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The detection of diabetes at an early stage is considered to be highly significant in the successful treatment of the disease. The patient has been reported to generate unique volatile organic compounds (VOCs) profiles in their exhaled breath which can be utilized as biomarkers to diagnosis the disease conditions. In this article, we theoretically report a simple breath sensor for the highly sensitive detection of isopropanol (IPA), which is the biomarker for both types of diabetes, in exhaled breath using a D-shaped composite plasmonic sensor (DSCPS). The sensing response of the sensor is characterized by using a full-vectorial finite element method (FEM) for the detailed analysis of DSCPS, where a porous TiO2 (P-TiO2) layer is used as low index sensing material on the top of thin Ag film. The design of the proposed sensor is based on the wavelength modulation technique. A maximum sensitivity of 0.25, 0.35, 0.45, and 1.35 nm/% can be achieved for 20%, 40%, 60%, and 80% volume fraction of IPA, respectively, with a 30% porosity of TiO2, which is the maximum filled porous voids that provides the highest sensitivity.

In this article, a highly sensitive surface plasmon resonance (SPR) based concave shaped refractive index sensor (CSRIS) is designed and analyzed using silver (Ag) nanowire. The SPR effect between the surface plasmon polariton (SPP) and core guided modes of the concave shape (CS) designed sensor is used to measure the variation in refractive index (RI) of analytes (na). The sensing performance and the coupling properties of proposed sensor are numerically analyzed using finite element method (FEM) based on COMSOL Multiphysics. Results exhibit a high wavelength and amplitude sensitivity of 9314.28 nm/RIU and 1494 RIU -1 , respectively for the RI varying between 1.33 to 1.38 with the resolution of 1.073×10 -5 RIU. The designed sensor is easy to fabricate as it requires the Ag nanowire to be deposited on the concave shaped microfluidic channel (CSMFC) which is later covered with measurand. various structural parameters, i.e. distance of channel from core, diameter of Ag nanowire, and channel size, are also optimized for better sensing response.

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core–shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors.

In this article, a cost-effective hollow core fiber (HCF)-based refractive index (RI) sensor using surface plasmon resonance (SPR) is designed and demonstrated. The sensor consists of a metal nanowire inside an HCF along with the sensing medium of various refractive indices. SPR effect between polaritons and the guided core mode of designed HCF is exploited to enhance the sensing performance. A full vectorial finite element method (FEM) is used for the design and analyses of the sensing probes which exhibit very high sensitivities of 12,400 nm/RIU, 10560 nm/RIU, and 6400 nm/RIU for copper (Cu), gold (Au), and silver (Ag), respectively with a resolution of 1.61 × 10−6 RIU. Additionally, the influence of metal wire dimension is also investigated in this paper. The reported simple and low-cost sensor exhibits high sensitivity for liquid with refractive indices slightly higher than that of the dielectric tube, such as olive oil, turpentine, kerosene, chloroform, carbon tetrachloride, glycerol, and toluene.

A dual core photonic crystal fiber (DCPCF) consisting single analyte channel is proposed in this article for the detection of petrol adulteration. The sensing probe is numerically studied using finite element method. The adulterated petrol sample is infiltrated in circular analyte channel which is situated at the center of the fiber between two solid light guiding cores. The mode coupling between these two cores as well as sensitivity of the designed probe are investigated by varying adulteration level of petrol. Also the structure is optimized step by step. The numerical simulation result shows very high sensitivity of 20,161.2 nm/RIU for practically usable small probe. A portable adulteration detection sensor can be manufactured using this simple structured DCPCF probe which will be useful to study environmental pollution, maintaining long engine lifetime, save revenue.

A highly sensitive refractive index (RI) sensor based on a microfluidic channel (MFC) incorporated in a single-mode fiber (SMF), filled with Ag-graphene composite nanowire is presented and analyzed here. The sensing performance and the coupling properties of designed sensor are numerically analyzed by using a full vectorial finite element method (FEM) incorporating amplitude and wavelength interrogation techniques in the detection range varied from ${n_a}$ = 1.330-1.350. The maximum wavelength and amplitude sensitivity are obtained of 13700 nm/RIU and 1026 RIU−1, respectively. Here, the Ag-graphene composite nanowire can not only solve the problem of oxidation but also enhances the sensitivity of the sensor. In addition of high sensitivity, it also provides better performance than other sensing devices based on similar technologies such as Ag nanowire-filled sensors. Moreover, the influences of polishing depth (D), nanowire radius (rn), graphene layer (Lg) and channel size (s) on the designed sensor, are also thoroughly investigated here. The present work can provide a base for designing a real-time, highly sensitivity, remote sensing, and distributed SPR based RI sensor.

