A portable biosensor system for bacterial concentration measurement in liquid and semi liquid media
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Transcript of A portable biosensor system for bacterial concentration measurement in liquid and semi liquid media
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A Portable Biosensor System for Bacterial Concentration Measurement in Liquid and Semi-Liquid Media
Marco GrossiDepartment of Electrical Energy and Information Engineering
University of Bologna, Italyhttp://www.researchgate.net/profile/Marco_Grossi
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Bacterial reproduction happens by means of binary scission.
• duplication of the bacterial chromosome• elongation of the cell• formation of a transverse septum centrally located• subdivision of a copy of the chromosome and cytoplasm in the two daughter cells
(A) Lag Phase
(B) Exponential Phase
(C) Stationary Phase
(D) Death Phase
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The standard reference technique for bacterial concentration measurement is the Plate Count method.
• It is the reference method
• Accurate and reliable results
• Long response times
• It is a laboratory method
Advantages Drawbacks
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A system composed of a liquid medium in direct contact with a couple of electrodes can be modeled with the following circuit.
Rm : medium resistance
Cm : medium capacitance
Ri : interface resistance
Ci : interface capacitance
When the frequency of the applied signal is lower than 1MHz
Rs = Rm + Ri Cs = Ci
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• a sine wave voltage Vin(t) is applied to the electrodes
• the current through the electrodes Iin(t) is measured
• the electrical parameters Rs and Cs are calculated
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Detect Time (DT): time needed for the bacterial population to reach the critical concentration CTH = 107 cfu/ml
The liquid sample is placed in a sensor in direct contact with a couple of electrodes. The electrical parameters Rs and Cs are measured at regular time intervals of 5 minutes.
Conc. < CTH: the electrical parameters Rs and Cs are almost constant.
Conc. > CTH: the electrical parameters Rs and Cs deviate from baseline value.
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Low contaminated samples feature high values of DT.Higher contaminated samples feature lower values of DT.
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• Shorter response time (2−12 hours vs 24−72 hours)
• The technique can be easily automated as part of an embedded system
• Need of calibration for the different sample types and different bacterial strains
• The electrical parameters are very sensitive to temperature variations
Advantages Drawbacks
The impedance technique has advantages and drawbacks if compared with the reference Plate Count method.
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Different commercial systems have been produced that measure the bacterial concentration with the impedance technique.
Bactometer(Biomerieux, France)
• 2ml sensor cell• up to 128 samples
• weight 130.2 kg
Bac Trac(Sy-Lab, Austria)• 20ml sensor cell• up to 64 samples
• weight 20 kg
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A portable biosensor system that measures bacterial concentration using the impedance technique has been built.
• Electronics boards: impedance measures and thermoregulation• Incubation chamber to store the sample• Both serial and wireless communication
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• The sample is loaded in the sterile incubation chamber• Thermoregulation is enabled
• Electrical parameters are measured every 5 minutes• At the end of the assay, DT is calculated and the bacterial
concentration is estimated
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Bacterial concentration measure in ice-cream samplesIncubation temperature 35 °C
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Bacterial concentration measure in raw milk samplesTwo incubation temperatures (a) 18 °C and (b) 30 °C
Shorter response time when incubated at 30°C
Better correlation when incubated at 18°C
A trade off between accuracy and measure time is needed
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Bacterial concentration measure in water samplesIncubation temperature 37 °C
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Bibliography
[1] Grossi M., Lanzoni M., Pompei A., Lazzarini R., Matteuzzi D., Riccò B. (2008). Detection of microbial concentration in ice-cream using the impedance technique. Biosensors & Bioelectronics, 23, 1616-1623.[2] Grossi M., Pompei A., Lanzoni M., Lazzarini R., Matteuzzi D., Riccò B. (2009). Total bacterial count in soft-frozen dairy products by impedance biosensor system. IEEE Sensors Journal, 9 (10), 1270-1276.[3] Grossi M., Lanzoni M., Pompei A., Lazzarini R., Matteuzzi D., Riccò B. (2010). An embedded portable biosensor system for bacterial concentration detection. Biosensors & Bioelectronics, 26, 983-990.[4] Grossi M., Lanzoni M., Pompei A., Lazzarini R., Matteuzzi D., Riccò B. (2011). A portable biosensor system for bacterial concentration measurements in cow’s raw milk. 4th IEEE International Workshop on Advances in Sensors and Interfaces, 132-136.[5] Grossi M., Lazzarini R., Lanzoni M., Pompei A., Matteuzzi D., Riccò B. (2013). A portable sensor with disposable electrodes for water bacterial quality assessment. IEEE Sensors Journal, 13 (5), 1775-1781.