No abstract

Surface-enhanced Raman scattering (SERS) has been a useful sensing technique, in which inelastic light scattering can be significantly enhanced by absorbing molecules onto rough metal surfaces or nanoparticles. Although many methods have been developed to prepare SERS substrates, it is still highly desirable and challenging to design SERS substrates, especially with highly ordered and controlled three-dimensional (3D) structures. In this work, we develop novel SERS substrates with regular volcano-shaped polymer structures using the versatile solvent on-film annealing method. Polystyrene (PS) nanospheres are first synthesized by surfactant-free emulsion polymerization and assembled on poly(methyl methacrylate) (PMMA) films. After annealing in acetic acid vapors, PMMA chains are selectively swollen and wet the surfaces of the PS nanospheres. By selectively removing the PS nanospheres using cyclohexane, volcano-shaped PMMA films can be obtained. Compared with flat PMMA films with water contact angles of ∼74°, volcano-shaped PMMA films exhibit higher water contact angles of ∼110°due to the sharp features and rough surfaces. The volcano-shaped PMMA films are then coated with gold nanoparticles (AuNPs) as SERS substrates. Using rhodamine 6G as the probe molecules, the SERS results show that the Raman signals of the volcano-shaped PMMA/AuNP hybrid substrates are much higher than those of the pristine PMMA films and PMMA films with AuNPs. For the volcano-shaped PMMA/ AuNP hybrid substrates using 400 nm PS nanospheres, a high enhancement factor (EF) value of ∼1.12 × 10 5 with a detection limit of 10 −8 M is obtained in a short integration time of 1 s. A linear calibration line with an R 2 value of 0.918 is also established, demonstrating the ability to determine the concentrations of the analytes. This work offers significant insight into developing novel SERS substrates, which is crucial for improving the detection limits of analytes.

In this paper, an effective approach is demonstrated for the fabrication of IrO 2 -decorated polystyrene@functionalized polypyrrole (core@shell; PS@PPyNH 2 ) microspheres. The synthesis begins with the preparation of monodispersive PS microspheres with a diameter of 490 nm, by a process of emulsifier-free emulsion polymerization, followed by a copolymerization process involving pyrrole and PyNH 2 monomers in a PS microsphere aqueous suspension, to produce uniform PS@PPyNH 2 microspheres with a diameter of 536 nm. The loading of 2 nm IrO 2 nanoparticles onto the PS@PPyNH 2 microspheres can be easily adjusted by tuning the pH value of the IrO 2 colloidal solution and the PS@PPyNH 2 suspension. At pH 4, we successfully obtain IrO 2 -decorated PS@PPyNH 2 microspheres via electrostatic attraction and hydrogen bonding simultaneously between the negatively-charged IrO 2 nanoparticles and the positively-charged PS@PPyNH 2 microspheres. These IrO 2 -decorated PS@PPyNH 2 microspheres exhibit a characteristic cyclic voltammetric profile, similar to that of an IrO 2 thin film. The charge storage capacity is 5.19 mA cm −2 , a value almost five times greater than that of PS@PPyNH 2 microspheres. In addition, these IrO 2 -decorated PS@PPyNH 2 microspheres exhibit excellent cell viability and biocompatibility.

The highly sensitive detection of hydrogen peroxide (H2O2) is of practical importance due to its involvement in the biofunction and signal transduction of cells. Various electrochemical techniques have been explored and studied for its detection, which can be realized through either enzymatic or non-enzymatic sensors. Particularly, non-enzymatic biosensors have been in great demand because of their high stability, high reproducibility, and less susceptible to environmental factors compared to the enzyme-based approach. However, many of them display inferior sensitivity or poor selectivity. Hence, this work aims to develop a highly sensitive non-enzymatic biosensor through structural and compositional approaches. From a structural point of view, Au inverse opals are utilized as the sensor scaffold due to their intriguing porous structure. The spatial arrangement of these materials resembles a honeycomb structure, which provides a high specific surface area, efficient mass transport, and strong mechanical stability. In addition to the benefits brought by inverse opals, we further incorporate a composite coating based on Cu2O to decorate the scaffold surface. Through the combination of a well-ordered pore structure with additional functionalization by composite formation, a synergistic improvement could be realized. To fabricate such structural biosensors, an expedited self-assembly process exploiting electrophoresis technique is first adopted to produce a colloidal crystal template. Subsequent electrodeposition processes are performed to construct the Au inverse opals and relevant functional coatings. The sensing performance of these 3D sensors is then evaluated by the detection of H2O2 using cyclic voltammetric analysis. Their structural and compositional characterizations are conducted by SEM, EDX, XPS, and Raman spectroscopy.

The detection of hydrogen peroxide (H2O2) is of practical importance due to its involvement in the functioning and signal transduction of living cells. Various electrochemical techniques have been explored using either enzymatic or non-enzymatic sensors. In particular, non-enzymatic biosensors have attracted considerable attention because of their impressive stability and reproducibility. In addition, they are less susceptible to environmental interferences. However, the primary drawback of non-enzymatic sensors is poor sensitivity and selectivity. Hence, we want to address this issue by fabricating Cu2O in an inverse opaline structure. Our process involves the preparation of Au inverse opals serving as a three-dimensional ordered macroporous conductive substrate that allows an excessive surface area and sufficient porosity for mass transport. The Cu2O is electrodeposited on the Au inverse opals for the detection of H2O2. Comprehensive electrochemical analysis and materials characterization are conducted and discussed.