One-step continuous synthesis of biocompatible gold nanorods for optical coherence tomography

We present a novel one-step flow process to synthesize biocompatible gold nanorods with tunable absorption and biocompatible surface ligands. Photothermal optical coherence tomography (OCT) of human breast tissue is successfully demonstrated using tailored gold nanorods designed to have strong absorption in the near-infrared range.     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical coherence tomography

The inclusion of small concentrations of nanoparticles can significantly enhance the thermal and electrical properties, and to a lesser degree the mechanical performance, of polymers. Dispersion of nanoparticles during mixing is problematic, with poor mixing resulting in particle agglomeration (i.e. particle clustering), which subsequently limits the potential for property enhancement. Achieving good dispersion is considered key to large-scale production and commercialization of polymer nanocomposites (PNCs), and a measurement technique capable of quantitatively characterizing particle loading and dispersion would significantly enhance product development. This paper presents the results of a study using a static light scattering technique, Fourier domain optical coherence tomography (FD-OCT), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs including epoxy resins reinforced with nanoclay platelets, silica microspheres or multi-walled carbon nanotubes (MWCNTs), and zinc oxide and lithium aluminate reinforced polypropylene.     

Analysis of rheology and wall depletion of microfibrillated cellulose suspension using optical coherence tomography

A rheometric method based on velocity profiling by optical coherence tomography (OCT) was used in the analysis of rheological and boundary layer flow properties of a 0.5% microfibrillated cellulose (MFC) suspension. The suspension showed typical shear thinning behaviour of MFC in the interior part of the tube, but the measured shear viscosities followed interestingly two successive power laws with an identical flow index (exponent) and a different consistency index. This kind of viscous behaviour, which has not been reported earlier for MFC, is likely related to a sudden structural change of the suspension. The near-wall flow showed existence of a slip layer of 2–12 μm thickness depending on the flow rate. Both the velocity profile measurement and the amplitude data obtained with OCT indicated that the slip layer was related to a concentration gradient appearing near the tube wall. Close to the wall the fluid appeared nearly Newtonian with high shear rates, and the viscosity approached almost that of pure water with decreasing distance from the wall. The flow rates given by a simple model that included the measured yield stress, viscous behavior, and slip behavior, was found to give the measured flow rates with a good accuracy.     

In vivo comparison of the optical clearing efficacy of optical clearing agents in human skin by quantifying permeability using optical coherence tomography

The objective of this work is to quantify and compare the optical clearing efficacy of glucose, propylene glycol, glycerol solutions through the human skin tissue in vivo by calculating permeability coefficient of three solutions. Currently, the permeability coefficient of agent in tissues was extracted from optical coherence tomography (OCT) amplitude data mainly through the OCT signal slope and the OCT amplitude methods. In this study, we report the OCT attenuation coefficient method which is a relatively novel and rarely reported methodology to measure the permeability coefficient during the optical skin clearing procedure. The permeability coefficients for 40% propylene glycol, glucose and glycerol were (2.74 ± 0.05) × 10(-6) cm s(-1), (1.78 ± 0.04) × 10(-6) cm s(-1) and (1.67 ± 0.04) × 10(-6) cm s(-1), respectively. It could be clearly seen that the permeability coefficient of the 40% propylene glycol solution is higher than that of 40% glucose solution, and the permeability coefficient of the 40% glucose solution is higher than that of the 40% glycerol solution. These indicate 40% propylene glycol solution is more effective than others in the human skin in vivo. We then compare and prove consistency of optical clearing efficacy figured out by three different methods.     

