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. 2017 May 19;6(5):e16229.
doi: 10.1038/lsa.2016.229. eCollection 2017 May.

Nanosphere Lithography for Optical Fiber Tip Nanoprobes

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Free PMC article

Nanosphere Lithography for Optical Fiber Tip Nanoprobes

Marco Pisco et al. Light Sci Appl. .
Free PMC article

Abstract

This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips. The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet. Polystyrene (PS) nanospheres are initially self-assembled in a hexagonal array on the surface of water. The created pattern is then transferred onto an optical fiber tip (OFT). The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber, such as metal coating, nanosphere size reduction and sphere removal. Ordered dielectric and metallo-dielectric sphere arrays, metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach. Furthermore, the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions. The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost. The method can be easily extended to simultaneously produce multiple fibers, opening a new route to the development of fiber-optic nanoprobes. Finally, we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes.

Keywords: SERS probes; lab-on-fiber; nanosphere lithography.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of the nanosphere assembly process and photograph of MCC islands (green blotches) floating on water.
Figure 2
Figure 2
Schematic representing the fabrication procedure for creating different fiber tip nanoprobes and SEM images (scale bar=3 μm) of real samples obtained using 1-μm nanospheres, corresponding to each geometric feature: CPA, SA and SR. A digital picture of a fiber tip showing an iridescent nanopattern is also shown.
Figure 3
Figure 3
(ae) FIBM and AFM (inset) images of OFTs patterned with CPA metallo-dielectric nanospheres with diameters of 200, 350, 500, 750 and 1000 nm. Scale bars=2 μm. (f) AFM section profiles of the same samples from the top (200 nm) to bottom (1000 nm). Figure reprinted with permission from Pisco et al..
Figure 4
Figure 4
FIBM micrographs (ac, e, f) and AFM three-dimensional image (d) of fiber tips patterned with CPA–SR gold structures. The periods are 200 (a), 350 (b), 500 (c), 750 (e) and 1000 nm (d, f). The FIBM scale bars are 1 μm.
Figure 5
Figure 5
Top (a, b) and tilted (c, d) FIBM views showing the PS spheres after size reduction (SA patterns) and a sketch of the anisotropic etching of a spherical particle (e). Scale bars=3 μm.
Figure 6
Figure 6
Fiber tips with SA patterns before (a, e) and after SR (b, c, f, g). The nanostructures were obtained starting with 500 (ad) and 1000 nm (ef) MCCs. (d, h) Section profiles measured along the light lines drawn in the AFM scans shown in c and g, respectively. Scale bars=3 μm.
Figure 7
Figure 7
Transmittance spectra of the CPA nanoprobes produced with 1000 nm microspheres.
Figure 8
Figure 8
(a) SEM micrographs of five repeats of the SA nanoprobe prepared using 1000-nm PS spheres. The scale bars in the SEM images are 5 μm. (b) Overlapped transmission spectra of the five SA nanoprobes.
Figure 9
Figure 9
(a) Transmittance of the CPA sample with a sphere diameter of 1000 nm. (b) SERS spectrum obtained from 1-μM CV solution by illuminating the cladding (in blue) and core zones (in red) of the CPA sample.

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