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Optical Sensors and Biomedical Applications
Nilesh J. VasaDepartment of Engineering Design, IIT Madras
njvasa@iitm ac [email protected]
इंजीिनयिरग
िडजाइन
Optical sensorsWhy the interest in optical sensors:High sensitivityS ll iSmall sizeMostly non-invasiveLarge bandwidthLarge bandwidthDistributed / multiplexed sensingRemote sensinggCompatibility with fiber-optic telemetryLow power, weightEt tEtc. etc.
LimitationCost (?)Cost (?)
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Amplitude / intensity based sensors
s,a
I0 I1 I0 e-a l=
l s = Absorption cross sectiona = Absorption coefficientp
= sNN = Number density
Laser
Sample cell
DetectorL
Single pass absorption
Transmittivity = I0 / I1Abosrbance = ln(I / I )Abosrbance = ln(I0 / I1)
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Spectral characteristics of CO2, CH4 and C2H2gases in terms of line intensity based on the HITRAN08 database at 100 kPa and 298 K
Michael E. Webber, Douglas S. Baer, and Ronald K. Hanson, (2001), “Ammonia monitoring near 1.5 m with diode-laser absorptionsensors”, Journal of Applied Optics, Volume 40, pp.31-42. 4
Multi-pass absorption spectroscopy technique for improving detection limit
LaserSample cell d
p g
DetectorMulti pass absorption
RSample cell
Laser
R R
(1 )
d
empty c RDetector
Laser
Intra cavity absorptionMirror Mirror
(1 )
(1 ( ) )
c Rd
c R N dIntra-cavity absorption
SampleR RTransientdigitizer
1 1 1( )
N
c empty
Detector
Laser
p ( ) empty
N = Concentration (number/cm3)L
Cavity-ringdown absorption()= Absorption cross section (cm2)c = speed of light in medium
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VOC Biomarker disease Healthy humans
Acetone ((CH3)2CO)
Diabetes, lung cancer 0.4 – 0.9 ppmBreath analysis using tunable diode laser
((CH3)2CO) Ammonia
(NH3)Kidney disease, asthma 0.3 – 2.9 ppm
Ethane (C2H6) asthma, lipid peroxidation, l d ti
Up to12 ppbLaserDetector
sceloderma, cystic fibrosis vitamin E
deficiency1-Butanol Adenocarcinoma,
Squamous cell> 14.0 ng/l –
30.3 ng/l
Breath sample
Squamous cell carcinoma
30.3 ng/l
3-Hydroxy 2-butanone
Adenocarcinoma, Squamous cell
carcinoma
> 6.2 ng/l –50.3 ng/lComputer
Acetaldehyde Alcoholism, lung cancer Up to 140 ppb
Methane (CH4) colonic fermentation and intestinal problems
3 – 8 ppm
Spectrum
Hexane tuberculosis, liverdisesase
Nitric oxide (NO)
Asthma, NO breath test to
10-50 ppb
Courtsey: Manfred Mürtz ([email protected]) is with theInstitute for Laser Medicine at the University of Düsseldorf, Germany.His current research topic is high-precision infrared laser spectroscopyand its applications in the life sciences. (NO) test to
monitor inflammation in asthma
Nitrous oxide (N2O)
1-20 ppb
C b O id ti t 1 10Carbon monoxide (CO)
Oxidative stress, respiratory infection,
anaemias
1-10 ppm
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Pulse oxymetry
Oxygen dissociation curveOxygen dissociation curve
Partial pressure of oxygen (kPa)
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Hemoglobin extinction curvesg
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Pulse oxymetry: working principle
HbO2Oxygen saturation = [HbO ] [Hb]2 [ ] [ ]2
ac 660 / dc 660Due to red absorbance
ac 660 / dc 660ac 940 / dc 940
RDue to IR absorbance 9
Phase based measurementsInterferometry techniques and their applications
Michelson Application: Plasma diagnostics, specie identification optical coherent
Interferometry techniques and their applications
specie identification, optical coherent tomography
Mach-Zehnder Specie identification, plasma diagnostics
Application: Gyroscopic measurementsSagnac
pp y p
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Two-beam interference( ) ( )E E E E k t E k t
1 2 01 1 02 2
221 2
cos( ) cos( )1 12 2
total
total total
E E E E kz t E kz t
I E E E
1/ 21 2 1 2 1 2
2 21 2( ) cos( )2
I I I I kz kz
1/ 2max 1 2 1 2
21 2( )2
I I I I I
1/ 2min 1 2 1 2
1 2( )2
I I I I I
max min
max min
Fringe visibility = V =
Wh
I II I
d f l i i liI I IWh
1 2
1 2
en , and perfect polarization alignment1 2 2 cos( )2total
I I I
I I I kz kz
1 2
max min
22 , 0 1
total
I I I V 11
Coherence length
Coherence length: Lc = λ2/(n∆λ ) λ is the central wavelength of the source, s t e ce t a a e e gt o t e sou ce,n is the refractive index of the medium, and ∆λ is the spectral width of the source 12
Optical coherence tomography (OCT)
Coherence length: ∆L = λ2/(n∆λ )
Sample
λ is the central wavelength of the source, n is the refractive index of the medium, and ∆λ is the spectral width of the source
Michelson interferometer
Interferometry uses a series of superimposed electromagnetic waves to gain insights regarding the waves. 13
Diagnostic imaging technique based on back-reflection of low-coherence radiation Non contact, non-invasive Real-time cross-sectional analysis Real time cross sectional analysis Micron resolution in situ
C ti• Continuous sources- Super luminescent/ super fluorescent fibers
center wavelength- center wavelength 800 nm(SLD), 1300 nm(SLD, LED) Power: 1 to 10 mWPower: 1 to 10 mW
- coherence length 10 to 15 μm
• Pulsed lasers- Ti:Al2O3 (800 nm), <3 m resolution
t idth l th ti- tune narrow-width wavelength over entire spectrum 14
Penetration depth and resolutionp
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Timed domain-OCT
• A two-dimensional cross-sectional imaging is acquired by performing successive rapid axial measurements of optical backscattering or back reflection profiles at different transverse positionsreflection profiles at different transverse positions •The result is a two-dimensional data set which represents the backscattering in a cross-sectional plane of the tissue
161. “Optical coherence tomography- principles and applications”, A. F. Fercher, W. Drexler, C. K. Hitzenberger and T.
