Synthesis of silver-palladium Janus nanoparticles using co-sputtering of independent sources: experimental and theorical study.

Janus-type nanoparticles are important because of their ability to combine distinct properties and functionalities in a single particle, making them extremely versatile and valuable in various scientific, technological, and industrial applications. In this work, bimetallic silver-palladium Janus nanoparticles were obtained for the first time using the inert gas condensation technique. In order to achieve this, an original synthesis equipment built by Mantis Ltd. was modified by the inclusion of an additional magnetron in a second chamber, which allowed us to use two monometallic targets to sputter the two metals independently. With this arrangement, we could find appropriate settings at room temperature to promote the synthesis of bimetallic Janus nanoparticles. The structural properties of the resulting nanoparticles were investigated by transmission electron microscopy (TEM), and the chemical composition was analyzed by TEM energy dispersive spectroscopy (TEM-EDS), which, together with structural analysis, confirmed the presence of Janus-type nanostructures. Results of molecular dynamics and TEM simulations show that the differences between the crystalline structures of the Pd and Ag regions observed in the TEM micrographs can be explained by small mismatches in the orientations of the two regions of the particle. A density functional theory structural aims to understand the atomic arrangement at the interface of the Janus particle.

Polyelectrolytes for Environmental, Agricultural, and Medical Applications.

In recent decades, polyelectrolytes (PELs) have attracted significant interest owing to a surge in research dedicated to the development of new technologies and applications at the biological level. Polyelectrolytes are macromolecules of which a substantial portion of the constituent units contains ionizable or ionic groups. These macromolecules demonstrate varied behaviors across different pH ranges, ionic strengths, and concentrations, making them fascinating subjects within the scientific community. The aim of this review is to present a comprehensive survey of the progress in the application studies of polyelectrolytes and their derivatives in various fields that are vital for the advancement, conservation, and technological progress of the planet, including agriculture, environmental science, and medicine. Through this bibliographic review, we seek to highlight the significance of these materials and their extensive range of applications in modern times.

Bisphenol A released and ultrastructural changes in dental composite resins

Dental composite resins may release bisphenol-A or similar molecules affecting patient health and the environment. This study measured bisphenol-A release from three commonly used in patients composite resins (Filtek™ Z350 XT, Filtek™ P60, Filtek™ Bulk Fill) immersed in three liquid mediums (artificial saliva, 0.001 M lactic acid and 15% ethanol) and assessed the changes in the surface micromorphology.The released BPA was measured by HPLC at basal time (t=0), 1 h, 1 d, 7 d and 30 d. Topographic analysis of specimens was performed by scanning electron microscopy (SEM). The data were analyzed using one-way ANOVA and Tukey post-hoc test (P < 0.05). BPA in solution increased significantly in the three DCRs immersed in 0.001 M lactic acid at all times. SEM micrographs of the specimen in 0.001 M lactic acid disclosed more structural defects than others. The surface of the three composite resins was morphologically affected by their immersion in all solutions. SEM evidenced that the dental materials underwent erosion and cracks with filler particles protruding from the surface. The morphological changes in tested dental materials produced by exposure to these solutions are potentially dangerous to patients by causing caries, infections, and partial loss of dental material.

Formación de biopelícula bacteriana sobre las superficies de pilares de cicatrización de PEEK y titanio

Objetivos. Explorar el efecto de las características de superficie sobre el volumen total y la viabilidad de la biopelícula formada sobre pilares de cicatrización de PEEK y titanio. Métodos. Los parámetros de rugosidad (S a y S k) y la energía superficial de pilares de cicatrización de PEEK y titanio (n=3) fueron determinados mediante microscopía confocal láser de barrido (CLSM) y ángulo de contacto, respectivamente. Se determinó luego el volumen total y la viabilidad de una biopelícula bacteriana multiespecie cultivada por 30 días, mediante CLSM y el reactivo LIVE/DEAD Kit BacLight. El tamaño del efecto se determinó mediante d de Cohen. Resultados. Los pilares de PEEK mostraron una mayor rugosidad que los de titanio (S a 0,41 µm vs 0,17 µm), pero no se observaron diferencias en la energía superficial. Si bien el volumen total de biopelícula fue mayor en titanio que en PEEK (696 µm3 vs 419 µm3), no hubo diferencias en la proporción de bacterias vivas entre ambos materiales. Conclusiones. La viabilidad de la biopelícula bacteriana formada no guarda relación directa con las características superficiales de pilares de cicatrización de PEEK y titanio.

