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

Tinkering with Light at the Nanoscale using Plasmonic Metasurfaces and Antennas: From Fano to Function

Surface plasmons are charge density oscillations that can couple strongly to light and be excited in, for instance, thin metal films and metal nanoparticles. The plasmonic excitation squeezes the light down to nanometric length scales, far smaller than the wavelength of the light. This localization of light can be utilized in several surface-enhanced spectroscopies, for photothermal therapy, in optical trapping methodologies and in refractometric sensing schemes. This thesis focuses on various excitation schemes and spectroscopic measurements of surface plasmons and their sensitivity to the dielectric surrounding the metal.Plasmonic excitations in metal films and nanoparticles have several common features, although only the former has successfully been commercialized as a refractometric biosensing platform. In a direct comparison of the two, both platforms performed equally well, from a sensitivity point-of-view. However, there are two significant advantages of nanoparticle plasmonic sensing schemes: The much relaxed excitation conditions and the miniscule size of the nanoparticle sensors. In a combination of these features, hundreds of individual nanoparticles were simultaneously interrogated in order to approach the few to single molecule detection limit. The data were obtained using a hyperspectral imaging methodology in combination with an enzymatic precipitation reaction that enhanced the plasmonic response from individual adsorbed molecules. The results demonstrated a sensitivity in the single molecule range, but a number of inhomogeneous broadening effects prevented counting the exact number of molecules per particle. In a different line of research, plasmonic nanoparticles placed in a large two dimensional array with small interparticle spacing and supported with a glass substrate were interrogated. The nanoplasmonic layer then act as a metamaterial that can support strongly asymmetric resonances, dispersive modes and even complete light absorption. These effects are due to a so-called Fano interference between the plasmon excitation and the reflection from the dielectric boundary. Complete absorption enhances the optical near-fields, which can be utilized in, for instance, surface enhanced spectroscopy techniques. However, minimizing the reflection has another interesting feature: A rapid phase jump of the reflected light. The phase is shown to vary about one order of magnitude faster than the reflected intensity and, therefore, also provides around one order of magnitude higher sensitivity to molecular adsorption. Altogether, the results presented in this thesis provides a basis for several interesting sensing schemes, as well as insight into some fundamentally intriguing phenomena regarding absorption, nanoscale coherence and light localization

Fano Interference between Localized Plasmons and Interface Reflections

Layers of subwavelength metal nanostructures that support localized surface plasmon resonances are of broad interest in applied nanotechnology, for example, in optical sensor development and solar energy harvesting devices. We measured specular reflection spectra as a function of incidence angle for two-dimensional layers of gold nanodisks on glass and found highly asymmetric line-shapes and a spectral red-shift of up to 0.2 eV, or 10% of the plasmon resonance energy, as the angle changed from normal toward grazing incidence. This dramatic angular dispersion is the result of a tunable Fano interference between the spectrally narrow plasmon emission and a "white" continuum caused by the interface reflection. The data are found to be in excellent agreement with predictions based on a theory for Fresnel reflection coefficients of an interface with subwavelength inclusions. The theory can also be used to derive analytical expressions for the Fano parameters

Nanostructured surface plasmon resonance sensors

No abstract availabl

Fano Interference between Localized Plasmons and Interface Reflections

Layers of subwavelength metal nanostructures that support localized surface plasmon resonances are of broad interest in applied nanotechnology, for example, in optical sensor development and solar energy harvesting devices. We measured specular reflection spectra as a function of incidence angle for two-dimensional layers of gold nanodisks on glass and found highly asymmetric line-shapes and a spectral red-shift of up to 0.2 eV, or 10% of the plasmon resonance energy, as the angle changed from normal toward grazing incidence. This dramatic angular dispersion is the result of a tunable Fano interference between the spectrally narrow plasmon emission and a “white” continuum caused by the interface reflection. The data are found to be in excellent agreement with predictions based on a theory for Fresnel reflection coefficients of an interface with subwavelength inclusions. The theory can also be used to derive analytical expressions for the Fano parameters

Complete Light Annihilation in an Ultrathin Layer of Gold Nanoparticles

We experimentally demonstrate that an incident light beam can be completely annihilated in a single layer of randomly distributed, widely spaced gold nanoparticle antennas. Under certain conditions, each antenna dissipates more than 10 times the number of photons that enter its geometric cross-sectional area. The underlying physics can be understood in terms of a critical coupling to localized plasmons in the nanoparticles or, equivalently, in terms of destructive optical Fano interference and so-called coherent absorption

Refractometric biosensing based on optical phase flips in sparse and short-range-ordered nanoplasmonic layers

Noble metal nanoparticles support localized surface plasmon resonances (LSPRs) that are extremely sensitive to the local dielectric properties of the environment within distances up to 10-100 nm from the metal surface. The significant overlap between the sensing volume of the nanoparticles and the size of biological macromolecules has made LSPR biosensing a key field for the application of plasmonics. Recent advancements in evaluating plasmonic refractometric sensors have suggested that the phase detection of light can surpass the sensitivity of standard intensity-based detection techniques. Here, we experimentally confirm that the phase of light can be used to precisely track local refractive index changes induced by biomolecular reactions, even for dilute and layers of short-range-ordered plasmonic nanoparticles. In particular, we demonstrate that the sensitivity can be enhanced by tuning in to a zero reflection condition, in which an abrupt phase flip of the reflected light is achieved. Using a cost-effective interference fringe tracking technique, we demonstrate that phase measurements yield an approximately one order of magnitude larger relative shift compared with traditional LSPR measurements for the model system of NeutrAvidin binding to biotinylated nanodisks