Institute of Biophysics, Johannes Kepler University, Gruberstraße 40, 4020 Linz, Austria.
GETec Microscopy GmbH, Seestadtstraße 27/Top 27, 1220 Vienna, Austria.
Sensors (Basel). 2020 Jul 2;20(13):3715. doi: 10.3390/s20133715.
Tracking of biological and physiological processes on the nanoscale is a central part of the growing field of nanomedicine. Although atomic force microscopy (AFM) is one of the most appropriate techniques in this area, investigations in non-transparent fluids such as human blood are not possible with conventional AFMs due to limitations caused by the optical readout. Here, we show a promising approach based on self-sensing cantilevers (SSC) as a replacement for optical readout in biological AFM imaging. Piezo-resistors, in the form of a Wheatstone bridge, are embedded into the cantilever, whereas two of them are placed at the bending edge. This enables the deflection of the cantilever to be precisely recorded by measuring the changes in resistance. Furthermore, the conventional acoustic or magnetic vibration excitation in intermittent contact mode can be replaced by a thermal excitation using a heating loop. We show further developments of existing approaches enabling stable measurements in turbid liquids. Different readout and excitation methods are compared under various environmental conditions, ranging from dry state to human blood. To demonstrate the applicability of our laser-free bio-AFM for nanomedical research, we have selected the hemostatic process of blood coagulation as well as ultra-flat red blood cells in different turbid fluids. Furthermore, the effects on noise and scanning speed of different media are compared. The technical realization is shown (1) on a conventional optical beam deflection (OBD)-based AFM, where we replaced the optical part by a new SSC nose cone, and (2) on an all-electric AFM, which we adapted for measurements in turbid liquids.
纳米尺度上生物和生理过程的跟踪是纳米医学这一快速发展领域的核心部分。尽管原子力显微镜（AFM）是该领域最适用的技术之一，但由于光学读出的限制，传统的 AFM 无法在不透明液体（如人血）中进行研究。在这里，我们展示了一种基于自感悬臂梁（SSC）的有前途的方法，该方法可替代生物 AFM 成像中的光学读出。悬臂梁中嵌入了压敏电阻器，形成惠斯通电桥，其中两个压敏电阻器放置在弯曲边缘。这使得通过测量电阻变化可以精确地记录悬臂梁的挠度。此外，可以用加热环代替传统的间歇接触模式中的声学或磁性振动激励。我们展示了进一步发展现有的方法，使在混浊液体中能够进行稳定的测量。在从干燥状态到人血的各种环境条件下，比较了不同的读出和激励方法。为了展示我们无激光生物 AFM 在纳米医学研究中的适用性，我们选择了血液凝固的止血过程以及不同混浊液体中的超平红细胞。此外，还比较了不同介质对噪声和扫描速度的影响。展示了技术实现（1）在基于传统的光学光束偏转（OBD）的 AFM 上，我们用新的 SSC 探头替代了光学部分，以及（2）在全电动 AFM 上，我们对其进行了适应以进行混浊液体中的测量。
