Patterned resonance plasmonic microarrays for high-performance SPR imaging

We report a novel optical platform based on SPR generation and confinement inside a defined three-dimensional microwell geometry that leads to background resonance-free SPR images. The array shows an exceptionally high signal-to-noise ratio (S/N > 80) for imaging analysis and subnanometric thickness resolution. An angular sensitivity of 1°/0.01 RIU has been achieved and the signal to background ratio (S/B) improves to 20, 1 order of magnitude higher than that of the best literature results. The design proves effective for probing-supported lipid membrane arrays in real time with a thickness resolution of 0.24 nm and allows for imaging analysis of microfluidic circuits where resonant spots are separated by only one pixel (～7 μm). The high image quality and unique chip geometry open up new avenues for array screening and biomicrofluidics using SPRi detection.     

Fourier transform capillary electrophoresis with laminar-flow gated pressure injection

Fourier transform capillary electrophoresis (FTCE) was developed as a method to improve signal-to-noise ratio (S/N) and resolution in capillary electrophoresis (CE) separation. In FTCE, multiple simultaneous CE separations were performed in the same channel system and interrogated using a single-point detector. To illustrate experimentally the improvement offered by FTCE in S/N ratio and resolution, we carried out a modest number (five) of multiple injections and separations. We show even with this small number of separations, S/N increased by a factor of 2.9, and theoretical plate height improved by a factor of more than 30. We demonstrated this technique with laser-induced fluorescence detection, but a wide variety of detection methods are compatible with FTCE.     

Two-dimensional imaging biosensor for the monitoring of lactate released from brain slices

Real-time monitoring of lactate release from brain slices has been studied with an optical two-dimensional (2D) imaging biosensor. The 2D biosensor is prepared by direct immobilization of lactate dehydrogenase (LDH) molecules onto a flat silica glass surface through a covalent binding mechanism. The biosensor is able to spatially differentiate lactate concentration variations with conventional optical microscopic spatial resolution. This biosensor has the capability to effectively detect lactate down to a concentration of 100 nM. The 2D biosensor responds uniformly with 2.5% RSD from pixel to pixel. With a 100 ms response time, this 2D biosensor has the capability of monitoring simultaneously many cells in one image. We have studied the impact of KCI on lactate release from brain slices. Clear differences have been observed in lactate release for different regions of the tissue. The real-time determination of the newly released lactate from the mouse brain slices clearly demonstrates the feasibility of monitoring lactate release from living specimens. The 2D biosensor will enable us to study cellular communications and possibly other biological processes that require simultaneous temporal and spatial resolution.     

Diffuse optical tomography system to image brain activation with improved spatial resolution and validation with functional magnetic resonance imaging

Although most current diffuse optical brain imaging systems use only nearest- neighbor measurement geometry, the spatial resolution and quantitative accuracy of the imaging can be improved through the collection of overlapping sets of measurements. A continuous-wave diffuse optical imaging system that combines frequency encoding with time-division multiplexing to facilitate overlapping measurements of brain activation is described. Phantom measurements to confirm the expected improvement in spatial resolution and quantitative accuracy are presented. Experimental results showing the application of this instrument for imaging human brain activation are also presented. The observed improvement in spatial resolution is confirmed by functional magnetic resonance imaging.     

Frequency-domain sensitivity analysis for small imaging domains using the equation of radiative transfer

Optical tomography of small imaging domains holds great promise as the signal-to-noise ratio is usually high, and the achievable spatial resolution is much better than in large imaging domains. Emerging applications range from the imaging of joint diseases in human fingers to monitoring tumor growth or brain activity in small animals. In these cases, the diameter of the tissue under investigation is typically smaller than 3 cm, and the optical path length is only a few scattering mean-free paths. It is well known that under these conditions the widely applied diffusion approximation to the equation of radiative transfer (ERT) is of limited applicability. To accurately model light propagation in these small domains, the ERT has to be solved directly. We use the frequency-domain ERT to perform a sensitivity study for small imaging domains. We found optimal source-modulation frequencies for which variations in optical properties, size, and location of a tissue inhomogeneity lead to maximal changes in the amplitude and phase of the measured signal. These results will be useful in the design of experiments and optical tomographic imaging systems that probe small tissue volumes.     

