The nanofluidic confinement apparatus: studying confinement-dependent nanoparticle behavior and diffusion

Abstract

The behavior of nanoparticles under nanofluidic confinement depends strongly on their distance to the confining walls; however, a measurement in which the gap distance is varied is challenging. Here, we present a versatile setup for investigating the behavior of nanoparticles as a function of the gap distance, which is controlled to the nanometer. The setup is designed as an open system that operates with a small amount of dispersion of ≈20 μL, permits the use of coated and patterned samples and allows high-numericalaperture microscopy access. Using the tool, we measure the vertical position (termed height) and the lateral diffusion of 60 nm, charged, Au nanospheres as a function of confinement between a glass surface and a polymer surface. Interferometric scattering detection provides an effective particle illumination time of less than 30 μs, which results in lateral and vertical position detection accuracy ≈10 nm for diffusing particles. We found the height of the particles to be consistently above that of the gap center, corresponding to a higher charge on the polymer substrate. In terms of diffusion, we found a strong monotonic decay of the diffusion constant with decreasing gap distance. This result cannot be explained by hydrodynamic effects, including the asymmetric vertical position of the particles in the gap. Instead we attribute it to an electroviscous effect. For strong confinement of less than 120 nm gap distance, we detect the onset of subdiffusion, which can be correlated to the motion of the particles along high-gap-distance paths.301

Nanofluidic rocking Brownian motors

“…Imaging of particles was performed by interferometric scattering detection, (25,27), which provides an excellent signal-to-noise ratio for the detection of small particles. The details are described in (25).…”

“…1 A and fig. S1) (26) using the nanofluidic confinement apparatus described in (27). We used closed-loop t-SPL (25) to pattern the thermally sensitive polymer polyphthalaldehyde with a sawtooth profile along complex-shaped transport tracks having a depth of 30 to 50 nm and a period of L 550 nm ( Fig.…”

Pneumatically Controlled Nanofluidic Devices for Contact‐Free Trapping and Manipulation of Nanoparticles

“…By fabricating devices with a lower initial nanofluidic channel height h c,0 , stable trapping could be already achieved at a gauge pressure p g of 0 mbar . More accurate and direct optical measurements of the nanofluidic channel height h c might be performed independently of the stiffness k r by two elaborate methods using either fixed particles to the nanofluidic channel walls or from the interference signal of the cover glass and PDMS device …”

Brownian motion of a charged colloid in restricted confinement

“…Consequently, the colloid motion was examined experimentally in the lateral direction [18,19]. However, its motion in the direction perpendicular to the confining surfaces, where the coupling between the PDDC and the interaction potential is pronounced, was only examined when the diffusion coefficient does not change throughout the colloid motion [20,21].…”