Objetivo. Explorar o efeito das características da superfície no volume total e viabilidade do biofilme formado em PEEK e pilares de cicatrização de titânio. Métodos. Parâmetros de rugosidade (S a e S k) e energia de superfície de PEEK e pilares de titânio (n = 3) foram determinados por microscopia confocal de varredura a laser (CLSM) e ângulo de contato, respectivamente. O volume total e a viabilidade de um biofilme bacteriano multiespécie cultivado por 30 dias foram então determinados usando CLSM e o reagente LIVE/DEAD Kit BacLight. O tamanho do efeito foi determinado usando o d de Cohen. Resultados. Os pilares de PEEK mostraram maior rugosidade do que os de titânio (S a 0,41 µm vs 0,17 µm), mas não foram observadas diferenças na energia de superfície. Embora o volume total de biofilme tenha sido maior no titânio do que no PEEK (696 µm3 vs 419 µm3), não houve diferenças na proporção de bactérias vivas entre os dois materiais. Conclusões. A viabilidade do biofilme bacteriano formado não está diretamente relacionada às características da superfície dos pilares de cicatrização de PEEK e titânio.

Objectives . To explore the effect of surface characteristics on the total volume and viability of a bacterial biofilm developed on the surface of PEEK and titanium healing abutments. Methods. Surface parameters S a and S k, as well as the surface energy of PEEK and titanium healing abutments (n=3) were determined using confocal laser scanning microscopy (CLSM) and contact angle, respectively. The total volume and viability of a multispecies bacterial biofilm cultivated for 30 days were determined using CLSM and the LIVE/DEAD BacLight reactive kit. Effect size was determined using Cohen's d. Results. PEEK healing abutments displayed a higher surface roughness than titanium (S a 0.41 µm vs 0.17 µm), although no differences in surface energy were observed. Despite the higher total volume of the biofilm measured on titanium abutments compared to PEEK (696 µm3 vs 419 µm3), no differences in the live/dead bacterial ratio were observed. Conclusions. Bacterial viability of the biofilm did not show a direct relation to the surface characteristics of PEEK and titanium healing abutments.

Study of the Efficiency of a Polycation Using the Diafiltration Technique in the Removal of the Antibiotic Oxytetracycline Used in Aquaculture.

The presence of antibiotics in aquatic systems in recent years has become a global environmental and public health concern due to the appearance of strains resistant to these antibiotics. Oxytetracycline (OXT) is a high-impact antibiotic used for both human and veterinary consumption, and it is the second most used antibiotic in aquaculture in Chile. Based on the above, this problem is addressed using a linear polymer whose structure is composed of aromatic rings and quaternary ammonium groups, which will help enhance the removal capacity of this antibiotic. To obtain the polycation, a radical polymerization synthesis was carried out using (4-vinylbenzyl)-trimethylammonium chloride as the monomer. The polycation was characterized via Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). The removal studies were conducted under different experimental conditions such as pH levels (3.0, 5.0, 7.0, 8.0, and 11.0), ionic strength (0.0-0.50 mg L-1 of NaCl), polymer dose (0.25-25.5 mg), variation of the antibiotic concentration (1-100 mg L-1), and evaluation of the maximum retention capacity, as well as load and discharge studies. The antibiotic retention removal was higher than 80.0%. The antibiotic removal performance is greatly affected by the effect of pH, ionic strength, molar ratio, and/or OXT concentration, as these parameters directly affect the electrostatic interactions between the polymer and the antibiotics. The diafiltration technique was shown to be highly efficient for the removal of OXT, with maximum removal capacities of 1273, 966, and 778 mg OXT g-1 polycation. In conclusion, it can be said that coupling water-soluble polymers to the diafiltration technique is an excellent low-cost way to address the problem of antibiotics in aquatic systems.

