11

A multi-channel fiber optic phosphorescent sensor for

monitoring dissolved oxygen M.S. Final Exam

Manasi S. Katragadda

Advisor: Dr. Kevin L. LearCommittee: Dr. Diego Krapf

and Dr. Kenneth Reardon

Department of Electrical and Computer Engineering Colorado State University

February 23, 2009

22

OutlineIntroduction and motivationBackgroundDesign and fabrication of multi-channel source and integration with detection systemMeasurements taken with multi-channel sensor instrumentMonitoring dissolved oxygen using multi-channel sensor instrumentConclusions and future work

33

OutlineIntroduction and motivationBackgroundDesign and fabrication of multi-channel source and integration with the detection systemMeasurements taken with multi-channel sensor instrumentMonitoring dissolved oxygen using multi-channel sensor instrumentConclusions and future work

44

toluene (source: paint solvents, thinners)

trichloroethylene (source: metal degreasing)

dichloroethylene, perchloroethylene (source: dry cleaning products)

vinyl chloride (source: PVC products)

http://www.epa.gov/

ApplicationIn-situ, real-time, simultaneous monitoring of multiple but chemically similar contaminants in ground water, such as

55

OutlineIntroduction and motivation

BackgroundDesign and fabrication of the multi-channel source and integration with the detection systemMeasurements taken with the multi-channel sensor instrumentMonitoring dissolved oxygen using the multi-channel sensor instrumentConclusions and future work

66

Chemical sensing mechanism

470 nm (blue) LED light excites the dye

Optical fiber (optode) tip

Phosphorescence signal (615 nm peak emission) quenched by oxygen

Oxygen sensitive phosphorescent dye [Ru(dpp)3

]2+

E.Coli

cells with enzymes consume diffused dissolved oxygen to metabolize analyte

oxygen

GROUND WATER

analyte

(e.g. toluene)

Monitoring contaminants with genetically engineered enzymes via indirect monitoring of DO in water

77

Absorption and emission spectrum of [Ru(dpp)3

]2+

Reproduced from Gao

et. al, Biotech. and Bioengr. 86, 425-433 (2004)

Absorption peak at ~470 nm Emission peak at ~620 nm

88

Transduction mechanisms in the multi-channel sensor

Phosphorescence detection by PMT

Analog to Digital conversion

Phosphorescence Amplification

by TIA

Data collection of digital signal

Voltage output

Phosphorescence optical power emission (620 nm)

Current output

Phosphorescence excitation by light source (470 nm LED)

Transducer Ru complex

Phosphorescence quenching by diffused O2

99

Multi-channel sensor architecture

A multiple source-single detector system based on time-division multiplexing

1010

Other options for channel switching

Configuration #1: A switched system

Fiber-optic switch

Source

Detector

O ptodesSource

Detector

Source

Detector

O ptodes

Commercial plastic fiber optic switches: highly expensive, approx. five thousand dollars)

Glass fiber optic switches that have been used for telecommunication purposes available readily commercially

11

Configuration #2: A single source-single detector replicated option

Multiple detectors are highly expensive

12

Time-division multiplexing for monitoring multiple optodes

12

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6Channel 7

Channel 8

Time (ms)

Voltage (V)

Phosphorescence signal

LED excitation pulse

13

Trace of the superposition of phosphorescence signals at the PMT

13

Time

Anal

og C

hann

el 0

Vol

tage

(V)

Channel 1 Channel 2Channel 3

Channel 4Channel 5

Channel 6

Channel 7

Channel 8

Phosphorescence signal (V)

Time

Anal

og C

hann

el 0

Vol

tage

(V)

Channel 1 Channel 2Channel 3

Channel 4Channel 5

Channel 6

Channel 7

Channel 8

Phosphorescence signal (V)

1414

OutlineIntroduction and motivationBackgroundDesign and fabrication of multi-channel source and integration with detection systemMeasurements taken with multi-channel sensor instrumentMonitoring dissolved oxygen using multi-channel sensor instrumentConclusions and future work

