A BIOLOGICAL MONITORING MODULE BASED ON A
CERAMIC MICROFLUIDIC PLATFORM
Walter Smetana
1
, Bruno Balluch
1,2
, Ibrahim Atassi
1,2
, Khatuna Elizbarowna Gvichiya
2
Erwin Gaubitzer
3,2
, Michael Edetsberger
3,2
and Gottfried Köhler
3
1
Institute of Sensor and Actuator Systems, Vienna University of Technology, Gusshausstrasse 27-29, Vienna, Austria
2
OnkoTec GmbH, Vestenötting 1, Waidhofen/Thaya, Austria
3
Max. F. Perutz Laboratories, Department of Biomolecular Structural Chemistry, University of Vienna, Vienna, Austria
Keywords: LTCC-technology, Microfluidic, FEA.
Abstract: A 3-dimensional mesofluidic biological monitoring module has been successfully designed and fabricated
using a low-temperature co-fired ceramic (LTCC) technology. This mesofluidic device consists of a
network of micro-channels, a spherical mixing cavity and measuring ports. A selection of appropriate
commercially available ceramic tapes has been chosen with regard to their biocompatibility performance.
Specific processing procedures required for the realization of such a complex structure are demonstrated.
Three dimensional numerical flow simulations have been conducted to characterize the concentration
profiles of liquids at a specific measuring port and verified by experiment.
1 INTRODUCTION
Microfluidic and mesofluidic analytical systems are
becoming increasingly popular in chemical and
biomedical applications due to the need of small
volume reagents, small wastes and short reaction
times. Microfluidic devices may be classified into
functionally limited labs-on-chip (LOC) and micro
total analysis systems (µTAS). Most LOCs are
single function and single layer devices such as
mixers, separation channels, etc. Micro total analysis
systems, on the other hand, are more complicated
and are capable of performing many functions such
as mixing, reaction, separation, etc. on a single
module. Generally these devices handle nanoliters of
reaction volumes and often accomplish their specific
tasks in milliseconds of reaction times. Most of these
systems are based on silicon, glass, poly-
methylmethacrylate (PMMA) or polydimethyl-
siloxane (PDMS) substrates (Anderson, 2000). A
range of rapid-prototyping methods using laser-
techniques for the fabrication of microfluidic
devices are reported in literature. Micro-stereo-
lithography, selective laser sintering, laser writing
method and microcladding techniques are applied
for generating complex 3-dimensional (3D)
microparts of polymer, metal and metal-matrix
composite (Kathuria, 2001, Yu, 2006).
Micropatterned ceramic components may be
fabricated in a rapid prototying process combining
stereolithography for the supply of master models
with low pressure moulding (Knitter, 2003). But true
3D microfluidic structures cannot be easily imple-
mented using these techniques due to process
limitations or material properties. The use of LTCC-
technology for microfluidic devices enables the
realization of multiple 3D microchannels, a feature
not easily attainable in other MEMS technologies
(Gongora-Rubio, 2001; Golonka, 2006). Therefore,
based on this experience LTCC technology has been
considered as an adequate approach to realize a
compact temperature controlled monitoring module
for biological reactions with low sample consump-
tion which may be considered as a µTAS device.
The process technique for making a 3D-
architecture with LTCCs is rather simple and
standardized. Device production in LTCC
technology covers the machining, punching or laser
drilling of vias and channels on individual layers.
The individual layers are stacked and laminated in a
heated platen press or in a heated isostatic press.
Subsequently the laminated stack is exposed to the
firing cycle which is a somewhat critical process
where heating rate, dwell time at burnout
75
Smetana W., Balluch B., Atassi I., Gvichiya K., Gaubitzer E., Edetsberger M. and Köhler G. (2009).
A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM.
In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 75-82
DOI: 10.5220/0001543400750082
Copyright
c
SciTePress
temperature and total firing cycle time have to be
matched to the thickness of the ceramic stack.
The field of nonlinear chemical kinetics has been
investigated about half a century. Still only a few
complex chemical reactions have been described by
means of an experimentally backed system of
coupled chemical equations. Moreover, in biological
relevant nonlinear systems most of the reactants, e.g.
proteins etc., are expensive to prepare and generally
only available in limited quantities. Therefore, it is
essential to use tiny reaction volumes for continuous
flow experiments, as realized in this reaction cell.
This hereby presented contribution outlines the
procedures of fabrication and characterization of a
reaction module designed to follow quantitatively
complex biochemical regulatory reaction networks
in vitro as a basis for advanced mathematical fitting.
