Fluorescent probes for Cu2+, Hg2+ and amino acids in aqueous solutions based on two mechanisms

• Three new polythiophene derivatives P1, P2, and P3 were synthesized via simple methods.
• P1, P2, and P3 showed high selectivity and sensitivity toward Hg2+ in methanol aqueous solutions at pH 3.
• P1 showed excellent sensitive and selective Cu2+ detection in Tris–HCl buffer solutions.
• Detection limit for Hg2+ and Cu2+ can be reached 10−8 M and 10−9 M respectively.
• The sensing processes for Hg2+ and Cu2+ were revealed to be mediated by electrostatic effect and complexation respectively.

The new polythiophene-based conjugated polymers Poly{3-[(4-{[2-(dimethylamino)ethyl]amino}cyclohexylidene)methyl]thiophene} (P1), Poly{3-[(4-{[3-(dimethylamino)propyl]amino}cyclohexylidene)methyl]thiophene} (P2) and Poly{3-{[4-(4-methylpiperazin-1-yl)cyclohexylidene]methyl}thiophene} (P3) have been synthesized by FeCl3 oxidative polymerization. Among the common metal ions tested, P1, P2 and P3 exhibited high selectivity and sensitivity toward Hg2+ in methanol aqueous solutions at pH 3 with a turn-off mode in which the detection limit of P3 for Hg2+ reached a level of 10−8 M. Additionally, the fluorescence of P1 in Tris–HCl buffer solution could be dramatically quenched in the presence of Cu2+ with a detection limit of 10−9 M. These sensing processes for Hg2+ and Cu2+ have been shown to be mediated by electrostatic effects and complexation. In addition, the P1–Cu2+ system was also employed as a turn-on fluorescence probe for the label-free detection of amino acids.

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