Morphological changes in blood vessels produced by hyperosmotic agents and measured by optical coherence tomography

Optical tissue clearing by hyperosmotic chemical agents significantly increases light depth penetration in skin and may improve light-based therapeutics such as laser treatment of cutaneous vascular lesions. A feasibility study was conducted to evaluate the potential role of optical clearing by glycerol in laser treatment of cutaneous vessels. Optical imaging was performed to investigate the morphological effects of glycerol on blood vessels of skin. Blood vessels were imaged using Doppler optical coherence tomography in in vivo hamster skin treated with glycerol. Images were obtained from the subdermal side to assess morphological changes in the blood vessels caused by glycerol and from the epidermal side to assess enhanced Doppler imaging of blood vessels. Application of glycerol to the subdermis resulted in venule stasis and for prolonged treatment times, arteriole stasis. In cases where flow remained in arterioles, an improved Doppler signal was detected from blood vessels when imaging transepidermally compared with the native condition. Intensity images indicated changes in blood optical properties and improved contrast of skin cross sections after glycerol application. The observed optical and morphological effects were reversed upon hydration of the skin with phosphate-buffered saline. The combination of increased depth of light penetration and the temporary slowing or cessation of flow in blood vessels could mean improved laser treatment of vessels.     

Quantification of glucose diffusion in human lung tissues by using Fourier domain optical coherence tomography

In this study, we report permeability coefficients of 30% glucose diffusion by the optical coherence tomography signal slope (OCTSS) method in four kinds of human lung tissue in vitro: normal lung tissue, benign granulomatosis lung tissue, squamous cell carcinoma and adenocarcinoma tumor. To quantify the permeability coefficient of the agent, the monitored region was 80 μm thickness at a tissue depth of ca 230 μm from the surface. The permeability coefficients of 30% glucose from 10 independent experiments were averaged and found to be (1.35 ± 0.13) × 10(-5) cm s(-1) from the normal lung tissue, (1.78 ± 0.21) × 10(-5) cm s(-1) from the benign granulomatosis lung tissue, (2.88 ± 0.19) × 10(-5) cm s(-1) from the adenocarcinoma tumor and (3.53 ± 0.25) × 10(-5) cm s(-1) from the squamous cell carcinoma, respectively. It could be clearly seen that the permeability coefficients of 30% glucose increase ca 32%, 113% and 162% in the benign granulomatosis, adenocarcinoma tumor and squamous cell carcinoma of human lung tissue compared with that from the normal lung tissue, respectively. Therefore, we inferred from this pilot study that the OCT imaging is a feasible method to distinguish normal and cancer lung tissue.     

An investigation of the accelerated thermal degradation of different epoxy resin composites using X-ray microcomputed tomography and optical coherence tomography

Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler-resin interface and surface characteristics.     

Optical coherence tomography in biomedical research

Optical coherence tomography (OCT) is a noninvasive, high-resolution, interferometric imaging modality using near-infrared light to acquire cross-sections and three-dimensional images of the subsurface microstructure of biological specimens. Because of rapid improvement of the acquisition speed and axial resolution of OCT over recent years, OCT is becoming increasingly attractive for applications in biomedical research. Therefore, OCT is no longer used solely for structural investigations of biological samples but also for functional examination, making it potentially useful in bioanalytical science. The combination of in vivo structural and functional findings makes it possible to obtain thorough knowledge on basic physiological and pathological processes. Advanced applications, for example, optical biopsy in visceral cavities, have been enabled by combining OCT with established imaging modalities. This report gives an outline of the state of the art and novel trends of innovative OCT approaches in biomedical research in which the main focus is on applications in fundamental research and pre-clinical utilization.     

The effect of wall depletion on the rheology of microfibrillated cellulose water suspensions by optical coherence tomography

