Effect of taper geometries and launch angle on evanescent wave penetration depth in optical fibers

A large penetration depth of an evanescent wave is the key to success for developing an ultra high-resolution fiber-based evanescent wave biosensor. Tapering the fiber and launching light at an angle has the potential of increasing the penetration depth of evanescent wave manifolds. The effects of tapering, launch angle and taper length of the fiber have been explored in detail using a ray-tracing model to calculate the highest possible penetration depth of the evanescent field. Evanescent wave penetration depths of the order of the size of living cells have been achieved by optimizing the parameters relating geometry of tapered fibers.     

Clarification of yeast cell suspensions by depth filtration

Depth filtration can be very attractive for initial clarification because of low capital costs and ease of operation. However, there is currently no fundamental understanding of the effects of the filter pore size and morphology on the overall capacity and filtrate quality. The objective of this study was to examine the flux, capacity, and filtrate turbidity of a series of depth filters with different pore size ratings and multilayer structures for the filtration of yeast cell suspensions. Data were analyzed using available fouling models to obtain insights into the flux decline mechanisms. Filters with small pore size provide high filtrate quality at low capacity, with the reverse being true for the larger pore sizes. The multilayer structure of commercial depth filters leads to improved performance, although the choice of layer properties is critical. The highest capacity was achieved using a multilayer filter in which the upper layer allows significant yeast cell penetration into the filter matrix but still protects the retentive layer that is needed for a high quality filtrate.     

Muco-ciliary transport in the lung

A two-layer Newtonian fluid model for muco-ciliary transport in the lung is developed where the viscosity of the upper mucous layer is very much greater than the viscosity of the lower periciliary layer. Theory is presented for both cases when the cilia penetrate, and do not penetrate, the very viscous mucous layer. Calculations suggest that, in normal circumstances, it is not essential for the cilia to penetrate the mucus to provide positive transport. However, it does suggest that there is a weak optimal penetration depth of the cilia of between 10-20% of the cilium length. In the case of high ciliary inactivity (e.g. 90% inactive), penetration of cilia into the mucus is essential for normal transport rates suggesting the mucociliary system may be deliberately overdesigned to cater for a whole range of pathological circumstances.     

Surface plasmon resonance imaging on a microchip for detection of DNA-modified gold nanoparticles deposited onto the surface in a non-cross-linking configuration

We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmon-coupled emission (SPCE). The effective fluorescence volume (detection volume) in SPCE experiments depends on two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distance-dependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann configuration), the detection volume is a product of evanescent wave penetration depth and distance-dependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10nm). The height of the detected volume size is 40-70nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann configuration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1-2attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules.     

Root growth in seedlings of annual pasture species

Summary The mean rate at which roots of 12 annual pasture species penetrated a yellow sand to a depth of 80 to 90 cm varied from 0.8 to 3.2 cm per day.Penetration rate was closely correlated with seed weight until roots reached a depth of about 20 cm. Thereafter rates became progressively less dependent on seed size.Penetration rate varied with time. In six species a minimum rate was reached at a depth of 18 to 24 cm. In two species rhythmic fluctuations in root penetration rate appeared to be associated with the development of new leaves on the shoot.Shading the shoots substantially reduced root penetration rate but the rhythmic fluctuations persisted. These observations are consistent with the hypothesis that the rate of root penetration is determined by the supply of metabolites to the root system.     

Vertical profiles of current velocity and dissolved oxygen saturation in biofilms on artificial and natural substrates

We determined vertical changes in current velocity and dissolved oxygen concentration in biofilms on artificial and natural substrates using microelectrodes. We used biofilms developed on glass slides dipped in an artificial stream for 3 months, artificial clay tiles dipped in an outdoor artificial stream for 3 months, and natural pebbles. In the biofilm on a glass slide, current velocity significantly decreased from the surface of the biofilm and became 0 cm s⁻¹ at the surface of the glass slide. Vertical profile of current velocity versus depth indicated a presence of a viscous sublayer of 0.2-mm thickness above the surface of glass slide. Dissolved oxygen (DO) concentration increased within the biofilm and attained the maximum (123%) at the surface of the glass slide, indicating active photosynthesis by sessile diatoms at the layer corresponding to the observed viscous sublayer. In the biofilm on an artificial tile, DO increased to 163% saturation at 24.849-mm depth, followed by rapid decrease (6%) at the surface of the tile. A similar result of remarkable decrease in DO saturation was also found in the biofilm on a natural pebble. These results suggest that smoothness of the substrate surface is related to the vertical profile of DO saturation. The thickness of the viscous sublayer and oxygen-depleted area (up to several hundred micrometers, μm) was sufficient for the presence of bacteria, protists, and other metazoan animals, suggesting high activity and diversity of those heterotrophs in the bottom part of biofilms.     

