A PHOTOELECTRIC DENSITOMETER FOR USE WITH SUSPENSIONS

A device for quickly and accurately measuring the population density of a suspension of microorganisms, permitting the preparation of yeast suspensions of known density to within 1 per cent error, was constructed with two Visitron photoelectric cells, a single light of high intensity and a good Wheatstone bridge for balancing the currents from the two photoelectric cells. A large Pyrex milk culture tube holding the suspension is placed in the path of one beam of light coming through a small longitudinal slit and thence to one photocell; a second similar slit directs another beam of light upon the second photocell, thus causing dissimilar currents to flow, the ratio of whose magnitudes may be measured by the bridge resistances. A relation between these currents and the relative light intensities is shown, and the one significant unmeasurable variable (the characteristic constant of a photocell) is practically eliminated by the use of a method of ratios. After careful standardization of technique the apparatus proved more accurate than other methods available for the purpose indicated. In rapid use its accuracy may be put safely at 1 per cent for measuring the densities of cultures of approximately the same age and composed of cells having comparable optical characteristics.     

Characteristics and mechanisms of the two types of photoelectric differential response of bacteriorhodopsin-based photocell

Bacteriorhodopsin (BR)-based photocells have been assigned possessing differential photoelectric response. But recently we found that the differential response described before, which occurred in milliseconds to seconds, outputting a positive pulse when light was on and a negative pulse when light was off, was not the intrinsic property of the BR molecule. It was partially caused by the measuring circuit. By measuring the photoelectric response signal of the BR film photocell to a short laser pulse, the impulse response function of the BR film photocell was obtained by data fitting with MATLAB software. A simulation system was accordingly developed. The output response signals of the BR film photocell under different stepping incident light were calculated. By simulation and analysis, it was concluded that the differential response caused by the intrinsic property of the BR molecule happened in microseconds time scale, and it produced a negative pulse when light was on and a positive pulse when light was off. It was much faster but much weaker than that described before.     

Methods for Measuring Phototaxis of Cell Populations and Individual Cells

Two quantitative methods have been devised for studying the phototactic response of Chlamydomonas. In the first procedure, the movement of a cell population is continuously monitored photometrically, yielding a permanent record of the time course of the response. The monitoring system consists of a pair of photovoltaic cells connected in a comparison circuit, and a dim red light which passes through the swimming chamber and strikes the photocells. A stimulus beam enters the chamber at right angles to the monitoring light. The movement of algae towards the stimulus light produces a difference in output between the photocells. With a continuous stimulus, this difference increases in a nearly linear fashion for several ninutes. The slope of the linear portion depends on such factors as stimulus ntensity and wavelength and is used as the index of the response. In the second procedure, a photomicrographic method is used to resolve the population response into its components; i.e., the number of cells responding, the directness of the swimming path, and the rate of swimming. The photographs are taken with a fixed exposure time, during which each cell in the field describes a swimming track on the film. Swimming rate is determined by measuring the length of the photographed track, while directness of path is indicated by the angle between the track and the stimulus light beam. The number of cells going towards the light is calculated from counts made while observing the culture through the microscope. These methods have been used to investigate the dependence of phototaxis on stimulus intensity and wavelength, age of culture, and pre-illumination. This work formed a portion of a doctoral thesis submitted by one of the authors (M. E. Feinleib) to Harvard University, Cambridge, Mass. The work was supported in part by a U.S. Public Health Fellowship, No. FI-GM-17, 305–04, and by a National Science Foundation research grant, No. G14266.     

A nephelometer for measurement of nematode populations

A nephelometer for measuring nematode populations is described in which a standard 18 mm culture tube is illuminated from below, and four selenium photocells are placed radially at 90° about the tube. This design minimizes fluctuations in readings due to movement of the nematodes at low population densities.     

