Nanochannels on a Fused-Silica Microchip and Liquid Properties Investigation by Time-Resolved Fluorescence Measurements

Abstract

We have fabricated nanometer-sized channels, demonstrated a technique for the introduction of liquid into the channels, and carried out time-resolved fluorescence measurements of aqueous solutions. In this study, 330-nm- and 850-nm-sized channels were fabricated on fused-silica substrates by fast atom beam etching and hydrofluoric acid bonding methods. A liquid introduction method utilizing capillary action was demonstrated. The liquid introduction was observed under an optical microscope, and the liquid velocity during the introduction was analyzed by surface energy and macroscale hydrodynamics. The liquid velocity due to capillary action in the nanometer-sized channel seemed more than four times slower than the estimation. Then, aqueous solutions of rhodamine 6G (R6G), sulforhodamine 101 (SR101), and rhodamine B (RB) in the channels were measured by time-resolved fluorescence spectroscopy; spectra of the same solution in a 250-microm-sized channel were also measured as a reference for the macrospace. Although the fluorescence spectra in the 330-nm-, 850-nm- and 250-microm-sized channels agreed with one another, the fluorescent decays in the nanometer-sized channels were faster for R6G and SR101 and slower for RB than the respective decays in the 250-microm-sized channels. The results suggested the solutions had lower dielectric constants and higher viscosities in the nanometer-sized channels.

Filling kinetics of liquids in nanochannels as narrow as 27 nm by capillary force

“…This is not in contradiction to our observations, since their channels were only 100 µm long [16], and we only observed a few bubbles for every millimeter after the channels were filled (Fig. 3b).…”

“…Yang et al reported the marching velocity of capillary menisci in 500-nm-deep silicon nitride channels [18]. Hibara et al reported filling kinetics in 300-nm-deep channels fabricated in fused silica [16]. Both investigated channels of rectangular cross-section and they also observed the l ∼ t 1/2 relation.…”

Chemistry in nanochannel confinement

“…The authors consider this indirect proof of the higher viscosity of water in the channel compared to the bulk solution. In other work [23,44] it was found that water in a 300 nm-sized quartz glass nanochannel was a factor of three slower than predicted by the Hagen-Poiseuille law.…”

“…The most sensitive method is fluorescence, although this is not a generally applicable technique because molecules must be labeled in order to be able to use it; this means that the very nature of the molecules to be studied may change such that they are no longer relevant for the chemical problem under study. Fluorescence has proven to be very useful for characterizing the properties of liquids [44], where it is mostly used as a tracer for velocity measurement or zone dispersion. It is essential in studies of DNA behavior and protein folding (in the latter, the fluorescence intensity depends on the folding state).…”

Fabrication and electroosmotic flow measurements in micro- and nanofluidic channels

“…Filling by capillary forces, electroosmotic flow (EOF) and an increased surface to volume ratio are major concerns, which influence the choice of suitable materials for nanochannels and its fabrication technique (Tas et al 2003). Sacrificial layer etching, nanoimprint lithography, e-beam lithography and other methods have already been successfully applied for nanochannel fabrication (Guo et al 2004;Yu et al 2003;Cao et al 2002a, b;Hibara et al 2002;Lee et al 2003;O'Brien et al 2003). Nanochannels were fabricated in glass, silicon, polyimide, PDMS and Au (Eijkel et al 2004;Hug et al 2003;Zaumseil et al 2003).…”