253 research outputs found
On-a-chip biosensing based on all-dielectric nanoresonators
Nanophotonics has become a key enabling technology in biomedicine with great
promises in early diagnosis and less invasive therapies. In this context, the
unique capability of plasmonic noble metal nanoparticles to concentrate light
on the nanometer scale has widely contributed to biosensing and enhanced
spectroscopy. Recently, high-refractive index dielectric nanostructures
featuring low loss resonances have been proposed as a promising alternative to
nanoplasmonics, potentially offering better sensing performances along with
full compatibility with the microelectronics industry. In this letter we report
the first demonstration of biosensing with silicon nanoresonators integrated in
state-of-the-art microfluidics. Our lab-on-a-chip platform enables detecting
Prostate Specific Antigen (PSA) cancer marker in human serum with a sensitivity
that meets clinical needs. These performances are directly compared with its
plasmonic counterpart based on gold nanorods. Our work opens new opportunities
in the development of future point-of-care devices towards a more personalized
healthcare
Unravelling the Role of Electric and Magnetic Dipoles in Biosensing with Si Nanoresonators
High refractive index dielectric nanoresonators are attracting much attention due to their ability to control both electric and magnetic components of light. Combining confined modes with reduced absorption losses, they have recently been proposed as an alternative to nanoplasmonic biosensors. In this context, we study the use of semi-random silicon nanocylinder arrays, fabricated with simple and scalable colloidal lithography for the efficient and reliable detection of biomolecules in biological samples. Interestingly, electric and magnetic dipole resonances are associated to two different transduction mechanisms: extinction decrease and resonance redshift, respectively. By contrasting both observables, we identify clear advantages in tracking changes in the extinction magnitude. Our data demonstrate that, despite its simplicity, the proposed platform is able to detect prostate specific antigen (PSA) in human serum with limits of detection meeting clinical needs.Peer ReviewedPostprint (author's final draft
Dimer-on-mirror SERS substrates with attogram sensitivity fabricated by colloidal lithography
Nanoplasmonic substrates with optimized field-enhancement properties are a key component in the continued development of surface-enhanced Raman scattering (SERS) molecular analysis but are challenging to produce inexpensively in large scale. We used a facile and cost-effective bottom-up technique, colloidal hole-mask lithography, to produce macroscopic dimer-on-mirror gold nanostructures. The optimized structures exhibit excellent SERS performance, as exemplified by detection of 2.5 and 50 attograms of BPE, a common SERS probe, using Raman microscopy and a simple handheld device, respectively. The corresponding Raman enhancement factor is of the order 10(11), which compares favourably to previously reported record performance values
Gas sensors based on localized surface plasmon resonances: synthesis of oxide films with embedded metal nanoparticles, theory and simulation, and sensitivity enhancement strategies
This work presents a comprehensive review on gas sensors based on localized surface plasmon resonance (LSPR) phenomenon, including the theory of LSPR, the synthesis of nanoparticle-embedded oxide thin films, and strategies to enhance the sensitivity of these optical sensors, supported by simulations of the electromagnetic properties. The LSPR phenomenon is known to be responsible for the unique colour effects observed in the ancient Roman Lycurgus Cup and at the windows of the medieval cathedrals. In both cases, the optical effects result from the interaction of the visible light (scattering and absorption) with the conduction band electrons of noble metal nanoparticles (gold, silver, and gold–silver alloys). These nanoparticles are dispersed in a dielectric matrix with a relatively high refractive index in order to push the resonance to the visible spectral range. At the same time, they have to be located at the surface to make LSPR sensitive to changes in the local dielectric environment, the property that is very attractive for sensing applications. Hence, an overview of gas sensors is presented, including electronic-nose systems, followed by a description of the surface plasmons that arise in noble metal thin films and nanoparticles. Afterwards, metal oxides are explored as robust and sensitive materials to host nanoparticles, followed by preparation methods of nanocomposite plasmonic thin films with sustainable techniques. Finally, several optical properties simulation methods are described, and the optical LSPR sensitivity of gold nanoparticles with different shapes, sensing volumes, and surroundings is calculated using the discrete dipole approximation method.This research was funded by the Portuguese Foundation for Science and Technology
(FCT) in the framework of the Strategic Funding UIDB/04650/2020; and by the project NANO4BIO
POCI-01-0145-FEDER-032299, with FCT reference PTDC/FISMAC/32299/2017. Marco S. Rodrigues
acknowledges FCT for his PhD Scholarship, SFRH/BD/118684/2016
Plasmonic Nanostructures for Nano-Scale Bio-Sensing
The optical properties of various nanostructures have been widely adopted for biological detection, from DNA sequencing to nano-scale single molecule biological function measurements. In particular, by employing localized surface plasmon resonance (LSPR), we can expect distinguished sensing performance with high sensitivity and resolution. This indicates that nano-scale detections can be realized by using the shift of resonance wavelength of LSPR in response to the refractive index change. In this paper, we overview various plasmonic nanostructures as potential sensing components. The qualitative descriptions of plasmonic nanostructures are supported by the physical phenomena such as plasmonic hybridization and Fano resonance. We present guidelines for designing specific nanostructures with regard to wavelength range and target sensing materials
A bimetallic nanoantenna for directional colour routing
Recent progress in nanophotonics includes demonstrations of meta-materials displaying negative refraction at optical frequencies, directional single photon sources, plasmonic analogies of electromagnetically induced transparency and spectacular Fano resonances. The physics behind these intriguing effects is to a large extent governed by the same single parameter—optical phase. Here we describe a nanophotonic structure built from pairs of closely spaced gold and silver disks that show phase accumulation through material-dependent plasmon resonances. The bimetallic dimers show exotic optical properties, in particular scattering of red and blue light in opposite directions, in spite of being as compact as ∼λ3/100. These spectral and spatial photon-sorting nanodevices can be fabricated on a wafer scale and offer a versatile platform for manipulating optical response through polarization, choice of materials and geometrical parameters, thereby opening possibilities for a wide range of practical applications
Mapping enzyme-substrate interactions: its potential to study the mechanism of enzymes
With the increase of the need to use more sustainable processes for the industry in our society, the modeling of enzymes has become crucial to fully comprehend their mechanism of action and use this knowledge to enhance and design their properties. A lot of methods to study enzymes computationally exist and they have been classified on sequence-based, structure-based, and the more new artificial intelligence-based ones. Albeit the abundance of methods to help predict the function of an enzyme, molecular modeling is crucial when trying to understand the enzyme mechanism, as they aim to correlate atomistic information with experimental data. Among them, methods that simulate the system dynamics at a molecular mechanics level of theory (classical force fields) have shown to offer a comprehensive study. In this book chapter, we will analyze these techniques, emphasizing the importance of precise modeling of enzyme-substrate interactions. In the end, a brief explanation of the transference of the information from research studies to the industry is given accompanied with two examples of family enzymes where their modeling has helped their exploitation.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (author's final draft
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