细菌视紫红质的光电响应特性和机制

在ITO导电玻璃上制备定向细菌视紫红质 (BR)电泳沉积膜或LB膜组成光电池系统 ,在短脉冲激光照射下 ,测定其脉冲响应光电压 ;在间断光照射下 ,测定其对光强变化产生的微分响应信号。对脉冲光电响应和微分响应的机理及其关系进行理论分析和解释 ,认为脉冲响应是BR分子内部生色团快速光极化引起的电荷分离和希夫碱及其周围氨基酸去质子化和再质子化过程引起的质子定向运输产生的位移电流 ,是一个快反应过程 ,是微分响应的早期反应和基础。微分响应则是由于菌紫质的光驱动质子泵产生的连续质子流在光开和光关瞬间引起光电池系统充放电以及测量电路的耦合特性引起的 ,是一个慢变化过程     

New multichannel kinetic spectrophotometer–fluorimeter with pulsed measuring beam for photosynthesis research

A multichannel kinetic spectrophotometer–fluorimeter with pulsed measuring beam and differential optics has been constructed for measurements of light-induced absorbance and fluorescence yield changes in isolated chlorophyll-proteins, thylakoids and intact cells including algae and photosynthetic bacteria. The measuring beam, provided by a short (2 μs) pulse from a xenon flash lamp, is divided into a sample and reference channel by a broad band beam splitter. The spectrum in each channel is analyzed separately by a photodiode array. The use of flash measuring beam and differential detection yields high signal-to-noise ratio (noise level of 2 × 10⁻⁴ in absorbance units per single flash) with negligible actinic effect. The instrument covers a spectral range between 300 and 1050 nm with a spectral resolution of 2.1, 6.4 or 12.8 nm dependent on the type of grating used. The optical design of the instrument enables measuring of the difference spectra during an actinic irradiation of samples with continuous light and/or saturation flashes. The time resolution of the spectrophotometer is limited by the length of Xe flash lamp pulses to 2 μs.     

双光子激发荧光各向异性度的成像

荧光各向异性度 (fluorescence anisotropy) 测量可以获得荧光分子的转动速度信息,进而了解分子质量、结构、以及与周边环境的相互作用情况 . 围绕一台双光子激发扫描荧光成像系统,通过改变外光路和图像记录与处理程序,从而实现了双光子激发荧光各向异性度成像,并针对一些典型样品和体系,展示了该方法的应用 . 实验中观察了 FITC 荧光分子、 FITC 结合的 CD44 抗体分子及与肿瘤细胞表面受体结合的 FITC-CD44 抗体分子 . 测量结果表明,不同分子质量、不同微观环境状态下的荧光分子,其各向异性度大小不同,在各向异性度图中能够被明显区分 . 荧光各向异性度成像能够定量测量样品微区的各向异性度值,并以二维图像的形式直观表达,是各向异性度测量与成像技术的良好结合 .     

Multi-Directional Plasmonic Splitter and Polarization Analyzer Based on the Catenary Metasurface

Owing to the unique properties of strongly confined and enhanced electric fields, surface plasmon polaritons (SPPs) provide a new platform for the realization of ultracompact plasmonic circuits. However, there are challenges in coupling light into SPPs efficiently and subsequently routing SPPs. Here, we propose a multi-directional SPP splitter and polarization analyzer based on the catenary metasurface. Based on the abundant electromagnetic modes and geometric phase modulation principle of catenary structure, the device has realized high-efficiency beam splitting for four different polarization states (x-polarization, y-polarization, LCP, and RCP). The central wavelength of the device is 632 nm and the operation bandwidth can reach 70 nm (585–655 nm). Based on the phenomenon of SPP beam splitting, we present a prototype of a polarization analyzer, which can detect the polarization state of incident light by adding photodetector with light intensity logic threshold in four directions. Moreover, by combining this device with dynamic polarization modulation techniques, it is possible to be served as a router or switch in integrated photonic circuits.

