Alessio Crescitelli

Chemical Detection in Water by Single-Walled Carbon Nanotubes-Based Optical Fiber Sensors

In this letter, the possibility to use single-walled carbon nanotubes (SWCNTs) as sensitive nanostructured material for the development of an optoelectronic sensor that can perform chemical detection in water has been investigated and demonstrated for the first time. The fabricated sensor has been employed in a reflectometric system involving single wavelength reflectance measurements. The good stability of the steady-state signal, the high sensitivity, as well as the good response dynamics obtained in the case of toluene detection confirm the potentiality of SWCNTs to be employed in a water environment.

Surface sensitivity of Rayleigh anomalies in metallic nanogratings

Sensing schemes based on Rayleigh anomalies (RAs) in metal nanogratings exhibit an impressive bulk refractive-index sensitivity determined solely by the grating period. However, the surface sensitivity (which is a key figure of merit for label-free chemical and biological sensing) needs to be carefully investigated to assess the actual applicability of this technological platform. In this paper, we explore the sensitivity of RAs in metal nanogratings when local refractive-index changes are considered. Our studies reveal that the surface sensitivity deteriorates up to two orders of magnitude by comparison with the corresponding bulk value; interestingly, this residual sensitivity is not attributable to the wavelength shift of the RAs, which are completely insensitive to local refractive-index changes, but rather to a strictly connected plasmonic effect. Our analysis for increasing overlay thickness reveals an ultimate surface sensitivity that approaches the RA bulk value, which turns out to be the upper-limit of grating-assisted surface-plasmon-polariton sensitivities.

Lab-on-fiber technology

Multimaterial Fibers.- Monolithic Silicon Photonic Crystal Fiber Tip Sensors.- Electrohydrodinamic Dispenser for Delivering Multiphase Samples at Nanoscale.- Lab-on-Fiber Technology: Towards Multifunctional Optical Nanoprobes.- Functional Metamaterials for Lab-on-a-fiber.- Nanofibers as Valuable Technological Platform for Lab on Fiber.- Lab-on-Fiber by Using the Breath Figures Technique.- Hybrid Nanoimprint-Soft Lithography for Highly Curved Surface with Sub-15 nm Resolution .- Overview of Micro- and Nanostructured Fiber Sensors .- Nanophotonics Within Silica Structured Optical Fibres.- Miniaturized Optical Tweezers Through Fiber-End Microfabrication.- Silicon-on-Insulator Microring Resonator Sensor Integrated on an Optical Fiber Facet.- Optical Fibers as Platforms for Subwavelength Plasmonic Structures..- Fiber-top and Ferrule-top Micromachined Devices: A New Platform of All-optical Sensors and Actuators.- Hydrogen Detection Using a Single Palladium Nano-aperture on a Fiber Tip.- Sensitive and Selective Lab-on-a-Fiber Sensor for Bacteria Detection in Water.- Photonic Crystal Fiber as a Lab-in-Fiber Optofluidic Platform.

Optical fiber meta-tips

We report on the first demonstration of a proof-of-principle optical fiber ‘meta-tip’, which integrates a phase-gradient plasmonic metasurface on the fiber tip. For illustration and validation purposes, we present numerical and experimental results pertaining to various prototypes implementing generalized forms of the Snell’s transmission/reflection laws at near-infrared wavelengths. In particular, we demonstrate several examples of beam steering and coupling with surface waves, in fairly good agreement with theory. Our results constitute a first step toward the integration of unprecedented (metasurface-enabled) light-manipulation capabilities in optical-fiber technology. By further enriching the emergent ‘lab-on-fiber’ framework, this may pave the way for the widespread diffusion of optical metasurfaces in real-world applications to communications, signal processing, imaging and sensing.

Impedimetric Label-Free Immunosensor on Disposable Modified Screen-Printed Electrodes for Ochratoxin A

An impedimetric label-free immunosensor on disposable screen-printed carbon electrodes (SPCE) for quantitative determination of Ochratoxin A (OTA) has been developed. After modification of the SPCE surface with gold nanoparticles (AuNPs), the anti-OTA was immobilized on the working electrode through a cysteamine layer. After each coating step, the modified surfaces were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The capacitance was chosen as the best parameter that describes the reproducible change in electrical properties of the electrode surface at different OTA concentrations and it was used to investigate the analytical parameters of the developed immunosensor. Under optimized conditions, the immunosensor showed a linear relationship between 0.3 and 20 ng/mL with a low detection limit of 0.25 ng/mL, making it suitable to control OTA content in many common food products. Lastly, the immunosensor was used to measure OTA in red wine samples and the results were compared with those registered with a competitive ELISA kit. The immunosensor was sensitive to OTA lower than 2 μg/kg, which represents the lower acceptable limit of OTA established by European legislation for common food products.

Investigation of Osmotic Distillation Technique for Beer Dealcoholization

A growing demand for low-alcohol drinks, due to health and social benefits resulting from lower alcohol consumption, has given rise to the development of techniques for alcohol reduction or elimination in beverages. The main difficulty is the development of a low alcohol content product with sensory properties similar to the original one. This work presents a preliminary study on the production of alcohol free beer (alcohol content = 0.5 %vol) by osmotic distillation technique, which allows to operate at low temperature and atmospheric pressure, using water as ethanol stripping agent. To this goal, a lab-scale plant equipped with a commercial membrane contactor with hollow fibers was set up. The effect of different stripping agents for ethanol removal on dealcoholization kinetics and on chemical and physical properties of the dealcoholized beer (i.e alcohol content, colour, pH, polyphenols, antioxidant activity) was investigated. Finally, the ethanol mass flux through the membrane during the dealcoholization process was measured and theoretically calculated with a good agreement.

Effect of bug damage and mold contamination on fatty acids and sterols of hazelnut oil

Fatty acid and sterol content of oil from nuts (cv Tonda di Giffoni) affected by two different biotic damages were characterized. Hazelnuts were sorted by a visual inspection of the kernels in three different samples (cimiciate, apparently healthy and moldy). The oil was extracted and analyzed by gas–liquid chromatography coupled to a flame ionization detector for fatty acid and sterol composition. The higher level of total polyunsaturated fatty acids (PUFA) in cimiciato oil compared to apparently healthy nuts was associated with the decrease in total monounsaturated fatty acids, resulting in a higher unsaturated/saturated acid ratio, while the PUFA content in moldy nut oil was lower than in apparently healthy nut oil. In both damaged samples, the appearance of four new chromatography peaks could be due to the presence of hydroperoxides, as proved by carrying out a TLC analysis. The overall phytosterol amount decreased in both cimiciato and moldy nut oils compared to the apparently healthy nut oil, and the main differences were observed in terms of sitosterol, campesterol and clerosterol.

Simple technique for integrating compact silicon devices within optical fibers

In this work, we present a simple fabrication process enabling the integration of a subwavelength amorphous silicon layer inside optical fibers by means of the arc discharge technique. To assess our method, we have fabricated a compact in-line Fabry-Perot interferometer consisting of a thin (<1  μm) a-Si:H layer completely embedded within a standard single-mode optical fiber. The device exhibits low loss (1.3 dB) and high interference fringe visibility (~80%) both in reflection and transmission, due to the high refractive index contrast between silica and a-Si:H. A high linear temperature sensitivity up to 106  pm/°C is demonstrated in the range 120°C-400°C. The proposed interferometer is attractive for point monitoring applications as well as for ultrahigh-temperature sensing in harsh environments.

Rapid Assessment of Gray Mold (Botrytis cinerea) Infection in Grapes with a Biosensor System

Botrytis cinerea is the causative agent of gray mold disease, which causes considerable economic losses to winemakers. The extent of gray mold infection of winegrapes is commonly visually estimated, a method that is prone to assessor bias. Here, we used rapid and simple enzyme-based screening consisting of carbon-electrode, screen-printed amperometric biosensors to estimate gluconic acid and glycerol concentration in winegrapes infected with different degrees of B. cinerea. The lower limits of quantification of the screen-printed amperometric biosensors were 3 mg/L for gluconic acid (corresponding to an infection rate of less than 1%) and 35 mg/L for glycerol; the response times with a flow rate of 0.5 mL/min were in a range of 0.5 to 2 min in the linear ranges of the two assays. This study demonstrates the efficacy of amperometric biosensors for rapid analysis of gluconic acid and glycerol in grapes. The measurements confirmed that concentrations of both compounds are highly correlated with the rate of B. cinerea infection (R2 = 0.98). Thus, the biosensor developed to measure gluconic acid in grapes (or must) was more precise and gave a faster response than methods that currently exist for determining the rate of B. cinerea infection of grape berries.

Chemical Composition and Antioxidant Properties of Five White Onion (Allium cepa L.) Landraces

Five onion landraces belonging to Bianca di Pompei cv., cultivated in Campania region (Italy), were characterized for their main quality parameters. The onion landraces were harvested at the end of the growth cycle corresponding to the ripening time and harvest month, respectively: February, March, April, May, and June. The total content of volatile compounds as well as the sulfur-containing compounds in Aprilatica was significantly ( ) higher than the other landraces investigated. The nutraceutical feature investigated through the total phenols, phenols profile, and antioxidant activity showed higher values for the samples harvested in spring months. High pungency values ranging from 9 to 14 μmol/g FW were found in all onion landraces investigated as enzymatically (alliinase) produced pyruvate (EPY). The organic acids profile (malic, citric, succinic, pyruvic, oxalic, ascorbic, and tartaric acids) highlighted malic and citric acids in higher amounts in all landraces. Fructose, glucose, and sucrose were found as soluble sugars and fructose was the most abundant. Generally, the results highlighted the growth temperature influence on the investigated quality parameters.