Design and performance of air flow-assisted ionization imaging mass spectrometry system

The imaging mass spectrometry（IMS） technology has experienced a rapid development in recent years.A new IMS technology which is based on air flow assisted ionization（AFAI） was reported.It allows for the convenient pretreatment of the samples and can image a large area of sample in a single measurement with high sensitivity.The AFAI in DESI mode was used as the ion source in this paper.The new IMS method is named AFADESI-IMS.The adoption of assisted air flow makes the sample pretreatment easy and convenient.An optimization of the distance between the ion transport tube and MS orifice increases the sensitivity of the system.For data processing,a program based on MATLAB with the function of numerical analysis was developed.A theoretical imaging resolution of a few hundred microns can be achieved.The composite AFAI-IMS images of different target analytes were imaged with high sensitivity.A typical AFAI-IMS image of the whole-body section of a rat was obtained in a single analytical measurement.The ability to image a large area for relevant samples in a single measurement with high sensitivity and repeatability is a significant advantage.The method has enormous potentials in the MS imaging of large and complicated samples.     

Compression strategies for the chemometric analysis of mass spectrometry imaging data

Application of chemometric methods to mass spectrometry imaging (MSI) data faces a bottleneck concerning the vast size of the experimental data sets. This drawback is critical when considering high‐resolution mass spectrometry data, which provide several thousand points for each considered pixel. In this work, different approaches have been tested to reduce the size of the analyzed data with the aim to allow the subsequent application of typical chemometric methods for image analysis. The standard approach for MSI data compression consists in binning mass spectra for each pixel to reduce the number of m/z values. In this work, a method is proposed to handle the huge size of MSI data based on the adaptation of a liquid chromatography‐mass spectrometry data compression method by the detection of regions of interest. Results showed that both approaches achieved high compression rates, although the proposed regions of interest–based method attains this reduction requiring lower computational requirements and keeping utter spectral information. For instance, typical compression rate reached values higher than 90% without loss of information in images and spectra.     

质谱成像分析技术、方法与应用进展

质谱成像技术作为分子成像及质谱领域的研究前沿和热点,近几年受到高度关注并得到迅速发展.本文针对质谱成像技术、方法及其应用的新进展进行了综述与展望,介绍了中国学者近几年在质谱成像分析新技术及其应用方面取得的重要进展.     

Imaging latent fingerprints by electrochemiluminescence

By exposing an electrode surface with a latent fingerprint to electrochemiluminescence (ECL)-generating luminophore, ECL is produced from the surface not covered by the fingerprint, generating a negative image. The fingerprint can also be pre-stained by luminophores, which generates ECL and yields a positive image (right). ITO=indium tin oxide.     

Non-invasive detection of superimposed latent fingerprints and inter-ridge trace evidence by infrared spectroscopic imaging

Current latent print and trace evidence collecting technologies are usually invasive and can be destructive to the original deposits. We describe a non-invasive vibrational spectroscopic approach that yields latent fingerprints that are overlaid on top of one another or that may contain trace evidence that needs to be distinguished from the print. Because of the variation in the chemical composition distribution within the fingerprint, we demonstrate that linear unmixing applied to the spectral content of the data can be used to provide images that reveal superimposed fingerprints. In addition, we demonstrate that the chemical composition of the trace evidence located in the region of the print can potentially be identified by its infrared spectrum. Thus, trace evidence found at a crime scene that previously could not be directly related to an individual, now has the potential to be directly related by its presence in the individual-identifying fingerprints. A portion of this work was presented at the 16th Meeting of the International Association of Forensic Sciences, Montpellier, France September 2–7, 2002.     