Within-lake patterns in depth penetration of emergent vegetation

SUMMARY. 1. Within-lake relations of wave exposure (WE), and substratum softness (cone penetration depth; CPD) and organic content (loss on ignition; LOI), to water depth penetration of the emergent vegetation (DPE) was investigated in seven eutrophic lakes in southern Sweden, ranging in area from 1 to 46km².
2. There was a positive relationship between WE and DPE within lakes. This relationship, however, only occurred for sites with relatively soft substrata, for which CPD and LOI were negatively related to both WE and DPE.
3. Analysis of aerial photographs revealed that expansion of the emergent vegetation towards open water, or recession from open water, was not related to wave exposure or water depth, except in one lake where expansion mainly occurred at high exposures.
4. For relatively static vegetation on soft substrata, regressions with CPD°.⁵ explained 62–88% of the within-lake variation of DPE. These regressions did not differ among lakes. Expanding and recessing vegetation were significantly dislocated towards shallower and deeper water, respectively, than predicted from the regression models for static vegetation.
5. Phragmites australis dominated at the lakeward edge of the emergent vegetation, followed in frequency by Typha angustifolia . More broad-leaved species were generally restricted to shallow water and very soft substrata.
6. The results suggest that changes in the distribution of emergent vegetation in moderately wave exposed eutrophic lakes can be predicted largely from substratum character and water depth.     

Photic Volume in Photobioreactors Supporting Ultrahigh Population Densities of the Photoautotroph Spirulina platensis

Characterization of the photic zone and light penetration depth in cultures with ultrahigh cell densities represents a major issue in mass cultures of phytoautotrophic microorganisms grown in enclosed photobioreactors. In a study of the effect of underwater optical properties on the penetration depth of photosynthetically active radiation, the inherent optical properties of algal suspensions, i.e., absorption and scattering coefficients, as well as their apparent optical properties, i.e., the reflectance and the vertical attenuation coefficient of downwelling irradiance, were determined by using high-spectral-resolution radiometric measurements. The vertical attenuation coefficient was used to estimate quantitatively the depth of light penetration into a reactor containing an ultrahigh cell density (chlorophyll concentration, up to 300,000 mg m(sup-3)). For such a high cell density, the photic volume in the reactor was found to be extremely small; nevertheless, it differed between the blue and red light (less than 0.06 mm) and the green light (about 0.5 mm). This suggests a singular role for green light under the unique circumstances existing in ultrahigh-cell-density cultures of photoautotrophs.     

Millimeter wave dosimetry of human skin

To identify the mechanisms of biological effects of mm waves it is important to develop accurate methods for evaluating absorption and penetration depth of mm waves in the epidermis and dermis. The main characteristics of mm wave skin dosimetry were calculated using a homogeneous unilayer model and two multilayer models of skin. These characteristics included reflection, power density (PD), penetration depth (delta), and specific absorption rate (SAR). The parameters of the models were found from fitting the models to the experimental data obtained from measurements of mm wave reflection from human skin. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. The thin SC produced little influence on the interaction of mm waves with skin. On the contrary, the thick SC in the palm played the role of a matching layer and significantly reduced reflection. In addition, the palmar skin manifested a broad peak in reflection within the 83-277 GHz range. The viable epidermis plus dermis, containing a large amount of free water, greatly attenuated mm wave energy. Therefore, the deeper fat layer had little effect on the PD and SAR profiles. We observed the appearance of a moderate SAR peak in the therapeutic frequency range (42-62 GHz) within the skin at a depth of 0.3-0.4 mm. Millimeter waves penetrate into the human skin deep enough (delta = 0.65 mm at 42 GHz) to affect most skin structures located in the epidermis and dermis.     

Detection of recombinant growth hormone by evanescent cascaded waveguide coupler on silica‐on‐silicon

An evanescent wave based biosensor is developed on the silica‐on‐silicon (SOS) with a cascaded waveguide coupler for the detection of recombinant growth hormone. So far, U ‐bends and tapered waveguides are demonstrated for increasing the penetration depth and enhancing sensitivity of the evanescent wave sensor. In this work, a monolithically integrated sensor platform containing a cascaded waveguide coupler with optical power splitters and combiners designed with S ‐bends and tapper waveguides is demonstrated for an enhanced detection of recombinant growth hormone. In the cascaded waveguide coupler, a large surface area to bind the antibody with increased penetration depth of evanescent wave to excite the tagged‐rbST is obtained by splitting the waveguide into multiple paths using Y splitters designed with s ‐bends and subsequently combining them back to a single waveguide through tapered waveguide and combiners. Hence a highly sensitive fluoroimmunoassay sensor is realized. Using the 2D FDTD (Finite‐difference time‐domain method) simulation of waveguide with a point source in Rsoft FullWAVE, the fluorescence coupling efficiency of straight and bend section of waveguide is analyzed. The sensor is demonstrated for the detection of fluorescently‐tagged recombinant growth hormone with the detection limit as low as 25 ng/ml. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

