Impedance-based bacterial detection system
First Claim
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1. An impedance-based microbial growth detection method comprising the steps of:
- providing at least one vessel containing a liquid sample suspected of containing microorganisms disposed between and in contact with a first electrode and a second electrode;
providing a time-varying electrical signal to the first electrode in contact with the liquid sample, wherein the second electrode is electrically connected to a phase-sensitive signal detector; and
selecting a frequency of said time-varying electrical signal so that an out-of-phase signal amplitude measured by said phase-sensitive signal detector becomes equal to zero at the selected frequency;
measuring the out-of-phase signal amplitude over time with the phase-sensitive signal detector at the selected frequency, wherein an increase in the signal amplitude over time at the selected frequency indicates microbial growth within the liquid sample; and
after measuring, detecting the presence or absence of microbial growth.
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Abstract
A method and apparatus for determining the presence or absence of microorganisms in a liquid sample. A vessel with an electrode disposed therein receives a volume of liquid to be tested. A second electrode is also provided, both electrodes in physical contact with the liquid sample. A time varying signal is applied to one electrode, and the other electrode is coupled to a phase sensitive signal detector. The phase sensitive signal detector determines a frequency at which an out of phase signal amplitude is zero. This zero-crossing frequency is used as a baseline, and changes in the zero-crossing frequency are an indication of microbial growth.
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14 Claims
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1. An impedance-based microbial growth detection method comprising the steps of:
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providing at least one vessel containing a liquid sample suspected of containing microorganisms disposed between and in contact with a first electrode and a second electrode; providing a time-varying electrical signal to the first electrode in contact with the liquid sample, wherein the second electrode is electrically connected to a phase-sensitive signal detector; and selecting a frequency of said time-varying electrical signal so that an out-of-phase signal amplitude measured by said phase-sensitive signal detector becomes equal to zero at the selected frequency; measuring the out-of-phase signal amplitude over time with the phase-sensitive signal detector at the selected frequency, wherein an increase in the signal amplitude over time at the selected frequency indicates microbial growth within the liquid sample; and after measuring, detecting the presence or absence of microbial growth. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An impedance-based microbial growth detection method comprising the steps of:
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providing a sample container having at least one vessel containing a liquid sample suspected of containing microorganisms disposed between and in contact with a first electrode and a second electrode; providing a time-varying electrical signal to the first electrode in contact with the liquid sample, wherein the second electrode is electrically connected to a phase-sensitive signal detector; and measuring an out-of-phase signal amplitude over time with the phase-sensitive signal detector, determining a frequency at which the out of phase amplitude is zero by tuning the frequency of said electrical signal so that the out-of-phase signal amplitude measured by said detector becomes equal to zero; repeating the determining step at predetermined time intervals; and after measuring and repeated determining, detecting the presence or absence of microbial growth, wherein an increase in said frequency over time is an indication of microbial growth within said liquid sample. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification