We describe a novel parallel method for the patterning of proteins with nanoscale resolution. Combining nanoimprint lithography (NIL) and molecular assembly patterning by lift-off (MAPL), we produced streptavidin patterns with feature sizes in the order of 100 nm. A stamp is imprinted into a heated PMMA film followed by a dry etching step that converts the topography into a PMMA/Nb 2 O 5 contrast. A biotin functionalized copolymer, poly(L-lysine)-graft-poly(ethylene glycol)-biotin (PLL-g-PEG/PEG-biotin), spontaneously adsorbs on the oxide surfaces. After PMMA lift-off, the background is backfilled with protein-resistant PLL-g-PEG. We show that streptavidin selectively adsorbs on the biotin areas and thus can be used as a universal platform for immobilization of biotin-tagged molecules. This novel process is a parallel patterning method that is fast, reproducible, and economic. The PEG-copolymer can be functionalized with a variety of bioactive groups and thus allows a great flexibility in terms of surface chemistry.

Thermoplastics have become attractive alternatives to glass/quartz for microfluidics, but the realization of thermoplastic nanofluidic devices has been slow in spite of the rather simple fabrication techniques that can be used to produce these devices. This slow transition has in part been attributed to insufficient understanding of surface charge effects on the transport properties of single molecules through thermoplastic nanochannels. We report the surface modification of thermoplastic nanochannels and an assessment of the associated surface charge density, zeta potential and electroosmotic flow (EOF). Mixed-scale fluidic networks were fabricated in poly(methylmethacrylate), PMMA. Oxygen plasma was used to generate surface-confined carboxylic acids with devices assembled using low temperature fusion bonding. Amination of the carboxylated surfaces using ethylenediamine (EDA) was accomplished via EDC coupling. XPS and ATR-FTIR revealed the presence of carboxyl and amine groups on the appropriately prepared surfaces. A modified conductance equation for nanochannels was developed to determine their surface conductance and was found to be in good agreement with our experimental results. The measured surface charge density and zeta potential of these devices were lower than glass nanofluidic devices and dependent on the surface modification adopted, as well as the size of the channel. This property, coupled to an apparent increase in fluid viscosity due to nanoconfinement, contributed to the suppression of the EOF in PMMA nanofluidic devices by an order of magnitude compared to the micro-scale devices. Carboxylated PMMA nanochannels were efficient for the transport and elongation of λ-DNA while these same DNA molecules were unable to translocate through aminated nanochannels.

Fluidic devices that employ nanoscale structures (<100 nm in one or two dimensions, slits or channels, respectively) are generating great interest due to the unique properties afforded by this size domain compared to their micro-scale counterparts. Examples of interesting nanoscale phenomena include the ability to preconcentrate ionic species at extremely high levels due to ion selective migration, unique molecular separation modalities, confined environments to allow biopolymer stretching and elongation and solid-phase bioreactions that are not constrained by mass transport artifacts. Indeed, many examples in the literature have demonstrated these unique opportunities, although predominately using glass, fused silica or silicon as the substrate material. Polymer microfluidics has established itself as an alternative to glass, fused silica, or silicon-based fluidic devices. The primary advantages arising from the use of polymers are the diverse fabrication protocols that can be used to produce the desired structures, the extensive array of physiochemical properties associated with different polymeric materials, and the simple and robust modification strategies that can be employed to alter the substrate's surface chemistry. However, while the strengths of polymer microfluidics is currently being realized, the evolution of polymer-based nanofluidics has only recently been reported. In this critical review, the opportunities afforded by polymer-based nanofluidics will be discussed using both elastomeric and thermoplastic materials. In particular, various fabrication modalities will be discussed along with the nanometre size domains that they can achieve for both elastomer and thermoplastic materials. Different polymer substrates that can be used for nanofluidics will be presented along with comparisons to inorganic nanodevices and the consequences of material differences on the fabrication and operation of nanofluidic devices (257 references).

