This document describes a new microfabrication process for producing microfluidic devices using a laser printer and lamination of polyester films. The process involves printing toner onto polyester films to define microchannel patterns. The printed films are then laminated together, with the toner binding the films and leaving blank regions that become channels. This creates software-defined channels approximately 6 μm deep from a single printed layer, or twice as deep from laminating two printed layers. The resulting devices were tested and shown to have some limitations but provide an attractive low-cost option for microfluidics fabrication compared to more expensive methods.

1. Subscriber access provided by University of Texas Libraries
Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth
Street N.W., Washington, DC 20036
Article
A Dry Process for Production of Microfluidic Devices
Based on the Lamination of Laser-Printed Polyester Films
Claudimir Lucio do Lago, Heron Dominguez Torres da Silva, Carlos Antonio
Neves, Jos Geraldo Alves Brito-Neto, and Jos Alberto Fracassi da Silva
Anal. Chem., 2003, 75 (15), 3853-3858• DOI: 10.1021/ac034437b • Publication Date (Web): 20 June 2003
Downloaded from http://pubs.acs.org on February 27, 2009
More About This Article
Additional resources and features associated with this article are available within the HTML version:
• Supporting Information
• Links to the 10 articles that cite this article, as of the time of this article download
• Access to high resolution figures
• Links to articles and content related to this article
• Copyright permission to reproduce figures and/or text from this article

2. A Dry Process for Production of Microfluidic
Devices Based on the Lamination of Laser-Printed
Polyester Films
Claudimir Lucio do Lago,* Heron Dominguez Torres da Silva, Carlos Antonio Neves, and
Jose´ Geraldo Alves Brito-Neto
Departamento de Quı´mica Fundamental, Instituto de Quı´mica, Universidade de Sa˜o Paulo, Av. Prof. Lineu Prestes 748,
CEP 05508-900, Sa˜o PaulosSP, Brazil
Jose´ Alberto Fracassi da Silva
Escola Polite´cnica, Universidade de Sa˜o Paulo, Av. Prof. Luciano Gualberto 158, travessa 3,
CEP 05508-900, Sa˜o PaulosSP, Brazil
A new microfabrication process based on a xerographic
process is described. A laser printer is used to selectively
deposit toner on a polyester film, which is subsequently
laminated against another polyester film. The toner layer
binds the two polyester films and allows the blank regions
to become channels for microfluidics. These software-
outlined channels are ∼6 µm deep. Approximately twice
this depth is obtained by laminating two printed films. The
resulting devices were not significantly damaged after 24
h of exposure to aqueous solutions of H3PO4, NaOH,
methanol, acetonitrile, or sodium dodecyl sulfate. Electric
tests with an impedance analyzer and microchannels filled
with KCl solution demonstrated that (1) wide channels
suffer from deformation of the top and bottom walls due
to the lamination of the polyester films and (2) the toner
walls are somewhat porous. Although these drawbacks
limit the maximum width of a channel and the minimum
distance between two channels, the process is an attrac-
tive option to other expensive, laborious, and time-
consuming methods for microchannels fabrication. The
process has been used to implement devices for electro-
spray tip and capillary electrophoresis with contactless
conductivity detection.
Miniaturization of devices and systems has been a permanent
objective of the analytical community. Portability, low consumption
of reagents, improved performance, and disposability are features
that motivate this search. Additionally, the reduction of scale
causes an increase of the importance of the interfacial region over
the behavior of the fluids that can lead to new strategies for
analytical systems. An approach used since the 1970s is to
implement microchannels on the basis of microelectronics pro-
cesses to pattern on silicon. However, microfluidics for chemistry
has continuously received new contributions, because the micro-
electronics processes do not match all the needs of the field.
Although the initial development of micrototal analytical
systems (µTAS) was focused on glass or quartz devices,1-3 the
introduction of new types of materials offered a new way for fast
prototyping and disposable devices. Indeed, plastic materials have
been extensively used for this purpose. Of course, the substitution
of silicon and glass by polymers renders new features that are
often more important than fast production and low cost. Duffy
and co-workers4 established a rapid prototyping procedure for
poly(dimethylsiloxane) (PDMS). This technique was recently
reviewed,5 and several applications of PDMS microchips have been
demonstrated.6-10 Manica and Ewing11 used the rapid PDMS
prototyping as a step for glass microchip fabrication. Unfortu-
nately, this technique still requires the use of silicon wafers and
the development of photoresists.
