CASE
STUDY

Detection of VOC gases andCO2 by active sample delivery via micropump

May 2022
Authors:
Pascal Buryszek
Florian Siemenroth
Jan EbbertCase study: Detection of VOC gases and CO2May 2022

Non-invasive and active
measuring of gases

Increased reaction time

Process and quality
monitoring

Sensing ambient gas phase compositions is a crucial task in today’s everyday life. Be it for containing
stable conditions or for supervising potential toxic concentrations, in many circumstances gas phaseanalysis has become a powerful tool.
When analysing cell growth, it is essential to observe carbon dioxide levels. Additionally, when ambient pollution has to be measured, volatile organic compound (VOC) sensors are used.
In the following experiment, it will be shown how via the mp6 micropump by Bartels MikrotechnikGmbH it has become possible to transport gas phases in microliter proportions to such sensors. It isof great importance to understand whether and how the procedure is functioning. Thus, the gas
phase biological experiment within a closed reservoir will be analysed.
For quantitative results, the gas will be conveyed to a VOC and a CO2 sensor at different fermentation stages and the development of both concentrations is going to be displayed and analysed.

What is microfluidics?
Microfluidics is the fine art of creation and manipulation of small portions of fluids, often realized by flow
within small, sub-millimeter-scale channels. These small dimensions allow the fluid flow to be controlledwith exquisite precision (Seifert, S. and Thiele, J. “Microfluidics: Theory and Practice for Beginners” (2020)).
Microfluidic systems are used in many applications, including medical testing, drug delivery, chemicalanalysis, chip cooling etc. These systems have the advantages of small volume, low cost and high throughput analysis (Gidde; 2020).
Further use of this method in the realm beyond academic research, such as that of commercial fine-chemical production, sensor development, or encapsulation of active substances, is presently being explored.
Microfluidics, though, is a demanding field and working area that requires both profound theoretical understanding and experimental skills as there is no standard in education and training on this method inmany fields of study that actually can benefit most from this technique (Seifert, Thiele).
Micropumps are essential components in the microfluidic systems. They are used to manipulate, transportand control the precise quantity of fluid in terms of microlitre and millilitre (Gidde; 2020). Compared toconventional syringe pumps, microfluidic pumps have the capability to be combined with other on-chipfunctional units to realize portable micro total analysis systems (μTAS) (Gao, Y. “Trapping and control ofbubbles in various microfluidic applications”. Lab on a chip 24 (2020)). Micropumps have been developedon various principles for many different applications viz. drug delivery and biomedical assays (Gidde; 2020).

About the mp6 micropump
The available, industrialized and commercialized example is the mp6 micropump by Bartels MikrotechnikGmbH. This micropump is a positive displacement membrane pump utilizing piezo buzzers. With a volumeof 2250 mm3 (30 mm x 15 mm x 5 mm) it is, as a micro pump, dimensionally very beneficial.
All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Detection of VOC gases and CO2
May 2022
It is built up in a „sandwich“ (stack) setup and combined and sealed in a laser welding process.

The laser melts single segments, so that the melted mass unites the parts. There is no glue in contact withthe fluid, but only the material the micropump is made from. Standard materials are PPSU
(Polyphenylsulfone), PI (Polyimide) and PP (Polypropylene). Due to the unibody and the fact that the pumpdoes not contain any moving parts, it is sterilizable, robust and reliable with a lifetime of more than 5000
hours. The micropump possesses two membrane stages in a series setup running with an 180° phase shift.
These two stages behave like two seperate micropumps connected in series causing pressure to double.
Besides, this principle makes it much more tolerant regarding gas bubbles. The mp6 is running at highvoltages which regulate the bending of the piezo membranes and the frequencies which define the numberof displacements per second. The peak-to-peak voltage amplitude ranges from 0-250 Vpp . Additionally,the mp6 operates at frequencies between 1-600 Hz. These electronic parameters applied to the piezo
membranes lead to the following typical fluidic values of the pump:▪
▪

Liquids (η ≅ 1 mPas): q = 5 - 8000 µl/min in free flow and p > 600 mbar
Gas: q > 25 ml/min in free flow and p > 150 mbar

The flow rate depends on the pressure. In addition, the performance of the mp6 is dependent on theviscosity of the liquids.
The mp6 micropump is made in Dortmund, Germany and leaves the factory after a 100% OQC (OutgoingQuality Control).

