介电微粒的光阱装载在空气中
Summary
A protocol for launching and stably trapping selected dielectric microparticles in air is presented.
Abstract
We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner.
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.
Introduction
Ashkin报道在1970年1他的小说成就的加速和辐射压力微粒捕集促进了光学捕获技术的发展为物理和生物物理学基础研究的主要工具。 2，3，4，5迄今为止，光学捕获的应用已主要集中在液体环境中，并且被用于研究非常广泛的系统中，从胶体到单个生物分子的力学性能的行为。 6，7，光学捕获的气态介质8中的应用，但是，需要解决几个新的技术问题。
最近，在空气/真空光学捕获已被越来越多地在基础研究应用。由于光学列维塔季翁潜在提供了一种系统的几乎完全的隔离从周围的环境中，光学悬浮粒子成为在小物体研究量子接地状态，4个测量高频引力波，9和搜索分数电荷的理想的实验室。 10此外，空气/真空的低粘度允许人们使用惯性测量布朗粒子11的瞬时速度和在很宽的范围之外的线性弹簧状制度运动的创建弹道运动。 12因此，详细的技术信息，并在气体介质光学陷阱的做法已成为更广泛的研究团体更有价值。
新的实验技术是必需的纳米/微粒装入在气体介质的光学陷阱。压电换能器（PZT），即转换ELECTR设备集成电路能量转换成机械性的声能，已用于小颗粒递送到空气/真空5,12光学陷阱由于光悬浮的第一示范。 1此后，几个加载技术已经被提出来加载使用由商业喷雾器13或声波发生器产生的挥发性气溶胶更小的颗粒。 14固体夹杂物（颗粒）浮动气溶胶随机经过靠近的重点和偶然被困住。一旦该气溶胶被捕获，溶剂蒸发出来和颗粒残留在光阱。然而，这些方法不能很好适合于从样品中识别所需的颗粒，装载所选粒子，如果从阱释放来跟踪其变化。该协议的目的是提供对在空气中选择性光阱装载，包括实验细节新从业人设置，与颗粒运动的同时在频域和时域分析相关联的PZT保持架和样品的外壳，陷阱装载，和数据采集的制造。对于在液体培养基中捕获的协议也已出版。 15,16
整个实验装置在商业倒置光学显微镜的发展。 图1示出了用于证明选择性光阱装载的步骤设置的示意图：释放休息微粒，用聚焦束提起选择粒子，测量其运动，并再次将其放置到衬底上。首先，平移阶段（横向和纵向）被用来使选定的微粒在基片上，以由物镜聚焦的捕集激光（波长1064纳米）的焦点（近红外校正长工作距离物镜：NA 0.4，放大倍数20X，工作ðistance20毫米）通过透明衬底。然后，压电发射器（一个机械预加载环型PZT）产生超声波振动，打破微粒和基材之间的粘合。因此，任何释放颗粒可以通过单束梯度激光陷阱聚焦在选定的粒子上抬起。一旦粒子被捕获，它被转换到包含用于静电激励两个平行的导电板样品外壳的中心。最后，一个数据采集系统（DAQ）同时记录了粒子的运动，由一个象限小区光检测器（QPD）捕获，并且所施加的电场。在结束测量之后，粒子被可控放置到衬底，以便它可以再次以可逆的方式被捕获。这整个过程可以重复数百次，而不颗粒损失来衡量的变化，如接触带电发生在几个俘获循环。请参考我们近期的F条或细节。 12
Protocol
Representative Results
Discussion
压电发射器被设计为优化选择PZT的动态性能。 PZT材料和超声波振动管理的正确选择是关键步骤，以产生一个成功的实验。 PZTs具有取决于换能器的类型（散装或层叠）不同的特性和成分的材料（硬或软）。由硬质的压电材料的一个大容量类型的PZT被选择的原因如下。首先，硬的压电材料具有较低的介电损耗，比软质材料更高的机械品质因数。其次，大容量型的PZT代表低级电负载和更容易以驱动在?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
All work performed under the support of the National Institute of Standards and Technology. Certain commercial equipment, instruments, or materials are identified to foster understanding of this protocol. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
Materials
| ScotchBlue Painter's Tape Original | 3M | 3M2090 | |
| Scotch 810 Magic Tape | 3M | 3M810 | |
| Function/Arbitrary Waveform generator | Agilent | HP33250A | |
| Power supply/Digital voltage supplier | Agilent | E3634A | |
| Ring-type piezoelectric transducer | American Piezo Company | item91 | |
| Electro-optic modulator | Con-Optics | 350−80-LA | |
| Amplifier for Electro-optic modulator | Con-Optics | 302RM | |
| Mitutoyo NIR infinity Corrected Objective | Edmund optics | 46-404 | Manufactured by Mitutoyo and Distributed by Edmund optics |
| LOCTITE SUPER GLUE LONGNECK BOTTLE | Loctite | 230992 | |
| 3D printer | MakerBot | Replicator 2 | |
| Polylactic acid (PLA) filament | MakerBot | True Red PLA Small Spool | |
| Data Acquisition system | National Instruments | 780114-01 | |
| Quadrant-cell photodetector | Newport | 2031 | |
| Translational stage | Newport | 562-XYZ | |
| Inverted optical microscope | Nikon Instruments | EclipsTE2000 | |
| Fluorescence filter (green) | Nikon Instruments | G-2B | |
| Flea3/CCD camera | Point Grey | FL3-U3-13S2M-CS | Trapping laser |
| Diode pumped neodymium yttrium vanadate(Nd:YVO4) | Spectra Physics | J20I-8S-12K/ BL-106C | |
| Indium tin oxide (ITO) Coated coverslips | SPI supplies | 06463B-AB | Polystyrene microparticles |
| Fast Drying Silver Paint | Tedpella | 16040-30 | |
| Dri-Cal size standards | Thermo Scientific | DC-20 | |
| Optical Fiber | Thorlabs | P1−1064PM-FC-5 | bottom plate |
| Aluminium plate | Thorlabs | CP4S | |
| High voltage power amplifier | TREK | PZD700A M/S |
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