Alternative methods of fabrication of plastic microdevices
include UV laser ablation and hot embossing techniques. UV laser
ablation is capable of micromachining many polymeric substrates,
such as polycarbonate, polystyrene, cellulose acetate, and poly-
(ethylene terephthalate) (PET), generating channels with con-
trolled rugosity and increased hydrophilicity.12-14 In hot embossing
* Fax: +55 11 3815 5579. E-mail: claudemi@iq.usp.br.
(1) Harrison, D. J.; Fluri, K.; Seiler, K.; Fan, Z.; Effenhauser, C. S.; Manz, A.
Science 1993, 261, 895-897.
(2) Effenhauser, C. S.; Manz, A.; Widmer, H. M. Anal. Chem. 1993, 65, 2637-
2642.
(3) Jacobson, S. C.; Hergenro¨der, R.; Koutny, L. B.; Ramsey, J. M. Anal. Chem.
1994, 66, 1114-1118.
(4) Duffy, D. C.; McDonald, J. C.; Schueller, O. J. A.; Whitesides, G. M. Anal.
Chem. 1998, 70, 4974-4984.
(5) McDonald, J. C.; Duffy, D. C.; Anderson, J. R.; Chiu, D. T.; Wu, H.; Schueller,
O. J. A.; Whitesides, G. M. Electrophoresis 2000, 21, 27-40.
(6) Martin, R. S.; Gawron, A. J.; Lunte, S. M.; Henry, C. S. Anal. Chem. 2000,
72, 3196-3202.
(7) Gawron, A. J.; Martin, R. S.; Lunte, S. M. Electrophoresis 2001, 22, 242-
248.
(8) Martin, R. S.; Ratzlaff, K. L.; Huynh, B. H.; Lunte, S. M. Anal. Chem. 2002,
74, 1136-1143.
(9) Ocvirk, G.; Munroe, M.; Tang, T.; Oleschuk, R.; Westra, K.; Harrison, J. D.
Electrophoresis 2000, 21, 107-115.
(10) Herbert, N. E.; Kuhr, W. G.; Brazill, S. A. Electrophoresis 2002, 23, 3750-
3759.
(11) Manica, D. P.; Ewing, A. G. Electrophoresis 2002, 23, 3735-3743.
Anal. Chem. 2003, 75, 3853-3858
10.1021/ac034437b CCC: $25.00 © 2003 American Chemical Society Analytical Chemistry, Vol. 75, No. 15, August 1, 2003 3853
Published on Web 06/20/2003

3. and wire-imprinting techniques,15-20 metallic templates containing
the channel patterns or wires, respectively, are heated and pressed
against the polymeric material. Using wires, only linear channels
are obtained. Weigl and co-workers21 have demonstrated that
lamination of plastic films renders a low-cost process to produce
several kinds of microfluidic devices.
Using polyester, Uchiyama and co-workers22 built an on-chip
fluorescence detector by incorporating a blue-light-emitting diode
and an optical fiber and direct polymerization on a glass template.
Recently, Tan and co-workers23 proposed the use of a photo-
copying machine to produce a master for molding of PDMS
devices. The master is formed by photocopying the desired image
over a transparency. The deposited toner layer defines the regions
that will result in channels in the PDMS device. For the equipment
used in that work, channel depth in the range of 8 to 14 µm was
obtained by using this toner-transparency master.
In this paper, toner deposited on polyester transparency is used
in a different fashion. Instead of producing a master, the microf-
luidic device is directly formed by using two transparencies as
the base, and the cover and the toner are used to define the
channels. This easy and fast process is described as well as its
characterization and some devices.
EXPERIMENTAL SECTION
Materials and Reagents. Transparency film CG3300 (3M,
Sumare´-SP, Brazil) was used as the base material. All solvents
and reagents were of analytical grade or better. Deionized water
was produced by a Nanopure UV system (Barnsted, Dubuque,
IA).
Fabrication Process. Although the process should be tailored
for each application, the basic steps are shown in Figure 1. A cover
plate is prepared by drilling a hole through a piece of transparency
film (I). The layout of the device is printed on a transparency film,
using white for the regions where the microfluidic channels will
be formed (II). The cover and the base are laminated together,
producing the channels with access holes (III). Reservoirs are
glued on the channel input holes (IV).
