Black silicon as a platform for bacterial detection.

Surface-enhanced Raman scattering (SERS) shows promise for identifying single bacteria, but the short range nature of the effect makes it most sensitive to the cell membrane, which provides limited information for species-level identification. Here, we show that a substrate based on black silicon can be used to impale bacteria on nanoscale SERS-active spikes, thereby producing spectra that convey information about the internal composition of the bacterial capsule. This approach holds great potential for the development of microfluidic devices for the removal and identification of single bacteria in important clinical diagnostics and environmental monitoring applications.

Ultra-pure, water-dispersed Au nanoparticles produced by femtosecond laser ablation and fragmentation.

Aqueous solutions of ultra-pure gold nanoparticles have been prepared by methods of femtosecond laser ablation from a solid target and fragmentation from already formed colloids. Despite the absence of protecting ligands, the solutions could be (1) fairly stable and poly size-dispersed; or (2) very stable and monodispersed, for the two fabrication modalities, respectively. Fluorescence quenching behavior and its intricacies were revealed by fluorescence lifetime imaging microscopy in rhodamine 6G water solution. We show that surface-enhanced Raman scattering of rhodamine 6G on gold nanoparticles can be detected with high fidelity down to micromolar concentrations using the nanoparticles. Application potential of pure gold nanoparticles with polydispersed and nearly monodispersed size distributions are discussed.

Optical fibers for miniaturized surface-enhanced Raman-scattering probes.

A range of optical fibers with surface-enhanced Raman scattering (SERS) functionalized tips have been evaluated for use as micro-scale sensing devices. In order to optimize the sensitivity of the optical fiber probe, the relationship between SERS intensity and different fiber parameters was investigated. It was found that the numerical aperture, core size, mode structure, and core material have a major effect on the probe performance, as does the numerical aperture of the microscope objective. The results suggest that an ideal fiber for SERS sensing should be single mode at the excitation wavelength and have low-background core material.