Scientists obtain reconfigurable 3D optical manipulation of microscopic particles


Mar 10, 2024

(Nanowerk Highlight) The power to exactly place microscopic particles into helpful three-dimensional configurations has been a long-standing purpose in fields starting from supplies science and photonics to organic sensing and drug supply. Colloidal particles, that are small particles suspended in a medium, can function constructing blocks for superior engineered supplies and gadgets if they are often manipulated and assembled with ample management.

The Quest for Exact 3D Particle Management

Through the years, scientists have developed numerous methods to deal with this problem. Self-assembly strategies depend on the particles’ pure tendencies to prepare into ordered constructions however supply restricted tunability. High-down fabrication approaches like lithography permit exact patterning however are sometimes restricted to planar geometries. And whereas optical tweezers, which use centered laser beams to entice and transfer particles, present dynamic management in three dimensions, the particles are solely held in place by the laser mild – as quickly because it’s turned off, Brownian movement causes them to float aside.

Regardless of a long time of progress, a versatile technique for assembling particles into steady, reconfigurable 3D constructions has remained elusive. However now, a analysis group from the College of Texas at Austin, might have discovered an answer. By combining optical trapping with a cleverly designed phase-change materials, they’ve developed a platform for manipulating colloidal particles with unprecedented versatility, which they time period optothermal manipulation utilizing part change (OMPC).

The core innovation of OMPC lies within the medium surrounding the particles. Quite than a easy liquid, the researchers make use of a particular gel composed of surfactant molecules that self-assemble right into a strong however reconfigurable scaffold. This matrix has a exceptional property – when heated by a centered laser, it domestically transitions from a inflexible “coagel” state to a softer “gel” part within the beam path. By transferring the laser focus, this part transition may be induced at arbitrary factors to dynamically management the medium’s rigidity in three dimensions.

A Breakthrough in Optothermal Manipulation

As described of their paper revealed in ACS Nano (“Three-Dimensional Optothermal Manipulation of Gentle-Absorbing Particles in Part-Change Gel Media”), the scientists exploit this reversible laser-induced part change for optothermal manipulation.

Working mechanism of optothermal manipulation using phase change

Working mechanism of optothermal manipulation utilizing part change (OMPC): (a) A laser beam is imposed on a particle embedded within the surfactant matrix. XP and ZP are the distances between the particle heart and the laser beam heart (intersection of beam axis and focal airplane) alongside the X and Z instructions, respectively. (b) Initially, the surfactant matrix across the particle exists in its coagel part. When the laser is imposed on the particle, the temperature rises, and the rise in each the vitality of the bilayers and the water content material between the bilayers alters the interplay potential between the particle and the surfactant. Because the temperature will increase past a transition temperature (TTR), the matrix reversibly modifications its part right into a gel state, permitting the particle to be manipulated. (Reprinted with permission by American Chemical Society)

“When the beam is concentrated on a light-absorbing particle, the particle heats up, melting the encircling gel and permitting the optical forces to maneuver it to a brand new place,” Professor Yuebing Zheng, principal investigator of this work, explains to Nanowerk. “Then, when the laser is switched off, the gel re-solidifies and locks the particle in place. By iteratively trapping, transferring, and immobilizing particles, advanced configurations may be constructed up piece by piece.”

Zheng and his group exhibit a number of modes of particle manipulation utilizing OMPC, together with pushing particles alongside the beam path, pulling them in direction of the main target, and ‘nudging’ them laterally. In comparison with current methods like optical tweezers in liquid media, this new technique presents the distinctive benefit of having the ability to stably maintain particles in place after the laser is turned off. The gel medium prevents Brownian movement from disrupting the assembled constructions, permitting for extra advanced and sturdy configurations.

They showcase the meeting of 3D cubic lattices, reconfigurable patterns, and even particles using alongside the floor of a bigger sphere. Importantly, the gel medium retains the crafted constructions for very long time durations, stopping the disruption that plagues liquid-based meeting. The group studies that particles remained of their assembled positions for over 120 days, demonstrating the long-term stability of this strategy.

