# Raman Spectroscopy as Noninvasive Method of Diagnosis of Pediatric Onset Inflammatory Bowel Disease
## 1 Introduction  
An early and accurate detection of chronic diseases is crucial in view of a proper intervention [1; 2; 3]. It can also contribute in facilitating the monitoring of disease progression and therapeutic response. In many chronic diseases, especially regarding pediatric patients, the diagnostic process can be time consuming and invasive so the search for noninvasive and accurate diagnostic tools is underway. In particular, the diagnosis of inflammatory bowel disease (IBD) in childhood, can be challenging [4; 5; 6]. The diagnosis is based on detection of chronic inflammation in the gastrointestinal (GI) tract and exclusion of other causes of inflammation. The differentiation of [PERSON]'s disease (CD) from ulcerative colitis (UC), and both of these from infectious diseases, allergic diseases, or primary immunodeficiency disorders (PIDs) with similar presentations is based on a combination of clinicalsuspicion, endoscopic and histological evaluation of the mucosa, and other additional tests in case of uncertainty [7]. An international group of European experts in pediatric inflammatory bowel disease (PIBD), mainly from the \"Porto\" IBD Working Group of the European Society of Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) stated that an \"accurate diagnosis of inflammatory bowel disease should be based on a combination of history, physical and laboratory examination, esophagagostroudenoscopy (EGD) and ileocolonoscopy with histology, and imaging of the small bowel [8]. It is critical to exclude enteric infections\". Even adhering to revised Porto IBD working group criteria for diagnosis, in some case distinguishing CD from UC and both from other disease is troublesome, especially in the subset of patients with early onset of disease. A noninvasive tool helpful, on the one hand, in reducing the burden of diagnosis and, on the other, in differentiating between CD and UC is a target for current and future research [9; 10; 11]. Nevertheless, the structural analysis of tissues didn't reveal successful in differentiating among inflammation subtypes. Calprotectin is a small calcium-binding protein of the S100 family of zinc-binding proteins, and is a major component of cytosol protein content in neutrophils and other cells involved in inflammatory process. In the presence of active intestinal inflammation, polymorphonuclear neutrophils migrate to the intestinal mucosa from the circulation. Any disturbance to the mucosal architecture due to the inflammatory process, results in leakage of neutrophils, and hence, calprotectin, into the lumen and its subsequent excretion in feces. The concentration of calprotectin in feces has been shown to correlate well with the disease activity in IBD and to help differentiate IBD from other functional intestinal disorders, such as irritable bowel syndrome [12; 13; 14]. Raman spectroscopy is an inelastic light-scattering phenomenon according to which the illumination of a molecule by a monochromatic laser light will give rise to an exchange of a quantum vibrational energy between the two that will result in a difference in vibrational frequency between incident and scattered light [15; 16; 17]. Consequently, this experimental method provides a vibrational spectrum that contains information relative to chemical bonds and symmetry of a specific molecule [18; 19]. As widely reported [20; 21; 22], it represents an essential methodology in chemistry, physics, biology and material science. For example, Raman spectroscopy is broadly employed in the investigation of changes in secondary structure at all stages of protein aggregation and amyloid fibril formation [23; 24]. It is commonly used in unravelling molecule-specific spectral signatures of different biomolecules including nucleic acids, lipids, carbohydrates and complex biological systems like tissues, cells, that are made up of such biomolecules [25].