In a groundbreaking development poised to redefine the landscape of bioparticle manipulation, researchers at Jinan University have introduced a novel class of flexible and stretchable on-chip optical tweezers (FSOT). These innovative instruments overcome long-standing limitations of conventional optical tweezing technologies by seamlessly integrating high-throughput capabilities with unprecedented mechanical adaptability. This advance promises to dramatically expand the utility of optical tweezing, particularly for biomedical applications conducted within complex, dynamic biological environments.
Optical tweezers have, for decades, been critical tools for the non-invasive, contactless manipulation of microscopic particles. Traditional single-beam configurations, however, have struggled to balance throughput and resolution, while holographic approaches remain fundamentally constrained by the diffraction limit, impeding stable trapping of nanoparticles smaller than 100 nanometers. Although recent on-chip adaptations utilizing waveguides, nanoplasmonics, and metasurfaces have elevated operational throughput and spatial precision, these systems are often confined to rigid substrates. As a result, their efficacy falters when applied to curved, pliable, or living tissues, precluding their use in many in vivo and clinically relevant scenarios.
The FSOT platform transcends these barriers by harnessing the principles of optothermal tension assembly to generate highly ordered arrays of titanium dioxide (TiO₂) microlenses. These arrays are initially fabricated on a delicate, flexible soap film before being transferred onto a stretchable polydimethylsiloxane (PDMS) substrate or directly onto biological tissues such as animal skin, intestinal surfaces, and even plant leaves. Each microlens focuses incident laser light into a photonic nanojet—an intense, highly localized light beam that surpasses the diffraction limit—thereby enabling stable optical trapping at scales well below 100 nanometers.
This capability fundamentally alters the throughput paradigm of optical tweezing. Rather than relying on a single optical trap, the FSOT array hosts thousands of discrete trapping sites, facilitating simultaneous manipulation and analysis of hundreds of bioparticles. This ensemble approach accommodates a remarkably broad size spectrum, effectively capturing nanoscale exosomes, bacterial pathogens such as Escherichia coli and Staphylococcus aureus, microalgae like Chlorella, and mammalian immune cells nearing 10 micrometers in diameter. Such versatility positions the FSOT as a powerful platform for high-content, multiscale biophysical studies previously unattainable with conventional tweezing methods.
Crucially, the integration of TiO₂ microlenses on a PDMS substrate renders the FSOT inherently flexible, permitting it to bend and adapt conformally to irregular biological surfaces. This mechanical adaptability enables direct application onto living tissues without loss of optical trapping performance. Computational modeling reveals that substrate curvature dynamically modulates optical force distributions in a manner dependent on particle size and geometry. Exploiting this phenomenon, the researchers demonstrated effective mechanical sorting by selectively separating E. coli from S. aureus through controlled bending of the device on the tissue surface. This capacity for in situ particle discrimination within curved biological milieus eliminates the constraints imposed by rigid, conventional substrates.
Beyond simple bending, the FSOT exhibits reversible stretchability with tunable inter-trap spacing. This dynamic reconfiguration allows precise control over the spatial arrangement of trapped microparticles. Leveraging this feature, the researchers conducted live studies of intercellular communication and immune recognition by manipulating the distance between pathogenic bacteria and macrophages. Real-time modulation of extracellular spacing revealed critical insights into phagocytosis mechanisms, highlighting the FSOT’s potential as a dynamically reconfigurable tool for probing cell-to-cell interactions with unprecedented temporal and spatial precision.
The optical performance of the FSOT is underpinned by the photonic nanojet effect—a phenomenon characterized by the concentration of light into an ultra-narrow beam beyond classical diffraction limits. The TiO₂ microlenses engineered here exploit this effect to generate stable traps capable of immobilizing even sub-100 nm particles. This enhanced resolution is a stark contrast to traditional single-focus systems, where diffraction restricts trapping to particle sizes on the order of the wavelength of incident light. The microlens array thereby expands the operational window of optical tweezers into the nanoscale regime while exponentially multiplying the number of traps accessible within the same irradiation area.
The fabrication methodology—optothermal tension assembly—enables precise and scalable ordering of microlenses on ultra-thin films. This process involves controlled thermally induced stresses that spatially organize TiO₂ nanoparticles into micrometer-scale spherical lenses. Subsequent integration into flexible PDMS substrates affords mechanical robustness alongside optical precision. Critically, the resulting composite maintains transparency and mechanical compliance—two essential attributes for uninterrupted optical functionality on living tissue surfaces.
This fusion of high-throughput nano-manipulation with substrate flexibility signals a paradigm shift in biomedical optical trapping technology. The FSOT platform’s bio-integrated design opens avenues for wearable diagnostic devices capable of real-time biomarker isolation and manipulation within natural physiological environments. Such in vivo functionality could revolutionize point-of-care diagnostics, targeted drug delivery studies, and personalized medicine by enabling direct optical interaction with biological targets in situ.
The impact of FSOT extends beyond biomedical engineering into fundamental biophysical research. Its capacity for simultaneous multi-size particle manipulation allows detailed population-level analyses, advancing understanding of complex biological systems. Moreover, the tunable inter-trap spacing facilitates investigations into the spatial dynamics of cellular signaling, immunological synapses, and microbial interactions, providing novel insights into mechanisms that govern health and disease.
Looking forward, this technology paves the way for intelligent biomanipulation systems integrating flexible photonics with microfluidics and electronic readouts. Such systems could perform autonomous, high-throughput sorting, sensing, and modulation of cellular microenvironments, revolutionizing laboratory automation and translational medicine. The combination of mechanical adaptability with sub-diffraction-limit resolution uniquely positions these optical tweezers as transformative tools in both research and clinical contexts.
In conclusion, the development of flexible, stretchable on-chip optical tweezers represents a monumental advance in the field of optical manipulation. By overcoming throughput bottlenecks, diffraction limitations, and substrate rigidity, these devices unlock new frontiers in bioparticle handling and analysis. As their integration with living systems progresses, FSOT are poised to become ubiquitous instruments in next-generation biomedical technologies, bringing precise, high-throughput optical control into the heart of complex biological realities.
Subject of Research: Advanced Optical Tweezing Technologies for Bioparticle Manipulation
Article Title: Flexible, Stretchable, On-Chip Optical Tweezers for High-Throughput Bioparticle Manipulation
Web References:
http://dx.doi.org/10.1038/s41377-026-02199-4
Image Credits: Hongbao Xin et al.
Keywords
Optical Tweezers, Flexible Photonics, Titanium Dioxide Microlenses, Photonic Nanojet, High-Throughput Bioparticle Manipulation, Sub-Diffraction-Limit Trapping, Polydimethylsiloxane (PDMS), Biomedical Engineering, In Vivo Optical Manipulation, Stretchable Optical Devices, Intercellular Interaction, Biophysical Analysis
