Performance evaluation of mapping and linear imaging FTIR microspectroscopy for the characterisation of paint cross sections

Different Fourier transform infrared microspectroscopic techniques, using attenuated total reflection (ATR) mode and single-element mercury–cadmium–telluride (MCT) detector (mapping) or multielement MCT detector (raster scanning), are compared with each other for the characterisation of inorganic compounds and organic substances in paint cross sections. All measurements have been performed on paint cross sections embedded in potassium bromide, a transparent salt in the mid-infrared region, in order to better identify the organic materials without the interference of the usual embedding resin. The limitations and advantages of the different techniques are presented in terms of spatial resolution, data quality and chemical information achieved. For all techniques, the chemical information obtained is found to be nearly identical. However, ATR mapping performed with a recently developed instrumentation shows the best results in terms of spectral quality and spatial resolution. In fact, thin organic layers (∼10 μm) have been not only identified but also accurately located. This paper also highlights the recent introduction of multielement detectors, which may represent a good compromise between mapping and imaging systems.     

Evaluation of scintillators and semiconductor detectors to image three-photon positron annihilation for positron emission tomography

Positron emission tomography (PET) is rapidly becoming the main nuclear imaging modality of the present century. The future of PET instrumentation relies on semiconductor detectors because of their excellent characteristics. Three-photon positron annihilation has been recently investigated as a novel imaging modality, which demands the crucial high energy resolution of semiconductor detector. In this work the evaluation of the NaI(Tl) scintillator and HPGe and CdZTe semiconductor detectors, to construct a simple three-photon positron annihilation scanner has been explored. The effect of detector and scanner size on spatial resolution (FWHM) is discussed. The characteristics: energy resolution versus count rate and point-spread function of the three-photon positron annihilation image profile from triple coincidence measurements were investigated.     

Synchrotron radiation FTIR imaging in minutes: a first step towards real-time cell imaging

FTIR microscopy with a focal plane array (FPA) of detectors enables routine chemical imaging on individual cells in only a few minutes. The brilliance of synchrotron radiation (SR) IR sources may enhance the signal obtained from such small biosamples containing small amounts of organic matter. We investigated individual cells obtained from a cell culture specifically developed for transmission FTIR imaging using either a Globar or an SR source coupled to the same instrumentation. SR-IR source focussing was optimized to control the energy distribution on the FPA of detectors. Here we show that accessing the IR absorption distribution from all the organic contents of cells at 1 × 1 μm pixel resolution was possible only with high circulating current (≥1.2 A) illuminating a limited number of the FPA’s detectors to increase the signal-to-noise ratio of IR images. Finally, a high-current SR ring is mandatory for collecting FTIR images of biosamples with a high contrast in minutes.     

Characteristics of NaI detector in positron imaging device HEADTOME employing circular ring array

In positron emission computed tomographs employing circular ring arrays of detectors, the performance of the imaging device has been specified ultimately by the characteristics of the detector. The responses of NaI detector were studied when detecting positron annihilation photon (511 keV). The study was mainly by using the NaI detector used in hybrid emission computed tomography (CT) "HEADTOME" we had developed. A series of measurements were carried out positioning two detectors with 40 cm distance and scanning 22Na point source in water. Both detectors was inclined from 0 degrees through 30 degrees to change incident angle of positron annihilation toward crystal face. Energy window was set from 100 to 700 keV. The results were presented as follows: Shortening the crystal length from 7 to 5 cm made sensitivity decrease about 10% and resolution deteriorate about 1 mm (FWHM). As the results of varying the width of the crystal, 20 mm width was optimal at any incident angle. The lead septum between the detectors was the thickness of 4 mm enough to reject multiple detector interactions (crosstalk). Beam mask which was made of lead in order to improve spatial resolution and placed on crystal face worked effectively for incident angles from 0 degrees to 15 degrees but degraded uniformity of spatial resolution from 0 degrees to through 30 degrees.     

Detection of trace materials with Fourier transform infrared spectroscopy using a multi-channel detector

