A spatial refractive index sensor using whispering gallery modes in an optically trapped microsphere

We propose the use of an optically trapped, dye doped polystyrene microsphere for spatial probing of the refractive index at any position in a fluid. We demonstrate the use of the dye embedded in the microsphere as an internal broadband excitation source, thus eliminating the need for a tunable excitation source. We measured the full width at half maximum of the TE and TM resonances, and their frequency spacing as a function of the refractive index of the immersion fluid. From these relations we obtained an absolute sensitivity of 5e-4 in local refractive index, even when the exact size of the microsphere was not a priori known.Comment: 3 pages, 3 figure

Single-Molecule Optical Biosensing:Recent Advances and Future Challenges

In recent years, the sensitivity and specificity of optical sensors has improved tremendously due to improvements in biochemical functionalization protocols and optical detection systems. As a result, single-molecule sensitivity has been reported in a range of biosensing assay formats. In this Perspective, we summarize optical sensors that achieve single-molecule sensitivity in direct label-free assays, sandwich assays, and competitive assays. We describe the advantages and disadvantages of single-molecule assays and summarize future challenges in the field including their optical miniaturization and integration, multimodal sensing capabilities, accessible time scales, and compatibility with real-life matrices such as biological fluids. We conclude by highlighting the possible application areas of optical single-molecule sensors that include not only healthcare but also the monitoring of the environment and industrial processes.</p

Efficient Mild Organosolv Lignin Extraction in a Flow-Through Setup Yielding Lignin with High beta-O-4 Content

Current lignin fractionation methods use harsh conditions that alter the native lignin structure, resulting in a recalcitrant material which is undesired for downstream processing. Milder fractionation processes allow for the isolation of lignins that are high in beta-aryl ether (beta-O-4) content, however, at reduced extraction efficiency. The development of improved lignin extraction methods using mild conditions is therefore desired. For this reason, a flow-through setup for mild ethanosolv extraction (120 degrees C) was developed. The influence of acid concentration, ethanol/water ratio, and the use of other linear alcohol co-solvents on the delignification efficiency and the beta-O-4 content were evaluated. With walnut shells as model feedstock, extraction efficiencies of over 55% were achieved, yielding lignin with a good structural quality in terms of beta-O-4 linking motifs (typically over 60 per 100 aromatic units). For example, lignin containing 66 beta-O-4 linking motifs was obtained with an 80:20 n-propanol/water ratio, 0.18 M H2SO4 with overall a good extraction efficiency of 57% after 5 h. The majority of the lignin was extracted in the first 2 hours and this lignin showed the best structural quality. Compared to batch extractions, both higher lignin extraction efficiency and higher beta-O-4 content were obtained using the flow setup