Metal nano-hole arrays, modulating resonances intensity and spectral position, span visible to near-infrared ranges, unlocking sensing applications. Displacing electric fields toward the interface with air, facilitated by a high-index material (SiN) substrate, refines the sensitive region and improve enhancement. Efficient and reproducible fabrication protocols, such as the modified nanosphere lithography (NSL) method, have been developed by our group for the creation of highly ordered nano-hole arrays (NHAs) in thin gold films. These arrays feature diverse properties, including thickness, hole shape, diameter, and lateral periodic or quasi-periodic spacing. Interference and coupling between plasmonic modes of different natures present a route for enhancement for SERS applications. Integrating these nanostructures within a fiber-based microfluidic system offers an innovative solution for pesticide detection. This system, characterized by straightforward fabrication, cost-effectiveness, sensitivity, and specificity, emerges as a formidable contender for in-situ environmental monitoring, encapsulating cutting-edge research and innovation in pest control.
The realization of periodic plasmonic nanostructures featuring macroscopic scale and easily controllable size and lattice spacing, is a challenging achievement for low-cost nanofabrication tools, which has not been completely explored so far. In this work, periodic array of different metal nanostructures have been easily prepared on large-area by exploiting a modified nano-sphere lithography (NSL) fabrication technique. A valuable ability is to couple the versatility offered by NSL with post-processing tools for a properly engineering of plasmonic nanoparticles. Obtaining dynamic tunability of metal nanostructures will allow the monitoring of electromagnetic near field distribution upon interaction with light of a desired wavelength. A rational design of such singular or collective optical properties can be used to focus and optimize the investigated functional features. Here, Au nano-prisms (NPs) and Au nanohole (NHs) arrays, tailored on the nanoscale, are investigated as innovative sensing platforms and as substrates for surface enhanced Raman scattering (SERS). Their localized “sensing volume”, defined as the penetration depth within which changes of the refractive index can be detected, demonstrated their excellent performances towards single-molecule detection.
Among all transduction methodologies reported in the field of solid state optical chemical sensors, the attention has been focused onto the optical sensing characterization by using propagating and localized surface plasmon resonance (SPR) techniques. The research in this field is always oriented in the improvement of the sensing features in terms of sensitivity and limits of detection. To this purpose different strategies have been proposed to realize advanced materials for high sensitive plasmonic devices. In this work nanostructured silica nanowires decorated by gold nanoparticles and active magneto-plasmonic transductors are considered as new biosensing transductors useful to increase the performance of sensitive devices.
We report on the potentiality of the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique for the deposition of
thin films of colloidal nanoparticles to be used for gas sensors based on electrical transduction mechanisms. The MAPLE
technique seems very promising, since it permits a good thickness control even on rough substrates, generally used to
enhance the active surface for gas adsorption.
TiO2 (with a capping layer of benzyl alcohol) and SnO2 (with a capping layer of trioctylphosphine) colloidal
nanoparticles were diluted in suitable solvents (0.2% concentration), frozen at liquid nitrogen temperature and ablated
with a ArF (λ=193 nm) or KrF (248 nm) excimer laser. The nanoparticle thin films were deposited on silica,
interdigitated alumina and <100> Si substrates and submitted to morphological (SEM-FEG), structural (XRD, FTIR),
optical (UV-Vis transmission) and electrical (sensing tests) characterizations.
A uniform distribution of TiO2 nanoparticles, with an average size of ~10 nm, was obtained on flat and rough substrates.
The deposited TiO2 nanoparticles preserved the anatase crystalline structure, as evidenced by the XRD spectra. FTIR
analysis showed that the SnO2 nanoparticles maintained the capping layer after the laser-assisted transfer process. This
protective layer was removed after annealing at 400 °C. The starting nanoparticle dimensions were preserved also in this
case. Electrical tests, performed on TiO2 nanoparticle films, in controlled atmosphere in presence of ethanol and acetone
vapors, evidenced a high value of the sensor response even at very low concentrations (20-200 ppm in dry air). In
contrast, in the case of SnO2 nanoparticle films, electrical tests to ethanol vapor presence showed poor gas sensing
properties probably due to the small nanoparticle sizes and interconnections.
Nanostructured TiO2 films and Au-TiO2 nanocomposite thin films prepared by sol-gel method have been deposited onto gold covered glass substrates and glass substrates in order to study their optical properties using Surface Plasmon Resonance and Optical Absorption measurements. Both techniques have been used to study the sensing features of both kind of films to different vapour organic compounds. A comparative study of the two techniques has allowed us to know the possible benefits than can be found when the sensing material is a nanocomposite thin film.
TiO2 dot and rod shaped colloidal nanocrystals (NCs) prepared by an hydrolytic colloidal route and capped with different surfactants have been spin coated onto gold substrates and onto quartz slides. Morphological, structural and optical characterization of the colloidal NCs and the thin films has been performed by means of Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and UV-VIS spectroscopy. Surface Plasmon Resonance (SPR) has been used as optical transduction method to test the sensing ability of the prepared films for alcohols vapours detection as a function of NC shape, capping molecule and thermal treatment.
Spin-coated layers of ZnPc and CuP have been used as chemically interacting materials for the detection of alcohols, amines, ketones, alkanes and pyridine for applications in food quality control. The UV-VIS variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between the VOCs species and the heterogeneous sensing layer shows a different behavior in the responses respect to the results obtained with each single compound.
Sol-gel organic synthesis of SnO2 thin films from tin ethoxide precursor is reported here as a promising and cheap alternative of the 'classical' chemical and physical preparation methods of the SnO2 thin films, for gas sensing applications. A simple, integrated circuit compatible test structure, for rapid evaluation of the sensing properties of the SnO2 sol-gel derived thin films is described. The main features of our microstructure consists of a a heating resistor integrated on chip, made of highly boron doped silicon and a metallization system from Au/W deposited on a planarized chemically vapor deposited SiO2 layer. The SnO2 films have shown the well-known increase-maximum-decrease dependence of chemoresistance as a function of temperature, with a maximum at about 380 degrees C, when they are measured in clean, dry air. The sensitivity of SnO2 films to high concentration of H2 in air was studied within a quartz furnace, externally heated in the temperature range from 200 to 450 degrees C. The relative sensitivity is equal to 100 percent at temperatures as low as 200 degrees C, while its maximum value is anticipated to be above 450 degrees C. The CO sensing properties of SnO2 layers were evaluated as a function of input power applied on the integrated heating resistor. We have obtained relative sensitivities of 30 percent for 500 ppm CO concentration in dry air and an input power of 209 mW.
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