Ruan Haowen, Haber Tom, Liu Yan, Brake Joshua, Kim Jinho, Berlin Jacob M, Yang Changhuei
Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Department of Molecular Medicine, Beckman Research Institute at City of Hope, Duarte, California 91010, USA.
Optica. 2017 Nov 20;4(11):1337-1343. doi: 10.1364/OPTICA.4.001337.
Optical scattering has traditionally limited the ability to focus light inside scattering media such as biological tissue. Recently developed wavefront shaping techniques promise to overcome this limit by tailoring an optical wavefront to constructively interfere at a target location deep inside scattering media. To find such a wavefront solution, a "guide-star" mechanism is required to identify the target location. However, developing guidestars of practical usefulness is challenging, especially in biological tissue, which hinders the translation of wavefront shaping techniques. Here, we demonstrate a guidestar mechanism that relies on magnetic modulation of small particles. This guidestar method features an optical modulation efficiency of 29% and enables micrometer-scale focusing inside biological tissue with a peak intensity-to-background ratio (PBR) of 140; both numbers are one order of magnitude higher than those achieved with the ultrasound guidestar, a popular guidestar method. We also demonstrate that light can be focused on cells labeled with magnetic particles, and to different target locations by magnetically controlling the position of a particle. Since magnetic fields have a large penetration depth even through bone structures like the skull, this optical focusing method holds great promise for deep-tissue applications such as optogenetic modulation of neurons, targeted light-based therapy, and imaging.
传统上，光散射限制了在诸如生物组织等散射介质内聚焦光的能力。最近开发的波前整形技术有望通过调整光波前来克服这一限制，使光波前在散射介质内部深处的目标位置产生相长干涉。为了找到这样的波前解决方案，需要一种“导星”机制来识别目标位置。然而，开发具有实际用途的导星具有挑战性，尤其是在生物组织中，这阻碍了波前整形技术的应用转化。在此，我们展示了一种基于小颗粒磁调制的导星机制。这种导星方法的光调制效率为29%，能够在生物组织内实现微米级聚焦，峰值强度与背景比（PBR）为140；这两个数值均比常用的导星方法——超声导星所达到的数值高出一个数量级。我们还证明了光可以聚焦在标记有磁性颗粒的细胞上，并且通过磁性控制颗粒的位置可以聚焦到不同的目标位置。由于磁场即使穿过像头骨这样的骨骼结构也具有较大的穿透深度，这种光学聚焦方法在诸如神经元的光遗传学调制、靶向光基治疗和成像等深层组织应用中具有巨大潜力。