Comparative Study of the Removal Efficiency of Nalidixic Acid by Poly[(4-vinylbenzyl)trimethylammonium Chloride] and N-Alkylated Chitosan through the Ultrafiltration Technique and Its Approximation through Theoretical Calculations.

Emerging antibiotic contaminants in water is a global problem because bacterial strains resistant to these antibiotics arise, risking human health. This study describes the use of poly[(4-vinylbenzyl) trimethylammonium chloride] and N-alkylated chitosan, two cationic polymers with different natures and structures to remove nalidixic acid. Both contain ammonium salt as a functional group. One of them is a synthetic polymer, and the other is a modified artificial polymer. The removal of the antibiotic was investigated under various experimental conditions (pH, ionic strength, and antibiotic concentration) using the technique of liquid-phase polymer-based retention (LPR). In addition, a stochastic algorithm provided by Fukui's functions is used. It was shown that alkylated N-chitosan presents 65.0% removal at pH 7, while poly[(4-vinylbenzyl)trimethylammonium chloride] removes 75.0% at pH 9. The interaction mechanisms that predominate the removal processes are electrostatic interactions, π-π interactions, and hydrogen bonding. The polymers reached maximum retention capacities of 1605 mg g-1 for poly[(4-vinylbenzyl) trimethylammonium chloride] and 561 mg g-1 of antibiotic per gram for alkylated poly(N-chitosan). In conclusion, the presence of aromatic groups improves the capacity and polymer-antibiotic interactions.

Study of the Antibacterial Capacity of a Biomaterial of Zeolites Saturated with Copper Ions (Cu2+) and Supported with Copper Oxide (CuO) Nanoparticles.

In this work, copper (II) ions were saturated and copper oxide nanoparticles (CuO NPs) were supported in natural zeolite from Chile; this was achieved by making the adsorbent material come into contact with a copper ion precursor solution and using mechanical agitation, respectively. The kinetic and physicochemical process of the adsorption of copper ions in the zeolite was studied, as well as the effect of the addition of CuO NPs on the antibacterial properties. The results showed that the saturation of copper (II) ions in the zeolite is an efficient process, obtaining a 27 g L-1 concentration of copper ions in a time of 30 min. The TEM images showed that a good dispersion of the CuO NPs was obtained via mechanical stirring. The material effectively inhibited the growth of Gram-negative and Gram-positive bacteria that have shown resistance to methicillin and carbapenem. Furthermore, the zeolite saturated with copper at the same concentration had a better bactericidal effect than the zeolite supported with CuO NPs. The results suggested that the ease of processing and low cost of copper (II) ion-saturated zeolitic material could potentially be used for dental biomedical applications, either directly or as a bactericidal additive for 3D printing filaments.

In-Situ Modification of Nanofiltration Membranes Using Carbon Nanotubes for Water Treatment.

Modification of thin-film composite (TFC) nanofiltration (NF) membranes to increase permeability and improve separation performance remains a significant challenge for water scarcity. This study aimed to enhance the permeability and selectivity of two commercial polyamide (PA) NF membranes, NF90 and NF270, by modifying them with carbon nanotubes (CNTs) using microwave (MW)-assisted in-situ growth. The conducting polymer, polypyrrole (Ppy), and a ferrocene catalyst were used to facilitate the growth process. Chemical and morphological analyses confirmed that the surface of both membranes was modified. The NF270-Ppy-CNT membrane was selected for ion rejection testing due to its superior permeability compared to the NF90-Ppy-CNT. The modified NF270 membrane showed a 14% increase in ion rejection while maintaining constant water permeability. The results demonstrated that it is feasible to attach CNTs to a polymeric surface without compromising its functional properties. The Spliegler-Kedem model was employed to model the rejection and permeate flux of NF270-Ppy-CNT and NF270 membranes, which indicated that diffusive transport contributes to the modification to increase NaCl rejection. The present study provides a promising approach for modifying membranes by in-situ CNT growth to improve their performance in water treatment applications, such as desalination.