A new chemical vapour deposition setup for the generation of anti-adhesive coatings on Si stamps used in nanoimprint lithography has been developed. This is suitable for controlled co-evaporation of more than one type of silane by directly injecting a premixed silane into an evacuated deposition reactor through a septum. This process was found to be very flexible and resulted in reproducible coatings. A surface coated with a mixture of mono-and trichlorosilanes shows a higher water contact angle than those of individual coatings, which is attributed to the interaction between the two types of silane molecules. In addition, the influence of process parameters, e.g. water content, temperature and number of imprints, on the coating quality will be discussed.

Mixed-scale nano- and microfluidic networks were fabricated in thermoplastics using simple and robust methods that did not require the use of sophisticated equipment to produce the nanostructures. High-precision micromilling (HPMM) and photolithography were used to generate mixed-scale molding tools that were subsequently used for producing fluidic networks into thermoplastics such as poly(methyl methacrylate), PMMA, cyclic olefin copolymer, COC, and polycarbonate, PC. Nanoslit arrays were imprinted into the polymer using a nanoimprinting tool, which was composed of an optical mask with patterns that were 2-7 µm in width and a depth defined by the Cr layer (100 nm), which was deposited onto glass. The device also contained a microchannel network that was hot embossed into the polymer substrate using a metal molding tool prepared via HPMM. The mixed-scale device could also be used as a master to produce a polymer stamp, which was made from polydimethylsiloxane, PDMS, and used to generate the mixed-scale fluidic network in a single step. Thermal fusion bonding of the cover plate to the substrate at a temperature below their respective T(g) was accomplished by oxygen plasma treatment of both the substrate and cover plate, which significantly reduced thermally induced structural deformation during assembly: ∼6% for PMMA and ∼9% for COC nanoslits. The electrokinetic transport properties of double-stranded DNA (dsDNA) through the polymeric nanoslits (PMMA and COC) were carried out. In these polymer devices, the dsDNA demonstrated a field-dependent electrophoretic mobility with intermittent transport dynamics. DNA mobilities were found to be 8.2 ± 0.7 × 10(-4) cm(2) V(-1) s(-1) and 7.6 ± 0.6 × 10(-4) cm(2) V(-1) s(-1) for PMMA and COC, respectively, at a field strength of 25 V cm(-1). The extension factors for λ-DNA were 0.46 in PMMA and 0.53 in COC for the nanoslits (2-6% standard deviation).

Development of all polymer-based nanofluidic devices using replication technologies, which is a prerequisite for providing devices for a larger user base, is hampered by undesired substrate deformation associated with the replication of multi-scale structures. Therefore, most nanofluidic devices have been fabricated in glass-like substrates or in a polymer resist layer coated on a substrate. This letter presents a rapid, high fidelity direct imprinting process to build polymer nanofluidic devices in a single step. Undesired substrate deformation during imprinting was significantly reduced through the use of a polymer stamp made from a UV-curable resin. The integrity of the enclosed all polymer-based nanofluidic system was verified by a fluorescein filling experiment and translocation/stretching of λ-DNA molecules through the nanochannels. It was also found that the funnel-like design of the nanochannel inlet significantly improved the entrance of DNA molecules into nanochannels compared to an abrupt nanochannel/microfluidic network interface.

Spatially periodic systems with localized asymmetric surface structures (ratchets) can induce directed transport of matter (liquid/particles) in the absence of net force. Here, we show that propulsion for the directed motion of water droplets levitating on heated ratchet surfaces in the Leidenfrost (film boiling) regime is significantly enhanced as the ratchet period decreases down to micro-and sub-micrometers. At the temperature range slightly above the threshold temperature of droplet motion, sub-micron ratchets yield water droplet velocities reaching *40 cm/s, a speed that has never been achieved with any chemical and topological gradient surfaces. This dramatic increase in the droplet velocity is attributed to an enhanced heat transfer through the local contacts between ratchet peaks and bottom of the droplet. A hydrophobic coating on the ratchet surfaces is found to further increase the droplet velocity and decrease the threshold temperature of the droplet motion. The results suggest that miniaturized ratchet surfaces can potentially be used in diverse applications requiring control over fluid transport and heat transfer such as two phase cooling systems for microprocessors and fuel injection for combustion technology and that for those applications the design of ratchet dimensions and surface chemistry are critically important.

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