The above procedure is called the single toner layer (STL)
method. An alternative method is the double toner layer (DTL)
that consists of laminating two printed films with mirrored images.
In this case, the resulting structure has about twice the thickness
of toner, and thus, the aspect ratio is improved.
The layouts of the devices were made in CorelDraw 7.0 (Corel,
Ottawa, Canada) and printed out by a LaserJet 6L with toner
cartridge C3906A (Hewlett-Packard, Palo Alto, CA), operating at
600 dots per inch (dpi) in the raster mode.
The scheme in Figure 1 suggests that the devices were
individually prepared. However, since transparency film size A4
was used, dozens of devices can be produced at the same time
and subsequently separated.
The drilling of the film is accomplished by adapting a paper
driller in order to make holes even at the center of an A4 film.
Although it is not presented in the above process, it is convenient
to print out a drilling guide on the cover film for the STL method.
The best performance for the lamination was obtained by using
a laminator AC91-230 (Gazela, Divino´polis, Minas Gerais, Brazil)
at 130 °C and 45 cm min-1. This equipment was originally
developed for plastification of documents. After the lamination,
the devices were sliced using scissors. The reservoirs were formed
by gluing pieces of 8-mm o.d. and 5-mm-long tubes of PVC or
polystyrene using bicomponent epoxy resin.
Characterization. Thermal characterization of the polyester
film and toner was carried out in a thermobalance Shimadzu TGA-
50 and in a differential scanning calorimeter, Shimadzu DSC-50
(Kyoto, Japan). The thickness of the toner layer was measured
using a profilometer Dektak 3030 (Sloan, Santa Barbara, CA).
Impedance measurements were made by an impedance analyzer
HP 4194A (Hewlett-Packard, Palo Alto, CA).
Applications. Electrophoresis experiments were carried out
in a modified apparatus that has been described elsewhere.24,25
The electrospray experiment was implemented using a high
(12) Roberts, M. A.; Rossier, J. S.; Bercier, P.; Girault, H. Anal. Chem. 1997,
69, 2035-2042.
(13) Rossier, J. S.; Schwarz, A.; Reymond, F.; Ferrigno, R.; Bianchi, F.; Girault,
H. H. Electrophoresis 1999, 20, 727-731.
(14) Rossier, J. S.; Ferrigno, R.; Girault, H. H. J. Electroanal. Chem. 2000, 492,
15-22.
(15) Martynova, L.; Locascio, L. E.; Gaitan, M.; Kramer, G. W.; Christensen, R.
G.; MacCrehan, W. A. Anal. Chem. 1997, 69, 4783-4789.
(16) Locascio, L. E.; Perso, C. E.; Lee, C. S. J. Chromatogr., A 1999, 857, 275-
284.
(17) Chen, Y.-H.; Wang, W.-C.; Young, K.-C.; Chang, T.-T.; Chen, S.-H. Clin. Chem.
1999, 45, 1938-1943.
(18) Chen, D.-C.; Hsu, F.-L.; Zhan, D.-Z.; Chen, C.-H. Anal. Chem. 2001, 73,
758-762.
(19) Grass, B.; Siepe, D.; Neyer, A.; Hergenro¨der, R. Fresenius’ J. Anal. Chem.
2001, 371, 228-233.
(20) Galloway, M.; Soper, S. A. Electrophoresis 2002, 23, 3760-3768.
(21) Weigl, B. H.; Bardell, R.; Schulte, T.; Battrell, F.; Hayenga, J. Biomed.
Microdevices 2001, 3, 267-274.
(22) Uchiyama, K.; Xu, W.; Qiu, J.; Hobo, T. Fresenius’ J. Anal. Chem. 2001,
371, 209-211.
(23) Tan, A.; Rodgers, K.; Murrihy, J. P.; O’Mathuna, C.; Glennon, J. D. Lab
Chip 2001, 1, 7-9.
(24) Fracassi da Silva, J. A.; Lago, C. L. Anal. Chem. 1998, 70, 4339-4343.
(25) Fracassi da Silva, J. A.; Guzman, N. A.; Lago, C. L. J. Chromatogr., A 2002,
942, 249-258.
Figure 1. Schematic of the main parts generated by the single toner
layer (STL) microfabrication process: I, perforated polyester cover;
II, printed polyester base (a, toner layer); III, cover (I) and base (II)
laminated together; IV, the final device (b, liquid reservoirs).