     

An improved no-moving-parts video-rate confocal microscope

Several years ago our research program developed a video-rate confocal microscope with no moving parts, based on synchronizing and aligning the scan of an image dissector tube (IDT) with the light returning from a microscope stage that has been acousto-optically scanned by a laser beam. Improvements on the original system have recently been completed. The laser power has been substantially increased and the laser scan is now brought into the Nikon Diaphot inverted microscope through the epi-illumination port. Aberrations in the scanned beam have been reduced by performing the beam shaping required by the acousto-optic deflectors using prisms instead of cylindrical lenses. The IDT is located at the side camera output port at the end of a simple, efficient light path. The new system is described in detail and results obtained using the microscope in reflection and fluorescence mode are presented.     

Imaging Membrane Potential with Two Types of Genetically Encoded Fluorescent Voltage Sensors

Genetically encoded voltage indicators (GEVIs) have improved to the point where they are beginning to be useful for in vivo recordings. While the ultimate goal is to image neuronal activity in vivo, one must be able to image activity of a single cell to ensure successful in vivo preparations. This procedure will describe how to image membrane potential in a single cell to provide a foundation to eventually image in vivo. Here we describe methods for imaging GEVIs consisting of a voltage-sensing domain fused to either a single fluorescent protein (FP) or two fluorescent proteins capable of Förster resonance energy transfer (FRET) in vitro. Using an image splitter enables the projection of images created by two different wavelengths onto the same charge-coupled device (CCD) camera simultaneously. The image splitter positions a second filter cube in the light path. This second filter cube consists of a dichroic and two emission filters to separate the donor and acceptor fluorescent wavelengths depending on the FPs of the GEVI. This setup enables the simultaneous recording of both the acceptor and donor fluorescent partners while the membrane potential is manipulated via whole cell patch clamp configuration. When using a GEVI consisting of a single FP, the second filter cube can be removed allowing the mirrors in the image splitter to project a single image onto the CCD camera.     

A simple and inexpensive 4π light collector and two designs for a light meter for light attenuation studies

SUMMARY. A simple 4π light collector is described suitable for light attenuation studies. It uses table tennis balls as light collectors and its spherical response is near to ideal. A circuit for a simple meter based on an operational amplifier is given as well as that for a direct-reading log-ratio meter. Both circuits are intended for use with selenium photocells. The cost of the materials for detector and simple meter is less than £30.     

Combination of Surface Plasmon Polaritons and Subwavelength Grating for Polarization Beam Splitting

Plasmonics - A polarization beam splitter (PBS) based on the plasmonic subwavelength grating (PSWG) is proposed and investigated. The PBS is composed by a directional coupler with a PSWG as the...     

An optical microsensor to measure fluorescent light intensity in biofilms

We have developed an optical microsensor to quantify fluorescent light intensity distribution in biofilms. The optical system consisted of a beam splitter, light couplers, filters and a spectrophotometer able to accept the fiberoptic cable to measure fluorescent light intensity. The emitted light, fluorescence from the biofilm, was collected at the tip of the optical microsensor and was transferred to a spectrophotometer via a fiberoptic cable. The total fluorescent light intensity was evaluated from the emission spectrum by numerical integration. The newly developed fiberoptic microsensor was tested using a Staphylococcus aureus strain producing yellow fluorescent protein (YFP) grown as biofilm. We used a 405-nm violet laser diode for excitation, and measured the emission intensity between 480 nm and 540 nm. The optical microsensor that quantifies fluorescent light intensity is a promising tool in biofilm research which often requires detection and quantification of fluorescent light intensity distribution generated by various fluorescent proteins.     

Das Autoselect-System – ein Automatensystem zur Selektion von Antibiotikaproduzenten,VII. Hemmhofmeßautomat

The zone reader of the Autoselect-system enables to measure the 64 inhibition zones of a quadratic bioassay plate with an accuracy of 0,1 mm within 3 minutes. A carriage moves each zone in the light beam. With a special photometrical device 3 defined areas of the inhibition zone can be measured quantitatively by 2 receivers. The indicated values of the diameters result from the analog treatment of the signals. By coupling to a computer the datas of the measuring and other desired informations are printed out.     

