Herein, we describe the fabrication and operation of a double-layer microfluidic system made of polydimethylsiloxane (PDMS). We demonstrate the potential of this device for trapping, directing the coordination pathway of a crystalline molecular material and controlling chemical reactions onto on-chip trapped structures.
The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment.
分子材料が長いため、このような分子エレクトロニクス、光学、センサー1-4のような分野での応用の彼らの幅広い多数の科学界で研究されてきました。これらの中で、有機導体があるため、フレキシブルディスプレイと統合された機能素子5,6におけるその中心的な役割の分子材料の特に刺激的なクラスです。しかし、分子系材料の電子電荷輸送を可能にするために使用される方法は、電荷移動錯体(のCTC)と電荷輸送塩(CTSS)7-10の形成に制限されます。頻繁に、CTCのとCTSSは、電気化学的方法によって、または直接的な化学酸化還元反応によって生成されます。多機能性が考えられるより複雑なアーキテクチャにドナーまたはアクセプター部分の制御された形質転換を妨げるプロセス。分子ベースの制御可能な生成と操作のための新たな体系的な方法のため、解明D材料は、材料科学や分子工学の分野における重要な課題のままで、成功した場合は、間違いなく新しい機能や新規技術的応用につながります。
この文脈では、マイクロ流体技術が最近による合成プロセス11,12の間の熱および質量移動、ならびに試薬の反応拡散量を制御する能力に分子系材料を合成するために使用されてきました。混合は、拡散のみ13-16を通して起こる流路内部よく制御された反応ゾーンの形成をもたらす達成することができる2つ以上の試薬 の流れとの間の安定したインターフェース、連続フローで、低レイノルズ数で、単に置きます。確かに、我々は以前に、このようなマイクロ流体チャネル17内の配位高分子(CPS)などの結晶性分子材料の合成経路をローカライズする層流を採用しています。この方法論は、グラムを示しているが、小説CPナノ構造を実現するためのreat約束、表面へのこのような構造の直接統合だけでなく、制御された化学処理、それらの形成は、その場 18 で実現するためにまだ持っていた後。この制限を克服するために、我々は最近、二層マイクロ流体デバイスに組み込まれたマイクロ流体空気圧ケージ(または弁)の作動は、有利には、この点で使用することができることを示しています。クエイクのグループ19の先駆的研究以来、マイクロ流体空気弁は、しばしば単一細胞捕捉および隔離20、酵素活性の調査21、小さな流体体積22のトラッピング、面23および蛋白質結晶24上の機能性材料のローカライズのために使用されています。しかし、我々は二層マイクロ流体デバイスは、トラップに使用することができることを示している、構成要素を読み出して表面18上に局在し、 その場で形成された構造に統合します。さらに、我々はまた、「マイクロ流体の補助配位子交換」18と有機結晶18,25の制御された化学的ドーピングの両方を可能にする、そのような技術は、トラップされた構造に制御された化学処理を行うために使用され得ることを実証しました。両方の場合において、CTCのは、制御されたマイクロ流体条件下で合成することができ、最新の研究では、多機能性は、同じ材料片で説明することができます。ここで、我々は、マイクロ流体チャネルの表面に配位CPの経路だけでなく、その局在を生成し、制御し、色素を含んだ流れを採用し、これらの二層マイクロ流体デバイスの性能を発揮し、最終的にはオンチップ上に制御された化学療法を評価します捕獲された構造。
The reported approach can be easily modified to fabricate different valve shapes to afford other applications such as fluid confinement. Indeed, the flexibility of this protocol also allows for modification of the thickness of the bottom layer, and thereby of the PDMS membrane, from a couple of tens to a few hundreds of microns to fulfill any application of interest. Moreover, dimensions of structures in each layer of the device can be optimized for the desired application and various heights of structures on the master molds can be simply achieved by spinning the photoresist at different velocities. Spinning the photoresist at a higher speed results in thinner structures.
To better implement the protocol, a clean room environment for the fabrication of the master molds is substantially essential; otherwise, the fabrication procedure will lead to defective master molds and thereby to unusable microfluidic devices. Two critical aspects should be emphasized in this protocol: i) the constant temperature of the oven that needs to be adjusted to 80 °C and ii) the programmed time period between processes that has to be complied accurately. Any modification of temperature and time frame in the protocol might lead to non-bonded chips, and thus, to non-functional devices.
The “turbulent free” conditions typically encountered in microfluidic systems have recently been employed for the generation of microstructures or molecular materials inside30 and outside single layer microfluidic chips31. In double-layer microfluidic chips, the laminar flow regime, and hence, the interface generated between continuous co-flows can be manipulated using pneumatic cages18,28. These devices also provide for effective control over the synthetic pathway, which in turn leads to precise localization and trapping on surfaces18.
