This document summarizes a capstone project to create a point-of-care device to continuously monitor urea and creatinine levels in urine samples from ICU patients. The device uses colorimetric reactions and a spectrophotometer to automate urine tests and provide results every 15 minutes. It incorporates pinch valves, reagent chambers, and electronics controlled by an Arduino board to process urine samples. Initial testing of the chemistry and prototype device demonstrated linear standard curves for urea and creatinine quantification. Future work includes further device miniaturization and clinical testing prior to regulatory approval and commercialization.

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absorbance,670nm
time (min : sec)
colour change over time for large volumes of sample
[urea = 0.3mg/dl] [Urea = 1mg/dl] urine sample A
Prototype for a Point of Care, Real Time Metabolic Sensor for ICU Patients
Ejay Eze, Divine Nsoesie, Hartson Obasiolu, Rebecca Rubin, and Emmanuel Tito
Advisor(s): Professor Eisenstein, Professor Montas, Fischell Department of Bioengineering, University of Maryland / Dr. Avelino Verceles, University of Maryland, Baltimore
Capstone Group two would like to extend thanks to Dr. Yu
Chen and Dr. Ian White, of the Fischell Department of
Bioengineering at the University of Maryland, for their
assistance with determining the short term optimal
strategy for reading and processing optical density. We
would also like to thank ASCO valves , a subsidiary of
Emerson, for their donation of the pinch valves which were
utilized in the project, and Worhtington Biochemical for
their donation of the urease that was used in the project.
Fully integrate spectrophotometer and
GUI with electronics
Implement automated washing step
Improve valve system so that not all
urine is diverted
 Integrate a volume sensor
Miniaturize device by utilizing higher
quality valves or pumps
Form a start up company
Perform clinical experiments to
precisely calibrate device values to
disease states
Apply for approval in the EU
Sell device to ICUs in the EU
Apply for FDA approval in the US
Sell device in US
Make a nice presentation for Capstone
class of 2045
•There were 4.4 million patients in the ICU
in 2005, 90% of whom were on urinary
catheters
•In order to monitor kidney and digestive
health, urine is collected for 24 hours, sent
to a lab, and the results are then sent to a
doctor to analyze with a pencil and paper.
•This time lag allows disease states to
progress, unnoticed and untreated for up
to thirty hours
•This device automates two tests- the
urine urea nitrogen test and urine
creatinine test, which provide insight into
protein metabolism and kidney health.
•Test results and basic analysis delivered
every fifteen minutes.
Motivation
Electronics
Figure 1: Circuit
design for control of
the pinch valves.
Five of the
connections
between the pinch
valves and the
Arduino are shown,
the remaining four
are identical.
Nine solenoid pinch valves are
controlled by an Arduino Uno. Each
pinch valve is damped by a resistor, a
diode, and a transistor. The power
supply was selected in order to deliver
the 5A of current the pinch valves
require.
Layout
Figure 3:
Simplified
flow
diagram of
the device,
showing
the path
that urine
takes
through the
device, and
what
happens in
each
chamber.
Each arrow
represents
a pinch
valve or a
flow plate.
Chemistry
Two classic colorimetric reactions were
used to quantify metabolic analytes. Urea
yields a blue product using the Berthelot
reaction, and creatinine yields an orange
product using the Jaffe reaction.
Chemistry was optimized for rapid and
reproducible color development, minimum
sample volume, and linearity for the
standard curves throughout normal
physiological ranges.
y = 1.1099x + 0.005
R² = 0.9999
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Absorbance,670nm
[urea], mg/dl
Urea nitrogen standard curve at 1:500 dilution
of 5mg/ml stock solution.
A
CB
Figure 4: A)Chemical equation for Berthelot reaction. 2-2-
dicarboxy indophenol is blue. B) Time course optimization for
the reaction. The reaction is complete at five minutes for all
concentrations of urea. C)Standard curve for Berthelot
reaction. It is linear over normal, abnormal and nonphysical
physiological ranges.
B
A
y = 8.0523x - 0.005
R² = 0.9984
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Absorbance,510nm
creatinine concentration, mg/ml
creatinine standard curve.
Figure 6: A) Chemical equation for the Jaffe Reaction. B)
Standard curve for the Jaffe Reaction in our set up. It is
linear over normal and abnormal physiological ranges.
Future Work
Acknowledgements
Figure 2:
CAD
drawing of
the divider
of the
device.
Vials of
reagents
are placed
in the
notches
shown,
pinch valves
are placed
in the
holes.