1,720,976 research outputs found
Interferogram Average over Wavelength Reflectance Spectroscopy: A Novel Interferometric Technique For Ultrasensitive Label-Free Biosensing with Porous Silicon
No full textPorous silicon (PSi) is a nanostructured material increasingly exploited for both refractometric and (bio)sensing applications, though currently suffering of restricted real applications due to insufficient sensitivity [1].
Here we report on development, characterization, and application (to both refractometry and biosensing) of a novel ultrasensitive technique for label-free discrimination of bulk and surface refractive index changes (namely, Interferogram Average over Wavelength –IAW– reflectance spectroscopy) using PSi interferometer.
The IAW reflectance spectroscopy relies on the calculation of the average value over wavelength of spectral interferograms, namely IAW value. Interferograms are calculated by subtraction (intensity, wavelength by wavelength) of the reflection spectrum, acquired after infiltration of the analyte within the nanopores of the PSi interferometer, from a reference reflection spectrum.
As to refractometric applications, a minimum bulk refraction index variation of 10-6 RIU was experimentally measured using NaCl aqueous solutions, with a theoretical detection limit (DL) of 10-8 RIU.
As proof-of-concept for label-free biosensing applications, the IAW spectroscopy was used to demonstrate detection of BSA adsorption on PSi surface down to a DL of 20 pM [1] while for a “real” biosensing application, concentrations of TNFα (a protein biomarker of inflammation and sepsis) were experimentally monitored through an aptasensor, reaching a DL of 200 pM. Both these results represent a 1000-fold improvement with respect to the commonly used FFT reflectance spectroscopy [2].
In conclusion, the IAW reflectance spectroscopy envisages bringing PSi optical (bio)sensors at the forefront of ultrasensitive label-free biosensing techniques, with application for point-of-care clinical analysis where low analyte concentrations are required to be detected.
Reference
[1] Mariani, S., Strambini, L. M., Barillaro, G., Anal. Chem. 88, 8502–8509 (2016).
[2] Mariani, S., Pino, L., Strambini, L. M., Tedeschi, L., Barillaro, G., ACS Sens., 1 (12), 1471–1479 (2016)
Towards an in-vitro liver lobule model
No full textIn-vitro culture of liver cells on bio-inspired chips., namely liver-on-chip, to form a 3D hepatic tissue morphologically close to its in-vivo counterpart is rapidly emerging for drug testing applications. This paper reports preliminary results towards fabrication of an in-vitro model of the smallest functional liver unit, which is the hepatic lobule. Simultaneous fabrication of out-of-plane micro-channels interconnected by in-plane nanometric-channels is demonstrated by electrochemical etching of n-type silicon in aqueous (48%) HF: (30%) H2O2=1:1 (by vol.) electrolyte through the synergistic work of back-side illumination, avalanche breakdown, and high oxidizing power chemicals
Interferogram average over wavelength spectroscopy: An ultrasensitive technique for biosensing with porous silicon interferometers
No full textHere we report on a high-sensitivity interferometric technique, namely Interferogram Averaged over Wavelength - IAW-reflectance spectroscopy, enabling sub-nanomolar detection (both nonspecific and specific) of proteins to be accomplished in direct (without any amplification) label-free mode using porous silicon (PSi) interferometers. The IAW reflectance spectroscopy is based on both calculation and elaboration of spectral interferograms. Interferograms are obtained by subtracting (intensity, wavelength by wavelength) reflectance spectra acquired on PSi interferometers in buffer solution after protein injection (at different concentrations) from a reference reflectance spectrum acquired in buffer solution before protein injection. The output signal, namely IAW value, is eventually obtained as the average value, calculated over a given wavelength interval, of each interferogram. Using the IAW technique nonspecific adsorption of Bovine Serum Albumin (BSA) down to 0.15 nM (DL=20 pM) and specific detection of Tumor Necrosis Factor (TNFα) down to 3 nM (DL=0.2 nM) was reliably achieved in direct label-free mode using PSi interferometers. Both the results represent a 10000-fold reduction in DL with respect to the current literature on the use of PSi for direct label-free measurements
Quasi-zero-voltage controlled etching of macropores in n-type silicon
No full textHere, we report an experimental study about the controlled etching of macropores in n-type silicon electrodes at quasi-zero anodic voltage using hydrofluoric acid-based photo-electrochemical etching (P-ECE). This breaks a new ground on the controlled electrochemical dissolution of n-type silicon, for which the use of anodic voltage above the electropolishing peaks (Vps, Jps) has been considered to be a golden rule for the etching control, so far. Remarkably, our experimental results clearly show that it is possible to control the etching of macropores at anodic voltages well below (close to zero Volt) the electropolishing peak and that the use of low anodic voltages is beneficial for the fabrication of regular macropores with large diameter (i.e. 10 μm) and spatial pitch (i.e. 20 μm)
Vertical high-order 1D silicon photonic crystals for integrated opto-fluidic microsystems
No full textHigh-order one-dimensional silicon micromachined photonic crystal with a reflectivity notch at λ∼ 1.55 μm
No full textLayer-by-layer nano-assembly of charged polyelectrolytes for label-free optical biosensing with nanostructured materials: The case of nanostructured porous silicon interferometers
No full textThe nano-assembly of charged polyelectrolytes via layer-by-layer (LbL) technology on porous silicon (PSi) interferometers is here demonstrated as an effective biofunctionalization approach for high-sensitivity/selectivity labelfree optical biosensing, using streptavidin/biotin affinity detection as case study. Nanostructured PSi interferometers are biofunctionalized with a nano-assembly of a positively-charged polyelectrolyte, namely, PAH (poly(allylamine hydrochloride)), and a negatively-charged biotinylated polyelectrolyte, namely, b-PMAA (poly(methacrylic acid)), via LbL technology. The nano-assembly is stable under operating conditions and enables the selective and sensitive detection of streptavidin with a sub-picomolar detection limit (namely, DL=0.6 pM), which is 105-fold lower than that achieved with PSi interferometers biofunctionalized using standard silane chemistry. Remarkably, the analytical performance achieved for LbL-biofunctionalized PSi interferometers is comparable to those of state-of-the-art label-free photonic and plasmonic platforms
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
