In this work, a trilayer graphene is used as a thin non dielectric spacer with a high index of refraction, between Au film
and Au NPs. Encouraged by the sharpness of the localized surface plasmon resonance LSPR induced by this system, we
performed sensitivity measurements to refractive index change in the surrounding medium of the sensor. The presence of
graphene led to both higher sensitivity and sharper full width at half maximum FWHM and thus higher figure of merit
FOM (2.8) compared to the system without graphene (2.1).
Surface plasmon resonance (SPR) biosensors have become a central tool for the study of biomolecular interactions,
chemical detection, and immunoassays in various fields. SPR biosensors offer unparalleled advantages such as label-free
and real-time analysis with very high sensitivity. To further push the limits of SPR capabilities, novel SPR structures and
approaches are being actively investigated. Here we experimentally demonstrate a graphene-based SPR biosensor. By
incorporating a graphene layer to the conventional gold thin film SPR structure, its biosensing sensitivity is significantly
increased. This is shown in a typical affinity biosensing experiment to measure the real-time binding kinetics of biotin-streptavidin.
In addition to higher sensitivity, we also obtain a much higher signal-to-noise ratio without the slightest
modification of the usual measurement setup. This implies that a considerably lower limit of detection can be made
possible with the novel structure. Moreover, our graphene-based SPR biosensors do not require sophisticated surface
functionalization schemes as in conventional SPR in order to function. Previous reports have also suggested that
graphene might effectively prevent non-specific binding of biomolecules on the sensor surface. With relatively simple
fabrication methods and large scalability, these combined distinctive advantages can enable future generation of high-performance
We study theoretically and experimentally the variation in localized surface plasmon resonance (LSPR) structure
(λmax=660 nm) as a function of dielectric coating thickness. The influence of the morphology and interparticle distance
on the LSPR spectra of a glass/Au NSs interface with a constant thickness of diamond (NCD) overcoating was
investigated through the calculation of theoretical transmission spectra. Ajusting the theoretical curve to experimental
LSPR spectra allowed fixing the geometry of the plasmonic interface and permitted to evaluate the change in the
wavelength at maximum absorption (λmax) as a function of the thickness of the NCD overlayers. The theoretical data
were compared with experimental ones obtained on glass/AuNSs/ NCD surface.
Photoluminescent porous Si (pSi) is a potentially attractive material for biosensor devices. Its ease of fabrication, large active surface area and unique optical properties are just some important attributes. Among other transduction techniques, it is possible to monitor the onset of molecular binding events through the effective quenching of the bright pSi photoluminescence. Here we present the study of effective quenching through a colloidal Ag nanoparticle interaction with pSi. Placing the metallic nanoparticles in close proximity to the light emitting pSi can effectively sweep away the charge carriers from the semiconductor surface and result in a carrier depletion region near the Si-nanoparticle interface. By labeling the targeted bio-species with a silver nanoparticle, and the pSi surface with an appropriate receptor molecule ; in-situ PL monitoring can provide a real-time transduction scheme for the pSi- based biosensor devices.
Recently, the development of Si-based optical sensors for protein and other biochemicals has become of great interest. Here, we examine the protein and Si-based substrate interaction by studying the BSA interaction with surface derivatized porous Si (pSi). The pSi fabricated through electrochemical anodization of crystalline silicon in hydrofluoric acid showed an average pore diameter of ~ 10 nm. Chemically functionalization of pSi by thermal reaction with undecylenic acid produced an organic monolayer covalently attached to the silicon surfaces. Bovine serum albumin (BSA) was then adsorbed onto the acid-terminated pSi surfaces. The resulting surfaces were characterized using scanning electron microscopy (SEM), ellipsometry and Fourier transform infrared spectroscopy (FTIR). Ellipsometry and SEM both showed that the BSA molecule penetrated more than 1 μm into the porous structure. SEM further revealed the damaged and partially lifted-off porous film from the silicon substrate after a prolonged BSA adsorption. It is caused by the BSA penetrating deep into the porous structure and anchoring itself tightly through strong electrostatic interaction with the acid-covered pSi sidewalls. A change in surface tension during BSA film formation then causes the pSi layer to buckle and lift-off from the underlying Si substrate. FTIR results from the undecylenic acid-modified pSi surfaces after BSA adsorption showed strong characteristic Amide I, II and III vibrational bands. The role of the surface chemistry, wetting properties, substrate porosity and topography will be discussed.