Bio-Based Polymeric Membranes: Development and Environmental Applications.

Nowadays, membrane technology is an efficient process for separating compounds with minimal structural abrasion; however, the manufacture of membranes still has several drawbacks to being profitable and competitive commercially under an environmentally friendly approach. In this sense, this review focuses on bio-based polymeric membranes as an alternative to solve the environmental concern caused by the use of polymeric materials of fossil origin. The fabrication of bio-based polymeric membranes is explained through a general description of elements such as the selection of bio-based polymers, the preparation methods, the usefulness of additives, the search for green solvents, and the characterization of the membranes. The advantages and disadvantages of bio-based polymeric membranes are discussed, and the application of bio-based membranes to recover organic and inorganic contaminants is also discussed.

Self-Assembled CNF/rGO/Tannin Composite: Study of the Physicochemical and Wound Healing Properties.

In this study, a conductive composite material, based on graphene oxide (GO), nanocellulose (CNF), and tannins (TA) from pine bark, reduced using polydopamine (PDA), was developed for wound dressing. The amount of CNF and TA was varied in the composite material, and a complete characterization including SEM, FTIR, XRD, XPS, and TGA was performed. Additionally, the conductivity, mechanical properties, cytotoxicity, and in vitro wound healing of the materials were evaluated. A successful physical interaction between CNF, TA, and GO was achieved. Increasing CNF amount in the composite reduced the thermal properties, surface charge, and conductivity, but its strength, cytotoxicity, and wound healing performance were improved. The TA incorporation slightly reduced the cell viability and migration, which may be associated with the doses used and the extract's chemical composition. However, the in-vitro-obtained results demonstrated that these composite materials can be suitable for wound healing.

Novel and effective hemostats based on graphene oxide-polymer aerogels: In vitro and in vivo evaluation.

In this study, graphene oxide (GO)-based aerogels cross-linked with chitosan (CS), gelatin (GEL), and polyvinyl alcohol (PVA) were characterized and their hemostatic efficiencies both in vitro and in vivo were investigated and compared to commercial materials (ChitoGauze®XR and Spongostan™). All aerogels exhibited highly porous structures and a negative surface charge density favorable to their interaction with blood cells. The in vitro studies showed that all aerogels coagulated >60 % of the blood contained in their structures after 240 s of the whole-blood clotting assay, the GO-CS aerogel being the one with the highest blood clotting. All aerogels showed high hemocompatibility, with hemolytic rates <5 %, indicating their use as biomaterials. Among them, the GO-GEL aerogel exhibited the lowest hemolytic activity, due possibly to its high GEL content compared to the GO amount. According to their blood clotting activity, aerogels did not promote coagulation through extrinsic and intrinsic pathways. However, their surfaces are suitable for accelerating hemostasis by promoting alternative routes. All aerogels adhered platelets and gathered RBCs on their surfaces, and in addition the GO-CS aerogel surface also promoted the formation of filamentous fibrin networks adhered on its structure. Furthermore, in vivo evaluations revealed that all aerogels significantly shortened the hemostatic times and reduced the blood loss amounts compared both to the Spongostan™ and ChitoGauze®XR commercial materials and to the gauze sponge (control group). The hemostatic performance in vitro and in vivo of these aerogels suggests that they could be used as hemostats for controlling profuse bleedings.

Hybrid Materials Based on Nanoparticles Functionalized with Alkylsilanes Covalently Anchored to Epoxy Matrices.

