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Description
Introduction
The analysis of volatile organic compounds (VOCs) as disease biomarkers released by the urine, it permits an early and non-invasive diagnosis of Urinary Tract Infections (UTI) [1]. For this purpose, an instrumental method like the electronic nose composed by micromachined metal oxide gas sensors has been taken under consideration. Escherichia coli (E.coli) is the pathogenic microorganism responsible for up to 80% of theUTI and it is here chosen as benchmark bacterium [2]. The purpose of this research work is to test the capability of the electronic nose approach to recognise the presence of E.coli, identificative of a possible UTI disturb [3], in urine samples.
Materials and Methods
In the research’s work, a device named miniMOx (JLM Innovation) has been involved. It is equipped with two micromachined metal oxide gas sensors (MOX): TGS8100 (Figaro) and CSS801 (CCMOSS). The MOX are capable to work with custom temperature modulation protocols controlled though their embedded heaters. This modulation periodically activates and freezes the interaction between gaseous molecules and the metal oxide surface, producing a periodic resistance vs. time curve as a response. In particular, a square wave of a 20 seconds period was applied. A warm semi-period was settled at voltage of Vheaters: 2.31 V for 10 seconds while the cold one at the voltage of Vheater = 1.65 V for the same amount of time. The resistance vs. time curves obtained were described through the ΔRcold-hot, ΔRcold and ΔRhot parameters. The ΔRcold-hot represents the subtraction between the sensor’s resistance measured at the end of the cold period and the resistance measured at the start of the warm period after 0.2 seconds. ΔRcold signifies the difference between the sensor’s resistance measured at the end of the cold period and after 0.2 seconds or at the beginning to the same period. ΔRhot respects the warm period. In the end, a Principal Component Analysis algorithm (PCA function on Matlab) was used to elaborate the data acquired with the described parameters. Three representative samples were taken under consideration: urine, urine contaminated with a pathogenic microorganism (Escherichia coli) and sterilized water as a control. The analysis’ procedure provided to place in contact the miniMOx for a time of 5 minutes with the head-space released from the samples, interspersed with 10 minutes for the sensors’ recovery in ambient air. In parallel, bacterial counts were performed to monitor the Escherichia coli concentration during the whole analysis.
Results and Discussion
The resistance vs. time curves was acquired with the two micromachined metal oxide gas sensors during the exposition at the VOCs released by uncontaminated urine and urine inoculated with E. coli at the initial concentration of 104 CFU/ml. The resistance values are lower during the warm semi-period (200-300KΩ with urine samples contaminated by E.coli, 100-200KΩ with urine samples uncontaminated) and larger during the semi-cold one (600-1000KΩ, with urine samples contaminated by E.coli, 250-650KΩ with urine samples uncontaminated), mainly due to thermal effect on the MOX semiconductor. The shape of these curves is sensitive to the surrounding atmosphere, with differences that can be properly resumed in terms of ΔRcold-hot and ΔRcold.PCA algorithm applied to the parameters explained before. The PCA Score Plot represents a scenario with three separated cluster, each one representative for sterilized water, urine and urine contaminated with Escherichia coli. Therfore, there is a separation between the two urine’s samples. Since the difference between the two urine’s samples is the E. coli presence, potentially the pathogenic microorganism is the responsible to the separation itself.
Conclusion
The custom measurement protocol developed with the commercial electronic nose miniMOx revealed suitable to discriminate between water, urine and urine with E. coli through the analysis of the VOCs released by them. Since E. coli causes different kind of diseases in the human body, an early detection of this pathogenic microorganism into the urine could prevent the illnesses development. In conclusion, the miniMOx could be an easy-to-use, low-cost device for the pre-screening diseases through the VOCs released by urine.
References
[1] Mills G. A., Walker V., “Headspace solid-phase microextraction profiling of volatile organic compounds in urine: Application to metabolic investigation”, Chromatogr. B Biomed Sci. Appl., 259-668, 2001.
[2] Persaud K.C., Pisanelli A.M., Evans P., Travers P. J., “Monitoring urinary tract infections and bacterial vaginosis”, Sens. Actuator B Chem., 116-120, 2005.
[3] Bernabei M., Pennazza G., Santonico M., Roscioni C., Paolesse R., Di Natale C., D’Amico A., “A preliminary study on the possibility to diagnose urinary tract cancers by an electronic nose”, Sens. Actuator B Chem., 1-4, 2007.