15

Design and fabrication of the multi- channel sensor

15

Multi-channel sensor

Acquisition Software written in LabVIEW

Instrument

Excitation sourcesystem

Detection system

1616

Internal schematic of the multi-channel instrument

C O M P U TE R

A/D

MUXCIRCUIT

LEDs 1-8

450/60 nm band pass filter 2× 2 50:50 fiber-optics Coupler/ splitter

PMTTIA

Light dump box

Optodes 1-8

POF

Detection systemSource system

DAQ

1717

Circuit schematic of the excitation source

1818

The excitation source: Top & Front view

S T c onne cto rs fo r op to des

C us tom f i lter H older w ith 450 /60 m fi lter

F ib er-opt ic coup le rs

L ight du m p box

D C P ow e r con nector ja ck LE D sou rce s

cir cui t ry b oard

E u ro sty le term in al st rip

D A Q (m oun te d below th e circ ui try boa rd ) P las tic

op tical f ib ers

1919

The detection system: Top & front viewFiber holder for coupling fibers into PMT

PMT Voltage output

Photomultiplier tube (PMT) module

620/100 nm filter

TIA electronics

PMT Voltage outputdisplay

2020

Front panel of multi-channel LabVIEW

vi

2121

Electronic channel switchingOur approach

o Electronic switching & no moving partso Economical as costs only one-half as much as a switched

system

A software program was written in LabVIEW as interface with the DAQ

o Multiplex and demultiplex signals to and from the PMT o Take traces of phosphorescence (V) versus time for every

channelo

Save data at the time of collection o Collect dark voltage after each cycle of measurement

2222

Outline

Introduction and motivationBackgroundDesign and fabrication of multi-channel source and integration with detection systemMeasurements taken with multi-channel sensor instrumentMonitoring dissolved oxygen using the multi-channel sensor instrumentConclusions and future work

23

LED power drop measurements

Analog inputDAQ

Analog gnd1M VR9V

Power supply(Radioshack)

Channels 1-8

Average power of the LEDs was studied for a few random channels with the ST connectorized photodiode (PDB 504-ST)

24

Results indicate a 4-5 minute warm up time

25

Summary of data taken for LED average power drop and noise

Case #

% drop in LED photo voltage

Vpp (mV)

LED dwell time (ms)

Power supply

LED location

Drive current (mA)

Supply voltage (DC)

Resistor (ohm) ICs

Long Electri cal connection

Shielded against EMI

1 4.46 1 100 radio shack

in multi-channel sensor 28.6 5 V 1M present no yes

4.47 1 500

4.57 1 1000

2 4.6 1 100 radio shack

in multi-channel sensor 28.6 5 V 1M absent no yes

3 0.9 1 100 radio shack

in multi-channel sensor 9.9 5 V 1M present no yes

4 5.75 1 100 radio shack

in multi-channel sensor

not measured<28.6 7.5 V 1M absent no yes

5 4 20 100 HP 6216A

in multi-channel sensor ~28.6 5 V 1M present no yes

26

5 4 20 100 HP 6216A

in multi-channel sensor ~28.6 5 V 1M present no yes

4 20 500

3.2 20 1000

6 0.22 1 100 battery external 9.6 9 V 100k present no yes

0.36 1 500

0.295 1 1000

27

Conclusions from the experiment LED drive current directly proportional to percent drop in LED powerPresence/absence of other variables had no effect on the percent drop in LED power Minimal noise amplitude of 1mV in photovoltage was observed due to minimum resolution of DAQPresence/absence of variables had no effect on 1 mV noise amplitude

28

Effect of duration of turn-off times on LED power drop

Smaller the turn-off time, smaller the power drop

0.695

0.697

0.699

0.701

0.703

0.705

0.707

0.709

0.711

0.713

0 50 100 150 200 250 300

Cha

nnel

5 L

ED

pho

tovo

ltage

(V

)

Elapsed time (s)

10s turn off time30s turn off time

29

Monitoring long-term stability of LED power

Measurement taken over 15 hours Stable, with negligible fluctuations of 0.3%

between 100-700 minutes

3030

Analysis of source insertion loss channel by channel

Insertion loss (dB) = 10 * log 10 (Launched photocurrent / Received photocurrent)

Results: Insertion loss varied from 14.5 dB to 18.5 dB for the channels

Multimeter

Case-2Multimeter

Measuring launched photocurrent

Measuring received photocurrent

3131

Detector insertion lossInsertion loss (dB) = 10 * log 10 (Optical power launched into the channel from the front panel / Optical power received by PMT)

where optical power launched into the channel from the front panel = photocurrent (nA) from fiber coupled red LED measured by photodiode / responsivity of PD @645 nm (A/W)

optical power actually received by PMT= TIA Voltage (V) measured from the front panel/ effective response of TIA & PMT

and effective response of TIA & PMT= (TIA gain of 120 kV/A) * (PMT responsivity of 2* 107 mA/W at 645nm)

