Use of a Novel Conductance Based Technology for Realtime Environmental Bacterial Aerosol Sensing

Miaomiao Tan, Fangxia Shen and MAOSHENG YAO

State Key Joint Laboratory for Environmental Simulation and Pollution Control College of Environmental Sciences and Engineering Peking University, Beijing 100871, China

     Abstract Number: 123
     Last modified: April 20, 2010

Abstract
In this study, a novel conductance based technology for sensing bacterial concentrations was demonstrated on a centimeter-size chip. The detection system includes the signal amplification, copper probes (sensing tip is 25 um in diameter) spaced at 2 mm and a sample loader composed of hydrophobic parafilm and a plastic sealing element. During the experiments, the conductance of Bacillus subtilis var niger, Pseudomonas fluorescens, and Escherichia coli in the form of ball-shape liquid (3.3 mm wide) were measured using the system developed. The conductance data were simulated verses the bacterial concentrations. As an application, the developed technology was applied to determine the concentration levels of some pure bacterial samples as well as environmental bioaerosols, and the results were compared with those obtained using the culturing technique.

Results indicated that the bacterial conductance was best described at 100 KHz for all species tested in considering that of DI water. The relationship between the conductance of bacterial suspensions and their concentrations was found to follow the basic model for all species tested: Y=C1+C2×e(-X/C3) where Y is the conductance (S), X is the bacterial concentration (N/ml), and C1-3 are species-specific constants. Gram negative P. fluorescens and E. coli assumed similar conductance curves, which were more flat than that of gram positive B. subtilis var niger. Experimental results indicated that for P. fluorescens and E. coli the culturing technique resulted in higher concentration levels (statistically significant) from 2 to 4 times that measured by the conductance based technology developed here. For B. subtilis var niger, both methods resulted in similar concentration levels. These differences might be due to membrane types, initial culturability and the obtained conductance curves. However, the total concentrations for environmental bacterial aerosols determined by conductance based technology were in line with literature data when considering the relationship between the total and the culturable ones. The conductance based technology here was shown to hold broad promise in realtime monitoring environmental biological agents.