Fiber loop ringdown DNA and bacteria sensors

Application of fiber loop ringdown spectroscopy technique for a new approach to beta-amyloid monitoring for Alzheimer Disease's early detection

A novel fiber optic biosensor was purposed for a new approach to monitor amyloid beta protein fragment 1-42 (Aβ42) for Alzheimer's Disease (AD) early detection. The sensor was fabricated by etching a part of fiber from single mode fiber loop in pure hydrofluoric acid solution and utilized as a Local Optical Refractometer (LOR) to monitor the change Aβ42 concentration in Artificial Cerebrospinal Fluid (ACSF). The Fiber Loop Ringdown Spectroscopy (FLRDS) technique is an ultra-sensitive measurement technique with low-cost, high sensitivity, real-time measurement, continuous measurement and portability features that was utilized with a fiber optic sensor for the first time for the detection of a biological signature in an ACSF environment. Here, the measurement is based on the total optical loss detection when specially fabricated sensor heads were immersed into ACSF solutions with and without different concentrations of Aβ42 biomarkers since the bulk refractive index change was performed. Baseline stability and the reference ring down times of the sensor head were measured in the air as 0.87% and 441.6μs ± 3.9μs, respectively. Afterward, the total optical loss of the system was measured when the sensor head was immersed in deionized water, ACSF solution, and ACSF solutions with Aβ42 in different concentrations. The lowest Aβ42 concentration of 2 ppm was detected by LOR. Results showed that LOR fabricated by single-mode fibers for FLRDS system design are promising candidates to be utilized as fiber optic biosensors after sensor head modification and have a high potential for early detection applications of not only AD but possibly also several fatal diseases such as diabetes and cancer.

Reflective temperature sensor based on a fiber Bragg grating combined with a fiber loop ringdown technique

In this paper, a reflective fiber sensing system combined with a fiber loop ringdown technique for temperature detection is proposed. A fiber Bragg grating (FBG) with an initial center wavelength of 1543.33 nm was set as the sensor head. The experimental results showed that the average sensitivity of temperature was 1.003 µs/°C in the temperature range of 30-38°C, and the resolution was 0.007°C, which is 14 times better than the current FBG sensing demodulator. In addition, the system has the advantages of simple structure, low cost, and insensitivity to optical power fluctuation.

Fiber loop ringdown humidity sensor

An optical fiber relative humidity (RH) sensor based on the evanescent field-fiber loop ringdown (EF-FLRD) technique is demonstrated. The sensor was placed inside a chamber that provides a humidity reference and is monitored by a humidity meter. The presence of moisture in the chamber changes the refractive index of the medium; thus the ringdown time changes due to a change in the EF scattering loss induced in the sensor head. The sensor demonstrated a fast response (∼1  s), high sensitivity, and excellent reproducibility and reversibly. The EF-FLRD sensor can measure RH in a wide dynamic range of 4% to 100% at a constant temperature of 20±1°C.

Real time interrogation technique for fiber Bragg grating enhanced fiber loop ringdown sensors array

A novel fiber Bragg grating aided fiber loop ringdown (FLRD) sensor array and the wavelength-time multiplexing based interrogation technique for the FLRD sensors array are proposed. The interrogation frequency of the system is formulated and the interrelationships among the parameters of the system are analyzed. To validate the performance of the proposed system, a five elements array is experimentally demonstrated, and the system shows the capability of real time monitoring every FLRD element with interrogation frequency of 125.5 Hz.

Double-looped Mach-Zehnder interferometer for achieving multiple ring-down interferograms

We put forward a double-looped Mach-Zehnder interferometer for acquiring continuous ring-down interferograms with two fiber-loop cavities with slightly different optical path lengths. Each group of pulses through the sample and reference loops creates a ring-down pulse train with equal time intervals in Vernier fashion, and interferes with each other to produce multiple ring-down interferograms successively by scanning of a delay line. The system requires a scanning range of only a few millimeters to obtain multiple ring-down interferograms. In a proof-of-concept demonstration, the intrinsic losses of two loops are estimated. The measured combined-loss of both loops is compared to the sum of the loop losses measured separately with a conventional fiber-loop ring-down system. The result obtained using the proposed system exhibits a difference of only 0.06 dB with that of the reference system.

Evanescent field-fiber loop ringdown glucose sensor

Evanescent field-fiber loop ringdown (EF-FLRD) is a relatively new hybrid sensing technique which combines a versatile sensing mechanism with a sensitivity-enhanced ringdown detection scheme. An array of low cost, fast response, and high sensitivity biosensors based on the EF-FLRD technique can be developed. In this work, new fiber loop ringdown glucose sensors using refractive index-difference evanescent field attenuation effect as a sensing mechanism are described. The sensor head consists of either a section of partially-etched bare single mode fiber or a section of the etched fiber with glucose oxidase (GOD) immobilized on the etched fiber surface. Effects of the sensor head, with and without the immobilized GOD, on the sensor's performance are comparatively examined. The sensors' responses to standard glucose solutions and synthetic urines in different glucose concentrations ranging from 50 mg/dl to 10 g/dl are studied. The sensors, with or without the immobilized GOD, showed a linear response to glucose concentrations in the range of 100 mg/dl to 1 g/dl, but a nonlinear response in the higher glucose concentration ranging from 1 to 10 g/dl. The detection sensitivities of the sensors for the glucose solutions and artificial urine samples are 75 and 50 mg/dl respectively, and the sampling rate of the sensors is 10 to 100 Hz. Estimated theoretical detection sensitivity of the EF-FLRD glucose sensors is 10 mg/dl, which is approximately 17 times lower than the glucose renal threshold concentration.