Gaiolas pneumáticas microfluídicos: uma nova abordagem para In-chip de cristal Trapping, Manipulação e controlada Tratamento Químico
Summary
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.
Abstract
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.
Introduction
Materiais moleculares têm sido muito estudada na comunidade científica devido ao seu amplo número de aplicações em campos como a eletrônica molecular, óptica e sensores 1-4. Entre estes, os condutores orgânicos são uma classe especialmente excitante de materiais moleculares por causa de seu papel central na displays flexíveis e dispositivos funcionais integradas 5,6. No entanto, as metodologias utilizadas para permitir o transporte de carga electrónica em materiais de base molecular estão restritas à formação de complexos de transporte de carga (CTCs) e sais de transporte de carga (CTSS) 7-10. Frequentemente, CTCs e CTSS são gerados por métodos electroquímicos, ou por reações redox químicos diretos; processos que dificultam uma transformação controlada de doadores ou aceitadores porções de arquiteturas mais complexas onde multifuncionalidade pode ser concebido. Assim, a elucidação dos novos métodos sistemáticos para a geração e manipulação de base molecular controlávelmateriais d continua a ser um desafio significativo nos campos da ciência de materiais e engenharia molecular, e se for bem sucedida, sem dúvida, levar a novas funções e novas aplicações tecnológicas.
Neste contexto, as tecnologias de microfluidos foram recentemente utilizados para sintetizar materiais de base molecular devido à sua capacidade para controlar a transferência de calor e massa, bem como o volume da reacção em difusão dos reagentes durante um processo sintético 11,12. Simplificando, em fluxos contínuos e em baixos números de Reynolds uma interface estável entre dois ou mais fluxos de reagentes pode ser alcançado, o que origina a formação de uma zona de reacção bem controlado no interior do percurso de escoamento, em que a mistura só ocorre através da difusão 13-16. Com efeito, temos utilizado anteriormente fluxos laminares para localizar a via de síntese dos materiais moleculares cristalinos, tais como polímeros de coordenação (CPS) dentro de canais de microfluidos 17. Embora esta metodologia revelou gpromessa reat na realização de nanoestruturas romance CP, a integração directa de tais estruturas em superfícies, bem como tratamento químico controlada após a sua formação tem ainda a ser realizado in situ 18. Para superar esta limitação, temos mostrado recentemente que a actuação de gaiolas de microfluidos pneumático (ou válvulas) incorporadas em dispositivos de microfluidos de duas camadas pode ser vantajosamente utilizado a este respeito. Desde o trabalho pioneiro de grupo 19 de Quake, válvulas pneumáticas microfluídicos têm sido frequentemente utilizada para interceptação de uma única célula e isolamento 20, as investigações de atividade enzimática 21, captura de pequenos volumes de fluido 22, a localização de materiais funcionais em superfícies 23 e cristalização de proteínas 24. No entanto, temos mostrado que os dispositivos microfluídicos camada dupla pode ser usado para armadilha, localizar e integrar in situ formado estruturas para ler componentes e em superfícies 18. Além disso, também têm demonstrado que tal tecnologia pode ser usada para realizar tratamentos químicos controlados em estruturas presas, permitindo que ambos, "troca de ligantes assistida microfluídico" 18 e doping química controlada de cristais orgânicos 18,25. Em ambos os casos, CTC pode ser sintetizado sob condições controladas de microfluidos, e no estudo mais recente, a multifuncionalidade poderia ser descrito na mesma peça de material. Aqui, demonstramos o desempenho destes dispositivos de microfluidos de camada dupla que empregam os fluxos de corante carregado, gerar e controlar a via de coordenação de um PC, e também a sua localização na superfície de um canal microfluídico e finalmente avaliar controlada tratamentos químicos para on-chip estruturas preso.
Protocol
Representative Results
Discussion
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.
Disclosures
The authors have nothing to disclose.
Acknowledgements
Authors would like to thank the financial support from Swiss National Science Foundation (SNF) through the project no. 200021_160174.
Materials
| 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 | – |