3854 Analytical Chemistry, Vol. 75, No. 15, August 1, 2003

4. voltage source PS/MJ30P0400 (Glassman, Whitehouse Station,
NJ).
RESULTS AND DISCUSSION
Characteristics of the Polyester and the Toner. According
to the material safety data sheet (MSDS),26 the toner inside the
cartridge C3906A is mainly composed of a styrene/acrylate
copolymer (45-55 wt %) and iron oxide (45-55 wt %). Its solubility
in water is negligible, and it is partially soluble in toluene and
xylene. The material should soften between 100 and 150 °C.
The thermogravimetric analysis (TGA) shows a mass loss of
50% at 400 °C. A reddish residue is formed at 900 °C, correspond-
ing to 48% of the initial mass. The analysis of this residue revealed
that it is mainly Fe2O3, corresponding to 45% (w/w) of the toner,
which is compatible with the manufacturer information.
The result of the CHN elemental analysis of the toner was
C44.8%H4.1%N0.1%. Considering the residue of 48.0% at 900 °C, there
is a difference of 3.0% that was attributed to oxygen. Thus, the
organic material has composition C86.2%H7.9%N0.2%O5.7%. For the sake
of comparison, polystyrene and poly(methyl methacrylate) (PMMA)
have composition C92.3%H7.7% and C60.0%H8.0%O32.0%, respectively.
These values suggest that the polymeric base of the toner is
composed of 82.1% polystyrene and 17.9% PMMA, which corre-
sponds to an average composition of C86.3%H7.8% N0.0%O5.9%.
Differential scanning analysis (DSC) revealed two endothermic
events at 70 and 106 °C, which should be related to the softening
of the two polymers used in the formulation of the toner.
The MSDS of the transparency film CG3300 indicates that it
is a coated poly(ethylene terephthalate).27 The coating contains
silica to improve the laser printing process. The film is 100 µm
thick and has transparency above 80% in the range from 400 nm
to at least 800 nm. There is a transition at 320 nm, and the material
becomes strongly absorbing below this wavelength.
The DSC analysis of the polyester film shows an endothermic
event starting at 200 °C and with a peak at 251 °C, and the TGA
shows the decomposition of the polymer above 400 °C. Thus, to
prevent the deformation of the polyester base during the process,
temperatures bellow 200 °C should be used.
The Fabrication Process. Figure 2a shows the appearance
of the toner deposited by the laser printer on the polyester film.
It is clear that the definition of the border of the channels is very
poor when compared to photolithography usually employed in the
fabrication of silicon or glass devices. The roughness of the toner
surface reveals that the printer does not completely melt the toner.
In fact, complete melting is not required for the original printing
purposes, because the objective of the printer is to glue the
particles of the toner to the paper or other base. The resolution
of the printer and the toner particle size determine the resolution
of the produced channels.
The presence of toner particles randomly deposited on the
region that would form the channels is also noticeable in Figure
2a. Fortunately, they are not present in an amount enough to
obstruct the channels.
The thickness of the toner layer, evaluated by profilometry, is
∼6 µm. This is an average value, because the surface is flexible and irregular. However, it is close to the value 7 ( 1 µm obtained
by measuring the mass of toner deposited by square centimeter
and the density of the fused material.
Figure 2b shows a 150-µm-wide DTL channel after being cut
with scissors. The deformations of the polyester film as well as
(26) Material Safety Data Sheet for the HP LaserJet Print Cartridge C3906A,
Hewlett-Packard: Boise, ID, 2002.
(27) Material Safety Data Sheet for the Laser Printer Transparency Film CG3300,
3M: St. Paul, MN, 1998.
Figure 2. Scanning electron micrographs of a 150-µm-wide chan-
nel. The toner particles appear as light gray regions. Picture (a) shows
a STL before lamination. Picture (b) shows a transverse cut of a DTL
channel after lamination and the remelted toner (I). The enlarged view
(c) shows a 6.35-µm-tall single toner particle deposited inside the
15.0-µm-tall channel.
Analytical Chemistry, Vol. 75, No. 15, August 1, 2003 3855

5. the residues left by the cutting process are apparent. The clear
material (I) at the border of the channel is the toner that acts as
glue and spacer between the sheets. Figure 2c is an enlarged
vision of the channel, which shows an isolated 6.35-µm particle
of toner deposited inside the channel. Although the cutting
process might modify the edge of the device, the height of the
channel (15.0 µm) is comparable to the expected value for a DTL
channel.
