Synthesis of isatin based polymers and preparation of the nanofiber membrane for amino acid detection

Fluorescent polymers are strong competitors in the preparation of flexible sensors due to their unique photoresponsivity, excellent processability, thermal stability, and mechanical stability. For developing the application of fluorescent polymers in the detection of amino acid, the polymers based on isatin were synthesized. The large steric hindrance of isatin groups endows the polymer with excellent solubility, so the samples could be processed into nanofibers (80–450 nm) by electrospinning. The polymer membranes exhibited bright yellow-green fluorescence at UV excited. After doping TiO₂ into electrospun membranes, the water contact angles of samples were reduced from 127° to 64°. The interstice between fibers and the hydrophilicity of the membrane facilitated the penetration of the amino acid solutions. It could be identified when the concentration of the targets were 0.03 mg/mL. The tryptophan caused fluorescence quenching of membrane due to the π-π* stacking. However, the significant hydrogen bonding of tyrosine enhanced photoluminescence emission of membrane. This work provides an effective strategy for portable and visual detection of amino acids.