Paper has been present in the world of analytical chemistry for centuries, but it seems that just a few years back it was rediscovered as a valuable substrate for sensors. We can easily list some of the countless advantages of this simple cellulosic substrate, including mechanical properties, three-dimensional fibrous structure, biocompatibility and biodegradability, easiness of production and modification, reasonable price, and availability all over the world. Those characteristics make paper a first-choice substrate for disposable sensors and integrated sensing platforms. Nowadays, numerous examples of paper-based sensors are being presented in the literature. This review describes some of the most prominent examples classifying them by type of detection: optical (colorimetric, fluorescence, surface-enhanced Raman spectroscopy, and transmittance methods) and electrochemical (voltammetric, potentiometric, and conductivity-based methods). We take a closer look at recent advances in immunoassays fabricated on paper, excluding simple lateral flow tests assembled on nitrocellulose. This review also summarizes the main advantages and disadvantages of the use of paper as a substrate for sensors, as well as its impact on their performance and application, presents a short history of paper in analytical chemistry, and discusses fabrication methods and available sources of paper.

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Aims/hypothesis A high-fat dietary intake induces obesity and subclinical inflammation, which play important roles in insulin resistance. Recent studies have suggested that increased concentrations of circulating lipopolysaccharide (LPS), promoted by changes in intestinal permeability, may have a pivotal role in insulin resistance. Thus, we investigated the effect of gut microbiota modulation on insulin resistance and macrophage infiltration. Methods Swiss mice were submitted to a high-fat diet with antibiotics or pair-feeding for 8 weeks. Metagenome analyses were performed on DNA samples from mouse faeces. Blood was collected to determine levels of glucose, insulin, LPS, cytokines and acetate. Liver, muscle and adipose tissue proteins were analysed by western blotting. In addition, liver and adipose tissue were analysed, blinded, using histology and immunohistochemistry. Results Antibiotic treatment greatly modified the gut microbiota, reducing levels of Bacteroidetes and Firmicutes, overall bacterial count and circulating LPS levels. This modulation reduced levels of fasting glucose, insulin, TNF-α and IL-6; reduced activation of toll-like receptor 4 (TLR4), c-Jun N-terminal kinase (JNK), inhibitor of κ light polypeptide gene enhancer in B cells, kinase β (IKKβ) and phosphorylated IRS-1 Ser307; and consequently improved glucose tolerance and insulin tolerance and action in metabolically active tissues. In addition, there was an increase in portal levels of circulating acetate, which probably contributed to an increase in 5′-AMP-activated protein kinase (AMPK) phosphorylation in mice. We observed a striking reduction in crown-like structures (CLS) and F4/80 + macrophage cells in the adipose tissue of antibiotic-treated mice. Conclusions/interpretation These results suggest that modulation of gut microbiota in obesity can improve insulin signalling and glucose tolerance by reducing circulating LPS levels and inflammatory signalling. Modulation also appears to increase levels of circulating acetate, which activates AMPK and finally leads to reduced macrophage infiltration.

A simple procedure for the development of a range of polymeric ion-selective electrodes (ISEs) with low detection limits is presented. The electrodes were prepared by using a plasticizer-free methyl methacrylate-decyl methacrylate copolymer as membrane matrix and poly(3-octylthiophene) as intermediate layer deposited by solvent casting on gold sputtered copper electrodes as a solid inner contact. Five different electrodes were developed for Ag+, Pb2+, Ca2+, K+, and I-, with detection limits mostly in the nanomolar range. In this work, the lowest detection limits reported thus far with solid contact ISEs for the detection of silver (2.0 x 10(-9) M), potassium (10(-7) M), and iodide (10(-8) M) are presented. The developed electrodes exhibited a good response time and excellent reproducibility.