Rheology of microfibrillated cellulose (MFC) water suspensions was characterized with a rotational rheometer, augmented with optical coherence tomography (OCT). To the best of the authors’ knowledge, this is the first time the behavior of MFC in the rheometer gap was characterized by this real-time imaging method. Two concentrations, 0.5 and 1 wt% were used, the latter also with 10^?3 and 10^?2 M NaCl. The aim was to follow the structure of the suspensions in a rotational rheometer during the measurements and observe wall depletion and other factors that can interfere with the rheological results. The stepped flow measurements were performed using a transparent cylindrical measuring system and combining the optical information to rheological parameters. OCT allows imaging in radial direction from the outer geometry boundary to the inner geometry boundary making both the shear rate profile and the structure of the suspension visible through the rheometer gap. Yield stress and maximum wall stress were determined by start-up of steady shear and logarithmic stress ramp methods and they both reflected in the stepped flow measurements. Above yield stress, floc size was inversely proportional to shear rate. Below the yield stress, flocs adhered to each other and the observed apparent constant shear stress was controlled by flow in the depleted boundary layer. With higher ionic strength (10^?2 M NaCl), the combination of yield stress and wall depletion favored the formation of vertical, cylindrical, rotating floc structures (rollers) coupled with a thicker water layer originating at the suspension—inner cylinder boundary at low shear rates.     

Electrochromic films of a methylcarbazole derivative: optimization of polymerization and optical contrast

The effect of the polymerization potential and time on the electrochemical and optical responses of electrogenerated films of poly-[3,6-bis(2-(3,4-ethylenedioxy)thienyl)-N-methylcarbazole] (PBEDOT-NMCz) was studied. Every electrogenerated film was characterized according to the charge consumed during polymerization, its redox charge density (calculated by integration of a control voltammogram), the efficiency of the polymerization process (defined as the charge consumed during electropolymerization to create one redox site), and its optical contrast. Within the studied polymerization potential range, 0.75 to 2 V, the charge consumed during polymerization increased with the potential, while the efficiency of the polymerization process decreased. The redox site production rate reached a maximum at 1.25 V. The optical contrast of the obtained films remained the same when polymerizing in the range between 0.75 and 1.25 V. Polymerization at more anodic potentials resulted in films of lower electrochromic quality (defined as the maximum contrast achievable). The optimal conditions for electropolymerization in terms of optimum energy consumption and the best electrochromic quality of the films were established.     

Molecular methods to measure intestinal bacteria: a review

The intestine is an exceptionally rich ecosystem encompassing a complex interaction among microorganisms, influenced by host factors, ingested food, and liquid. Characterizing the intestinal microbiota is currently an active area of research. Various molecular-based methods are available to characterize the intestinal microbiota, but all methods possess relative strengths, as well as salient weaknesses. It is important that researchers are cognizant of the limitations of these methods, and that they take the appropriate steps to mitigate weaknesses. Here, we discuss methodologies used to monitor intestinal bacteria including: (i) traditional clone libraries; (ii) direct sequencing using next-generation parallel sequencing technology; (iii) denaturing gradient gel electrophoresis and temperature gradient gel electrophoresis; (iv) terminal restriction fragment length polymorphism analysis; (v) fluorescent in situ hybridization; and (vi) quantitative PCR. In addition, we also discuss experimental design, sample collection and storage, DNA extraction, gene targets, PCR bias, and methods to reduce PCR bias.     

Thin film composite optical waveguides for sensor applications: a review

We review the design and fabrication of thin-film composite optical waveguides (OWG) with high refractive index for sensor applications. A highly sensitive optical sensor device has been developed on the basis of thin-film, composite OWG. The thin-film OWG was deposited onto the surface of a potassium-ion-exchanged (K⁺) glass OWG by sputtering or spin coating (5–9 mm wide, and with tapers at both ends). By allowing an adiabatic transition of the guided light from the secondary OWG to the thin-film OWG, the electric field of the evanescent wave at the thin film was enhanced. The attenuation of the guided light in the thin film layer was small, and the guided light intensity changed sensitively with the refractive index of the cladding layer. Our experimental results demonstrate that thin-film, composite OWG gas sensors or immunosensors are much more sensitive than sensors based on other technologies.     

