2021
Authors
Dos Santos, PSS; De Almeida, JMMM; Pastoriza Santos, I; Coelho, LCC;
Publication
SENSORS
Abstract
Surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) are among the most common and powerful label-free refractive index-based biosensing techniques available nowadays. Focusing on LSPR sensors, their performance is highly dependent on the size, shape, and nature of the nanomaterial employed. Indeed, the tailoring of those parameters allows the development of LSPR sensors with a tunable wavelength range between the ultra-violet (UV) and near infra-red (NIR). Furthermore, dealing with LSPR along optical fiber technology, with their low attenuation coefficients at NIR, allow for the possibility to create ultra-sensitive and long-range sensing networks to be deployed in a variety of both biological and chemical sensors. This work provides a detailed review of the key science underpinning such systems as well as recent progress in the development of several LSPR-based biosensors in the NIR wavelengths, including an overview of the LSPR phenomena along recent developments in the field of nanomaterials and nanostructure development towards NIR sensing. The review ends with a consideration of key advances in terms of nanostructure characteristics for LSPR sensing and prospects for future research and advances in this field.
2021
Authors
Vasconcelos, H; de Almeida, JMMM; Matias, A; Saraiva, C; Jorge, PAS; Coelho, LCC;
Publication
TRENDS IN FOOD SCIENCE & TECHNOLOGY
Abstract
Background: Biogenic amines (BAs) are compounds considered to be contaminants of foodstuff and are cause of poisoning. The main BAs found in foods are cadaverine, putrescine, tyramine, histamine, spermine and spermidine. The number of food poisoning cases associated with BAs in food has increased in the recent years reinforcing the need for early detection to ensure high levels of food quality and safety. Scope and approach: This review aims to provide a general approach to the different BAs detected in foods their concentrations and sample treatments. These compounds are found in varying concentrations in a wide variety of foods such as fish, meat, fruits, vegetables, cheese, wine, and beer. It also refers the different analytical techniques currently used for the detection of BAs, as well as the different treatments of the samples and innovations of the techniques currently used that allow greater sensitivity and speed of the analyzes and with obtaining detection limits lower and lower. Key findings and conclusions: BAs are present in a wide variety of foods and their concentration is highly influenced by the storage conditions of food products. BAs can be precursors of nitrosamines, which have been linked to carcinogenic and mutagenic activity. Several analytical techniques and sample treatments have been improved in the last few years for better and faster detection of BAs.
2021
Authors
Saraiva, C; Silva, AC; Garcia Diez, J; Cenci Goga, B; Grispoldi, L; Silva, AF; Almeida, JM;
Publication
FOODS
Abstract
Listeria monocytogenes has been referred to as a concern microorganism in cheese making due to its ability to survive and grow in a wide range of environmental conditions, such as refrigeration temperatures, low pH and high salt concentration at the end of the production process. Since cheese may be a potential hazard for consumers, especially high-risk consumers (e.g., pregnant, young children, the elderly, people with medical conditions), efforts of the dairy industry have been aimed at investigating new conservation techniques based on natural additives to meet consumers' demands on less processed foods without compromising the food safety. Thus, the aim of this study was to evaluate the efficacy of Myrtus communis L. (myrtle) and Rosmarinus officinalis L. (rosemary) essential oils (EO) against Listeria monocytogenes ATCC 679 spiked in sheep cheese before ripening. After the cheesemaking process, the samples were stored at 8 degrees C for 2 h, 1 d, 3 d, 14 d and 28 d. The composition of EO was identified by gas chromatography-mass spectrometry (GC-MS) analysis. Constituents such as 1,8-cineole, limonene, methyl-eugenol, alpha-pinene, alpha-terpineol, alpha-terpinolene and beta-pinene were present in both EO, accounting for 44.61% and 39.76% from the total of chemical compounds identified for myrtle and rosemary EO, respectively. According to the chemical classification, both EO were mainly composed of monoterpenes. Minimum inhibitory concentration (MIC) against L. monocytogenes was obtained at 31.25 mu L/mL to myrtle EO and at 0.40 mu L/mL to rosemary EO. Then, cheeses were inoculated with L. monocytogenes (Ca. 6 log CFU/mL) and EO was added at MIC value. The addition of rosemary and myrtle EO displayed lower counts of L. monocytogenes (p < 0.01) (about 1-2 log CFU/g) during the ripening period compared to control samples. Ripening only influences (p < 0.001) the growth of L. monocytogenes in control samples. Since rosemary and myrtle EO do not exert any negative impact on the growth of native microflora (p > 0.05), their use as natural antimicrobial additives in cheese demonstrated a potential for dairy processors to assure safety against L. monocytogenes.