This device consists of a mixing module which
provides fast mixing of reactants and four sensor
ports for simultaneous measurements. The
functionality was proved using the well known
oscillatory behaviour of the chlorite-iodide reaction
(Kügler, 2008).
2 DESIGN
Figure 1 shows the schematic of the monitoring
module also used as model for establishing finite
element analyses (FEA).
The module comprises a spherical reactor cell
where continuous mixing of the reagent fluids is
provided. Besides this mixing chamber the module
is equipped with pH-, oxygen-, temperature- and
iodide sensitive sensors for reaction monitoring as
well as with SMA-connectors for glass fibres
required for absorption or fluorescence
spectroscopic analyses (figure 2). Pumping a thermal
fluid through embedded ducts provides temperature
control. A network of micro-channels with cross
section dimensions varying from 200 µm x 200 µm
up to 2 mm x 2 mm are connecting the different
measuring sections within the ceramic module.
Special attention has to be spent on the selection of
appropriate ceramic tape material with regard to
biocompatibility and suitability to build up a
complex 3-dimensional structure which contains a
large number of cavities and channels.
Figure 1: Scheme of the monitoring module with reactor
cell and channel system.
Figure 2: Biological monitoring module (completely
assembled with sensor-, inlet-, outlet- ports and sockets for
optical fibers).
3 DEVICE FABRICATION
3.1 Biocompatibility Testing
Three different lead-free tapes have been considered
for this application like the ESL 41020, Ferro A6
and CeramTec GC-tape. The tapes should be
biocompatible but nevertheless cells should not
adhere and proliferate to a large extent on their
surfaces. The latter requirements are critical with
regard to clogging of channels by cell
agglomerations. In order to compare the
biocompatibility, proliferation, viability and
adherence of HeLa (human, cervix epithelial) cells
grown on sintered LTCC-tapes have been evaluated
using standard test procedures.
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76
3.1.1 Proliferation Test
As a first biocompatibility testing the ability of
HeLa cells to proliferate on different LTCC tapes in
contrast to glass and standard plastic surfaces was
observed. The influence on cell proliferation was
tested with the Bromodeoxyuridine (BrdU) assay
(Gire, 1998) (Calbiochem, USA). BrdU
incorporation is detected immunochemically with
unlabelled primary antibodies and HRPO labeled
secondary antibodies.
HeLa cells were exposed in a 96 well plate (1 x
10
5
cells/well) with the different test disks (4 mm x
4 mm) for 23 hours in DMEM (Dulbecco's mod.
Eagle-Medium) containing 4.500 mg Glucose, 4.5
mM L-Glutamine, 44 mM Na-bicarbonate, 100
units/ml Penicillin, 100 µg/ml Streptomycin, 0.9
mM Na-pyruvate and 10 % fetal calf serum in a 6
volume % CO
2
humified atmosphere at 37 °C
(standard conditions). During the final 3 hours of
incubation BrdU is added. The BrdU concentration
is measured using a multi-plate reader (BIORAD) at
λ
abs
= 455nm and λ
reference
= 655 nm.
Figure 3: Biocompatibility testing for HeLa cells on fired
LTCC- samples (CeramTec GC, ESL 41020, FERRO A6),
glass-cover slides (Assistent, Germany), Copper (Cu) and
standard plastic dishes (control-sample); Colour marking:
black: proliferation rates, red: percentage of viable cells,
blue: percentage of total cells compared to control group.
The results of the proliferation test are shown in
figure 3 (black bars). With exception of the
CeramTec GC-tape and the Cu- disks, the detected
proliferation-rates of all other test samples are equal
or even higher (glass support) compared to the
growing rate of the control group on plastic support
(100 ± 8.7 %). Also the deviation is comparable to
the control group. In contrast CeramTec tapes show
a 30-40 % reduction in proliferation. Nevertheless
this reduced proliferation is low in comparison with
cells incubated with Cu-disks, which under the same
conditions show a proliferation rate of 2-3 %
compared to control group.
3.1.2 Viability Testing
Next to the determination of proliferation rates it is
necessary to analyze the ability of cells to adhere to
surfaces and to determine the percentage of viable
cells. For this test series HeLa cells were incubated
in standard culture dishes with a diameter of 10 cm
(about 5 x 10
5
cells/dish) for 23 hours in DMEM
under standard conditions. The fired LTCC tapes to
be tested, glass cover slides and Cu-plates were
used with lateral dimensions of about 2.5 cm x 4 cm.
