André R.T.S. Araujo

Determination of total and oxidized glutathione in human whole blood with a sequential injection analysis system

This work reports the development of a simple, robust, automated sequential injection analysis (SIA) system for the enzymatic determination of total (tGSH) and oxidized (GSSG) glutathione in human whole blood. The reduced (GSH) glutathione concentration is then obtained as the difference between the tGSH and GSSG concentrations. The determination was based on the DTNB-GSSG reductase recycling assay, which couples the specificity of the GSSG reductase (GR) with an amplification of the response to glutathione, followed by spectrophotometric detection of the 2-nitro-5-thiobenzoic acid (TNB) formed (lambda=412 nm). The implementation of this reaction in a SIA flow system with an in-line dilution strategy permitted the necessary distinct application ranges for tGSH and for GSSG. It also guaranteed the exact timing of fluidic manipulations and precise control of the reaction conditions. The influence of parameters such as reagents concentration, temperature, pH, flow rate of the carrier buffer solution, as well as reaction coil length, etc., on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions subsequently selected. Linear calibration plots were obtained for GSH and GSSG concentrations up to 3.00 and 1.50 microM, with detection limits of 0.031 and 0.014 microM, respectively. The developed methodology showed good precision, with a relative standard deviation (R.S.D.)<5.0% (n=10) for determination of both glutathione forms. Statistical evaluation showed good compliance, for a 95% confidence level, between the results obtained with the SIA system and those furnished by the comparison batch procedure.

Nanoparticle-based assays in automated flow systems: A review.

Nanoparticles (NPs) exhibit a number of distinctive and entrancing properties that explain their ever increasing application in analytical chemistry, mainly as chemosensors, signaling tags, catalysts, analytical signal enhancers, reactive species generators, analyte recognition and scavenging/separation entities. The prospect of associating NPs with automated flow-based analytical is undoubtedly a challenging perspective as it would permit confined, cost-effective and reliable analysis, within a shorter timeframe, while exploiting the features of NPs. This article aims at examining state-of-the-art on continuous flow analysis and microfluidic approaches involving NPs such as noble metals (gold and silver), magnetic materials, carbon, silica or quantum dots. Emphasis is devoted to NP format, main practical achievements and fields of application. In this context, the functionalization of NPs with distinct chemical species and ligands is debated in what concerns the motivations and strengths of developed approaches. The utilization of NPs to improve detectors performance in electrochemical application is out of the scope of this review. The works discussed in this review were published in the period of time comprised between the years 2000 and 2013.

Flow system for the automatic screening of the effect of phenolic compounds on the luminol–hydrogen peroxide–peroxidase chemiluminescence system

In this work, an automated flow-based procedure for the screening of the effect of the different phenolic compounds on the chemiluminescence (CL) luminol-hydrogen peroxide-horseradish peroxidase (HRP) system is presented. This procedure involves the combination of multisyringe flow injection analysis (MFSIA) and sequential injection analysis (SIA) techniques and exploits the ability of the different subgroups of phenols, such as cholorophenols, nitrophenols, methylphenols and polyphenols, to enhance or inhibit the described CL system. The implementation of this reaction in the SIA-MSFIA system enabled favourable and precise conditions to evaluate the effect of phenolic compounds, as it involves an in-line reaction between the phenolic derivative, hydrogen peroxide and peroxidase and subsequent oxidized HRP intermediates generation prior to the fast reaction with the chemiluminogenic reagent. Several studies were then performed with the aim of establishing the appropriate flow system configuration and reaction conditions. It was shown that phenol and chlorophenols produce an enhanced CL response and nitrophenols, methylphenols and polyphenols are inhibitors within the range of concentrations studied (1-100 mg/L). Based on these studies, the developed method was applied to the determination of total polyphenol and phenol content in wine/grape seeds and water samples, respectively, and the results obtained showed good agreement with those furnished by the corresponding Folin-Ciocalteu and 4-aminoantipyrine reference methods. The developed approach is further pursued by designing an automated generic tool for performing studies of peroxidase-catalysed CL reactions of luminol focused on the detection of compounds that will affect the rate of those reactions.

