Repetitive Electrical Sensing of Optically Trapped Microparticles in Motorized Liquid Flows

Abstract

Recently, electrical sensing methods for tiny objects, such as microparticles, cells, viruses, and allergen particles, have attracted much attention. However, the details of microfluidic devices have not yet been optimized because of problems with the detection frequency and the signal-to-noise (S/N) ratio. Herein, we propose applying optical forces acting on microparticles to the electrical measurement technique. First, an optical force acting on a single microparticle is quantitatively measured in the steady liquid flows. Next, the effects of acceleration and deceleration on the unsteady motions of the microparticles in the liquids are numerically evaluated, which may cause a release of the particle during the quick motions of the fluids. Finally, optical manipulation of the microparticles is combined with electrical sensing. An optically trapped microparticle can be transported to a sensing portion embedded in the microchannel by controlling a motorized stage, and the reciprocal motion of the microparticle in the channel enables us to repeatedly obtain electrical signals in a single trial. After superposing the signals by synchronizing the periodic motions, the S/N ratio is drastically improved, and weak signals that are usually hidden behind noise are clearly recognized. The present results will shed light on various research fields using weak signal detections of single molecules and nanoparticles as well as microparticles.

Synchronized resistive-pulse analysis with flow visualization for single micro- and nanoscale objects driven by optical vortex in double orifice

“…The electrophoretic effect results in further modulation on the particle velocity in the orifice on the order of 10 m/s under the applied voltage of 1 V; the velocity of the electrophoresis, , is written as , where and V/m denote the electrophoretic mobility of the particle and external electric field, respectively. The is based on the Smoluchowski equation, where mV 50 , F/m, , and Pa s denote the -potential of the particle, the permittivity of vacuum, relative permittivity and viscosity of surrounding liquid, respectively. As a result is calculated as m/s, which is on the same order of that caused by the fluid drag force.…”

“…Previous works 48 , 49 indicated that the repetitive acquisition of the pulses improves reproducibility and resolution of the resistive pulse analysis. Furthermore, we previously performed the repetitive pulse acquisition using a single-orifice device with a standard Gaussian optical tweezer 50 , which improved the S/N ratio of the waveform. The optical manipulation helps stable translocation of the target particles; near the micro- and nanoscale structure, the complex electrohydrodynamic flow is locally induced, often preventing the particle driven by the electrophoresis from entering the sensing portion.…”

Electrical Sensing of Au Nanoparticles Manipulated by an Optical Vortex

“…The present electrical measurement setup is constructed based on our previous study. 16 Single Au NP Sensing Based on the Coulter Principle. Many works about electrical sensing of small objects based on the conventional Coulter principle have already been published and reviewed, 3−5 where resistive pulses caused by the volume exclusion of target particles were often measured.…”

“…11−14 We also previously proposed some methods for the measurement of resistive pulses, controlling the transport of target particles using optical manipulation techniques. 15,16 Such optical techniques have been used in various research fields 17−19 since the potential of optical tweezers was demonstrated by Ashkin and his coworkers. 20−23 Optical manipulation of biological cells, 24,25 biomacromolecules, 26 and small colloid particles 27,28 was used to accurately determine the positions or to form ordered structures.…”

“…3,4,38,39 Recently, several novel methods were also proposed to improve the sensing accuracy of electrical measurements of small particles. 16,40,41 The present study provides a method to recover the weakness of nanoparticle electrical measurements using an optical vortex. It has already been reported that fluidic channels and particles usually have surface charges, which form electric double layers (EDLs) that become thicker or thinner depending on salt concentrations.…”