Exchange interaction between localized magnetic moments mediated by free charge carriers is responsible for a non-monotonic dependence of the low-temperature energy band-gap in dilute magnetic semiconductors. We found that in weakly doped Mn-ZnO films, increasing the exchange interaction by increasing the concentration of free charge carriers results in a red-shift of the near-band-edge emission peak at room temperature. An increase of Mn concentration widens the band gap, and a blue-shift prevails. Exchange interaction can be used to tune the room-temperature optical properties of the wide-band gap semiconductor ZnO.

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO₃ ⁻). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H₂O₂. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO₃ ⁻ film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H₂O₂ with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO₃ ⁻/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM⁻¹ cm⁻²), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.