Thermospray generation directly into a flame furnace—An alternative to improve the detection power in atomic absorption spectrometry

Recent developments and applications in the production of thermosprays directly into flame furnaces to improve the analytical sensitivity in atomic absorption spectrometry are reviewed in this manuscript. Principles, characteristics, instrumentation, and applications of this analytical technique for trace elements determination in several matrices are discussed. The use of preconcentration procedures to allow low detection limits for ultra-trace levels using TS-FF-AAS is presented and current perspectives and future trends of this technique are also discussed.

Automatic flow methodology for kinetic and inhibition studies of reactions with poorly water-soluble substrates in ionic liquid systems.

In the present work an automatic generic tool, based on sequential injection analysis (SIA) for kinetic and inhibition studies of reactions with poorly water-soluble compounds in ionic liquid (IL)-containing systems, is described. The oxidation of the poorly water-soluble phenolic compound, caffeic acid, catalyzed by the mushroom tyrosinase, in different 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)])/buffer mixtures as reaction media, was investigated. This determination was based on measuring depletion rate of the substrate caffeic acid at its maximum wavelength (λ(max) 311 nm). The influence of several parameters such as substrate and enzyme concentration, temperature, pH, delay times and measurement periods on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions subsequently selected. The obtained results showed that tyrosinase was active in oxidising caffeic acid in this water-miscible IL and the presence of an impaired tyrosinase activity with increase in [bmim][BF(4)] concentration as an increase in the apparent Michaelis-Menten constant (K(M)(app)) was observed while the maximum reaction rate (V(max)(app)) remained fairly constant. The results were compared to those obtained when the assay was performed in water/methanol mixtures under the same conditions to substantiate [bmim][BF(4)] as an alternative to conventional organic solvents. Additionally, it was shown that tyrosinase is effectively inhibited by the substrate analogues tested (trans-cinnamic acid and 3,4-dihydroxybenzoic acid) in the IL-containing aqueous system used.

Flow Injection Analysis with Immobilized Enzymes in Nonaqueous Media

Biocatalysis in nonaqueous media currently constitutes a promising research area which has already demonstrated its potential in numerous and varied applications. Several possibilities exist for the analysis of a wide range of poorly water-soluble analytes present in samples of food, pharmaceuticals, petrochemicals and cosmetic products, among others. The idea of assembling this kind of biocatalysis with flow management approaches clearly seems to be advantageous since it permits confined, precise and reliable analysis within a shorter timeframe while minimising human exposure to organic solvents and toxic effluent production. This article reviews the state-of-the-art of flowing stream systems comprising immobilized enzymes in nonaqueous media. Particular emphasis is devoted to categorising the enzymatic preparations operating in an organic environment: enzyme electrodes and enzyme reactors. The main approaches exploiting the use of immobilized enzymes in water-restricted environments using flow injection analysis for analytical purposes are presented in detail and possible future trends are discussed.

Sequential injection system for phospholipase A2 activity evaluation: studies on liposomes using an environment-sensitive fluorescent probe.

This work reports the development of an automatic methodology based on the use of 1-anilinonaphthalene-8-sulfonate (ANS) as an interfacial fluorescent probe for detecting the hydrophobic environment shift around the probe, caused by the hydrolytic action of PLA(2) on the liposomes. The implementation of this reaction in a sequential injection analysis (SIA) system along with the use of the mixing chambers permitted the evaluation of PLA(2) activity and assessment of the inhibitory effect of the non-steroidal anti-inflammatory drugs (NSAIDs) on PLA(2) activity. Several studies were performed with the aim of establishing the appropriate flow system configuration: the liposome substrate; PLA(2) and ANS optimum concentrations and incubation times before and after the enzyme addition. Based on these studies, the optimum reaction conditions were selected. It was shown that PLA(2) is effectively inhibited by the NSAIDs tested (meloxicam, tolmetin and ibuprofen) and by the alpha-lipoic acid, used as a positive control. Results obtained from the flow system are in agreement with those provided by the comparison batch procedures. The proposed methodology is in fact more efficient and rapid than the comparison batch experiments, enabling the exact timing of fluidic manipulations and precise control of the reaction conditions.

