Student Projects
Contact Information
University/Department: University of Memphis/Department of Biomedical Engineering
Team Member: Felynncia Rainey
Advisors:
Erno Lindner, PhD
Roy William, PhD
Fernado Garay, PhD
Amy Curry, PhD
Brian Kelly, PhD
E-mail Address: frainey@memphis.edu
Project Information
Title:
LabVIEW Controlled Flow Analytical System for Electrochemical Analysis of Microliter Samples
Description:
A multi-purpose, automated flow analytical system (AFAS) has been designed and implemented. The system is composed of a potentiostat, peristaltic pump, sampling actuator/valve, and an electrochemical flow-through cell. The instruments in the system are controlled via software written in National Instruments' LabVIEW. The AFAS is aimed at monitoring the anesthetic drug propofol. Currently there is no known quantitative method of determining propofol concentration in patients at the bedside.
Products:
LabVIEW Version 8.5.1
DIAdem Version 10.0.0f2541
USI: 1.5.0.3128
DataFinder: (1.3.0.2541)
National Instruments Hardware
DAQ Hardware: NI USB-6221
The Challenge:
- u Meter and measure microliter quantities of analyte within seconds/minutes
- Eliminate human error in sampling and measurement
- Monitor the concentration of continuously flowing solutions
- Implement a variety of sampling methods and fluidic schemes
- Implement, monitor, and repeat serial assays
- Test large numbers of sensors and microfabricated electrodes
LabVIEW has been chosen as the system platform because it allows one to (1) integrate and control multiple instruments; (2) design a sophisticated user-friendly graphical interface; and (3) design a system that can evolve according to the needs of future researchers.
The Solution:
The automated flow analytical systems (AFAS) is composed of a flow-through electrochemical cell in combination with a computer controlled actuator (Modular Valve Positoner (367898), Hamilton Company, Reno, NV), multi-position valve (6-port Distribution Valve/6-port Loop Valve (36781/ 38760), Hamilton Company, Reno,NV), peristaltic pump (Miniplus3 Peristaltic Pump (F1155006), Gilson Incorporated, Middleton, WI), and potentiostat (CV-27 Cyclic Voltammagraph (MF9030), in combination with a PA-1 Pre-Amplifier Bioanalytical Systems Incorporated, West Lafayette, IN).
The AFAS has a user-friendly graphical interface which allows for easy configuration of the system. Experimental protocols are automatically saved and can be reloaded. Repetitive analytical tasks are made simple by a cycle control, which repeats the experiment a specified number of times. Experimental data and parameters are automatically saved under filenames that identify the experiment name, cycle, and experiment number. Experimental files are searchable by the experimental parameters, which can be useful in data mining. Automated analysis of data is accomplished through Visual Basic scripts written in DIAdem.
Two valves are used with the AFAS (Figure 1). The 6-position distribution valve (Figure 1b) is used to selectively sample an analyte for a specified period of time. This valve is useful in situations where many different analyte solutions are necessary. The 6-port loop valve (Figure 1a) is used to inject a sample into a stream of background/carrier solution (flow-injection analysis). The sample is loaded into the sample loop. The valve is rotated to inject the sample into the carrier solution. This valve can be used to inject microliter analyte volumes, which greatly reduces the needed sample volume. This feature is beneficial when the sample/analyte is very expensive, precious and/or limited in quantity.
Figure 1a: 6 Loop Valve (Flow injection schematic)
Figure 1b: 6 Position Valve (Sequential sampling schematic)
The control program utilizes the COM1 and COM2 serial ports and an USB port to communicate with the various instruments (Figure 2a). The COM1 port of the computer is connected directly to the input port of the Modular Valve Positioner. COM2 is connected to the Minipuls3 pump through the 506C Interface. The potentiostat is connected via a USB port through the NI-6221 DAQ card. A picture of the system setup is displayed in Figure 2b.
Figure 2a: Communication for instruments in AFAS (Red arrows). Fluid/Sample flow lines (blue arrows).
Figue 2b: Setup of the system showing: potentiostat, sampling valve, flow cell, and pump.
Analyte is sampled by the sampling valve and is moved into the flow-through electrochemical cell. The electrochemical cell contains the sensor and is where the measurement takes place. Data is written to and read from the sensor by the potentiostat via the NI USB-6221 DAQ card. The peristaltic pump controls the flow rate of the solution. The AFAS control program coordinates all of these events. The front panel of the control program can be divided into five sections (Figure 3).
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Figure 3: Front panel of the AFAS control software.