The TGA and DSC analyses of the toner and polyester suggest
that it is possible to remelt the toner in the range of 110 to 150
°C without significant thermal decomposition of the toner or
softening of the polyester film. In fact, our studies have demon-
strated that, even somewhat below 100 °C, the toner remelts, and
thus, the sealing process occurs. This ample range of temperature
is desirable, because it makes the lamination a flexible process
that can be implemented by different approaches. Indeed, a good
lamination is obtained by the correct combination of temperature,
time, and pressure. The excess of one or more of these factors
can lead to an excessive flow of the toner and the consequent
blocking of the channel.
Chemical Resistance. Pieces of printed polyester film and
laminated devices were submitted to solutions commonly used
in capillary electrophoresis. The following aqueous solutions were
employed: H3PO4 (pH 2), NaOH (pH 12), methanol 20% (v/v),
acetonitrile 20% (v/v), sodium dodecyl sulfate (SDS) in phosphate
buffer (pH 7), and SDS in borate buffer (pH 9). The qualitative
test consisted of visual evaluation of the polyester film (color,
brightness, flexibility) and toner adhesion as well as the solution
leakage in laminated devices. In all cases, no significant evidence
of deterioration was found, even after 48 h. Tests were carried
out at 60 °C for 12 h, and the same result was obtained. Of course,
because of the nature of the materials used, pure organic solvents
should not be used.
Electrical Characterization. Some test devices were pre-
pared, and the channels were filled with 1 mol L-1 KCl solution
in order to evaluate the electrical behavior from 100 Hz up to 5
MHz in an impedance analyzer.
Figure 3 shows an example of the device to evaluate the cross-
talk between vicinal channels, in which a toner barrier separates
two parallel 200-µm-wide channels along 10 mm. Both the process
STL and DTL were investigated. In an ideal case, only capacitive
cross-talk would be expected, because the toner barrier would
behave as a dielectric. The spectrum in Figure 4 suggests that a
400-µm DTL barrier behaves as a dielectric, because the phase is
about -90°, and the logarithm of the modulus linearly decreases
as function of the logarithm of the frequency, as would be expected
for a capacitor. The transition observed when frequency ap-
proaches 1 MHz is due to capacitive leakage of the setup and
should not represent a real limitation. On the other hand, the low
and constant impedance modulus and phase 0° suggest that the
50-µm DTL barrier behaves as a resistor, i.e., there is flow of
solution between both channels.
This experiment was carried out in duplicate with devices
containing 50-, 100-, 200-, or 400-µm toner barriers. For the DTL
process, the leakage was observed for 50- and 100-µm barriers.
For the STL process, even a 200-µm toner barrier was not enough
to perfectly isolate parallel channels. These results suggest that
the porosity of the toner layer is not completely eliminated after
the lamination step. The DTL process seems to be more effective,
probably because the two toner layers remelt together, forming
a more compact material.
In another test, straight 24-mm-long STL and DTL channels
were prepared with different widths (50, 100, 150, 200, 400, and
800 µm). Often, obstruction of the 50-µm-wide channels was
observed, and the devices were discarded. The other devices were
used to estimate the depth of the channels using their geometry,
the conductivity of the filling solution, and the impedance of the
channels. Table 1 shows the average of two evaluations of the
depth when the STL and DTL processes are used to produce
channels in the range from 100 to 800 µm.
For both processes, the depths of the 100-, 150-, and 200-µm-
wide channels agree with those obtained by profilometry (6 µm)
and the surface density of the toner layer (7 µm). However, the
depth of the 400- and 800-µm wide channels are considerably
smaller.
Figure 3. Device for evaluation of the cross-talk effect between
two 200-µm-wide parallel channels separated by a 10-mm-long toner
barrier (a). In this example, a 400-µm-wide barrier was formed. The
8-mm-o.d. PVC reservoirs (b) were glued with epoxy resin.
Figure 4. Impedance spectra of parallel channels with 400-µm (a)
and 50-µm (b) toner barriers. |Z| and θ are the impedance modulus
and phase angle, respectively, and f is the frequency. Noisy regions
of the traces for the 400-µm barrier are due to the high impedance at
low frequency.
