Quantum cascade laser spectrometer for trace-gas detection of exhaled Carbonyl Sulfide Gerard Wysocki, Stephen So, Matt McCurdy, Chad Roller, Damien Weidmann, Anatoliy A. Kosterev, J. Patrick Frantz, Robert F. Curl, and Frank K. Tittel Rice University, 6100 Main Street, Houston, TX, 77005, USA
http://www.ece.rice.edu/lasersci
QCL Sensor Wavelength Calibration
Motivation
1000 spectra averaged acquired within t = 4 s and fitted to 300 ppb OCS reference spectrum
S.M. Studer et.al.,“Patterns and Significance of Exhaled-Breath Biomarkers in Lung Transplant Recipients with Acute Allograf Rejection”, J. of Heart and Lung Transplant, 20(11), 1158 (2001)
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As well as in patients with liver disease S.S. Sehnert et.al., “Breath biomarkers for detection of human liver diseases: preliminary study”, Biomarkers, 7(2), 174 (2002)
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Application of quantum-cascade (QC) lasers allows the design of a compact sensitive, and selective trace-gas sensor
•
Goal: non-invasive rapid, in situ detection of trace-gases in exhaled human breath
-0.10 0
• • •
Absorption (sample)
-1 0.00 -0.05 100
200 300 points
400
Pulse repetition rate: 125 kHz Subthreshold current saw-tooth signal: Imax= 35 mA; t = 3.2 ms Range of a single frequency scan : ~ 0.3 cm-1
Data points Polynomial fit
-0.05
⎡ ⎤ ∆ν ⎥ δA ≈ σ ⎢ 2 ⎢ ∫ g (ν )dν ⎥ ⎣ ⎦
-3
tg(α) = 0.174 C OCS= 52.2 ppb
-3
2x10
-0.10
0 -2
0
-0.15
1x10
2x10
-2
3x10
-2
-3
Polynomial fit: -4 -7 2 Y = - 4.7 x 10 * X - 6.05 x 10 *X
-0.30
50
100
150
200
250
300
350
400
δA A
⋅ 52.2 ppb ≈ 0.27 ppb
4x10
∆ν - average data point spacing g(ν) – reference spectra recorded for 300ppb normalized by:
-3
2x10
1x10
-3
∫ g (ν )dν = 1
-4
σ = 2.52 x 10
0 -1x10
A - area under the spectral line
-3
2057.5
2057.6
2057.7
2057.8
-1
Wavenumber [cm ]
QC laser power optimization
= 2.2 × 10 −6
-3
0
0
Points
OCS Sensor Architecture
C (1σ ) =
52.2 ppb OCS + N2 @ 60 torr
6x10
12
Theoretical detection limit:
-2
4x10
Absorption (reference 300 ppb OCS) -3
8x10
-0.20 -0.25
• Compact for clinical/hospital use • Dimensions: 5.35 in x 3.00 in x 1.50 in • Ethernet, Serial, JTAG access for control and read out • Flash memory for long term storage • PC independent operation • Up to 12.5 MSPS 12-bit ADC
Standard error in the best-fit coefficient1:
4x10
Absorption
Elevated COS concentrations in exhaled breath have been reported in lung transplants recipients suffering from acute rejection
0.00
Measured data points Linear fit
-3
6x10
Fit residual
•
0.10 0.05
DSP System Controller Card
yi = A ⋅ g (ν i )
-3
8x10
Calibration curve
Etalon fringe pattern
Nitric Oxide (NO): Inflammatory and immune responses (e.g. asthma) and vascular smooth muscle response (6-100 ppb) Ethylene (H2C=CH2): Oxidative stress, cancer Carbon Monoxide (CO): Smoking response, CO poisoning, vascular smooth muscle response (400-3000 ppb)
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Relative wavenumber [cm ]
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May 16 – 21, 2004
Detection Sensitivity of QCL sensor
fast frequency scan
Breath analysis is a non invasive way of human disease detection e.g.: detector signal [a.u.]
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San Francisco, California, USA
1
A.A. Kosterev et al., Applied Optics, Vol. 40, No.30, p. 5522
OCS Concentration Calibration of QCL Sensor
DSP Fast Data Acquisition Architecture
60 cm
Multipass Cell PM
PC
20
-3
-2x10
0.2
2057.5
-19
6.0x10
-19
4.0x10
-19
2.0x10
0.0 2020
2040
2060
2080
2100 -1
O CS 150 ppb CO2 5 %
2 0 5 7 .0
Absorption
P 24
P 46
2 0 5 7 .5
2 0 5 8 .0 -1
W a v e n u m b e r [c m ]
2 0 5 8 .5
2
Sample Reference
0
200
300
400
100
200
Subthreshold current 20
0
5x10
-3
2x10
400
500
250
Subthreshold Current
300
30 0
10
0
20
30
250 ppb
200 ppb
150 ppb
40
Reference Cell Control / Ready
Signal Conditioner
80
100
200
300
400
COCS= 8.4 ppb
2057.5
500
2057.6
-1
2057.7
Wavenumber [cm ] 1x10
-2
5x10
-3
CO2 in patient's breath Fit by the refernce spectrum of 5% CO2
-3
-3
SPI
ADC
120
Measurement No.
