Cell samples flowing along a microfluidic tube are scanned with an optical coherence tomography (OCT) system and their correlation times in M-mode scans are calibrated. In particular, the variations of correlation time with waiting time after 5 and 10 % ethanol are applied to the cell samples are compared for understanding the evolution of cell morphology in the cell death pathways of apoptosis and necrosis, respectively. Also, Au nanorings (NRIs) are taken up by cells for increasing the scattering strength in OCT scanning and hence increasing the signal-to-noise ratio. It is found that when cells are incubated with 5 % ethanol, the correlation time keeps decreasing with waiting time and then increases at 7 hours. On the other hand, when cells are incubated with 10 % ethanol, the correlation time keeps decreasing with waiting time all the way up to 7 hours. This difference may imply that the correlation time from OCT scanning may be determined not only by the size of cell fragment, but also by the smoothness of the cell fragment in a scale of several hundred nm during the apoptosis and necrosis processes. In particular, the results imply that the surface smoothness of the apoptotic bodies formed at the final stage of an apoptosis process is higher than that of the cell fragments formed at the final stage of a necrosis process. This OCT scanning technique has the potential application to the determination of cell death condition with the function similar to cell flow cytometry.
Photosensitizer can be taken up directly by cells or through the linkage with gold nanoparticles (NPs). When gold NPs linked with a photosensitizer are taken up by cells, both photodynamic (PDT) and photothermal effects for damaging cells can be generated under the illumination of a light source of an appropriate wavelength. The gold NPs and photosensitizer can escape from cells through an exocytosis process such that the efficiency of cell damage may decay with time. In this study, we investigate the dependencies of cell damage efficiency, gold nanoring (NRI) and photosensitizer amounts stayed in cells on the delay time. In particular, we differentiate the two possible escape pathways of the photosensitizer, AlPcS, i.e., AlPcS escape alone after its linkage with Au NRI is broken and AlPcS escape together with the linked Au NRI. Also, we intend to understand the dependence of the aforementioned AlPcS escape pathway on the location of Au NRIs inside a cell after they are taken up. It is found that generally, the PDT-induced cell damage efficiency decays more slowly when AlPcS is taken up together with linked Au NRI, compared with the case that AlPcS is taken up alone by cells. This trend indicates that the photosensitizer is more stable when it is linked with an Au NP. This result is confirmed by the observations of Au NRI and photosensitizer escapes through mass spectrometry, flow cytometry, and confocal fluorescent microscopy.
A cell spheroid can be as large as 1 mm in diameter, containing more than 300,000 cells. It can be used for simulating a cancer tumor in cell treatment study. In this study, the cell uptake behaviors in cell spheroids are investigated. In particular, the penetration depths of Au nanoring, Au nanorod, and photosensitizer (AlPcS) in cell spheroids are evaluated based on a newly proposed technique of using confocal fluorescent microscopy. By using a geometric computation process, we can estimate the width of a fluorescent belt region, which corresponds to the uptake depth. Based on such evaluations, we can understand whether the quiescent viable cells in the middle layer of a cell spheroid. Also, by using a cell culture insert, we can estimate the uptake Au nanoparticle number per cell through mass spectrometry measurement. It is found that after 48-hour incubation time, the Au nanoparticles and photosensitizer all have the penetration depths in the range of 110-140 m. Such uptake penetration depths control the cell damage depths under laser illuminations. For observing the uptake depths, we use different fluorescent dyes to incubate the cell spheroids. It is found that the penetration depth of a dye also relies on its molecular weight. The smaller uptake penetration depths of Au nanoparticles into a cell spheroid can be attributed to the settlement of Au nanoparticles in the incubation solutions such that the upper portion of a cell spheroid has no access to the Au nanoparticles.
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