An ultrasensitive PVDF-based molecularly imprinted fluorescent test strip for the rapid and off-line detection of 4-NP with improved anti-coffee ring effect

Portable fluorescent test strips with off-line visual detection have become a hit in the field of target analysis. Yet, common fluorescent test strips are mainly based on filter papers, which usually suffer from poor visual detection effect owing to the "coffee ring effect". Herein, an ingenious ratio fluorescent test strip was successfully prepared based on the polyvinylidene fluoride (PVDF) hydrophobic membrane for rapid, selective and off-line visual detection of 4-nitrophenol (4-NP). Interestingly, two surprising discoveries were made: one was, strategically used, the green-emission fluorescence polydopamine (F-PDA) function as both fluorescence functional monomer and response signal during the synthesis of ratiometric fluorescent probe (CdTe@SiO2@F-PDA/MIPs), which greatly shortened the detection time of 4-NP. Another was, the PVDF membrane with hydrophobicity and colorless fluorescent background effectively overcame the "coffee ring effect"and fluorescence background interference. Compared with other hydrophobic membranes, the PVDF hydrophobic membrane was rough enough to load more CdTe@SiO2@F-PDA/MIPs, which provided more recognition sites for 4-NP detection. Finally, the PVDF fluorescent test strip exhibited a much lower detection limit of 2.77 nM within 1.5 min (90 s). The visual detection comparison experiment showed that the color changes of the PVDF fluorescent test strip to 4-NP were lightly identifiable and more obvious than that with a traditional filter paper. Moreover, the detection reliability of CdTe@SiO2@F-PDA/MIPs was verified by the comparison experiment of high-performance liquid chromatography (HPLC), and satisfactory results were ultimately obtained.