Glassy carbon electrodes are modified with a thin film of a cellulose-chitosan nanocomposite. Cellulose nanofibrils (of ca. 4 nm diameter and 250 nm length) are employed as an inert backbone and chitosan (poly-d-glucosamine, low molecular weight, 75 -85% deacetylated) is introduced as a structural binder and "receptor" or molecular binding site. The composite films are formed in a solvent evaporation method and prepared in approximately 0.8 mm thickness. The adsorption of three molecular systems into the cellulose-chitosan films is investigated and approximate Langmuirian binding constants are evaluated: i) Fe(CN) 6 4À (K Ferrocyanide ¼ 2.2 Â 10 3 mol À1 dm 3 in 0.1 M phosphate buffer at pH 6) is observed to bind to ammonium chitosan functionalities (present at pH < 7), ii) triclosan (K Triclosan ¼ 2.6 Â 10 3 mol À1 dm 3 in 0.1 M phosphate buffer pH 9.5) is shown to bind only weakly and under alkaline conditions, and iii) the anionic surfactant dodecylsulfate (K SDS ¼ 3.3 Â 10 4 mol À1 dm 3 in 0.1 M phosphate buffer pH 6) is shown to bind relatively more strongly in acidic media. The competitive binding of Fe(CN) 6 4À and dodecylsulfate anions is proposed as a way to accumulate and indirectly determine the anionic surfactant.