Department of Electrical and Computer Engineering, Clemson University, Clemson, SC, 29634, USA.
Advanced Materials Research Laboratory, Clemson University, Anderson, SC, 29625, USA.
Sci Rep. 2018 Jan 11;8(1):497. doi: 10.1038/s41598-017-18806-9.
A microwave technique is demonstrated to measure floating giant unilamellar vesicle (GUV) membranes in a 25 μm wide and 18.8 μm high microfluidic channel. The measurement is conducted at 2.7 and 7.9 GHz, at which a split-ring resonator (SRR) operates at odd modes. A 500 nm wide and 100 μm long SRR split gap is used to scan GUVs that are slightly larger than 25 μm in diameter. The smaller fluidic channel induces flattened GUV membrane sections, which make close contact with the SRR gap surface. The used GUVs are synthesized with POPC (16:0-18:1 PC 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), SM (16:0 Egg Sphingomyelin) and cholesterol at different molecular compositions. It is shown that SM and POPC bilayers have different dielectric permittivity values, which also change with measurement frequencies. The obtained membrane permittivity values, e.g. 73.64-j6.13 for POPC at 2.7 GHz, are more than 10 times larger than previously reported results. The discrepancy is likely due to the measurement of dielectric polarization parallel with, other than perpendicular to, the membrane surface. POPC and SM-rich GUV surface sections are also clearly identified. Further work is needed to verify the obtained large permittivity values and enable accurate analysis of membrane composition.
一种微波技术被展示用于测量 25μm 宽和 18.8μm 高的微流道中的漂浮的巨大单层囊泡（GUV）膜。该测量在 2.7 和 7.9GHz 下进行，在此处，分裂环谐振器（SRR）以奇模运行。使用 500nm 宽和 100μm 长的 SRR 分裂间隙来扫描直径略大于 25μm 的 GUV。较小的流道诱导 GUV 膜部分变平，并与 SRR 间隙表面紧密接触。所使用的 GUV 由 POPC（16:0-18:1 PC 1-棕榈酰基-2-油酰基-sn-甘油-3-磷酸胆碱）、SM（16:0 卵 Sphinomyelin）和胆固醇以不同的分子组成合成。结果表明，SM 和 POPC 双层具有不同的介电常数值，并且该值随测量频率而变化。获得的膜介电常数值，例如在 2.7GHz 下的 POPC 为 73.64-j6.13，比以前报道的结果大 10 多倍。这种差异可能是由于测量的介电极化与膜表面平行，而不是垂直于膜表面。POPC 和 SM 丰富的 GUV 表面部分也被清楚地识别。需要进一步的工作来验证所获得的大介电常数值，并能够对膜组成进行准确分析。
