Highly Efficient Novel Vibrational Spectroscopic Methods

Food, Medicinal Plant, Material and Cancer Analysis

  • Fig. 1: Application fieldsFig. 1: Application fields
  • Fig. 1: Application fields
  • Fig. 2: Development  of spectrometers
  • Fig. 3: 3d-image: distribution of proteins in Urtica dioica

The number of publications including the term “vibrational spectroscopy” is permanently increasing. According to the SciFinder database of the American Chemical Society (ACS) 2444 papers have been published in 2010, 3053 in 2013 and 3288 in 2015 – altogether 17082 between 2010 and 2015. The reason for the increasing popularity can be explained on one hand by the efficient technical advancements and improved data processing algorithms, on the other hand by the advantages the method offers to the operator. This is especially true in case of high sample throughput compared to separation techniques, mass spectrometry, etc.: Easy handling, short analysis time, non-invasive, qualitative and quantitative analysis. It is the aim of this article to summarize the actual technical advancements in the first step and to introduce selected spectroscopic methods established in Professor Huck´s working group in the field of food, medicinal plant, material, and cancer analysis (Fig. 1).

Technical Advancements
In the last couple of years fundamental technical advancements could be on one side achieved in the design of portable instruments and high-resolution spectro-meters on the other side. The change from room filling instruments in the 70ies towards small spectrometers - the smallest NIR spectrometer currently just has a weight of 60 gram - was enabled by introducing micro-electro-mechanical systems (MEMS) for generating optical-mechanical functions in the near infrared region (4,000-12,000 cm-1) and linear variable filters (LVF) in combination with attenuated total reflection (ATR) mid infrared (MIR; 400-4,000 cm-1) spectroscopy (Fig. 2). Handheld Raman spectrometers are nowadays equipped with a 1064-nm excitation laser for sufficient fluorescence suppression. When miniaturizing instruments, special care must be taken that the spectral performance is comparable to expensive and technical advanced benchtop instruments.
 
Further advancements in the field of imaging/mapping technology offer a resolution down to 4 µm. Applying focal plane array (FPA) detectors short analyses times can be achieved.

The latest generation of Raman-spectrometers enables a resolution down to approx. 1 µm delivering complementary spectral information compared to IR, which is a highly promising attempt especially in the field of cancer analysis. Atomic force microscopy (AFM) combined with infrared spectroscopy enables high resolution material investigations in the nano-meter range.

 
Highly efficient applications
In food technology the number of false declarations is permanently increasing. Furthermore, cheap products from low-cost-countries and suppliers are putting pressure on the market. Determination of geographic origin, species in parallel to quantitative analysis of potent ingredients play an increasing role. More and more information upon nutrition values, e.g. anti-oxidative potential, are demanded. In the framework of the Interreg IV project “Originalp” funded by the European Union (www.originalp.eu) it was possible for the first time to protect typical Alpine products, e.g. apples, according to their geographic origin and to quantify potent ingredients (carbohydrates, phenols, alpha-farnesene) in parallel to the anti-oxidative potential. For this reason a novel apple rotating machine for the automatic NIR-spectroscopic analysis was developed [1]. In combination with official quality seals, this novel analytical tool provides even for the producer and the consumer assurance concerning origin and quality of the product. Since the horse meat scandal in 2013, novel analytical techniques for fast and easy food fraud detection are in constant demand. Therefore, we have recently developed a hand-held NIR based method allowing to control the quality of veal sausages within the packing and to determine falsification by pork meat and fat [2] methods for laboratory use of high performance Fourier transform-NIR (FT-NIR).
 
For medicinal plant quality control (“phytomics”), similar spectroscopic systems are developed, enabling in parallel the determination of origin/species, quantitative determination of ingredients and anti-oxidative potential,  and additionally exact analysis of optimum harvest time. For this purpose, handheld NIR/MIR spectrometers are applied for in-field analysis enabling recognition of day-time variations in ingredients concentration [3].  With MIR-/NIR-imaging spectroscopy, the distribution of potent ingredients, e.g. proteins in Urtica dioica, can be displayed in 3D, offering new insights into the distribution of potent ingredients (Fig. 3) [4]. The signal for secondary metabolites in low concentrations can be selectively enhanced by applying surface enhanced infrared spectroscopy (SEIRS). Quantum mechanical based simulation of spectra can provide additional support for a deeper understanding of signals and coherence.
 
MIR-/NIR-/Raman spectroscopy offer excellent tools for the characterisation of several different materials, including polymers, which contain IR active aliphatic, olefinic  and aromatic CH systems in combination with –NH,-OH, -COOH and –C=O functional groups or combinations thereof such as –NH-CO (amide) and –NH-COO (urethane). It is possible to determine even chemical as well as physical parameters. Chemical reaction, constitution (composition, additives, impurities), configuration (cis/trans, tacticity), conformation (trans/gauche), state (amorphous/crystalline) and orientation can be checked simultaneously and non-invasively. Conformity is influencing structure and properties of a material fundamentally. In polymer research bulk-samples, solids, and emulsions must be investigated. For this attempt diffuse reflection spectroscopy is highly suitable [5].
 
