基于尖锐纳米加工针尖的高分辨率光子力显微镜
High resolution photonic force microscopy based on sharp nano-fabricated tips
摘要：
亚纳米分辨率的图像可以通过原子力显微镜（AFM）在沉积在硬衬底上的样品上实现。然而，由于尖端引起的变形，对软界面（例如生物膜）进行成像仍然极具挑战性。光子力显微镜（PhFM），基于光镊（OT），是一个有趣的替代软扫描探针显微镜。使用光代替物理悬臂来保持扫描探针导致刚度（$k_{OT}\sim0.1-0.001$ pN/nm），其可以比标准悬臂的刚度（$k_{AFM}\sim 10$ pN/nm）低2-3个数量级。结合纳米分辨率的位移测量的捕获探针，这允许成像软材料没有力引起的伪影。然而，光学捕获探针的尺寸，通常选择为$\sim μ$ m-尺寸球，到目前为止限制了PhFM的分辨率。在这里，我们展示了一种新的和简单的nanofabelet协议，大规模生产光学可捕获的石英颗粒，模仿AFM的尖端。我们证明和量化的稳定捕获的颗粒与尖尖锐的35 nm，最小的PhFM中使用的日期。光栅扫描图像的刚性纳米结构的功能小于80 nm，与我们的提示获得的AFM图像比较以及相同的样品。对感染疟疾的活红细胞膜进行成像不会产生可见的伪影，而是揭示了与细胞内寄生虫活动有关的称为旋钮的亚微米结构特征。在PhFM中使用纳米工程颗粒开辟了以高分辨率成像软和生物样品的道路。
英文摘要：
Sub-nm resolution images can be achieved by Atomic Force Microscopy (AFM) on samples that are deposited on hard substrates. However, it is still extremely challenging to image soft interfaces, such as biological membranes, due to the deformations induced by the tip. Photonic Force Microscopy (PhFM), based on optical tweezers (OT), represents an interesting alternative for soft scanning-probe microscopy. Using light instead of a physical cantilever to hold the scanning probe results in a stiffness ($k_{OT}\sim0.1-0.001$ pN/nm) which can be 2-3 orders of magnitude lower than that of standard cantilevers ($k_{AFM}\sim 10$ pN/nm). Combined with nm resolution of displacement measurements of the trapped probe, this allows for imaging soft materials without force-induced artefacts. However, the size of the optically trapped probe, often chosen as a $\sim μ$m-size sphere, has so far limited the resolution of PhFM. Here we show a novel and simple nanofabrication protocol to massively produce optically trappable quartz particles which mimic the sharp tips of AFM. We demonstrate and quantify the stable trapping of particles with tips as sharp as 35 nm, the smallest used in PhFM to date. Raster scan images of rigid nanostructures with features smaller than 80 nm obtained with our tips compare well with AFM images of the same samples. Imaging the membrane of living malaria-infected red blood cells produces no visible artefacts and reveals the sub-micron structural features termed knobs, related to the parasite activity within the cell. The use of nano-engineered particles in PhFM opens the way to imaging soft and biological samples at high resolution.
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