Recent Developments in Lateral Flow Assays for Salmonella Detection in Food Products: A Review.

Salmonellosis is a disease transmitted by contaminated food and is one of the leading causes of infections worldwide, making the early detection of Salmonella of crucial importance for public health. However, current detection methods are laborious and time-consuming, thus impacting the entire food supply chain and leading to production losses and economic sanctions. To mitigate these issues, a number of different biosensors have been developed, including lateral flow assays (LFAs), which have emerged as valuable tools in pathogen detection due to their portability, ease of use, time efficiency, and cost effectiveness. The performance of LFAs has been considerably enhanced by the development of new nanomaterials over the years. In this review, we address the principles and formats of the assay and discuss future prospects and challenges with an emphasis on LFAs developed for the detection of different Salmonella serovars in food.

Lateral flow assay applied to pesticides detection: recent trends and progress.

Devices based on lateral flow assay (LFA) have been gaining more and more space in the detection market mainly due to their simplicity, speed, and low cost. These devices have excellent sensing format versatility and make these strips an ideal choice for field applications. The COVID-19 pandemic boosted the democratization of this method as a "point of care testing" (POCT), and the trend is that these devices become protagonists for the monitoring of pesticides in the environment. However, designing LFA devices for detecting and monitoring pesticides in the environment is still a challenge. This is because analytes are small molecules and have only one antigenic determinant, which makes it difficult to apply direct immunoassays. Furthermore, most LFA devices provide only qualitative or semi-quantitative results and have a limited number of applications in multi-residue analysis. Here, we present the state of the art on the use of LFA in the environmental monitoring of pesticides. Based on well-documented results, we review all available LFA formats and strategies for pesticide detection, which may have important implications for the future of monitoring pesticides in the environment. The main advances, challenges, and perspectives of these devices for a direction in this field of study are also presented.

Virola oleifera-capped gold nanoparticles showing radical-scavenging activity and low cytotoxicity.

The development of effective nanoparticle therapeutics has been hindered by their surface characteristics, such as hydrophobicity and charge. Therefore, the success of biomedical applications with nanoparticles is governed by the control of these characteristics. In this article, we report an efficient green capping method for gold nanoparticles (AuNPs) by a reduction with sodium citrate and capping with Virola oleifera (Vo), which is a green exudate rich in polyphenols and flavonoids. The Vo-capped AuNPs were characterized by UV, DLS, FTIR, Raman, TEM, DPPH, FRAP and their cytotoxicity was evaluated on the viability of Murine macrophage cell. The AuNPs had an average particle size of 15 nm and were stable over a long time, as indicated by their unchanged SPR and zeta potential values. These nanoparticles were assessed for their antioxidant potential using DPPH and FRAP and demonstrated the highest antioxidant activities and low cytotoxicity. We propose that the Virola oleifera-capped AuNPs have potential biomedical applications.

Probing the Sulfur-Modified Capping Layer of Gold Nanoparticles Using Surface Enhanced Raman Spectroscopy (SERS) Effects.

Gold nanoparticles (AuNP) exhibit particular plasmonic properties when stimulated by visible light, which makes them a promising tool to many applications in sensor technology and biomedical applications, especially when associated to sulfur-based compounds. Sulfur species form a great variety of self-assembled structures that cap AuNP and this interaction rules the optical and plasmonic properties of the system. Here, we report the behavior of citrate-stabilized gold nanospheres in two distinct sulfur colloidal solutions, namely, thiocyanate and sulfide ionic solutions. Citrate-capped gold nanospheres were characterized using ultraviolet-visible (UV-Vis) absorption, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). In the presence of sulfur species, we have observed the formation of NP clusters and chain-like structures, giving rise to surface-enhanced effects. Surface-enhanced Raman spectroscopy (SERS) pointed to a modification in citrate vibrational modes, which suggests substitution of citrate by either thiocyanate or sulfide ions with distinct dynamics, as showed by in situ fluorescence. Moreover, we report the emergence of surface-enhanced infrared absorption (SEIRA) effect, which corroborates SERS conclusions. Further, SEIRA shows a great potential as a tool for specification of sulfur compounds in colloidal solutions, which is particularly useful when dealing with sensor technology.

Electrochemical and Morphological Investigations of Ga Addition to Pt Electrocatalyst Supported on Carbon.

