Ag-nanoparticle-decorated Ge nanocap arrays protruding from porous anodic aluminum oxide as sensitive and reproducible surface-enhanced Raman scattering substrates

Advanced Nanoporous Anodic Alumina-Based Optical Sensors for Biomedical Applications

Close-packed hexagonal array nanopores are widely used both in research and industry. A self-ordered nanoporous structure makes anodic aluminum oxide (AAO) one of the most popular nanomaterials. This paper describes the main formation mechanisms for AAO, the AAO fabrication process, and optical sensor applications. The paper is focused on four types of AAO-based optical biosensor technology: surface-Enhanced Raman Scattering (SERS), surface Plasmon Resonance (SPR), reflectometric Interference Spectroscopy (RIfS), and photoluminescence Spectroscopy (PL). AAO-based optical biosensors feature very good selectivity, specificity, and reusability.

Plasmonic 3D Semiconductor-Metal Nanopore Arrays for Reliable Surface-Enhanced Raman Scattering Detection and In-Site Catalytic Reaction Monitoring

It is urgent to develop a rapid, reliable, and in-site determination method to detect or monitor trace amounts of toxic substances in the field. Here, we report an alternative surface-enhanced Raman scattering (SERS) method coupled with a portable Raman device on a plasmonic three-dimension (3D) hot spot sensing surface. Plasmonic Ag nanoparticles (AgNPs) were uniformly deposited on 3D TiO₂ nanopore arrays as a sensitive SERS substrate, and further coated with graphene oxide (GO). We demonstrate the plasmon-induced SERS enhancement (5.8-fold) and the improvement of catalytic activity by incorporation of plasmonic AgNPs into the 3D TiO₂ nanopore arrays. The modification of GO on the TiO₂-Ag nanopore array further increases by a 6.2-fold Raman enhancement compared to TiO₂-Ag while maintaining good uniformity (RSD < 10%). The optimized TiO₂-Ag-GO substrate shows powerful quantitative detection potential for drug residues in fish scales via a simple scrubbing method, and the limit of detection (LOD) for crystal violet (CV) was 10^-8 M. The SERS substrate also showed detection practicability of pesticide residues in banana peel with an LOD of 10^-7 M. In addition, our TiO₂-Ag-GO substrate exhibits excellent SERS self-monitoring performance for catalytic reduction of multiple organics in NaBH₄ solution, and the substrate shows good recyclability of 6 cycles. Such a 3D TiO₂-Ag-GO substrate is a promising SERS substrate with good sensitivity, uniformity, and reusability, and may be utilized for further miniaturization for point of analytical applications.

Aptamer-based surface-enhanced Raman scattering-microfluidic sensor for sensitive and selective polychlorinated biphenyls detection

A surface-enhanced Raman scattering (SERS) measurement of 3,3',4,4'-tetrachlorobiphenyl (PCB77) with aptamer capturing in a microfluidic device was demonstrated. To construct the microfluidic chip, an ordered Ag nanocrown array was fabricated over a patterned polydimethylsiloxane (PDMS) that was achieved by replicating an anodic aluminum oxide (AAO) template. The patterned PDMS sheet was covered with another PDMS sheet having two input channel grooves to form a close chip. The Ag nanocrown array was used for the SERS enhancement area and the detection zone. PCB 77 aptamers were injected into one channel and the other allows for analytes (PCBs). The mercapto aptamers captured the targets in the mixed zone and were immobilized to the SERS detection zone via S-Ag bonds so as to further improve both the SERS sensitivity and selectivity of PCB77. Such an aptamer-based microfluidic chip realized a rapid SERS detection. The lowest detectable concentration of 1.0 × 10(-8) M was achieved for PCB77. This work demonstrates that the aptamer-modified SERS microfluidic sensor can be utilized for selective detections of organic pollutants in the environment.

Gallium/gold composite microspheres fixed on a silicon substrate for surface enhanced Raman scattering

Gallium/gold composite microspheres fixed on a silicon substrate were successfully fabricated and used as a SERS substrate to detect malachite green molecules.