Development of tip-enhanced optical spectroscopy for biological applications: a review

Tip-enhanced optical spectroscopy is an approach that holds a good deal of promise for the nanoscale characterisation of matter. Tip-enhanced Raman spectroscopy (TERS) has been demonstrated on a variety of samples: inorganic, organic and biological. Imaging using TERS has been shown for carbon nanotubes due to their high scattering efficiency. There are a number of compelling motivations to consider alternative approaches for biological samples; most importantly, the potential for heat damage of biomolecules and long acquisition times. These issues may be addressed through the development of tip-enhanced coherent anti-Stokes Raman scattering microscopy.     

Multi-colored electrochromic polymer with enhanced optical contrast

A new π-conjugated monomer was synthesized which contains an electron-donating unit 3,4-ethylenedioxythiophene and electron withdrawing quinoxaline-based heterocycle to examine the effects of imine unit on the optoelectronic and redox properties of the resulting polymer. Electroactivity of monomer and electrochemical redox behavior of its polymer were investigated by cyclic voltammetry. An irreversible anodic wave at +0.85 V vs Ag wire reference electrode corresponding to the monomer oxidation was observed. Spectroelectrochemical analysis revealed that the neutral polymer has an absorbance at 820 nm. The band gap of the polymer was determined as 1.0 eV from the onset of the π-π∗ transition. The polymer shows multi-colored electrochromic behavior with five distinct states: brick red (−0.3 V), orange (+0.4 V), brown (+0.7 V), green (+0.85 V), gray (+1.2 V). The polymer revealed 34% optical contrast at 460 nm and an excellent optical contrast of 99% in the NIR region.     

Improved signal-to-noise ratio in laboratory-based phase contrast tomography

In conventional X-ray microtomography (μCT), the three-dimensional (3D) distribution of the attenuation coefficient of X-rays is measured and reconstructed in a 3D volume. As spatial resolution increases, the refraction of X-rays becomes a significant phenomenon in the imaging process. Although this so-called phase contrast was initially a cumbersome feature in lab-based μCT, special phase retrieval algorithms were developed to exploit these effects. Clear advantages in terms of visualization and analysis can be seen when phase retrieval algorithms are applied, including an increased signal-to-noise ratio. In this work, this is demonstrated both on simulated and measured data.     

Aspects of quantum coherence in the optical Bloch equations

Aspects of coherence and decoherence are analyzed within the optical Bloch equations. By rewriting the analytic solution in an alternate form, we are able to emphasize a number of unusual features: (a) despite the Markovian nature of the bath, coherence at long times can be retained; (b) the long-time asymptotic degree of coherence in the system is intertwined with the asymptotic difference in level populations; (c) the traditional population-relaxation and decoherence times, T1 and T2, lose their meaning when the system is in the presence of an external field, and are replaced by more general overall time scales; (d) increasing the field strength, quantified by the Rabi frequency Omega, increases the rate of decoherence rather than reducing it, as one might expect; and (e) maximum asymptotic coherence is reached when the system parameters satisfy Omega2=1(T1T2).     

Photochromically-controlled, reversibly-activated MRI and optical contrast agent

The contrast agent which tethers a spiropyran group to a Gd-DO3A moiety has higher relaxivity and fluorescence intensity in the dark; the relaxivity and fluorescence intensity decrease after irradiation with visible light.     

Picosecond time scale optical coherence experiments in mixed molecular crystals: pentacene in naphthalene

Picosecond time scale high-power pulse optical coherence measurements including photon echo and the stimulated photon echo are obtained with a mode-locked dye laser synchronously pumped by a double Q-switched and mode-locked Nd: YAG laser. Effects on coherence arising from excitation with gaussian laser pulses rather than square pulses are examined. Preliminary echo decay measurements are reported.     

NTCDA-TTF first axial fusion: emergent panchromatic, NIR optical, multi-state redox and high optical contrast photooxidation

The first synthetic entry into axially fused NTCDA/PMDA-TTF multipolar molecules demonstrates a high optical contrast photooxidation, panchromism, low HOMO-LUMO gap, generation of a stable radical cation, NIR absorption/emission beyond 2150/800 nm and theoretically calculated NLO activity.