Mechanical property analysis of stored red blood cell using optical tweezers

The deformation of human red blood cells subjected to direct stretching by optical tweezers was analyzed. The maximum force exerted by optical tweezers on the cell via a polystyrene microbead 5 μm in diameter was 315 pN. Digital image correlation (DIC) method was introduced to calculate the force and the deformation of the cell for the first time. Force–extension relation curves of the biconcave cell were quantitatively assessed when erythrocytes were stored in Alsever's Solution for 2 days, 5 days, 7 days and 14 days respectively. Experiment results demonstrated that the deformability of red blood cells was impaired with the stored time.     

The elastic properties of single double-stranded DNA chains of different lengths as measured with optical tweezers

Optical tweezers are microscopic tools with extraordinary precision in the determination of the position (±2 nm) of a colloid (diameter: ∼2.0 μm) in 3D-space and in the measurement of small forces in the range between 0.1 and 100 pN (pN=10⁻¹² N). Experiments are reported in which single double-stranded (ds)-DNA chains of different length [2,000 base pairs (bp), 3,000, 4,000, and 6,000 bp] are spanned between two colloidal particles by use of appropriate molecular linkers. For the forces applied (≤40 pN) a fully reversible and well reproducible force–extension dependence is found. The data can be well described by both the worm-like chain model or by an approach developed by R. G. Winkler. For the resulting persistence length, a pronounced dependence on the ionic concentration in the surrounding medium is found.     

Mechanical properties of single motor molecules studied by three-dimensional thermal force probing in optical tweezers.

A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general     

A method for an approximate determination of a polymer-rich-domain concentration in phase-separated poly(N-isopropylacrylamide) aqueous solution by means of confocal Raman microspectroscopy combined with optical tweezers

The paper demonstrates that a confocal Raman microspectroscope combined with optical tweezers is a promising technique to estimate polymer concentration in polymer-rich domain in phase-separated-aqueous polymer solution. The sample polymer is poly-(N-isopropylacrylamide) (PNIPAM) that is well-known as a representative thermo-responsive polymer. Optical tweezers can selectively trap the polymer-rich domain at the focal point in non-contact and non-intrusive modes. Such situation allows us to determine polymer concentration in the domain, which has been unclear due to a lack of appropriate analytical technique. It is applicable for a variety of other thermo-responsive polymers.     

A valve‐based microfluidic device for on‐chip single cell treatments

Assays toward single‐cell analysis have attracted the attention in biological and biomedical researches to reveal cellular mechanisms as well as heterogeneity. Yet nowadays microfluidic devices for single‐cell analysis have several drawbacks: some would cause cell damage due to the hydraulic forces directly acting on cells, while others could not implement biological assays since they could not immobilize cells while manipulating the reagents at the same time. In this work, we presented a two‐layer pneumatic valve‐based platform to implement cell immobilization and treatment on‐chip simultaneously, and cells after treatment could be collected non‐destructively for further analysis. Target cells could be encapsulated in sodium alginate droplets which solidified into hydrogel when reacted with Ca²⁺. The size of hydrogel beads could be precisely controlled by modulating flow rates of continuous/disperse phases. While regulating fluid resistance between the main channel and passages by the integrated pneumatic valves, on‐chip capture and release of hydrogel beads was implemented. As a proof of concept for on‐chip single‐cell treatments, we showed cellular live/dead staining based on our devices. This method would have potential in single cell manipulation for biochemical cellular assays.     

Preparation of stable second‐order nonlinear optical films by sol–gel technique

A stable nonlinear optical (NLO) film containing “T” type alkoxysilane dye was prepared by sol–gel technology. This crosslinked “T” type alkoxysilane dye was synthesized and fully characterized by FTIR, UV–Vis spectra, and ¹H‐NMR. Followed by hydrolysis and copolymerization processes of the alkoxysilane with γ‐glycidoxypropyl trimethoxysilane (KH560) and tetraethoxysilane (TEOS), high quality inorganic–organic hybrid second‐order NLO films were obtained by spin coating. The “T” type structure of the alkoxysilane was found to be effective for improving the temporal stability of the optical nonlinearity due to the reduction in the relaxation of the chromophore in the film materials. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantification of 5‐aminolevulinic acid by CE using dynamic pH junction technique

An online dynamic pH junction preconcentration method was developed for quantification of 5‐aminolevulinic acid (ALA) by CE with the separation time less than 6 min. The optimal dynamic pH junction of ALA was carried out between pH 9.3 borate buffer (BGE, 40 mM) and pH 2.5 phosphate buffer (sample matrix, 40 mM) when 4.1 cm of sample plug was hydrodynamically injected into an uncoated fused‐silica capillary (48.5 cm in length, id of 50 μm). If a 24 kV separation voltage was applied, the calibration curve of ALA peak area (200 nm) showed good linearity (R² = 0.9991) ranging from 0.01 to 6.5 mg/mL. The reproducibility of this system was excellent with RSDs (n = 10) of 2.5% for peak area response and 0.6% for migration time at ALA concentration of 0.5 mg/mL. The LOD was evaluated as 1.0 μg/mL (S/N > 3). Compared to conventional CE procedure, the sensitivity was successfully improved over 50‐fold. The analytical results of pharmaceutical formulations show a good agreement with those by HPLC (r = 0.94).     

