(394e) Multi-Frequency Impedance Method for the Rapid Detection of Viable Micro-Organisms

We present a novel culture-based electrical method for detecting presence of viable micro-organisms in suspensions that is significantly faster than existing methods. In our previous work, we have used our method to detect presence of viable bacteria in various samples, and in this paper, we extend our work to detect viable yeast and mold. 

The principle underlying our method of detection is the polarizability of viable microbial cells. Cell membranes of viable microbial cells do not, in general, allow charge-carrying ions to pass through. So, in the presence of an alternating electric field, there occurs a build-up of charge at the membrane, causing the cells to act like capacitors. As they multiply, there occurs a corresponding increase in the charges thus stored in the interior of the suspension (its “bulk capacitance”), and this increase in bulk capacitance serves as our “signature” indicating the presence of live micro- organisms. The bulk capacitance is estimated by first confining an aliquot drawn from the suspension of interest into a long microfluidic channel with electrodes at either end, measuring the electrical Impedance (Z) measurements at multiple frequencies (ω) ranging from 1 KHz to 100 MHz, and then analyzing the Zvs ω data to obtain an estimate of the bulk capacitance. Both the microfluidic geometry and the high frequencies used serve to overcome the effects of interfacial (double-layer) capacitances at the electrodes, which usually make it difficult to measure bulk capacitance.

The results obtained are used to demonstrate the ability of our method to extend it to detect viable yeasts and molds. We show that, for slow growing yeast and mold (doubling time of 6-8 hrs), our method is able to detect ~5, -10, of Dekkera anomala and Aspergillus brasiliensis in growth media in 60 and 45 hrs, respectively, with a threshold concentration of detection of ~5000-8000 CFU/ml.