This paper is consisted in the synthesis of platinum-based electrocatalysts supported on carbon (Vulcan XC-72) and investigation of the addition of gallium in their physicochemical and electrochemical properties toward ethanol oxidation reaction (EOR). PtGa/C electrocatalysts were prepared through thermal decomposition of polymeric precursor method at a temperature of 350°C. Six different compositions were homemade: Pt50Ga50/C, Pt60Ga40/C, Pt70Ga30/C, Pt80Ga20/C, Pt90Ga10/C, and Pt100/C. These electrocatalysts were electrochemically characterized by cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in the presence and absence of ethanol 1.0 mol L-1. Thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were also carried out for a physicochemical characterization of those materials. XRD results showed the main peaks of face-centered cubic Pt. The particle sizes obtained from XRD and TEM analysis range from 7.2 nm to 12.9 nm. The CV results indicate behavior typical of Pt-based electrocatalysts in acid medium. The CV, EIS, and CA data reveal that the addition of up to 31% of gallium to the Pt highly improves catalytic activity on EOR response when compared to Pt100/C.

Facile Synthesis of Monodisperse Gold Nanocrystals Using Virola oleifera.

The development of new routes and strategies for nanotechnology applications that only employ green synthesis has inspired investigators to devise natural systems. Among these systems, the synthesis of gold nanoparticles using plant extracts has been actively developed as an alternative, efficient, cost-effective, and environmentally safe method for producing nanoparticles, and this approach is also suitable for large-scale synthesis. This study reports reproducible and completely natural gold nanocrystals that were synthesized using Virola oleifera extract. V. oleifera resin is rich in epicatechin, ferulic acid, gallic acid, and flavonoids (i.e., quercetin and eriodictyol). These gold nanoparticles play three roles. First, these nanoparticles exhibit remarkable stability based on their zeta potential. Second, these nanoparticles are functionalized with flavonoids, and third, an efficient, economical, and environmentally friendly mechanism can be employed to produce green nanoparticles with organic compounds on the surface. Our model is capable of reducing the resin of V. oleifera, which creates stability and opens a new avenue for biological applications. This method does not require painstaking conditions or hazardous agents and is a rapid, efficient, and green approach for the fabrication of monodisperse gold nanoparticles. Graphical Abstract The Virola oleifera reduction method for the synthesis of gold nanoparticles (AuNP's).

Osmotic stress transcription factor 1b (Ostf1b) promotes migration properties with the modulation of epithelial mesenchymal transition (EMT) phenotype in human embryonic kidney cell.

Osmoregulation is an essential mechanism for euryhaline fish. Gill cells undergo rapid mechanism to maintain the cellular homeostasis during osmotic stress. Reports have suggested that gill cells may be able to migrate between primary filament and secondary lamella during seawater acclimination. However, the factor that can trigger such process is not well-known. Previously, we identified the osmotic stress transcription factor 1b (Ostf1b) in medaka and found that it is an early hypertonic responsive gene and can activate the c-Jun N-terminal kinase (JNK) pathway. In this report, we aim to know if Ostf1b plays the role in the migration. Ostf1b was ectopic expressed in the human embryonic kidney cell line (HEK293) to understand the Ostf1b function. Results clearly demonstrated that Ostf1b could constitutively activate the Rho kinase 1 (ROCK1) and myosin light chain 2 (MLC2) signalling pathway that promotes cell migration, epithelial mesenchymal transition (EMT) and cytoskeletal dynamics through stress fibre formation. The study supports the notion of cell migration and cytoskeleton rearrangement theories in osmoregulation.

Small weight gain is not associated with development of insulin resistance in healthy, physically active individuals.

UNLABELLED: We investigated whether weight gain alters insulin sensitivity and leptin levels in physically active individuals. Six (5 males and 1 female; age 26.6+/-1.0 years; BMI 21.5+/-0.9, body fat 17.4+/-2.2%) healthy individuals were enrolled in an overfeeding study (caloric surplus 22.5-26.5 kcal/kg/day) to achieve up to 10% weight gain over 4-6 week period with subsequent weight maintenance over additional 2 weeks. The participants were requested to maintain their previous physical activity which in all of them included 45-60 min training sessions at the gym 2-3 times/week. RESULTS: BMI increased to 23.4+/-0.9 (4.4 kg weight gain; p<0.05) and body fat to 21.0+/-2.8% (p < 0.05) over the period of active weight gain and remained stable over the two week period of weight maintenance; fasting plasma glucose and serum insulin remained unchanged; serum leptin nearly doubled (3.8+/-1.0 vs 6.4+/-1.9 ng/ mL; p < 0.05); insulin sensitivity, when expressed per kg of the total body (11.1+/-1.6 vs 12.4+/-2.1 mg/kg/min; p = NS), and lean body mass (13.4+/-1.9 vs 15.7+/-2.6 mg/kgLBM/min; p = NS), did not decrease after weight gain. On the contrary, insulin action had improved in 5 out of 6 individuals. In conclusion, the data presented in this preliminary report indicate that a small weight gain due to overfeeding in lean, healthy, physically active individuals is associated with rise in circulating leptin levels but not with worsening of insulin action.