Tensile tests of polypropylene monitored by SAXS. Comparing the stretch‐hold technique to the dynamic technique

Advanced instrumentation at synchrotron beamlines facilitates considerable reduction of the exposure required for the recording of low‐noise small‐angle X‐ray scattering (SAXS) patterns. Concerning the monitoring of tensile tests on polymer materials by SAXS means that change‐over from the stretch‐hold technique to more practical dynamic straining is possible, although the strain rate is still by a factor of 100 lower than that relevant in industry and service. As hard‐elastic polypropylene (PP) is tested, considerably different scattering patterns are recorded after switching to the dynamic technique. Even though during exposure the elongation is no longer constant when applying the dynamic technique, the images collected in stretch‐hold technique appear much more blurred. The observed immediate relaxation of nanostructure induced by stopping the extensometer is analyzed by means of the multidimensional chord distribution function (CDF): The extension of the crystalline lamellae is increasing. Their thicknesses are becoming non‐uniform. The range of order is shortening. Cross‐hatched lamellae are formed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 721–726, 2008     

Dual capacitor technique for measurement of through‐plane modulus of thin polymer films

Polymer thin films are widely used as coatings and interlevel dielectrics in microelectronic applications. In thin‐film structures, stresses are generated due to interaction with adjacent layers and film shrinkage due to solvent evaporation or curing. This causes polymer chain orientation resulting in anisotropic (direction dependent) film properties. The dual capacitor technique has been developed to measure in situ, the through‐plane (z) stress‐strain behavior of thin polymer films. A parallel plate capacitor device and an interdigitated electrode structure were used as sensors to detect changes in dielectric permittivity and thickness of thin polymer films under compression. The analytical and finite element models used to interpret the capacitance measurements have been presented. The Clausius–Mossotti equation was used to determine the volume change in the film from the permittivity measurements. Results have been reported for 10–14 μm thick, Cyclotene 4026‐46 benzocyclobutene films and 10–12 μm thick films of polyimide PI‐2611. The Cyclotene 4026‐46 films were found to be mechanically isotropic, whereas the PI‐2611 films were highly anisotropic. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1634–1644, 2000     

A method for the detection of alcohol vapours based on optical sensing of magnesium 5,10,15,20-tetraphenyl porphyrin thin film by an optical spectrometer and principal component analysis

In this work we have proposed a method for the detection of alcohol vapours, i.e. methanol, ethanol and isopropanol, based on the optical sensing response of magnesium 5,10,15,20-tetraphenyl porphyrin (MgTPP) thin films, as measured by optical spectrometry with the assistance of chemometric analysis. We have implemented a scheme which allows a laboratory UV–vis spectrometer to act as a so-called “electronic nose” with very little modification. MgTPP thin films were prepared by a spin coating technique, using chloroform as the solvent, and then subjected to thermal annealing at 280 °C in an argon atmosphere. These MgTPP optical gas sensors presented significant responses with methanol compared to ethanol and isopropanol, based on the dynamic flow of alcohol vapours at the same mol% of alcohol concentration. Density functional theory (DFT) calculations were performed to model the underlying mechanism of this selectivity. The performance of the optical gas sensors was optimised by varying the fabrication parameters. It is hoped that the MgTPP thin film together with an off-the-shelf optical spectrometer and a simple chemometrics algorithm can be a valuable tool for the analysis of alcoholic content in the beverage industry.     

Non‐optical bimorph‐based force sensor for scanning near‐field optical microscopy of biological materials: characteristics,design and applications

A non‐optical force sensor that allows operation both in lateral (shear) and in vertical (tapping) force detection modes has been introduced for dynamic tip–sample distance regulation in scanning near‐field optical microscopy (SNOM) of biological samples. The sensor is based on a rectangular bimorph cantilever consisting of two thin piezoceramic layers bonded to a brass centre shim. One of the piezo layers serves as the probe dither and another as the responder of the sensed forces. The sensor is driven with a home‐made Q‐control electronics so that its sensitivity and bandwidth can be adjusted. The dynamics, characteristics and design considerations of the sensor are theoretically and experimentally discussed. Driving the bimorph cantilever at its eigenfrequency with appropriate force feedback allows one to obtain a quality factor (Q‐factor) up to 10³ in water, suitable for different sample softness and imaging environments. The high sensitivity of the sensor is demonstrated both by shear force and by tapping mode imaging of soft biological samples in their natural state. Near‐field optical resolution of better than 100 nm on red blood cells in water has been obtained. The experimental results suggest that this SNOM sensor would be a promising set‐up for biological applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Nanoscale three‐dimensional optical visualization method for a deformation of elastomer printing plate to realize soft nano‐printing technology