Cells were incubated in the presence of these
materials and on standard culture surfaces as control.
The number of cells and their viability was
evaluated with propidium-iodide (Zarnai, 2001)
using a Nucleocounter (Chemometec, Denmark).
The results of the viability tests are presented in
figure 3.
No significant reduction in number of total cells
(blue bars) has been detected for all LTTC samples
and glass as their percentage of total cells, in relation
to the control group, are comparable within the error
limits caused by inaccuracies of seeding the cells.
Only samples grown on Cu show about 40 % less
cells than the other samples.
Additionally not any significant reduction in
percentage of viable cells (red bars) was shown for
cells grown on LTCC tapes or glass support. Again,
only samples grown on Cu-plates show a diminution
of about 40 %.
3.1.3 Adhesion Testing
The side walls of channels and cavities are formed
by the laser machined edges of tapes. To observe
cell adhesion, which may rely on tape material but
also on surface finishing a test method has been
designed which enables to examine the potential
adhesion of cells on the laser machined edges of the
tapes. To evaluate the influence of the ceramic tapes
on the adhesion of cells on glass surfaces, CeramTec
and ESL ceramic tapes with laser-micro machined
tapering channels with decreasing channel width
(see figure 4-A) were mounted on standard glass
cover slides (Assistant, Germany) with a super
adhesive (Loctite). HeLa cells were seeded on the
cover slides (10
5
cells) and incubated over night in
DMEM medium under standard conditions. The
growth behaviour of the cells was evaluated using a
light transmission microscope.
A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM
77
Figure 4: A: Test sample of a ceramic tape coupon
carrying a continuous row of channel segments with
decreasing width (central circular opening is 10 mm in
diameter, the channel width is 2.122, 1.175, 0.672, 0.394,
0.228, 0.168 mm and 2.208, 1.224, 0.653, 0.396, 0.102,
0.054 mm for channels 1 to 6 of the ESL (D, F) and
CeramTec (C, E) tape, respectively. C, E: HeLa cells
grown on glass cover slides with a mounted fired
CeramTec-tape at channels 0-1 (C) and 2-3 (E). D-F:
HeLa cells grown on glass cover slides with a mounted
fired ESL-tape at channels 0-1 (D) and 3-4 (F). B: HeLa
cells grown on glass cover slides surrounded by mounting
glue (arrow). Micrographs were performed with a Zeiss
Axiovert S100TV at 10x magnification and a Digital
Camera (Nikon DMX1200).
Exemplary the results for the CeramTec and the
ESL tapes are shown in figure 4. It could be
demonstrated that the initial circular opening and
channel 1 machined in the CeramTec GC tape and
the ESL tape show only a poor influence on the
adherence of HeLa cells (figure 4-C, D; cell density
in circular opening: 250 – 300 cells/mm
2
, channel 1:
200 – 220 cells/mm
2
) but already at channels 2 and 3
(figure 4-E) with a width of about 0.6 mm a
significant decrease in adherence can be observed
for CeramTec tapes (cell density in channel 2: 45
cells/mm
2
, channel 3: 19 cells/mm
2
) as no significant
number of cells is observed at this area. In contrast
the fired ESL-tape shows quite a different cell
adherence performance. Also in channels 3-4 (figure
4-F) a rather dense cell population of cells (cell
density in channel 3 and 4: ca. 100 cells/mm
2
) and
even aggregation near to the edges are observed.
Only for smaller channels with width of about 0.2
mm a decrease of adherence can be observed (data
not shown). The mounting glue has not any effect on
the adherence behavior of HeLa cells to the glass
surface (figure 4-B).
3.1.4 Summary of Biocompatibility Testing
It can be concluded that all three LTCC materials
tested do not affect the viability of the cells, as the
total number of cells counted after the same period
was found identical within an error interval of ± 10
% for all LTCC-materials, standard plastic as well
as glass. An increased cell death compared to the
control group could not be found for any of the
standard materials. Only copper showed a significant
influence on viability, cell adherence and
proliferation. If only the proliferation characteristic
is considered, a distinction in tape performance can
be made. Whereas the ESL-tape shows a similar
behaviour with respect to the control assay of a
standard plastic support, FERRO-tape reacts similar
to a glass support and shows an increased
proliferation. Only the fired CeramTec-tape exhibits
a significant decrease in proliferation (figure 3).
