Nanofluidic Structures Research Articles

Optofluidic device for ultra-sensitive detection of proteins using surface-enhanced Raman spectroscopy

An optofluidic device is reported in this paper that can highly improve the robustness of surface-enhanced Raman scattering (SERS) detection and provide fingerprint information of proteins with a concentration in the nanogram per liter range within minutes. Moreover, the conformational change of protein can also be obtained using this device. Fabricated by standard photolithography processes, the optofluidic device has a step microfluidic–nanofluidic structure, which provides robust SERS detection. The sensitivity of the device is investigated using insulin and albumin as target analytes at a concentration of 0.9 ng/L. The ability to detect conformational changes of proteins using this technology is also shown by probing these analytes before and after their denaturation.

Decreasing effective nanofluidic filter size by modulating electrical double layers: Separation enhancement in microfabricated nanofluidic filters

Conventional methods for separating biomolecules are based on steric interactions between the biomolecules and randomly oriented gel fibers. The recently developed artificial molecular sieves also rely on steric interactions for separation. In this work, we present an experimental investigation of a method that can be used in these sieves to increase separation selectivity and resolution. This method exploits the electrostatic repulsion between the charged molecules and the charged nanofluidic structure. Although this method has been mentioned in the previous work, it has not been examined in detail. We characterize this method by comparing the selectivity with that achieved in devices with different dimensions. The results of this study are relevant to the optimization of chip-based gel-free biomolecule separation and analysis.

LARGE AREA NANOSCALE PATTERNING BY INTERFEROMETRIC LITHOGRAPHY – NANOPHOTONICS AND NANOFLUIDICS

Interferometric lithography offers a facile, inexpensive, large-area fabrication capability for the formation of large areas of nanoscale periodic features. A self-aligned frequency doubling process to a 22-nm half-pitch is demonstrated. Many investigations of nanoscale phenomena require large-area samples, both for scientific investigations and certainly for ultimate large-scale applications. The utility of interferometric lithography is demonstrated to applications in nanophotonics and nanofluidics. For nanophotonics, metamaterial fabrication, negative index metamaterials and plasmonic applications are discussed. Two approaches to the fabrication of nanofluidic structures: etching and oxidation of silicon substrates, and colloidal deposition of silica nanoparticles to form porous walls and roofs followed by calcination to remove the photoresist and sinter the particles. These later structures have evident biomimetic functionality.

A Review of Nanofluidic Patents

Nanofluidics is a relatively new area of research, generally viewed as the study of the behavior, manipulation, and control of fluids at nanometer (<100 nm) scales. At nanometer scales, fluids exhibit unique physical behaviors which are not present in larger structures. Nanofluidic structures have been successfully applied to technologies including analytical separations and the manipulation of proteins, RNA and DNA. There are increasing numbers of applications emerging, as well as innovative fabrication methods enabling the development of these applications. This review covers some of the recent and significant patents relating to nanofluidic devices and methods. We particularly focus on nanofluidic patents targeted to separate, sense and manipulate biofluids and the presence of macromolecules therein. Moreover, several important fabrication methods are reviewed relating to forming microscale and nanoscale fluidic structures. This study found that a majority of the current nanofluidic patents are intended for bioengineering and biotechnology applications, and none of these patents used gas as a working fluid. To date, the number of nanofluidic patents has been very limited, though it is expected that the nanofluidic area will grow in the near future.

Nanochannels fabricated in polydimethylsiloxane using sacrificial electrospun polyethylene oxide nanofibers

The authors have used electrospun polyethylene oxide nanofibers as sacrificial templates to form nanofluidic channels in polydimethylsiloxane (PDMS). By depositing fibers on silicon templates incorporating larger structures, the authors demonstrate that these nanochannels can be integrated easily with microfluidics. They use fluorescence microscopy to image channels filled with dye solution. The utility of the hybrid micro- and nanofluidic PDMS structures for single molecule observation and manipulation was demonstrated by introducing single molecules of λ-DNA into the channels. This nanofabrication technique allows the simple construction of integrated micro- and nanofluidic PDMS structures without lithographic nanofabrication techniques.

Dynamic control of nanofluidic channels in protein drug delivery vehicles

Abstract Proteocubosomic nanocarriers are three-dimensional (3D) self-assembly periodic nanofluidic structures that have a surface topology of open nanochannels, which is apparent also in natural and self-assembled viral capsids. Here, proteins are nanoconfined in a hydrated self-assembly mixture of amphiphilic monoolein (MO) and octylglucoside (OG) forming cubosomic nanostructures. The generated periodic 3D nanochannel network architectures are investigated by means of synchrotron X-ray diffraction. The structural behavior of the ternary MO/OG/transferrin and MO/OG/immunoglobulin systems as well as the binary MO/OG mixture is studied in excess aqueous environment in the temperature range from 1 to 99 °C. The results indicate that 5% OG molar fraction in protein-containing monoolein systems favors the formation of a swollen bicontinuous cubic liquid crystalline structure with large water channels (D large ). Thus, it is feasible to dynamically adjust the diameters of the nanofluidic aqueous channels in the proteocubosomic carrier via the incorporation of a suitable amphiphilic additive. The obtained results may inspire the development of novel stimuli-responsive protein drug delivery nanovehicles and biocompatible self-regulating nanofluidic devices.