Lasser, Reports on Progress in Physics, Vol 66, pp. 239-303, 2003.
Frequency domain-OCTFrequency domain OCT• Medical:
– Ophthalmology (flagship of Biomedical OCT)Biomedical OCT)
– Gastroenterology – Dermatology
Endoscopic OCT in intra– Endoscopic OCT in intra-arterial imaging
– Dentistry
• Non-Medical: – Nondestructive evaluation of
highly scattering polymer-highly scattering polymermatrix composites to estimate residual porosity, fibre architecture and structural i t itintegrity
– Nondestructive evaluation of paints and coatingsOptical profilometer– Optical profilometer
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Patient with impaired vision:at e t t pa ed s oThe cause is a macular hole
Patientʼs othe e e isionPatientʼs other eye vision:Impending macular hole, which can be treatedwhich can be treated
http://rleweb.mit.edu/Publications/currents/cur11-2/11-2oct.htm 19
Commercial OCT versus Ultra-high-resolution-OCTresolution OCT
mm
m
W Drexler et al “Ultrahigh resolution ophthalmic optical coherence tomography”W. Drexler et al., Ultrahigh-resolution ophthalmic optical coherence tomography , Nature Medicine 7, 502-507 (2001)
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INTRODUCTION
Application of OCT: Dental cariesINTRODUCTION
• Dental caries – most prevalent oral disease• The mineral equilibrium of the tooth affected• Early diagnosis helps in arresting caries• Early diagnosis helps in arresting caries
progression and non-invasive reversal of caries
DENTAL CARIES• Enamel outermost layer of tooth• Dietary habits change the pH around enamel
E l i b f– Early caries - subsurface mineral loss
– Secondary caries –voids/gaps below cavity g p yrestoration
Micro leakageSecondary cariesEarly caries
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Dental caries: Imaging
B-scans recorded up to a depth of 2 mm indepth of 2 mm in extracted tooth samples
Dark spots seen at a depth of 105 μm from the surface of the toothsurface of the tooth
Unfilled resin filling22
Artificial demineralisation, 840 nm OCT images of tooth surfaces
Before demineralisation
after artificial demineralisation with pH 4.8 for
12 h
24 h
36 h36 h
48 h
60 h
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Dental Restoration: ImagingRestofill composite filling imaged with 1310 nm OCT with two different fillingRestofill composite filling imaged with 1310 nm OCT with two different filling procedures
(a) etch, bond and fill
(b) bond and fill
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Swept-Source OCT:
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Differential absorption based OCT
ScatteringScattering
( ) ( )ln ln ln I Ir ON o ONS d S d dOCT ON OCT OFF a s
ln , ln , ln( ) ( )
S d S d dOCT ON OCT OFF a sI Ir OFF o OFF
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Elemental analysis of species using laser induced breakdown spectroscopy techniquebreakdown spectroscopy technique
[1] pulsed laser beam is focused onto the surface
[2] Radiation
[3] the material starts to evaporate
[2] Radiation energy is locally coupled into the material
[4] Within this material vapor and the surrounding gas atmosphere a plasma is p pgenerated
H: Region of energy deposition P: Plasma
[7] Crater is formed[5] leading to the excitation of the material constituents and
E: element specific emission[6] their spontaneous emission of radiation. [7] The plasma decays and emits element specific radiation
Ref: Reinhard Noll, Laser-Induced Breakdown Spectroscopy: Fundamentals and Applications, Chapter 2, pg-8, c Springer-Verlag Berlin Heidelberg 2012 27
emits element-specific radiation
Plasma Emission Spectra in LIBS
continuous spectrum caused by free-free transition
Plasma cooled down and intensity of Emission lineyincreases
Decay of plasma temperature and intensity ofemission lines
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FeaturesThe following features set the LIBS apart from the pre-existing methods for evaluation:•Non-destructive Nature
– Essentially, non-destructive (20-200 ng ablation)•Independent of material properties•Entirely an optical technique only a visual access of the sample is required•Entirely an optical technique, only a visual access of the sample is required
– Non-invasive•No need to prepare the sample for analysis
The following features set the LIBS apart from the pre-existing methods for evaluation:•Analysis of Alloy and Metallurgical Applications•Environmental Applications•Archaeology and Art•Archaeology and Art•Pharmaceutical Applications•Forensics
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Laser Induced Breakdown Spectroscopy StudiesStudies
Experimental Setup- Laser induced breakdownt (LIBS) bi d ith t l dspectroscopy (LIBS) combined with temporal and
spatial measurements.
