Studies On Nanotube-based Micro-nanofluidic Chip

Micro-nanofluidic chip is a coin-sized chip,which could integrate with many functional components,including reaction chambers,particle generators,droplets sorter etc...These components form a network of micro-nano channels that control fluid throughout the entire system.The chip can realize some conventional functions of chemical or biological laboratories.When the size of fluid channel is reduced to micrometre range or even nanometer range,novel fluid transport properties will emerge from the combination of Van der Waals force,electrostatic force,capillary force,etc…And such properties greatly impact on the application of micro-nanofluidic chips about fluid manipulating,biosensing,protein detection and DNA sequencing.Therefore,the major challenge to explore these properties lies in building a distinct micro-nanofluidic system with specific nanochannels.Since boron nitride nanotubes and carbon nanotubes possess nano-sized hollow structures,they tend to be great candidates for being integrated into micro-nanofluidic chips.However,current research on micro-nanofluidic chips integrated with nanotubes is still in its infancy.And the chips include two structural forms:one is horizontal structure,in which nanotube connects microfluidic reservoirs on its two sides,and the other is vertical structure in which a nanotube pierces an ultralthin membrane and connects two fluid reservoirs.There are still plenty of problems to be solved,for instance,the electron beam lithography technology for horizontal structure fabrication has low lithography efficiency and low-volume production of chips;the micro-nanofluidic chip with vertical structure is not suitable for optical detection,and has poor stability and short service life,etc.Aiming at these problems,we describe the fabrication and ion transport properties of a micro-nano fluidic chip which integrated with a nanotube as nanochannel.SU-8 photoresist has good mechanical,optical properties and chemical stability,and is suitable for microstructure fabrication.Firstly,we studied the photolithography process for SU-8 microfluidic structure and fabricated a microfluidic chip of which the structure depth is 13.5±0.3?m.The chip was packaged by PDMS bonding.Then KCl electrolyte solution was injected into the chip,-0.1⁰.1 V voltage was applied between the two isolated microfluid channel and there was no current detected,thus there is no leakage in the chip.Compared with other methods,the fabrication method described in this work simplifies the processes,and can achieve large scale fabrication.Moreover,it shows the possibility for fabricating multi-channel structures.Micro-nanofluidic chip based on nanotube was fabricated using the SU-8photolithography parameters mentioned above.According to the bottom-up assembling method,nanotubes were adhered to the substrate before microfluidic structure fabrication.Si/SiO₂ substrate with marks on it was fabricated by electron beam evaporation or reactive ion etching for locating the nanotubes.BNNT was adhered to the substrate by coating BNNTs suspension on the substrate.As for CNT,it was grown laterally on the substrate surface.Then SU-8 microfluid channels were fabricated on two sides of the tube,and the chip was packaged by means of PDMS bonding.This kind of chip is expected to be applied in biomolecule detection,research on nanofluid properties and ion transport mechanisms in nano-confined space.Finally,different concentrations of KCl solution were injected into the chip.The scan voltage was applied to both sides of the nanotube by a patch clamp amplifier device,and the ion current generated in the nanotube was detected.It is find that it took 3 h for the ionization equilibrium after the KCl solution was implanted into the boron nitride nanotube,in the case of carbon nanotube,it need 10 h.In addition,due to different thickness of electric double layer in the nanotube at different concentrations,electro-osmotic flow in the nanotubes was affected.This leads to a non-linear relationship between ion conductivity,₄9)4)?8?,and KCl concentration,c.In the boron nitride nanotubes,there is a relationship of₄9)4)?8?^{80.43.In the carbon nanotube,the relationship is₄9}4)?8?⁽80.69.This work provide a preliminary study for the application of nanotube-based micro-nanofluidic chips in fluid manipulating,ion gating,DNA and protein detection.