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DEVELOPMENT OF DETECTORS FOR PSEUDO-CHEMICAL WARFARE AGENT FORMAZAN

COMPLEXES

By Conor Rees

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Chemical Warfare Agents • Most modern countries posses stockpiles of weaponized

agents • Increasing threats from extremist countries and groups on the

usage of agents e.g. Al-Qaeda, North Korea • Used as recently as 2013 in the Syrian capital • Counter measures need to be taken • Detectors need to be: Durable, selective, portable, cheap

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Existing Techniques: IMS / MS• Ion Mobility Spectroscopy• Mass spectroscopy • Disadvantages:

• Expensive • Training • Moderately large

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Existing Techniques: Chemical tests • Test papers

• Disadvantages• Easily contaminated• Subject to false positives• Identify by human eye

• Enzymes • Nerve agent immobilized-enzyme alarm detector (NAIAD) • Disadvantages

• Poor shelf life• Bulky • Storage problems

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HGV (Highly selective, Greatly enhanced responses & times, Very easy to use)• Developed by Dr. Ian Fallis Cardiff • Very fast responses • Small and easily portable• Swabs are already in use in airports etc. • Would be easy to integrate

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Need For Project • Colour change in swabs are very intense• However very hard for humans to see slight colour change over time • Swabs do not give an indication if antidote is needed• Detector needed to inform user on impending danger • Do not want to inject antidote if no presence of warfare agent, as can lead

to seizures and other side effects

N. B. Munro, A. P. Watson, K. R. Ambrose, and G.D. Griffin, Environmental Health Perspectives, 1990, 89, 205-215

(on left) Mark I NAAK kit

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Aims of Project • Begin to develop a sensor to detect significant colour

change over time • Detectors need to be:

• Cheap • Portable • Small • Simplistic • Sensitive

• 2 methods approached:• Image analysis program

• Potentially using a smart device (e.g. mobile phone) • Spectroscopic analysis

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Spectroscopic Analysis: Experimental • Construction of spectrometer

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Calibrating Micrometer to Wavelengths • First step to develop the spectroscopic analysis was to

calibrate the micrometer • Achieved through spectroscopic analysis of coloured

filters with specific wavelengths

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Absorbance from Orange 550nm long pass filter

Micrometer position / m-6

Abso

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Absorbance from Green 495nm long pass filter

Micrometer Position / m-6

Abso

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[arb

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Calibrating Micrometer to Wavelengths • From the previous graphs, points of intense absorbance

were found and analyzed to determine the exact wavelength compared to the spectrometer

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05

Orange 550nm long pass Filter

Micrometer position / m-6

Abso

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[arb

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1.15 1.2 1.25 1.3 1.35 1.4 1.45

Absorbance from Green 495nm long pass filter

Micrometer Position / m-6

Abso

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[arb

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Analysis of Formazan Complexes • Calibrated spectrometer was now able to detect

absorbance based on micrometer positions • The next step was to analyze real formazan complexes • While also analyzing the sensitivity of the spectrometer

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Analysis of Formazan Complexes • Absorption becomes difficult to observe past a dilution

factor of 2 as the signal to noise ratio decreases as the dilution factor increases

• Therefore a more sensitive analysis was proposed

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.2

0.4

0.6

0.8

1

1.2

Absorbance from Non diluted formazan complex

Micrometer Position / m-6

Abso

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[arb

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.050.1

0.150.2

0.250.3

0.350.4

0.45

Absorbance from formazan complex at dilu-tion factor 2

Micrometer position / m-6

Abso

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[arb

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y un

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.020.040.060.080.1

0.120.140.160.180.2

Absorbance from formazan complex at dilu-tion factor 4

Micrometer position / m-6

Abso

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[arb

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“Boxed” Analysis • Moves a defined box along light spectrum seen through grating • Gives a higher wavelength resolution by separating wavelengths • This removes light contamination as the box concentrates on a

particular wavelengths

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“Boxed” Analysis• Improves sensitivity of the spectrometer • Very effective in measuring absorbance of complexes • Sensitivity of spectrometer stops at a dilution factor 4

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Non diluted formazan complex

Micrometer Position / m-6

Abso

rban

ce /

[arb

irtar

y un

it]

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

non diluted formazan complex (box analysis)

Micrometer Position / m-6

Abso

rban

ce /

[arb

itrar

y un

it]

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

formazan complex at dilution factor 2 (boxed analysis)

Micrometer position / m-6

Abso

rban

ce /

[arb

itrar

y un

it]

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

formazan complex at dilution factor 2

Micrometer position / m-6

Abso

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ce /

[arb

itrar

y un

it]

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Image Analysis Program • Program utilizes the CCID chip from a camera to analyze colours of

the solutions • Exact wavelengths of the solutions cannot be found from the pixels • Approximate wavelengths are used instead, e.g. red vs non red • An image is loaded to the program where it is converted to an RGB • It is then split into 3 separate image bands of red, green and blue

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Image Analysis Program • From the three split image bands, arrays of pixel values are

created and a histogram created depending on which colour is selected

• Program used “kmeans” clustering to determine the most dominant colours in an image

• A threshold was written in to the clustering to increase the sensitivity

• Program will then inform the user if there is a danger

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Moving Forward • Moving forward with the

spectroscopic analysis:• Using a SQUIGGLE motor • Small LED as light source • Replacing heavy steel components with

plastic • Encasing spectrometer components

with a casing to improve signal to noise ratio

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Moving Forward• Image analysis program:

• Adding a “centroiding” component to the program • Finding LD50 of warfare agent, swab testing this and analyzing • Developing to make more user friendly

• Using both methods in conjunction • Conducting spectroscopic analysis• Using program to identify clusters of light intensity

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Thanks for listening• Any Questions?