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ApplicationsApplications• In Archaeology and Cultural Heritage
– Portability of LIBSNeed not be in contact with sample for analysing– Need not be in contact with sample for analysing
• In Biomedical applications– Composition of tissuesp– To detect excess or deficiency of minerals in tissue,
teeth, nails, or bonesI i d i• In industries– Metallurgical
• Alloy composition• Alloy composition– Radiology– Geological and extraterrestrial Samplesg p
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Forensic analysisLIBS when used in conjunction with refractive index (RI),provided high (>90%) discriminating power for several
l t i l di b l t bilglass types, including beverage glass, automobileheadlamp glass, and float glass from automobile side andrear windows LIBS and RI exhibited a lower discriminatingrear windows. LIBS and RI exhibited a lower discriminatingpower for automobile side-mirror glass, a glass typecommonly found in forensic casework.Single pulse LIBS, used in conjunction with RI, can provide an inexpensive screening for forensic glass samples and may also have utility in other trace analyses.
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• Spontaneous process
Spontaneous Raman Spectroscopy Technique for gas sensing
• Spontaneous process
• Scattered photon into arbitrary direction
• Anti‐stokes lines much weaker
• Weak interaction process (scattering≈ 30 2)10‐30 cm2)
• Two photon process: allows study of molecular vibrations which are not infrared‐active
Advantages:Advantages:• any type of laser source can be employed• the signal of virtually all the species present within the probe volume inside the gas chamber
can be determined
Disadvantages:• multi‐dimensional measurement is not possible • single‐shot accuracy is relatively low
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Breath analysis using a differential ion mobility sensory g y
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is electric field dependency of ion mobility
and K0 is low field mobility constant. Different ions have different alpha characteristics and ion-mobilities
UV Photo-Ionization lamp (10.6 eV/ Krypton filled/ Heraeus Noblelight PKR-106) with C102RF Excitation system. Volatile organic compound gases with ionization energies less than 10.6eV such as acetone (9.69 eV), ammonia (10.15 eV) and hexane (10.13 eV) are ionized by theUV source.
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(a)
(b)
Differential-IMS Sensor output forDifferential IMS Sensor output for detection of (a) acetone, (b) hexane.
.36
Dual-UV Source Differential Ion Mobility Sensor
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Breath analysis
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Summary1) Intensity / Amplitude based optical sensors
1.1) Absorption spectroscopy based breath analysis) p p py y1.2) Pulse oxymetry
2) Phase based optical sensors) p2.1) Optical coherence tomography
3) UV Photoionization based differential mobility sensor3) UV Photoionization based differential mobility sensor3.1) Detection of volatile organic compounds (VOCs)
Challenges1) Real-time, in-vivo measurements2) Detection of malignant tissues3) Diagnostic and therapeutic applications
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3) Diagnostic and therapeutic applications
LIBS Studies Trace Gas Sensing Pulsed Nd3+:YAG laser base LIBSto determine the elementalcomposition of samples
Current research work is focusedon applications of broadband lightsources such as superluminescentcomposition of samples
irrespective of their states (solid,liquid or gas).Applications: i) Space exploration;
sources such as superluminescentdiode (SLED) in 1.5 m andsupercontinuum light sources in 2m for simultaneous sensing ofpp ) p p ;
ii) Remote LIBS for detecting thecontaminant layer on wind turbineblades; iii) Condition monitoring, such
gmultiple gases.Applications: i) Simultaneousmeasure- ment of NH3 and H2O; ii)
as dissolved Cu in high voltagetransformer oil.
3Bio gas sensing; iii) Particleconcentration measurement
S
Multipass cell
lSuperluminescentDiode (SLED)
Optical spectrumanalyzer
Optical fibercoupling
Acknowledgements• Kyushu University, Japan• Applied Optics Laboratory, IIT Madras, Indiapp p y, ,• Research Scholars of Opto-mechatronics Laboratory
THANK YOUH NK YOU
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Notes: Date: / /
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