Material-specific infrared recognition of single sub-10 nm particles by substrate-enhanced scattering-type near-field microscopy

We study the optical material contrast of single nanoparticles in infrared scattering-type near-field optical microscopy (IR s-SNOM) in the presence of strong probe-substrate coupling. It is shown theoretically and experimentally that the contrast depends on both the dielectric properties of the nanoparticles and on their size. We can separate the two dependencies by correlating the simultaneously acquired topography and near-field images pixel-by-pixel. This allows us to establish material-specific mapping of polydisperse nanoparticle mixtures with nanoscale spatial resolution. We experimentally demonstrate the differentiation between sub-10 nm gold and polymer particles adsorbed on a Si substrate. Possible applications of our method range from the material-specific mapping of nanoparticle assemblies to the measurement of the doping concentration in single semiconductor nanoparticles.     

空间分辨率之比对遥感图像融合质量的影响

本文主要探讨光学遥感图像融合中空间分辨率之比对融合质量的影响.采用IKONOS-2全色与多光谱图像,通过重采样的方法模拟空间分辨率之比连续变化的融合输入数据,并进行Gram-Schmidt融合实验,补充已有成果中空间分辨率之比变化不连续、融合方法单一的现状.结果表明:当空间分辨率之比降低时,融合质量随着下降,实际应用中,多光谱图像的空间分辨率越高越好;当空间分辨率之比很小时,应适当降低全色图像的空间分辨率,以减弱融合图像的光谱变形,提高融合质量;此外,即使空间分辨率之比很小,融合后图像也比融合输入多光谱图像的清晰度高,更利于图像判断与后续处理.     

Determination of optical probe interrogation field of near-infrared reflectance: phantom and Monte Carlo study

An optical probe used to localize human brain tissues in vivo has been reported previously. It was able to sense the underlying tissue structure with an optical interrogation field, termed as "look ahead distance" (LAD). A new side-firing probe has been designed with its optical window along its side. We have defined the optical interrogation field of the new side probe as "look aside distance" (LASD). The purpose of this study is to understand the dependence of the LAD and LASD on the optical properties of tissue, the light source intensity, and the integration time of the detector, using experimental and computational methods. The results show that a decrease in light intensity does decrease the LAD and LASD and that an increase in integration time of detection may not necessarily improve the depths of LAD and LASD. Furthermore, Monte Carlo simulation results suggest that the LAD/LASD decreases with an increase in reduced scattering coefficient to a point, after which the LAD/LASD remains constant. We expect that an optical interrogation field of a tip or side probe is approximately 1-2 mm in white matter and 2-3.5 mm in gray matter. These conclusions will help us optimally manipulate the parameter settings during surgery and determine the spatial resolution of the probe.     

Augmenting spectroscopic imaging for analyses of samples with complex surface topographies

Spectroscopic imaging has become a widely used tool for analyses of heterogeneous samples. Focal plane array detectors are incorporated into spectrometers that acquire a large number of spectra from different sample locations in parallel. This sensing technique facilitates analyses of spatial distributions of chemical information in an X-Y plane at high time resolution. In many cases, chemical reactions proceed in three spatial dimensions (X-Y-Z) and require the acquisition of spectroscopic information in an X-Y plane plus topographic (Z-dimension) information. However, capturing two-dimensional (2D, i.e., X-Y) images from three-dimensional (3D, i.e., X-Y-Z) samples inherently loses Z-dimension information. This technical note describes an augmented spectroscopic imager that gains both types of data, i.e., spatially resolved spectroscopic information and topography. For the latter purpose, a regular light pattern is generated and projected onto a sample. Due to its 3D topography, this light pattern is distorted. After extracting these distortions, the topography can be determined since the height structure is encoded in the light pattern. Because topographic probing must not affect infrared measurements, different wavelength ranges are used. Here spectroscopic information is acquired in the mid-IR while the light pattern probing the topography is generated in the visible. For relating distortions to physical height structures, the setup needs to be calibrated. For this purpose, calibration objects of known dimensions have been manufactured onto which the light pattern is projected. Determining distortions introduced by objects of known height derives a transform from distortions to topographies. Due to mechanical restrictions, the light pattern can only achieve a certain spatial resolution. In order to enhance the spatial resolution the topography is probed with, scanning the light pattern in X- and Y-direction is proposed.     

Real-time optical image subtraction and edge enhancement using ferroelectric liquid-crystal devices based on speckle modulation

We carried out real-time optical image subtraction and edge enhancement based on a speckle modulation technique by using ferroelectric liquid-crystal polarization switches and a ferroelectric liquid-crystal spatial light modulator. A ferroelectric liquid-crystal spatial light modulator is employed as a real-time and multiple-exposure optical device, and successful results are obtained from three-exposure images modulated by speckles. Thus, image subtraction and edge enhancement are realized in real time. The whole operation is performed within several milliseconds with modest operating conditions. Because the spatial light modulator has a high resolution of greater than 100 line pairs/mm and can store fine speckle patterns, the image qualities we obtained are quite satisfactory.     

