Fig. 1. Method of real-time control of MNF diameter with high accuracy and precision[17]. (a) Schematic of experimental setup for MNF tapering device; (b) effective refractive indices of the supported modes as functions of MNF diameter at 785 nm; (c) normalized transmission curve during the tapering process at 785 nm, the inset is transmission at 1550 nm; (d) magnified transmission intensity curve with solid line and its derivative with dotted line as functions of time; (e) SEM image of as-fabricated MN

Fig. 2. Spatial distributions of optical fields guided by MNF[4]. 3D view of z-direction Poynting vectors of MNF at 633 nm wavelength with diameters of (a) 800 nm, (b) 400 nm, (c) 200 nm; 2D view of MNF with diameters of (d) 800 nm, (e) 400 nm, (f) 300 nm, (g) 200 nm

Fig. 3. Schematic of MNF sensing[2]

Fig. 4. Absorption sensor based on coiled MNF[30]. (a) Schematic of the fabrication process; (b) dependence of the measured optical losses at 630 nm on the analyte concentration

Fig. 5. Ultra-sensitive MNF absorption detection in microfluidic chip[31]. (a) Optical microscope image of a tapered fiber with waist diameter of 900 nm; (b) micrograph of the cross section of PDMS microchannel; (c)(d) micrographs of MNF in microfluidic chip before and after fluorescence excitation; (e)(f) transmission spectra of MB and CB-BSA obtained at different concentrations using a 900-nm-diameter MNF

Fig. 6. Ultra-sensitive MNF fluorescence detection in microfluidic chip[32]. (a) Schematic of the biconical MNF fluorescence sensing system; (b) fluorescence spectra of R6G at different concentrations; (c) fluorescence spectra of QD-labeled streptavidin at different concentrations

Fig. 7. fL-scale optical nanofiber sensor[35]. (a) Micrograph of the nanofiber and narrow channel microfluidic chip integration; (b) micrographs of the fluorescence spots excited by 800-nm-diameter nanofiber with different fluorescein concentration and the corresponding fluorescence intensity, scale bar is 5 μm

Fig. 8. Single nanoparticle detection using a nanofiber pair[37]. (a) Schematic of the sensing system; (b) Transmitted power of the fiber during a time interval of 10 s when the PS nanoparticles are binding to the surface of the nanofiber; (c) microscopy image of the nanofiber with single PS nanoparticles bound to its surface in an aqueous environment; (d) SEM image of a portion of the nanofiber, where PS nanoparticles (radius is 100 nm) are bound on its surface

Fig. 9. GNP amplified MNF biosensor for cancer biomarker detection[38]. (a) Diagram of the immunoassay for AFP detection using GNP as signal amplification labels; (b) diagram of the integration of MNF and microfluidic chip; (c) secondary antibody-functionalized GNP enhanced sensor response to bovine serum samples spiked with different concentrations of AFP

Fig. 10. Schematic of optofluidic MNF grating. (a) Schematic of the sensor configuration [47]; (b) schematic of the functionalization of the MNF grating probe[47]; (c) equivalent planar structure of the optofluidic MNF grating[49]

Fig. 11. Schematic of MNF resonator. (a)(e) Loop; (b)(f) knot; (c)(g) ring; (d)(h) multicoil resonators[60]; (i) schematic of the MNF multicoil resonator refractive index sensor cross section [56]; (j) schematic of the LCORR sensor cross section[61]

Fig. 12. Detection of miRNAs using MNF-capillary interferometer[71]. (a) Schematic of the fabrication procedure of interferometer; (b) SEM image of the interferometer in cross-sectional view; (c) response of the sensor for activation of capillary inner surface and detection of miRNA-let7a, the inset is measured transmission spectra before and after miRNA hybridization

Fig. 13. Microfluidic flow rate sensor based on MNF coupler[74]. (a) Schematic of MNF coupler wrapping around a gold-coated glass capillary and embedding in the UV-curable adhesive; (b) typical output spectrum of MNF coupler; (c) wavelength shift with different flow rates under three typical incident power values