Zhuang Tian

High-sensitivity DNA biosensor based on optical fiber taper interferometer coated with conjugated polymer tentacle

A sensitive bio-probe to in situ detect unlabeled single-stranded DNA targets based on optical microfiber taper interferometer coated by a high ordered pore arrays conjugated polymer has been presented. The polymer coating serves as tentacles to catch single-stranded DNA molecules by π-π conjugated interaction and varies the surface refractive index of the optical microfiber. The microfiber taper interferometer translates the refractive index information into wavelength shift of the interference fringe. The sensor exhibits DNA concentration sensitivity of 2.393 nm/log M and the lowest detection ability of 10(-10) M or even lower.

Potential for Simultaneous Measurement of Magnetic Field and Temperature Utilizing Fiber Taper Modal Interferometer and Magnetic Fluid

A single taper-based fiber modal interferometer with magnetic fluid integrated, which can have responses of dip wavelength and extinction ratio on the external magnetic field and temperature changes, is demonstrated. Within the magnetic field range from 50 to 100 Oe, the measured sensitivities are 88 pm/Oe and -0.1419 dB/Oe for dip wavelength and extinction ratio, respectively, and within the temperature range from 30 to 80 °C, the sensitivities are -282.67 pm/°C and -0.0528 dB/°C for dip wavelength and extinction ratio, respectively. A full analysis to the sensing mechanism is given and experimental results can verify the concepts of the device. The presented structure is featured with simplification, easy fabrication, and high sensitivity and should have potential applications in simultaneous magnetic field and temperature measurements.

Nonradiation Cellular Thermometry Based on Interfacial Thermally Induced Phase Transformation in Polymer Coating of Optical Microfiber

A nonradiation approach based on thermoresponsive polymer coated silica microfibers has been developed. A highly thermoresponsive and biocompatible poly(N-isopropylacrylamide) (pNIPAM) was surface functionlized to conjugate to the tapered silica microfiber with waist diameter of 7.5 μm. The interfacial phase transtition of coating triggered by the lower critical solution temperature (LCST) causes a drastic molecular morphological change in the body temperature range of 35-42 °C. This surface morphological change strongly modulates optical path difference between the higher order and the fundamental mode propagating in the microfiber because of the evanescent-field interaction and, therefore, shifts the intermodal interference fringe. Owing to the nonradiation-based nature, the thermoresponsive polymer coated microfiber enables an improved thermal sensitivity of 18.74 nm/°C and, hence, a high-temperature resolution of millidegree. Furthermore, the micrometer-sized footprint enables its easy implantation in human organs for cellular thermometry and for the potential of in vivo applications.

A tapered optical fiber interferometer study on the microdynamics phase separation mechanism of the poly(N-isopropylacrylamide) aqueous solution

Phase separation process of poly (N-isopropylacrylamide) (PNIPAM) aqueous solution was investigated by tapered optical fiber technique in this work. The optical transmission spectra revealed the transition of molecular conformation and aggregation of molecular chains in the course of phase separation and identified the lower critical solution temperatures (LCST) in a simple and clear way. It was found that upon heating PNIPAM chains changed from expanded coils to collapsed globules and then aggregated. It offers a new characterization technique for studying phase separation of polymer solutions or blends, and could provide abundant information of the interaction between two different macromolecules, revealing the internal mechanism of the interaction.

Magnetic field sensor utilizing bent fiber taper and magnetic fluid

A magnetic field sensor is demonstrated by placing a bent-fiber taper modal interferometer inside a magnetic fluid sealed with an organic glass base. Owing to the strong refractive index dependency of the interferometer and magneto-optics property of the fluid, our sensor exhibits high sensitivity to the external magnetic field change. A linear wavelength dependency of ~58pm/Oe is experimentally obtained within a magnetic field range from 30 to 80 Oe. Our structure is featured of high sensitivity, fiber-compatibility, compactness, and robustness.

Magnetic field sensor utilizing rectangular-microfiber-based Sagnac loop interferometer

We fabricate a magnetic field sensor by immersing a rectangular microfiber into a magnetic fluid in a Sagnac polarization interferometer. The measured sensitivity is ∼98pm/Oe in the magnetic field range from 0 to 85Oe.

A stable, Label-free Silica Fiber Taper Interferometer Biosensor Based on Mesoporous Fe3O4@SiO2 Nanospheres

A high-sensitivity biosensor based on mesoporous Fe<inf>3</inf>O<inf>4</inf>@SiO<inf>2</inf> nanospheres coated fiber taper interferometer is presented. And the special selectivity of SiO<inf>2</inf> film improves concentration sensitivity reaching to 1.0524 nm/log M with good linearity.

High-sensitivity temperature sensor based on highly-birefringent microfiber

We demonstrate an ultrasensitive temperature sensor by sealing a highly-birefringent microfiber into an alcoholinfiltrated copper capillary. With a Sagnac loop configuration, the interferometric spectrum is strongly dependent on the external refractive index (RI) with sensitivity of 36800nm/RIU around RI=1.356. As mainly derived from the ultrahigh RI sensitivity, the temperature response can reach as high as −14.72 nm/°C in the range of 30.9-36.9 °C. The measured response time is ~8s, as determined by the heat-conducting characteristic of the device and the diameter of the copper capillary. Our sensor is featured with low cost, easy fabrication and robustness.