Improved sensitivity to insulin in obese subjects following weight loss is accompanied by reduced protein-tyrosine phosphatases in adipose tissue.

Insulin resistance in adipose tissue in human obesity is associated with increased protein-tyrosine phosphatase (PTPase) activity and elevated levels of the PTPases leukocyte common antigen-related PTPase (LAR) and PTP1B. To determine whether the improved insulin sensitivity associated with weight loss in obese subjects is accompanied by reversible changes in PTPases, we obtained subcutaneous adipose tissue from seven obese subjects (mean body mass index [BMI], 40.4 kg/m2) before and after a loss of 10% of body weight and again after a 4-week maintenance period. Weight loss was accompanied by an 18.5% decrease in overall adipose tissue PTPase activity (P = .015) that was further reduced to 22.3% of the control value (P = .005) at the end of the maintenance period. By immunoblot analysis, the abundance of LAR was decreased by 21% (P = .04) and abundance of PTP1B was decreased by 40% (P < .004) after the initial weight loss, and the decreases persisted during the maintenance period. Enhanced insulin sensitivity following weight loss, evident from a 26% decrease in fasting insulin levels (P < .05), was also closely correlated with the reduction in the abundance of both LAR (R2 = .80, P < .01) and PTP1B (R2 = .64, P = .03). These results support the hypothesis that LAR and PTP1B may be reversibly involved in the pathogenesis of insulin resistance, and may be therapeutic targets in insulin-resistant states.

Response of leptin to short-term and prolonged overfeeding in humans.

As one of the postulated roles of the ob gene product, leptin, is regulation of energy balance and preservation of normal body composition, we investigated the effect of acute and chronic calorie excess (weight gain) on serum leptin in humans. Two protocols were employed: 1) acute (12-h) massive (120 Cal/kg) voluntary overfeeding of eight healthy individuals; and 2) chronic overfeeding to attain 10% weight gain, with its subsequent maintenance for additional 2 weeks, involving six normal males. In the acute experiments (protocol 1), circulating leptin rose by 40% over baseline (P < 0.01) during the final hours of overfeeding; this increase persisted until the next morning. At the point of achievement and the 2-week maintenance of 10% weight gain (protocol 2), a more than 3-fold rise in the basal leptin concentration was observed (P < 0.01). A direct linear relationship was found between the magnitude of the leptin response to weight gain and the percent gain of body fat (r = 0.88; P < 0.01). In summary, 1) in contrast to normal food intake (8), short term massive overfeeding is associated with a moderate elevation of circulating leptin levels that persists until next feeding cycle is initiated; and 2) a 10% weight gain causes different changes in the body composition, and the resulting rise in circulating leptin parallels the increase in the percentage of body fat. In conclusion, these studies document acute elevation of leptin in response to positive energy balance and suggest that developing resistance to leptin is associated with bigger fat deposition during weight gain in humans.

Serum immunoreactive-leptin concentrations in normal-weight and obese humans.

BACKGROUND: Leptin, the product of the ob gene, is a hormone secreted by adipocytes. Animals with mutations in the ob gene are obese and lose weight when given leptin, but little is known about the physiologic actions of leptin in humans. METHODS: Using a newly developed radioimmunoassay, wer measured serum concentrations of leptin in 136 normal-weight subjects and 139 obese subjects (body-mass index, > or = 27.3 for men and > or = 27.8 for women; the body-mass index was defined as the weight in kilograms divided by the square of the height in meters). The measurements were repeated in seven obese subjects after weight loss and during maintenance of the lower weight. The ob messenger RNA (mRNA) content of adipocytes was determined in 27 normal-weight and 27 obese subjects. RESULTS: The mean (+/- SD) serum leptin concentrations were 31.3 +/- 24.1 ng per milliliter in the obese subjects and 7.5 +/- 9.3 ng per milliliter in the normal-weight subjects (P < 0.001). There was a strong positive correlation between serum leptin concentrations and the percentage of body fat (r = 0.85, P < 0.001). The ob mRNA content of adipocytes was about twice as high in the obese subjects as in the normal-weight subjects (P < 0.001) and was correlated with the percentage of body fat (r = 0.68, P < 0.001) in the 54 subjects in whom it was measured. In the seven obese subjects studied after weight loss, both serum leptin concentrations and ob mRNA content of adipocytes declined, but these measures increased again during the maintenance of the lower weight. CONCLUSIONS: Serum leptin concentrations are correlated with the percentage of body fat, suggesting that most obese persons are insensitive to endogenous leptin production.