Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Paper
Lab on a Chip
2-pyridine carboxaldehyde, 130 mM methyl acrylate, and 65
mM 2,2-diazobicyclooctane (DABCO).
This process is undesirable, as it adds time and introduces
additional handling steps. There have been only three inline
interfaces for DMF and MS reported in the literature, all
coupling droplet processing with electrospray ionization (ESI)
MS. The first is a device containing both a DMF module and a
microchannel nanoESI emitter.20 A challenge for this system is
the labour-intensive fabrication steps required to make the
devices. A second technique uses an eductor interface,
comprising a transfer capillary inserted between the plates of
a two-plate DMF device connected to a tapered gas nozzle and
a metal ESI emitter.21 Droplets are pulled from the DMF device
to the emitter by a pressure differential generated when a
pulse of gas is applied to the nozzle. The third inline interface
for DMF and ESI MS22 consists of a pulled glass capillary
nanoESI emitter inserted between the top and bottom
substrates of the two-plate DMF device. Although the latter
two examples are relatively simple to setup and operate, they
both require external hardware and alignment of the emitter
with respect to the DMF device, which can be tricky.
Here we report the first DMF system used for microchemi-
cal synthesis coupled to mass spectrometry. This innovation
builds on the work of (1) Abdelgawad et al.,23 who reported
one-plate DMF devices made from flexible substrates that can
be used to move droplets on non-planar surfaces (in a
phenomenon known as ‘‘All-Terrain Droplet Actuation,’’ or
ATDA), and (2) Kirby et al.,24 who developed folded nanoESI
emitters made from a similar flexible substrate. Here, we have
combined these techniques to form an integrated device
format that we call ‘‘microfluidic origami,’’ comprising a DMF
device and nanoESI emitter on a single flexible substrate.
Moreover, we report a new two-plate-to-one-plate DMF inter-
face (relying on conventional definitions of these formats),
which allows for transfer of droplets between a dispensing and
mixing region and an analysis region of a device. Finally, we
have used this device for in-line monitoring of the Morita–
Baylis–Hillman (MBH) reaction. We speculate microfluidic
origami will eventually be useful for real-time analysis of
reaction rates and reaction pathways for a wide range of
microscale synthetic processes.
DMF-nanoESI device fabrication and assembly
Polyimide tape substrates were adhered to glass slides and
coated with metal (20 nm chromium adhesion layer and 100
nm gold) and AZ1500 photoresist by Telic (Valencia, CA, USA).
These substrates were used to form DMF device bottom plates
in the University of Toronto Emerging Communications
Technology Institute (ECTI) cleanroom facility using conven-
tional techniques. Briefly, the substrates were UV exposed (365
nm, 29.8 mW cm22, 10 s) through a transparent photomask
(Pacific Arts and Design, Markham, ON, Canada) using a Karl-
Su¨ss MA6 mask aligner (Garching, Germany). They were then
developed in MF321 (3 min) and post-baked on a hot plate
(100 uC, 2 min) before being immersed in gold etchant (30 s)
and then CR-4 (1 min). The remaining photoresist was
removed in AZ300T (10 min), and the substrates were rinsed
with acetone and methanol, dried under a stream of nitrogen,
and dried on a hot plate (90 uC, 2 min). Patterned contact pads
and the tip of the MS spray voltage wire (see below) were
covered in low-tack dicing tape (Semiconductor Equipment
Corporation, Moorpark, CA, USA) before coating with 2.2 mm
of Parylene-C using a vapour deposition instrument (Specialty
Coating Systems, Indianapolis, IN, USA). 200 nm of Teflon-AF
was applied by spin coating (1% wt/wt solution in Fluorinert
FC-40, 1600 rpm, 60 s) followed by post-baking on a hot plate
(160 uC, 10 min).
DMF device top plates were prepared from indium tin oxide
(ITO) coated polyethylene terephthalate (PET) (60 V sq21, 125
mm thickness) from Sigma Aldrich (Oakville, ON, Canada).
Each substrate (approximately 32 6 50 mm) was adhered to a
glass microscope slide using high strength acrylic adhesive
(300LSE, 3M, London, ON, Canada). The glass slide was
shorter than the ITO PET film substrate such that there was a
10 mm overhang of film at one edge. These substrates were
also coated with Teflon AF (200 nm, as above), and the bare
edge of the ITO PET film was coated with Teflon-AF by wiping
with a lint-free swab that had been dipped in 1% wt/wt Teflon-
AF in FC-40 before a post-bake on a hot plate (160 uC, 10 min).
As shown in Fig. 1(a), the DMF device comprises three
distinct regions: the two-plate DMF platform, the one-plate
DMF platform and the folded nanoESI emitter. The two-plate
DMF region includes 19 square actuation electrodes (2.2 6 2.2
mm each), four reagent reservoir electrodes (three 5 6 5 mm
and one 4.75 6 6.68 mm), one mixing electrode (4.75 6 6.68
mm, with a single 2.2 6 2.2 mm electrode cutout) and a
trapezoidal electrode (bases 6.68 mm and 2.8 mm, length 6.68
mm), with inter-electrode gaps of 40–130 mm. The one-plate
DMF region includes a linear array of 12 square electrodes (2.8
6 2.8 mm each) separated by 40 mm inter-electrode gaps, a
DMF counter electrode ground wire (1 mm wide) separated
from the square electrodes by a 40 mm gap, and a MS spray
voltage wire (250 mm wide) that is separated from the DMF
counter-electrode by a 200 mm gap. Both wires are adjacent to
the linear array of square electrodes across the length of the
one-plate region of the device. Each driving and ground
electrode on the bottom plate is connected to a series of
contact pads (not shown).
Experimental
Reagents and materials
Polyimide tape (87.5 mm total thickness; 50 mm polyimide with
37.5 mm silicone adhesive) was purchased from Argon
Masking, Inc. (Monrovia, CA, USA). Unless otherwise specified,
reagents were obtained from Sigma Aldrich (Oakville, ON,
Canada). Photolithography reagents were from Rohm and
Haas (Marlborough, MA, USA) and CR-4 chromium etchant
was from Cyantek (Fremont, CA, USA). Parylene-C dimer was
purchased from Specialty Coating Systems (Indianapolis, IN,
USA) and Teflon-AF was from Dupont (Wilmington, DE, USA).
HPLC grade methanol and deionized water (diH2O) with a
resistivity of 18 MV cm at 25 uC were used in all experiments.
MBH reagent and catalyst solutions were prepared in diH2O
from pure standards at the following concentrations: 100 mM
2534 | Lab Chip, 2013, 13, 2533–2540
This journal is ß The Royal Society of Chemistry 2013