The Recent Advances in Raman Microscopy and Imaging Techniques for Biosensors

Raman microspectroscopy is now well established as one of the most powerful analytical techniques for a diverse range of applications in physical (material) and biological sciences. Consequently, the technique provides exceptional analytical opportunities to the science and technology of biosensing due to its capability to analyze both parts of a biosensor system—biologically sensitive components, and a variety of materials and systems used in physicochemical transducers. Recent technological developments in Raman spectral imaging have brought additional possibilities in two- and three-dimensional (2D and 3D) characterization of the biosensor’s constituents and their changes on a submicrometer scale in a label-free, real-time nondestructive method of detection. In this report, the essential components and features of a modern confocal Raman microscope are reviewed using the instance of Thermo Scientific DXRxi Raman imaging microscope, and examples of the potential applications of Raman microscopy and imaging for constituents of biosensors are presented.

Tilted Two-Dimensional Array Multifocus Confocal Raman Microspectroscopy

A simple and efficient two-dimensional multifocus confocal Raman microspectroscopy featuring the tilted-array technique is demonstrated. Raman scattering from a 4 × 4 square foci array passing through a 4 × 4 confocal pinhole array is tilted with a periscope. The tilted array of Raman scattering signals is dispersed by an imaging spectrograph onto a CCD detector, giving 16 independent Raman spectra formed as 16 bands with different heights on the sensor. Use of a state-of-the-art imaging spectrograph enables high-precision wavenumber duplicability of the 16 spectra. This high duplicability makes the simultaneously obtained spectra endurable for multivariate spectral analyses, which is demonstrated by a singular value decomposition analysis for Raman spectra of liquid indene. Although the present implementation attains only 16 measurement points, the number of points can be extended to larger than 100 without any technical leaps. Limit of parallelization depends on the interval of measurement points as well as the performance of the optical system. Criteria for finding the maximum feasible number are discussed.

Quantitative analysis of the redox states of cytochromes in a living L929 (NCTC) cell by resonance Raman microspectroscopy

Raman spectra and images of a living L929 (NCTC) cell have been measured with 532 nm excitation. Both reduced and oxidized forms of cytochromes b and c (cyt b and cyt c) have been observed in situ without any pretreatment. The redox states of cyts b and c have been assessed quantitatively with a spectral analysis. It has been found that reduced cyt c is more abundant than oxidized cyt c, while oxidized cyt b is slightly more abundant than reduced cyt b in a living cell.

Casting new physicochemical light on the fundamental biological processes in single living cells by using Raman microspectroscopy

This Personal Account highlights the capabilities of spontaneous Raman microspectroscopy for studying fundamental biological processes in a single living cell. Raman microspectroscopy provides time- and space-resolved vibrational Raman spectra that contain detailed information on the structure and dynamics of biomolecules in a cell. By using yeast as a model system, we have made great progress in the development of this methodology. The results that we have obtained so far are described herein with an emphasis placed on how three cellular processes, that is, cell-division, respiration, and cell-death, are traced and elucidated with the use of time- and space-resolved structural information that is extracted from the Raman spectra. For cell-division, compositional- and structural changes of various biomolecules are observed during the course of the whole cell cycle. For respiration, the redox state of mitochondrial cytochromes, which is inferred from the resonance Raman bands of cytochromes, is used to evaluate the respiration activity of a single cell, as well as that of isolated mitochondrial particles. Special reference is made to the "Raman spectroscopic signature of life", which is a characteristic Raman band at 1602 cm(-1) that is found in yeast cells. This signature reflects the cellular metabolic activity and may serve as a measure of mitochondrial dysfunction. For cell-death, "cross-talk" between the mitochondria and the vacuole in a dying cell is suggested.

Evaluation of photodynamic treatment using aluminum phthalocyanine tetrasulfonate chloride as a photosensitizer: new approach

Photodynamic therapy (PDT) has been the subject of several clinical studies. Evidence to date suggests that direct cell death may involve apoptosis. T(24) cells (bladder cancer cells, ATCC-Nr. HTB-4) were subjected to PDT with aluminum phthalocyanine tetrasulfonate chloride (AlS(4)Pc-Cl) and red laser light at 670 nm. Morphological changes after PDT were visualized under confocal microscopy. Raman microspectroscopy is considered as one of the newly established methods used for the detection of cytochrome c as an apoptotic marker. Results showed that PDT treated T(24) cells seem to undergo apoptosis after irradiation with 3 J cm(-2). Cytochrome c could not be detected from cells incubated with AlS(4)Pc-Cl using Raman spectroscopy whereas AlS(4)Pc-Cl seems to interfere with the Raman spectrum of cytochrome c.

Resonance Raman quantification of the redox state of cytochromes b and c in-vivo and in-vitro

We observe the redox state changes with respiration of cytochromes b and c in mitochondria in a living Saccharomyces cerevisiae cell as well as in isolated mitochondria with the very use of Raman microspectroscopy. The possibility of monitoring the respiration activity of mitochondria in vivo and in vitro by Raman microspectroscopic quantification of the cytochrome redox states is suggested. It will lead to a new means to assess mitochondrial respiration activity in vivo and in vitro without using any labelling or genetic manipulation.