We report on a synthetic approach to produce self-supported flexible surface-enhanced Raman scattering (SERS) active membranes consisting of polyamide (PA) nanofibers grafted with vertical Ag-nanosheets, via a combinatorial process of electrospinning PA-nanofiber membranes, assembling Au-nanoparticles on the PA-nanofibers as seeds for subsequent growth of Ag-nanosheets, and electrodepositing Ag-nanosheets on the electrospun PA-nanofibers. As a high density of Ag-nanosheets are vertically grown around each PA-nanofiber in the three-dimensional (3D) networked PA-nanofiber membranes, homogeneous nano-scaled gaps between the neighboring Ag-nanosheets are formed, leading to a high density of 3D SERS "hot spots" within the Ag-nanosheet-grafted PA-nanofiber membranes. The Ag-nanosheet-grafted PA-nanofiber membranes demonstrate high SERS activity with excellent Raman signal reproducibility for rhodamine 6G over the whole membrane. For a SERS-based trial analysis of polychlorinated biphenyls (PCBs, a kind of global environmental hazard), the 3D SERS substrate membranes are modified with mono-6-β-cychlodextrin to effectively capture PCB molecules. As a result, not only a low concentration down to 10(-6) M is reached, but also two congeners of PCBs in their mixed solution are identified, showing promising potential in SERS-based rapid detection of trace organic pollutants such as PCBs in the environment.

Large area arrays of length-tunable alumina nanotips on the joints of hexagonally patterned conical-pores in an anodic aluminum oxide (AAO) template are achieved via a repeated process of anodizing Al foil for pore growth downwards and phosphoric acid etching for pore-widening. By top-view sputtering Ag on the alumina nanotip arrays, hexagonally patterned arrays of Ag-nanorods (Ag-NRs) on the alumina nanotips and uniformly distributed Ag-nanoparticles (Ag-NPs) on the upper rim of the inner surface of the conical-pores are obtained and they exhibit strong surface-enhanced Raman scattering (SERS) activity due to the high density of sub-10 nm gaps between the nearest neighboring Ag-NRs and between the adjacent Ag-NPs. The resultant nanostructures are tailored to attain an optimal SERS enhancement factor of $3.2 Â 10 7 by tuning the Ag-sputtering duration. SERS measurements demonstrate that the as-fabricated large-scale Ag-nanostructures can serve as highly sensitive and reproducible SERS substrates. Finite element method calculation also confirms that the fabricated substrates possess excellent SERS activity. By modifying the Ag-NR arrays with mono-6-thio-b-cyclodextrin, the SERS detection limit of PCB-77 (a congener of polychlorinated biphenyls (PCBs)) reaches 10 À6 M, showing potential in SERS-based rapid detection of trace PCBs, a kind of global environmental hazardous material.

An improved label-free approach for highly sensitive and selective detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio I(656 cm(-1))/I(733 cm(-1)) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10(-8) M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment.