For the first time, a new disubstituted polyacetylene (P1) was utilized to sense alpha-amino acids based on a "turn-on" model, through an indirect approach. Thus, first, the strong blue fluorescence of P1 was quenched by trace copper ions efficiently, then the addition of alpha-amino acids to the P1/Cu2+ complex could recover the strong fluorescence of P1 to report the presence of alpha-amino acids. Interestingly, the P1/Cu2+ complex demonstrated much higher sensitivity towards histidine, with the detection limit of similar to 2 ppm (similar to 1.3 x 10(-5) mol/L). With the aid of a normal UV lamp, histidine could be differed from other alpha-amino acids visually by the observation of its strong blue fluorescence, at the concentration as low as 4.0 x 10(-5) mol/L Due to the convenient synthesis of P1, and the so far reported many other conjugated fluorescent polymers, the work reported here might open up a new avenue to develop new biosensors. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.