Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

Abstract

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provided.

Keywords: laser direct-write; lithography; nanotechnology; near field; subwavelength.

Figure 1

(a) Schematic description of photonic nanojet-mediated nanopatterning using a microsphere. (b,c) Atomic force microscope (AFM) topography maps of a nanohole (b) and a nanochannel (c) ablated on a polycarbonate substrate using a photonic nanojet and pulsed irradiation. Adapted with permission from [20]. Copyright 2008 Springer Nature. (d) Theoretical intensity distributions of the optical field generated by a dielectric microsphere ($n_p$ = 1.5 and $n_m$ = 1.0) under plane-wave illumination and for different values of the size parameter $q$. Linearly polarized light along the x-axis is incident from the bottom. Adapted with permission from [17]. Copyright 2017 Optical Society of America.

Figure 2

(a) Scanning electron micrograph (SEM) of a core-shell microsphere. Scale bar 100 nm. Reprinted with permission from [43] Copyright 2018 John Wiley & Sons, Inc. (b,c) Optical field distribution of core-shell microspheres with refractive index of the core 1.5 and that of the shell 1.33 (b) and 2.0 (c) under plane wave illumination. The field amplitudes are normalized to their maxima. Reprinted with permission from [21] Copyright 2010 Elsevier. (d,e) Surface-decorated microspheres. Top (d1) and side (d2) views of a microsphere decorated with four rings. (d3) Width and working distance versus ring number. Reprinted with permission from [47] Copyright 2015 Optical Society of America. Top (e1) and side (e2) views of a center-covered microsphere. In blue the cover. (e3) Nanojet width for various cover ratios. The insets show scanning micrographs and lateral intensity profile at the focal spot for cover-ratio of 0.0 and 0.777, respectively. Adapted with permission from [48] Copyright 2016 Springer Nature.

Figure 3

(a1) Scanning electron micrograph of an AFM cantilever with a microsphere. The inset is an optical image of the laser-illuminated sphere with the nanojet clearly visible. (a2) Schematic (top) and scanning electron micrograph (bottom) of out-of-plane scans. (a3) Scanning electron micrograph showing the letters IIT created with scanning probe photonic nanojet lithography. Adapted with permission from [68] Copyright 2017 American Chemical Society. (b1) Schematic showing a moving Janus microsphere motor near the photoresist surface under exposure to UV-light. (b2) Illustration of the magnetic guidance of sphere motion. (b3,b4) Patterns created by turning the magnetic field by 90° (b3) and 120° (b4). Scale bars 5 µm. Adapted with permission from [71] Copyright 2014 Springer Nature.

Figure 4

Nanojet lithography under oblique illumination (a1) Polar chart depicting three controllable variables (α, β, τ) for arbitrary nanopatterning. (a2) Linear relationship between the tilt angle (α) and shift distance of the focal position. (b1–b6) Examples of designed and generated periodic nanopatterns. Scale bars 1 μm. Adapted with permission from [73] Copyright 2017 American Chemical Society.

Figure 5

Parallelization of photonic nanojets. (a) Polypropylene substrate coated with acrylic adhesive for transporting microsphere array (referred to as the ‘Ribbon’) onto a Si surface. The inset shows a scanning electron micrograph of the array. Adapted with permission from [85] Copyright 2011 Elsevier. (b1) Schematic diagram of nanojet lithography under oblique illumination. (b2,b3) Scanning electron micrograph of H-shape arrays produced with tilted nanojets. Reprinted with permission from [88] Copyright 2009 Institute of Physics.

Figure 6

Nanostructures for photonics. (a) Measured dark-field scattering spectra of the circular and elliptical Au nanodisks fabricated with nanojet lithography under oblique illumination. The inset shows SEM images of the Au nanoellipses. Reprinted with permission from [97] Copyright 2012 The Japan Society of Applied Physics. (b1) Simulated energy field of the bright and dark mode of an Ag-SiO₂-Ag dimer. (b2) Experimental extinction spectra of Ag-SiO₂-Ag dimers with thickness 15 nm for Ag and 10, 15 and 20 nm for SiO₂. The low energy side of the spectra highlights the shift of the dark plasmon mode when varying the SiO₂ thickness. Adapted with permission from [94] Copyright 2012 American Chemical Society.

Figure 7

Nanostructures for electronics. (a1) Illustration of the fabrication of nanotransistors by means of nanojet-mediated laser sintering. (a2) Optical dark-field and SEM images of sintered nanowires (NWs). (a3) Characteristic I–V curves of the OFET with and without NWs. Adapted with permission from [29], Copyright 2010 John Wiley & Sons, Inc. (b1) Serpentine resistors patterned by exploiting an array of individually addressable hollow pyramids. Scale bar 100 µm. (b2) Plot of the resistance versus resistor length (black dots) with linear fitting (red line). (c1–b3) SEM image of electrode pads with the nanowires. The scale bar 5 µm. (c4). I–V curves for different gate voltages, highlighting the characteristic transistor behavior. Adapted with permission from [91], Copyright 2013 Springer Nature.

Figure 8

SEIRA spectroscopy. (a) SEM image of C-ring Au nanodisks prepared by multi-exposure angled nanojet lithography. (b) Theoretical polarized transmission spectra of C-rings for outer diameters of 560 nm (red lines), 600 nm (blue lines), and 680 nm (green lines). (c) Charge and field energy distributions of the resonance modes for various polarization states. (d) Standard transmission spectrum of osmium carbonyl clusters (molecular structure in the inset) (d1). (d2) Measured transmission spectra and (d3) vibrational strength of the C-ring array with osmium carbonyl clusters excited with Ex and Ey polarizations. Black and gold curves are baselines. Adapted with permission from [73], Copyright 2017 American Chemical Society.