3856 Analytical Chemistry, Vol. 75, No. 15, August 1, 2003

6. In fact, several other tests confirm this trend, and it is probably
related to the deformation of the polyester film caused by the
lamination process. Blank regions are not supported by the toner
layer and become prone to deformation by the heat and pressure
of the lamination. Narrow channels do not significantly suffer from
this deformation because of the reinforcement given by the
proximity of the toner walls.
These tests reveal some important features that one should
have in mind when a device is being conceived. Narrow channels
(below 100 µm) and barriers (below 400 µm) should be avoided.
The resolution of the HP LaserJet 6L printer is 42 µm (600 dpi),
which is very close to the 50 µm used in the tests, and ultimately
determines the limiting resolution of the whole process. On the
other hand, wide channels (above 200 µm) do not have the desired
geometry. Fortunately, wide channels are seldom used.
Application Example: Contactless Conductivity Detection
in Capillary Electrophoresis. Since the introduction of the
contactless conductivity detection to capillary electrophoresis,24,28
several research groups have used it for detection of inorganic
and organic species, and recently it has also been applied to
separations in microchip format.29-35 Figure 5 shows the layout
of a device for a microchip electrophoresis with this kind of
detector. The device has the usual layout for microchip electro-
phoresis with a double-T injection element (500-µm long) and a
3.4-cm separation channel. The DTL method was used to produce
150-µm-wide channels.
Adhesive copper tape (3M, Auckland, New Zealand) strips
were glued outside the polyester film near the end of the
separation channel to work as the electrodes. The electronics of
the detector has been described elsewhere.24,25 Running electrolyte
was 30-mmol L-1 MES/His (pH 6.0). The sample (100 µmol L-1
KCl, NaCl, and LiCl) was electrokinetically injected at 1.0 kV until
current stabilization (∼1 min). The electropherogram shown in
Figure 6 was obtained at 1.0 kV, which corresponds to an electric
field of 294 V cm-1 along the 2.2-cm path between the injection
and detection points.
In addition to the low cost and ease of fabrication, the thickness
of the polyester film (100 µm) provides a suitable barrier to
contactless conductometric detection. Other fabrication techniques
require that the substrate be etched.34
Application Example: Electrospray Tip. In 1997, Ramsey
and Ramsey36 and Karger and co-workers37 introduced microfluidic
devices for electrospray ionization, which is one of the most
important ionization sources for mass spectrometry. Polymer chips
have also been used to this end.38-40
Figure 7 shows an application example of fabrication of a
microfluidic device for electrospray generation. The layout is quite
simple and consists basically of a reservoir and a straight DTL
channel that ends at the edge of the device. This outlet is easily
made by cutting the border of the laminated set with scissors.
(28) Zemann, A. J.; Schnell, E.; Volgger, D.; Bonn, G. K. Anal. Chem. 1998, 70,
563-567.
(29) Guijt, R. M.; Baltussen, E.; van der Steen, G.; Frank, H.; Billiet, H.;
Schalkhammer, T.; Laugere, F.; Vellekoop, M.; Berthold, A.; Sarro, L.; van
Dedem, G. W. K. Electrophoresis 2001, 22, 2537-2541.
(30) Lichtenberg, J.; Rooij, N. F.; Verpoorte, E. Electrophoresis 2002, 23, 3769-
3780.
(31) Pumera, M.; Wang, J.; Opekar, F.; Jelı´nek, I.; Feldman, H. L.; Hardt, S. Anal.
Chem. 2002, 74, 1968-1971.
(32) Wang, J.; Pumera, M. Anal. Chem. 2002, 74, 5919-5923.
(33) Wang, J.; Pumera, M.; Collins, G. E.; Mulchandani, A. Anal. Chem. 2002,
74, 6121-6125.
(34) Tanyanyiwa, J.; Hauser, P. C. Anal. Chem. 2002, 74, 6378-6382.
(35) Wang, J.; Pumera, M. Anal. Chem. 2003, 75, 341-345.
(36) Ramsey, R. S.; Ramsey, J. M. Anal. Chem. 1997, 69, 1174-1178.
(37) Xue, Q.; Foret, F.; Dunayevskiy, Y. M.; Zavracky, P. M.; McGruer, N. E.;
Karger, B. L. Anal. Chem. 1997, 69, 426-430.
(38) Yuan, C.-H.; Shiea, J. Anal. Chem. 2001, 73, 1080-1083.