Results: Insertion loss measured to be between 11 dB to 14.9 dB

3232

Summary of insertion loss measurements

CHANNEL 1 CHANNEL 2 CHANNEL 3 CHANNEL 4 CHANNEL 5 CHANNEL 6 CHANNEL 7 CHANNEL 8

17.79±.. 0.24

16.36 ± 0.34

17.34 ± 0.05

18.42 ± 0.23

18.53 ±1.32

14.54 ± 0.05

18.8 ± 0.09

17.5 ± 0.1

14.07 ± 0.16

13.79 ± .09

14.18 ± .03

14.54 ± 0.06

12.02 ± 0.04

14.88 ± 0

11.62 ± .04

11 ± 0.12

Detector insertion loss[Avg

(dB) ±

Stdev

(dB)] Source insertion loss [Avg

(dB) ±

Stdev

(dB)]

Source insertion loss: ~4 dB difference between strongest and weakest channelDet. insertion loss:~4.5 dB difference between strongest and weakest channel

3333

Studying optodes

to determine if they are the cause of non-repeatibility

ST connectors on front panel of McFOFI source

ST-ST 1mpatchcords

Water continuously bubbled withcompressed air

Optodein air

Channels 1-8

O #4

O #8 O #1 O #7

O #2 O #5 O #3 O #6

O=optode

1,2,3,4= optodes prepared in August and September2008

5,6,7,8= optodes freshlyprepared on Dec 162008

Channels 1-8 turned on, LED dwell time=3s

3434

Observation: All optodes drop by approximately 0.3 V.

Can be concluded that these fluctuations were due to a common system issue and not due to aging of optodes.

3535

ST connectors on front panel of McFOFI source

Experimental set-up

Optodein air

Channels 1-8

O #4

O #8 O #1 O #7

O #2 O #5

O #6

O=optode

1,2, 4=optodesprepared in August and September2008

5,6,7,8= optodes freshlyprepared on Dec 162008

9V

10K

Channels 1-8 turned on,LED dwell time= 3s

Red LED (640 nm)

Monitoring blue LEDs to check if they are the cause of non-repeatability

3636

Since red LED remains on all the time, it is present in all channels.

It could be possible that fluctuations between 4200-6000s were due to a common system component.

Not understood if the power of the blue LEDs was actually drifting.

3737

Testing of transimpedance

impedance amplifier (TIA) stability

0.83

0.84

0.85

0.86

0.87

0.88

0.89

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Elapsed time (s)

Cha

nnel

1 T

IA o

utpu

t vol

tage

A percentage drop of only 0.2% in the TIA output voltage observed at the end of the two hours. TIA not cause of non-repeatability.

DAQ didn’t cause any fluctuations either.

3838

Monitoring drift in dark voltage of the multi-channel system

Plot of dark voltage output of the multi-channel system measured by the PMT, with a dwell time of 3s

Optode tips wrapped in aluminum foil

Optode tips wrapped in black plastic

Dark voltage a significant source of non-repeatibility

3939

Studying attenuation in a ST-ST POF patchcord

  Channel 1 (V) 

Channel 2 (V) 

Channel 3 (V) 

Channel 4 (V) 

Channel 5 (V) 

Channel 6 (V) 

Channel 7 (V) 

Channel 8 (V) 

With 1m ST‐ST Patchcord  

0.48  0.46 0.44 0.44 0.39 0.39 0.39 0.31

Without 1m ST‐ST Patchcord  

0.84  1.04 1.01 0.93 0.85 0.90 0.86 0.95

Conclusion: Phosphorescence signal (no 1m patchcord

connected to optode) was two to three times larger than phosphorescence when a 1m patchcord

was connected to optode

40

Measurement of system crosstalk

Channels 1-8

Optodein air

Crosstalk for channels: -8.4 dB to -12 dB.

Cross talk not symmetric.

Crosstalk= 10* log (Undesired signal from neighboring channel/desired signal)

41

Measurement of Uniformity

Uniformity = (1-

RSD) *100%

Uniformity calculated to be 89.4%.

Uniformity = [(Min+Max)/2] ±

difference

where difference= Max-

[(Min+Max)/2] =[(Min+Max)/2] –

Min

Uniformity= 0.987 V ±

0.274 V

4242

Outline

Introduction and motivationBackgroundDesign and fabrication of multi-channel source and integration with the detection systemMeasurements taken with multi-channel sensor instrumentMonitoring dissolved oxygen using multi-channel sensor instrumentConclusions and future work

43

Experimental set-up for taking measurements with Cole-Palmer DO meter

Glass Flask

Ru(dpp) 3

OptodeHot Plate and stirrer

Dissolved oxygen meter Cole - Parmer

Model # 001971

Nitrogen/air outlet

Excitation source

Detection system

Dissolved oxygen

electrode

Nitrogen/air inlet

Water

To computer

Glass Flask

Ru(dpp) 3

OptodeHot Plate and stirrer

Dissolved oxygen meter Cole - Parmer

Model # 001971

Nitrogen/air outlet

Excitation source

Detection system

Dissolved oxygen

electrode

Nitrogen/air inlet

Water

4444

Measurement Set 1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 1 2 3 4 5 6 7 8 9 10

