A Bandwidth Detection System to Monitor Single Cells

Jerry J. Wilmink, Jonathon D. Wells, Advisor: Franz Baudenbacher

Department of Biomedical Engineering Vanderbilt University

BME 273, Group 9, 2002

IntroductionIntroductionIn light of the recent bioterrorism attacks there is a heightened concern for detection of harmful agents at the cellular level. This project aims to work in conjunction with an existing biosensor project for activity detection, specifically dealing with the development of a cell based sensing technology. This Vanderbilt University project receives its funding through Defense Advanced Research Projects Agency. The overall goal of the project is to use BioMEMS devices to quantify and classify the impact of various toxins on cell physiology into signatures. Creation of these signatures will foster the identification of specific harmful agents, based on pre-documented physiological pathway alterations within excitable cells in response to exposure.

Array Array ElectrodesElectrodes

BioMEMS devices are fabricated onto a silicon chip and segmented into two separate layers. The control layer utilizes peristaltic pumps to direct the cellular flow within the fluidics layer. The fluidics layer, where the cell is trapped in a sub-nanoliter volume between two valves while toxins are introduced, is sealed against inter-digitated array electrodes. The electrodes allow us to monitor the cell’s metabolic activity. Various measurements from the electrodes, such as the trans-membrane potential of an excitable cell, would allow us to quantify and classify the impact of various toxins on cell physiology.

What is a BioMEMS Device?Control LayerControl Layer

Fluidics Fluidics LayerLayer

Sub-nanoliter Volume (Sub-nanoliter Volume (.25nL, .25nL, 100x100um100x100um))

Design GoalsDesign Goals

Envisioned DeliverableEnvisioned DeliverableDesign a detection system to measure and visually Design a detection system to measure and visually monitor the transmembrane potential of an excitable monitor the transmembrane potential of an excitable

cellcell

Create a design schematic within Innovation Workbench to assist in defining our problem

Design the hardware for 4 data acquisition boards, each having 64 channels (256), to read out the Hamamatsu photodiode array incorporating custom designed amplifiers and National Instruments data acquisition boards

Design a Labview program to read and record voltages from the 4 x 64 channel NI data acquisition system, to read out a high speed photodiode array, and

control the optical imaging recording camera and potentiostat readout from the interdigitiated electrode array

Interface the photodiode array with an inverted microscope

Devise a calibration protocol for the manipulation of data acquired from the photodiode array

Record the trans-membrane potential of an excitable cell

ProjectProject

Inverting Microscope

Light from Microscope

BioMEMS Device

Photodiode Array

Light Voltage Voltage

Signal Gain Computer Hardware Data Processing

2D Array Output of Intensity of Signal

Amplifier Board NI DAQ Board Labview Program

DesignDesign

BioMEMS Device

Photodiode Array

Inverting Microscope

ExperimentalExperimental

Photodiode

Amplifier Board

NI DAQ BoardPower Supply

Oscilloscope

Labview Program

SetupSetup

MethodologyMethodology

Step 1: Research and Define ProblemStep 1: Research and Define ProblemResearch Problem:

DARPA proposal General BioMEMS literature

Define Problem: Used Innovation Workbench and DesignSafe to define the problem and

to address the specific aspects of our design problem Generated a list of equipment needed:

• Labview; used to control the 256-channel data acquisition system, read out a high-speed photodiode array, optical image-recording camera, and potentiostat readout of the interdigitated electrode array

• Hamamatsu photodiode array; to generate an appropriate wavelength and to convert to corresponding voltage

• National Instruments data acquisition system; used to read out the high speed photodiode array

• Inverted Microscope; to observe and document dyes characteristics, corresponding to discrete wavelengths, within a particular excitable cell

• Optical Image recording camera

• BioMEMS devices; to monitor the excitability of cardiac myocytes, neurons, and endothelial cells; excitable cells

Step 2: Equipment Setup and Initial TestingStep 2: Equipment Setup and Initial Testing Equipment Setup:

Hardware Setup National Instruments 64-channel Data Acquisition Card inserted into computer

port Power Supply manually prepared for connection to Amplifier Board, to provide

