Near-field sensor array with 65-GHz CMOS oscillators for rapid detection of viable Escherichia coli

In this study, the growth of Escherichia coli was monitored using a complementary metal-oxide-semiconductor (CMOS) near-field sensor array. Each of the 1488 integrated elements, arranged in a 3 mm square, has a resonator that oscillates at 65 GHz. The effective capacitance of the resonator is altered by changes in the dielectric properties of the sensor surface, which shifts the resonance frequency. Growth curves of E. coli at different initial concentrations (OD₆₀₀ = 0.01, 0.03, and 0.05) were monitored. A suspension with initial turbidity of OD₆₀₀ = 0.05 was cultured in a medium, and the sensor successfully distinguished between viable E. coli and heat-treated dead E. coli in 20 min. Moreover, the apparent suppression of growth was observed in the presence of 500 μg/mL streptomycin. As the sensor is composed of arrayed elements, and the area of sensitivity distribution of the element is larger than the size of one bacteria, the variation in the output value of each element may reflect the number and movement of bacteria. This study revealed that the presence of viable E. coli could be rapidly confirmed by using the change in permittivity caused by the displacement of media by E. coli near the sensor surface.