Measurements of Nano Particles’Brownian Motion near the Boundary in a High Concentration Solution

A quantitative immunosensing technique based on the measurement of nanoparticles’ Brownian motion is one of newly innovative bio-sensor chip on miniaturized devices and still in developing. There are some advantages of the technique such as highly compatible to any lab-on-chip device and easily fabricated without micro-electro-mechanical-system (MEMS) process. However, there are still some physical phenomena needed to research in order to optimize this technique. Boundary effect can no more be neglected in a micro system, therefore; this study aims to investigate Brownian motion behaviors in the micro channel, which combines effects of high concentrated nanoparticles, surface modification, different size of nanoparticles and very closed to boundary.
The sizes of particles are chosen by simulating real virus and anti-virus. The measurements and analysis of Brownian motion are primarily set up by using micro Particle-Tracking-Velocimetry (μ-PTV) and secondly set up by Fluorescent Correlation Spectroscopy (FCS). By the velocity profiles, it could be easily found out that Brownian motion present as Gaussian distribution; still, Brownian velocity can be obtained by calculating the standard deviation of particles’ velocity. Another secondly method of measurement Brownian motion is FCS which records the intensity signal of particles and analyzes by autocorrelation function which measures the self-similarity of a time signal and obtains the diffusion coefficient. Whatever analyzed methods be used, the results present that Brownian motion gets slow when the particles close to the boundary due to the boundary effect and no slip condition. The radius of particles is proportional to inversely square Brownian velocity. As concentration of solution gets larger, the effective viscosity of solution gets larger, which makes the Brownian motion becomes slower. Surface modification makes the surface become hydrophobic, and Brownian motion is measured comparing with hydrophilic but the there is no apparently different Brownian velocity between two surfaces. Finally, as smart phone with high pixels camera become popular, analysis program could be written as application, therefore; this innovative technique can be bring into the daily life.