Cyclic Epipedography─Monitoring Contact Angle Changes in Dipping a Microsphere into a Liquid and Lifting from It.

We propose cyclic epipedography to monitor the wetting characteristics of a microsphere on a stem with a liquid by tracking the level of a liquid line on the sphere when the sphere is dipped into and lifted from the liquid, and therefore the level of the liquid plane at infinity changes with respect to the sphere. Analysis of still images of a video taken with a horizontally held microscope determines the two levels. The sphere allows viewing of the liquid line without being obscured by the meniscus the liquid forms with its container's wall.

Whispering Gallery Mode Dip Sensor for Aqueous Sensing.

We report fabrication of a 4 mm thick, preassembled whispering gallery mode (WGM) sensor that can be repeatedly dipped into aqueous solutions and lifted. We built the viable photonic sensor assembly by bending an optical fiber by 90° and molding its tip into a sphere, thus, a long stem holding a submillimeter sensor at the end of a short arm of fiber, and positioning a pair of parallel cone-tipped tapers along the long stem so that the tips touch the sensor. Our sensor head is an optical fiber device just a few millimeters thick and yet has a sensitivity of the resonance wavelength shift comparable to the one obtained with conventional WGM sensors in a planar arrangement.

Comparison of retention behavior of oligolysine and oligoarginine in ion-pairing chromatography using heptafluorobutyric acid.

This paper describes the retention behavior of oligolysine and oligoarginine peptides of different lengths as a function of heptafluorobutyric acid (HFBA) concentration in ion-pairing reversed-phase chromatography in isocratic elution. A mixture of oligolysine and a mixture of oligoarginine with number of amino acid residues (dp) from two to eight were conveniently prepared by one-pot protease-catalyzed synthesis. Analysis of the logarithm of the retention factor k as a function of [HFBA] for each oligopeptide component, using a closed pairing model, provided values for (1) number (n) of paired HFBA anions per peptide molecule, (2) equilibrium constant (K(ip,m)) for ion pairing between oligopeptides and HFBA anions, and (3) product of the phase ratio and the distribution constant of the paired oligopeptide between the mobile and stationary phases (βK(d,ip)).

All-photonic, dynamic control of optical path length in a silica sphere resonator.

We demonstrate dynamic control of the optical path length for probe light in a spherical dielectric resonator simply by multiplexing intense control light of another color and adjusting its wavelength. The fractional change in the path length, monitored by the resonance wavelengths of whispering gallery modes of the probe light, was nearly equal to the fractional change in the wavelength of the control light. The control was effective in both increasing and decreasing the wavelength, but the weaker the control light or the faster the wavelength change, the narrower the range of control.

Reversed phase ion-pairing chromatography of an oligolysine mixture in different mobile phases: effort of searching critical chromatography conditions.

Our earlier study [J. Chromatogr. A 1218 (2011) 7765] on separation of an oligolysine mixture consisting of chains with 2-8 lysine residues (number of lysine residues, dp=2-8) by ion-pairing reversed-phase chromatography using heptafluorobutyric acid (HFBA) as an ion pairing reagent at fixed mobile phase acetonitrile (ACN) content was extended to isocratic elution conditions with different ACN percentages.

Light turn-on transient of a whispering gallery mode resonance spectrum in different gas atmospheres.

We examine the resonance spectrum change after turning on the light to feed the fiber taper evanescently coupled to a silica whispering gallery mode (WGM) resonator surrounded by different gases at different pressures. The resonance shifted to a longer wavelength, indicating a temperature rise, before reaching a steady state. The increment was proportional to the power of the light and approximately reciprocally proportional to the thermal conductivity of the surrounding gas, whereas the rate of the shift was approximately proportional to the thermal conductivity.

Resonance shifts of transverse-electric whispering gallery modes in a spheroidal resonator.

A variational method was applied to find the wave function of a transverse-electric whispering gallery mode (WGM) in a spheroidal resonator of a uniform refractive index (RI). It was found that the electric field is tangential to the resonator surface as in the sphere, up to the linear order of the ellipticity. Using the wave function, the resonance shift due to adsorption of a thin, uniform dielectric layer onto the surface and the shift by a uniform RI change in the surroundings were evaluated in the perturbation theory.

Cooperative effect in ion pairing of oligolysine with heptafluorobutyric acid in reversed-phase chromatography.

The retention behavior of an oligolysine mixture, consisting of two to eight residues, was examined at different concentrations of heptafluorobutyric acid (HFBA) in the mobile phase using a C18 column. A single ion record (SIR) mode of the mass spectrometer produced a distinct retention time for each oligomer component. As the concentration of HFBA increased, the retention time of each oligomer increased.

MicroParticle photophysics illuminates viral bio-sensing.

The authors present an approach for specific and rapid unlabeled detection of a virus by using a microsphere-based whispering gallery mode sensor that transduces the interaction of a whole virus with an anchored antibody. They show theoretically that this sensor can detect a single virion below the mass of HIV. A micro-fluidic device is presented that enables the discrimination between viruses of similar size and shape.

Coupled whispering gallery modes in a multilayer-coated microsphere.

Whispering gallery modes in a microsphere coated with three layers of high, low, and high refractive indices (RIs) are considered. Coastal modes and inland modes, centered on the outer and inner high-RI layers, exist as different radial modes. At right values of RI and thickness of the three layers, an inland mode and a coastal mode couple to produce a radial distribution of the photonic field that resembles bonding and antibonding orbitals.

Detection of protein orientation on the silica microsphere surface using transverse electric/transverse magnetic whispering gallery modes.

