There exists a high demand for simple and affordable blood glucose monitoring methods. For this purpose, new generations of biosensors are being developed for possible in vivo or dermal use. We present (non)sulphated cellulose nanocrystal/magnetite thin films to act as dermal and oral glucose biosensors. The biocompatible (N-CNC)-Fe3O4 and (S-CNC)-Fe3O4 hybrid systems exhibit peroxidase-like activity, indicated by an almost instant color change when in the presence of glucose and ABTS. Both types of biosensors detect glucose concentrations as low as 5 mM (which corresponds to the level of glucose in biological fluids), with (S-CNC)-Fe3O4 being 1.5 - 2 times as sensitive as (N-CNC)-Fe3O4. Hybrid catalytic activity is more pronounced at room temperature and in acidic environments. The hybrids can therefore be used to determine glucose levels by using sweat and saliva – non-blood bodily secretions which tend to be slightly to moderately acidic and have relatively low glucose levels.