FTIR spectroscopy is one of the most powerful methods for material characterization. However, the sensitivity of this analytical tool is often very limited especially for materials with weak infrared absorption or when spectral bands of the targeted trace material overlap with the spectral bands of major components. Fortunately, for heterogeneous samples, there is an opportunity to improve the sensitivity of detection by using an imaging approach. This paper explores the opportunity of enhancing the sensitivity of FTIR spectroscopy to detect trace amounts of materials using the FTIR imaging approach based on a focal plane array (FPA) detector. Model sample tablets of ibuprofen in hydroxypropyl methylcellulose (HPMC) have been used to exemplify the detection limits of FTIR spectroscopy using: (a) a conventional mercury cadmium telluride (MCT) detector and (b) a FPA detector. The sensitivity level was compared and it has been found that for this particular set of samples, the lowest concentration of ibuprofen in HPMC that can be detected using attenuated total reflection (ATR) measuring mode with the single element MCT detector was 0.35 wt% while using the FPA detector, the presence of drug has been detected in a sample that contains as little as 0.075 wt% of drug. The application of using this enhanced sensitivity offered by the multi-channel detector to probe trace amounts of drug particles left on the surface of a finger after handling a small amount of the drug has also been demonstrated. These results have broad implications for forensic, biomedical and pharmaceutical research.     

Performance of triple coincidence imaging as an addition to dedicated PET

In this work, we investigate the performance of semiconductor detectors imaging capabilities in three-photon annihilation processes in order to combine this novel imaging modality with conventional positron emission tomography. The spatial resolution is studied as a function of detector positions and selected energy window. This was measured from different experimental arrangements and found to be in the range between 3.3–3.9 cm with a mean of 3.5±0.1 cm. Scatter and random events, coincidence timing resolution and count rate performance are discussed.     

Application of micro-FTIR imaging in the Earth sciences

In this paper we describe recent applications of micro-infrared imaging in the Earth sciences. We address, in particular, the use of Fourier-transform infrared (FTIR) spectroscopy in characterizing the zoning and speciation of H and C in a variety of geological materials, including microporous minerals, nominally anhydrous volcanic minerals (NAMs), and crystal inclusions. These investigations show that use of the modern techniques of FTIR imaging enables detection of the zoning of volatile species across the studied samples, and possible configuration changes of structurally-bound carbon molecular species (e.g., CO₂ vs CO₃) during crystal growth. Such features, which are not accessible with other micro-analytical techniques, may provide information about the physicochemical properties which act as constraints in the genesis of the samples, and important information about the evolution of the geological system. Tests performed with focal-plane-array detectors (FPA) show that resolution close to the diffraction limit can be achieved if the amounts of the target molecules in the sample are substantially different. We also point out the possibility of using FTIR imaging for investigations under non-ambient conditions.     

Cryogenic instrumentation and detector limits in FTS

The desire to measure atmospheric emission spectra of the upper atmosphere has led to the development of cryogenically cooled infrared Fourier transform spectrometers. These spectrometers combine the sensitivity advantage of a Fourier transform spectrometer with the sensitivity gains obtainable with modern infrared detectors operated at low photon backgrounds. The temperature required to obtain maximum sensitivity is primarily determined by the wavelength region of interest, longer wavelengths requiring lower temperatures. In order to take full advantage of reduced background operation, the preamplifier must be cooled in order to reduce the noise. Low noise preamplifiers capable of operation down to liquid helium temperatures have been developed. Three cryogenically cooled spectrometers of significantly different design are discussed. The first instrument is a standard Michelson interferometer cooled to 10 K with supercritical helium and capable of 1 wave number resolution. This interferometer has been successfully flown on a rocket and obtained measurements of atmospheric limb emission at tangent altitudes from 70 km to 150 km. The second is a field widened prism interferometer which operates at liquid nitrogen temperature and has been flown on a rocket and obtained measurements of atmospheric emission in the 2 to 8 micrometer region during an aurora. The third is a balloon borne liquid nitrogen cooled interferometer which incorporates cat's eye retroreflectors for end mirrors and is capable of 0.1 wave number resolution. This spectrometer has successfully flown on a balloon several times and obtained measurements of atmospheric limb emission at tangent altitudes from 0 km to 30 km.     

多种超分辨荧光成像技术比较和进展评述

所见即所得是生命科学研究的中心哲学,贯穿在不断认识单个分子、分子复合体、分子动态行为和整个分子网络的历程中。活的动态的分子才是有功能的,这决定了荧光显微成像在生命科学研究中成为不可替代的工具。但是当荧光成像聚焦到分子水平的时候,所见并不能给出想要得到的。这个障碍是由于受光学衍射极限的限制,荧光显微镜无法在衍射受限的空间内分辨出目标物。超分辨荧光成像技术突破衍射极限的限制,在纳米尺度至单分子水平可视化生物分子,以前所未有的时空分辨率研究活细胞结构和动态过程,已成为生命科学研究的有力工具,并逐渐应用到材料科学、催化反应过程和光刻等领域。超分辨成像技术原理不同,其具有的技术性能各异,限制了各自特定的技术特色和应用范围。目前主流的超分辨成像技术包括3种:结构光照明显微镜技术(structured illumination microscopy, SIM)、受激发射损耗显微技术(stimulated emission depletion, STED)和单分子定位成像技术(single molecule localization microscopy, SMLM)。这些显微镜采用不同的复杂技术,但是策略却是相同和简单的,即通过牺牲时间分辨率来提升衍射受限的空间内相邻两个发光点的空间分辨。该文通过对这3种技术的原理比较和在生物研究中的应用进展介绍,明确了不同超分辨成像技术的技术优势和适用的应用方向,以方便研究者在未来研究中做合理的选择。     

