Capacitive Impedance Bacterial Detection System
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Solution Overview
Problem
Current methods for detecting microbes in clinical samples, such as bacteria in blood, are slow due to the need for bacterial culture and require expensive and complex sensors, with temperature fluctuations affecting dielectric impedance measurements, and high sample consumption in microfluidic chambers.
Innovation Solution
An impedance-based detection method using a disposable array of small-volume chambers with electrodes, where a time-varying electrical signal is applied to detect changes in capacitive impedance, allowing for faster and more sensitive bacterial growth detection without the need for complex sensors or precise temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dielectric impedance measurement is used for bacterial detection, then detection sensitivity is improved, but temperature sensitivity causes measurement instability
Solution Approach 1:
The patent changes the measurement parameter from general dielectric impedance to specifically the capacitive component of impedance. By using frequency-dependent capacitive measurements rather than conductive measurements, the system achieves temperature insensitivity while maintaining detection sensitivity. The capacitive component remains stable across temperature variations unlike the conductive component.
2Productivity
If small-volume chambers are used for bacterial culture, then detection speed is improved, but sample accessibility for downstream analysis becomes difficult
Solution Approach 1:
The patent divides the culture system into two distinct segments: a small-volume array of chambers (0.25-2 mL) for rapid detection and a separate downstream analysis system. The array format enables fast detection while automated liquid handling systems bridge the gap by transferring samples from the small chambers to larger vessels for identification and susceptibility testing.
Solution Approach 2:
The patent introduces automated liquid handling systems as an intermediary between the small-volume culture chambers and downstream analysis equipment. This mediator enables easy sample access and transfer without requiring manual manipulation of the small chambers, thus maintaining both detection speed and operational ease.
3Measurement precision
If individual chemical sensors are deployed in each chamber, then detection accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent replaces complex chemical sensors with a simpler electrical measurement system. Instead of using chemical sensors to detect bacterial metabolites, the system uses electrodes to measure the capacitive component of impedance, which changes as bacteria grow in the chamber. This substitution dramatically reduces system complexity and cost while maintaining detection accuracy.
Solution Approach 2:
The patent uses electrical field interaction as a non-invasive copy or proxy for chemical detection. Rather than directly measuring chemical changes with complex sensors, the system measures the electrical properties (capacitance) of the medium, which are affected by bacterial presence and growth. This indirect measurement approach simplifies the detection system.
4Reliability
If conventional culture methods are used, then reliable bacterial detection is achieved, but detection time is extended
Solution Approach 1:
The patent implements continuous monitoring of the capacitive component of impedance throughout the culture process. Rather than taking discrete samples at intervals, the system continuously measures electrical properties, allowing immediate detection of bacterial growth events. This continuous action maintains reliability while reducing the average detection time compared to conventional periodic sampling.
Solution Approach 2:
The patent performs preliminary detection of bacterial presence using the small-volume array chambers with capacitive measurements before committing to full downstream analysis. This preliminary action quickly identifies positive samples, allowing resources to be focused only on confirmed positives and reducing overall detection time for negative samples.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables faster bacterial detection by using small-volume chambers, comparing neighboring wells, and employing a sensitive capacitive detection mechanism, reducing time-to-detection and sample consumption while maintaining low costs and ease of access to positive chambers.
Implementation Method 1
employing a sensitive capacitive detection mechanism
Implementation Method 2
Dielectric impedance measurement has been evaluated as an alternative to the use of chemical sensors
Data Source
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AI summary
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.