A thin-core-fiber-based (TCF-based) dual S-tapered fiber sensor for label free DNA hybridization detection has been proposed and experimentally demonstrated. The proposed biosensor is constructed by splicing a TCF of about 645 μm in length with two segments of single-mode fibers (SMFs), and the two S-tapers are fabricatedat the splicing joints by using a commercial fusion splicer.By functionalizing the fiber surface with monolayer Poly-L-lysine (PLL) and single-stranded DNA (ssDNA) probes, label-free detection of target ssDNA is achieved. The sensor functionalization and the hybridization processes for 1 nM target ssDNA are monitored through real-time analysis of thetransmission spectral evolution. Owing to its compactness, low cost, fast response, real-time detection and good specificity and repeatability, the proposed biosensor is expected to find potential applications in label-free biomolecule detection.

A compact S‐tapered fibre biosensor functionalised with class I hydrophobin HGFI found in Grifola frondosa has been proposed for the first time to accrue label‐free detection of reaction between goat–anti‐rabbit immunoglobulin G (IgG) (GAR, antibody) and rabbit–anti‐hemagglutinin IgG (R, antigen). The HGFI nanolayer self‐assembled on fibre surface provides a distinguished analytical platform to implement biocompatible binding owing to its prominent amphiphilicity and remarkable optical as well as biochemical properties. Water contact angle measurements, atomic force microscopy, and immunofluorescence assay are utilised to characterize the modification properties of siliconised substrate surface with HGFI. Functionalisation of the S‐tapered fibre is achieved by exploiting self‐assembly of HGFI and immobilisation of GAR for specific R detection. HGFI with a concentration of 300 μg/ml allows the formation of a self‐assembled amphipathic film on fibre surface, which can adsorb antibody smoothly with such desirable merits as ease of operation, fast response, good stability, good repeatability, and no side effects. Immunoassay experiments are conducted based on dip wavelengths interrogation of the interferometric transmission spectrum. In this study, we propose a novel antigen detection scheme, which could be extended for the detection of other biomolecules owing to its high integration, good specificity, real‐time detection, and simple detection scheme.

A compact, low-cost, fiber-compatible magnetic field sensor based on multimodal interference in an S-taper and up-fusion-taper fiber modal interferometer is designed and experimentally demonstrated. The spectral characteristics in response to applied magnetic field and environmental temperature have been analyzed in detail. Experimental results indicate that the magnetic sensitivity reaches -0.03464 nm/Oe for a magnetic field ranging from 40 to 160 Oe. The proposed sensor has a maximum temperature sensitivity of 0.04889 nm/°C when the temperature increases from 27 to 45 °C. The effect of temperature on wavelength shift could be resolved by using a matrix containing the magnetic field and temperature sensitivities for two selected interferometric dips.

A whispering gallery mode (WGM) microresonator based on grapefruit microstructured optical fibers (MOFs) is proposed for in-situ DNA biosensing. The MOF microresonator has a porous structure that offers natural microfluidic channels to load microfluidic samples of volume down to 100 μL. Moreover, the WGM mechanism greatly enhances the interaction between WGM light and liquid sample kept inside the microcavity. The inner surface of the microcavity is functionalized with poly-L-lysine monolayer to achieve label-free binding of the single-strand probe DNA (ssDNA) through electrostatic force, and the probe immobilization as well as DNA hybridization processes are monitored in real time. The linear fitting of resonance wavelength shift versus DNA concentration in logarithmic scale indicates that DNA detection is available from 0.01 fmol/μL to 100 fmol/μL. The proposed WGM microresonator biosensor possesses such desirable merits as ease of operation, fast response, label free method, and high specificity, making it a promising candidate for in-situ DNA detection and related biosensing applications.

A compact and label-free biosensor based on coreless-fiber-coupled microcavity is proposed and experimentally demonstrated for bovine serum albumin (BSA) detection. The microcavity is fabricated in a coreless fiber by on-line fiber cutting-welding micromachining. Experimental results show that the BSA samples with different concentration and refractive index ranging from 1.3344 to 1.3349 are clearly discriminated by spectral characteristics of the coreless-fiber-coupled microcavity, with a sensitivity of 1.602 nm/(mg/ml). The device presents superiorities such as miniature size, standardized production control, reliable quality, and cost effective, which makes it a good candidate for the detection of low-concentration micro-samples analytes in the fields of life sciences, biological engineering, and biopharmaceutical industry.