Nano Sensors Group | Illinois

Discrete Frequency Infrared Spectroscopy

Discrete Frequency Infrared Spectroscopy with high-performance mid-IR photonic crystal resonators

Mid-infrared (mid-IR) spectroscopic imaging is an emerging combination of fundamental vibrational absorption spectroscopy and microscopy that provides a powerful analytical tool for visualizing the molecular content of a sample without the use of dyes, stains or destructive procedures.1 Over the last 15 years, numerous applications including those in polymer composites, forensics, environmental science, geology, human tissue pathologies, palaeontology and plants have been reported.1, 2, 3, 4, 5, 6, 7, 8, 9 Almost all mid-IR imaging data acquired today are using Fourier transform infrared (FT-IR), in which a specimen is illuminated by broadband radiation using a Michelson interferometer. In this setup, intensity values at the detector are recorded at each of thousands of specific positions of the moving mirror and a Fourier transform is used to convert the time-domain signal to the wavelength domain. FT-IR imaging spectrometers are high-precision instruments but necessitate the acquisition of a continuous absorption spectrum over a large bandwidth. Despite the strengths of interferometer-based data acquisition,10 alternative approaches could be beneficial for many applications. The need to scan an entire interferogram/time and resulting large data sizes can become crippling limitations, especially as the spatial resolution of microspectroscopic imaging increases.11, 12 For many routine applications, such as environmental monitoring and industrial process control, only a small portion of the spectrum contains useful information, and a more rapid, robust, and inexpensive instrument than an FT-IR spectrometer would be most appropriate. In cases where the relevant spectral wavelengths are known, a simpler imaging approach to acquire only these data would enable spectroscopic imaging to be applied in settings that have thus far been impossible. For example, multiple studies show that only a few wavelengths over the broad mid-IR range are required to provide all the information required for tissue histopathology,13, 14 which can be speeded up 100-fold if only these frequencies could be recorded. This alternate approach to the dominant FT-IR imaging approach is emerging as a viable alternative and is termed discrete frequency IR (DF-IR) spectroscopic imaging.1 A significant topic of interest in this area is the development of a variety of devices for discrete frequency illumination, including selective emitters and resonant filters in mid-IR, and their optimal integration into an imaging system.
Here we demonstrate an approach for mid-IR spectroscopic imaging at selected discrete wavelengths using narrowband resonant filtering of a broadband thermal source, enabled by high-performance guided-mode Fano resonances in one-layer, large-area mid-IR photonic crystals on a glass substrate. This considerably simplifies instrumentation as well as overhead of data acquisition, storage and analysis for large format imaging with array detectors. DF-IR spectroscopy and imaging can be generalized to other IR spectral regions and can serve as an analytical tool for environmental and biomedical applications.
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elated Papers:

1.         Bhargava R. Infrared Spectroscopic Imaging: The Next Generation. Applied Spectroscopy 66, 1091-1120 (2012).
2.         Levin IW, Bhargava R. FOURIER TRANSFORM INFRARED VIBRATIONAL SPECTROSCOPIC IMAGING: Integrating Microscopy and Molecular Recognition. Annual Review of Physical Chemistry 56, 429-474 (2005).
3.         Colarusso P, Kidder LH, Levin IW, Fraser JC, Arens JF, Lewis EN. Infrared Spectroscopic Imaging: From Planetary to Cellular Systems. Appl Spectrosc 52, 106A-120A (1998).
4.         Barron C, Parker ML, Mills ENC, Rouau X, Wilson RH. FTIR imaging of wheat endosperm cell walls in situ reveals compositional and architectural heterogeneity related to grain hardness. Planta 220, 667-677 (2005).
5.         Steiner G, Koch E. Trends in Fourier transform infrared spectroscopic imaging. Anal Bioanal Chem 394, 671-678 (2009).
6.         Ricci C, Nyadong L, Fernandez F, Newton P, Kazarian S. Combined Fourier-transform infrared imaging and desorption electrospray-ionization linear ion-trap mass spectrometry for analysis of counterfeit antimalarial tablets. Anal Bioanal Chem 387, 551-559 (2007).
7.         Wysoczanski R, Tani K. Spectroscopic FTIR imaging of water species in silicic volcanic glasses and melt inclusions: An example from the Izu-Bonin arc. Journal of Volcanology and Geothermal Research 156, 302-314 (2006).
8.         Sabbah S, Rusch P, Gerhard J-H, Harig R. Detection and tracking of gas clouds in an urban area by imaging infrared spectroscopy. In: Proceedings of SPIE, Vol. 8743 Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XIX (ed^(eds Shen SS, Lewis PE). SPIE, Bellingham (2013).
9.         Reisz RR, et al. Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains. Nature 496, 210-214 (2013).
10.       Griffiths PR, de Haseth JA. Fourier Transform Infrared Spectrometry, 2nd ed. Wiley-Interscience, Hoboken, NJ (2007).
11.       Reddy RK, Walsh MJ, Schulmerich MV, Carney PS, Bhargava R. High-Definition Infrared Spectroscopic Imaging. Applied Spectroscopy 67, 93-105 (2013).
12.       Nasse MJ, et al. High-resolution Fourier-transform infrared chemical imaging with multiple synchrotron beams. Nat Meth 8, 413-416 (2011).
13.       Fernandez DC, Bhargava R, Hewitt SM, Levin IW. Infrared spectroscopic imaging for histopathologic recognition. Nat Biotech 23, 469-474 (2005).
14.       Bhargava R, Fernandez DC, Hewitt SM, Levin IW. High throughput assessment of cells and tissues: Bayesian classification of spectral metrics from infrared vibrational spectroscopic imaging data. Biochimica et Biophysica Acta (BBA) - Biomembranes 1758, 830-845 (2006).