Microfluidic Device for the Detection of V. cholerae in Drinking - - PowerPoint PPT Presentation

Microfluidic Device for the Detection of V. cholerae in Drinking Water

Cholera Microbusters, Inc. CEO: Dr. Orlin Velev Designers: Jeffrey Millman, Katherine Schadel, Chris Shaul, Lao Yang

Cholera Microbusters, Inc.

Overview

Goal and Motivation Cholera: Cause and Detection Available Detection Tools Silver Enhancement Technique The Microfluidic Advantage Device Concept Optimization of Design Features Future Challenges

Cholera Microbusters, Inc.

Goal

To design a small, accurate, and inexpensive

microfluidic device for the detection of cholera

Help local health officials identify outbreaks Provide residents and travelers with an affordable,

discrete, and quick means of assessing risk

Cholera Microbusters, Inc.

Motivation

Cholera

Fatal if not promptly

treated

Predominant in Asia,

Africa, Latin America

Mass infections in

refugee camps and after natural disasters

Problematic in tropical

areas popular with tourists

IV drip treatment of cholera victims at a refugee camp in Mozambique.

[Medecins Sans Frontiers/Doctors Without Borders] http://www.designthatmatters.org/proto_portfolio/cholera_t reatment/multimedia/msf_moz_cholera_camp.jpg

Cholera Microbusters, Inc.

Motivation: Scope of the Problem

http://www.die-reisemedizin.de/data/krankheiten/images/cholera.jpg

Cholera Microbusters, Inc.

Cholera: Cause and Detection

Vibrio cholerae

Aquatic bacterium Cholera toxin (CT) Chlorine ion

imbalance

Severe dehydration Resistant to

vaccination and antibiotics

Most devices detect CT

• nly

Vibrio cholerae

http://www.crystalinks.com/cholera.jpg

Cholera Microbusters, Inc.

Available Detection Tools

Naturally Specific Antibodies Labeling

Fluorescent markers Gold colloids

Immunoassay with Gold-Colloid Labeling

Courtesy Shalini Gupta, NCSU chemical engineering graduate student

Cholera Microbusters, Inc.

Commercially Available Device

The SMART

Gold-Labeled Antibodies

• Limit of detection 6 million cells

per mL

Portable External Requirements

• Buffer
• Reaction vial
• Eyedroppers
• Swabs

The SMART by New Horizons Diagnostic Corporation (Columbia Maryland, USA)

http://www.nhdiag.com/cholera_bt.shtml

Cholera Microbusters, Inc.

Silver Enhancement Technique

Amplified level of

detection

Implemented on

microfluidic devices recently

No known

environmental or safety hazards

Immunoassay with Gold Labeling and Silver-Enhancement

Courtesy Shalini Gupta, NCSU chemical engineering graduate student

Cholera Microbusters, Inc.

The Microfluidic Advantage

Smaller devices Drastically reduced

reagent volumes

Decreased waste

Examples of previously developed microfluidic devices currently on the market.

Courtesy Dr. Orlin Velev, NCSU chemical engineering professor

Microchannel Prototype RNA Fingerprinting DNA Assays

Cholera Microbusters, Inc.

Device Concept

Sample collection Assay and result Credit-card-sized diagnostic device with reagent and reaction chambers

Cholera Microbusters, Inc.

Device Considerations

Polydimethylsiloxane

(PDMS) Rubber

Elastomer Antibody binding

techniques studied

Ease of microfabrication

Finger-Actuated Micro-

Pump

Sample collector Reagent dispenser

The importance of rounded

• chambers. (Ahn et al. 2004)

Cholera Microbusters, Inc.

Finger-Actuated Micro-Pump Optimization

Purpose

Determine effective

volume

Deliver sufficient volume

Constraints on

Diameter

Large enough to be

easily handled

Small enough to fit on a

microfluidic device

Chamber Wall Chamber Finger-Actuated Micro-Pump

Cholera Microbusters, Inc.

Theoretical Analysis

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + − = 3

2 2 2

r rR R R h Vd π

Chamber Wall Dead Volume Effective Volume Chamber Wall Dead Volume Effective Volume Chamber with Elastic Top and Bottom Chamber with Elastic Top and Rigid Bottom

Cholera Microbusters, Inc.

20 40 60 80 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 Diameter (inches) % Dead Volume

Theoretical Analysis

Percent dead volume decreases as diameter

increases

Not a function of height

Cholera Microbusters, Inc.

Experimental Analysis

Two Scenarios

Sample collector Reagent dispenser

Constructed from Silicone

Rubber

Independent Variables

Diameter Thickness

All numbers in millimeters

Cholera Microbusters, Inc.

0.0% 20.0% 40.0% 60.0% 80.0% 0.3 0.5 0.7 0.9 1.1 Diameter (inches) % Dead Volume 0.0625 inches 0.0313 inches 0.0200 inches

Reagent Dispenser Experimental Data

Percent dead volume decreases as diameter

increases

Not a clear function of height

Height

Cholera Microbusters, Inc.

0.0% 20.0% 40.0% 60.0% 80.0% 0.3 0.5 0.7 0.9 1.1 Diameter (inches) % Dead Volume 0.0625 inches 0.0313 inches 0.0200 inches

Sample Collector Experimental Data

Percent dead volume increases as diameter

increases

Not a clear function of height

Height

Cholera Microbusters, Inc.

Chamber Optimization Results

Sample Collector

1-inch diameter Larger size because of higher percent dead volume

Reagent Dispenser

0.625-inch diameter Smaller size because of lower percent dead volume Smaller amount of reagents

Height

0.0625-inch No effect on dead volume Greater total volume

Cholera Microbusters, Inc.

Channel Sizing Optimization

Guiding Principles

Low fill-up time of about 1 second Manufacturing costs Device size

Method

Extrapolation from experimental data Mechanical energy balance with estimates of frictional

terms (length, expansions, contractions, bends)

Cholera Microbusters, Inc.

Channel Sizing Optimization

1 2 3 4 5 6 0.4 0.6 0.8 1 1.2 1.4 1.6 Channel Width (mm) Fill-up Time (s)

Optimal channel width of 1 mm

Cholera Microbusters, Inc.

Five-Pump Design

All numbers in millimeters

Cholera Microbusters, Inc.

Five-Pump Design

Cholera Microbusters, Inc.

Five-Pump Design

Cholera Microbusters, Inc.

Conclusions

Finger-actuated No external

requirements

Portable Disposable Smaller, simpler

alternative to commercially available options

Cholera Microbusters, Inc.

Future Challenges

Final device selection Build prototype Operating procedure Valve system to prevent backflow Economic analysis

Cholera Microbusters, Inc.

Acknowledgements

• Dr. Orlin Velev’s

research group, for their help and access to laboratory equipment

• Dr. Lisa Bullard, for

her advice and assistance

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