Suspended-core microstructured fiber for refractometric detection of liquids.

A silica suspended-core microstructured optical fiber sensor for detection of liquids, operating at 1550 nm, is analyzed. The sensing principle is based on the evanescent wave overlap into a tested analyte, which is filled via capillary forces into the cladding holes. Validations for analytes in the refractive index range of 1.35-1.43 are carried out with liquid-analyte-filling-length limits being studied both theoretically and experimentally. We prove, for the first time to our knowledge, that an extreme sensitivity of 342.86 dB/RIU and resolution of 4.4×10-5 can be achieved. This sensor represents a high-quality alternative for applications requiring a facile, low-cost solution.

In vivo optical detection of pH in microscopic tissue samples of Arabidopsis thaliana.

Minimally invasive in vivo measurement of pH in microscopic biological samples of µm or µl size, e.g. plant cells, tissues and saps, may help to explain complex biological processes. Consequently, techniques to achieve such measurements are a focus of interest for botanists. This paper describes a technique for the in vivo measurement of pH in the range pH5.0 to pH7.8 in microscopic plant tissue samples of Arabidopsis thaliana based on a ratiometric fluorescence method using low-loss robust tapered fiber probes. For this purpose tapered fiber probes were prepared and coated with a detection layer containing ion-paired fluorescent pH-transducer 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (c-HPTS). A fluorescence ratiometric approach was employed based on excitation at 415 nm and 450 nm and on the comparison of the fluorescence response at 515 nm. The suitability of tapered fiber probes for local detection of pH between 5.0 and 7.8 was demonstrated. A pH sensitivity of 0.15 pH units was achieved within the pH ranges 5.0-5.9 and 7.1-7.8, and this was improved to 0.04 pH units within the pH range 5.9-7.1. Spatial resolution of the probes was better than 20 µm and a time response within 15-20s was achieved. Despite the minute dimensions of the tapered fiber probes the setup developed was relatively robust and compact in construction and performed reliably. It has been successfully employed for the in vivo local determination of pH of mechanically resistant plant tissues of A. thaliana of microscopic scale. The detection of momentary pH gradients across the intact plant seems to be a good tool for the determination of changes in pH in response to experimental treatments affecting for example enzyme activities, availability of mineral nutrients, hormonal control of plant development and plant responses to environmental cues.

High capacity optical channels for bioinformation transfer: acupuncture meridians.

Mammalian bodies are hierarchical systems whose internal cooperation and coherent activity require high capacity information transfer between the central control unit--the brain--and the periphery--the organs. A communication system capable of meeting information capacity requirements should be based on transmission of electromagnetic signals. Structures that fulfill requirements for such information transfer have not yet been analyzed. Acupuncture meridians have been demonstrated experimentally in some animals. They might represent systems of information transfer between the brain and the peripheral organs. The ducts of the meridians may correspond to optical fibers operating from the far infrared to the visible wavelength region. The main features of a model of the duct as an optical fiber are delineated and its properties outlined. However, to analyze essentials of the transmission capabilities, the whole meridian structure should be mapped and a more comprehensive set of physical parameters measured. In particular, experimental data concerning morphological arrangements of ordered water in the ducts and corpuscles, and a complete content of the biological particles in the flowing water and its permittivity are missing.