Microfluïdische Pneumatische Cages: een nieuwe benadering voor de In-chip Crystal Trapping, manipulatie en gecontroleerde chemische behandeling
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
Moleculaire materialen zijn al lang bestudeerd in de wetenschappelijke gemeenschap vanwege hun brede aantal toepassingen op gebieden zoals moleculaire elektronica, optica en sensoren 1-4. Onder deze organische geleiders zijn een bijzonder spannende klasse van moleculaire materialen vanwege hun centrale rol in flexibele displays en geïntegreerde functionele apparaten 5,6. Echter, methoden gebruikt om elektronische ladingstransport in moleculaire materialen op basis van in staat zijn beperkt tot de vorming van ladingstransport complexen (CTC's) en ladingstransport zouten (CTSS) 7-10. Vaak CTCs en CTSS worden gegenereerd door elektrochemische methoden of door directe chemische redoxreacties; processen die een gecontroleerde transformatie van de donor of acceptor groepen belemmeren om meer complexe architecturen, waar multifunctionaliteit gedacht kan worden. Dienovereenkomstig, de opheldering van nieuwe systematische methoden voor de regelbare opwekking en manipulatie van moleculaire basend materialen blijft een belangrijke uitdaging op het gebied van materiaalkunde en moleculaire technologie, en, indien succesvol zal ongetwijfeld leiden tot nieuwe functies en nieuwe technologische toepassingen.
In dit verband hebben microfluidic technologieën onlangs gebruikt om moleculaire synthetiseren gebaseerde materialen vanwege hun vermogen tot warmte- en massaoverdracht en de reactie-diffusie hoeveelheid reagentia regelen tijdens een synthesewerkwijze 11,12. Eenvoudig gezegd continu stromen en bij lage Reynoldsgetallen een stabiel raakvlak van twee of meer reagentia stromen kunnen worden bereikt, die de vorming van een goed gecontroleerde reactiezone in de stroombaan, waarbij het mengen alleen plaatsvindt door diffusie 13-16 verschaft. Inderdaad hebben we eerder werkzaam laminaire stroom naar de syntheseroute van kristallijne moleculaire materialen zoals coördinatie polymeren (CP) in microkanalen 17 lokaliseren. Hoewel deze methode is gebleken great belofte realiseren nieuwe CP nanostructuren, de directe integratie van dergelijke structuren op oppervlakken, alsmede gecontroleerde chemische behandeling na maar hun formatie in situ 18 worden gerealiseerd. Om deze beperking te overwinnen, hebben we onlangs aangetoond dat de activering van microfluïdische pneumatische kooien (of kleppen) opgenomen in tweelaags microfluïdische inrichtingen met voordeel kunnen worden gebruikt in dit opzicht. Aangezien het pionierswerk van groep beving 19 zijn microfluïde pneumatische kleppen vaak gebruikt voor eencellige trapping en isolatie 20, enzymatische activiteit onderzoeken 21, vangen van kleine fluïdumvolumes 22, lokalisatie van functionele materialen op oppervlakken 23 en eiwitkristallisatie 24. Wij hebben echter aangetoond dat dubbellaags microfluïdische inrichtingen kunnen worden gebruikt voor het vangen, lokaliseren en te integreren in situ gevormde structuren uitlezen componenten en op oppervlakken 18. Verder hebben we ook aangetoond dat dergelijke technologie kan worden gebruikt om gecontroleerde chemische behandelingen uitvoeren op opgesloten structuren, zodat beide, 'microfluïdische ondersteunde ligand uitwisseling "18 en gecontroleerde chemische dotering van organische kristallen 18,25. In beide gevallen kan CTCs worden gesynthetiseerd onder gecontroleerde omstandigheden microfluïdische en in de meest recente studie konden multifunctionaliteit in hetzelfde materiaaldeel worden beschreven. Hierin tonen we de prestaties van deze dubbellaagse microfluïdische elementen die gebruikmaken kleurstof beladen stromen genereren en controleren van de coördinatie route van een CP en de lokalisatie op het oppervlak van een microfluïde kanaal en uiteindelijk beoordelen gecontroleerde chemische behandelingen op on-chip ingesloten structuren.
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 | – |