(39) Rohner, T. C.; Rossier, J. S.; Girault, H. H. Anal. Chem. 2001, 73, 5353-
5357.
(40) Gobry, V.; van Oostrum, J.; Martinelli, M.; Rohner, T. C.; Reymond, F.;
Rossier, J. S.; Girault, H. H. Proteomics 2002, 2, 405-412.
Table 1. Channel Depths Evaluated by Impedance
Analyses
channel width
µm
STL channel deptha
µm
DTL channel deptha
µm
100 6 ( 2 14 ( 5
150 5 ( 2 14.6 ( 0.1
200 5 ( 1 12 ( 1
400 3.5 ( 0.2 9 ( 2
800 2.58 ( 0.05 6.5 ( 0.2
a Average of two measurements and the resulting estimated standard
deviation.
Figure 5. Device layout for microchip electrophoresis with contact-
less conductivity detection. Double-T element for 500-µm-plug injec-
tion. Copper strips (a) were used as the electrodes. The PVC
reservoirs (b) were glued with epoxy resin.
Figure 6. Electrophoretic separation of K+ (1), Na+ (2), and Li+
(3), 100 µmol L-1 each. Running buffer: MES/His 30 mmol L-1 (pH
6.0). Electrokinetic injection at 1.0 kV for 1 min. Separation voltage,
1.0 kV. Contactless conductivity detection at 530 kHz and 10 Vpp.
Analytical Chemistry, Vol. 75, No. 15, August 1, 2003 3857

7. The border was dipped in a silicone OV1 (Carlo Erba, Sa˜o Paulos
SP, Brazil) solution, forming a hydrophobic layer that prevents
the aqueous solutions from spreading along the edge.
A Plexiglas base was built to hold the device. The solution in
the reservoir was pressurized at 50 cm of water while 3-3.5 kV
was applied to the electrode. The counter electrode, consisting
of a copper foil, was placed 3 mm distant from the tip.
The electrospray phenomenon was observed from a solution
drop hanging at the tip (Figure 8). For a 1 mmol L-1 KCl water/
methanol 9:1 (v/v) solution, a stable Taylor’s cone is established
with a current of 170 and 240 nA for 150- and 200-µm-wide
channels, respectively. This current level and the fact that light
emission was not observed suggest that what was taking place
was only the electrospray without corona discharge. The steady-
state condition is obtained when the amount of solution reaching
the tip by pumping equals the sprayed amount. Thus, different
pumping pressures should be required for other channel dimen-
sions.
CONCLUSIONS
The toner-polyester process is quite simple, allowing one to
employ easily obtainable materials and equipment. In this paper,
we have described only one example, but most of the components
can be substituted. For example, there are several alternatives to
the drawing software, the laminator can be replaced by a domestic
iron, or a photocopying machine can be used instead of a laser
printer.
Compared to the photolithographic approaches commonly
used in other microfabrication process, the presented process has
disadvantages regarding the aspect ratio and compactness of the
walls. However, to our knowledge, it is the simplest, easiest,
fastest, and lowest-cost way to produce prototypes and disposable
microfluidic devices. The absence of significant amounts of
solutions and materials hazardous to the environment is another
quality to be emphasized.
ACKNOWLEDGMENT
This work was supported by the Conselho Nacional de
Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) and Fundac¸a˜o
de Amparo a` Pesquisa do Estado de Sa˜o Paulo (FAPESP). The
authors thank CNPq and FAPESP for the fellowships, Dr. Jivaldo
R. Matos for the thermal analyses, and Dr. Z. G. Richter for the
English revision. This work was presented at The 8th Latin-
American Symposium on Biotechnology, Biomedical, Biophar-
maceutical, and Industrial Applications of Capillary Electrophoresis
and Microchip Technology, Mar del Plata, Argentina, 2002 (OP-
A23, PP-A41, PP-A42, PP-A43).
Received for review April 28, 2003. Accepted May 14,
2003.
AC034437B
Figure 7. A device for the electrospray source. The DTL process
was used to produce the structure (a). The outlet was made by cutting
the border with scissors, resulting in a device (b) with a sharp end.
The outlet was dipped in a silicone solution to make the tip
hydrophobic.
Figure 8. Electrospray tip. The drop of KCl solution at the outlet of
the channel (a) is distorted by the electrostatic field, generating the
Taylor’s cone (b).
3858 Analytical Chemistry, Vol. 75, No. 15, August 1, 2003