Although lateral flow assays (LFAs) are currently being a handful of diagnostic technologies that can identify severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other common respiratory viruses in one strip, it remains a grand challenge to substantially enhance their sensitivity. We propose here a straightforward method to overcome such drawbacks by employing nitrocellulose (NC) membrane femtosecond laser micromachining to control the analyte flow rate. The findings provided in this work indicate that tailoring the diameters of the μ-channels in NC can effectively expedite the immunological reaction time between the analyte and the labeled antibody, leading to an observable signal increase compared to pristine LFA.
Surface Lattice Resonances (SLRs) found in uniform plasmonic metasurfaces feature high Q-factors, enabling applications in sensing and nanolasing. To scale up their production, we introduce the Capillary-force-Assisted Particle Assembly method (CAPA). It allows to assemble colloidal nanoparticles onto patterned templates. We demonstrate large hexagonal and square lattices comprised of single-crystal Ag nanoparticles with high quality SLRs. They can be excited into optomechanical oscillations which modulate the LSPR and in turn the SLR over time, giving the metasurface intriguing properties in the ultrafast regime. Moreover, we tailored the SLR to match the excitation wavelength used in Raman spectroscopy. This allowed to create SERS substrates with improved performance, achieving 100 times higher sensitivity at the target wavelength. Finally, we interfaced plasmonic metasurfaces with gain media and registered room temperature nanolasing. The demonstrated applications showcase the versatility of CAPA and we expect self-assembly to play a major role in the development of large scale metasurfaces and nanophotonics devices.
Lithuania is recognized as a laser-tech cluster and therefore the Materials Engineering and Nanotechnologies study program carried out at the Kaunas University of Technology is tempting to address the competencies required by the beneficiaries. Students are introduced to Optics and Laser technologies via three recently revised dedicated courses that have theory lectures, practical tasks, and laboratory works. The endeavor starts at the basic level like geometrical optics, light interference, diffraction, etc. going through modern optics covering optical devices and processes, and finalizes with a deeper understanding of topics covering nonlinear and ultrafast laser optics, plasmonics, and laser material processing. The study program is unique in a way that it provides double degree diplomas both in Physics and Materials Engineering fields. Considering the challenges and needs of the laser-related industry in Lithuania the courses in Optics were adapted to include fundamental and applied research-based topics along with problem-based learning tasks directly related to the real-life problems that expand the content of the classical textbooks. Lab work tasks are performed at university research laboratories employing the state-of-the-art femtosecond laser, laser micromachining workstation, and transient absorption spectrometer allowing students to get familiar with the locally produced photonics products. Handson experiences with contemporary technologies together with a critical amount of fundamental knowledge in photonics later on stimulate students seeking a job position in the laser/optics-related industry in Lithuania. The feedback from the students shows that the problem-based learning approach and teamwork allow students to get a better understanding and more in-depth knowledge of the field and teaches soft skills expected by employers.
The ability to precisely manipulate nanoscale objects and form defined assemblies with extraordinary optical properties has been attracting researchers’ interest for decades. Top-down lithography approaches were the first choice to define sub-wavelength patterns of metasurfaces. Recently, template-based self-assembly methods emerged allowing to deposit chemically synthesized nanoparticle (NP) colloids into tailored traps. Clean-room lithography techniques are required only once—to produce the template master, which can be replicated in an elastomer and used as the NP deposition template. The capillary force deposition ensured nearly 100% yield of tailored single or multi-particle assemblies over cm scales. When the pitch between scattering NPs overlaps the localized surface plasmon band, a high-quality surface lattice resonance (SLR) emerges. We have demonstrated that the SLR can couple to the NP optomechanical oscillations or can be exploited for sensing and nanolasing applications.
In this work, enhancement of the second harmonic response of organic nanofibers deposited on encapsulated and robust
plasmonic active substrate is experimentally demonstrated. Organic nanofibers grown from functionalized paraquaterphenylene
(CNHP4) molecules have been transferred on lithographically defined regular arrays of gold
nanostructures, which subsequently have been coated with thin films of diamond-like carbon with 25, 55 and 100 nm
thickness. Femtosecond laser scanning microscopy enables us to identify enhancement of the second harmonic response
of the fibers. This is facilitated by a preservation of the field enhancement effects, which appear on the nanostructures
and remain significant on top of the coating layer.
