Journal of IiME Volume 1 Issue 2 www.investinme.org Visible and near-infrared (Vis-NIR) spectroscopy: Introduction and Perspectives for Diagnosis of CFS symptoms should carefully be examined. Physicians should, through a careful investigation of the patient’s medical history and appropriate testing, rule out other diseases including mononucleosis, Lyme disease, thyroid conditions, diabetes, multiple sclerosis, various cancers, depression and bipolar disorder. We feel that the main problems in CFS studies can be attributed to the objectivity of diagnosis and absence of biomarkers. Our research group, composed of a virologist, spectroscopist, physician, and clinical laboratory technologist, has been studying visible and near-infrared (Vis-NIR) spectroscopy (Fig. 1). We decided to apply Vis-NIR spectroscopy to the study of CFS. In this review, we introduce the method and its possible uses for CFS research. Vis-NIR spectroscopy and multivariate analysis The short wavelength (SW)-NIR region and the red region, the so called “optical window” from 600 to 1,100 nm, are together the most useful region for measuring biological samples [7]. The absorption of hemoglobin and water is extensive in the region below 600 nm and above 1,100 nm, respectively, which limits spectroscopic and microscopic studies [8]. Absorption in the SW-NIR region is due to combinations and overtones of vibration such as the stretching and bending of hydrogen-bearing functional groups including –CH, -OH and –NH [9]. Water, melanin, and bilirubin in animals were absorbed by the radiation of this region [8]. In addition, oxyhemoglobin, deoxyhemoglobin, and oxidized cytochrome c oxidase have characteristic absorption spectra in the SW-NIR region [10]. Recently, biologically important molecules such as albumin [11-13], cholesterol [14, 15], globulin [11-13], glucose [13, 16-24], protein [12, 15, 25-28], urea [12, 13, 27], lipid [15], linoleic acid [15], collagen [15], DNA [15], and α-elastin [15] have also been investigated by Vis-NIR spectroscopy. However, there has been considerable debate as to whether the accuracy and stability of Vis-NIR calibration models for non-invasive transcutaneous monitoring of blood glucose levels in patients with diabetes met criteria for clinical diagnosis [18, 29, 30]. Creatine [27], lactate [22, 31], triacetin [20], triglyceride [13], βlipoprotein [25], Vibrio cholerae [32], Escherichia coli [33, 34], Yeast [35, 36], Ethanol [36, 37], RNA [28], Acetate [34], Ammonia [22, 34], Glycerol [34], and Glutamine [22] have also been quantitatively determined by VisNIR spectroscopy. Representative biomolecules studied by Vis-NIR spectroscopy are listed in Table 1. Vis-NIR spectroscopy has been recognized as having diagnostic potential ever since Jöbsis first used it to demonstrate oxygenation in cats [38]. Vis-NIR spectroscopy has also been applied in the clinical setting to aging [39, 40], Alzheimer’s disease [41], cancer [42-50], chronic fatigue syndrome [51-54], dermatological conditions [43], diabetes [18, 21, 55], epilepsy [56], human immunodeficiency virus (HIV) infection [57], seizure types [58], migraine [59], cervical Invest in ME Charity Nr 1114035 dysplasia [60], atherosclerotic plaques [61], rheumatoid arthritis [62], hemodynamics [63], glioma [64], intraocular pressure [65], hemorrhagic shock [66], skin moisture [67], brain edema [68], optic neuritis [69], and maternal hypotension [70] (Table 2). The number of diseases studied by Vis-NIR spectroscopy has been increasing, although most studies have focused on the monitoring of oxyhemoglobin and deoxyhemoglobin. At present, the diagnostic application of this method in the medical field is rare. The development of laboratory instrumentation for Vis-NIR spectroscopy has been well reviewed [71]. Manufacturers and commercially available instrumentation has also been listed [72], and the number of manufacturers has shown further dramatic increase. The range of wavelengths and modes of measurement available must be paid greater attention to select a suitable instrument for analysis. Cuvettes are sometimes used for measurements. Quartz and polystyrene cuvettes are preferable because much Vis-NIR spectral information on quartz and polystyrene has been reported. The methods of measurement are divided into four types: transmission, reflection, transflection, and interactance in spectroscopy [73]. In transmission spectroscopy, radiation transmitted through sample is measured. In reflection spectroscopy, radiation reflected on the surface is measured. In transflection spectroscopy, which is a combination of the transmission and reflection methods, radiation is transmitted through the sample and scattered back from a reflector on the opposite side. In interactance spectroscopy, radiation transmitted through the sample is collected in contact with the surface of the sample with the end of a fibre optic probe, which has both a radiator and a detector [74]. The availability of fibre optic probes is one advantage of Vis-NIR spectroscopy. Vis-NIR spectroscopy enables the rapid, non-destructive, accurate, and simultaneous determination of multiple components in both liquid and solid samples [75]. However, it also has disadvantages. (continued on page 10) Fig. 2. Characteristics of near-infrared radiation. Ultraviolet (UV), visible (Vis), and infrared (IR) radiation is highly absorbed, whereas near-infrared (NIR) radiation is relatively little absorbed, by water and haemoglobin. Notably, 600-1,100 nm including the red region and short wavelength region of near-infrared (SW-NIR) radiation is called the “optical window”, because this region is suitable for biological analysis. Modified from Fig. 1 in Sakudo et al. [103] with permission from Nippon Rinsho Co. Page 9/72
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