Past spatial patterning, the group additionally explores the usage of their OMPC approach to manage the interplay of nanostructures with 2D supplies. By elevating and reducing a silicon particle above a monolayer of tungsten diselenide, they’ll tune the energy and spectral profile of sunshine emission from the 2D materials. This functionality may very well be harnessed for optical sensing, mild emission, and different nanophotonic purposes.

A Large Vary of Potential Purposes

The implications of this work prolong to a variety of potential purposes. In photonics, the flexibility to assemble 3D lattices of dielectric particles may allow the creation of photonic crystals with tunable bandgaps and optical metamaterials with unique properties. Reconfigurable nanostructures may additionally discover use in adaptive optics and tunable lenses. Within the discipline of organic sensing, the exact positioning of colloidal particles functionalized with biomolecules like antibodies or enzymes may result in superior biosensors with improved sensitivity and specificity. And within the context of drug supply, the optical manipulation of drug-loaded nanocarriers may present a way of focused therapeutics.

Whereas the present work establishes a powerful proof of idea, the scientists notice that there’s nonetheless room for enchancment. “The pliability of the OMPC approach is at the moment restricted by the guide positioning of a single laser beam, which may very well be augmented sooner or later with algorithms for automated management and multi-beam manipulation,” notes Zheng. “Exploring a broader palette of gel supplies may additionally broaden the achievable temperature ranges and particle compatibilities.”

Working mechanism of optothermal manipulation using phase change

Versatility of OMPC: (a) Schematic and sequential microscopic photographs of a 3D array of 1.5 µm Si particles exactly organized by way of OMPC. Imaging airplane is indicated by the particle highlighted by the dashed circle. All different particles are on totally different planes however kind a dice (dashed traces; additionally see Supporting Data). (b) Schematic and closing optical microscopic photographs of particles organized in (i) a two-dimensional “2” sample, which is reconfigured into (ii) a three-dimensional “3” sample. Particles of the “3” sample are at various heights on a tilted digital airplane. The 2 microscopic photographs present the identical “3” sample at two totally different imaging planes the place the foci are on the particles highlighted by the dashed circles. (c) Schematic and optical photographs of a 1.5 µm Si particle manipulated on the floor of a ten µm PS particle. Place of the imaging airplane is highlighted within the higher proper nook (unit: µm). The Si particle is manipulated from the left backside (first panel) to the correct backside (final panel) of the PS particle. The schematics on the underside proper nook present the relative place of the Si particle with respect to the PS particle. Scale bar: 5 µm. (Reprinted with permission by American Chemical Society)

The researchers additionally acknowledge challenges that must be addressed for sensible purposes. The micron-scale undulations within the gel medium and the laser positioning accuracy at the moment restrict the manipulation of sub-500 nm particles. Optimizing the gel synthesis and implementing closed-loop suggestions management may assist overcome these limitations. The group additionally notes that additional work is required to allow the simultaneous translation and rotation of high-aspect-ratio constructions like nanowires.

Wanting forward, the group is exploring a number of avenues to advance the OMPC platform. Efforts are underway to automate the particle meeting course of utilizing image-based suggestions algorithms, which may significantly improve the pace and complexity of achievable constructions. They’re additionally investigating the usage of a number of laser beams for parallel manipulation and the incorporation of spatial mild modulators for dynamic beam shaping. Increasing the library of appropriate supplies, together with stimuli-responsive polymers and liquid crystals, is one other space of lively analysis.

“Within the broader context of nanotechnology, our work represents an thrilling step in direction of the purpose of programmable matter – the concept supplies may be designed to dynamically reconfigure themselves in response to exterior stimuli,” Zheng concludes. “By offering a way to reversibly assemble and disassemble microscopic constructing blocks on demand, this optothermal manipulation approach brings us nearer to realizing this imaginative and prescient.”

By combining the precision of optical trapping with the steadiness of phase-change media, this work provides an necessary new instrument to the toolkit of nanotechnology. Whereas there may be nonetheless work to be achieved to totally harness the capabilities of OMPC, it marks an thrilling stride in direction of our potential to manufacture functionalized micro- and nanostructures on demand. As analysis on this space progresses, we are able to anticipate a future the place reconfigurable 3D nanostructures are routinely used to push the boundaries of supplies science, photonics, biology, and past.

Michael Berger


– Michael is writer of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Expertise,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Abilities and Instruments Making Expertise Invisible
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