Blood Culture Detector With Reference LED for CO2 Monitoring
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Solution Overview
Problem
Current blood culture monitoring systems using colorimetric sensors can produce false negatives due to bottle displacement and optical system degradation, leading to inaccurate CO2 level readings and increased false-positive rates.
Innovation Solution
Incorporating a reference LED with a specific wavelength, such as near-infrared or blue, to provide a stable intensity reading independent of CO2 concentration changes, allowing for real-time monitoring and compensation of non-growth related changes in the optical system, such as bottle position and dust accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single LED is used to illuminate the colorimetric sensor, then the system is simple, but bottle displacement and optical degradation cause false negatives and reduced reliability
Solution Approach 1:
The illumination system is segmented into two independent LED sources: a sensor LED for measuring CO2 levels and a reference LED for monitoring optical system stability. This segmentation allows independent optimization of each LED's function and enables separate monitoring of growth-related vs. system-degradation-related changes.
Solution Approach 2:
The reference LED acts as an intermediary element that introduces a stable reference signal into the optical system. By comparing the sensor LED signal against the reference LED signal, the system can compensate for bottle displacement and optical degradation, isolating the true CO2-related changes from artifacts.
2Reliability
If no reference measurement is provided, then the system is simple, but optical system degradation leads to false-positive rates increasing
Solution Approach 1:
The reference LED provides continuous feedback about the optical system's state (bottle position, dust accumulation, LED aging). This feedback signal is used to dynamically adjust or compensate the sensor LED measurements, allowing the system to correct for optical degradation in real-time and reduce false-positive rates.
3Measurement precision
If the system monitors only CO2 changes, then the measurement is direct, but bottle displacement is misinterpreted as growth changes
Solution Approach 1:
The system adds a new dimension to the measurement by introducing the reference LED signal as a separate measurement channel. This creates a two-dimensional measurement space: one dimension for CO2-related changes (sensor LED) and another for optical system stability (reference LED). By analyzing changes in both dimensions simultaneously, the system can distinguish between true CO2 changes and artifacts caused by bottle displacement.
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 approach reduces false-positive rates and improves sensing accuracy by distinguishing between microbial growth-related and non-growth related changes, ensuring reliable CO2 monitoring and maintaining system reliability over time.
Implementation Method 1
The sensor (2) changes its color as the percentage of CO2 in the bottle varies from 0% to 100%; the color varies from blue to yellow, respectively.
Implementation Method 2
Much of the remaining light is scattered from the surface and interior of the sensor.
Implementation Method 3
A silicon photodetector (5) 'stares' (i.e., continuously monitors the scattered intensity signal) at the region in the sensor (2) where the light from the LED interacts with the sensor.
Implementation Method 4
A red Light Emitting Diode (LED) (4) shines onto the bottom of the BacT bottle (1).
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A detector arrangement is disclosed for a blood culture bottle incorporating a colorimetric sensor which is subject to change of color due to change in pH or C02 of a sample medium within the blood culture bottle. The detector arrangement includes a sensor LED illuminating the colorimetric sensor, a reference LED illuminating the colorimetric sensor, a control circuit for selectively and alternately activating the sensor LED and the reference LED, and a photodetector. The photodetector measures reflectance from the colorimetric sensor during the selective and alternating illumination of the colorimetric sensor with the sensor LED and the reference LED and generates intensity signals. The reference LED is selected to have a peak wavelength of illumination such that the intensity signals of the photodetector from illumination by the reference LED are not substantially affected by changes in the color of the colorimetric sensor.