Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

In this work, we introduce a novel multimode fiber (MMF) – seven core fiber (SCF) – MMF (MCM) optical fiber biosensor, also known as the WaveFlex biosensor (plasma wave assisted fiber biosensor), based on localized surface plasmon resonance (LSPR) for qualitative detection of xanthine. Xanthine is a purine base widely distributed in human blood and tissues, and commonly used as an indicator for various disease detections. The MCM sensor incorporates a tapered optical fiber structure, fabricated using the combiner manufacturing system (CMS), and is designed with SCF and MMF. By effectively harnessing LSPR, the sensor boosts the attachment points of biomolecules on the probe surface through immobilized tungsten disulfide (WS₂)-thin layers, gold nanoparticles (AuNPs), and carbon nitride quantum dots (C₃N-QDs). The functionalization of xanthine oxidase (XO) on the sensing probe further enhances the sensor's specificity. The proposed WaveFlex biosensor exhibits a remarkable sensitivity of 3.2 nm/mM and a low detection limit of 96.75 µM within the linear detection range of 100 - 900 µM. Moreover, the sensor probe demonstrates excellent reusability, reproducibility, stability, and selectivity. With its sensitivity, biocompatibility, and immense potential for detecting human serum and fish products, this WaveFlex biosensor presents a promising platform for future applications.

Infections caused by Vibrio parahaemolyticus (V. parahaemolyticus) can be highly fatal, making rapid and sensitive detection of them is essential. A new optical fiber biosensor based on localized surface plasmon resonance (LSPR) phenomenon is developed in this paper. A tapered-in-tapered fiber structure based on MFM is constructed by using four-core fiber (FCF) and multi-mode fiber (MMF) to qualitatively detect different concentrations of V. parahaemolyticus. The sensor successfully excites the LSPR phenomenon and increases the attachment point of biomolecules on the probe surface by fixing gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS₂-NPs) and cerium dioxide nanorods (CeO₂-NRs). The functionalization of polyclonal antibodies on the probe surface can improve the specificity of the sensor. The linear detection range of the developed sensor was 1 × 10⁰-1 × 10⁷ CFU/mL, the sensitivity was 1.61 nm/[CFU/mL], and the detection limit was 0.14 CFU/mL. In addition, the reusability, reproducibility, stability, and selectivity of the sensor probe are also tested, which shows that the sensor has great application prospects.

Acrylamide (AA), a harmful aliphatic amide, is produced during the thermal processing of food as a result of the Maillard reaction between asparagine and reducing sugars. It has neurotoxic effects and can cause cognitive impairment with long-term exposure. Moreover, chronic intake of AA may increase the risk of various types of cancer, including pancreatic and thyroid cancer. AA is often found in foods cooked at high temperatures, thereby highlighting its role in food quality assessment. Therefore, there is a need for more accurate, practical, rapid, and straightforward methods to detect AA in various samples. In this study, a highly sensitive and selective smart fiber-optic WaveFlex biosensing method based on localized surface plasmon resonance (LSPR) is proposed for the detection of AA. The fiber surface is functionalized with gold nanoparticles (AuNPs), multi-walled carbon nanotubes (MWCNTs) and zinc oxide nanowires (ZnO-NWs) to provide a larger surface area for the immobilization of AA antibodies, which in turn significantly improved the sensor's performance. The results showed that the developed sensor could efficiently detect AA with high specificity due to the presence of AA antibodies. Subsequent research confirmed that the proposed biosensor exhibited excellent stability, repeatability, and reusability, with a limit of detection (LOD) of 0.438 μg/mL and a sensitivity of 0.685 nm/(μg/mL). Thus, the proposed optical fiber sensor holds significant potential for detecting the presence of AA in various deep-fried foods prepared at high temperatures.

This paper presents the development of taper-in-taper fiber (TITF)–optical fiber-based sensors for chemical and biological detection. TITF structure is a fiber structure formed by fabricating a taper again on the taper region of the traditional taper fiber. The experimental results show that the TITF structure has a lower transmitted intensity than the common taper fiber structure. It is demonstrated that the structure of TITF is more conducive to evanescent waves, thereby making it more sensitive to changes in the refractive index (RI) of the external environment. To confirm this, measurements of ethanol solutions with different water contents are taken using the TITF structure to showcase the chemical sensing, thus verifying its sensitivity to RI changes in the external environment. The sensor can measure ethanol solutions from 0 to 100% with a sensitivity of 4.06 a.u./%. Thereafter, the TITF sensor is modified with ZnO-NPs to enhance its sensitivity for biological sensing (creatinine detection). The transmitted intensity of different concentrations of creatinine solution (0–2000 μM) is measured using the proposed sensor. The sensor showed good linearity and a high sensitivity of 0.11 a.u./μM for creatinine solution. Therefore, it is demonstrated that the TITF sensor with ZnO-NPs can be used for effective biological sensing.

In this work, the fabrication method of a U-shaped optical fiber (UOF) structure using single-mode fiber is proposed. Few UOF sensors have been developed to date, but the fabrication process has not been described in detail. Here, its subsequent homemade fabrication, optimization strategies, and analysis are thoroughly explored. Further, the influence of transmission on U-shaped diameter is explored. The transmitted intensity is mainly used to assess the strength of the evanescent field. For this purpose, three different diameters of 2 mm, 4 mm, and 6 mm UOFs are fabricated. The results show that the transmission of the U-shaped structure is dependent on the diameter of the UOF. Thereafter, different concentrations of glucose solutions are detected using the optimized stable UOF structure to showcase the sensing properties. Overall, this work is essential for beginners who want to conduct research on optical fiber sensors with a curved shape.