Zero-mode waveguides have become important tools for the detection of single molecules. There are still, however, serious challenges because large molecules need to be packed into nano-holes. To circumvent this problem, we investigate and numerically simulate a novel planar sub-wavelength 3-dimension (3D) structure, which is named as near-field spot. It enables the detection of a single molecule in highly concentrated solutions. The near-field spot can produce evanescent waves at the dielectric/water interface, which exponentially decay as they travel away from the dielectric/water interface. These evanescent waves are keys for the detection of fluorescently tagged single molecules. A numerical simulation of the proposed device shows that the performance is comparable with a zero-mode waveguide. Additional degrees-of-freedom, however, can potentially supersede its performance.

Short acquisition time and small volumes of incubated bacterial cultures are ideal for the routine and rapid identification or screening of electricigens in research and applications of microbial fuel cells. In this study, a functional substrate based on colloidal photonic crystals (PCs) was developed both for the filtration and identification of electricigens by surface-enhanced Raman scattering (SERS). The fabrication of the substrate was simplified by electroless plating of silver on filtration-based self-assembled PCs on a filter membrane. The silver-plated ordered PC structure provided a 10⁷-fold enhancement of Raman intensity compared to that obtained with a bare PC substrate. The substrate allowed for a "drop and measure" method of bacterial identification within 5 min with a 5 μL sample volume only. The results showed that not only the electricigens Geobacter sp. and Shewanella sp. could be discriminated with species and strain specificity, but also Geobacter sp. and pilus-mutated Geobacter sp. strains. The developed silver-plated PC filter offers tremendous opportunities in energetic, environmental, and clinical applications.