Optical tweezers have been used for biological studies since shortly after their inception. However, over the years research has suggested that the intense laser light used to create optical traps may damage the specimens being studied. This review aims to provide a brief overview of optical tweezers and the possible mechanisms for damage, and more importantly examines the role of optical micromachines as tools for biological studies. This review covers the achievements to date in the field of optical micromachines: improvements in the ability to produce micromachines, including multi-body microrobots; and design considerations for both optical microrobots and the optical trapping set-up used for controlling them are all discussed. The review focuses especially on the role of micromachines in biological research, and explores some of the potential that the technology has in this area.

Optical microrobotics is an emerging field that has the potential to improve upon current optical tweezer studies through avenues such as limiting the exposure of biological molecules of interest to laser radiation and overcoming the current limitations of low forces and unwanted interactions between nearby optical traps. However, optical microrobotics has been historically limited to rigid, single-body end-effectors rather than even simple machines, limiting the tasks that can be performed. Additionally, while multi-body machines such as microlevers exist in the literature, they have not yet been successfully demonstrated as tools for biological studies, such as molecule stretching. In this work we have taken a step towards moving the field forward by developing two types of microlever, produced using two-photon absorption polymerisation, to perform the first lever-assisted stretches of double-stranded DNA. The aim of the work is to provide a proof of concept for using optical micromachines for single molecule studies. Both styles of microlevers were successfully used to stretch single duplexes of DNA, and the results were analysed with the worm-like chain model to show that they were in good agreement.

Advances in nanofabrication over the past twenty years have enabled the creation and use of ever-more interesting and useful micromachines. Optical micromachines are a particularly attractive subset of these for researchers in biological and soft-matter sciences, due to their potential to aid in optical tweezer studies of laser-sensitive samples. However, the development of multi-component micromachines is made difficult due to the dominance of surface forces at this scale, which is made all the more relevant in the high-salt concentrations used for biological studies. This study concerns the design of simple, first-class lever micromachines for use in environments with different salt concentrations, in an attempt to provide a guideline for design requirements of functional optical micromachines for use in physiological conditions.

Optical micromachines have the potential to improve the capabilities of optical tweezers by amplifying forces and allowing for indirect handling and probing of specimens. However, systematic design and testing of micromachine performance is still an emerging field. In this work we have designed and tested an unsupported microlever, suitable for general-purpose optical tweezer studies, that demonstrates stable trapping performance and repeatable doubling of applied forces. Stable trapping was ensured by analysing images to monitor focus shift when levers oscillated repeatedly, before the best-performing design was selected for force amplification. This study also shows that direct measurement of trap stiffness using the equipartition theorem appears to be a valid method for measuring applied forces on the spherical handles of microlevers.