In this work, the surface modification of zinc oxide nanoparticles (ZnO-NPs) with 3-glycidyloxy-propyl-trimethoxysilane (GPTMS) was investigated. The ZnO-NPs were synthesized using the physical method of continuous arc discharge in controlled atmosphere (DARC-AC). The surface modification was carried out using a chemical method with constant agitation for 24 h at room temperature. This surface functionalization of zinc oxide nanoparticles (ZnO-NPs-GPTMS) was experimentally confirmed by infrared spectroscopy (FT-IR), TGA, and XRD, and its morphological characterization was performed with SEM. The increase in mechanical bending properties in the two final hybrid materials compared to the base polymers was verified. An average increase of 67% was achieved with a moderate decrease in ductility. In the case of compressive strength, they showed mixed results, maintaining the properties. With respect to thermal properties, it was observed that inorganic reinforcement conferred resistance to degradation on the base material, giving a greater resistance to high temperatures.

An in vitro study on the inhibition and ultrastructural alterations of Candida albicans biofilm by zinc oxide nanowires in a PMMA matrix.

OBJECTIVES: The purpose of this study was (i) to investigate whether nanocomposite poly(methyl-methacrylate)-zinc oxide nanowires (PMMA-ZnO-NWs) have C. albicans antibiofilm activity; (ii) to evaluate the interaction between components of the nanocomposites based on PMMA-ZnO-NWs by Raman spectroscopy; and (iii) to assess ultrastructural alterations. DESIGN: Sixty-eight rectangles (17 PMMA (control) and 51 PMMA-ZnO-NWs (250, 500, 1000 ppm ZnO nanowires) were fabricated. C. albicans ATCC 10231 and a C. albicans clinical strain were tested. Adherence, biofilm formation and ultrastructural alterations were assessed by transmission electron microscopy. Raman mapping images and spectra were analyzed using main component analysis. RESULTS: Nanocomposite PMMA-ZnO-NWs inhibited the formation of C. albicans biofilms 94% at 1000 ppm and 80% at 500 ppm against both C. albicans strains. PMMA-ZnO-NWs induced ultrastructural alterations, including cell wall damage and disorganization of the cytoplasmic membrane, resulting in cell lysis. Raman spectroscopy showed new vibrational modes (300-365-485-600 cm-1) for PMMA and ZnO-NW interactions. CONCLUSIONS: PMMA-ZnO-NWs inhibited C. albicans dose-dependent biofilm formation and led to changes in the structures and cell membrane. Raman spectroscopy showed chemical interactions between ZnO-NWs and PMMA, as suggested by the appearance of new bands at 301 and 485 cm-1.

Laves Phase in a 12% Cr Martensitic/Ferritic Steel: Evolution and Characterization of Nanoparticles at 650 °C.

A 12% Cr martensitic/ferritic with tailor-made microstructure was characterized by HRTEM after tempering (780 °C/2 h) and isothermal aging at 650 °C during 2 months and 1 year. The investigation was focused on the precipitation behavior of Laves phase nanoparticles and its contribution to creep response at 650 °C. Although, dense precipitation of Laves phase occurs during the heat treatment (196 nm), addition of 3.8% tungsten (W) promotes a high growth rate of this particle at 650 °C. The excessive addition of W induces a high driving force for the growth of this particle reaching a mean size of 300 nm at 2 months and 400 nm at 1 year. However, some small Laves phase nanoparticles inside the grain were detected at 1 year of isothermal aging, suggesting a low coarsening rate maybe due to low diffusion of W in the matrix. Results of creep test at 650 °C suggest most of the precipitation hardening is granted by fine dispersion of Ta-rich carbonitrides (Ta-MX), i.e., Laves phase is too coarse to contribute to the pinning force of the subgrain structure in the designed alloy.

Solvothermal Synthesis and Photocatalytic Activity of BiOBr Microspheres with Hierarchical Morphologies.