Printed electronics, in which microcircuit patterns are fabricated using printing methods, are the focus of considerable attention for the fabrication of devices such as flat panel displays, solar cells, and flexible electronics. In particular, gravure offset printing is considered to be a highly promising approach for rapid printing of fine patterns with well‐controlled thickness. At present, however, because of the occurrence of side etching during fabrication of metal printing plates, features with dimensions of less than 10 µm cannot be printed. In order to overcome this problem, we have previously proposed the use of a rubber printing plate fabricated by photolithography and molding, which is free from side‐etching issues. However, deformation of the printing plate can have a detrimental influence on the transferred pattern. In the present study, we developed a method for visualizing the deformation of a printing plate containing both micropatterns and nanopatterns, in order to study its effect on the printing process. The results were compared with those predicted by an analytic equation under a uniform controlled pressure. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure‐based redesign of proteins for minimal T‐cell epitope content

The protein universe displays a wealth of therapeutically relevant activities, but T‐cell driven immune responses to non‐“self” biological agents present a major impediment to harnessing the full diversity of these molecular functions. Mutagenic T‐cell epitope deletion seeks to mitigate the immune response, but can typically address only a small number of epitopes. Here, we pursue a “bottom‐up” approach that redesigns an entire protein to remain native‐like but contain few if any immunogenic epitopes. We do so by extending the Rosetta flexible‐backbone protein design software with an epitope scoring mechanism and appropriate constraints. The method is benchmarked with a diverse panel of proteins and applied to three targets of therapeutic interest. We show that the deimmunized designs indeed have minimal predicted epitope content and are native‐like in terms of various quality measures, and moreover that they display levels of native sequence recovery comparable to those of non‐deimmunized designs. © 2013 Wiley Periodicals, Inc.     

Evaluation and application of argon and helium microstrip plasma for the determination of mercury by the cold vapor technique and optical emission spectrometry

The suitability of a 2.45-GHz atmospheric pressure, low-power microwave microstrip plasma (MSP) operated with Ar and He for the determination of Hg by continuous-flow cold vapor (CV) generation, using SnCl₂/HCl as the reducing agent, and optical emission spectrometry (OES) using a small CCD spectrometer was studied. The areas of stability for a discharge in the Ar and in the He MSP enclosed in a cylindrical channel in a quartz wafer were investigated. The excitation temperatures as measured for discharge gas atoms (Ar I, He I), and the electron number densities at 35–40 W and 15–400 mL min⁻¹ were found to be at the order of 3,200–5,500 K and 0.8 × 10¹⁴–1.6 × 10¹⁴ cm⁻³, respectively. The relative intensity of the Hg I 253.6-nm line and the signal-to-background ratio as a function of the forward power (35–40 W) as well as of the flow rate of the working gas (15–400 mL min⁻¹) were evaluated and discussed. For the selected measurement conditions, the Ar MSP was established to have the lower detection limit for Hg (0.6 ng mL⁻¹) compared with the He MSP. The linearity range is up to 300 ng mL⁻¹ and the precision is on the order of 1–3%. With the optimized CV Ar MSP-OES method a determination of Hg in spiked domestic and natural waters at concentration levels of 20–100 μg L⁻¹ and an accuracy of 1–4% could be performed. In an NIST domestic sludge standard reference material, Hg (3.64 μg g⁻¹) could be determined with a relative standard deviation of 4% and an agreement better than 4%.     

Synthesis of chitosan‐based thermo‐ and pH‐responsive porous nanoparticles by temperature‐dependent self‐assembly method and their application in drug release

In this research, thermo‐ and pH‐responsive chitosan‐based porous nanoparticles were prepared by the temperature‐dependent self assembly method. The chitosan‐graft‐poly(N‐isopropylacrylamide) (CS‐g‐PNIPAAm) copolymer solution was prepared through polymerization of N‐isopropylacrylamide (NIPAAm) monomer in the presence of chitosan (CS) solution using cerium ammounium nitrate as the initiator. Then, CS‐g‐PNIPAAm solution was diluted by deionized water and heated to 40 °C for CS‐g‐PNIPAAm self‐assembly. After that, CS‐g‐PNIPAAm assembled to form micelles in which shell layer was CS. Crosslinking agent was used to reinforce the micelle structure to form nanoparticle. The molar ratio of CS/NIPAAm in the feed mixture was changed to investigate its effect on structure, morphology, thermal‐ and pH‐responsive properties of the nanoparticles. TEM images showed that a porous structure of nanoparticles was developed. The synthesized nanoparticles carried positive charges on the surface and exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in‐vitro release experiment. These porous particles with environmentally sensitive properties are expected to be utilized in hydrophilic drug delivery system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5126–5136, 2009     

Control of cell growth direction by direct fabrication of periodic micro‐ and submicrometer arrays on polymers

In this work, we describe a laser‐assisted microstructuring technique called Direct Laser Interference Patterning to produce topographical cues for tumor cells in a one‐step process. Line‐like patterns with spatial periods ranging from 500 nm to 10 μm are fabricated on polyimide (PI) films. The resulting structures exhibit a well‐defined shape and quality even for patterns with small periodic distances. Subsequently, the behavior of mouse mammary adenocarcinoma cells over those structures is evaluated. The results show that cell growth is well aligned to the direction of the patterns (over 60% lying within 0° to 15° to either side of the surface lines) for all evaluated structure sizes. Moreover, cells grown on patterns with 500 nm spatial period are the most narrowly aligned (up to 80% found between 0° and 15°), showing the potential of the technique. The fabrication process of the PI patterns is supported by a mathematical model of the underlying photo‐chemical ablation process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis and characterization of copolymaleimides containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications

We report the synthesis of a nematic copolymer, P(CBMS‐co‐M₃), prepared by free radical polymerization of an equimolecular mixture of p‐(4‐cyanobiphenyl‐4′‐yloxy)methylstyrene (CBMS) and N‐[3‐(4‐cyanobiphenyl‐4′‐yloxy)propyl]maleimide (M₃) and two isotropic alternating copolymers, P(S‐alt‐M_n) (n = 3,6) prepared by chemical modification of poly(styrene‐alt‐maleimide), P(S‐alt‐M), by n‐(4‐cyanobiphenyl‐4′‐yloxy)alkan‐1‐ol. These copolymaleimides were characterized by NMR, DSC, and optical microscopy. Some corona poling experiments were performed and the second harmonic coefficients d₃₁ and d₃₃ were measured. It was shown that one can gain in net polar ordering by starting with a liquid crystalline system. The ratio d₃₃/d₃₁ was much larger than 3, in agreement with the molecular statistical models for electric field poling of liquid crystals. At ambient conditions, changes of d₃₃ and d₃₁ are 15% over 325 days. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 513–524, 1999     

Synthesis and characterization of stimuli‐responsive porous/hollow nanoparticles by self‐assembly of chitosan‐based graft copolymers and application in drug release

In this research, stimuli‐responsive porous/hollow nanoparticles were prepared by the self‐assembly method. First, chitosan‐graft‐poly(N‐isopropylacrylamide) (CS‐g‐PNIPAAm) copolymers were synthesized through polymerization of N‐isopropylacrylamide (NIPAAm) monomer in the presence of chitosan (CS) solution using ceric ammounium nitrate as the initiator. Then, the CS‐g‐PNIPAAm copolymers were dissolved in the acetic acid aqueous solution and heated to 40 °C to induce their self‐assembly. After CS‐g‐PNIPAAm assembled to form micelles, a cross‐linking agent was used to reinforce the structure to form nanoparticles. The molecular weight of grafted PNIPAAm on CS chains was changed to investigate its effect on the structure, morphology, thermo‐, and pH‐responsive properties of the nanoparticles. TEM images showed that a porous or hollow structure in the interior of nanoparticles was developed, depending on the medium temperature. The synthesized nanoparticles carried positive charges on the surface and exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing the pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in vitro release experiment. These porous/hollow particles with environmentally sensitive properties are expected to be used in hydrophilic drug delivery system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2377–2387, 2010     

Label‐free aptamer‐based partial filling technique for enantioseparation and determination of dl‐tryptophan with micellar electrokinetic chromatography

In this study, a simple and reproducible method for enantioseparation and determination of dl ‐tryptophan (dl ‐T rp) was developed by using a partial filling technique in combination with MEKC . The corresponding l ‐T rp specific DNA aptamer was used as a chiral selector. Sodium cholate was used to form the chiral micelles and to enhance the enantioseparation of the enantiomers. Effects of aptamer concentration, filling time, buffer composition, and separation voltage on the enantioseparation were evaluated. The M g²⁺ and Na⁺ concentration in separation buffer was found to effectively affect the separation efficiency and reproducibility. Under the optimal conditions, d ‐ and l ‐T rp were completely enantioseparated in less than 9 min. This aptamer‐based partial‐filling approach has the potential to be extended to the separation of other enantiomers after the replacement of corresponding specific aptamers.