The interest in the development of nanoscale plasmonic technologies has dramatically increased in recent years. The photonic properties of plasmonic nanopatterns can be controlled and tuned via their ...size, shape, or the arrangement of their constituents. In this work, we propose a 2D hybrid metallic polymeric nanostructure based on the octupolar framework with enhanced sensing property. We analyze its plasmonic features both numerically and experimentally, demonstrating the higher values of their relevant figures of merit: we estimated a surface-enhanced Raman spectroscopy (SERS) enhancement factor of 9 × 107 and a SPR bulk sensitivity of 430 nm/RIU. In addition, our nanostructure exhibits a dual resonance in the visible and near-infrared region, enabling our system toward multispectral plasmonic analysis. Finally, we illustrate our design engineering strategy as enabled by electron beam lithography by the outstanding performance of a SERS-based biosensor that targets the Shiga toxin 2a, a clinically relevant bacterial toxin. To the best of our knowledge, this is the first time that a SERS fingerprint of this toxin has been evidenced.
Technologies based on plasmonic nanostructures are a rapidly growing field that aims to be a valid alternative to conventional diagnostic tools. One of the main goals in their technological ...development consists of the design of systems for sensitive and specific detection of pathogens in water. Among these, rotaviruses represent the main cause of childhood viral gastroenteritis in humans. In this work, we design functionalized plasmonic label-free nanosensors based on localized surface plasmon resonance (LSPR) sensing to detect ultralow concentrations of rotavirus. We demonstrate the possibility of detecting in a specific way amounts lower than 1 × 103 plaque forming unit (PFU)/mL of the Rotavirus in water using a very low sample volume (2 μL). These results together with those obtained in our specificity tests performed with two different viruses (bovine herpesvirus, BHV1; and equine viral arteritis, EVA) confirm that our device is very promising to develop a rapid, simple, very sensitive, and specific immunoassay for detection of rotavirus. To the best of our knowledge, this is the first time that LSPR nanobiosensing has been used for the sensitive and specific detection of rotavirus.
The optical properties and functionality of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystal quantum dots (NQDs) are presented. These NQDs showed chemical robustness ...over months and years and band-gap tunability in the near infrared spectral regime, with a reliance on the NQD size and composition. Furthermore, these NQDs exhibit high emission quantum efficiencies of up to 65% and an exciton emission band that is narrower than that of the corresponding PbSe NQDs. In addition, the emission bands showed a peculiar energy shift with respect to the relevant absorption band, changing from a Stokes shift to an anti-Stokes shift, with an increase of the NQD diameter. The described core-shell structures and the corresponding PbSe core NQDs were used as passive Q-switches in eye-safe lasers of Er:glass, where they act as saturable absorbers. The absorber saturation investigations revealed a relatively large ground-state cross-section of absorption (sigma gs = 10(-16) - 10(-15) cm2) and a behavior of a "fast" absorber with an effective lifetime of tau eff approximately 4.0 ps is proposed. This lifetime is associated with the formation of multiple excitons at the measured pumping power. The product of sigma gs and tau eff enables sufficient Q-switching performance and tunability in the near infrared spectral regime. The amplified spontaneous emission properties of PbSe NQDs were examined under continuous illumination by a diode laser at room temperature, suitable for standard device conditions. The results revealed a relatively large gain parameter (g = 2.63 - 6.67 cm-1). The conductivity properties of PbSe NQD self-assembled solids, annealed at 200 degrees C, showed an Ohmic behavior at the measured voltages (up to 30 V), which is governed by a variable-range-hopping charge transport mechanism.
The introduction, within a π-conjugated donor−acceptor molecule, of an intermediate barrier to electron tunneling and its size scaling and influence on electronic polarization properties have ...remained so far elusive issues of great potential interest toward the fine-tuning of the linear and nonlinear optical properties of molecular materials. Paracyclophane (pCP) provides a most relevant cornerstone for more elaborate compounds where donor and acceptor substituents are made to interact through a sterically constrained π−π stack. A first attempt in this direction is reported here with the synthesis of a model dipolar 4-(4-dihexylaminostyryl)-16-(4-nitrostyryl)2.2paracyclophane and the subsequent experimental and theoretical study of its quadratic nonlinear optical properties. A major outcome of this investigation is the evidence of a significant “through-space” charge transfer as unambiguously designated by the strong departure of the β quadratic hyperpolarizability tensor of the full doubly substituted molecule (60 × 10-30 esu) from the additive β value (18 × 10-30 esu) expected for strictly noninteracting singly substituted pCP moieties. This desired increase of nonlinear efficiency upon substitution is not offset by the usual red-shift of the absorption spectrum which generally curtails application perspectives in more common uninterrupted conjugated chains. The collective nonlinear polarization behavior involving the full end-to-end molecular structure is confirmed by theoretical calculations using the Collective Electron Oscillator (CEO) approach which furthermore indicates a significantly enhanced role of electron−hole pair delocalization in the higher order nonlinear response, compared to the linear polarizability or the static dipole moment.
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