Technologies for sensing VOC-gases and CO2
The SCD40 CO2 - and SGP40 VOC-sensors by Sensirion function around metal oxide (MOx) films.
MOx-films, e.g. SnO2 , are placed between two electrodes. The SGP40 identifies electrical resitivity changes
ΔR of the MOx-film. These fluctuations are induced by heating the material underneath the coating,causing oxygen particles to dissociate from their bond with the metal. Because of the negative charge ofthe oxygen particles as well as their high reactivity, the ions react with the ambient gases that flow throughthe tube attached to the sensors. Subsequently, electrons are released and diffuse inside the MOx-film.
It is evident, that this variation of the charge carrier density brings along resistivity fluctuations that highly
depend on the number of reactions between gas and oxygen particles. Therefore, the sensor is able toaccurately measure and evaluate the ambient VOC-concentration (Zakrzewska, A. “Mixed oxides as gassensors”. Thin Solid Films (2001)).

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Detection of VOC gases and CO2
May 2022

Comparison of the MOx-technology and conductive polymers
MOx-technology holds many advantages that couple with some deficiencies. To accurately display theimportance of MOx-films, its convenient to compare these techniques to other approaches, e.g. conductive
polymers (CP).
Most importantly, MOx-structures are characterized by excellent sensitivities detecting far into the ppm
or even ppb regions. Due to the occuring chemical reactions, respond times are also superior. Since single
particles are involved into the process, MOx-lifetimes are comparably long as well. Naturally, this comesalong with comparably low expenses (Chiu, S.-W. “Towards a Chemiresistive Sensor-Intergrated Electronic
Nose: A Review”. Sensors (2013) ; Tomić, M. “VOCs Sensing by Metal Oxides, Conductive Polymers andCarbon-based materials”. Nanomaterials (2021)).
However, the constant electron flow is accompanied by pretty high energy consumptions. Additionally,
since every electron dispensed has an influence on the resisitivity change, MOx-technologies serve very
little selectivites. Thus, usage as a sensor for whole groups of elements or molecules such as VOCs isadvised.
The advantage of conductive polymers compared to metal oxides lies within their low energy consumption
as well as an improved selectivity. It is also worth noting that CPs are commonly working at room
temperatures. Additional improvement in comparison to MOx-films is the resilience against acidic
damaging. Nonetheless, its high affectibility towards humidity and temperature makes handling outside
lab environments difficult. Even though subtraction of these factors is possible, the additional installments
are what make CPs less conventient (Chiu, S.-W. “Towards a Chemiresistive Sensor-Intergrated Electronic
Nose: A Review”. Sensors (2013) ; Tomić, M. “VOCs Sensing by Metal Oxides, Conductive Polymers andCarbon-based materials”. Nanomaterials (2021)).

Sensing VOC- and CO2-gases with the mp6 micropump
Due to the request for higher safety and efficiency in industrial processes, the use of sensors increases
continuously. Since various sensors can not be used with completely passive feeding, the mp6 micropumpfrom Bartels Mikrotechnik GmbH opens up new fields of application. Due to their simple setup, they canbe produced at a low cost level. Additionally, thanks to their particle tolerance, they prove efficient underambient conditions.
With its small dimensions, the mp6 micropump can either be used as a subassembly together with thesensor or as an OEM (original equipment manufacturer) component to be integrated into a more complex
unit. Especially for portable instruments, where miniaturization plays an important role, the low energy
consumption comes into play. Battery operation may be easily realized. Depending on the customers needs,
the driving electronics are either integrated into the main PCB (printed circuit board) of the unit or eveninside an enlarged pump housing.
The use of an inert polymer in combination with an optimized placement of the pump inside the systemenables operation under the most demanding conditions.
The micropump mp6 provides a minimum flow rate of 6 ml/min for liquids (with dynamic viscosities ofη ≅ 1 mPas and 18 ml/min for gases. By using the available evaluation kit, the pump performance can betested in the target application and the driving parameters can be defined.
For once the CO2 concentration gives information about the grown cellcultures. The higher the emitted
amopunt of CO2 the higher the number of individual cell already developed.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Detection of VOC gases and CO2
May 2022

To verify whether differences in gas concentrations can be detected after passing through the mp6
micropumps, a reservoir including a sealed lid with four ports is utilized.
One port is connected to a pressure sensor by Honeywell to monitor the pressure inside the reservoir.
Additionally, two valves which are connected antiparallel to each other can regulate pressure differences
within a margin of their opening pressure (40 mbar).
For the Sensor setup, two ports are reserved in order to transport produced gases via a closed-loop. The
VOC-Sensor SGP40 by Sensirion is connected to a breadboard while the electrical supply for the CO2Sensor SCD40, which is also manufactured by Sensirion, is assured by the mp-Multiboard2 by Bartels
Mikrotechnik GmbH. To prevent fresh oxgen flowing into the reservoir, active valves are implemented
that also ensure clean tubes.
If needed, a fourth port for fluid transportation into or out of the reservoir is available.

Results
Functional CO2- and VOC-sensing has been observed. By filling the reservoir with yeast and a nutrient
medium the fermentation of beer has been observed and could be verified by sensor results.

It shall be noted that high VOC-concentrations correspond to low count rates by the SGP40 sensor because
the sensor is observing the degree of air quality, hence the inverse of pollution levels. Moreover, the CO2
concentration is directly given in ppm while the VOC-sensor only provides count rates, whose quantitative
All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Detection of VOC gases and CO2
May 2022
concentrations were not calculated yet. The most probable main component accountable for VOC-counts
is ethanol (C2H5OH).
It is logical that by letting the mixture ferment more cells are produced. Thus the carbon dioxide
concentration rises with developed fermentation processes to a point beyond the sensors sensing limits.
Furthermore, by observing
the amount of VOC counts
it is possible to determine
the ethanol content within
the reservoir. Via mentioned
setup, the dilution of beer istraced. As can be seen, thelower
theethanol
concentration the higher
the detected VOC counts.
Following these findings,
the ethanol concentration isobtained and monitored
through gas phase analysis
without any contamination.
In conclusion, CO2 as well as VOC concentrations rise with advanced fermentation. That way, by simply
assigning a reference (e.g. beer with 4.8% C2H5OH), the fermentation process of yeast into beer can beprotocolled industrially with very little space and resources needed. Since all data can be obtained via
gas phase analysis, contaminants are mostly excluded from the measurement.

Components and systems used:
••
•
•
•

mp6 micropump by Bartels Mikrotechnik
mp-Multiboard2 by Bartels Mikrotechnik
SCD41 (CO2) development board by Sensirion
SGP40 (VOC) sensor by Sensirion
Active SMV valve by Takasago

Acknowledgement:
Our partner, Sensirion from Stäfa, Switzerland, was instrumental in defining our research path, whereby
we were able to develop a great solution for a microfluidic system that can measure VOC and CO2 values
by feeding MOX sensors actively. For that, we are extremely grateful and we are looking forward to ourclose collaboration.
In case you are interested in the above-described microfluidic componenents or if you are interested ingetting in touch with either one of us, Sensirion or Bartels Mikrotechnik, please feel free to contact us.
You can find the contact details below.

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.

Case study: Detection of VOC gases and CO2
May 2022
Bartels Mikrotechnik is a globally active manufacturer and development service provider inthe field of microfluidics. In the microEngineering division, the company supports industrial
customers in the modification, adaptation and new development of high-performance andmarket-oriented product solutions through the innovative means of microsystems technology.
The second division, microComponents, produces and distributes microfluidic products andsystems, especially for miniaturized and portable applications. Our key products are micropumps that convey smallest quantities of gases or liquids and are used in a variety of ways inbiotechnology, pharmaceuticals, medical technology and numerous other applications.
Bartels Mikrotechnik with passion for microfluidics!

Follow us:Contact us:
Bartels Mikrotechnik GmbH
Konrad-Adenauer-Allee 1144263 Dortmund Germany

www.bartels-mikrotechnik.de
info@bartels-mikrotechnik.de
Tel: +49-231-47730-500

All values are approximate and no guarantee of specific technical properties.
Changes in the course of technical progress are possible without notice.