Preparation and Application of thin hydrogel film in optical sensors

Otapanjem kitozana u otopini octene kiseline te umrežavanjem pomoću 2,2'-bipiridin-4,4'-dikarboksilne kiseline dobiva se hidrogel koji na svakom mjestu umreženja posjeduje bidentantni N-donorni ligand koji ima sposobnost kompleksiranja Fe iona. Dodatkom Fe(II) soli u vodenoj otopini dolazi do kompleksiranja željeza unutar hidrogela. Dodatkom pomoćnog liganda, kao što je TPTZ (2,4,6-tri(2-pyridyl)-1,3,5-triazine), hidrogelu koji unutar svoje mreže posjeduje kompleksirano željezo dolazi do nastajanja plavo obojenog hidrogel-(2,2'-bipiridin-Fe(II)-TPTZ) kompleksa. Djelovanjem oksidansa, kao što je H2O2, na takav hidrogel dolazi do njegovog obezbojenja, a redukcijskim djelovanjem antioksidanasa ponovno nastaje plavo obojenje. Ova reakcija oksidacije-redukcije unutar dobivenog hidrogela je reverzibilna.By dissolving chitosan within acetic acid solution followed by crosslinking via 2,2'-bipyridine-4,4'-dicarboxylic acid a hydrogel containing a bidentate nitrogen ligand at each crosslink site is formed which has the ability to bind Fe ions. Addition of Fe(II) salts in aqueous solution creates an iron complex within the hydrogel. An additional ligand such as TPTZ (2,4,6-tri(2-pyridyl)-1,3,5-triazine) has the ability to bind to iron which is already bound within the hydrogel forming a blue colored hydrogel-(2,2'-bipyridine-Fe(II)-TPTZ) complex. Oxidation said complex via oxidizing agent such as hydrogen peroxide induces loss of color after which it is possible to again reduce the colorless Fe(III)-TPTZ complex via an antioxidative agent that results in return of the blue color. The Aforementioned oxidation-reduction reaction has been proven to be reversible