Electrospun nanofibrous membranes incorporating an imidazole-appended p-phenylene-Cu(ii) ensemble as fluoroprobes for the detection of His-proteins.

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Tetra-imidazole-appended p-phenylene-Cu(ii) doped nanofibrous membranes (IP-Cu-NMs) as portable chemoprobes were prepared using the electrospinning method. Fluorescence changes were observed upon dropping amino acids and proteins containing histidine residues onto the surface. IP-Cu-NMs prepared with 1.0 equivalent of Cu(ii) showed non-emissive properties, indicating that Cu(ii) induced the quenching with an aggregation-caused quenching (ACQ) effect. The fluorescence intensity of IP-Cu-NMs was enhanced approximately 25-fold upon dropping histidine onto the film, which is a "turn-on" system. In contrast, no significant fluorescence intensities were observed upon dropping other amino acids, such as valine, serine, phenylalanine, alanine, cysteine, lysine, leucine, asparagine, glutamic acid, glycine, methionine and arginine. IP-Cu-NMs achieved a low detection limit of 6.24 ppb observed by the fluorescence change. The results indicate that IP-Cu-NMs could be used to selectively detect histidine. More interestingly, the fluorescence of IP-Cu-NMs exhibited a strong emission with "turn-on" when proteins containing different numbers of His were dropped onto IP-Cu-NMs, and the intensity was dependent on the number of His residues in the protein. The enhanced fluorescence of IP-Cu-NMs with His could be recovered by treatment with Cu(ii) solution, suggesting the fluorescence reversibility of IP-Cu-NMs. Furthermore, this advanced convenient method was found to be valid up to 80% with excellent linearity for His detection over the range of 0-10 ppm in urine as a biological sample.