In Situ Curing of Sliding SU-8 Droplet over a Microcontact Printed Pattern for Tunable Fabrication of a Polydimethylsiloxane Nanoslit

Abstract

A tunable process for polydimethylsiloxane (PDMS) nanoslit fabrication is developed for nanofluidic applications. A microcontact printing (μCP) of a laterally spreading self-assembled hexadecanethiol (HDT) layer, combined with in situ curing of a sliding SU-8 droplet, enables precise and independent tuning of a nanoslit-mold width and height using a single μCP master mold. The SU-8 nanoslit-mold is replicated using a hard-soft composite PDMS to prevent channel collapse at low (<0.2) aspect ratio (height over width). The fluidic characteristics as well as dimensions of nanoslits fabricated with various conditions are analyzed using a fluorescein sample and AFM images. Finally, concentration polarization-based sample preconcentration is successfully demonstrated at the nanoslit boundary where an electric double-layer is overlapped.

Electroosmotic Effects on Sample Concentration at the Interface of a Micro/Nanochannel

“…Similarly, Rhodamine 6G in a cation-selective preconcentration chip was concentrated to ∼350 μM with 1 mM phosphate buffer at pH 7.4 . When the buffer concentration decreased to 200 and 100 μM, the maximum concentration of a preconcentrated fluorescein plug also decreased to ∼80 and ∼40 μM, respectively . However, fluorescein was concentrated to ∼4 mM with 10 mM phosphate buffer/15 mM NaCl at pH 7.4.…”

“…The incorporation of nanodimensioned features on lab-on-a-chip devices is growing as nanofabrication techniques have matured. − One technique, electropreconcentration with nanochannels, − nanopores, or nanoporous polymers, − has been developed to concentrate samples at the micronano interface. The ease of implementation, high concentrating efficiency with charged biomolecules, and simple operating conditions make it an attractive technique. ,− Basically, the nanochannel will become ion permselective when its electric double layer (EDL) is near or at overlap conditions. − This ion permselective nanochannel functions as a charge selective filter.…”

Beyond Gel Electrophoresis: Microfluidic Separations, Fluorescence Burst Analysis, and DNA Stretching

“…656 There is also work on integrating electrodes into the nanoslit. 657 Other techniques beyond “etch and bond” have also been explored, including photolithography with sacrificial materials, 658 high-precision micromilling and thermoplastics, 659 microcontact printing 660 and a novel “nanoglassblowing” technique. 661 …”

Electropreconcentration‐induced local pH change

“…As a strategy for detecting trace level of samples, various methods have been developed for sample preconcentration . Among these, the ion‐permselective nanochannel‐based sample preconcentration or electropreconcentration has received considerable attention due to advantages including ease of implementation and high trapping efficiency with charged molecules . The electropreconcentration, to be exact, is a redistribution of co‐ions caused by the ion‐permselective characteristic of the nanochannel when the electrical double layer (EDL) overlap condition is formed .…”