Section 1 contains the Experimental Procedure panel. The Experimental Procedure control is an array of clusters. Each index of the array is a step in the Experimental Procedure. The cluster contains a Combo Box (Valve position selection), three numeric controls (Pump, Wait, RPM), and a Boolean control (Measure). The Experimental Procedure allows the user to select a specific valve position/solution. The user can control how how fast and how long the solution is flowed. The user can also control when and if to stop the flow of solution. The user also is able to turn measurement On or Off at each stop.
Section 2 contains drop-down menus. To optimize the use of screen space, controls not needed during the running of an experiment are placed into drop-down menus. The drop-down menus are (a) Experimental Procedure, (b) Valve, and (c) Electrochemical Parameters (Figure 4).
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Figure 4: Drop Down Menus (Experimental Procedure, Valve, and Electrochemical Parameters)
Each of these menus and their options are described below.
Experimental Procedure Menu Options
- New (Short-cut Key: Ctrl+N): Loads a new Experimental Procedure
- Open (Short-cut Key: Ctrl+O): Loads a previously saved Experimental Procedure
- Start (Short-cut Key: Ctrl+S) : Starts the Experimental Procedure
Valve Menu Options
Allows the user to select the valve that is currently in use in the system. Selection of either valve option opens a pop-up window and allows the user to specify the solutions attached to each position. The user can also use the default position names by checking the Use Label Names check box (Figure 5). The menu options are as follows: (1) 6 Position (Ctrl+P) and (2) 6 Loop (Ctrl+L)
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Figure 5: 6 Position Valve Pop-up Window: Selection of position names. Position names shown in Experimental Procedure.
Electrochemical Parameter Menu Options
This menu allows the user to select from two electroanalytical techniques. Selection of either menu option opens a pop-up window which allows the user to enter the technique parameters. The waveform approximation of the parameters is displayed on the front panel. A user-defined stabilization/accumulation potential is applied for a specified time period prior to the application of the electroanalytical technique.
- Cyclic Voltammetry (Crtl+Y) - A triangular potential waveform is written to the DAQ card. The applied waveform is configured by entering the waveform parameters in the Cyclic Voltammetry Parameters pop-up window. (Figure 6a)
- Chronoamperometry (Ctrl+H) - A pulse potential waveform is written to the DAQ card. The applied waveform is configured by entering the waveform parameters in the Chronoamperometry Parameters pop-up window. (Figure 6b)
The applied waveform is written sensor via the potentiostat coupled with the NI USB-6221 DAQ card. Simultaneously, the response of sensor to the applied waveform is read and displayed on the front panel. This is the Measured Signal.
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Figure 6a: Cyclic Voltammetry Pop-up Window and display of Applied Waveform
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Figure 6b: Chronoamperometry Pop-up Window and display of Applied Waveform
Section 3 of the AFAS control program contains the follow controls and indicators:
- Cycles – The cycle control determines how many times the experimental protocol will be run. This control allows the AFAS is to automatically perform repeated experiments.
- Path to Write – This is the folder path in which the protocol and any data will be saved.
- File Name – This is the file name under which the experimental protocol and any experimental data will be saved. The data will be saved as a .txt and .tdms files and the protocol will be saved as a .dat
- Applied Waveform - The applied waveform is a graphical representation of the electrochemical technique parameters.
Section 4 of the AFAS control program contains the following indicators:
- Present Cycle – The present cycle indicator indicates in which cycle the protocol is running.
- Present Step - The present step is the step in the Experimental Procedure that is currently running.
- Pump Time Left [seconds] – The pump time left indicator indicates the amount of pump time left in the current protocol step.
- Wait Time Left [seconds] – The wait time left indicator indicates the amount of wait time left in the current protocol step.
- Total Time[seconds] – The total time indicates the time it takes to run the measurement for the current protocol step.
- Accumulation Time [seconds] – The accumulation time indicator indicates the current progress of the accumulation time for the measurement for the current protocol step.
- Elapsed Time [seconds] – The elapsed time indicator indicates the amount of time that has elapsed since the beginning of the measurement for the current protocol step.
- Number of Data – The number of data indicator indicates the number of data points that will be taken for the measurement for the current protocol step. (Note: This is internally set within the AFAS program).
Section 5 of the AFAS control program contains the following indicators:
- Measured Signal – The measured signal indicator is a graphical representation of the electrode/sensor response to the applied waveform.
Videos 1 and 2 show the functionality of the AFAS program. (Note: Please enable captions when viewing videos)
Video 1: Video of experimental procedure, menu functions, etc.
Figure 2: Video measurement experiment and automatic repeating of experiments.
