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Fluorescence Label Simulator for U.S. Army Hydration Sensor Module (HSM)
Fluorescence Label Simulator for U.S. Army Hydration Sensor Module (HSM)
Sponsored by Gaia Medical Institute
James Chianglin | Kyle Felsman | Marina Fernandez | Michael Frausto | John Lee
MAE 156B Sponsored Project, Winter 2014
Department of Mechanical and Aerospace Engineering
University of California, San Diego
Professor: Dr. Jerry Tustaniswkyj
Figure 1: Final design of test bed
Background:
Background:
Rapid dehydration monitoring is urgently needed within the U.S. Army and in many sectors of the civilian market. Army operations in hot and dry environments require that soldiers be well hydrated in order to perform optimally in dangerous combat situations. Similarly, high-endurance athletes and senior citizens need to be aware of their level of dehydration to prevent injuries and severe health problems. Hydration is incredibly difficult to monitor in the field, and can be divided into three general levels: hydrated, moderately dehydrated, and severely dehydrated. Being able to detect the onset, as well as the severity/level of dehydration is crucial for not only completing a mission successfully, but also for maintaining a healthy level of hydration during everyday activities. Therefore, there is a need for quick, portable tests to detect dehydration and determine the severity. Gaia Medical is developing a commercial, hand-held device similar to the size and functionality of a pregnancy test to be completed in five years’ time. The device will contain three main components: a saliva module, the test strip cartridge and the digital reader. The reader will illuminate the test strip, detect its fluorescence, process the information gathered, and then display the results.The final product requires a digital reader and further development to become a viable product. Gaia Medical and the Mechanical and Aerospace Engineering (MAE) department at the University of California, San Diego, sponsored an MAE 156B team to take over the first step in the module’s initial development. The team was tasked with creating an LED simulator to mimic the fluorescence of the saliva biomarkers, as well building a test-bed in which the LED simulator and nitrocellulose strips will be tested throughout the development of the final product.
Objective:
Objective:
The project objective is to deliver the following requirements and deliverables:
The project objective is to deliver the following requirements and deliverables:
Requirements
LED Simulator
Replicate the fluorescence of saliva biomarkers in terms of wavelength and light intensity
Variable adjustment in light source brightness
Self-contained unit easily inserted and removed from the test bed
Test Bed
Distance adjustable rack with the measurement capability for 10mm travel with an accuracy of ±1mm
Minimal stray light to enter test bed
Ability to swap and secure photosensor and LED Simulator
Ability to hold LED Simulator in vertical and horizontal orientations
Deliverables
All CAD models of hardware and drawings with tolerances
Assembly drawings/models
Bill of Materials (BOM)
Analysis package (Dimensional tolerances, mechanical stress/strain, stray light)
Electronics schematics of LED, photosensor, and data capture system
Design for electronic readout of data (may be through PC-based data capture system)
Required software to perform test
Complete test bed and LED Simulator
Testing Report and analysis
Data from several key tests on the simulator and test bed will help Gaia identify potential risk areas in the production version of the dehydration monitor. The Fluorescence Label Simulator will provide a reliable testing device for saliva test strips and help Gaia develop reader software, electronics, and sampling devices in later stages of the HSM development.
Final Design:
Figure 2: Annotated Cross Section of test bed
Figure 2 shows the final design of the test bed. The material used to construct the black box was Acrylonitrile Butadiene Styrene(ABS) plastic due to it being light, rigid and of high emissivity. The plates around the LED and filter carriage were also constructed with ABS plastic to lower the reflectivity of light. The gears and mount for the potentiometer were outside of the housing and therefore could be made using acrylic. The main features of the black box test bed include the threaded rod, sliding door, guide rails, potentiometer, LED and filter carriage, and photosensor mount. The box was constructed to minimize the amount of stray light that would enter the box as well as height adjustment without opening the box. The LED and photosensor were connected to a National Instrument USB-6009 data acquisition device, which powers and reads data from the sensor. The height of the carriage unit can then be modified smoothly due to the guide rails.
Figure 2 shows the final design of the test bed. The material used to construct the black box was Acrylonitrile Butadiene Styrene(ABS) plastic due to it being light, rigid and of high emissivity. The plates around the LED and filter carriage were also constructed with ABS plastic to lower the reflectivity of light. The gears and mount for the potentiometer were outside of the housing and therefore could be made using acrylic. The main features of the black box test bed include the threaded rod, sliding door, guide rails, potentiometer, LED and filter carriage, and photosensor mount. The box was constructed to minimize the amount of stray light that would enter the box as well as height adjustment without opening the box. The LED and photosensor were connected to a National Instrument USB-6009 data acquisition device, which powers and reads data from the sensor. The height of the carriage unit can then be modified smoothly due to the guide rails.
Figure 3: LED Simulator
The replication of a fluorescent biomarker's wavelength used an LED of similar wavelength. The LEDs intensity can be altered with distance, filters and Pulse Width Modulation (PWM), allowing it to simulate a transient nature of the fluorescent signal. This LED was soldered to a protoboard which was then mounted onto an acrylic slide and painted with an ultra-flat paint to give it high emissivity. These slides were similar in design with those of the filter slides in order to allow them to be stacked and quickly changed. This allows for adjustable optics and room for future biomarkers test. The LED slide was placed inside the carriage area on top of the filters, then pressed down with a set screw. This simulated the fluorescence wavelengths and decreased the intensity of the LED.
Summary of Performance Results:
Figure 4. LED Power Test: Band pass Filter - Linear Regime (R_LED = 10k ohms)
Figure 5. Wavelength vs. Intensity Test with 520nm Bandpass Filter
Height adjustment system accuracy: ± 0.15 mm
The dwell time of all photosensors tested is shorter than can be reasonably detected by the DAQ sample rate
The LED and band pass filter test demonstrated low level light output with a wavelength of 520 nm ± 10 nm, seen in Figure 5
The test-bed did not introduce stray light to the photosensor so long as a gap was not visible at the bottom of the sliding door
The Sensl photomultiplier exhibited a sigmoid shape for plots of photosensor intensity vs. LED power
The linear range of the Sensl photomultiplier: 0 mV to ~100 mV photosensor intensity with an R2 > 0.95, seen in Figure 4
A maximum SNR of 425 and CV of 0.24% was achieved for the Sensl photomultiplier
Drift in photosensor intensity was observed
The theoretical transmission for the density filter was nearly 3 times greater than the observed transmission
An exponential decay curve best models the photosensor intensity vs. distance data
The Vishay VBPW34S photodiode exhibits a highly linear relationship between photosensor intensity and LED power
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