Tuneable design of a pulp fibre-based colorimetric sensor and its visual recognition mechanism for ppb levels of Ag+

Abstract A novel biomass pulp fibre (PF)-based colorimetric sensor was prepared by grafting l -lysine ( l -lys) onto the surface of PFs via a Schiff base reaction. The grafted l -lys contained two specific synergistic recognition groups (–COOH and –NH 2 ), which only recognize Ag + . The as-prepared sensor (DAPF- l -lys) showed excellent selective recognition of Ag + and an obvious visual colour change from light-yellow to brown in aqueous solutions containing other ions (Cu 2+ , Pb 2+ , Mn 2+ , Mg 2+ , Cd 2+ , Ca 2+ , H 2 O, Al 3+ , Hg 2+ , Cr 6+ , K + , Na + and Zn 2+ ). The visual limit of detection for Ag + was 10 –7  mol/L. Furthermore, DAPF- l -lys responded to Ag + within 30 s based on the dynamic conditions of the detection method. The biomass PF matrix possessed the excellent properties, including a large external surface area, a short transit distance and good flexibility. When specific synergistic recognition groups were grafted onto the PF of the prepared PF-based colorimetric sensor, Ag + could be rapidly absorbed and enriched on the surface of DAPF- l -lys through only bi-dentate ligand chelation between Ag + and the synergistic recognition groups (–COOH and –NH 2 ) of DAPF- l -lys. Thus, the DAPF- l -lys colorimetric sensor exhibited promising prospects for on-site identification of Ag + (the level of ppb ) due to its high selectivity and sensitivity. Graphic abstract