[Paper Review] Scalable trapping of single nanosized extracellular vesicles using plasmonics

Chuchuan Hong, Justus C. Ndukaife|arXiv (Cornell University)|Feb 14, 2023

Gold and Silver Nanoparticles Synthesis and Applications29 references4 citations

TL;DR

This paper presents a scalable, non-invasive hybrid nanotweezers platform that combines geometry-induced electrohydrodynamic (GET) forces with plasmonic cavities to enable parallel, rapid, and stable trapping of single nanosized extracellular vesicles (EVs) in seconds. By integrating nanoscale plasmonic cavities at GET trap centers, the system achieves instantaneous plasmon-enhanced optical trapping without photothermal damage, enabling high-throughput single-EV spectroscopy and imaging.

ABSTRACT

Heterogeneous nanoscale particles released by cells known as extracellular vesicles (EVs) are actively investigated for early disease detection1, monitoring2, and advanced therapeutics3. Due to their extremely small size, the stable trapping of nano-sized EVs using diffraction-limited optical tweezers4 has been met with challenges. Plasmon-enhanced optical trapping can confine light to the nanoscale to generate tight trapping potentials. Unfortunately, a long-standing challenge is that plasmonic tweezers have limited throughput and cannot provide rapid delivery and trapping of particles at plasmonic hotspots while precluding the intrinsic plasmon-induced photothermal heating effect at the same time. We report our original geometry-induced electrohydrodynamic tweezers (GET) that generate multiple electrohydrodynamic potentials for the parallelized transport and trapping of single EVs in parallel within seconds while enhancing the imaging of single trapped EVs. We show that the integration of nanoscale plasmonic cavities at the center of each GET trap results in the parallel placement of single EVs near plasmonic cavities enabling instantaneous plasmon-enhanced optical trapping upon laser illumination without any detrimental heating effect for the first time. These non-invasive scalable hybrid nanotweezers open new horizons for high-throughput tether-free plasmon-enhanced single EV trapping and spectroscopy. Other potential areas of impact include nanoplastics characterization, and scalable hybrid integration for quantum photonics.

Motivation & Objective

• To overcome the throughput and photothermal limitations of conventional plasmonic optical tweezers for single extracellular vesicle (EV) manipulation.
• To enable rapid, parallel transport and stable trapping of single nanosized EVs using electrohydrodynamic forces.
• To integrate plasmonic cavities at trap centers for instant plasmon-enhanced optical trapping upon laser illumination.
• To eliminate photothermal heating effects during trapping, preserving EV integrity.
• To establish a scalable, tether-free platform for high-throughput single-EV analysis and spectroscopy.

Proposed method

• Design of geometry-induced electrohydrodynamic tweezers (GET) with multiple microfluidic channels to generate parallel electrohydrodynamic potentials.
• Integration of nanoscale plasmonic cavities at the center of each GET trap to confine light at the nanoscale.
• Use of laser illumination to excite plasmonic cavities, creating tight optical trapping potentials for single EVs.
• Employment of dielectrophoretic and electrokinetic forces to transport EVs toward plasmonic hotspots rapidly.
• Optimization of trap geometry and plasmonic structure to maximize trapping efficiency and minimize photothermal heating.
• Real-time imaging and spectroscopy of trapped EVs enabled by enhanced local electromagnetic fields at plasmonic cavities.

Experimental results

Research questions

• RQ1 Can electrohydrodynamic forces enable rapid, parallel transport of single EVs toward plasmonic traps without external labeling or tethering?
• RQ2 How can plasmonic cavities be integrated into microfluidic traps to achieve instantaneous, stable optical trapping of single EVs?
• RQ3 Can plasmon-enhanced trapping be achieved without inducing significant photothermal heating that damages EVs?
• RQ4 What is the maximum throughput achievable for single-EV trapping using this hybrid electrohydrodynamic-plasmonic platform?
• RQ5 Can this system enable high-resolution imaging and spectroscopy of individual EVs in real time?

Key findings

• The hybrid GET-plasmonic system enables parallel trapping of single extracellular vesicles within seconds, achieving high throughput without physical tethering.
• Plasmonic cavities integrated at trap centers allow instantaneous plasmon-enhanced optical trapping upon laser illumination, with no measurable photothermal heating.
• Single EVs are stably confined near plasmonic hotspots, enabling enhanced optical imaging and spectroscopy due to strong local field enhancement.
• The system demonstrates non-invasive, label-free, and scalable manipulation of single EVs, overcoming limitations of conventional optical tweezers.
• The platform supports high-throughput analysis, with potential for applications in nanoplastics detection and quantum photonics integration.
• Experimental results confirm that the electrohydrodynamic transport efficiently delivers EVs to plasmonic traps, achieving stable trapping with high spatial precision.