Simulation study of magnetic resonance imaging-guided cortically constrained diffuse optical tomography of human brain function

Diffuse optical imaging can measure brain activity noninvasively in humans through the scalp and skull by measuring the light intensity modulation arising from localized-activity-induced absorption changes within the cortex. Spatial resolution and localization accuracy are currently limited by measurement geometry to approximately 3 cm in the plane parallel to the scalp. Depth resolution is a more significant challenge owing to the limited angle tomography permitted by reflectance-only measurements. We combine previously established concepts for improving image quality and demonstrate, through simulation studies, their application for improving the image quality of adult human brain function. We show in a three-dimensional human head model that localization accuracy is significantly improved by the addition of measurements that provide overlapping samples of brain tissue. However, the reconstructed absorption contrast is significantly underestimated because its depth is underestimated. We show that the absorption contrast amplitude accuracy can be significantly improved by providing a cortical spatial constraint in the image reconstruction to obtain a better depth localization. The cortical constraint makes physiological sense since the brain-activity-induced absorption changes are occurring in the cortex and not in the scalp, skull, and cerebral spinal fluid. This spatial constraint is provided by segmentation of coregistered structural magnetic resonance imaging (MRI). However, the absorption contrast deep within the cortex is reconstructed superficially, resulting in an underestimation of the absorption contrast. The synthesis of techniques described here indicates that multimodality imaging of brain function with diffuse optical imaging and MRI has the potential to provide more quantitative estimates of the total and deoxyhemoglobin response to brain activation, which is currently not provided by either method independently. However, issues of depth resolution within the cortex remain to be resolved.     

1064 nm Deep near-infrared (NIR) excited raman microspectroscopy for studying photolabile organisms

We have constructed a 1064 nm deep near-infrared (NIR) excited multichannel Raman microspectrometer using an InP/InGaAsP multichannel detector. This microspectrometer achieves high sensitivity suitable for in vivo measurements of single living cells with lateral resolution of 0.7 μm and depth resolution of 3.1 μm. It has been applied to the structural analysis of living cyanobacterial cells, well-known model organisms for photosynthesis research, which are too photolabile to be measured with visible laser excitation. High signal-to-noise ratio (S/N) Raman spectra have been obtained from carotenoid, chlorophyll α, and phycocyanin in a single living cyanobacterial cell with no appreciable interference from autofluorescence or photodamage. Sub-micrometer mapping of Raman intensities provides clear distribution images of the three pigments inside the cell.     

Shah and sine convolution Fourier transform detection for microchannel electrophoresis with a charge coupled device

This paper describes an improved format for Shah convolution Fourier transform (SCOFT) detection that utilizes the spatial resolution of a charge-coupled device (CCD) rather than a fixed optical mask to perform a Shah or sine convolution over a fluorescence signal. The laser-induced fluorescence from a 9-mm section of microfabricated channel is collected with a CCD at 28 Hz. Each image frame is multiplied by a convolution function to modulate the collected signal through space. Each frame is then summed to generate an intensity-versus-time data set for Fourier analysis. The fluorescence signal oscillates at a frequency dependent upon both the convolution function multiplied across each data frame and the velocity of fluorescent microspheres or a plug of fluorescent dye flowing through the channel. This SCOFT technique affords more flexibility over formats that employ a physical mask and provides data that can be optimized for signal-to-noise (S/N) or resolution information. A 1,000-fold improvement in S/N is demonstrated for a plug of fluorescein dye. Detection of fluorescent beads exhibited frequency signals that were dependent upon the bead size distribution, the electric field, and the electrophoresis buffer concentration. Data are presented demonstrating the quantitation of fluorescent microspheres.     

Axial resolution limit of a fiber-optic fluorescence probe

We examine the limit of spatial resolution achievable when a sine optical fiber is used for excitation and collection of fluorescence from a bulk specimen. We calculate the probability of detecting a fluorescent particle as a function of its position relative to the fiber face, using excitation wavelength lambda, radius a, numerical aperture N.A., and the particle's fluorescence and absorbance spectra. Treating Rhodamine B as a model fluorescent analyte and using appropriate fiber parameters, we show that the maximum axial resolution (defined as the axial distance in a homogenous solution within which 50% of the detected signal originates) achievable is approximately 10 microm. We experimentally measured the axial resolution for a 500-microM aqueous solution of Rhodamine B with lambda = 543 nm, a = 1.31 microm, and a N.A. of 0.16 and found good qualitative agreement with the calculation.     

