Aflatoxins are a kind of fungal toxin that causes great damage to humans and animals due to its wide distribution, secretive nature, and high toxicity. For the purpose of achieving qualitative and quantitative detection of aflatoxin B1 (AFB1), a novel tri-taper-in-taper fiber-optic structure based on core mismatch of four-core fiber with a multimode fiber-based WaveFlex biosensor is developed and tested. The sensor probe's surface is coated with gold nanoparticles (AuNPs). Multi-walled carbon nanotubes and zinc oxide nanoparticles are sequentially immobilized on the sensing probe surface to enhance the sensor's sensing capabilities. Then, the AFB1 antibody is utilized to functionalize the sensor to possess specific selectivity. After the modification of nanomaterials and the corresponding bioreceptors, the final sensor structure is formed. By stimulating the localized surface plasmon resonance phenomenon of AuNPs, different concentrations of AFB1 can be detected. The sensor demonstrates high sensitivity (38.29 nm/μM) as well as low LOD (7.12 nM) within the range of 0–100 nM for detection. The sensor is also found to be stable and reproducible in repeated measurements, indicating its potential for practical application. Additionally, it exhibits satisfactory specific recognition of AFB1. These results show that AFB1 can be detected in food and agricultural products using LSPR-based optical fiber sensors, which could have significant ramifications for public health and food safety.

This article discusses optically active nanomaterials and their optical biosensing applications. In addition to enhancing their sensitivity, these nanomaterials also increase their biocompatibility. For this reason, nanomaterials, particularly those based on their chemical compositions, such as carbon-based nanomaterials, inorganic-based nanomaterials, organic-based nanomaterials, and composite-based nanomaterials for biosensing applications are investigated thoroughly. These nanomaterials are used extensively in the field of fiber optic biosensing to improve response time, detection limit, and nature of specificity. Consequently, this article describes contemporary and application-based research that will be of great use to researchers in the nanomaterial-based optical sensing field. The difficulties encountered during the synthesis, characterization, and application of nanomaterials are also enumerated, and their future prospects are outlined for the reader’s benefit.

Optical fiber sensors based on tapered optical fiber (TOF) structure have attracted a considerable amount of attention from researchers due to the advantages of simple fabrication, high stability, and diverse structures, and have great potential for applications in many fields such as physics, chemistry, and biology. Compared with conventional optical fibers, TOF with their unique structural characteristics significantly improves the sensitivity and response speed of fiber-optic sensors and broadens the application range. This review presents an overview of the latest research status and characteristics of fiber-optic sensors and TOF sensors. Then, the working principle of TOF sensors, fabrication schemes of TOF structures, novel TOF structures in recent years, and the growing emerging application areas are described. Finally, the development trends and challenges of TOF sensors are prospected. The objective of this review is to convey novel perspectives and strategies for the performance optimization and design of TOF sensors based on fiber-optic sensing technologies.

Alpha-fetoprotein (AFP), a biomarker for liver cancer detection, has important clinical significance. Here, an S-tapered WaveFlex fiber biosensor is developed that is based on the structure of multimode fiber (MMF)-multi-core fiber (MCF)-MMF and leaks more energy when excited by light. ZnO nanowires (ZnO-NWs)/ WS ₂ nanosheets (WS ₂ -NSs) and gold nanoparticles (AuNPs) are functionalized on the probe surface to further enhance the sensing performance. One-dimensional ZnO-NWs possess a larger specific surface area and can provide more sites for antibodies. The fold structure of WS ₂ -NSs provides ample space for functionalization. The combination of the above two nanomaterials is conducive to the immobilization of AuNPs and AFP antibodies and improves the performance of the developed biosensor. AuNPs and AFP antibodies are used to generate localized surface plasmon resonance (LSPR) and enhance the specificity of the probe, respectively. The developed probe is employed to detect AFP solution in the range of 0 to 1000 ng/mL, and the sensitivity and limit of detection are obtained as 1.32 nm/log(ng/mL) and 84 pg/mL, respectively. Moreover, the practical application capability of the probe is verified by the selectivity test, pH test, reproducibility, and reusability experiments. The results demonstrate the potential application of the developed S-tapered WaveFlex AFP sensor in the detection of liver cancer markers.

Shigella, a highly infectious and pathogenic Gram-negative bacterium, is widely prevalent in everyday food items, prompting significant research due to its potential hazards. Addressing the need for Shigella detection, this study introduces a WaveFlex biosensor based on localized surface plasmon resonance (LSPR) using fiber optics. The sensor is tailored to detect a specific subspecies of Shigella , specifically Shigella sonnei (S. sonnei). It is fabricated using a combination of multimode fiber (MMF) and four-core fiber (FCF), creating a core-mismatched W-type fiber structure designed for efficient mode coupling. Furthermore, this sensor is enhanced with the utilization of nanomaterials, including cerium oxide nanorods (CeO2-NRs), zinc oxide nanowires (ZnO-NWs), and copper selenide@gold nanocomposites (Cu3Se2@Au-NCs). CeO2-NRs and ZnO-NWs contribute to improve biocompatibility and increase surface area for antibody functionalization, while Cu3Se2@Au-NCs promote the LSPR effect and enhance sensing performance. To enhance specificity, the optical fiber coated with these engineered nanomaterials is functionalized with S. sonnei antibody. The results of this work showcase the effective detection of Shigella bacteria by the proposed WaveFlex sensor, offering exceptional sensitivity (0.28 nm/(CFU/mL)), a low limit of detection (LoD) of 0.96 CFU/mL, and a swift detection time of 10 minutes. These findings underscore the sensor's potential for widespread applications in areas such as food safety, medical diagnostics, and environmental monitoring. This study significantly advances bacterial detection technology and contributes to the assurance of public health and food safety.

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.