Optical tweezers have become powerful tools to manipulate biomolecular systems, but are increasingly difficult to use when the size of the molecules is <1 microm. Many important biological structures and processes, however, occur on the submicron length scale. Therefore, we developed and characterized an optical manipulation protocol that makes this length scale accessible by stretching the molecule in the axial direction of the laser beam, thus avoiding limiting artifacts from steric hindrances from the microscope coverslip and other surface effects. The molecule is held under constant mechanical tension by a combination of optical gradient forces and backscattering forces, eliminating the need for electronic feedback. We demonstrate the utility of this method through a measurement of the force-extension relationship of a 1298 bp ds-DNA molecule.
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机译：光学镊子已经成为操纵生物分子系统的强大工具，但是当分子的大小小于1微米时，镊子就变得越来越难使用。但是，许多重要的生物学结构和过程都发生在亚微米长度范围内。因此，我们开发并表征了一种光学操作规程，该规程通过在激光束的轴向拉伸分子来访问此长度范围，从而避免了由于显微镜盖玻片和其他表面效应引起的空间位阻而限制了伪影。分子通过光学梯度力和反向散射力的结合而保持在恒定的机械张力下，从而无需电子反馈。我们通过测量1298 bp ds-DNA分子的力-延伸关系证明了该方法的实用性。
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