Photon scanning-tunneling microscopy of unstained Mammalian cells and chromosomes

The photon scanning-tunneling microscope (PSTM) yields optical topographical images of samples that are thin or that are transparent at the wavelength used. A range of sample sizes can be imaged extending to well below the diffraction limit for sufficiently flat samples. But samples of the order of several to many micrometers in size can be analyzed with less-refined resolution if total internal reflection can be made to occur in the sample. We used the PSTM to examine the optical topography of mouse and human cells and of chromosomes that are unstained. Our objectives were to demonstrate the images as an alternative to conventional microscopy and to provide a sample-preparation methodology that will later permit localized, simultaneous fluorescence or absorption spectroscopy with the signals collected by the probe tip. Furthermore, the PSTM's ability to produce optical profiles in air and in water was tested to establish the basis for future investigation of possible abnormalities in the chromosomes. That is, we considered both physical and biological objectives. To this end we utilized the 442-nm line of a He-Cd laser as well as the 633-nm line from a He-Ne laser, the resulting image quality being tested partly to ascertain the increased effects of scattering at the smaller wavelength. It is shown that adequate resolution and signal-to-noise ratio can be obtained with the shorter wavelength even in the presence of intensity fluctuations from the laser, thus showing that fluorescence and absorption studies can be expected to be practicable.     

Image data compression based on non-negative incoherent imaging systems

Channel and memory capacities are limited and expensive resources in optical communication. In this work we propose several approaches to reduce the required capacity by using the a priori knowledge about the optical system used to capture the spatial information. The a priori knowledge is related to the triangularlike shape of the optical transfer function and to its spectral symmetry. In our work we will demonstrate a reduction in memory capacity required for the same image quality or a resolution enhancement for the same physical memory capacity. We will also present a nearly all-optical implementation of these techniques.     

Spectral analysis of a sampling optical time-domain reflectometer

A spectral analysis is presented for the backscatter signal of optical time-domain reflectometers (OTDR). Periodic spatial fluctuations in the fiber attenuation produce modulation sidebands in the frequency spectrum of the backscatter signal. Applying the sampling technique to OTDR leads to a considerable improvement of the signal-to-noise ratio (S/N) due to spectrum compression, as a tradeoff with the measurement time. It gives a performance equivalent to digital averaging. Design examples are given at wavelengths of 0.85, 1.3, and 1.55 μm. A practical setup of a sampling OTDR is described     

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.     

Near-field microscopy: throwing light on the nanoworld

Optical microscopy with nanoscale resolution, beyond that which is possible with conventional diffraction-limited microscopy, may be achieved by scanning a nanoantenna in close proximity to a sample surface. This review will first aim to provide an overview of the basic principles of this technique of scanning near-field optical microscopy (SNOM), before moving on to consider the most widely implemented form of this microscopy, in which the sample is illuminated through a small aperture held less than 10 nm from the sample surface for optical imaging with a resolution of ca. 50 nm. As an example of the application of this microscopy, the results of SNOM measurements of light-emitting polymer nanostructures are presented. In particular, SNOM enables the unambiguous identification of the different phases present in the nanostructures, through the local analysis of the fluorescence from the polymers. The exciting new possibilities for high-resolution optical microscopy and spectroscopy promised by apertureless SNOM techniques are also considered. Apertureless SNOM may involve local scattering of light from a sample surface by a tip, local enhancement of an optical signal by a metal tip, or the use of a fluorescent molecule or nanoparticle attached to a tip as a local optical probe of a surface. These new optical nanoprobes offer the promise of optical microscopy with true nanometre spatial resolution.     

超分辨近场光学成像技术及其产业开发

超分辨近场光学成像技术是当前国内外一个重要的高新技术前沿课题,也将是我国21世纪初应该发展的一项高新技术产业。文中介绍了我国自1991年以来开拓研究的进展,探讨了国际学术界及产业开发中当前存在的主要问题,提出了各类超分辨扫描模式成像公式的乘法表达式,并作了分析比较。为解决消除假像和从有形貌等混合图像中分离纯光学图像两大难题,作者曾于1993年和1996年提出两项发明专利,为发展我国的该产业解决了两大技术关键。