These results are also validated by the adherence
test. When cell growth on a glass support was
restricted by sidewalls of a narrow channel
configuration, the cells reacted differently to ESL-
and CeramTec-tapes: Whereas on ESL tapes the
cells grow even in channels of very small width, it
was not the case for channels machined into
CeramTec-tapes. For these samples the area near to
the glass – ceramic interface was widely free of cells
and an efficient growth of cells was only detectable
in rather wide channels. The reasons of the
difference in cell adhesion on the channel walls are
still under investigation. It might be related to the
difference in surface energy as result of laser
machining. The quality of the cutting edges and the
surface of channel walls are defined by the
absorption of laser energy in the tape material which
may vary in dependence on the composition of the
selected LTCC- material.
The results show, that on the one hand side fired
ceramic tapes are generally biocompatible and do
not restrict the viability of cells, and on the other
hand side cells adherence can be specifically
influenced by the material selected. CeramTec GC
tape should be preferred, when adherence to the
walls of the chamber or channels should be
restricted as e.g. in microscopic observation
chambers where single cells are preferentially
observed in the center of an optical window and a
cell agglomeration along the side walls or growth
into micro fluidic flow channels should be avoided.
BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices
78
3.2 Processing Procedures
The CeramTec GC tape has been proved as a
suitable candidate for the realization of the
monitoring module not only with regard to the
results of the biocompatibility tests but also due to
its performance characteristic during processing.
Since the module comprises a complex network of
channels and cavities a tape material is required
which does not tend to sag during firing. Beyond the
green GC-tape with a thickness of 325 µm provides
an adequate ruggedness for handling.
The three dimensional LTCC-structure is
realized by forming a stack of adequately laser
machined (diode pumped Nd:YAG-laser (Rofin
Sinar, Germany) equipped with an acoustic optical
switch, operating power: 12 W at TEM00-mode)
single layers of tapes which are laminated and
finally exposed to a firing process. For the
realization of the complex module a single tape
shows a rather delicate structure since it is
penetrated by large-area laser machined
perforations. A standard LTCC-processing
technology cannot be easily applied for the
realization of the module since it comprises 133
ceramic layers, which deviates from the number of
tapes usually applied for conventional applications.
Figure 5: Inside view of reactor cell with various channels
and ducts (collated stack of tapes before lamination).
Special attention has to be paid on the lamination
of the ceramic tapes since the module contains a
large number of cavities and channels (e.g. the
reactor cell has a cavity volume of 1 cm
3
). The
finished sheets are collated in a mould (figure 5) and
aligned by registration pins providing that
successive layers are rotated by 90° to compensate
for the texture (preferential orientation) induced by
the fabrication of green tape. The lamination of the
stack of tapes has been carried out in a heated platen
press (Wabash).
A range of experimental work has been
conducted (Wang, 2008) in order to optimize
lamination parameters which should contribute to
provide the shape integrity of channel and cavity
structures. Sagging and delamination are typical for
relatively wide channels (width equal to 500 µm or
more) whilst contraction is characteristic for narrow
channels (width equal to 200 µm and less). The
application of sacrificial material for filling cavities
and channel structures is a valuable approach to
avoid sagging as well as the risk of delamination.
The selection of an appropriate sacrificial material is
absolutely essential for this complex microstructure
device. It has been found out that the main task of
the sacrificial material is to provide a uniform
pressure distribution within the LTCC-tape stack
during lamination. An additional supporting function
of cavity structures during firing is not required
since the considered LTCC material shows in all the
phases of the firing process an adequate strength and
stability. This substance should evaporate during the
burnout phase of the sintering process without
damaging the structure of the module. So the
approach was to find a material, which is
accommodated to the shrinkage performance of the
tape. An obstruction of material’s shrinkage should
be avoided. Some authors recommend carbon black
as sacrificial volume material (SVM) which may be
applied as tape or paste (Birol, 2005). This material
decomposes and exhausts at rather high temperature
when sintering of tape already starts. Different
polymer materials have been tested as potential
candidates acting as SVM since they decompose and
burn out at a temperature < 400 °C (before tape-
shrinkage is starting).
Best results have been attained with PMMA
chosen as SVM. It is also part of the organic
constituents of the considered tape and exhausts free
of residues at the burnout temperature of tape. The
organic sacrificial material has been used in powder
form. Channels and cavities are filled by a vacuum
sucking technique. It has been found out that a
uniform pressure of only 30 bar (sample
temperature: 70 °C, lamination time: 3 minutes) has
to be applied onto the ceramic layer stack which
enables to maintain the rectangular cross-section of
the buried channels while still avoiding delamination
of the ceramic batch. The applied pressure was
reasonably lower than recommended for
conventional applications.