This paper presents a custom designed, fully automated UV holographic lithography system based on Lloyd‘s mirror
interferometer geometry. This system was used to record large area (50×50 mm2) 1D and 2D periodic patterns with
periodicity of 288 nm in a positive tone photoresist layer spin coated on crystalline silicon substrate. Produced structures
were investigated with atomic force and scanning electron microscopes.
The investigation of relaxation processes in noble metal nanoparticles upon ultrafast excitations by femtosecond laser
pulses is useful to understand the origin and the enhancement mechanism of the nonlinear optical properties for metaldielectric
nanocomposites. In the current work we analyze diamond like carbon (DLC) film based copper and silver
nanocomposites with different metal content synthesized employing unbalanced magnetron sputtering of metal targets
with argon ions in acetylene gas atmosphere. Surface morphology and nanoparticle sizes were analyzed employing
scanning electron and atomic force microscopy. Optical properties of the nanocomposite films were analyzed employing
UV-VIS-NIR spectrometry. Transient absorption measurements were obtained employing Yb:KGW femtosecond laser
spectroscopic system (HARPIA, Light Conversion Ltd.). Energy relaxation dynamics in Cu nanoparticles showed some
significant differences from Ag nanoparticles. The increase of excitation intensity hasn’t show additional nonlinear
effects for the excited state relaxation dynamics for both kinds of samples.
Forming structures similar to or smaller than the optical wavelength offers a wide range of possibilities to modify the
optical properties of materials. Tunable optical nanostructures can be applied as materials for surface-enhanced
spectroscopy, optical filters, plasmonic devices, and sensors. In this work we present experimental results on technology
and properties of periodical, polymer based optical structures modified by ordered adsorption of silver nanoparticles.
These structures were formed combining UV hardening and dip coating from colloidal solutions. We have investigated
the influence of silver nanoparticles assembly on the ambient conditions (deposition temperature and time) and surface
features (periodicities and shape) of the template micro structures. Optical absorbance as well as morphology of the
structures containing silver nanoparticles were investigated by UV-VIS spectroscopy, AFM, SEM and optical
microscopy. The influence of silver nanoparticles on the optical properties of the structures was investigated by polarized
light spectroscopy (Grating Light Reflection Spectroscopy - GLRS). From the results of this study we propose a low cost
procedure for fabricating structures that could be potentially new type of plasmonic sensors exploiting surface enhanced
plasmon resonance in silver nano structures.
Aligned ensembles of nanoscopic nanofibers from organic molecules such as para-phenylenes for photonic applications
can be fabricated by self-assembled molecular growth on a suited dielectric substrate. Epitaxy together
with alignment due to electric surface fields determines the growth directions. In this paper we demonstrate
how aligned growth along arbitrary directions can be realized by depositing the molecules on a micro-structured
and gold covered Silicon surface, consisting of channels and ridges. For the correct combination of ridge width
and deposition temperature fibers grow perpendicular to the ridge edge, emitting light polarized along the ridges
after UV excitation.
KEYWORDS: Diffraction, Diffraction gratings, Scanning electron microscopy, Silicon, Reactive ion etching, Computer simulations, Geometrical optics, Microfluidics, Chemical elements, Chemical analysis
In the present research we have fabricated and investigated microfluidic device (system of periodic groves - diffraction
grating) employing contact photolithography combined with the reactive ion etching (RIE). Relative diffraction
efficiency of diffraction gratings (originally produced in silicon substrates) was measured experimentally and simulated
using linear dimensions of gratings defined by scanning electron microscopy (SEM). The main experimental results were
compared with the computer simulations where the standard software ("PCGrate-S 6.1") was employed to calculate
relative diffraction efficiency of diffraction gratings for the different wavelengths of visible light. Comparing two
evaluation methods: direct (electron microscopy) and indirect (relative diffraction efficiency measured at different angles
of incidence for the three wavelengths of light) we have demonstrated feasibility of optical methods in control of
geometrical dimensions of periodic structures at the microscopic range.
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