A dense array of small coupled waveguides in fiber technology: trefoil channels of microstructured optical fibers

Surface-enhanced Raman scattering-active photonic crystal fiber probe: Towards next generation liquid biopsy sensor with ultra high sensitivity

The tremendous enhancement factors that surface-enhanced Raman scattering (SERS) possesses coupled with the flexibility of photonic crystal fibers (PCFs) pave the way to a new generation of ultrasensitive biosensors. Thanks to the unique structure of PCFs, which allows direct incorporation of an analyte into the axially aligned air channels, interaction between the analyte and excitation light could be increased many folds leading to flexible, reliable and sensitive probes that can be used in preclinical or clinical biosensing. SERS-active PCF probes provide unique opportunity to develop an opto-fluidic liquid biopsy needle sensor that enables one-step integrated sample collection and testing for disease diagnosis. Specificity being a key parameter to biosensors, the PCF inside the biopsy needle could be functionalized with targeting moieties to detect specific biomarkers. In this review article, we present some of the most promising recent biosensors based on PCFs including hollow-core PCFs, suspended-core PCFs and side-channel PCFs. We provide a wide range of applications of such platform using Raman spectroscopy, label free SERS or labeled SERS detection and analyze some of the main challenges to be addressed for translating it to a clinically viable next generation sensitive biopsy needle sensing probe.

Ultrasensitive optofluidic surface-enhanced Raman scattering detection with flow-through multihole capillaries

3-Dimensional surface-enhanced Raman scattering (SERS) detection integrated with optofluidics offers many advantages over conventional SERS conducted under planar and static conditions. In this paper, we developed a novel optofluidic SERS platform based on nanoparticle-functionalized flow-through multihole capillaries for rapid, reliable, and ultrasensitive analyte detection. The unique configuration not only provides 3-dimensional geometry for significantly increased SERS-active area and inherent fluidic channels for rapid and efficient sample delivery, but also confines and transmits light along the capillary for large SERS signal accumulation. Using a capillary consisting of thousands of micrometer-sized holes adsorbed with gold nanoparticles, we investigated the proposed optofluidic SERS system using the transverse and longitudinal detection methods, where the SERS excitation and collection were perpendicular to and along the capillary, respectively. A detection limit better than 100 fM for rhodamine 6G was achieved with an enhancement factor exceeding 10(8).