Gvindzhiliia Georgii, Sivun Dmitry, Naderer Christoph, Jacak Jaroslaw, Klar Thomas A
Institute of Applied Physics, Johannes Kepler University Linz, 4040 Linz, Austria.
Department of Medical Engineering, University of Applied Sciences Upper Austria, 4020 Linz, Austria.
ACS Appl Opt Mater. 2023 May 12;1(5):945-951. doi: 10.1021/acsaom.3c00031. eCollection 2023 May 26.
Stimulated emission depletion (STED) has been used to break the diffraction limit in fluorescence microscopy. Inspired by this success, similar methods were used to reduce the structure size in three-dimensional, subdiffractional optical lithography. So far, only a very limited number of radical polymerization starters proved to be suitable for STED-inspired lithography. In this contribution, we introduce the starter Michler's ethyl ketone (MEK), which has not been used so far for STED-inspired lithography. In contrast to the commonly used 7-diethylamino-3-thenoylcoumarin (DETC), nanostructures written with MEK show low autofluorescence in the visible range. Therefore, MEK is promising for being used as a starter for protein or cell scaffolds in physiological research because the autofluorescence of DETC so far excluded the use of the green emission channel in multicolor fluorescence or confocal microscopy. In turn, because of the weak transitions of MEK in the visible spectrum, STED, in its original sense, cannot be applied to deplete MEK in the outer rim of the point spread function. However, a 660 nm laser can be used for depletion because this wavelength is well within the absorption spectrum of transient states, possibly of triplet states. We show that polymerization can be fully stopped by applying transient state absorption at 660 nm and that structure sizes down to approx. 40 nm in the lateral and axial directions can be achieved, which means 1/20 of the optical wavelength used for writing.
受激辐射损耗（STED）已被用于突破荧光显微镜中的衍射极限。受此成功启发，类似方法被用于三维亚衍射光学光刻中以减小结构尺寸。到目前为止，仅有极少数自由基聚合引发剂被证明适用于受STED启发的光刻。在本论文中，我们介绍了米氏乙基酮（MEK）引发剂，它迄今尚未用于受STED启发的光刻。与常用的7 - 二乙氨基 - 3 - 噻吩甲酰基香豆素（DETC）相比，用MEK写入的纳米结构在可见光范围内显示出低自发荧光。因此，MEK有望用作生理研究中蛋白质或细胞支架的引发剂，因为迄今为止DETC的自发荧光排除了在多色荧光或共聚焦显微镜中使用绿色发射通道。反过来，由于MEK在可见光谱中的跃迁较弱，从其原始意义上讲，STED不能用于耗尽点扩散函数外缘的MEK。然而，660 nm激光可用于耗尽，因为该波长恰好在瞬态（可能是三重态）的吸收光谱范围内。我们表明，通过施加660 nm的瞬态吸收可以完全停止聚合反应，并且在横向和轴向上可以实现低至约40 nm的结构尺寸，这意味着是用于写入的光波长的1/20。
