Bifunctional SERS Paper Chips Based on Three-Layered Plasmonic Metal-Coated ZnO Nanoflowers for Fast Enrichment and Ultrasensitive Detection of Multiple Antibiotics

In this study, cellulose filter paper (CFP) was used to create three-dimensional ZnO nanoflowers coated with three-layered plasmonic metals (Ag@Au@Ag) by using an in situ generated method. The substrate was created as a surface-enhanced Raman scattering (SERS) paper chip with dual functions for quick enrichment and ultrasensitive antibiotic detection. It was possible to detect amoxicillin, ciprofloxacin, and tetracycline quantitatively with good linear responses at low detection limits of 1, 10, and 10 nM, respectively, thanks to the characteristics of three-dimensional nanostructures, the charge transfer effect of ZnO–plasmonic metal, and electromagnetic coupling of Ag@Au@Ag. Even with a paper chip and a mobile phone–Raman spectrometer integrated system, it was possible to identify human urine antibiotics at ppb levels with high accuracy. Meanwhile, 10 min detection of the antibiotics was accomplished by merely soaking them in their analyte solutions due to CFP wicking. With the help of PCA-LDA analysis, the multiplexed SERS spectral data of the three antibiotics could be successfully separated. Additionally, the paper chip’s exceptional mechanical endurance even against 30-fold and strong ultrasonication was made possible by the in situ growing method. The bifunctional, affordable, and long-lasting SERS paper chip has a lot of potential for on-site and point-of-care drug detection.