中国省际碳足迹广度、深度评价及时空格局

借鉴三维生态足迹方法构建了碳足迹广度、深度测算模型,对吸纳碳排放所占用的自然资本流量、存量进行区分,核算了2000—2016年中国30个省(市、自治区)碳足迹广度和碳足迹深度,并对其进行空间关联性分析。结果显示:①中国碳足迹广度受碳足迹和碳生态承载力的综合影响,由0.173 hm~2/人升至0.329 hm~2/人又降至0.301 hm~2/人;碳足迹广度高值区集中于东北、西北和西南地区,其自然资本流量尚未完全占用,低值区集中于东部沿海和中部,其自然资本流量已不足以补偿碳排放。②2008年起中国碳足迹深度突破自然原长1,数值由1.04升至1.42又降至1.31;研究期内碳足迹深度始终处于自然原长1的有10个地区,高值区集中于东部沿海和中部,尤其是上海可达298.83,以存量资本耗竭为主且生态持续性弱。吸纳碳排放所占用的流量资本和存量资本存在地域互补性。③中国碳足迹广度、深度呈显著的空间正相关。碳足迹广度H-H集聚区分布于东北和西北,该类集聚有减弱趋势;碳足迹深度H-H集聚区主要分布于东部沿海且向中部扩散,该类集聚有增强趋势。通过引入碳足迹广度、深度两项指标对碳足迹的研究方法进行了深化和完善,在碳排放对生态环境影响规模的刻画和表达上取得了较优于传统碳足迹的评价结果。     

Dynamic shear stress in parallel-plate flow chambers

An in vitro model using a parallel-plate fluid flow chamber is supposed to simulate in vivo fluid shear stresses on various cell types exposed to dynamic fluid flow in their physiological environment. The metabolic response of cells in vitro is associated with the wall shear stress. However, parallel-plate flow chambers have not been characterized for dynamic fluid flow experiments. We use a dimensionless ratio h / lambda(v), in determining the exact magnitude of the dynamic wall shear stress, with its oscillating components scaled by a shear factor T. It is shown that, in order to expose cells to predictable levels of dynamic fluid shear stress, two conditions have to be met: (1) h / lambda(v) < 2, where h is the distance between the plates and lambda(v) is the viscous penetration depth; and (2) f(0) < f(c) / m, where the critical frequency f(c) is the upper threshold for this flow regime, m is the highest harmonic mode of the flow, and f(0) is the fundamental frequency of fluid flow.     

Trailing flagella rotate faster than leading flagella in unipolar cells of Spirillum volutans.

In unipolar cells of Spirillum volutans, the flagellar rotation frequency is halved, approximately, when the flagellar bundle reorientates to rotate about the cell body and reverse the swimming direction. The viscous drag resulting from a concomitant increase in flagellar wave amplitude is probably responsible for the reduced frequency of flagellar rotation.     

Mechanical compliance of the endocardium

Radio-frequency (RF) ablation is an accepted treatment for cardiac arrhythmias related to abnormal focal cardiac substrate. The penetration depth of the electrode into the endocardium affects lesion size, a critical determinant of success of RF ablation. We measured the relation between the mechanical compliance and the penetration depth of RF ablation catheter electrode at frequently ablated areas of the endocardium and examined the influence of time after death on mechanical properties of the tissue. We measured force versus time for eight insertion depths of the catheter electrode into full-thickness endocardial samples derived from the mitral valve annulus, the left ventricular free wall and the tricuspid valve annulus. We varied the time after death at 15, 40 min, 3, 8, and 18 h and repeated our measurements. At 15 min after death, the first 0.5 mm penetration depth caused the fastest relaxation at 55 s. Force decay decreased dramatically at 15 min after death as the penetration depth increased from 0.5 to 4 mm. We used the force data sampled at 60 s after insertion to approximate the elasticity. We observed the relations between the force versus the insertion depth. The force increased by a factor of 5 for the mitral valve annulus and 8 for the left free wall from 15 min to 18 h. We derived coefficients of a second-order polynomial equation relating the force data to insertion depth with R²>0.99.     

