Search

The extensive use of antibiotics has become a serious concern due to certain deficiencies in wastewater facilities, their resistance to removal, and their toxic effects on the natural environment. Therefore, substantial attention has been given to the detection of antibiotics because of their potential detriment to the ecosystem and human health. In the present study, a novel design of indium tin oxide (ITO) coated U-shaped fiber optic lossy mode resonance (LMR) biosensor is presented for the sensitive detection of the antibiotic ciprofloxacin (CIP). The performance of the designed U-shaped LMR sensor is characterized in terms of its sensitivity, full width at half maximum (FWHM), the figure of merit (FOM), and the limit of detection (LOD). For the proposed U-shaped LMR sensing probe, the various crucial factors such as the thickness (d) of the ITO layer, sensing region length (L), and bending radius (R) are optimized. The thickness of the ITO layer is optimized in such a way that two LMR curves are observed in the transmission spectrum and, thereafter, the performance parameters are evaluated for each LMR. It is observed that the designed U-shaped LMR sensor with optimized parameters shows an approximately seven-fold enhancement in sensitivity compared to the straight-core fiber optic LMR sensor. The numerical results revealed that the designed U-shaped fiber optic LMR biosensor can provide a maximum sensitivity of 17,209.9 nm/RIU with the highest FOM of 91.42 RIU−1, and LOD of 6.3 × 10−5 RIU for the detection of CIP hydrochloride in the concentration range of 0.001 to 0.029 mol∙dm−3. Thus, it is believed that the designed LMR biosensor can practically explore its potential use in environmental monitoring and biomedical applications and hence, opens a new window of opportunity for the researchers working in the field of U-shaped fiber optic LMR biosensing. [ABSTRACT FROM AUTHOR]

A graphene-coated U-shaped fiber surface plasmon resonance sensor with high refractive index sensitivity is proposed. With the combination of graphene coating and U-shape design, the proposed sensor exhibits a significantly enhanced sensitivity as compared with the conventional Au-based straight fiber surface plasmon resonance sensor. The refractive index sensitivity of 15.52 μm/RIU (refractive index unit) is achieved by coating monolayer graphene on U-shaped fiber with a bent radius of 1.1 cm. A sensitivity enhancement factor of about 5-fold is obtained when compared with the conventional straight fiber surface plasmon resonance sensor with and without monolayer graphene coating. The effect of Au thickness, number of graphene layers, and the bent radius on the sensor performance was investigated. The high sensitivity of the proposed graphene-coated U-shaped fiber surface plasmon resonance sensor makes it a promising candidate for biosensing and chemical sensing. [ABSTRACT FROM AUTHOR]

The U-shaped multimode fiber structure is proposed to measure the refractive index of liquid. In the previous work, the U-shaped structure by single-mode fiber has been widely investigated. However, the large bending loss restricted its practical applications, especially for the reflection-type fiber probe. To reduce the bending losses, the multimode fiber is used as the bending section of the fiber sensor in this study. The structures with different bending radiuses are fabricated to verify this design. Moreover, to simplify the interrogation method, the differential intensity interrogation method is used by cascading two fiber Bragg gratings after the U-shaped fiber structure. The low bending loss of the proposed structure is helpful to measure the reflected light power by fiber Bragg gratings. The influence of incident light power fluctuation was largely suppressed by this differential method. In addition, the sensitivity is also increased by a factor of 2 compared with the intensity interrogation method using one-cascaded fiber Bragg grating. The experimental results show that the refractive index sensitivities are −115.09 dB/RIU in the refractive index range of 1.3405-1.3874 and −260.24 dB/RIU in the refractive index range of 1.3874-1.4223, respectively. [ABSTRACT FROM AUTHOR]

An optical temperature sensor using a U-shaped microfiber incorporated with the thermal expansion of a metal plate and the reflection of a silver coated mirror is demonstrated. A microfiber about 5.8 μm waist diameter is fabricated using the systematic flame brushing technique, and lately, U-shaped structure is made. The proposed sensing mechanism uses the expansion of the metal plate and the reflectivity of the silver-coated circular shape mirror and measures the average output power change with respect to temperature variations. Two types of metal are investigated in this study, namely Aluminum (Al) and Copper (Cu), which have different thermal expansion coefficients. Therefore, when heated, the expansion of the metals occurs in a different degree, which affects the sensing mechanism, and therefore, a difference has been observed in terms of power loss with respect to the temperature variation. The sensitivity of the U-shape microfiber by using Al and Cu metal plates are measured as 0.0018 dB m/ ºC and 0.0007 dB m/ ºC, respectively. Moreover, the effect of a reflective mirror has also been investigated by placing the mirror on the top of the metal plates. With the inclusion of the mirror in the experimental set-up, the sensitivity of the U-shape microfiber using Al and Cu metal plates are measured as 0.0019 dB m/ ºC and 0.0012 dB m/ ºC, respectively. [ABSTRACT FROM AUTHOR]