+/-15 V and +/-7.5 V Software Setup Installed National Instruments Driver Program Installed NI Labview 6.0

Initial Testing:Each of the 64 channels on DAQ Board were tested for voltage sensitivity through the

LabView Testing PanelROADBLOCK #1: Channel Input Error- LabView was reading ½ of our 64 channels through the Test Panel. Resulted from a default channel configuration setting of Differential Readout, thus resulting in the difference between one voltage is referenced to another voltage of a different channel, thus limiting the channels available to 32. Solution: Channels were reconfigured to Sequential Readouts for voltages, for which each channel voltage is referenced to ground.

Program Capabilities: Designate specific channels to read and store input voltages in a 2D array Display real-time voltages from specified channels and save data for these

selected channels in spreadsheet form Graphically represent input voltage readings while maintaining signal

characteristics

ROADBLOCK #2ROADBLOCK #2: Channel Voltage Drifting- : Channel Voltage Drifting- Upon testing random channels using the DAQ Channel Test Panel, neighboring channels were found to be registering errant voltages.

Solution: Voltage Drift is a common source of error when neighboring channels on a DAQ panel, which have no input voltage, are not grounded.

Step 3: Design Labview VI programStep 3: Design Labview VI program

Step 4: Modify LabView program Step 4: Modify LabView program

New Program Considerations: The input voltages are stored as a 2D array, with the column dimension specifying

the channel number and the row dimension specifying the Scan NumberROADBLOCK #3: Random Photodiode Pin Layout- There was no simple scheme to organize the array pixels to create a visual representation within Labview, because of the unsystematic layout of pins within the photodiode. Solution: Manually separate each channel by indexing, determine the exact layout of the channels within the photodiode array, and position the individual pixels on the Front Panel according to the position within the photodiode.

This array was transposed and indexed to allow data to be extracted from specific channels and repositioned on the front panel of LabView

Channel layout within the PDA was determined by the pin configuration, with each pin corresponding to a specific channel within Labview

Using the position of each channel within the PDA, the coordinates of the color boxes (individual pixels each specific to 1 of 4 DAQ boards, labeled ‘device’ and 1 of 64 channels) were used for positioning within the 16x16 array

Here we want to incorporate a visual representation of the position-dependant Here we want to incorporate a visual representation of the position-dependant voltages received from the photodiode arrayvoltages received from the photodiode array

Key LabView Features:

ResultsResults

Mult Port SubVI allows user to specify inputs: device,

channel #, scan #, and scan rate; while outputting 2D

arrayed data

Using a for-loop, scans are constantly averaged with a

mean function loop to decrease size of data for

each channel

Average voltages multiplied by constant,

creates a greater difference in color

thresholds of color boxes

Boolean control to save program to file

The color boxes were spatially arranged to correspond to each device and channel

number

Results: LabviewResults: Labview ProgramProgram

A Labview program has been designed to:

Read and record voltages from a photodiode array, for a single 64 Channel NI DAQ board

Save acquired data into a spreadsheet for future analysis

Can graphically represent the analog signal preserving integral signal characteristics for each of the 64 channels

16 X 16 pixel array that represents the intensity of a channel’s voltage as a color

ConclusionConclusion

Future PlansFuture Plans The installation of the remaining 3 NI DAQ boards, will allow us to read from all

256 channels, thus completing our 16 X 16 color box array

Interface the photodiode array with an inverted microscope and a BioMEMS device, thus allowing acquisition of cellular measurements by quantifying discrete wavelengths as voltages, which will be sent to the Labview program for data manipulation

Use data to devise a calibration protocol to easily correlate the voltages from the 256 channels to the trans-membrane potential of an excitable cell

Record the trans-membrane potential of excitable cells, and begin creating signatures to quantify the quantify and classify the impact of various toxins on cell physiology

AcknowledgementsAcknowledgementsThis work was completed using the funding provided by the DARPA grant

ReferencesReferences(1) Andreas

(2) Roger Hebert, Sales Rep. for National Instruments

(3) National Instruments LabView 6.0 Instruction Manual and Measurements and Analysis Manual