The AFAS allows the user to implement complex flow-analytical tasks/techniques, including: sample/solution selection and precise metering; stop-flow and hydrodynamic voltammetry; flow-injection analysis; continuous monitoring; multipoint calibration with sample measurements; and immunoassays; where the ability to have precisely controlled intermittent conditioning/washing steps is crucial. Some of the flow analytical techniques are displayed in Figure 7. Figure 7a-b displays transients from a flow-injection analysis experiment. Figure 7a shows the response to increasing volumes of an analyte (5 to 54 microliters). Figure 7b shows the response to increasing concentrations of analyte. Figure 7c displays transients where measurement was performed in continuously flowing analyte solution. In all case, increases in the response is directly correlated to either increases in concentration and/or sample volume.
Figure 7a. Injections of varying volumes of analyte.
Figure 7b. Injections of varying concentrations of analyte.
Figure 7c. Flowing bulk solution of varying concentrations
Data Processing/Analysis
The AFAS software outputs the TDMS data file that has the following searchable parameters: User, Experiment Date/Time, Experiment Name, Current, Potential, Time, Accumulation Potential and Time, Initial Potential, Potential 1, Potential 2, Scan Rate, Number of Scans, Number of Steps, Electrode/Sensor Identification, Electrochemical Technique, Potential 1 Time, and Potential 2 Time. (Note: Listed before is a compete list of searchable parameter. These parameters vary by experimental technique.) The searchable parameters are grouped under the channels: Sensor Information, Experiment Information, Electrochemical Results, and Electrochemical Parameters . The parameters may be searched independently or in combination. Figure 8 shows an expanded view of an experimental data file loaded in DIAdem's data portal. Visual Basic scripts, used for automated data analysis, are written in DIAdem. The scripts perform the following data manipulation: FFT, Low Pass Filter, Steady State Value, Peak Value, Area Under Curve (Charge).
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Application
The AFAS is aimed at monitoring the drug propofol. Propofol is an anesthetic/analgesic typically administered to ICU patients requiring mechanical ventilation. The goal of clinicians is to keep the patient slightly sleepy and pain free.[1] Propofol is often administered as a bolus injection to sedate the patient. The patients are kept sedated via an intravenous drip.[2] Current standard dosing paradigms are not universal to all patients. Consequently, some patients may be under sedated while others may be over sedated. Patient under-sedation can affect patient comfort, proper patient-ventilator synchronization and blood oxygenation. [3] Patient over-sedation can result in more serious conditions, such as the development propofol infusion syndrome. Propofol infusion syndrome is caused by the long term use of high doses of propofol. It is characterized by many physiological dysfunctions, such as metabolic acidosis, hemodynamic changes, acute renal failure, rhabdomyolysis, hypertriglyceridemia , hyperlipidemia, and cardiac dysfunction.[4] In rare cases propofol infusion syndrome can even lead to patient death. Because of these situations, a method for the bedside continuous monitoring of propofol is needed. Current offline methods of detection include using blood gas-chromatography/mass-spectrometry and involves processing the sample with organic solvents.[5] These methods are unsuitable for bedside monitoring because the sample preparation is time consuming and the instrumentation is often large/bulky. The goal of our group is to develop an electrochemical sensor that can be used for the bedside continuous monitoring of propofol in patients. The AFAS will be used to test the sensor and simulate a bedside continuous monitoring environment
Conclusion
It has been demonstrated that the AFAS has fulfilled the design goals. It is able to measure microliter quantities of analyte, and implement a variety of sampling and fluidic schemes. Through the cycle control, the ability to repeat assays is made simple. Also, because the system is automated, large quantities of electrode and/or sensors can be tested more efficiently.
Note: The control program is named FAS_Redoing_ver4.vi. All other included VIs are subVIs and are not intended for front panel display.
References
[1] Devlin, JW. Roberts, RJ. Pharmacology of Commonly used Analgesics and Sedatives in the ICU: Benzodiazepines, Propofol, and Opioids. Critical Care Clinics. 25(3):431-49
[2] Hohener, D. Blumenthal, S. Borgeat, A. Sedation and regional anaesthesia in the adult patient. British Journal of Anaesthesia. 2009. 100(1): 8–16
[3] Cox, CE. Reed, SD. Govert, GA. et.al. Economic evaluation of propofol andlorazepam for critically ill patients undergoing mechanical ventilation. Critical Care Medicine. 2008. 36(3):706-14
[4] Orsini, J. Nadkarni, A. Chen, J. Cohen, N. Propofol Infusion Syndrome: Case Report and Literature Review. American Journal of Health-System Pharmacists. 2009. 66:901-15
[5] Guitton, J. Desage, M. Lepape, A. et.al. Quantitation of propofolin whole blood by gas chromatography-mass spectrometry. Journal of Chromatography B. 1995. 669:358-65
[6]Vantersberghe, C. Camu, F. Propofol. Handbook of Experimental Pharmacology. 2008. 182:227-52
