An new injection system is presented for shear-driven chromatography. The device has been fabricated by high aspect ratio etching of silicon. The performance of the injection slit is studied through the aid of computational fluid dynamics, and the first experimental results are presented

Berg, A. van den

Clicq, D.

Desmet, G.

Eghbali, H.

Gardeniers, H.

Malsche, W. de

Vervoort, N.

English

de Malsche, Wim

Gardeniers, Johannes G.E.

van den Berg, Albert

University of Twente Research Information

EXTENDING THE FUNCTIONALITIES OF SHEAR-DRIVEN CHROMATOGRAPHY NANO-CHANNELSUSING HIGH ASPECT RATIO ETCHINGW. De Malsche 1,2, D. Clicq 1, H. Eghbali 1, N. Vervoort 1, H. Gardeniers 2, A.van den Berg 2 and G. Desmet 11Department of Chemical Engineering, Vrije Universiteit Brussel, Belgium2MESA+ Research Institute, University of Twente, The NetherlandsABSTRACTAn new injection system is presented for shear-driven chromatography. The device hasbeen fabricated by high aspect ratio etching of silicon. The performance of the injection slitis studied through the aid of computational fluid dynamics, and the first experimentalresults are presented.Keywords: Shear-driven chromatography, injection system, high aspect ratio etching,computational fluid dynamics, nano-channels1. INTRODUCTIONIn recent work [1,2], we reported on the possibility to separate 4-component coumarin dyemixtures in less than 0.1 seconds using shear-driven flows in 1-dimensional nano-channels(Fig. 1). The combination of high velocities and ultra-thin liquid layers is very beneficial toconduct separations and reactions requiring rapid mass transfer between different phases, asis the case for liquid chromatography.Although we demonstrated the powerful chromatographic separation performances of thesystem, the shear-driven chromatography (SDC) channel systems we are using still lack anumber of critical functionalities (gradient elution, parallel array operation, coupling toMS,….) so as to be competitive with existing chromatographic instruments.In the present study, we are exploring the possibilities of using wet and dry etchingtechniques to integrate the SDC channels with minimal volume connections to i) an arrayof injection wells connecting directly to one member of a parallel SDC channel arraythrough a narrow rectangular injection slit, ii) an array of accurately positioned buffer wellsto perform on-column gradient mixing.2. EXPERIMENTALThe injection slits were machined by backside KOH etching of a silicon substrate until amembrane of 50 microns was obtained. The through hole was subsequently generated bydeep reactive ion etching from the front side. The channel was formed between twopolished substrates, one relatively short silicon substrate ( 10 mm long) containing an arrayof RIE etched spacers in a silicon nitride layer with a height which can vary between 100nm and a few µm and held within a stationary frame, and one relatively large glass9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA106 0-9743611-1-9/µTAS2005/$20©2005TRF9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA107substrate (50 mm long) which is completely flat and held in a translation stage-drivenmoving frame. Moving the larger substrate past the shorter, any type of liquid can bedragged (i.e., is shear-driven) through the nano-channel space formed between both gaps atvelocities up to centimetres per second and independently of the channel depth.Figure 1. CCD-camera images (stopped-flow image) of the separation of a mixture of 4 coumarindyes (C440, C450, C460 and C480) in a channel with d=280nm (sample concentration=1 mM) andcoated with a monolayer of C8 (separation time = 1.44 s).3. RESULTS AND DISCUSSIONSince flow hydrodynamics play an important role in the performance of the injection andoutlet slits, all designs have been supported using extensive computational fluid dynamics(CFD) simulation studies. Fig. 3 shows a CFD generated image of the injection plugswhich can be created using the injection slit shown in Fig. 2. This figure shows a WYKO(optical profilometry) scan of one of the injection slits coupling the channel with a samplewell machined at the back of the channel substrate. CFD revealed a linear relationshipbetween the injection time and the width of the injected peak. This allows a controlledinjection of a well defined plug.With this injection system experiments were carried out according to the procedure in Fig.3. Fig. 4 depicts a plug of a dye which was introduced in the channel. At time 0, the filledreservoir with dye was moved by 0.1 mm, after which the reservoir was replenished bybuffer and the shear driven principle was performed at 2 mm/s. Theoretically this shouldlead to a 0.05 mm wide plug which is confirmed by the experiment, see Fig. 4.Figure 2. Wyko scan of injection slit.500 µm100µm1 mm9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA108Figure 3. CFD simulation of the different steps during injection: a) Sample loaded into injection slit;b) sample is injected into the channel (by displacement of the moving wall); c) Sample in theinjection slit is replaced by buffer; d) Injected plug is moved through the channel by restarting themotion of the movable wall.Figure 4. Injection of coumarin 440 dissolved in methanol (0.5 mM) in a channel with a depth of400 nm.4. CONCLUSIONSA new injection system for shear-driven chromatography has been evaluated by CFD andthe device has been fabricated and tested. This paves the way for injecting well-definedplugs for future chromatographic separations. Experimental work is under way to evaluatethe performance of all fabricated structures.ACKNOWLEDGEMENTSWe like to thank Jan van Nieuwkasteele and Johan Bomer for their expert adviceconcerning micromachining technology.REFERENCES[1] Clicq, D., Vervoort N., Baron G.V. and Desmet G., 2004, LC-GC Europe, 17(5), 278-290.[2] Clicq, D., Pappaert, K., Vankrunkelsven, S., Vervoort, N., Baron, G.V. and DesmetG., 2004, Anal. Chem. 76(23), 430A-439A.

Extending the functionalities of shear-driven chromatography nano-channels using high aspect ratio etching

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Extending the functionalities of shear-driven chromatography nano-channels using high aspect ratio etching

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