Document authentication at molecular levels using desorption atmospheric pressure chemical ionization mass spectrometry imaging

Molecular images of documents were obtained by sequentially scanning the surface of the document using desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI‐MS), which was operated in either a gasless, solvent‐free or methanol vapor‐assisted mode. The decay process of the ink used for handwriting was monitored by following the signal intensities recorded by DAPCI‐MS. Handwritings made using four types of inks on four kinds of paper surfaces were tested. By studying the dynamic decay of the inks, DAPCI‐MS imaging differentiated a 10‐min old from two 4 h old samples. Non‐destructive forensic analysis of forged signatures either handwritten or computer‐assisted was achieved according to the difference of the contour in DAPCI images, which was attributed to the strength personalized by different writers. Distinction of the order of writing/stamping on documents and detection of illegal printings were accomplished with a spatial resolution of about 140 µm. A Matlab® written program was developed to facilitate the visualization of the similarity between signature images obtained by DAPCI‐MS. The experimental results show that DAPCI‐MS imaging provides rich information at the molecular level and thus can be used for the reliable document analysis in forensic applications. © 2013 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd.     

Profiling and imaging of tissues by imaging ion mobility-mass spectrometry

Molecular profiling and imaging mass spectrometry (IMS) of tissues can often result in complex spectra that are difficult to interpret without additional information about specific signals. This report describes increasing data dimensionality in IMS by combining two-dimensional separations at each spatial location on the basis of imaging ion mobility-mass spectrometry (IM-MS). Analyte ions are separated on the basis of both ion-neutral collision cross section and m/z, which provides rapid separation of isobaric, but structurally distinct ions. The advantages of imaging using ion mobility prior to MS analysis are demonstrated for profiling of human glioma and selective lipid imaging from rat brain.     

介质阻挡放电离子源质谱分析

敞开式离子化质谱可对表面样品进行直接快速分析而受到关注,成为质谱分析的热点研究方向.介质阻挡放电离子源是一种基于等离子体放电机理的敞开式离子源,近年来得到了较快的发展.本文着重介绍该离子源的基本原理、性能特征以及应用进展,并对其发展趋势进行了展望.     

Decellularization of intact tissue enables MALDI imaging mass spectrometry analysis of the extracellular matrix

Matrix‐assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) is a powerful molecular mapping technology that offers unbiased visualization of the spatial arrangement of biomolecules in tissue. Although there has been a significant increase in the number of applications employing this technology, the extracellular matrix (ECM) has received little attention, likely because ECM proteins are mostly large, insoluble and heavily cross‐linked. We have developed a new sample preparation approach to enable MALDI IMS analysis of ECM proteins in tissue. Prior to freezing and sectioning, intact tissues are decellularized by incubation in sodium dodecyl sulfate. Decellularization removes the highly abundant, soluble species that dominate a MALDI IMS spectrum while preserving the structural integrity of the ECM. In situ tryptic hydrolysis and imaging of tryptic peptides are then carried out to accommodate the large sizes of ECM proteins. This new approach allows the use of MALDI IMS for identification of spatially specific changes in ECM protein expression and modification in tissue. Copyright © 2015 John Wiley & Sons, Ltd.     

Biological tissue imaging with time-of-flight secondary ion mass spectrometry and cluster ion sources

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) using liquid metal ion guns (LMIGs) is now sensitive enough to produce molecular-ion images directly from biological tissue samples. Primary cluster ions strike a spot on the sample to produce a mass spectrum. An image of this sample is achieved by rastering the irradiated point over the sample surface. The use of secondary ion mass spectrometry for mapping biological tissue surfaces provides unique analytical capabilities; in particular, it enables in a single acquisition a large variety of biological compounds to be localised on a micrometer scale and scrutinised for colocalisations. Without any treatment of the sample, this method is fully compatible with subsequent and complementary analyses like fluorescence microscopy, histochemical staining, or even matrix-assisted laser desorption/ionisation imaging. Basic physical concepts, required instrumentation (ion source and mass analyzer), sample preparation methods, image acquisition, image processing, and emerging biological applications will be described and discussed.     

