Significance Optical tweezers are non-contact and high-precision particle trapping and manipulation tools that have been widely used in many scientific fields, such as physics, biology, and chemistry. However, traditional optical tweezers exhibit problems such as sample thermal damage caused by opto-thermal effects, which greatly limit the trapping ability and application range of samples. To solve these problems, opto-thermal tweezer technology has been proposed, which combines optical and heat effects for particle trapping and manipulation. Studies have shown that under certain conditions, the opto-thermal field can assist particle trapping through the optical heating or cooling effect of materials. Accordingly, various novel opto-thermal tweezer technologies have been proposed and developed. Compared with traditional optical tweezers, opto-thermal tweezers utilize the combined effect of optical and thermal fields to yield a lower laser power requirement, higher trapping accuracy, wider trapping region, and considerably reduced thermal damage of biomedical samples. To provide an overview and perspective on its development, this paper elaborates on the basic principle of opto-thermal tweezers, provides a detailed introduction to the development and application of some representative opto-thermal tweezer technologies, and discusses their future developmental prospects. Progress Over the past decade, significant improvements and advancements have been achieved in the field of opto-thermal tweezer technology. Because most particles exhibit a " heat-averse " response to thermal effects, in 2018, Lin et at . proposed the concept of opto-thermoelectric nanotweezers. This involved the creation of a thermoelectric field within a solution by incorporating cetyltrimethylammonium chloride (CTAC), enabling the trapping of " heat-averse " particles (Fig. 3). In 2022, Wang et at . enhanced this technology by substituting an opto-thermal substrate with graphene, which possesses a much broader absorption spectrum. They also utilized a direct laser-writing technique to pattern the graphene substrate, achieving patterned traps and holographic manipulation of multiple particles (Fig. 4). To facilitate the application of opto-thermal tweezers in the biological field, in 2023, Chen et at . proposed a novel set of highly adaptable opto-thermal nano-tweezers that combines the principles of thermal penetration flow and dissipative force, where a dissipative force is used to trap various particles (Fig. 5). In 2021, Li et at . utilized the optical refrigeration effect for particle trapping. They employed laser irradiation on a ytterbium-doped yttrium lithium fluoride (Yb: YLF) substrate to generate a localized laser cooling effect for particle trapping (Fig. 6). In 2023, Kollipara et at . invented a new type of hypothermal opto-thermophoretic tweezers that reverses the particle's Soret coefficient by reducing the environmental temperature and utilizes laser irradiation of the substrate for opto-thermal trapping (Fig. 7). In 2022, Ding et at . proposed an opto-thermal manipulation method for light-driven micro/nanoscale rotors to achieve lateral rotation of particles along a direction perpendicular to the optical axis. By adding NaCl, PEG, and other reagents to the solution, they achieved a force balance at a specific distance from the light beam and provided lateral torque to the particles using an uneven charge distribution on the substrate (Fig. 8). In 2019, Li et at . successfully realized an opto-thermal control method capable of manipulating particles in air. They applied a thin CTAC layer onto glass and converted it into a quasi-liquid phase through laser irradiation using an optical scattering force to propel the particles (Fig. 9). The significant advantages of opto-thermal tweezers have been fully exploited in many fields such as materials science and biomedicine. In 2017, Lin et at . successfully achieved a low-power reconfigurable opto-thermoelectric printing technology using opto-thermal tweezers, enabling the printing and assembly of colloidal particles (Fig. 10). In 2022, Wang et at . utilized the highly efficient trapping ability of plasmonic-thermoelectric nano-tweezers for manipulating metal particles and combined it with a focused plasmonic enhancement effect to achieve super-resolution surface enhanced Raman spectroscopy (SERS) scanning imaging for two-dimensional material samples (Fig. 11). In the same year, Deng et at . manipulated silver nanoparticles into cells using graphene-based thermoelectric optical tweezers, which excited electromagnetic field hotspots and enabled in situ Raman spectroscopy detection at different positions within the cells (Fig. 12). In 2023, Chen et at . combined opto-thermal tweezer technology and clustered regularly interspaced short palindromic repeats (CRISPR) technology to propose an innovative CRISPR-driven opto-thermal nano-tweezer technology, which effectively aggregates biomolecules to meet the operational requirements of CRISPR technology (Fig. 13). Conclusions and Prospects Compared with traditional optical tweezers, opto-thermal tweezer technology offers many advantages, such as a lower laser power requirement, higher trapping accuracy, stronger trapping force, and wider trapping region. These advantages enhance the performance of particle trapping and manipulation and significantly reduce the thermal damage experienced by the trapped sample particles. The development of opto-thermal tweezer technology has also included improved biocompatibility, and its application range has expanded to various fields. However, opto-thermal tweezer technology still faces challenges, particularly in the development of material substrates and surfactants and high-throughput large-scale particle manipulation. Despite these challenges, opto-thermal tweezers will be further developed as a major tool for particle trapping, and their application fields will continue to expand.