I5S: wide-field light microscopy with 100-nm-scale resolution in three dimensions

A new type of wide-field fluorescence microscopy is described, which produces 100-nm-scale spatial resolution in all three dimensions, by using structured illumination in a microscope that has two opposing objective lenses. Illumination light is split by a grating and a beam splitter into six mutually coherent beams, three of which enter the specimen through each objective lens. The resulting illumination intensity pattern contains high spatial frequency components both axially and laterally. In addition, the emission is collected by both objective lenses coherently, and combined interferometrically on a single camera, resulting in a detection transfer function with axially extended support. These two effects combine to produce near-isotropic resolution. Experimental images of test samples and biological specimens confirm the theoretical predictions.     

A laser Doppler scanner for imaging blood flow in skin

This paper describes a novel medical instrument that produces an image of blood flow in the capillaries under the skin surface. A laser beam is used to detect blood cell motion from the Doppler broadening of the laser light scattered from the skin. The image is generated by scanning the laser beam in a raster. The design of a practical clinical instrument is outlined and some preliminary results are presented.     

A portable system for measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of sampling

SUMMARY. This paper describes the design, construction and testing of a portable monitoring system capable of measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of operation. The unit is powered by rechargeable batteries and can be used to provide instantaneous readings or continuous records of each variable when used with a suitable chart recorder. Circuits for measuring conductivity and light-ratio are of a novel design. The conductivity circuit measures conductance by the voltage drop across a low-value resistor connected in series with the conductivity cell. The light-ratio circuit measures light intensities by digitizing signals from two photocells and comparing their ratios over short periods of time. The paper includes examples of results obtained with the instrument in a wide range of applications and compares the performance of the Mackereth oxygen electrode with, and without, a small water-circulating attachment.     

Determination of polypeptide chain molecular weights of human and bovine band 3 protein from erythrocyte membranes by low-angle laser light scattering combined with high-performance gel chromatography in the presence of sodium dodecyl sulfate

Polypeptide chain molecular weights of human and bovine band 3 proteins which are glycoproteins of the erythrocyte membrane were determined as 101,000 +/- 2000 for the former and 107,000 +/- 2000 for the latter by using the low-angle laser light scattering technique combined with a high-performance gel chromatography column, an ultraviolet spectrophotometer and a differential refractometer in the presence of sodium dodecyl sulfate. The advantage of this method is that, unlike the sedimentation equilibrium technique, neither information on the binding to proteins of all ligands present nor the partial specific volume is required to evaluate the polypeptide chain molecular weight of proteins in a multicomponent system.     

A low-cost polyacrylamide gel scanning densitometer

A simple, low-cost, home-built acrylamide gel scanning densitometer is described. The instrument was designed to provide gel scans for the purpose of comparing the relative rates of mobility of bands. It does not include provisions for large volume, integration of peaks, or micrometer resolution. The key to the simplicity of the device was through the use of a rotary rather than a transverse gel carriage. A turntable was attached directly to the shaft of a synchronous clock motor with a slow rate of rotation. A curved gel holder, placed on the turntable, carries the gel through the light beam. A commercial strip chart recorder is used with the scanner.     

SEARCH FOR MITOGENETIC RADIATION BY MEANS OF THE PHOTOELECTRIC METHOD

The intensity of mitogenetic radiation was estimated from data given by Gurwitsch. The sensitivity of the biological method and of the physical methods were compared. With onion-base pulp and onion roots as mitogenetic inductors, the photographic method gave no perceptible blackening for exposures up to 184 hours. A photoelectric counter tube was described with cadmium as photoelectric metal. Its sensitivity was such that a radiation intensity of 10 to 15 quanta per cm.² per second of the Hg line 2536 A was detectable. Spurious effects produced by the counter tube were described and means for their avoidance given. A number of different biological materials, all supposed to be excellent mitogenetic radiators, were investigated by means of the counter tube. No mitogenetic radiation could be detected.