A patterned anisotropic nanofluidic sieving structure for continuous-flow separation of DNA and proteins

Microfabricated regular sieving structures hold great promise as an alternative to gels to improve the speed and resolution of biomolecule separation. In contrast to disordered porous gel networks, these regular structures also provide well defined environments ideal for the study of molecular dynamics in confining spaces. However, the use of regular sieving structures has, to date, been limited to the separation of long DNA molecules, however separation of smaller, physiologically relevant macromolecules, such as proteins, still remains a challenge. Here we report a microfabricated anisotropic sieving structure consisting of a two-dimensional periodic nanofluidic filter array. The designed structural anisotropy causes different-sized or -charged biomolecules to follow distinct trajectories, leading to efficient separation. Continuous-flow size-based separation of DNA and proteins, as well as electrostatic separation of proteins, was achieved, demonstrating the potential use of this device as a generic molecular sieving structure for an integrated biomolecule sample preparation and analysis system.

Nanofluidic structures for single biomolecule fluorescent detection

Fluid-filled nanofabricated cavities can be used to increase the spatial resolution of single molecule confocal microscopy based techniques by creating smaller and more uniformly illuminated probe volumes. Such structures may also be used to temporarily stretch single macromolecules, permitting the resolution of molecular details that would otherwise be beyond the capabilities of a diffraction limited system.

A Stable Ultra Low Flow Reference Electrode Using a Nanochannel Glass Array Junction

This paper describes the development of a novel pressure-driven nanofluidic- flowing liquid junction (NFLJ) reference electrode with an invariant liquid junction potential, for use in potentiometric sensors. These NFLJ reference electrodes have been shown to have a stable and reproducible potential with electrolyte flow under 5 ml per year. Use of the NFLJ reference electrode will result in sensors with outstanding precision that are maintenance free for periods of one year or more. This research is based on an innovative combination of nanochannel glass (NCG) and the nanofluidic liquid junction structure. The typical NCG array used for NFLJ reference electrodes has fewer than 200 channels with IDs smaller than 500 nm. Sensors using the NFLJ reference electrode demonstrate better potential stability, faster response time, and longer operational life than conventional commercial gel filled reference electrodes and are competitive with laboratory quartz fiber electrodes.

Nanofluidic tuning of photonic crystal circuits

By integrating soft-lithography-based nanofluidics with silicon nanophotonics, we demonstrate dynamic, liquid-based addressing and high deltan/n (approximately 0.1) refractive index modulation of individual features within photonic structures at subwavelength length scales. We show ultracompact tunable spectral filtering through nanofluidic targeting of a single row of holes within a planar photonic crystal. We accomplished this with an optofluidic integration architecture comprising a nanophotonic layer, a nanofluidic delivery structure, and a microfluidic control engine. Variants of this technique could enable dynamic reconfiguration of photonic circuits, selective introduction of optical nonlinearities, or delivery of single molecules into resonant cavities for biodetection.

Towards nano-fluidics by solvent deformation of electron beam resist

Improvements in the fabrication technology of planar micro- and nano-fluidic systems are continually being sought. In this work, we demonstrate and characterize a potential method for making planar nano-fluidic channels in cross-linked UV-3 resist using a single-step electron-beam lithography process. Earlier work indicated that the fluids used in the resist development process influenced the final form of the nano-fluidic structures. In this study the development, rinsing and drying conditions for the resist processing have been investigated in detail to find the best conditions for channel formation. The process was then exploited to construct more complex planar nano-fluidic features, including Y- and T-shaped junctions that are required for practical systems.

Aggregation structure and thermal conductivity of nanofluids

AbstractNanofluids are obtained by suspending metallic nanoparticles in conventional base liquids. Such a new class of heat‐transfer fluid is superior to the base liquids in energy‐transport performance, which depends on the distribution, volume fraction and thermal properties of the suspended nanoparticles. The theory of Brownian motion and the diffusion‐limited aggregation model are applied to simulate random motion and the aggregation process of the nanoparticles. A theoretical model is developed to predict the thermal conductivity of nanofluids. Comparison between the theoretical and experimental results shows the validity and accuracy of the theoretical model.

Vertically aligned carbon nanofibers as sacrificial templates for nanofluidic structures

We report a method to fabricate nanoscale pipes (“nanopipes”) suitable for fluidic transport. Vertically aligned carbon nanofibers grown by plasma-enhanced chemical vapor deposition are used as sacrificial templates for nanopipes with internal diameters as small as 30 nm and lengths up to several micrometers that are oriented perpendicular to the substrate. This method provides a high level of control over the nanopipe location, number, length, and diameter, permitting them to be deterministically positioned on a substrate and arranged into arrays.

Confinement-induced entropic recoil of single DNA molecules in a nanofluidic structure.

The behavior of DNA molecules is observed in a nanofluidic device near the interface of two regions that produce different configuration entropies. An electric field is applied to drive the molecules partway across the interface. Upon removal of the field, the molecules recoil to the higher-entropy region with a profile characteristic of a force localized to the interface and independent of length. This is consistent with a confinement-mediated entropic force, distinct from the well-known entropic elasticity common to all polymers. An estimate of the hydrodynamic drag is used to produce a lower bound for the force. The phenomenon can be exploited to separate long-strand polyelectrolytes according to length.

Structure and dynamics of nanofluids: Theory and simulations to calculate viscosity

The simplified expression of the Pozhar-Gubbins (PG) rigorous, nonequilibrium statistical mechanical theory of dense, strongly inhomogeneous fluids is used to calculate the viscosity of model fluids confined in a slit pore of several molecular diameters in width in terms of the equilibrium structure factors (i.e., the number density and pair correlation functions) of these nanofluids obtained by means of the equilibrium molecular dynamic simulations. These results are compared to those obtained by means of the nonequilibrium molecular dynamic simulations of the planar Poiseuille flow of the model nanofluids, and to the results supplied by several heuristic expressions for the nanofluid viscosity. This comparison proves that the PG transport theory provides a reliable, quantitatively accurate description of the viscosity coefficients of the model nanofluids while all the heauristic approaches fail. This success of the PG prediction of the nanofluid viscosity is because the theoretical expression accounts accurately for the nanofluid structure.