Tapered optical fiber DNA biosensor for detecting Leptospira DNA

Objective: To establish a DNA detection platform based on a tapered optical fiber to detect Leptospira DNA by targeting the leptospiral secY gene.Methods: The biosensor works on the principle of light propagating in the special geometry of the optical fiber tapered from a waist diameter of 125 to 12 μm. The fiber surface was functionalized through a cascade of chemical treatments and the immobilization of a DNA capture probe targeting the secY gene. The presence of the target DNA was determined from the wavelength shift in the optical transmission spectrum.Results: The biosensor demonstrated good sensitivity, detecting Leptospira DNA at 0.001 ng/μL, and was selective for Leptospira DNA without cross-reactivity with non-leptospiral microorganisms. The biosensor specifically detected DNA that was specifically amplified through the loop-mediated isothermal amplification approach.Conclusions: These findings warrant the potential of this platform to be developed as a novel alternative approach to diagnose leptospirosis.

Temperature sensor based on a single-mode tapered optical fiber

A temperature sensor is demonstrated and fabricated by coating the single-mode tapered optical fiber with temperature-sensitive silicone rubber. It works on the change of the evanescent fields in the tapered optical fiber. Small changes in the refractive index of coating film greatly influence the power of evanescent fields, which modulate the transmission optical power in the waist region. The range of temperature measured is from -20℃ to 70 ℃. The results show that the temperature sensor has high temperature sensitivity （0.012 mW/℃） and good repeatability.

Measurement of refrative index based on fiber Mach-Zehnder interference

In order to detect the refractive index of liquid with high precision,based on modular interference,Mach-Zehnder optical fiber refractive rate sensor was studied.Sensor structure is composed of ordinary single-mode fiber and multimode fiber,according to the singlemode multimode singlemode sequence to fuse together,and the fused optical fiber is used to process the taper.As a result,the diameter of the sensing head is about 10μm.Experimental results show that,as liquid refractive index increases range from 1.33 to 1.35,the loss peak of the transmission spectrum will shift to long wave direction.

Nonadiabatic Tapered Optical Fiber for Biosensor Applications

A brief review on biconical tapered fiber sensors for biosensing applications is presented. A variety of configurations and formats of this sensor have been devised for label free biosensing based on measuring small refractive index changes. The biconical nonadiabatic tapered optical fiber offers a number of favorable properties for optical sensing, which have been exploited in several biosensing applications, including cell, protein, and DNA sensors. The types of these sensors present a low-cost fiber biosensor featuring a miniature sensing probe, label-free direct detection, and high sensitivity.

Graphene-and Multi-Walled Carbon Nanotubes-Coated Tapered Plastic Optical Fiber for Detection of Lard Adulteration in Olive Oil

A rapid and high-performance sensor for lard adulterant in edible oil was developed using the tapered plastic optical fiber(POF)coated with graphene and multi-walled carbon nanotubes.The coating material was deposited onto a tapered POF with a taper waist diameter and a taper length of 0.45 mm and 1 cm,respectively.The addition of the coating material was used to increase the sensitivity and selectivity coefficient of the tapered POF toward the lard substance.The sensing mechanism is based on a simultaneous interaction of lard substance and an evanescent wave of tapered POF with the coating layers.The results showed that graphene coating on the tapered POF increased the selectivity coefficient of the tapered POF towards lard substance from 33.54 to 324.19,and it gave a sensitivity of 0.427 dBm/%.In comparison,multi-walled carbon nanotubes coating increased the selectivity coefficient to 71.65 and increased its sensitivity to 1.189 dBm/%.Thus,the proposed configuration of the tapered POF with the coating material offered a simple configuration for a rapid,high sensitivity and selectivity detection of lard adulterant in edible oils.

Evanescent Wave Absorption Sensor Based Tapered Plastic Optical Fiber Coated with Monolayer Graphene for Ethanol Molecules Detection

An evanescent wave absorption （EWA） sensor based tapered plastic optical fiber （TPOF） coated with monolayer graphene film for ethanol molecules detection is demonstrated in this study. The continuous and monolayer graphene films were grown on a Cu foil by using chemical vapor deposition （CVD） technology. Polymethyl methacrylate （PMMA） was used as the carrier to support the transfer of graphene from Cu foil to the skinless tapered optical fiber core. The accuracy of the TPOF sensor with graphene （G-TPOF sensor） is much higher than that without gra- phene （TPOF sensor）, which can be attributed to the molecules enriched on the surface of graphene. The absorbance （A） and the concentrations of ethanol solution show an excellent proportional relationship in a range of 0--100%. The dynamic response of the G-TPOF sensor has shown strong reversibility, repeatability and stability at room temperature. The response time and recovery time of the G-TPOF sensor for different concentrations are all less than 30 s. Beyond that, we selected the Chinese liquor as the analyte, and the results are consistent with the concen- tration-list obtained in the experiment.

Optical trapping and orientation of Escherichia coli cells using two tapered fiber probes

We report on the optical trapping and orientation of Escherichia coli(E.coli) cells using two tapered fiber probes.With a laser beam at 980 nm wavelength launched into probe I, an E. coli chain consisting of three cells was formed at the tip of probe I. After launching a beam at 980 nm into probe II, the E.coli at the end of the chain was trapped and oriented via the optical torques yielded by two probes. The orientation of the E. coli was controlled by adjusting the laser power of probe II. Experimental results were interpreted by theoretical analysis and numericalsimulations.

Single-Mode Modified Tapered Fiber Structure Functionalized With GO-PVA Composite Layer for Relative Humidity Sensing

A sensitive tapered optical fiber sensor incorporating graphene oxide(GO)and polyvinyl alcohol(PVA)composite film for the rapid measurement of changes in relative humidity was proposed and experimentally demonstrated.The sensing principle was based on the intensity modulation of the transmitted light induced by the refractive index changes of the sensitive coatings.The sensing region was obtained by tapering a section of single-mode optical fiber(SMF)from its original 125µm diameter down to 9.03µm.The tapered structure was then modified through deposition of GO/PVA nanocomposites by using the dip-coating technique.The field emission scanning electron microscope(FESEM)and Raman spectroscopy were used to characterize the structure of the composite film.As evidenced by a Fourier transform infrared spectroscopy(FTIR)analysis,the presence of oxygen functional groups(such as−OH and COOH)on the GO structure enabled the attachment of PVA molecules through hydrogen bonding and strong adhesion between GO/PVA layers.The performance of the sensor was tested over a wide range(20%RH to 99.9%RH)of relative humidity.The sensor showed a good response with its signal increasing linearly with the surrounding humidity.The tapered optical fiber sensor with the coating of GO/0.3g PVA achieved the highest sensitivity[0.5290RH(%)].The stability,repeatability,reversibility,as well as response time of the designated sensor were also measured and analyzed.