磷光碳点粉末的合成及其在抗背景干扰的潜指纹成像中的应用

以乙二胺、磷酸和硼酸为反应物,采用水热法制备了荧光碳点(CDs)溶液,进一步加热水热反应溶液,获得了磷光CDs粉末。利用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、紫外可见(UV-Vis)吸收光谱和光致发光光谱等对CDs的结构、形貌和尺寸、表面基团与化学组成以及光学特性进行了表征。结果表明,合成的CDs粉末为无定型碳,形貌为单分散的近球形,尺寸分布在 3.78~7.64 nm范围之内,其表面存在大量的 N、P和 B杂原子基团。CDs粉末在 365 nm紫外光照射下呈现明亮的蓝色荧光,关闭激发光后,呈现长达10 s的绿色室温磷光。该CDs粉末可作为指纹试剂应用于具有复杂背景图案且有强荧光发射基质表面的潜指纹(LFPs)显现。显现后的LFPs在激发光关闭后均呈现明亮完整的磷光指纹图谱,指纹细节特征清晰可辨,有效消除了背景图案与背景荧光干扰。同时,制备的CDs粉末对不同干扰背景客体表面老化7 d的LFPs也能够显现出清晰可识别的磷光指纹图谱。     

Monitoring time‐dependent degradation of phospholipids in sectioned tissues by MALDI imaging mass spectrometry

Imaging mass spectrometry (IMS) is useful for visualizing the localization of phospholipids on biological tissue surfaces creating great opportunities for IMS in lipidomic investigations. With advancements in IMS of lipids, there is a demand for large‐scale tissue studies necessitating stable, efficient and well‐defined sample handling procedures. Our work within this article shows the effects of different storage conditions on the phospholipid composition of sectioned tissues from mouse organs. We have taken serial sections from mouse brain, kidney and liver thaw mounted unto ITO‐coated glass slides and stored them under various conditions later analyzing them at fixed time points. A global decrease in phospholipid signal intensity is shown to occur and to be a function of time and temperature. Contrary to the global decrease, oxidized phospholipid and lysophospholipid species are found to increase within 2 h and 24 h, respectively, when mounted sections are kept at ambient room conditions. Imaging experiments reveal that degradation products increase globally across the tissue. Degradation is shown to be inhibited by cold temperatures, with sample integrity maintained up to a week after storage in ?80 °C freezer under N₂ atmosphere. Overall, the results demonstrate a timeline of the effects of lipid degradation specific to sectioned tissues and provide several lipid species which can serve as markers of degradation. Importantly, the timeline demonstrates oxidative sample degradation begins appearing within the normal timescale of IMS sample preparation of lipids (i.e. 1–2 h) and that long‐term degradation is global. Taken together, these results strengthen the notion that standardized procedures are required for phospholipid IMS of large sample sets, or in studies where many serial sections are prepared together but analyzed over time such as in 3‐D IMS reconstruction experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Displaced dual‐mode imaging with desorption electrospray ionization for simultaneous mass spectrometry imaging in both polarities and with several scan modes

Displaced dual‐mode imaging (DDI) is introduced as a method for simultaneous imaging in positive and negative‐ion mode on the same sample with desorption electrospray ionization imaging, as well as a method for simultaneous imaging in full‐scan and tandem mass spectrometry (MS/MS) mode. DDI is performed by using a smaller row distance in the y‐direction than the desired image resolution and recording for example every second row in positive‐ion mode and the other half of the rows in negative‐ion mode, thus resulting in two separate images. This causes some degree of oversampling, which is thus utilized to obtain complementary mass spectrometric of the sample. Imaging with both polarities is exemplified on an imprint of a Hypericum perforatum leaf containing secondary metabolites which ionize in both polarites and a mouse kidney containing phospholipids which ionize in positive or negative mode only. Simultaneous full‐scan and MS/MS imaging was demonstrated on the same mouse kidney, as the mouse had been given a relatively low dose of the antidepressive drug amitriptyline. While the full‐scan data allowed imaging of the endogenous phospholipids, the drug and its metabolites were only visible in the MS/MS images. The latter approach is useful, for example in whole‐body imaging experiments where the full‐scan data gives an overview of the tissue, and the MS/MS mode provides the sensitivity to image trace amounts of drugs and metabolites. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimization of automated matrix deposition for biomolecular mapping using a spotter

Imaging mass spectrometry using matrix-assisted laser desorption/ionization allows the detailed mapping of biomolecules directly from tissue. Matrix deposition is the key step for successful imaging. The appropriate concentration and deposition of matrix is critical for extraction, desorption, and ionization of molecules from tissue without losing molecular localization. The main challenge to meet these criteria is to deposit matrix droplets homogeneously on the tissue section. This work shows how a chemical inkjet printer was used for this purpose resulting in the imaging of phosphatidylcholines and sulfatides. The intricacies involved in effective matrix deposition are discussed.     

