relaxation time of the oil-water interfaces obtained from singe-particle microrheology depend strongly on the surface nature of the tracer particles, especially when the oil phase is viscoelastic.     

Unveiling the origin of performance enhancement of photovoltaic devices by upconversion nanoparticles

To better utilize the infrared(IR)region in sunlight for photovoltaic devices(PVs),upconversion nanoparticles(UCNPs)have been proposed to improve power conversion efficiency(PCE).However,researchers recently have found that the upconversion(UC)effect is negligible in PVs performance improvement for their ultra-low UC photoluminescence quantum yields of UCNPs solid film,while the real mechanism of UCNPs in PVs has not been clearly studied.Herein,based on the material inorganic perovskitesγ-CsPbI₃,NaYF₄:20%Yb³⁺,2%Er³⁺UCNPs were integrated into different transport layer to optimize device performance.Compared with reference device,the short-circuit current density and PCE of optimized device reached 20.87 mA/cm²(20.39 mA/cm²)and 18.34%(17.72%),respectively,without sacrificing open-circuit voltage and filling factor.Further experimental characterizations verified that the improved performance was attributable to enhanced visible light absorption instead of IR.To theoretically explain the statement,the light field distribution in device was simulated and the absorption in different layers was calculated.The results revealed that the introduction of UCNPs with different refractive index from other layers caused light field disturbance,and improved visible light captured by γ-CsPbI₃.Importantly,through experiments and theoretical calculation,the research deeply explored the potential mechanism of UCNPs in optimizing PVs performance.     

Diffusive dynamics of vesicles tethered to a fluid supported bilayer by single-particle tracking

We recently introduced a method to tether intact phospholipid vesicles onto a fluid supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005, 127, 1356-1357). Once tethered, the vesicles can diffuse in two dimensions parallel to the supported membrane surface. The average diffusion coefficient, D, is typically 0.2 microm(2)/s; this is 3-5 times smaller than for individual lipid or DNA-lipid conjugate diffusion in supported bilayers. In this article, we investigate the origin of this difference in the diffusive dynamics of tethered vesicles by single-particle tracking under collision-free conditions. D is insensitive to tethered vesicle size from 30 to 200 nm, as well as a 3-fold change in the viscosity of the bulk medium. The addition of macromolecules such as poly(ethylene glycol) reversibly stops the motion of tethered vesicles without causing the exchange of lipids between the tethered vesicle and supported bilayer. This is explained as a depletion effect at the interface between tethered vesicles and the supported bilayer. Ca ions lead to transient vesicle-vesicle interactions when tethered vesicles contain negatively charged lipids, and vesicle diffusion is greatly reduced upon Ca ion addition when negatively charged lipids are present both in the supported bilayer and tethered vesicles. Both effects are interesting in their own right, and they also suggest that tethered vesicle-supported bilayer interactions are possible; this may be the origin of the reduction in D for tethered vesicles. In addition, the effects of surface defects that reversibly trap diffusing vesicles are modeled by Monte Carlo simulations. This shows that a significant reduction in D can be observed while maintaining normal diffusion behavior on the time scale of our experiments.     

Correction: The morphology and surface charge-dependent cellular uptake efficiency of upconversion nanostructures revealed by single-particle optical microscopy

Correction for ‘The morphology and surface charge-dependent cellular uptake efficiency of upconversion nanostructures revealed by single-particle optical microscopy’ by Di Zhang et al., Chem. Sci., 2018, 9, 5260–5269, DOI: 10.1039/C8SC01828F.

In the Experimental section of the article, the concentration of citrate was incorrectly given as 0.05 M. The correct concentration of citrate is 2 M.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Crosslinking of and coupling to viral capsid proteins by tyrosine oxidation

Cowpea mosaic virus is composed of 60 identical copies of a two-subunit protein organized in pentameric assemblies around the icosahedral 5-fold symmetry axis. Treatment of the virus with the Ni(II) complex of the tripeptide GGH and a peroxide oxidant, or irradiation in the presence of Ru(bpy)(3)(2+) and persulfate generates covalent crosslinks across the pentameric subunit boundaries, effectively stitching the subunits together. Intersubunit crosslinking was found to occur exclusively at adjacent tyrosine residues (Y52-Y103), as predicted from the X-ray crystal structure of the capsid, and to be more extensive with the photochemical ruthenium system. The Ni/GGH oxidative procedure was also used to make covalent attachments to the virion by trapping with a functionalized disulfide reagent.     

Intelligent routes to the controlled synthesis of nanoparticles

We describe an autonomous 'black-box' system for the controlled synthesis of fluorescent nanoparticles. The system uses a microfluidic reactor to carry out the synthesis and an in-line spectrometer to monitor the emission spectra of the emergent particles. The acquired data is fed into a control algorithm which reduces each spectrum to a scalar 'dissatisfaction coefficient' and then intelligently updates the reaction conditions in an effort to minimise this coefficient and so drive the system towards a desired goal. In the tests reported here, CdSe nanoparticles were prepared by separately injecting solutions of CdO and Se into the two inlets of a heated y-shaped microfluidic reactor. A noise-tolerant global search algorithm was then used to efficiently identify-without any human intervention-the injection rates and temperature that yielded the optimum intensity for a chosen emission wavelength.     