Dissolved oxygen (ppm)

Phos

phor

esce

nce

sign

al (V

)

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

Channel 8

45

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5 6 7 8 9 10

Dissolved oxygen (ppm)

Phos

phor

esce

nce

sign

al (V

)

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

Channel 8

Measurement

Set 2

46Modified from http://www.artisan-scientific.com

DO display

DI Water

Optode Air inlet

Nitrogen inlet

Multi-channel phosphorescent sensor system

Experimental set-up for taking measurements with BioFLO-III DO meter

47

Measurement Set-3

0.21

0.23

0.25

0.27

0.29

0.31

0.33

0 2 4 6 8 10Dissolved oxygen (ppm)

Phos

phor

esce

nce

signa

l (V

)

Channel 1 (V)Channel 5 (V)Channel 6 (V)Channel 8 (V)

48

Front panel connections to multichannel source

No optode;black capon STconnector

Channels 1-8

Water in the fermentor reaction chamber

Optodes in air

Beaker with water

Inlet for mixed gas

Source system

Optodes with 1 m ST-ST patch cords

Optodes with 1 m ST-ST patch cords absent

Covered tightly with black plastic

Covered tightly with a black shroud

No optode;black capon STconnector

Channels 1-8

Water in the fermentor reaction chamber

Optodes in air

Beaker with water

Inlet for mixed gas

Source system

Optodes with 1 m ST-ST patch cords

Optodes with 1 m ST-ST patch cords absent

Covered tightly with black plastic

Covered tightly with a black shroud

49

Data obtained after shielding experimental apparatus, Set-4

y = -0.0208x + 0.6352R2 = 0.9473

y = -0.025x + 0.592

y = -0.0197x + 0.4939R2 = 0.9511

R2 = 0.9265

0.310

0.360

0.410

0.460

0.510

0.560

0.610

0.660

0 1 2 3 4 5 6 7 8 9 10

Dissolved oxygen (ppm)

Phos

phor

esce

nce

sign

al (V

)

Channel 2Channel 3Channel 4Linear (Channel 2)Linear (Channel 3)Linear (Channel 4)

Sensitivity approx. 0.02 V/ppm

Limit of detection measured to be 2 ppm

50

Experimental set-up for taking measurements with YSI 5100 DO meter

Hot plate stirrer

Air inlet

Nitrogen inlet

Deionized

water

Multichannel phosphorescent sensor system

Optode

Dissolved oxygen Meter (YSI 5100)

Dissolved oxygen probe

51

0.150

0.170

0.190

0.210

0.230

0.250

0.270

0.290

0.310

0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000 9.000 10.000

Oxygen concentration (ppm)

Phos

phor

esce

nce

sign

al (V

)

Channel 2 Channel 3 Channel 4

Data points had R2=0.3 to 0.7. Not completely linear as expected

Data obtained with the YSI meter, Set-5

5252

OutlineIntroduction and motivationBackgroundDesign and fabrication of the multi-channel source and integration with the detection systemMeasurements taken with the multi-channel sensor instrumentMonitoring dissolved oxygen using the multi-channel sensor instrumentConclusions and future work

5353

ConclusionsA multi-channel fiber optic sensor for dissolved oxygen monitoring was fabricated and tested

Cost –effective electronic time division multiplexing technique was used instead of fiber optic switches

Future Application: Ground water quality monitoring

Parameters like cross talk, uniformity, sensitivity, LOD were investigated

LOD: 2 ppmSensitivity: 0.02 V/ppm

Source insertion loss: between 14.5 dB to 18.8 dB Detector insertion loss: between 11 dB to 14.9 dB

System crosstalk: -8.4 dB to -12 dB

5454

Future workContinuous monitoring of oxygen over long period is suggested with multiple optodes and calculation of parameters like LOD, sensitivity

Limited literature on these aspects: only single optodes discussed

Optoelectronic system modeling and simulation

Optodes integrated with biosensors in the future

5555

AcknowledgementsThanks to

o

Dr. Kevin Lear o

Students, Optoelectronics Group, ECE Sean Pieper, Weina Wang, Rashid Safaisini, Rongjin Yan, Bob Pownall, Santano Mestas, Wesley

o

Dr. Diego Krapf, ECEo

Bob Adame, Physics

o

Dr. Ken Reardon, Dr. David Dandy, CBEo

Zhong

Zhong, Tara Schumacher, Tim Gonzalez,

Prafulla

Shede, CBE

56

Thanks……..

56