Fiber-optic evanescent wave fourier transform infrared (FEW-FTIR) spectroscopy of polymer surfaces and living tissue

The new method of fiber-optic evanescent wave Fourier transform infrared (FEW-FTIR) spectroscopy has been applied to studies of polymer surfaces and the diagnostics of normal, precancerous and cancerous tissue. This technique using optical fibers and fiber-optic sensors operating in the attenuated total reflection (ATR) mode in the mid-infrared (IR) region of the spectrum (850 – 1850 cm⁻¹) has found recently application in the area of tissue diagnostics. The method is suitable for noninvasive and rapid (seconds) direct measurements of the spectra of normal and pathological tissues in vitro, ex vivo, and in vivo. The FEW-FTIR technique is an ideal diagnostic tool for different types of soft, porous, foam, and rough polymer surfaces. Inhomogeneous coatings and defects on polymer surfaces as well as layer structures have also been detected by this method. It is convenient to apply this method to analyze large pieces of soft plastics and/or surfaces covered by plastics, since these types of surfaces are comparatively hard to analyze by traditional absorption spectroscopy. The FEW-FTIR technique is non-destructive, fast (15 seconds), and remote (up to a fiber length of 3m). In addition, it is sensitive enough to detect any changes in the vibrational spectra of a polymer surface, without heating and damaging it. The surfaces of polyethylene crumpled bags and rumpled films have been investigated in the range of 2000 – 1000 cm⁻¹. The distinct spectra of these surfaces as well as spectra of polytetrafluoroethylene have been recorded. The spectra of white and colored foams and different plastics have also been studied. Weak but distinct spectra have been recorded for carbon fibers (black, narrow fibers with a diameter of about 10 μm). Using the FEW-FTIR technique, measurements can be taken without preparing the sample. High quality spectra have also been obtained for the bulk and surfaces of apple, banana, grapefruit, and other food products. The method is expected to be further developed for geological and microelectronic applications.