Optical tweezing has revolutionized non-contact, precision manipulation of microparticles, yet fundamental constraints persist. Conventional single-beam optical tweezers offer limited throughput, while holographic approaches remain confined by the diffraction limit, preventing stable trapping of sub-100 nm objects. Recent on-chip implementations using waveguides, nanoplasmonics or metasurfaces have improved throughput and resolution, but their reliance on rigid substrates hinders operation within dynamic, curved physiological environments, severely limiting in situ biomedical applicability.
To overcome these challenges—low throughput, size restrictions, and substrate rigidity—a research team led by Professors Hongbao Xin and Baojun Li at Jinan University has developed flexible, stretchable on-chip optical tweezers (FSOT). The innovation is based on optothermal tension assembly, which allows large-scale, organized titanium dioxide (TiO 2 ) microlens arrays to be fabricated on a flexible soap film and subsequently transferred onto polydimethylsiloxane (PDMS) or directly onto biological tissue surfaces (Fig. 1a, b). Each microlens generates a photonic nanojet, enabling optical trapping beyond the diffraction limit. Collectively, the array produces thousands of discrete optical traps, allowing simultaneous capture of hundreds of particles spanning two orders of magnitude in size—from sub‑100 nm exosomes to ~10 µm macrophages, including E. coli , S. aureus , Chlorella , and immune cells (Fig. 1c). This capability provides a powerful platform for high‑throughput, multi‑scale bioparticle analysis.
The FSOT platform exhibits three transformative characteristics:
1. High‑Throughput and Sub‑Diffraction‑Limit Trapping
Unlike single‑beam tweezers, the FSOT’s microlens array generates numerous optical traps in parallel. The photonic nanojet effect ensures stable capture of nanoparticles, overcoming the classical diffraction barrier. This allows concurrent manipulation of diverse bioparticles across a wide size range, enabling new forms of population‑level biophysical analysis.
2. Conformal Operation on Curved Biological Surfaces
Owing to its flexible PDMS substrate, the FSOT can bend and adapt to irregular curvatures (Fig. 2a). Remarkably, the microlens array can be directly transferred onto living tissues, including plant leaves, animal skin, and intestinal surfaces, where it successfully performs high‑throughput trapping of exosomes and bacteria (Fig. 2b‑d). Computational models reveal that substrate curvature modulates optical forces in a size‑ and shape‑dependent manner, enabling efficient mechanical sorting—demonstrated by the separation of E. coli from S. aureus through controlled bending (Fig. 2e). This functionality allows in situ particle manipulation on tissue surfaces, eliminating the need for flat, artificial substrates.
3. Stretchability for Tunable Inter‑Cellular Interaction Studies
Beyond bending, the FSOT is reversibly stretchable, permitting precise adjustment of inter‑trap distances (Fig. 3). This feature was harnessed to control the spacing between bacteria and macrophages, thereby regulating immune recognition and phagocytosis in real time. By varying the stretch, the team could probe how inter‑particle distance influences cellular communication, offering a dynamically reconfigurable platform for studying inter‑cellular processes.
In summary, the FSOT platform merges high‑throughput optical trapping with flexible, bio‑integrated photonics. It transcends the rigidity of conventional optical tweezers and earlier on‑chip designs, opening avenues for in vivo sensing, wearable diagnostic devices, and intelligent biomanipulation systems capable of operating within realistic biological environments.
Light Science & Applications
Flexible, stretchable, on-chip optical tweezers for high-throughput bioparticle manipulation