Abstract
This paper presents a technique for in-situ remote query monitoring of bacteria growth utilizing a printed thin or thick-film sensor comprised of an inductor-capacitor (LC) resonant circuit. The sensor, which is placed within the biological medium of interest and remotely detected using a loop antenna, measures the complex permittivity of the medium. Since bacteria growth increases the complex permittivity of a biological medium the LC sensor can be used to determine bacteria concentration. This paper presents results on monitoring of three different bacteria strains, Bacillus subtilis, Escherichia coli JM109, and Pseudomonas putida, demonstrating application of the sensor for monitoring bacteria growth in milk, meat, and beer. Due to its low unit cost and remote query detection, the sensor is potentially useful for commercial scale monitoring of food quality.
Highlights
Bacteria are a major source of contamination in water and food supplies resulting in both food poisoning and disease outbreaks [1]
A wireless, passive remote-query sensor technology is presented for monitoring bacteria growth
The sensor is immersed in the medium of interest, and the complex permittivity of the medium calculated from the electromagnetic response of the sensor
Summary
Bacteria are a major source of contamination in water and food supplies resulting in both food poisoning and disease outbreaks [1]. One of the major applications of microbiological impedance devices is to determine the initial bacteria count in a food medium through a technique called Impedance Detection Time (IDT) [12,13,14,15,16]. The sensor is immersed in the biological medium of interest, and the impedance spectrum of the sensor remotely detected by measuring the impedance across the terminals of a loop antenna used to monitor the sensor, see Fig. 2. To eliminate effects due to variation in the polyurethane coating thickness we first measure the complex permittivity of deionized water using the LC sensor and a strip-line cavity [21]. The complex permittivity of a biological medium increases with bacteria concentration causing a change in the capacitance of the interdigital capacitor, and in turn shifting fZ and f0. The sensor is a simple resonant circuit consisting of conductor lines printed on a paper or plastic substrate, which allows it to be inexpensively fabricated and used on a disposable basis
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