Respiratory response of cell-based sensors to toxicants measured by using pseudo-random signals

Cell-based sensors using such as Pseudomonas putida and Bacillus subtilis were applied to examine the toxicity of chemicals. Both toxicant and substrate solutions were introduced into the sensor system according to M-series and anti-symmetric M-series pseudo-random binary signals, Xn (n=15, minimal pulse width 4 min, period 60 min) and Yn (n=30, minimal pulse width 4 min, period 120 min). Toxicants such as Ag+, formaldehyde, azide, and hypo-chlorite were used to demonstrate the proposed method. The individual responses of substrate and toxicant were obtained at a time by calculating the cross-correlation function between the input and the output signals. Effects of toxicant on the response of substrate and the response of toxicant itself can be observed at a time, so that the method appears to be useful in studying the behavior of microorganisms in the presence of toxicants.