Fabrication of long-range ordered, broccoli-like SERS arrays and application in detecting endocrine disrupting chemicals

Abstract

Periodic broccoli-shaped Au and Ag surface-enhanced Raman spectroscopy (SERS) arrays were fabricated by combining ordered SiO 2 colloidal crystal templates with the physical deposition technique. The SiO 2 colloidal crystal-assisted Au and Ag SERS substrates have a long-range, adjustable periodic structure and a clean surface without incorporating any reductants or surfactant chemicals. Different from depositing directly on the flat substrates, the colloidal crystal-assisted nanostructure array has a larger effective surface area under the same projected area of laser irradiation, which exposes more "hot spots". An increased roughness and a larger surface area have also been created as the highly bumpy surface feature of the broccoli-shaped SERS morphologies, resulting in a greater Raman amplification than the conventional metal film over nanosphere (MFON). SERS performances by Au and Ag SERS arrays reveal that the long-range broccoli-like morphology is a promising SERS platform as it is highly sensitive, reproducible and stable. The colloidal crystal-assisted Ag SERS array has a slightly higher enhancement factor (EF) than the Au SERS array, and they both are of the order of 10 7 enhancement. Compared to our previous work, which directly deposited noble metal nanoparticles onto flat substrates, the EF of the colloidal crystal-assisted SERS array is improved by one to two orders of magnitude. Finite-difference time-domain (FDTD) simulation was performed to estimate the electromagnetic field distribution. Finally, two endocrine disrupting chemicals (EDCs) (dioctyl phthalate (DOP) and dibutyl phthalate (DBP), homologous series) at different concentrations were successfully identified by Au and Ag SERS arrays with the detection limits of 0.24 Â 10 À9 M and 0.22 Â 10 À9 M, respectively. This study suggests that the broccoli-like Au and Ag SERS arrays are promising candidates for chemical sensing and this SERS substrate fabrication technique can be accessible to the standard industrial processes. † Electronic supplementary information (ESI) available: FE-SEM images of SiO 2 colloidal crystal-assisted Ag SERS substrates at different deposition time (90 s, 180 s, and 300 s). EFs calculation of the broccoli-shaped Au and Ag SERS substrates. See

Highly monodispersed Ag embedded SiO2nanostructured thin film for sensitive SERS substrate: growth, characterization and detection of dye molecules

“…al. 26 have reported similar results. They showed that broccoli-shaped Ag deposited on SiO 2 colloidal crystal templates by physical deposition technique gives good enhancement.…”

“…N bulk =AhC bulk NA, where A is the area of the laser focal spot, h is the focal depth of the laser, and h is 13µm according to the work. 26 C bulk is the concentration of R6G bulk solution, here C bulk =10 -3 M, NA is the Avogadro constant surf ൌ ܸܰ ‫ܣ‬ ‫ݎߨ‬ ଶ The above calculations (see Fig.S11 †) were done for the 20 µl R6G solution (1x10 -3 M) and the R6G -absorbed on Ag@SiO 2 (1x10 -11 M, 20 µl) which were spread on the 1x1 cm 2 prepare substrate. A laser spot area of 5 µm and power of (15 mW) was applied with an accumulation number of 1sec for all recordings.…”

Analysis on superhydrophobic silver decorated copper Oxide nanostructured thin films for SERS studies

“…The decrease in the peak intensity is related to the reduced number of the R6G molecules in the collection volume of the Raman spectroscope. The change in peak shape and the shift in peak position are related to the change in the chemical bonding of the R6G molecules due to interactions between the molecules and the environment [27,28]. The spectral intensity of R6G on annealed Ag@CuO thin films shows improved SERS performance as compared to the as prepared counterparts from Fig.…”

Preparation of a native β-cyclodextrin modified plasmonic hydrogel substrate and its use as a surface-enhanced Raman scattering scaffold for antibiotics identification

“…1,2 As a molecule vibrational spectroscopy, the Raman technique showing abundant molecule information is highly suitable for the detection of complex pollutants. 3,4 For the SERS technology, one of the most important issues is substrate fabrication. A great progress has been achieved, but there are still challenges in the SERS substrate development.…”