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Capacitive biomass sensor


Key words Biomass, sensor, permittivity, capacitance, conductivity, fermentation, microorganism, bacteria, yeast, fungi, cell culture, non-invasive technique
Latest version 2013/09/05
Completed by INRA - IATE

How does it work?

Primary objective To measure the concentration of living microorganisms in a culture medium.
Working principle The rapid determination of microorganism concentration in fermentation media is a challenging task. Suspended solids, gas bubbles, dead cell bodies, etc. impair strongly routine techniques such as turbidity measurements. The living cell concentration determination usually involves a time requiring culture step, therefore being unsuitable for process control. Accordingly, most industrial bioprocesses have to rely on indirect biomass estimation techniques.

Permittivity can be used as a direct and convenient indicator of microbial cell concentration. From an electrical point of view, a culture medium can be considered as a conductive liquid, in which microbial cells are suspended bodies, containing also a conductive medium, surrounded by an insulating layer, the cytoplasmic membrane.

When an electrical field is applied to the suspension, the microbial cells act as tiny capacitors, accumulating electric charges at the membrane interface.

The sensor measures both the medium permittivity and conductivity and compute the concentration of living cells (= biomass) using calibration data.

Thanks to an advanced design, the sensor can accurately measure low permittivities even in high conductive media (up to 100 mS/cm).

Dead cells, in which the membrane is non-functional, are not detected. Cell fragments, suspended solids and gas bubbles affect only marginally the measurement.

The technique is non-invasive (no sample withdrawal) and can be applied to any living cells suspension (bacteria, yeast, fungi, animal and plant cells) (5)(6)(7)(9).

Additional effects The cells metabolism is not affected by the sensing technique, because the applied electrical field is low (a few V/cm) and limited to a small volume (a few cm³) around the sensor head.

The sensor can be used to evaluate the salt concentration in food products thanks to the measurement of the conductivity – mainly dependent on salt concentration - using permittivity to take into account the effect of the food product matrix structure (prototype studies) (8).

Important process parameters
Important product parameters cell concentration should reach a threshold concentration depending on cell size (around 1 to 5 g/l for bacterial cells; around 0.1 to 0.5 g/l for yeast cells; around 0.01 to 0.05 g/l for animal cells) to be measured accurately

What can it be used for?

Products Any microbial cell suspension: bacteria, yeast and fungi (e.g. lactic starter production, baker's yeast production, brewery, antibiotic, amino acids), animal (mammal, insect) and plant cells

Salted products (ham, salmon)

Operations Monitoring
Solutions for short comings Rapid online measurement of microorganism growth

Online monitoring of fermentations and cell cultures

Optimisation of cell cultures

What can it NOT be used for?

Products Any other product than cell cultures.

If used as a salt sensor, dry and non-salted products.

Operations The technique cannot be used as a mean to detect microbial contaminations in food or water.
Other limitations not known
Risks or hazards None


Maturity This technology has been described through 4 patents (1)(2)(3)(4). The sensor is commercially available as a biomass sensor for use at lab and industrial scale. It is at lab stage as a salt sensor.
Modularity /Implementation The sensor can be adapted on existing bioreactors. The commercial version is currently sold in a case that is designed to hold both the capacitive sensor and an optical probe.
Consumer aspects Not known.
Legal aspects Please check local legislation.
Environmental aspects No waste, no use of solvants.

Further Information

Institutes INRA - IATE
Companies Fogale Nanotech
References Patents:

1. Tessier P., Barbeau J.Y., Arnoux A.S., Ossart F., Ghommidh C. 2003. Use of a capacitive probe to determine the biomass of small bacteria. WO/2003/069334.

2. Arnoux A.S. Preziosi-Belloy L., Esteban G., Teissier P., Barbeau J.Y, Ghommidh C. 2005. Procédé et dispositif pour mesurer et caractériser en ligne une biomasse dans un processus de fermentation de bactéries lactiques et procédé de pilotage associé. French patent N°2867278

3. Preziosi-Belloy L., Ossart F., Esteban G., Ghommidh C. 2005. Procédé et dispositif pour mesurer et caractériser une biomasse, application à une mesure en ligne de données de biomasse dans un processus de fermentation, et procédé de pilotage associé. French patent N° 2867279

4. Ossart F., Esteban G., Ghommidh C. 2006. Procédé et dispositif de détermination de biomasse dans un milieu, notamment d'un milieu contenant des cellules biologiques, et appareil de mesure mettant en œuvre ce procédé. French patent N°1784480


5. Mas S., Ossart F., Ghommidh C. 2001. On-line determination of flocculating yeast concentration and growth rate using a capacitance probe. Biotechnol. Lett., 23, 1125-1129.

6. Sarrafzadeh M.H., Belloy L., Esteban G., Navarro J.M., Ghommidh C. 2005. Dielectric monitoring of growth and sporulation of Bacillus thuringiensis. Biotechnol. Lett., 7, 511-517.

7. Arnoux A., Preziosi-Belloy L., Esteban G., P. Teissier P., Ghommidh C. 2005. Lactic acid bacteria biomass monitoring in highly conductive media using a dielectric permittivity. Biotechnol. Lett. 27, 1551-1557.

8. Chevalier D., Ossart F., Ghommidh C. 2006. Development of a non-destructive salt and moisture measurement method in salmon (Salmo salar) fillets using impedance technology. Food Control, 17, 342-347.

9. Tibayrenc P, Preziosi-Belloy L, Ghommidh C. 2011. On-line monitoring of dielectrical properties of yeast cells during a stress-model alcoholic fermentation. Process Biochem., 46, 1, 193-201.

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Created by Hte inra on 7 June 2012, at 12:17