Micro-to-Nano Bimodal Single-Particle Sensing Using Optical Tweezers

Abstract

Recently, electrical sensing techniques for single objects, such as nanoparticles, biomolecules, and viruses, have attracted a great deal of attention. To achieve both high throughput and high measurement accuracy, target objects need to be quickly transported to a small sensing section embedded in a fluidic channel. In the present study, we propose a novel method to improve the signal-to-noise (S/N) ratio of electrical signals of single particles, using optical tweezers and a microchannel. Optically trapping a 2 μm microparticle in a micro-orifice that has a comparable dimension of 3.0 μm (W), 2.5 μm (H), and 3.0 μm (L), the electrical signal from a small target particle that passes by the microparticle is sharpened and separated from the background noise. By irradiation with nearinfrared light, the micro-orifice can be switched between opening and closing by optical tweezers, which works effectively to bring target particles to the sensing section using liquid flows and electrophoretic transport. As a result, the S/N ratio of electrical sensing of the smaller particle is improved by a factor of 5. The present microfluidic chip enables us to electrically detect particles of several hundreds of nanometers. Based on the present method, identification of single nanoparticles will also be feasible by using machine learning in the near future.

Toward Nano- and Microplastic Sensors: Identification of Nano- and Microplastic Particles via Artificial Intelligence Combined with a Plasmonic Probe Functionalized with an Estrogen Receptor

“…Optical and electrochemical sensing strategies integrated with discrimination capability for the particle size and type represent a growing field. , In particular, different optical and/or electrochemical platforms were developed for this purpose. − For instance, the coupling between optical tweezers and ML was demonstrated for microplastics classification in terms of both size and material . However, this approach was not proven for plastic nanoparticles and requires an expensive and complex experimental setup.…”

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Micro- and Nanofluidic pH Sensors Based on Electrodiffusioosmosis

“…To separate the sample and reference solutions, nanochannels were used. The composite structure of micro- and nanochannels is effective in focusing strong electric fields on the nanochannel, which serves as the sensing region [ 39 ]. Three types of nanochannels were prepared for pH sensors, and their cross-sectional views are depicted in Figure 2 .…”

pH Sensing Based on Ionic Current Rectification Using Triple-Barreled Glass Microelectrodes

“…In previous studies, we reported a possibility of electrohydrodynamic flows induced by electrokinetic transport through ion-exchange membranes. − It was experimentally and theoretically determined that selective ion transport could drive a liquid flow under an applied voltage of a few volts in aqueous solutions. Especially in nanochannels, electroosmotic flows (EOFs) effectively worked to transport and transform nanoobjects, e.g., deoxyribonucleic acid (DNA) , and nanoparticles. − Focusing on ionic current responses, the detailed properties of target objects and liquids were clarified. Here, it is important to measure ion concentrations and electric fields locally in liquids.…”