Thermal gravimetric analyses have been
conducted to optimize the sintering profile
(especially to provide a complete and slow burn out
of the organics before sintering) in order to avoid
A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM
79
crack formation or delamination. The binder
decomposition process was studied by means of
Thermogravimetric Analysis (TGA) coupled with a
Mass-Spectrometer (MS) to detect simultaneously
the evolved gases (Balluch, 2008). Additionally, the
binder burnout was analyzed by Dynamic Scanning
Calorimetry (DSC). TGA revealed multistage
decomposition behaviour of the binder system. The
binder degradation is predominately governed by
exothermic reactions in the temperature range up to
400 °C and the course of the heat flow may be
correlated with the evolution of carbon dioxide. The
heat flow of GC-tape shows two exothermic peaks:
one at 250 °C and a major one at 364 °C. For the
GC-tape the first exothermic peak corresponds to the
maximum degradation rate in the TGA as can be
seen in the insert of figure 6.
Figure 6: Comparison of the heat flow signal with the ion
current for carbon dioxide for GC-tape.
The results of this study yield a useful approach
to establish the firing profile of the considered
LTCC with regard to heating rate and intermediate
dwell time for the preheat phase of firing process.
Based on the results of TGA it becomes evident that
for the burnout stage of the GC-tape firing process
an appropriate dwell time depending on the mass of
LTCC-module has to be established. It has to be
provided that the PMMA starts to pyrolyze slowly
which enables to exhaust the gaseous decomposition
products via the channels. In contrast a rapid
decomposition of the organic filler induces a sudden
intensified production of gaseous burnout products
which cannot escape adequately via the channels and
finally results in a destruction of the LTCC module.
The burnout phase of the firing schedule has to be
adapted to these requirements whereas an adequate
dwell time (depending on the mass of the LTCC
module) at the critical degradation temperature of
the filler is of great importance. Practical
experiments have shown that a dwell time at 250 °C
is ignorable if an adequate slow heat rate is selected.
A sufficient long dwell time at 350 °C for the total
binder burnout is obligatory to be provided.
Firing of the samples has been conducted in a
box furnace of Heraeus (heating rate for temperature
range 25 °C – 350 °C: 0.8 °C/min, holding time at
350 °C: 6 h, heating rate for temperature range 350
°C – 500 °C: 0.8 °C, holding time at 500 °C: 4 h,
heating rate for temperature range 500 °C – 920 °C:
1.8 °C/min, holding time at peak temperature of 920
°C: 1 h, cooling rate: 2 °C/min). Another parameter,
which has to be considered during the firing cycle,
was the temperature distribution within the sample.
A temperature gradient > 6 °C within the ceramic
module during the total firing cycle has to be
avoided with regard to potential crack formation and
fracture of the module (Kluge, 2006).
4 DEVICE CHARACTERIZATION
The influence of arrangement of inlet-channels
along the perimeter of the reactor cell and the sink
on the bottom of the cell on the flow performance of
liquids within the reactor cell has been studied for
different flow conditions by means of FEA using the
FLUENT program package. The characterization of
the device is based on time - dependent flow
simulations. The numerical model describes the flow
of dyed and pure water entering through different
inlets at varying mass flow rates and passing into the
spherical cavity of the reactor cell and the channel
system. The local distribution of fluid at the
spectroscopic port is predicted and contrasted with
the results attained by spectroscopic analyses of light
absorption at the considered port.
Exemplarily the flow characteristic for a
representative assumption has been derived by
numerical simulation and validated by experiment.
The flow condition described starts with filling the
cavity by injection of pure water at the radial inlets 1
and 2 (figure 1 and 7). The mixing initiated as a step
inflow of dyed water (0.5 % trypan blue) is imposed
on the radial inlet 2, which means that a stream of
constant mass flow–rate and dye–concentration is
applied at the respective inlet (figure 7). In the
meantime the average residence time of dye
concentration is measured at the optical port (figure
1).
The propagation of the streamlines depends
strongly on the position of the inlet along the
meridian of the spherical cavity as can be seen in
figure 7 for the corresponding inlet arrangement.
BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices
80
The inlet 1 (“In 1”) is placed 0.45 mm higher than
inlet 2 (“In 2”). Within a period of 2.5 s the
streamlines of the fluid entering inlet 1 are already
diffusing into the interconnecting channels while
those of the fluid starting from inlet 2 are still ending
in the mixing chamber.