In present work we report the fabrication and characterization of optical fiber pH sensor using smart hydrogel coating over Zinc Oxide (ZnO) microflowers. ZnO microflowers were hydrothermally grown over chemically etched tapered multi-mode fiber (MMF). Mainly, the sensing head contains two layers in which one is ZnO microflower and another is pH sensitive hydrogel layer. The variation in pH of liquid around the sensing probe causes the swelling and shrinkage of hydrogel which leads the change in its refractive index (RI). The work of ZnO microflower is to enhance the evanescent waves that interact with the change in RI of hydrogel which causes the variations of wavelength dips with respect to each pH solutions. The sensitivity was estimated by using wavelength interrogation technique. The ZnO microflower based sensor is highly sensitive for wide range pH values (both high and low range of pH varied from pH = 3 to pH = 7 and pH = 7 to pH = 11, respectively). The sensitivity of ZnO microflower based MMF sensor was found to be 2.59 nm/pH and 0.70 nm/pH for both acidic and basic media, respectively. In addition to high sensitivity, the proposed sensor shows fast response time and good stability and reproducibility.

An optical fiber sensor is fabricated and characterized in this communication for salinity detection. The proposed sensor consists of a multimode fiber (MMF) and a section of no core fiber (NCF) with a round tip. The sensor detects the intensity variation of the back reflected light caused by changing concentration of the salt solution surrounding the probe. The parameters of the sensor were studied for better performance. A down tapering is also introduced to enhance the sensitivity of the sensor and a high sensitivity of 0.773 dB/% is obtained for a salinity range of 0–20%. Due to its high sensitivity, low cost and compact size, the proposed sensor can be very much useful in water quality monitoring for environmental, healthcare and industrial applications.

In the present study we report the fabrication and characterization of no-core fiber sensor (NCFS) using smart hydrogel coating for pH measurement. The no-core fiber (NCF) is stubbed between two single-mode fibers with SMA connector before immobilizing of smart hydrogel. The wavelength interrogation technique is used to calculate the sensitivity of the proposed sensor. The result shows a high sensitivity of 1.94 nm/pH for a wide range of pH values varied from 3 to 10 with a good linear response. In addition to high sensitivity, the fabricated sensor provides a fast response time with a good stability, repeatability and reproducibility.

In the present paper the fabrication and characterization of down-tapered optical fiber based pH sensor have been reported. The sensing probe is formed by fusing single mode fibers (SMF) to make it down-tapered which is spliced with multi-mode fiber (MMF). The sensing region is immobilized with sol-gel prepared by mixture of tetraethyl orthosilicate with three different pH indicators on to cladding of middle SMF. The proposed sensor utilizes intensity interrogation method and operates in low and high pH values. The maximum sensitivity of 0.49 dBm/pH is obtained with a good linear response for wide range of pH value varied from 4 to 13. In addition to high sensitivity, this sensor has additional advantages of good stability, fast response time and capable of using in remote sensing.

An intrinsic intensity modulated no core fiber sensor (NCFS) is presented in this paper for rapid detection of adulteration in petrol with kerosene. The sensing principle is based on the phenomenon of absorption of evanescent waves. The sensing head of NCFS is fabricated by stubbing a small section of no core fiber (NCF) between two multi-mode fibers (MMF). A high sensitivity 390 nW/% and 110 nW/% are obtained by the proposed sensor for low and high level of adulteration. The intensity variation and confinement loss with different concentrations of the kerosene in petrol are then verified theoretically by using finite element method. It is found that the theoretical results agree very well with experimental results. The proposed sensor exhibits fast response time and good repeatability in addition to its high sensitivity. The sensor can be useful in industries and automotive companies due to its small size, easy to fabricate, safe with inflammable fuels and required small amount for detection.

In this paper, a hexagonal structure of ethanol filled solid core photonic crystal fiber having dispersion shifted properties is presented. The guiding properties, like effective mode area and dispersion, of the ethanol filled photonic crystal fiber are studied by using the full vectorial finite element method. The numerical simulation results show that the selectively filling of the ethanol in the cladding holes of photonic crystal fiber shifts the zero dispersion wavelength from near infrared region (0.98 μm) to mid infrared region (1.55 μm). This kind of photonic crystal fiber structure is very useful for dispersion compensating tool, sensing applications, fiber laser devices and non-linear applications like supercontinuum generation.

In the present paper a novel cone shaped nano-fiber (CSNF) pH sensor using multi-mode fiber (MMF) has been fabricated and demonstrated. Three different pH indicators, chlorophenol red, bromothymol blue and cresol red with precursor tetraethyl orthosilicate (TEOS) have been used for fabrication of pH sensing layer. A significant enhancement in sensing properties of pH sensor with TiO 2 thin film has been observed. The pH sensor with TiO 2 thin film shows the quite high sensitivity (1.16 dBm/pH) as compared to sensor with simple pH coating (0.81 dBm/pH) at 1550 nm with a good linear response. Moreover, the sensor with TiO 2 film exhibits fast response time of ∼ 25 s for pH values ranging from 4 to 11 with excellent stability and durability.