Innovation in Thermalism: An Example in Beira Interior Region of Portugal

Portugal is one of the richest European countries in thermal waters, and the majority of the spas are located inland in the northern and central regions. Thermal spa treatment is a touristic product that is highly recognized for its potential in the exploration of endogenous regional resources. Consequently, the development of new and competitive thermal tourism products can play an important role in the development of the inland regions, contributing effectively to addressing the economic asymmetries of the region. Based on their physico-chemical properties, thermal waters can have different therapeutic indications, including in dermatology. In the region of the Beira Interior there are two spas with thermal water presenting therapeutic dermatological applications, and the use of these waters in dermocosmetic formulations is proposed as one of the most relevant applications of innovation tools in the Thermal Spa sector. A number of cosmetic companies have encapsulated active molecules in nanoscale systems to enhance product performance. The properties of the nanocarriers systems, namely liposomes, polymeric and solid lipid nanoparticles as well nanoemulsions, are fundamental to increase the skin permeation/penetration. Furthermore, these systems have the capacity to preserve the original and unique properties of the thermal water and ensure the stability of the other active components during more time. The development of dermocosmetics based on thermal water carried in nanobiotechnological systems is proposed for its contribution to the differentiation amongst local, unique and genuine products, especially relevant in the case of products with high economic impact in tourism markets.

Automatic miniaturized flow methodology with in-line solid-phase extraction for quinine determination in biological samples

The present work describes an analytical platform based on a multipumping flow injection analysis (MPFS) technique combined with in-line solid-phase extraction (SPE). The flow network has been tested with the determination of quinine in biological samples using fluorometry as the detection technique. Amberlite XAD-4 resin has been used as a solid phase and the implementation of a pH control strategy resulted in a simple and environmental approach for the preconcentration of quinine. Two solenoid valves allowed the deviation of the flow towards the resin column to carry out SPE procedures. The influence of parameters such as concentration, flow rate and volume of the different solutions on the sensitivity and performance of the MPFS was studied. Dynamic calibration ranges (0.78–150 ng mL−1) for quinine determination were applied by using a variable sample volume (120–1000 μL). The developed methodology provided high relative extraction recoveries from human urine samples (85–115%). The proposed automatic methodology turns out to be very efficient and sustainable compared to the available procedures and it could prove to be an attractive alternative tool to perform in-line sample pre-treatment and subsequent direct determination of relevant organic compounds in pharmaceutical and clinical analyses.

Mesoporous Silica Nanoparticles for Targeted and Stimuli‐Responsive Delivery of Chemotherapeutics: A Review

Mesoporous silica nanoparticles (MSNs) exhibit the typical characteristics of inorganic materials that make them promising drug delivery carriers for cancer therapy. Their structural properties allow the targeted delivery of chemotherapeutic drugs to enhance drug efficacy and reduce adverse effects. The functionalization of MSNs with targeting ligands to a specific tissue/cell and stimuli‐responsive capping materials to seal drugs inside the MSNs pores are widely studied for biomedical and pharmaceutical applications. Furthermore, multiple stimuli‐responsive MSN‐based drug delivery systems are developed to enhance the delivery of anticancer drugs to their specific target and thereby improve the release of the drugs at the intended site. In addition, several toxicity studies are conducted to evaluate the biosafety and biocompatibility of MSNs. Although MSNs present reduced toxicity compared to colloidal silica, they can induce cytotoxicity associated with oxidative stress by increased reactive oxygen species production and decreased glutathione levels that can ultimately lead to cell death. However, different modifications to control morphology and surface composition can be applied to overcome the biocompatibility concerns. In this review, a comprehensive overview of the controlled synthesis, functionalization, targeting and biocompatibility of MSNs, as well as their biomedical application as a chemotherapeutic delivery system is provided.