Figure 7: Propagation of streamlines of fluids entering
inlet “In 1” (blue) and inlet “In 2” (red) with flow rates of
2 ml/min within a period of 2.5 s.
The model of the complete module was
constructed and meshed with the program package
GAMBIT (Fluent Inc.) Mesh elements were mainly
hexahedral and only few tetrahedral elements were
required for completely meshing the module. In all,
the model (including the recirculation tube) has a
volume of 3 cm³ and includes a total number of
292,194 mesh elements, of which 161,374 are
hexahedral, 128,737 are tetrahedral and 2,083 are
pyramidal.
The curves in figure 8 describe the increase of
the dye volume in the optical port from initially pure
water to the mixed state. For the supply of inlets
with liquids two Flodos Stepdos 03 pumps were
used and for providing the flow circulation a Flodos
NF 5 diaphragm pump was applied. The flow rates
considered in simulation and experiment are 2
ml/min at both inlets. At the optical port the
absorbance was measured using a uv-vis array-
spectrometer (EPP2000-50 µm Slit, StellarNet Inc.).
The absorbance–characteristic in a scaled
presentation is shown in figure 8. The steady state
mixed flow condition at the optical port corresponds
to a dye concentration of 47 %. It can be noticed that
the ideal and the computed curves are almost
identical. However, the experimentally derived
characteristic shows a slightly less rate of rise as
well as oscillating peaks. The oscillating peaks may
be attributed to the pulsating characteristic of the
pumps in use. Furthermore it must be noted that the
equilibrated state concentration condition is attained
also within the same period if the injection flow rate
at the inlet ports has been varied synchronously
while keeping the total sum of mass flow rates
constant. If all three inlet ports are used
simultaneously for the supply of the module
different mass flow rates have to be selected to
provide the desired mean concentration profile at the
optical port.
Figure 8: Dye concentration vs. time characteristic at the
optical port.
Besides the performed dye distribution tests, the
functionality of the microfluidic reaction module has
been demonstrated by observing the time evolution
of the iodine concentration due to the iodide-chlorite
reaction, which involves only 2 inorganic ions and is
characterized by an established set of reaction
mechanisms according to the LLKE-model, which is
named after its authors Lengyel, Li, Kustin and
Epstein (Kügler, 2008). This complex reaction
model involves an autocatalytic step and the
coupling of different reactions can cause complex
reaction patterns like oscillatory behaviour when
measured under certain conditions in continuous
flow. An intermediate of the chemical reaction leads
also to production of the starting compound, which
accelerates the reaction until the respective reaction
partner is used up, but when the reaction is
performed under continuous flow conditions
oscillatory behaviour results which can be observed
continuously. Figure 9 shows the oscillations
observed for the iodine absorption measured around
470 nm (i.e. in a range between 456 to 484 nm).
This means, that the optical density of the product is
measured as a mean value over 60 pixels of the
CCD-array (full black curve). The red curve shows
the final result when the time dependence is
additionally averaged over 20 seconds. The figure
demonstrates that such an autocatalytic reaction can
be measured in the microfluidic reaction module,
although the total reaction volume and also the
optical path of the optical detection port is very
A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM
81
small. Nevertheless oscillatory behaviour can also
found under such conditions. The device is sensitive
enough to record small concentration changes giving
rise to changes in the optical density below 0.001. In
future experiments the microfluidic module will be
used for measuring complex kinetics in biochemical
systems. In that case, limited amounts of reactive
compounds, e.g. of enzymes, are available and the
use of small reaction volumes is an essential
prerequisite to allow quantitative measurements.
Figure 9: Oscillations of the I
2
absorption observed in the
module produced by the reaction of I
-
and ClO
2-
in
continuous flow.
5 CONCLUSIONS
The influence of different ceramic materials on the
viability and proliferation of HeLa cells has been
tested as a first basic characterization of the
biocompatibility. In respect to their use in micro
fluidic devices the growth of cells in channels of
different width has been visualized. The LTCC-
technology has been proved as a very versatile
method to build up complex three-dimensional
multilevel channel structures including even large-
volume cavities, which are suitable for biological
and diagnostic applications.
ACKNOWLEDGEMENTS
The financial support of this work by the WWTF,
project MA05 "Inverse methods in biology and
chemistry” as well as by the FFG, project N209
"Nanoflu" is greatly acknowledged by the authors.
This project is integrated within EU 4M Project
(Contract Number NMP2-CT-2004-500274). The
maintenance with ceramic tapes and many useful
advices during the course of tape processing by Dr.
C. P. Kluge (CeramTec AG) are especially
appreciated.
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