Signal Conditioner
SH B
SCI
Sample was taken from lung transplant patient suffering from bronchiolitis* Sampling was performed using chemically inert 1 liter tedlar sampling bags and analyzed within 2 hours after collection Spectrum was measured at a total pressure of 60 torr
100
200
300
400
500
Points
• Spectral noise level is inversely proportional to laser power • Modulation of laser bias produce fluctuations of laser power which limits the effective range of frequency scans • Effect is reduced by amplitude modulation of laser current pulses
CCO = 5.1 % 2
* The authors wish to thank Dr. Remzi Bag and Carolyn M. Paraguaya from Baylor College of Medicine, Houston, TX for supplying breath samples
0 2055.8
2055.9
-1
Wavenumber [cm ]
2056.0
Reference Detector Delay A
Sample Detector
SPI Interface
100 spectra averaged acquired within t = 0.4 s and fitted to 300 ppb OCS reference spectrum
OCS 50 ppb @ 60 torr 0
SH A
F2812 DSP
DAC
40
Signal Conditioner
300 ppb
OCS in patient's breath Fit by the reference spectrum of 50 ppb OCS
0
0
-5x10
300
200
50
OCS and CO2 Concentration Measurements in Exhaled Breath
Points
OCS 50 ppb @ 60 torr
150
1x10 1
500
0
100
1000 spectra averaged acquired within t = 4 s and fitted to 300 ppb OCS reference spectrum
3
0 100
50
-3
Points
-3
0
2
0
Points
2 0 5 6 .5
1
40
Subthreshold current 20
0
0 .0
3
40
0
Data points Linear fit
50
300 250 200 150 100 50 0
Optics
Reference Cell
SCI Interface
Thermoelectric Cooler
1
-3
2057.8
100
Laser peak power [a.u.]
Sample Reference
5x10
2057.7
1/cm
0 0
2
-5x10
P 10
-2
P 49
1.0x1 0
P 11
-2
P 26
-2
2.0x1 0
P 12
3.0x1 0
P 48
4.0x1 0
-2
P 13
-2
P 14
A b s o r b tio n
wavenumber [cm ]
5.0x1 0
2057.8
3
Detector signal [V]
R - branch
[mA]
-1
-2
Line strength [cm /molec. cm ]
-18
1.0x10
2057.6
Reference concentration [ppb]
QCL Pulse Amplitude Modulation
Line intensity: 7.49·10-19 cm-1/molecule⋅cm-2 Minimal spectral interference by nearby CO2 and H2O absorption lines Availability of a CO2 line within the fast tuning range of the QCL for ventilation monitoring simultaneously with an OCS measurement
-18
P - branch
2057.7 -1
1.2x10
-19
2057.6
2057.5
QCL
Pulse trigger
0.00
150
QCL Pulser
Delay B
wavenumber [cm ]
OCS ro-vibrational Spectrum
8.0x10
0.4
10 5
RB – reference beam M – mirror BS – beam splitter PM – off-axis parabolic mirror
QCL – quantum cascade laser chip LH - laser housing CL – collimating lens SB – sample beam
0.6 15
Scattering of the concentration measurement: σ = 1.2 ppb
100 ppb
-3
2x10
0
DAQ CARD NI 6024E
PCMCIA
0.8
200
300 ppb 200 ppb 100 ppb 50 ppb 30 ppb
0.02
75 ppb
25
250
50 ppb
4x10
0.27 ppb ⋅ 1000 100 = 0.85 ppb
0.04
300
40 ppb
-3
t
FUNCTION GENERATOR
Laser line width: FWHM: ~0.04 cm-1
OCS P(11) pressure =1.2 torr COCS ≈ 1.6 ppm
6x10
[mA]
TRIGGER PULSE GENERATOR
SAMPLE
t REFERENCE
PULSE AMPLITUDE CONTROL
REFERENCE SAMPLE
Absorption
GATE GENERATOR
APEAK/σNOISE
absorption
-3
TRACK & HOLD’s
t
PULSED QCL DRIVER
Theoretical sensitivity:
30 ppb
-3
8x10
MCT DETECTOR
absorption
M M
Absorption
CL
Absorption
QCL
Measured concentration [ppb]
-2
1x10
BS LH
Calibration curve
laser peak power [a.u.]: 2.5 1.5 0.75
Concentration [ppb]
M
RB
FWHMOCS/FWHMQCL
SB
Detector signal [V]
MULTIPASS HERRIOTT CELL
Pulse Trigger
Serial Port Transceiver
PC Workstation
Signal Conditioner
Analog Delay Generator
Conclusions • Sensitivity of current QC laser based OCS sensor is at the ~ 1.2 ppb level • Sensor has capability of simultaneous COS and CO2 concentration measurements • Conversion to autonomous, compact, high speed processing and control electronics demonstrated • Studies to date of exhaled breath in lung transplant recipients show low OCS content which suggests the following: Further increase of sensor sensitivity Develop chemical “amplification” methodology Further optimization of breath collection technique
