Yunyun Huang

In-situ DNA hybridization detection with a reflective microfiber grating biosensor

A label-free fiber-optic biosensor with a reflective microfiber Bragg grating (mFBG) configuration for in-situ DNA hybridization detection has been proposed and experimentally demonstrated. A single straight Bragg grating inscribed in the silica microfiber provides two well-defined resonances in reflection, which show different response to external medium refractive index (RI) and present the same temperature sensitivity. By monitoring the wavelength separation between these two resonances, temperature-compensated RI measurement has been achieved. The label-free bio-recognition scheme used demonstrates that the sensor relies on the surface functionalization of a monolayer of poly-l-lysine (PLL), synthetic DNA sequences that bind with high specificity to a given target. In addition to monitoring the surface functionalization of the fiber in real-time, the results also show how the fiber biosensor can detect the presence of the DNA hybridization with high specificity, in various concentration of target DNA solutions, with lowest detectable concentration of 0.5 µM.

Highly sensitive detection of urinary protein variations using tilted fiber grating sensors with plasmonic nanocoatings

Surface plasmon resonance (SPR) optical fiber biosensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for high sensitivity biological sample measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. The biosensor configuration reported in this work uses a tilted fiber Bragg grating (TFBG) in a commercial single mode fiber coated with a nanometer scale silver film. The key point is that by reducing the silver film thickness to around 20-30 nm (rather than 50 nm for optimal SPR excitation), different modes of the TFBG spectrum present very high but opposite sensitivities to refractive index (RI) changes around the TFBG. Experimental results obtained with the coated TFBG embedded inside a microfluidic channel show an amplitude sensitivity greater than 8000 dB/RIU (Refractive Index Unit) and a limit of detection of 10(-5)RIU. Using this device, the effect of different concentrations of protein in rat urine was clearly differentiated between healthy samples, nephropatic samples and samples from individuals under treatment, with a protein concentration sensitivity of 5.5 dB/(mg/ml) and a limit of detection of 1.5 × 10(-3)mg/ml. Those results show a clear relationship between protein outflow and variations in the RI of the urine samples between 1.3400 and 1.3408, pointing the way to the evaluation and development of new drugs for nephropathy treatments. The integration of TFBGs with microfluidic channels enables precise measurement control over samples with sub-microliter volumes and does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices. Integration of the TFBG with a hypodermic needle on the other hand would allow similar measurements in vivo. The proposed optical fiber/microfluidic plasmonic biosensor represents an appealing solution for rapid, low consumption and highly sensitive detection of analytes at low concentrations in medicine as well as in chemical and environmental monitoring.

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.

Type IIa Bragg gratings formed in microfibers.

In this Letter, Type IIa Bragg gratings are inscribed into microfibers. The large germanium-doped core region of the multimode fiber provides the necessary photosensitivity to form a Type IIa grating when it is drawn down to the microscale. Reducing the diameter of the microfiber due to lower saturate modulation and the amplified tension-strain transformation effect can accelerate the formation of a Type IIa grating. This provides an efficient method for the fabrication of fiber gratings with 800°C temperature resistance.

Ultrasensitive and in situ DNA detection in various pH environments based on a microfiber with a graphene oxide linking layer

Correction for ‘Ultrasensitive and in situ DNA detection in various pH environments based on a microfiber with a graphene oxide linking layer’ by Yunyun Huang et al., RSC Adv., 2017, 7, 13177–13183.

Real-time, in-situ analysis of silver ions using nucleic acid probes modified silica microfiber interferometry

A sensitive Ag+ sensor based on nucleic acid probes modified silica microfiber interferometry is designed and developed. The probes on microfiber surface plays the part on catching Ag+ as tentacles, while their conformation change from random coils to hairpins. It induces the fiber surface refractive index change, which is captured by the optical fiber and translated into a significant wavelength shift in the interferometric fringe. Such a combination enables an improved concentration sensitivity of 0.22nm/log M and limit of detection of 1.36 × 10-9M, taking the advantage of real-time and in-situ analysis. It shows good selectivity in the present of many other metal ions and offers potential to analysis in real matrix, especially in the environmental samples must be analyzed in a short time. This may provide insights into the preparation of sensing platforms for optical quantification of other small molecular, supplementing the existing tools.

Silk fibroin diaphragm-based fiber-tip Fabry-Perot pressure sensor.

A miniature fiber-optic Fabry-Perot is built on the tip of a single mode fiber with a thin silk fibroin film as the diaphragm for pressure measurement. The silk fibroin film is regenerated from aqueous silk fibroin solution obtained by an environmentally benign fabrication process, which exhibits excellent optical and physicochemical properties, such as transparency in visible and near infrared region, membrane-forming ability, good adhesion, and high mechanical strength. The resulted Fabry-Perot pressure sensor is therefore highly biocompatible and shows good airtightness with a response of 12.3 nm/kPa in terms of cavity length change.

Understanding the pH-dependent interaction between graphene oxide and single-stranded DNA through a fiber-optic interferometer.

A method based on a fiber-optic interferometer to study the pH-dependent interaction between graphene oxide and single-stranded DNA chains is carried out with the assistance of a scanning electron microscope and a confocal laser scanning microscope. The various wavelength shifts of the interferometric fringes of the transmission spectrum reveal the different strengths of interaction between graphene oxide and single-stranded DNA in various pH environments. The present work demonstrates the feasibility of optical fibers for studying the interaction between graphene oxide and biomolecules. It provides a potential means to understand the intermolecular interactions. This technique might effectively supplement the existing tools.

Etching Bragg gratings in Panda fibers for the temperature-independent refractive index sensing

We demonstrate the evolution of the Bragg gratings inscribed in Panda fibers with chemical etching. The resonance wavelengths can blueshift with cladding reduction similar to the conventional counterparts. But the wavelength separation between the two polarizations is co-determined by the stress and the asymmetric shape effects. The fast and slow axes of the fiber can be reversed with each other and zero birefringence can be achieved by chemical etching the structure. When the stress-applying parts of the fiber are removed, the finalizing grating can be exploited for the temperature-independent refractive index sensing, since the modes corresponding to the two polarizations exhibit the dissimilar responses to the external refractive index change but the same response to temperature. Our device is featured with easy achievement, spectral controllability, and relative robustness.

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.