Chemical Imaging with a Solid-State near Infrared Spectrometer Based on a Digital Micro-Mirror Array Device Coupled with Hadamard Transform Spectroscopy

Chemical imaging is demonstrated by using an innovative near infrared spectrometer that uses a digital micro-mirror array device (DMD) to provide both spatial and spectral resolution. Hadamard transform spectroscopy is used to enhance the signal-to-noise ratio of the measurement compared to single point raster scanning. The concept is demonstrated by collecting a spectral image of a polymer sample composed of separate regions of polystyrene and polypropylene. The resulting image is composed of 63 spectral resolution elements across the first overtone region of the near infrared spectrum (1538–1818 nm), as well as 65 spatial resolution elements across the longitudinal direction of the DMD (11.3 mm).     

AIEgens in cell-based multiplex fluorescence imaging

Fluorescence imaging is an important branch of bioimaging. It is non-invasive and provides superior spatial and temporal resolution during the real-time monitoring of biological samples of interest. Although the spatial resolution limit of optical microscopes is about 200 nm, due to the diffraction limit, with the application of super-resolution fluorescence microscopy technologies this limit has been pushed below 30 nm. This makes it feasible to visualize biological structures in subcellular levels and to monitor subcellular biological processes in real time. However, due to the complexity of the biological structure and components within cells, simultaneous staining and monitoring multiple intracellular components with different coloured fluorophores is often needed during multiplex imaging, to better understand biological processes. Aggregation-induced emission luminogens(AIEgen) and AIEgen based nanoparticles(NPs) have presented many advantages in fluorescence imaging, with strong potential for biological science and nano-medicine. Herein this review, we focus on the advantages of AIEgen and AIEgen NP in cell-based fluorescence imaging, and the latest advances of AIEgens in cell-based multiplex imaging are summarized and discussed. The future perspectives are proposed.     

Development and analytical applications of multispectral imaging techniques: an overview

A multispectral imaging spectrometer is an instrument that can simultaneously record spectral and spatial information of a sample. Chemical and physical properties of the sample can be elucidated from such images. By synergistic use of an acousto-optic tunable filter and a progressive scan camera capable of snap shot recording it was possible to develop a novel imaging spectrometer with a spatial resolution of a few microns and which can record, grab and store up to 33 images per second (at a function of time) or 16 images per second (as a function of wavelength). This overview article summarizes the instrumentation development of various imaging spectrometers and their applications including its use as the detector for the determination of identity and sequences of peptides synthesized by the combinatorial solid phase method.     

Development and analytical applications of multispectral imaging techniques: An overview

A multispectral imaging spectrometer is an instrument that can simultaneously record spectral and spatial information of a sample. Chemical and physical properties of the sample can be elucidated from such images. By synergistic use of an acousto-optic tunable filter and a progressive scan camera capable of snap shot recording it was possible to develop a novel imaging spectrometer with a spatial resolution of a few microns and which can record, grab and store up to 33 images per second (at a function of time) or 16 images per second (as a function of wavelength). This overview article summarizes the instrumentation development of various imaging spectrometers and their applications including its use as the detector for the determination of identity and sequences of peptides synthesized by the combinatorial solid phase method.     

Analysis of sludge extracts by high resolution GC with selective detectors

Combination of various GC detectors by using a Varian effluent splitter with glass capillary columns has been found to be a rapid procedure for profiling organics extracted from sludges and river sediments. The selectivity and the increased sensitivity of the thermionic nitrogen-phosphorus detector (TSD), the electron capture detector (ECD), and the flame photometric detector (FPD) over the flame ionization detectors (FID) or mass spectrometers allow the detection of compounds present at trace levels without need for extensive sample cleanup. Furthermore, the combination of two selective detectors may supplement the information with regard to the chemical functionalities required for structure elucidation.     