Microfluidic routes to the controlled production of nanoparticles

A microfluidic procedure for the controlled production of cadmium sulfide nanoparticles is described.     

Quantitative characterization of changes in dynamical behavior for single-particle tracking studies

Single-particle tracking experiments have been used widely to study the heterogeneity of a sample. Segments with dissimilar diffusive behaviors are associated with different intermediate states, usually by visual inspection of the tracking trace. A likelihood-based, systematic approach is presented to remove this incertitude. Maximum likelihood estimators are derived for the determination of diffusion coefficients. A likelihood ratio test is applied to the localization of the changes in them. Simulations suggest that the proposed procedure is statistically robust and is able to quantitatively recover time-dependent changes in diffusion coefficients even in the presence of large measurement noise.     

Rational design and biomedical applications of DNA-functionalized upconversion nanoparticles

In this review, we mainly introduced recent progress of DNA-functionalized upconversion materials, providing an overview of the design and applications in biosensing, bioimaging and disease therapy. The challenges and future perspectives are also discussed, aiming to promote their applications in materials science and biomedicine.     

How to compare diffusion processes assessed by single-particle tracking and pulsed field gradient nuclear magnetic resonance

Heterogeneous diffusion processes occur in many different fields such as transport in living cells or diffusion in porous media. A characterization of the transport parameters of such processes can be achieved by ensemble-based methods, such as pulsed field gradient nuclear magnetic resonance (PFG NMR), or by trajectory-based methods obtained from single-particle tracking (SPT) experiments. In this paper, we study the general relationship between both methods and its application to heterogeneous systems. We derive analytical expressions for the distribution of diffusivities from SPT and further relate it to NMR spin-echo diffusion attenuation functions. To exemplify the applicability of this approach, we employ a well-established two-region exchange model, which has widely been used in the context of PFG NMR studies of multiphase systems subjected to interphase molecular exchange processes. This type of systems, which can also describe a layered liquid with layer-dependent self-diffusion coefficients, has also recently gained attention in SPT experiments. We reformulate the results of the two-region exchange model in terms of SPT-observables and compare its predictions to that obtained using the exact transformation which we derived.     

International interlaboratory study for sizing and quantification of Ag nanoparticles in food simulants by single-particle ICPMS

This publication describes the first international intercomparison of particle-size determination by single-particle inductively coupled plasma mass spectrometry (sp-ICPMS). Concentrated monodisperse silver nanoparticle suspensions with particle diameters of 20, 40 and 100 nm and a blank solution were sent to 23 laboratories in Europe, the USA and Canada. Laboratories prepared eight nanoparticle preparations in two food simulants (distilled water; 10 % ethanol) and reported median particle size, Ag particle mass concentration and Ag particle number concentrations. Average repeatability and reproducibility standard deviation (s _r and s _R) for the median particle diameter were 1 and 14 nm, respectively. Relative precision was worse for Ag particle number concentrations (RSD _r?=?11 %; RSD _R?=?78 %). While further improvements of the method, especially with respect to software tools for evaluation, hardware options for shorter dwell times, calibration standards for determining nebuliser efficiency and further experience by laboratories are certainly desirable, the results of this study demonstrate the suitability of sp-ICPMS for the detection and quantification of certain kinds of nanoparticles.     

稀土掺杂上转换纳米粒子的表面功能化修饰及其生物应用

稀土掺杂上转换纳米粒子(RED-UCNPs)作为一种新型高效的上转换发光纳米材料,具有反斯托克斯位移大,发射光谱窄、发光寿命长、材料毒性低等优点,已成为荧光标记、光动力学治疗、生物成像和构建生物传感器等领域的研究热点。然而,目前广泛使用的溶剂热法合成的RED-UCNPs生物相容性和亲水性差,而且不具备与生物分子之间相偶联的活性基团,因此对RED-UCNPs进行表面功能化修饰就显得格外重要。本文重点综述了RED-UCNPs的表面功能化修饰的类型及其应用现状,为RED-UCNPs的进一步研究开发和应用提供思路和参考依据。     

White-light emissive upconversion nanoparticles for visual and colorimetric determination of the pesticide thiram

Microchimica Acta - A chip-based array is described for magnetic solid-phase microextraction (MSPME) of the ions of Pt, Au and Bi. Magnetic porous organic polymers (MOPs) prepared from magnetite...     

