Optical Fiber Sensors for Biocide Monitoring: Examples, Transduction Materials, and Prospects

Robust Transparent Titanium Dioxide Coating Based on the AACVD Process for Anticorrosion Marine Exploration

Transparent and robust titanium dioxide (TiO₂) coatings were prepared by the facile aerosol-assisted chemical vapor deposition (AACVD) method. The effects of deposition temperature and precursor concentration on the crystal growth and optical properties of TiO₂ coating were investigated. It is found that the obtained TiO₂ coating has strong adhesion to the substrate, which can effectively avoid mechanical scratches and wear by sharp objects, adhesive tape and steel wool. Besides, in the marine corrosion protection test, both the open circuit potential and electrochemical impedance of TiO₂ coating immersed in artificial seawater for different times are greater than those of the bare S420 steel substrate. Particularly, the high-frequency phase angle of the TiO₂ coating increases, and the impedance value at low frequency of 0.10 Hz is about 2 orders of magnitude higher than that of the bare S420 substrate. In addition, the significant decrease of corrosion products on the surface further proves that the deposited TiO₂ coating exhibits better corrosion inhibition and excellent anticorrosion properties, which is expected in application of the surface coating protection of the marine exploration lens.

Two-photon direct laser writing of micro Fabry-Perot cavity on single-mode fiber for refractive index sensing

Using the two-photon polymerization (TPP) lithography, here we propose and experimentally demonstrate a fiber-tipped Fabry-Perot interferometer (FPI) for liquid refractive index (RI) measurement. To fit the aqueous environment, the FPI is designed as an open-cell microstructure consisting of well-crafted surfaces together with supporting rods, where the major spectral interference occurs between the waveguide's facet and the printed surface. Subsequently, the sensing performances of the fiber FPI are comprehensively studied under various RI as well as temperature configurations. The RI sensitivity is obtained to be ∼1058 nm/RIU with a low detection limit of 4.5× 10^-6 RIU, which is comparable to that of previous reported FPIs. And the temperature cross-sensitivity reaches a value of 8.2 × 10^-5 RIU/°C, indicating the good reliability for RI monitoring. Compared to other fiber FPIs, our sensor exhibits substantial advantages such as ease of fabrication, highly smooth cavity surfaces, and sufficient mechanical strength, providing a practical and competitive solution for chemical and biological sensing.

Molecularly Imprinted Polymer-Coated Optical Waveguide for Attogram Sensing

Ultrahigh sensitivity and selectivity are the ultimate goals of sensor development. For such purposes, we propose a sensing platform in which an optical fiber-waveguide-fiber (OFWF) structure is integrated with a molecularly imprinted polymer (MIP). The OFWF works as a highly efficient probe light launcher and signal light collector, and the MIP layer acts as a highly selective and sensitive sensing interface. In the MIP design, a high-molecular refractive index monomer (2-phenylphenoxyethyl acrylate) was copolymerized with a MIP functional monomer (acrylic acid). The resulting high-refractive index MIP layers could effectively extract the probe light from the waveguide and send it to the MIP sensing interface. Moreover, a highly elastic cross-linker (poly(ethylene glycol) 600 diacrylate) was employed to increase the MIP mesh size, which could effectively increase the penetrability of the analyte. Rhodamine B (Rh B) is widely used in the textile industry, and its contamination may lead to serious public health problems. As a proof of concept, the Rh B chromophore was used as a molecular template, and the thin MIP layer was cured on the waveguide surface by utilizing the evanescent wave of the 405 nm propagating light in the waveguide. The MIP-OFWF sensing platform afforded highly selective monitoring of the absorption spectra of the components in a mixture solution of Rh B and methyl blue. It also afforded an extremely low detection limit of approximately 6.5 × 10^-17 g/mL, with an absolute mass of 20-30 ag.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

Detection of the Chilli Leaf Curl Virus Using an Attenuated Total Reflection-Mediated Localized Surface-Plasmon-Resonance-Based Optical Platform

The development of a nanoparticle-based optical platform has been presented as a biosensor for detecting target-specific plant virus DNA. The binding dynamics of gold nanoparticles has been studied on the amine-functionalized surface by the attenuated total reflection (ATR)-based evanescent wave absorption method monitoring the localized surface plasmon resonance (LSPR). The developed surface was established as a refractive index sensor by monitoring the LSPR absorption peak of gold nanoparticles. This nanoparticle-immobilized surface was explored to establish as a biosensing platform with target-specific immunoglobulin (IgG) antibody-antigen interaction. The IgG concentration-dependent variation of absorbance was correlated with the refractive index change. After successfully establishing this ATR configuration as an LSPR-based biosensor, the single-stranded DNA of the chilli leaf curl virus was detected using its complementary DNA sequence as a receptor. The limit of detection of this sensor was determined to be 1.0 μg/mL for this target viral DNA. This ATR absorption technique has enormous potential as an LSPR based nano-biosensor for the detection of other begomoviruses.