As mentioned earlier, pneumatic actuation in double-layer microfluidic chips has been previously employed for various applications such as cell trapping20, enzymatic activity studies21 and protein crystallization24. However, the main objective of the reported approach is to propose a platform to be used for trapping and directing the coordination pathway of a crystalline molecular material and controlling chemical reactions onto on-chip trapped structures18,25.
The described method does not only allow trapping of anisotropic structures but can be used to localize particles onto surfaces. Future studies can be effectively directed towards the design of new valve shapes for additional application in biology, materials science and sensor technologies. The combination of different valve shapes as well as altered channel heights and membrane thicknesses can be employed to fulfill specific applications, such as chemical studies based on diffusional mixing and the localization of material growth.
A further application of the described microfluidic platforms is in the controlled chemical doping of crystals, which can lead to a rationalized formation of interfaces in crystalline structures19. This approach also provides for a wide range of post-treatments of on-chip trapped structures; a methodology that will undoubtedly open new horizons in materials engineering.
It is important to underline that the number of technologies enabling controlled chemical reactions under dynamic conditions and onto crystalline matter are very limited at present, hence making this approach very attractive in materials-related fields. However, a major limitation of this technology is the use of PDMS. PDMS elastomer is incompatible with many organic solvents, which limits the number of reactions that can be conducted inside these microfluidic chips. In future, the development of other elastomers that can tolerate and be stable against a broader number of organic solvents will be highly required in order to expand this field of research to other materials and chemistries.
The authors have nothing to disclose.
Authors would like to thank the financial support from Swiss National Science Foundation (SNF) through the project no. 200021_160174.
High resolution film masks | Microlitho, UK | – | Features down to 5um |
SU8 photoresist | MicroChem Corp., USA | SU8-3050 | – |
Silicon wafers | Silicon Materials Inc., Germany | 4" Silicon Wafers | Front surface: polished, Back surface: etched |
Silicone Elastomer KIT (PDMS) | Dow Corning, USA | Sylgard® 184 | – |
Spinner | Suiss MicroTech, Germany | Delta 80 spinner | – |
UV-Optometer | Gigahertz-Optik Inc., USA | X1-1 | – |
Mask Aligner | Suiss MicroTech, Germany | Karl Suss MA/BA6 | – |
SU8 developer | Micro resist technology GmbH, Germany | mr-Dev 600 | – |
Trimethylsilyl chloride | Sigma-Aldrich, Switzerland | 386529 | ≥97%, CAUTION: Handle it only under fume hood. |
Biopsy puncher | Miltex GmBH, Germany | 33-31AA-P/25 | 1 mm |
Biopsy puncher | Miltex GmBH, Germany | 33-31A-P/25 | 1.5 mm |
Glass coverslip | Menzel-Glaser, Germany | BB024040SC | 24 mm × 60 mm, #5 |
Laboratory Corona Treater | Electro-Technic Products, USA | BD-20ACV | – |
PTFE tubing | PKM SA, Switzerland | AWG-TFS-XXX | AWG 20TFS, roll of 100 m |
Silicone rubber tubing | Hi-Tek Products, UK | – | 1 mm I.D. |
neMESYS Syringe Pumps | Cetoni GmbH, Germany | Low Pressure (290N) | – |
High resolution camera | Zeiss, Germany | Axiocam MRc 5 | – |
Fluorescent inverted microscope | Zeiss, Germany | Axio Observer A1 | Operable at two wavelengths i.e. 350 nm and 488 nm |
Green polystyrene fluorescent particles | Fisher Scientific, Switzerland | 11523363 | Size: 5.0 um, solid content: 1% |
Silver nitrate (AgNO3) | Sigma-Aldrich, Switzerland | 209139 | ≥99.0%, |
L-Cysteine (Cys) | Sigma-Aldrich, Switzerland | W326305 | ≥97.0%, |
Disposable weighing dish | Sigma-Aldrich, Switzerland | Z154881 | L × W × H : 86 mm × 86 mm × 25 mm |
Disposable weighing dish | Sigma-Aldrich, Switzerland | Z708593 | Hexagonal, Size XL |
Plastic spatula | Semadeni, Switzerland | 3340 | L × W : 135 mm x 14 mm |
Dye, Bemacron ROT E-G | Bezema, Switzerland | BZ 911.231 | Red |
Stereomicroscope | Wild Heerbrugg, Switzerland | Wild M8 | 500x magnification |
Disposable scalpels | B. Braun, Switzerland | 233-5320 | Nr. 20 |
L-Ascorbic acid | Sigma-Aldrich, Switzerland | A4403 | – |