Measurement of the amplitude and phase of the electrophoretic and electroosmotic mobility based on fast single-particle tracking

The electrophoretic mobility of micron-scale particles is of crucial importance in applications related to pharmacy, electronic ink displays, printing, and food technology as well as in fundamental studies in these fields. Particle mobility measurements are often limited in accuracy because they are based on ensemble averages and because a correction for electroosmosis needs to be made based on a model. Single-particle approaches are better suited for examining polydisperse samples, but existing implementations either require multiple measurements to take the effect of electroosmosis into account or are limited in accuracy by short measurement times. In this work, accurate characterization of monodisperse and polydisperse samples is achieved by measuring the electrophoretic mobility on a particle-to-particle basis while suppressing electroosmosis. Electroosmosis can be suppressed by measuring in the middle of a microchannel while applying an AC voltage with a sufficiently high frequency. An accurate measurement of the electrophoretic mobility is obtained by analyzing the oscillating particle motion for per particle with a high-speed camera measuring at , synchronized to the applied electric field. Attention is paid to take into account the effect of the rolling shutter and the non-uniform sampling in order to obtain the accurate amplitude and phase of the electrophoretic mobility. The accuracy of method is experimentally verified and compared with a commercial apparatus for polystyrene microspheres in water. The method is further demonstrated on a range of particle materials and particle sizes and for a mixture of positively and negatively charged particles.     

Controlled encapsidation of gold nanoparticles by a viral protein shell

Icosahedral virus capsids demonstrate a high degree of selectivity in packaging cognate nucleic acid components during assembly. This packaging specificity, when integrated as part of a nanotechnological protocol, has the potential to encapsidate a wide array of foreign materials for delivery of therapeutics or biosensors into target cells. Red clover necrotic mosaic virus (RCNMV) exclusively packages two genomic ssRNAs initiated by a specific protein:RNA interaction between the RCNMV coat protein (CP) and the viral RNA origin of assembly (OAS) element. In the present work, an oligonucleotide mimic of the RCNMV OAS sequences is attached to Au nanoparticles as a recognition signal to initiate the virion-like assembly by RCNMV CP. Covalent linkage of the OAS to Au functions as a trigger for specific encapsidation and demonstrates that foreign cargo can be packaged into RCNMV virions.     

Synthesis of improved upconversion nanoparticles as ultrasensitive fluorescence probe for mycotoxins

Rare earth-doped upconversion nanoparticles (UCNPs) have promising potentials in biodetection due to their unique frequency upconverting capability and high detection sensitivity. This paper reports an improved UCNPs-based fluorescence probe for dual-sensing of Aflatoxin B1 (AFB1) and Deoxynivalenol (DON) using a magnetism-induced separation and the specific formation of antibody-targets complex. Herein, the improved UCNPs, which were namely NaYF₄:Yb/Ho/Gd and NaYF₄:Yb/Tm/Gd, were systematically studied based on the optimization of reaction time, temperature and the concentration of dopant ions with simultaneous phase and size controlled NaYF₄ nanoparticles; and the targets were detected using the pattern of competitive combination assay. Under an optimized condition, the advanced fluorescent probes revealed stronger fluorescent properties, broader biological applications and better storage stabilities compared to traditional UCNPs-based ones; and ultrasensitive determinations of AFB1 and DON were achieved under a wide sensing range of 0.001–0.1 ng ml⁻¹ with the limit of detection (LOD) of 0.001 ng ml⁻¹. Additionally, the applicability of the improved nanosensor for the detection of mycotoxins was also confirmed in adulterated oil samples.     

Facile patterning of upconversion NaYF4:Yb,Er nanoparticles

Different kinds of highly ordered patterns of NaYF(4):Yb,Er nanoparticles on gold substrates were fabricated using a simple method combining micro-contact printing and "breath figures" techniques. Ordered arrays of water droplets were first formed in the hydrophilic regions of patterned self-assembled monolayers (SAMs). This was subsequently submerged in a chloroform solution of NaYF(4):Yb,Er nanoparticles. The particles were spontaneously assembled at the interface of chloroform/water droplet surface, leading to different kinds of uniform patterns after solvent evaporation. The structures of NaYF(4):Yb,Er particles patterns depended on the dimension of the substrate, the concentration of the NaYF(4):Yb,Er nanoparticles and the water condensation process.     

Solution NMR studies of the maturation intermediates of a 13 MDa viral capsid

Dynamic regions of proteins often play essential roles in function, assembly, or maturation of macromolecular complexes. When X-ray crystallography and cryo-electron microscopy are used to investigate macromolecular structures, information about these dynamic regions is lost because of conformational disorder or flexibility. Structural studies on the precursor capsid conformations of the lambdoid bacteriophage HK97, a model system for macromolecular maturation, reveal that essential regions tend to be disordered at early maturation stages. In the Prohead II intermediate, the regions that have the greatest disorder are the N-terminal residues and the E-loop, a region involved in the formation of inter-subunit cross-links. The N-terminus of the subunits in the 13 MDa procapsid is sufficiently dynamic to be studied by solution nuclear magnetic resonance (NMR) spectroscopy. NMR measurements enabled the identification and assignment of resonances to specific residues, assessment of the region's behavior within the context of the capsid, and monitoring of changes in these residues during the maturation process. In the precursor Prohead II and immature EI-III states, the N-termini are found to make transient interactions with the interior capsid surface, while at least a subset of N-termini in EI-III becomes more flexible with time. No resonances are observed for the fully mature Head II capsid, which is consistent with its completely ordered structure. NMR spectroscopy complements the current X-ray crystallography and cryo-electron microscopy data of HK97 by providing key information about the behavior of essential dynamic regions only inferred by other techniques.