2021
Authors
Viveiros, D; de Almeida, JMMM; Coelho, L; Vasconcelos, H; Maia, JM; Amorim, VA; Jorge, PAS; Marques, PVS;
Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY
Abstract
A detailed study of turn around point (TAP) long period fiber gratings (LPFGs) with coupling to the asymmetric cladding modes of a standard single-mode fiber (SMF-28e), fabricated by femtosecond (fs) laser direct writing was realized. The entire fabrication process, including the coating with different titanium dioxide (TiO2) film thicknesses of LPFGs and the corrections needed to achieve coated devices operating precisely in the TAP condition with coupling to the asymmetric cladding modes, was addressed. The significant fabrication details are also given, such as inscription periods, shape and localization of the refractive index modifications across the core. The fabrication process described allows the optimization of the LPFGs sensitivity in regards to the surrounding refractive index (SRI). Optimization of the writing parameters to obtain gratings working at the TAP for two different media surrounding the fiber (water and air) was achieved. It was demonstrated that for a grating period of 191.8 mu m, the LP1,12 mode exhibits a TAP at 1442.7 nm in air, and for a period of 192.5 mu m, the same mode exhibits a TAP at 1448.6 nm in water. The LPFGs operating at the TAP in air and water were coated with 10, 20, and 30 nm thin TiO2 film thicknesses and the spectral behavior characterized. The wavelength sensitivity to the surrounding refractive index (SRI) was assessed in the range between 1.3700 to 1.4120, and a maximum sensitivity of similar to 8051.4 nm/RIU was measured for the 192.5 mu m LPFG coated with a 30 nm thick TiO2 film.
2021
Authors
Dias, B; Santos, P; Jorge, PAS; de Almeida, JMMM; Coelho, LCC;
Publication
IEEE INSTRUMENTATION & MEASUREMENT MAGAZINE
Abstract
The use of Long-Period Fiber Gratings (LPFGs) as sensors has been thoroughly researched, given the multitude of parameters these structures can monitor by themselves (such as temperature, strain, curvature) and the potential for combination with other materials that allow for monitoring of parameters such as humidity, pH and chemical concentration, at a low price and with easy fabrication processes available. This interest has increased the need for the development of interrogation systems for these sensors, particularly in the C-band spectral region. Given the cost and physical limitations (such as size and weight) of traditional solutions like Optical Spectrum Analyzers (OSA), the development of low-cost approaches for LPFG spectral analysis became an important topic that needed further development. The development of a simple curve fitting routine for LPFG spectra is reported in this article, along with a framework for automatic detection of certain physical phenomena such as corrosion and the presence of chemical species, among others.
2021
Authors
Figueira, RB; de Almeida, JM; Ferreira, B; Coelho, L; Silva, CJR;
Publication
MATERIALS ADVANCES
Abstract
Optical fiber sensing systems have been widely developed for several fields such as biomedical diagnosis, food technology, military and industrial applications and civil engineering. Nowadays, the growth and advances of optical fiber sensors (OFS) are focused on the development of novel sensing concepts and transducers as well as sensor cost reduction. This review provides an overview of the state-of-the-art of OFS based on sol-gel materials for diverse applications with particular emphasis on OFS for structural health monitoring of concrete structures. The types of precursors used in the development of sol-gel materials for OFS functionalization to monitor a wide range of analytes are debated. The main advantages of OFS compared to other sensing systems such as electrochemical sensors are also considered. An interdisciplinary review to a broad audience of engineers and materials scientists is provided and the relationship between the chemistry of sol-gel material synthesis and the development of OFS is considered. To the best of the authors' knowledge, no review manuscripts were found in which the fields of sol-gel chemistry and OFS are correlated. The authors consider that this review will serve as a reference as well as provide insights for experts into the application of sol-gel chemistry and OFS in the civil engineering field.
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