RESUMO
A novel flow-guided assembly approach is presented to accurately align and position nanowire arrays in pre-defined locations with high throughput and large-scale manufacturing capability. In this approach, a polymer solution is first filled in an array of microfluidic channels. Then a gas flow is introduced to blow out most of the solution while pushing a little leftover against the channel wall for assembly into polymer nanowires. In this way, highly ordered nanowires are conveniently aligned in the flow direction and patterned along both sides of the microchannels. In this study, we demonstrated this flow-guided assembly process by producing millimetre-long nanowires across a 5 × 12 mm area in the same orientation and with basic 'I-shape', 'T-shape', and 'cross' patterns. The assembled polymer nanowires were further converted to conductive carbon nanowires through a standard carbonization process. After being integrated into electronic sensors, high sensitivity was found in model protein sensing tests. This new nanowire manufacturing approach is anticipated to open new doors to the fabrication of nanowire-based sensing systems and serve as good manufacturing practice for its simplicity, low cost, alignment reliability, and high throughput.
RESUMO
Visualizing single DNA dynamics in flow provides a wealth of physical insights in biophysics and complex flow study. However, large signal fluctuations, generated from diversified conformations, deformation history dependent dynamics and flow induced stochastic tumbling, often frustrate its wide adoption in single molecule and polymer flow study. We use a hybrid field microfluidic (HFM) approach, in which an electric field is imposed at desired locations and appropriate moments to balance the flow stress on charged molecules, to effectively regulate the initial conformations and the deformation dynamics of macromolecules in flow. With λ-DNA and a steady laminar shear flow as the model system, we herein studied the performance of HFM on regulating DNA trapping, relaxation, coil-stretch transition, and accumulation. DNA molecules were found to get captured in the focused planes when motions caused by flow, and the electric field were balanced. The trapped macromolecules relaxed in two different routes while eventually became more uniform in size and globule conformations. When removing the electric field, the sudden stretching dynamics of DNA molecules exhibited a more pronounced extension overshoot in their transient response under a true step function of flow stress while similar behaviors to what other pioneering work in steady shear flow. Such regulation strategies could be useful to control the conformations of other important macromolecules (e.g., proteins) and help better reveal their molecular dynamics.