Recebido em 1/2/06; aceito em 9/1/07; publicado na web em 2/7/07 REACTIVE OXYGEN AND NITROGEN SPECIES, ANTIOXIDANTS AND MARKERS OF OXIDATIVE DAMAGE IN HUMAN BLOOD: MAIN ANALYTICAL METHODS FOR THEIR DETERMINATION. We review here the chemistry of reactive oxygen and nitrogen species, their biological sources and targets; particularly, biomolecules implicated in the redox balance of the human blood, and appraise the analytical methods available for their detection and quantification. Those biomolecules are represented by the enzymatic antioxidant defense machinery, whereas coadjutant reducing protection is provided by several low molecular weight molecules. Biomolecules can be injured by RONS yielding a large repertoire of oxidized products, some of which can be taken as biomarkers of oxidative damage. Their reliable determination is of utmost interest for their potentiality in diagnosis, prevention and treatment of maladies. Keywords: biomarkers of oxidative stress; oxidative and nitrosative stress; antioxidants. INTRODUÇÃO O balanço redox em líquidos biológicos, organelas, células ou tecidos é determinado pela presença de pares redox responsáveis pelo fluxo de elétrons. Esses sofrem freqüentes interconversões entre o estado reduzido e o oxidado. Alguns desses pares redox são interligados ("redox cycling"), outros constituem sistemas redox independentes. O balanço redox, na célula, relaciona-se à soma dos produtos do potencial de redução e da capacidade redutora de uma série de pares redox, acoplados, presentes. A capacidade re-dutora pode ser estimada pela determinação da concentração de espécies reduzidas em um par redox e, o potencial de redução, pelo emprego da Equação de Nernst 1. Em termos matemáticos, isto pode ser representado por: onde E i é o potencial de redução da semi-célula para um dado par redox e [espécie reduzida] i é a concentração das espécies reduzi-das em um par redox. Mudanças no balanço redox de sistemas biológicos podem cau-sar o estresse oxidativo 1. A intensidade e patogenicidade destes desequilíbrios vão depender, naturalmente, das concentrações lo-cais de espécies pró e antioxidantes, das constantes de velocidade de reação com moléculas-alvo e da compartimentalização celular destes processos, em que fatores de solubilidade e difusibilidade são determinantes 2. ESTRESSE OXIDATIVO A produção de espécies reativas de oxigênio (ERO), de nitrogê-nio (ERN), entre outras espécies reativas, é parte integrante do me-tabolismo humano e é observada em diversas condições fisiológi-cas. ERO e ERN têm importante função biológica, como na fago-citose, fenômeno em que essas espécies são produzidas para elimi-nar o agente agressor. Por outro lado, quando sua produção é exacer-bada, o organismo dispõe de um eficiente sistema antioxidante que consegue controlar e restabelecer o equilíbrio. O estresse oxidativo resulta do desequilíbrio entre o sistema pró e antioxidante 1,3 , com predomínio dos oxidantes, com dano conseqüente (Figura 1). A cé-lula, unidade da vida, é uma verdadeira usina de pró e antioxidan...

The influence of different surface pretreatment procedures on the electrochemical response of a polycrystalline gold electrode was evaluated. Mechanical polishing with slurry alumina (M), chemical oxidation with H 2 SO 4 /H 2 O 2 (C), electrochemical polishing (potential cycling between À 0.1 V and 1.2 V vs. SCE) (E), chemical reduction with ethanol, and combinations among these treatments were employed to change the surface electrode characteristics. The efficiency of the proposed pretreatments was evaluated by electrochemical responses towards the redox couple ferri(II/III)-ammonium sulfate and by the formation of a self-assembly monolayer of 3-mercaptopropionic acid (3 MPA SAM) on gold electrodes. The procedure (C) allowed important gold surfaces activation. Using procedures (C) and (E) the roughness of polycrystalline gold surfaces was significantly minimized and more reproducible surfaces could be obtained. From the profile of reductive desorption of 3 MPA SAM it was possible to verify that reduced gold surfaces generated better packed monolayers than oxidized ones and a comparative study using CV and DPV techniques showed that between the two desorption peaks, the one localized at more negative potential values corresponds to the cleavage of Au-S bond from the chemisorbed thiol. In general, the improvement in the studied electrochemical responses could not only be attributed to an increase in the real surface area of the electrode, but to the chemical surface states set off by the pretreatment procedure.

This paper describes the formation of a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) under different concentrations on a gold sensor disk, monitoring in situ and in real time using surface plasmon resonance spectroscopy (SPR). The film thickness and dielectric constant were determined for a fully formed monolayer using one-color approach SPR. The kinetic studies of the film formation in ethanol solution indicated that the self-assembled monolayer is formed in a two-step adsorption process. In this sense, this unpublished route was applied on the basis of a model where many molecules are adsorbed at an initial step and then can be desorbed and/or rearranged to form a perfect monolayer.

The use of biosensors in point‐of‐care (POC) testing devices has attracted considerable attention in the past few years, mainly because of their high specificity, portability, and relatively low cost. Coupling these devices with miniaturized electrochemical transducers has shown great potential toward simple, rapid, and cost‐effective analysis that can be performed in the field, especially for healthcare, environmental monitoring, and food quality control. For this reason, the number of publications in this field has grown exponentially over the past decade, making it a trending topic in current research. Although great improvement has been achieved in the field of electrochemical biosensing, there are still some challenges to overcome, especially concerning the improvement of sensing materials and miniaturization. In this Review, we summarize some of the most recent advances achieved in POC electrochemical biosensor applications, focusing on new materials and modifiers for biorecognition developed to improve sensitivity, specificity, stability, and response time.