Department of Medical Pharmacology and Physiology, University of Missouri, USA.
Analyst. 2017 May 2;142(9):1482-1491. doi: 10.1039/c6an02662a.
It is widely held that the melanosome is an exemplar of the absorption features of melanin-containing cells, which are assumed to be uniform in both size and optical characteristics. In recent years, however, it has become increasingly apparent that this is a strikingly poor assumption. Indeed, melanin extracted from natural sources and synthetic melanin both show wide variability in their degree of polymerization (molecular weight) and spectroscopic characteristics. In the current study, imaging spectrophotometry performed on individual cells of immortalized melanin-producing cell lines revealed broad distributions in their sizes: 9.5-36.2 μm for Hs936 human melanoma cells, 10.9-20.8 μm for T47D human breast cancer cells, 5.3-43.5 μm for B16F1 mouse melanoma cells, and 6.4-54.2 μm for B16F10 mouse melanoma cells. The color appearance (from translucent to yellow to nearly black), absorption spectrum, and absorption (extinction) coefficient at 532 nm (28.73 to 364.75, 0.01 to 40.17, 5.88 to 977.19, and 0.01 to 1120 cm for Hs936, T47D, B16F1, and B16F10 cells, respectively) of an individual cell also vary widely and cannot be adequately described by a 'typical' value. In comparison, human red blood cells are much more uniform in size (6.0-8.1 μm diameter; 1.9-3.2 μm thickness), although they too show a broad range of absorptivities, with extinction coefficients in the range of 65 to 370 cm when measured at 532 nm. To further evaluate the impact of these findings on photoacoustic bioanalysis, we performed simulations of the generation of photoacoustic signals expected from these cell types. These simulations revealed that their variation in optical features exerts a pronounced effect on the amplitude and shape of the photoacoustic signals generated from these cell types. Finally, we compared the photoacoustic signal generated from these cells under ideal conditions (i.e., a single cell in isolation) versus a heterogeneous real-world sample, demonstrating that when a single or few cancer cells are present within a blood droplet, the photoacoustic signal is indistinguishable from that measured from blood alone. These outcomes have important ramifications for the early photoacoustic detection of cancer cells and circulating tumor emboli, while pointing to the potential of single-cell imaging spectrophotometry to assess heterogeneity within cell populations in more quantitative terms.
人们普遍认为黑素体是含黑色素细胞吸收特征的典型代表，这些细胞被认为在大小和光学特性上都是均匀的。然而，近年来越来越明显的是，这种假设是非常糟糕的。事实上，从天然来源提取的黑色素和合成黑色素在聚合度（分子量）和光谱特征上都显示出很大的可变性。在目前的研究中，对永生黑色素产生细胞系的单个细胞进行成像分光光度法显示，其大小分布广泛：Hs936 人黑素瘤细胞为 9.5-36.2μm，T47D 人乳腺癌细胞为 10.9-20.8μm，B16F1 小鼠黑素瘤细胞为 5.3-43.5μm，B16F10 小鼠黑素瘤细胞为 6.4-54.2μm。单个细胞的颜色外观（从半透明到黄色到几乎黑色）、吸收光谱和在 532nm 处的吸收（消光）系数（28.73 至 364.75、0.01 至 40.17、5.88 至 977.19 和 0.01 至 1120cm，分别为 Hs936、T47D、B16F1 和 B16F10 细胞）也差异很大，不能用一个“典型”值来充分描述。相比之下，人类红细胞在大小（直径 6.0-8.1μm；厚度 1.9-3.2μm）上更加均匀，尽管它们也显示出广泛的吸收率范围，在 532nm 处测量时，消光系数在 65 到 370cm 之间。为了进一步评估这些发现对光声生物分析的影响，我们对这些细胞类型产生的光声信号进行了模拟。这些模拟表明，它们光学特征的变化对这些细胞类型产生的光声信号的幅度和形状有显著影响。最后，我们比较了在理想条件下（即在单独的一个细胞中）和在异质实际样本中这些细胞产生的光声信号，证明了当一个或几个癌细胞存在于一个血滴中时，光声信号与仅从血液中测量的信号无法区分。这些结果对癌症细胞和循环肿瘤栓子的早期光声检测具有重要意义，同时也表明单细胞成像分光光度法有可能以更定量的方式评估细胞群体内的异质性。