BiOBr microspheres with hierarchical morphologies (BiOBr-MicSphe) has potential application in heterogeneous photocatalysis for decontamination of water and air. For this reason, the synthesis, characterization an evaluation of photocatalytic activity of these materials become important. In this article, BiOBr-MicSphe were synthesized using different ranges of reaction temperature (120-200 °C) and reaction time (12 h - 24 h). Samples grown at 145 °C and 18 h showed the higher photocatalytic activity on gallic acid degradation. Morphological properties, chemical composition and structural analysis revealed that sample with higher photocatalytic activity exhibited a microspherical morphology with pure BiOBr tetragonal phase. Besides, adsorption-desorption analysis showed a smaller pore diameter for sample grown at 145 °C and 18 hrs. The results showed that the reaction temperature has a strong influence on the different properties of the material, affecting the photocatalytic activity.

Development of Graphene Oxide Composite Aerogel with Proanthocyanidins with Hemostatic Properties As a Delivery System.

The graphene aerogels' potential for use as both a hemostatic agent and dermal delivery system has scarcely been investigated. In this study, we used a sol-gel process for generating dry and stable composite aerogels based on graphene oxide (GO) and poly(vinyl alcohol) (PVA). Furthermore, we incorporated natural extract of País grape seed (SD) and skin (SK), rich in proanthocyanidins (PAs or condensed tannins). The effect of the incorporation of the grape extracts was investigated in relation to the aerogels' structure, coagulation performance and the release of the extracts. The results demonstrated that they have a porous structure and low density, capable of absorbing water and blood. The incorporation of 12% (w/w) of PA extracts into the aerogel increased the negative zeta potential of the material by 33% (-18.3 ± 1.3 mV), and the coagulation time was reduced by 37% and 28% during the first 30 and 60 s of contact between the aerogel and whole blood, respectively. The release of extracts from the GO-PVA-SD and GO-PVA-SK aerogels was prolonged to 3 h with 20%, probably due to the existence of strong binding between PAs andGO-PVA, both characterized by the presence of aromatic and hydroxyl groups that can form noncovalent bonds but are strong and stable enough to avoid a greater release into the medium. This study provides a new GO-based aerogel, which has a great potential use in the field of dermal delivery, wound healing and/or the treatment of trauma bleeding.

Quality and high yield synthesis of Ag nanowires by microwave-assisted hydrothermal method.

Silver nanowires (Ag-NWs) were obtained using microwave-assisted hydrothermal method (MAH). The main advantage of the method is its high NWs production which is greater than 90%. It is also easy, fast, and highly reproducible process. One of the drawbacks presented so far in the synthesis of nanostructures by polyol path is the high temperature used in the process, which is superior than the boiling point of solvent (ethylene glycol), and also its excessive reaction time. Here, Ag-NWs with diameters of 70 to 110 nm were synthesized in 5 min in large quantities. Results showed that dimensions and shape of nanowires were very susceptible to changes with reaction parameters. The reactor power and reactor fill capacity were important for the synthesis. It was found that the reaction time needs to be decreased because of the NWs which start to deform and break up due to significant increase in the pressure's system. Energy-dispersive X-ray spectroscopy and electron diffraction analysis (SAED) did not show corresponding phases of AgO. Some aspects about synthesis parameters which are related to the percent yield and size of nanowires are also discussed.

Growth of vertically aligned ZnO nanorods using textured ZnO films.

