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Surface-enhanced Raman spectroscopy (SERS) has become one of the most important analytical tools and has been widely applied in many fields. However, the preparation of large-scale SERS substrates is still a challenge for practical applications. In this work, the approach of applying stepwise anodic aluminum oxidation (AAO) potentials was adopted to prepare the SERS substrate templates with the nanotip structure, on which the Ag/Au nanoparticles (NPs) nanoarrays with the regular hexagonal structure and adjustable gaps were prepared by sputtering Ag-NPs or Au-NPs on the nanotips. Due to the formation of "hotspots", these ordered Ag/Au nanoarrays exhibited strong SERS activity for detecting R6G with a concentration as low as 10⁻1⁴ M. Furthermore, we also prepared the transparent SERS substrates based on the as-fabricated AAO templates, and for practical application, these SERS substrates could be directly placed on the surface of food to probe the residual pesticides. For example, using the transparent SERS substrates, the residual pesticides such as carbendazim and chlorothalonil on the surface of edible mushroom Lentinus edodes could be detected with the lower detection limit below 10 μg/L. Therefore, this work has not only demonstrated a simplified approach to preparing large-scale effective SERS substrates but also provided a practical approach to rapid detection of agricultural pesticide residues useful for food safety inspection. [Display omitted] • Stepped anodic aluminum oxidation (AAO) potentials were adopted to prepare the templates with the regular nanotip structure. • This approach has simplified the previous fabrication process of multiple steps of anode oxidation and acid etching. • Au/Ag nanoparticles were sputtered on the AAO templates for achieving SERS nanoarray substrates with high SERS activity. • The prepared transparent SERS substrates could be placed directly on the surface of food for pesticide detection. [ABSTRACT FROM AUTHOR]

Abstract: A class of nanoporous TiO2 gas sensors processed by novel anodic aluminum oxidation (AAO) of Al thin films and microelectromechnical systems (MEMS) techniques are presented. To enhance the sensitivity and reduce the sensing dimensions of a gas sensor, a nanoporous surface of the gas-sensitive material on the sensor is required. These sensors can be implemented on silicon or silicon dioxide substrate featuring a thin membrane of micro-hotplate structure featuring micro-heaters, thermometers and electrodes, and thus operate as chemoresistive devices. Combining the AAO method with dry-etch process, a homogeneous and nanoporous SiO2 surface of the sensor can be effectively configured by modulating various hole diameters and depth, hence replacing conventional photolithography and electrochemical etch. The process integration including AAO, reactive ion etch (RIE) and microfabrication is mainly developed and a feasibility study of PVD TiO2 thin film deposition upon the porous device is also provided. TiO2 thin films deposited on the nanoporous surface are investigated and compared with non-porous TiO2 films. It is encouraging that our fabrication process is able to provide relatively high surface area to enhance sensitivity of the sensor without additional doping steps. Our promising experimental results have revealed these miniature and cost-effective devices are not only compatible, but applicable to smart bio-chemical sensors of next generation. [Copyright &y& Elsevier]

Nanostructured membrane structures have been fabricated by a combination of anodic aluminum oxidation (AAO) and atomic layer deposition (ALD) for use as platforms for the synthesis of highly uniform heterogeneous catalysts. The ALD method makes it possible to control pore diameters on the Angstrom scale even when the overall pore diameter is 10’s to 100’s of nanometers. AAO membranes imbedded in an aluminum sealing ring have been tested for flow properties and found to follow Knudsen diffusion behavior. Vanadia-coated membranes have been tested for the catalytic oxidative dehydrogenation of cyclohexane and show improved selectivity at the same conversion compared to conventional powdered alumina supported vanadia catalysts. [ABSTRACT FROM AUTHOR]