The state of adsorbed protein molecules can be examined by comparing the shifts in a narrow line resonance wavelength of transverse electric (TE) and transverse magnetic (TM) whispering gallery modes (WGM) when the molecules adsorb onto a transparent microsphere that houses WGM. In adsorption of bovine serum albumin (BSA) onto an aminopropyl-modified silica microsphere, the TM/TE shift ratio indicated highly anisotropic polarizability of BSA in the direction normal to the surface, most likely ascribed to anchoring the heart-shaped protein molecule by one of its tips. The polarization-dependent resonance shift was confirmed when the surrounding refractive index was uniformly changed by adding salt, which would simulate adsorption of large objects.

Nanolayer characterization through wavelength multiplexing of a microsphere resonator.

We optically characterize nanolayer (<150 nm) formation in situ on a silica microsphere in an aqueous environment by simultaneously following the shifts of whispering-gallery modes at two wavelengths. This approach was inspired by layer perturbation theory, which indicates that these two measurements can be used to determine independently both the thickness and the optical dielectric constant. The theory is verified for extreme cases and used to characterize a biophysically relevant hydrogel nanolayer with an extremely small excess refractive index of 0.

Hydrogel formation between enantiomeric B-A-B-type block copolymers of polylactides (PLLA or PDLA: A) and polyoxyethylene (PEG: B); PEG-PLLA-PEG and PEG-PDLA-PEG.

A mixed suspension of the enantiomeric B-A-B triblock copolymers, polyoxyethylene-block-poly(L-lactide)-block-polyoxyethylene (PEG-PLLA-PEG) and polyoxyethylene-block-poly(D-lactide)-block-polyoxyethylene (PEG-PDLA-PEG), was found to induce reversible gel-to-sol transition depending on the polymer concentration and temperature. The storage and loss moduli of the gel formed at lower temperature were much higher than those of the gel prepared from the corresponding ABA-type triblock copolymers because of the higher polymer concentration in the former. Although the stereo-complexation of the PLLA and PDLA blocks occurred at higher temperature also in the B-A-B copolymers, it was not responsible for the gelation of the mixed suspension.

Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities.

We have developed a novel, spectroscopic technique for high-sensitivity, label-free DNA quantification. We demonstrate that an optical resonance (whispering gallery mode) excited in a micron-sized silica sphere can be used to detect and measure nucleic acids. The surface of the silica sphere is chemically modified with oligonucleotides.

Scale-up study of high osmotic pressure chromatography for separation of poly(epsilon-caprolactone).

Methods to prepare fractions of poly(epsilon-caprolactone) with a narrow molecular mass distribution in large quantities have been examined using high osmotic pressure chromatography under the theta condition. Effects of column dimension and coupling columns in series on the separation resolution were studied. We found that use of a thicker column can improve the resolution if adverse effects of viscous fingering are avoided.

Shift of whispering-gallery modes in microspheres by protein adsorption.

Biosensors based on the shift of whispering-gallery modes in microspheres accompanying protein adsorption are described by use of a perturbation theory. For random spatial adsorption, theory predicts that the shift should be inversely proportional to microsphere radius R and proportional to protein surface density and excess polarizability. Measurements are found to be consistent with the theory, and the correspondence enables the average surface area occupied by a single protein to be estimated.

Removal of dihydroxy-terminated components from monomethoxy-terminated poly(ethylene glycol).

A preparative method to remove dihydroxy-terminated components in a sample of presumably monomethoxy, monohydroxy-terminated poly(ethylene glycol) (PEG) is presented. Purification of the monomethoxy-terminated component allows one to prepare a diblock copolymer of PEG and poly(lactic acid) (PLLA) free of a PLLA-PEG-PLLA triblock copolymer in various biomedical applications of the copolymer. Efficiency of the purification is compared for high osmotic pressure chromatography (HOPC) and preparative size exclusion chromatography (SEC).

Composition analysis of poly(ethylene glycol)-poly(L-lactide) diblock copolymer studied by two-dimensional column chromatography.

We used two-dimensional column chromatography to analyze the composition of a sample of presumably a diblock copolymer of poly(ethylene glycol) (PEG) and poly(L-lactide) synthesized from monomethoxy-terminated PEG. The first dimension of the separation is phase fluctuation chromatography to prepare fractions that contain various components of the copolymer in different ratios. The second dimension is size-exclusion chromatography, NMR, and HPLC at the critical condition of PEG.

Can the serum protein binding of valproic acid limit the hepatic elimination?

In the previous study, we determined the in vivo binding parameters of valproic acid to serum proteins in seven healthy young adults at steady-state. In this study, we determined the effects of serum protein binding on hepatic elimination with the use of observed data obtained from our previous study of valproic acid. A regression analysis between the binding parameters and the pharmacokinetic parameters was performed.

Effect of unbound clearance on binding parameters of valproic acid to serum proteins.

Nine healthy subjects received 400 mg sodium valproate orally in the fasting state. Binding parameters of valproic acid to serum proteins were determined by Scatchard analysis for individual series of valproic acid data. Total and unbound (intrinsic) clearances (CLt and CLu) were calculated by dividing the dose by the appropriate area under the serum drug concentration-time curve.

Binding parameters of valproic acid to serum protein in healthy adults at steady state.

Two hundred milligrams of valproic acid (VPA) was administered orally to seven healthy adults at 9:00 and 21:00 h for 5 consecutive days, including the morning dose on day 6. On the sixth day, blood samples were drawn at 0, 0.17, 0.