Nano materials are more frequently used for different purposes. Vibrational spectroscopy offers the possibility to check physico-chemical parameters (particle size, specific surface area, porosity, derivatisation etc.) simple and fast. AFM-IR enables recording high resolution images in the nano meter range [6].
 
In cancer detection MIR-/NIR-/Raman spectroscopy are playing an increasing role. Imaging techniques are applied for the selective detection of tumor distribution within the tissue at several stages of illness. Based on this knowledge, optical fiber probes can be installed enabling direct measurements in the body [7]. 2-dimensional correlation spectroscopy (2D-COS) offers generating additional information concerning spectral resolution.
 
Future Outlook
Especially the further development of hand-held NR spectrometers is developing very fast. In the next years, instruments will be available which are smaller than a smart-phone enabling the user to get a wealth of information concerning e.g. food. Data transfer will be achieved using Bluetooth and WLAN, respectively.
 
Acknowledgements
Third party funding is the basis for the ongoing research. Therefore, I want to thank the European Union (Interreg IV project “Originalp”), the ministry for health and the ministry for transport, innovation and technology (BMG, BMVIT, Vienna, Austria; Project “Novel Analytical Tools for Quality Control”), the Tyrolean government (Innsbruck, Austria; project “Ora Squamous Cell Carcinoma”), as well as several other sponsors.
 
Author
Christian W. Huck
Institute of Analytical Chemistry and Radiochemistry, CCB – Center for Chemistry and Biomedicine, Leopold-Franzens University, Innsbruck, Austria
 
Literature
[1]  Matthias Schmutzler, Christian W. Huck: Automatic sample rotation for simultaneous determination of geographical origin and quality characteristics of apples based on near infrared spectroscopy (NIRS), Vibrational Spectroscopy 2014, in press., DOI: 10.1016/j.vibspec.2014.02.010
[2]  Matthias Schmutzler, Anel Beganovic, Gerhard Böhler, Christian W. Huck: Methods for detection of pork adulteration in veal product based on FT-NIR spectroscopy for laboratory, industrial and on-site analysis, Food Control 2015, 57, 258–267, DOI: 10.1016/j.foodcont.2015.04.019.
[3] D. Clara, C.K. Pezzei, S.A. Schönbichler, M. Popp, J. Krolitzek, G.K. Bonn, C.W. Huck: Comparison of near-infrared diffuse reflectance (NIR) and attenuated-total-reflectance mid-infrared (ATR-IR) spectroscopic determination of the antioxidant capacity of Sambuci flos with classic wet chemical methods (assays), Analytical Methods 2016, 8, 97–104, DOI: 10.1039/C5AY01314C.
[4]  D. Pallua, J.; Pezzei, C.; Huck-Pezzei, V.; A. Schonbichler, S.; K. Bittner, L.; K. Bonn, G.; Saeed, A.; Majeed, S.; Farooq, A.; Najam-ul-Haq, M.; Abel, G.; Popp, M.; W. Huck, C. Curr. Bioact. Compd. 2011, 7, 12.
[5]  N. Heigl, A. Greiderer,C.H. Petter, O. Kolomiets, H.W. Siesler, M. Ulbricht, G.K. Bonn, C.W. Huck: Simultaneous Determination of the Micro-, Meso-, and Macropore Size Fractions of Porous Polymers by a Combined Use of Fourier Transform Near-Infrared Diffuse Reflection Spectroscopy and Multivariate Techniques, Analytical Chemistry 2008, 80, 8493–8500, DOI: 10.1021/ac8013059.
[6]  Nico Heigl, Christine H. Petter, Mohammad Najam-Ul-Hacq, Matthias Rainer, Rainer M. Vallant, Günther Karl Bonn, Christian W. Huck: When size matters near infrared reflection spectroscopy of nanostructured materials, Journal of Near Infrared Spectroscopy 2008, 16, 211, DOI: 10.1255/jnirs.780.
[7]  Huck Christian W.; Huck-Pezzei Verena: Advances in Multidimensional Approach of Infrared Imaging Spectra and Morphology of Oral Squamous Cell Carcinoma (OSCC); Schlapa, J., Ed.; Novapublisher, NY, USA, 2014.
 
Contact
Prof. Christian W. Huck
Institute of Analytical Chemistry and Radiochemistry
Center for Chemistry and Biomedicine (CCB)
Leopold-Franzens University
Innsbruck, Austria
 

 

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