In vivo Infrared Spectroscopy

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1 In vivo Infrared Spectroscopy Zhe Xia March 29, 2017

2 Outline Introduction Theory Instrument Case study Conclusion

3 Introduction In vivo: Latin for within the living, In vivo studies focus on the effects of various biological entities are tested on whole, living organisms Why in vivo? It allows observing the overall effects of an experiment on a living subject In vitro studies could yield misleading results eg, drug discovery 1

4 Infrared Spectroscopy (IR): a spectroscopic approach that studies the interaction of infrared radiation with matter. Vibration modes of molecules

5 Theory Molecule vibration Including the oscillation of bond length and angles Absorption of IR light causes molecular vibrations Numbers of vibration mode depend on number of atoms and the symmetry

6 Different bonds requires different amount of energies Wavenumber of peak depends on the bond strength and the mass of atoms ν = 1 2πc k μ Where ν is wavenumber (cm -1 ) c is speed of light k is the force constant of the bond μ is the reduced mass μ = m 1m 2 m 1 +m 2 m is the atomic mass of atoms

7 Different bonds requires different amount of energies Wavenumber of peak depends on the bond strength and the mass of atoms ν = 1 2πc Where ν is wavenumber (cm -1 ) c is speed of light k is the force constant of the bond Diagnostic peak for different functional group The fingerprint region (<1200cm -1 ) also has useful information μ is the reduced mass μ = m 1m 2 m is the atomic mass of atoms k μ m 1 +m 2

8 Instrument Fourier transform infrared (FTIR) spectrometry Components: Light source: a black-body source Michelson interferometer: generate interferogram signal Sample holder: sample vial Detector: measure the special interferogram signal Computer: manipulate the data

9 Thermo N. Introduction to fourier transform infrared spectrometry. Thermo Nicolet Corporation: Madison-USA, 2001.

Michelson interferometer An incoming traveling plane wave of amplitude and intensity impinges on a beam splitter S that both transmits and reflects 50% of the incident light.

10 Michelson interferometer An incoming traveling plane wave of amplitude and intensity impinges on a beam splitter S that both transmits and reflects 50% of the incident light. Each of these two waves is reflected back from a mirror (M1 or M2) and is incident on the beam splitter S. The wave that is reflected back from the movable mirror M2 and transmitted by S interferes with the wave that is reflected from the fixed mirror M1 and reflected from S. Engel, T., Reid, P., & Hehre, W. Physical chemistry (3rd ed.), 2013, Boston: Pearson Education.

Noninvasive and fast measurement of blood glucose in vivo by near infrared

11 Fibre-optical Probe collection of the NIR spectra on rat's hind leg shaved (left) the NIR fiber-optical probe (right) Xue, J. et al. Noninvasive and fast measurement of blood glucose in vivo by near infrared (NIR) spectroscopy. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017, 179,

12 Case study

13 Photoacoustic (PA) gas cell consists of a T-shaped resonator with two cylindrical cavities perpendicularly connected, the absorption and the resonance cavity

14 Procedure analyze the different layers of the skin and determine the dominant contributor of absorbance determine and analyze the influence of variable skin glucose on the PA (Photoacoustic) spectra for the diabetic volunteer determination of glucose level by non-invasive PA measurement, compared to the invasive test, a series of oral glucose tolerance tests (OGTT) on healthy and diabetic volunteers

15 Result the main spectral features of the photoacoustic spectra measured in skin are in good agreement with the spectra for S. corneum the dominant absorbance from the S. corneum

16 the well-known spectral features of glucose appearing at 1033, 1077, 1128, 1163, and 1213 cm 1 can be observed while the glucose concentration in blood is increasing.

18 Figure A shows the time course of the glucose level as measured every 5 min noninvasively and by the test strip system for a healthy volunteer. After glucose administration, the level of blood and of interstitial glucose rose from the initial value of ~ mg/dl to ~ mg/dl over 2 h and then decayed to the starting value. The different methods of glucose analysis, invasive and non-invasive, yield similar glucose concentrations The correlation between the invasive (test strip ) and the non-invasive glucose measurement is shown in Figure B. The mean prediction error calculated from this correlation is approximately 11 mg/dl.

19 Figure C shows the time course of the glucose level as measured every 5 min noninvasively as well as by the test strip system and by a subcutaneous sensor in the abdominal wall for a type I diabetes volunteer. The glucose level increased rapidly to values between 120 and 140 mg/dl and further over the next 2h and finally reached values above 200 mg/dl, persisting much longer than for a healthy person. The different methods of glucose determination yield similar glucose concentrations over the time of the OGTT, although the lag of the glucose concentration measured by the subcutaneous sensor in the fat tissue is evident. This can be explained by the slow equilibration of blood glucose and tissue glucose in this skin region. The correlation between the blood glucose and the epidermal glucose concentration measured by the noninvasive photoacoustic method is shown in Figure D. The mean prediction error calculated from this correlation is approximately 15 mg/dl.

20 In addition to the OGTT carried out for the healthy and diabetic patient, the selectivity and specificity of the approach by measuring the PA spectra of a healthy patient during a nonglucose changing situation was tested. In this case, the PA measurements were conducted just like for the OGTTs shown in Figure A,C, but instead of drinking a glucose solution the patient took 300 ml of water. The results of this test are shown in Figure E,F indicating that the system provides enough selectivity to represent changes exclusively arising from the modulation of the glucose concentration in the epidermis.

21 Conclusion Advantage non-destructive technique provides a precise measurement method which requires no external calibration Data collection fast can increase sensitivity No sampling procedure Disadvantage the overlap of absorption contributions from complex matrix Individual variability compared to the reference metric issues

22 Conclusion In vivo IR could be used in biolanalytical studies and the Fourier transform infrared (FTIR) spectrometer is used in the analysis Fingerprint region is very important for analysis

23 Reference 1. Atanasov A.G. et al. Discovery and resupply of pharmacologically active plant-derived natural products: A review. Biotechnology advances, 2015, 33(8): Engel, T., Reid, P., & Hehre, W. Physical chemistry (3rd ed.), 2013, Boston: Pearson Education. 3. Thermo Nicolet. Introduction to Fourier transform infrared spectrometry. Thermo Nicolet Corporation: Madison-USA, Xue, J. et al. Noninvasive and fast measurement of blood glucose in vivo by near infrared (NIR) spectroscopy. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017, 179, Pleitez, M. A. et al. In vivo noninvasive monitoring of glucose concentration in human epidermis by mid-infrared pulsed photoacoustic spectroscopy. Analytical chemistry, 2012, 85(2), p

24 Thank you!

25 Questions?

Noninvasive Blood Glucose Analysis using Near Infrared Absorption Spectroscopy. Abstract

Progress Report No. 2-3, March 31, 1999 The Home Automation and Healthcare Consortium Noninvasive Blood Glucose Analysis using Near Infrared Absorption Spectroscopy Prof. Kamal Youcef-Toumi Principal Investigator