The development of diffraction-unlimited fluorescence microscopy has paved the way for a detailed understanding of cellular dynamics since live-cell investigations with resolutions below 100 nm have become available. This allows studying labelled specimen such as proteins and their distribution within a cell at a new level of detail. However, examining the cell membrane as a site of interaction between the cell’s internal processes and external signals with fluorescence microscopy (FM) leads to the difficulty that certain types of fluorescent dyes can alter the physicochemical properties of a cell. Investigating the cell membrane in a contact-free way and without any labelling or special pre-treatment is one of the greatest strengths of scanning ion conductance microscopy (SICM), which uses a fine pipette tip to determine the specimen’s topography. Since FM and SICM can both be applied to living cells and provide a resolution below the diffraction limit, correlating data from these two techniques seems to be a promising approach to further the understanding of the cell membrane’s organization and the mechanisms involved in transport processes across it. In the following, we briefly introduce the different approaches to super-resolved fluorescence microscopy (SRFM) and review applications of correlating SICM and FM (diffraction-limited) as well as SICM and SRFM (diffraction-unlimited). Finally, we discuss potential implementations of combined SRFM/SICM instruments and pitfalls that may arise during the development of such instruments.
Bioanalytical Reviews is the successor of the former review journal with the same name, and it complements Springer's successful and reputed review book series program in the flourishing and exciting area of the Bioanalytical Sciences.Bioanalytical Reviews (BAR) publishes reviews covering all aspects of bioanalytical sciences.It therefore is a unique source of quick and authoritative information for anybody using bioanalytical methods in areas such as medicine, biology, biochemistry, genetics, pharmacology, biotechnology, and the like.Reviews of methods include all modern tools applied, including mass spectrometry, HPLC (in its various forms), capillary electrophoresis, biosensors, bioelectroanalysis, fluorescence, IR/Raman, and other optical spectroscopies, NMR radiometry, and methods related to bioimaging.In particular the series volumes provide reviews on perspective new instrumental approaches as they apply to bioanalysis, and on the use of micro-/nano-materials such as micro-and nanoparticles.Articles on μ-total analytical systems (μ-TAS) and on labs-on-a-chip also fall into this category.In terms of applications, reviews on novel bioanalytical methods based on the use of enzymes, DNAzymes, antibodies, cell slices, to mention the more typical ones, are highly welcome.Articles on subjects related to the areas including genomics, proteomics, metabolomics, high-throughput screening, but also bioinformatics and statistics as they relate to bioanalytical methods are of course also welcome.Reviews cover both fundamental aspects and practical applications.Reviews published in BAR are (a) of wider scope and authoratively written (rather than a record of the research of single authors), (b) critical, but balanced and unbiased; (c) timely, with the latest references.BAR does not publish (a) reviews describing established methods of bioanalysis; (b) reviews that lack wider scope, (c) reviews of mainly theoretical nature.
To date, the most commonly applied method for detecting constituents in exhaled breath is gas chromatography (GC) coupled with mass spectrometry (GC-MS). Despite the ability to accurately detect a wide range of volatile organic compounds (VOCs), GC-MS-based instruments are frequently large and expensive, and the analysis is time consuming. Modern exhaled breath analysis requires on-line sampling and real-time selective biomarker detection with high sensitivity, precision, and accuracy. Therefore, optical sensing strategies are increasingly adopted and have emerged as a promising alternative method to meet these requirements. In particular, the mid-infrared wavelength regime has substantial potential, as almost any biomedically relevant gaseous molecule has species-characteristic vibrational, ro-vibrational, and rotational transitions in this frequency range. This chapter provides an overview on the fundamental principles and recent developments in this emerging field with a focus on technological and application examples in the infrared regime, as these sensing devices have already demonstrated their potential serving as a smart diagnostic tool in exhaled breath analysis.
Photoacoustic spectroscopy is a viable tool for trace gas detection in various application fields. In recent years, this technique has been exploited more and more for modern breath analysis as well. Within this chapter, a holistic overview of photoacoustic spectroscopy is presented, while maintaining the relationship to breath analysis. Therefore, a concise description of the fundamentals of photoacoustic spectroscopy is provided. This is essential for understanding the scopes and limits of this outstanding measurement technique being described within this chapter. In the past several different types of photoacoustic measurement setups for trace gas detection have emerged, including different light sources, modulation techniques, and detection schemes. These are described shortly and advantages as well as disadvantages, especially in relation to breath analysis, are highlighted. Though being a promising sensor principle, measurement devices based on photoacoustic spectroscopy are still rare on the sensor market, especially when it comes to trace gas detection in complex gas matrices, e.g., human breath exhale. One main reason is due to possible molecular interactions influencing the relaxational behavior of the analyte altering the sensor signal. Recent results shedding light on the intricate relaxational processes within complex gas matrices are discussed in detail, providing approaches to overcome this issue. Finally, various applications of photoacoustic spectroscopy in breath analysis are described demonstrating the great potential of this technology.