A hydrothermal method to grow vertical-aligned ZnO nanorod arrays on ZnO films obtained by atomic layer deposition (ALD) is presented. The growth of ZnO nanorods is studied as function of the crystallographic orientation of the ZnO films deposited on silicon (100) substrates. Different thicknesses of ZnO films around 40 to 180 nm were obtained and characterized before carrying out the growth process by hydrothermal methods. A textured ZnO layer with preferential direction in the normal c-axes is formed on substrates by the decomposition of diethylzinc to provide nucleation sites for vertical nanorod growth. Crystallographic orientation of the ZnO nanorods and ZnO-ALD films was determined by X-ray diffraction analysis. Composition, morphologies, length, size, and diameter of the nanorods were studied using a scanning electron microscope and energy dispersed x-ray spectroscopy analyses. In this work, it is demonstrated that crystallinity of the ZnO-ALD films plays an important role in the vertical-aligned ZnO nanorod growth. The nanorod arrays synthesized in solution had a diameter, length, density, and orientation desirable for a potential application as photosensitive materials in the manufacture of semiconductor-polymer solar cells. PACS: 61.46.Hk, Nanocrystals; 61.46.Km, Structure of nanowires and nanorods; 81.07.Gf, Nanowires; 81.15.Gh, Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.).

[Evaluation of plasmatic A protein as only marker during first trimester of pregnancy]. / Evaluación de la proteína A plasmática asociada al embarazo como marcador único durante el primer trimestre.

BACKGROUND: One of main targets of prenatal diagnosis is Down's syndrome. Biochemical and sonographic markers together are efficient. The use of a single marker has not shown the same efficiency, although it has not been sufficient evaluated. OBJECTIVE: To shown results of PAPP-A as a single marker in first pregnancy trimester. MATERIALS AND METHODS: Prospective, cross-sectional and random study, which evaluated 400 women with biochemical marker PAPP-A in the first pregnancy trimester. RESULTS: PAPP-A detected a true positive case (0.3%), 28 false positive cases (7.0%) and 371 true negative cases (92.8%), there were no false negative cases. Between 9 to 11 weeks, rate of false positives fluctuated between 5.5 and 6.7%, in 12th week it was 1.2% and in 13th week 18.2%. PAPP-A has 95.1% of specificity (weeks 9 to 12) and 82.2% of maternal age. DISCUSSION: A 5% of false positive rate is acceptable for prenatal diagnosis markers. It has been reported that PAPP-A is less discriminatory at 10 weeks of gestation. In this study the rate fluctuated between 6 and 7% (weeks 9 to 11), which increased at 13th week. Markers with low false positive rate stimulate the use of prenatal screening. CONCLUSIONS: The use of combined markers: biochemical (free fraction of beta-hGC, PAPP-A) and sonographic, are most recommendable in the first trimester of the pregnancy because of them low rate of false positives. PAPP-A can be used as a single marker between 9 to 11 weeks; false positive cases must be studied with combined markers.

[Specificity of biochemical markers of pregnancy second trimester]. / Especificidad de marcadores bioquímicos del segundo trimestre de embarazo.

BACKGROUND: During the second trimester of 21 trisomy pregnancies, median of maternal serum concentrations of alpha-fetoprotein, not conjugated estriol, beta fraction, and inhibin A differ from normal values, and it can be used to select high risk patients. OBJECTIVE: To evaluate specificity of different forms of second trimester biochemical markers association in a group of healthy pregnant women and determine levels considered as low risk. PATIENTS AND METHODS: Random and cross-sectional study in 363 pregnant women with prenatal diagnosis to evaluate specificity of different combinations of biochemical markers. Down's syndrome and defects of neural tube rates of detection were defined as the percentage of pregnancies with tests of detection of true negatives and false positives. RESULTS: Total beta fraction has differences during weeks 13 to 14, with 70% of cases between 23,000 to 70,000 units, with 1.38% of false positives; alpha-fetoprotein fluctuated between 22 to 30 units, with 5.2% of false positives; conjugated estriol increases between 1.2 to 2.2 units during 2nd quarterly, with 6.3% of false positives; and inhibin has an increase, with 70% of cases located between 125 to 486.5 units, with 10.44% of false positives. CONCLUSIONS: Marker formula with greater specificity was type IV, included alpha-fetoprotein, not conjugated estriol and beta fraction. In the isolated form, alpha-fetoprotein marker demonstrates greater specificity.