A side-polished macro bend fiber sensor is fabricated and demonstrated here. The working principle is based on the macro bending loss and evanescent field absorption. A sensitivity of 90nW/% and 45nW/% are obtained for low and high level of adulteration respectively.

A wide range and highly sensitive U shaped optical fiber pH sensor utilizing titanium dioxide (TiO 2 ) layer with multiple sol-gel coating has been fabricated and demonstrated in this paper. TiO 2 layer is deposited over uncladded U-shaped fiber to enhance the evanescent field in the pH sensing film. The wide range sensing film is prepared by using three different indicators of various pH ranges. The higher sensitivity of 0.68 dBm/pH was obtained for double layer of sol-gel at 1550 nm with a good linear response. The sensor is also demonstrated for stability, durability and fast response time.

In this work, a highly sensitive surface plasmon resonance (SPR) sensor based on a single mode fiber (SMF) incorporating a large microfluidic channel (MFC) for refractive index (RI) sensing is designed and optimized using a full-vectorial finite element method (FEM). The fluidic channel size can be varied according to the requirement due to the availability of the large cladding diameter of SMF, which makes it simple and easy to fabricate. The proposed novel sensor is favourable to both analytes and metallic strips. The D-shaped hollow section above the core is filled with the measurand analytes and a gold (Au) strip is deposited on the base of the MFC, as it is known as the most attractive metal for SPR. Our numerical simulations illustrate that the confinement loss of the designed sensor is highly influenced by the distance of the MFC from the core along with the width and thickness of the Au strip. The designed sensor shows an average sensitivity of 1350 nm/RIU and maximum sensitivity of 8250 nm/RIU in the sensing range of 1.33-1.35 and 1.41-1.43, respectively. However, for a small variation of na at a step of 0.005, within ranges like 1.415, 1.420, and 1.425, we have achieved a maximum sensitivity of 7000 nm/RIU, 9000 nm/RIU and 11000 nm/RIU, respectively. This novel SPR sensor with MFC can open up a new opportunity in the application of chemical and biological sensing.

The present work describes the fabrication and characterization of an optical fiber pH sensor using a sol–gel technique. The sensing head configuration is incorporated using a short section of no-core fiber, coated with tetraethyl orthosilicate and spliced at the end of a single mode fiber with a bulge. Different types of indicators (bromophenol blue, cresol red, and chlorophenol red) were used to achieve a wide pH range from 2 to 13. High sensitivities of the fabricated device were found to be 1.02 and ? 0.93 ?? nm / pH for acidic and alkaline solutions, respectively. From the characterization results, it was noted that there is an impact of ionic strength and an effect of the temperature of liquid on the response characteristic, which is an advantage of the existing device over the other pH sensors. The fabricated sensor exhibited good reflection spectrum, indicating a blueshift in resonance wavelength for alkaline solutions and a redshift for acidic solutions.

A wide range U shaped fiber optic pH sensor utilizing titanium dioxide (TiO2) layer with sol-gel coating, has been fabricated and demonstrated in this paper. A high sensitivity of 0.37 dBm/pH is observed with fast response time of 14 s.

In this paper we fabricate a hetro core optical fiber sensor for concentration measurement. The obtained sensitivity for 10% to 45% is 0.24 dBm/% and for 45% to 100% It is 0.14 dBm/%.

In this paper a cone tapered surface plasmon resonance (SPR) based chemical fiber sensor is fabricated and demonstrated for the detection of low water content in ethanol. Here the 11nm thickness of Aluminum (Al) is used to coat tip of probe to generate Plasmon wave. The output power has been found to increase linearly with water content in the range 1–10% due to the increase in refractive index (RI) of ethanolabove which, as the percentage of water increases in step of 20% it shows abrupt decrease in RI hence decrease in the output power. The compact size of sensor and its low cost fabrication makes it useful for many applications in the field of chemical and biochemical sensing.

The formation of chemically etched optical fiber for use in refractive index sensor is addressed. This presented design of a refractive index (RI) sensor is based on recording the power loss exhibited by radiation propagating through an etched multimode fiber (MMF) immersed in the liquid under study. The decreasing diameters of fibers are found to be strongly dependent on the temperature and etchant composition. This experiment was performed for different unclad etched fibers for same sensing length and the RI changes from 1.33 RIU to 1.38 RIU. When the multimode fiber (MMF) is etched for 12 hours the sensitivity of the sensor is approximately 204.25dBm/RIU, which is larger than without etched fiber having sensitivity 127.2dBm/RIU.

In this paper we present a surface plasmon resonance (SPR) based fiber sensor for measurement of refractive index (RI) at different concentration of glycerol and acetone. The sensing head of fiber probe was fabricated by depositing aluminum (Al) on the unclad portion of multi-mode fiber (MMF). The experimental result shows the sensitivity obtained in power measurement of SPR fiber probe was −106.95 dBm/RIU and −408.90 dBm/RIU for glycerol and acetone. Due to the small size and good sensitivity low cost of our SPR based fiber sensor have many commercial and practical uses.