Real-time detection of single-living pancreatic β-cell by laser tweezers Raman spectroscopy: High glucose stimulation

Discrimination of Single Living Rat Pancreatic α, β, δ, and Pancreatic Polypeptide (PP) Cells Using Raman Spectroscopy

Primary pancreatic α, β, δ, and pancreatic polypeptide (PP) cells are reliable cell models for diabetes research. However, the separation and purification of these cells in living conditions remains an obstacle for researchers. The interaction of visible light with cellular molecules can produce Raman scattering, which can be analyzed to obtain cellular intrinsic molecular fingerprints. It has been speculated that primary pancreatic α, β, δ, and PP cells can be identified and separated from each other according to their spectral differences. To test this hypothesis, Raman spectra detection was performed on rat islet cells. Single islet cells identified by Raman scattering under living conditions were verified using immunohistochemistry. Thus, Raman data were acquired from a pure line of islet cells as a training sample and then used to establish the discriminant function. Then, using the principal component analysis-linear discriminate analysis (PCA-LDA) method, the four types of islet cells could be identified and discriminated by Raman spectroscopy. This study provides a label-free and noninvasive method for discriminating islet cell types in a randomly distributed mixed islet cell population via their physical properties rather than by using antibodies or fluorescence labeling.

Quantitative Raman spectral changes of the differentiation of mesenchymal stem cells into islet-like cells by biochemical component analysis and multiple peak fitting

Mesenchymal stem cells (MSCs) differentiate into islet-like cells, providing a possible solution for type I diabetes treatment. To search for the precise molecular mechanism of the directional differentiation of MSC-derived islet-like cells, biomolecular composition, and structural conformation information during MSC differentiation, is required. Because islet-like cells lack specific surface markers, the commonly employed immunostaining technique is not suitable for their identification, physical separation, and enrichment. Combining Raman spectroscopic data, a fitting accuracy-improved biochemical component analysis, and multiple peaks fitting approach, we identified the quantitative biochemical and intensity change of Raman peaks that show the differentiation of MSCs into islet-like cells. Along with increases in protein and glycogen content, and decreases in deoxyribonucleic acid and ribonucleic acid content, in islet-like cells relative to MSCs, it was found that a characteristic peak of insulin (665  cm-1) has twice the intensity in islet-like cells relative to MSCs, indicating differentiation of MSCs into islet-like cells was successful. Importantly, these Raman signatures provide useful information on the structural and pathological states during MSC differentiation and help to develop noninvasive and label-free Raman sorting methods for stem cells and their lineages.

Label-free detection of insulin and glucagon within human islets of Langerhans using Raman spectroscopy

Intrahepatic transplantation of donor islets of Langerhans is a promising therapy for patients with type 1 diabetes. It is of critical importance to accurately monitor islet quality before transplantation, which is currently done by standard histological methods that are performed off-line and require extensive sample preparation. As an alternative, we propose Raman spectroscopy which is a non-destructive and label-free technique that allows continuous real-time monitoring of the tissue to study biological changes as they occur. By performing Raman spectroscopic measurements on purified insulin and glucagon, we showed that the 520 cm(-1) band assigned to disulfide bridges in insulin, and the 1552 cm(-1) band assigned to tryptophan in glucagon are mutually exclusive and could therefore be used as indirect markers for the label-free distinction between both hormones. High-resolution hyperspectral Raman imaging for these bands showed the distribution of disulfide bridges and tryptophan at sub-micrometer scale, which correlated with the location of insulin and glucagon as revealed by conventional immunohistochemistry. As a measure for this correlation, quantitative analysis was performed comparing the Raman images with the fluorescence images, resulting in Dice coefficients (ranging between 0 and 1) of 0.36 for insulin and 0.19 for glucagon. Although the use of separate microscope systems with different spatial resolution and the use of indirect Raman markers cause some image mismatch, our findings indicate that Raman bands for disulfide bridges and tryptophan can be used as distinctive markers for the label-free detection of insulin and glucagon in human islets of Langerhans.

Recent advances in laser tweezers Raman spectroscopy (LTRS) for label-free analysis of single cells

Laser tweezers Raman spectroscopy (LTRS), a technique that integrates optical tweezers with confocal Raman spectroscopy, is a variation of micro-Raman spectroscopy that enables the manipulation and biochemical analysis of single biological particles in suspension. This article provides an overview of the LTRS method, with an emphasis on highlighting recent advances over the past several years in the development of the technology and several new biological and biomedical applications that have been demonstrated. A perspective on the future developments of this powerful cytometric technology will also be presented.

Three powerful research tools from single cells into single molecules: AFM, laser tweezers, and Raman spectroscopy

By using three physical techniques (atomic force microscopy (AFM), laser tweezers, and Raman spectroscopy), many excellent works in single-cell/molecule research have been accomplished. In this review, we present a brief introduction to the principles of these three techniques, and their capabilities toward single-cell/molecule research are highlighted. Afterward, the advances in single-cell/molecule research that have been facilitated by these three techniques are described. Following this, their complementary assets for single-cell/molecule research are analyzed, and the necessity of integrating the functions of these three techniques into one instrument is proposed.