Experimental ATR device for real-time FTIR imaging of living cells using brilliant synchrotron radiation sources

In this contribution we present the design of an original Attenuated Total Reflection (ATR)-based device designed for an IR microscope coupled to a FPA detector and optimized for in-vivo cell imaging. The optical element has been designed to perform real time experiments of cell biochemical processes. The device includes a manually removable Ge-crystal that guarantees an ease manipulation during the cell culture and a large flat surface to support the cell growth and the required change of the culture wells. This layout will allow performing sequential ATR IR imaging with the crystal immersed in the culture wells, minimizing contributions due to water vapors in the optical system. Using existing brilliant synchrotron radiation sources this ATR device may collect images at the surface of the Ge crystal at a sub-cellular spatial resolution with a penetration depth of the evanescent wave inside the sample of ~ 500 nm within few seconds. A brief summary of the cellular components that should be detected with such optical device is also presented.     

Silver nanoparticulate enhanced aqueous silane/siloxane exterior facade emulsions and their efficacy against algae and cyanobacteria biofouling

Silver nanoparticulate enhanced aqueous silane/siloxane emulsions and their efficacy against biofouling mechanisms are presented within this study. Different concentrations of silver nanoparticulates were added into viscous shear-thinning aqueous treatments and key attributes required for facade remedial applications assessed. Water repellence, biofouling resistance, and aesthetical alteration were studied to assess key treatment attributes. In addition, assessment of the porosity, sorptivity, and treatment depth was used to identify penetration and facade protection efficacy and morphological alteration of the masonry substrate. Results showed that silver nanoparticulate incorporation did not impede treatment penetration, better water repellent attributes were achieved with increased concentration while effectively conserving the morphology and aesthetics of the substrate. It was concluded that the reduced bioreceptivity observed primarily stemmed from the silver nanoparticulates ability to sanitise the surface, and that only small concentrations (<0.5%wt) were required to attain significantly beneficial improvements. Treatments were deemed practically and commercially viable for retrofit and heritage projects.     

Small efficient cell-penetrating peptides derived from scorpion toxin maurocalcine

Maurocalcine is the first demonstrated example of an animal toxin peptide with efficient cell penetration properties. Although it is a highly competitive cell-penetrating peptide (CPP), its relatively large size of 33 amino acids and the presence of three internal disulfide bridges may hamper its development for in vitro and in vivo applications. Here, we demonstrate that several efficient CPPs can be derived from maurocalcine by replacing Cys residues by isosteric 2-aminobutyric acid residues and sequence truncation down to peptides of up to 9 residues in length. A surprising finding is that all of the truncated maurocalcine analogues possessed cell penetration properties, indicating that the maurocalcine is a highly specialized CPP. Careful examination of the cell penetration properties of the truncated analogues indicates that several maurocalcine-derived peptides should be of great interest for cell delivery applications where peptide size matters.     

Two-step protocol to incorporate cells in thermoresponsive hydrogels

One of the stumbling blocks in the formation of a thermoresponsive cell-hydrogel hybrid (TCH) is the efficient incorporation of cells in thermoresponsive hydrogels (TH) using traditional top-down (i.e., cells penetrate in the pre-set gels from top surface) approach. This approach is slow and tedious because the hydrogel needs to soak in the cells culture for a long time to allow cells to penetrate from the gel surface in to the bulk of the gel. In addition, cell incorporation into TH is difficult because elevated dissolution temperatures of gelators are detrimental to cell viability, whereas the highly viscous gel state that formed at ambient temperatures retards the penetration of cells. We propose a bottom-up approach (i.e., cells mixed prior to gel setting) using a novel two-step protocol. The first step is the rapid cooling of the agarose solution from its dissolution temperature (98 degrees C) to 37 degrees C and equilibrating for 3-4 min. The second step is the mixing of fibroblasts with the agarose solution and natural cooling to the room temperature to form the TCH. With this novel protocol, 90% of fibroblasts are found to be trapped in the cell-gel hybrid.     

Image filtering for two-photon deep imaging of lymphonodes

Non-linear excitation microscopy is considered an ideal spectroscopic method for imaging thick tissues in vivo due to the reduced scattering of infrared radiation. Although imaging has been reported on brain neocortex at 600-800 mum of depth, much less uniform tissues, such as lymphonodes, are characterized by highly anisotropic light scattering that limits the penetration length. We show that the most severe limitation for deep imaging of lymphonodes appears to be the tissue scattering and the diffuse fluorescence emission of labeled cell (lymphocytes) in layers above the focusing plane. We report a study of the penetration depth of the infrared radiation in a model system and in ex vivo lymphonodes and discuss the possibility to apply Fourier filtering to the images in order to improve the observation depth.     

Localization of β-Galactosidase in Cells of Escherichia coli by Low Voltage Electron Bombardment

By using low voltage electrons to bombard dried cells of Escherichia coli, the inactivation of the enzyme β-galactosidase as a function of depth of electron penetration has been studied. There is little inactivation for a penetration of 100 A, but considerable for a penetration of 300 A. An analysis of the data for six initial electron energies shows that there exist outer and inner bounds of the enzyme region which are approximately 300 and 700 A below the cell surface, respectively.