Industrial problem solving using infrared photoacoustic spectroscopy

Until recently photoacoustic detectors coupled to infrared spectrophotometers were low signal-to-noise devices. Often long acquisition times and low resolution were used in order to obtain any spectrum at all.However, newer designs of photoacoustic detectors which are optimized for use in the infrared have become available. Nearly theoretical signal-to-noise values of 2000/l for a single 8 cm^–1 scan have been observed using the MTEC photoacoustic detector on the Perkin-Elmer Model 1800 FT-IR. Using this combination of photoacoustic detector and the Model 1800, it is feasible to conduct quantitative measurements and so it becomes very important to understand the parameters of the measurements which determine the precision.This paper will discuss the various types of analysis that can be performed on industrial samples by using a photoacoustic detector. Aspects of sample handling and the effect of mirror velocity in the interferometer on quantitative analysis will be discussed. Not only will quantitative results be reported, but also the results of spectral difference calculations, which require the same precision as quantitative measurements, will be presented. Depth profiling and sample identification will also be discussed.     

Performance of a portable, electromechanically-cooled HPGe detector for site characterization

Characterization is a first step to site cleanup or decommissioning of a disused nuclear facility. Good knowledge of the inventory of nuclides present, both type and location, is important in the design of an effective plan of remediation. Several systems based on HPGe detectors have been developed, both commercially and at laboratories, and are already in use for this purpose. Their use is somewhat complicated by the need for cryogenic cooling of the HPGe detector. Handling of liquid nitrogen in field situations is always difficult. Recent developments in low-power electromechanical cooling for HPGe detectors have made possible the construction of low weight, portable HPGe spectrometers with sufficient efficiency to perform the needed measurements in reasonable count times, without the need for liquid nitrogen. A mobile system was modified to use a battery-powered, Sterling-engine cooler on a nominal 40% relative efficiency detector. This system was characterized for efficiency and uniformity of response. The baseline spectra were analyzed using the DOE EML 1-meter methods to obtain representative MDA values for several nuclides of interest and typical counting times.     

Performance of a gaseous detector based energy dispersive X-ray fluorescence imaging system: Analysis of human teeth treated with dental amalgam

Energy dispersive X-ray fluorescence (EDXRF) imaging systems are of great interest in many applications of different areas, once they allow us to get images of the spatial elemental distribution in the samples. The detector system used in this study is based on a micro patterned gas detector, named Micro-Hole and Strip Plate. The full field of view system, with an active area of 28 × 28 mm² presents some important features for EDXRF imaging applications, such as a position resolution below 125 μm, an intrinsic energy resolution of about 14% full width at half maximum for 5.9 keV X-rays, and a counting rate capability of 0.5 MHz. In this work, analysis of human teeth treated by dental amalgam was performed by using the EDXRF imaging system mentioned above. The goal of the analysis is to evaluate the system capabilities in the biomedical field by measuring the drift of the major constituents of a dental amalgam, Zn and Hg, throughout the tooth structures. The elemental distribution pattern of these elements obtained during the analysis suggests diffusion of these elements from the amalgam to teeth tissues.     

Imaging applications for chemical analysis utilizing charge coupled device array detectors

Scientific charge transfer devices (CTDs) are rapidly becoming the detector of choice for optical chemical analysis. The high sensitivity and resolution of these detectors make them ideal for a wide range of chemical imaging applications. In this article we highlight some of the current trends and future research directions of CTDs as imaging detectors for chemical analysis.     

Detectability enhancement of spectrophotometric detectors by the use of multidimensional gas chromatography

Multidimensional gas chromatography (2D GC) is demonstrated as a way to improve limits of detectability of spectrophotometric detectors. UV and IR detectors are generally less sensitive than mass spectrometers or other GC detectors. This has placed some limitations on the useful capabilities provided by spectrophotometric detectors, such as the ability to provide structure‐related information for a particular analyte. In this paper, we report results from interfacing a 2D GC instrument to a UV detector. Symmetry factor and the ratio of retention time divided by peak width did not show deterioration of the quality of chromatography when a megabore column was used with this detector. Furthermore, an increase in the limits of detectability over that attainable in a single‐column system was realized by using the 2D GC system. However, the low flow (1 mL/min) imposed by the use of a microbore column (250 μm ID) caused significant tailing when the UV detector was used.     

浅谈2014年诺贝尔化学奖:超高分辨率荧光显微成像

超分辨显微成像技术是近些年来发展最快、受关注度最高的光学成像技术之一。这类技术突破了光学衍射极限,将显微镜的分辨率从几百纳米提高到几十纳米,为生命科学研究提供了一个强大工具。目前主流的超分辨率显微技术主要基于点扩散函数调制和单分子定位的原理来实现。其主要贡献者也成为2014年诺贝尔化学奖的获得者。本文简要讲述超分辨显微技术的发展历程并对其发展趋势进行展望。