A concise review of mass spectrometry imaging

Mass spectrometric imaging allows the investigation of the spatial distribution of molecules at complex surfaces. The combination of molecular speciation with local analysis renders a chemical microscope that can be used for the direct biomolecular characterization of histological tissue surfaces. MS based imaging advantageously allows label-free detection and mapping of a wide-range of biological compounds whose presence or absence can be the direct result of disease pathology. Successful detection of the analytes of interest at the desired spatial resolution requires careful attention to several steps in the mass spectrometry imaging protocol. This review will describe and discuss a selected number of crucial developments in ionization, instrumentation, and application of this innovative technology. The focus of this review is on the latest developments in imaging MS. Selected biological applications are employed to illustrate some of the novel features discussed. Two commonly used MS imaging techniques, secondary ion mass spectrometric (SIMS) imaging and matrix-assisted laser desorption ionization (MALDI) mass spectrometric imaging, center this review. New instrumental developments are discussed that extend spatial resolution, mass resolving power, mass accuracy, tandem-MS capabilities, and offer new gas-phase separation capabilities for both imaging techniques. It will be shown how the success of MS imaging is crucially dependent on sample preparation protocols as they dictate the nature and mass range of detected biomolecules that can be imaged. Finally, developments in data analysis strategies for large imaging datasets will be briefly discussed.     

A quick and effective multivariate statistical strategy for imaging mass spectrometry

A new multivariate statistical strategy for analyzing large datasets that are produced by imaging mass spectrometry（IMS） techniques is reported.The strategy divides the whole datacube of the sample into several subsets and analyses them one by one to obtain the results.Instead of analyzing the whole datacube at one time,the strategy makes the analysis easier and decreases the computation time greatly.In this report,the IMS data are produced by the air flow-assisted ionization IMS（AFAI-IMS）.The strategy can be used in combination with most multivariate statistical analysis methods.In this paper,the strategy was combined with the principal component analysis（PCA） and partial least square analysis（PLS）.It was proven to be effective by analyzing the handwriting sample.By using the strategy,the m/z corresponding to the specific lipids in rat brain tissue were distinguished successfully.Moreover the analysis time grew linearly instead of exponentially as the size of sample increased.The strategy developed in this study has enormous potential for searching for the mjz of potential biomarkers quickly and effectively.     

Multivariate statistical identification of human bladder carcinomas using ambient ionization imaging mass spectrometry

Diagnosis of human bladder cancer in untreated tissue sections is achieved by using imaging data from desorption electrospray ionization mass spectrometry (DESI-MS) combined with multivariate statistical analysis. We use the distinctive DESI-MS glycerophospholipid (GP) mass spectral profiles to visually characterize and formally classify twenty pairs (40 tissue samples) of human cancerous and adjacent normal bladder tissue samples. The individual ion images derived from the acquired profiles correlate with standard histological hematoxylin and eosin (H&E)-stained serial sections. The profiles allow us to classify the disease status of the tissue samples with high accuracy as judged by reference histological data. To achieve this, the data from the twenty pairs were divided into a training set and a validation set. Spectra from the tumor and normal regions of each of the tissue sections in the training set were used for orthogonal projection to latent structures (O-PLS) treated partial least-square discriminate analysis (PLS-DA). This predictive model was then validated by using the validation set and showed a 5% error rate for classification and a misclassification rate of 12%. It was also used to create synthetic images of the tissue sections showing pixel-by-pixel disease classification of the tissue and these data agreed well with the independent classification that uses histological data by a certified pathologist. This represents the first application of multivariate statistical methods for classification by ambient ionization although these methods have been applied previously to other MS imaging methods. The results are encouraging in terms of the development of a method that could be utilized in a clinical setting through visualization and diagnosis of intact tissue.