Fabrication of lab-on chip platforms by hot embossing and photo patterning

In this paper, we review the approaches developed in our laboratory to fabricate polymer-based microfluidic devices to suit a range of applications in bio- or chemical analysis. Thermoplastic materials such as polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are used to fabricate microfluidic devices via hot embossing. To emboss microchannels, we use hard stamps fabricated in silicon or soft stamps molded on poly(dimethylsiloxane) (PDMS). Hard stamps are fabricated on silicon wafers through photolithography and deep reactive ion etching (DRIE). Soft stamps are fabricated by casting PDMS prepolymer on silicon molds. To enclose the fluidic channels, direct fusion bonding was found to produce the highest bond strength with minimal structural deformation. One-step photolithographic methods have also been explored to produce via photochemical patterning microfluidic structures in photocurable materials. We use the photocurable capabilities of a PDMS copolymer, which incorporates a methacrylate crosslinker. Microfluidic channels are produced via one step-photopatterning processes by crosslinking the prepolymer mixture through a photomask. The smaller feature size attainable was 100 microm. Structures with higher spatial resolution are fabricated through a photoimprinting process whereby a mold is pressed against the precured mixture during UV crosslinking exposure. The application of the fabricated fluidic devices in electrophoretic ion analysis is also presented.     

Studies on interaction of green silver nanoparticles with whole bacteria by surface characterization techniques

The use of silver nanoparticles (AgNPs) with their novel and distinct physical, chemical, and biological properties, has proven to be an alternative for the development of new antibacterial agents. In particular, the possibility to generate AgNPs coated with novel capping agents, such as phytomolecules obtained via a green synthesis (G-AgNPs), is attracting great attention in scientific research.Recently, we showed that membrane interactions seem to be involved in the antibacterial activity of AgNPs obtained via a green chemical synthesis using the aqueous leaf extract of chicory (Cichorium intybus L.). Furthermore, we observed that these G-AgNPs exhibited higher antibacterial activity than those obtained by chemical synthesis.In order to achieve the green AgNPs mode of action as well as their cellular target, we aimed to study the antibacterial activity of this novel green AgNPs against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The effect of the G-AgNPs on the bacterial surface was first evaluated by zeta potential measurements and correlated with direct plate count agar method. Afterwards, atomic force microscopy was applied to directly unravel the effects of these G-AgNPs on bacterial envelopes.Overall, the data obtained in this study seems correlate with a multi-step mechanism by which G-AgNPs-lipid membrane interactions is the first step prior to membrane disruption, resulting in antibacterial activity.     

Structural Changes of Ag+�CNa+ Annealed Ion-Exchanged Silicate Glasses Scanning Electron Microscopy, Far-Infrared Reflectivity, UV-Visible Absorption, and TEM Investigation

The effect of silver ionic exchange on the glass structure in a molten bath at 350 °C was presented in a previous paper Catan et al. [1] (J NonCryst Solids 354:1026–1031, 2008). In this paper, the experiment is driven for a temperature near 310 °C, the eutectic of a 10% AgNO₃–NaNO₃ molten salt. The various exchanged silicate glasses are further annealed to obtain silver particles in the matrix. Infrared spectroscopy combined with UV/Visible spectroscopy and scanning electron microscopy analysis allowed to correlate the silver-ion penetration and particle formation with the degree of polymerisation of the silicate network. The previous results have demonstrated an insertion of silver ions in the glass structure that is about 10% higher than the departure of sodium ions. Infrared results obtained after ion exchange have proved that local alterations lead to a higher degree of depolymerisation of the silicate network. Here, the annealing of the samples promotes the formation of silver nanoparticles, the infrared measurements prove that the aggregation is correlated to a repolymerisation of the silicate network. Transmission electron microscopy (TEM) is used to evaluate the distribution size of the silver particles after annealing and to correlate it to the evolution of the absorption curves. The TEM observations prove that the particle are below the incident wavelength but shape factor could lead to scattering contribution when particle growths and to absorption spectra evolution.     

Mechanisms of genetic regulation of the lactate dehydrogenase isoenzyme spectrum in the erythrocytes of silver-black foxes]

The spectrum of lactate dehydrogenase (LDH) isozymes in erythrocytes of silver foxes was investigated by means of electrophoretic and immunochemical methods. By means of electrophoresis it is shown that differences in LDH isozyme spectrum between the animals homozygous for the gene Ldr-1a and those homozygous for the gene Ldr-1b are most conspisions at the age of 90-100 days of postnatal development. By means of the immunochemical method three groups of animals are distinguished differing in the LDH content in erythrocytes: the animals with a high LDH content (81.0 mcg/ml) and with a low LDH content (54.14 mcg/ml), which are homozygous for the gene Ldr-1b and Ldr-1a respectively, and the animals with intermediate LDH content (64.58 mcg/ml), which are heterozygous. The data obtained suggest that the effect of the gene Ldr-1a is associated with the decrease of the quantity of A subunits of LDH. It is assumed that the mechanism of the gene Ldr-1a action is realized either by means of the decrease of the synthesis of the A LDH subunits, or by means of the increase of the rate of their degradation.     

Comparative effectiveness of antimicrobial action of antiseptics against pathogens of chronic purulent otitis media]

Comparable antimicrobial and disinfecting action of decamethoxine and silver preparations on pathogens of chronic purulent otitis media (CPOM) was studied. The clinical isolates of staphylococci proved to be most sensitive to decamethoxine whose MBcC conformed to 16.5 micrograms/ml. The antimicrobial action on Proteus spp. and Pseudomonas aeruginosa was less pronounced. The required concentrations for bactericidal action on these pathogens were 69 and 93.5 micrograms/ml, respectively. The antimicrobial activity of the silver preparations such as poviargol, collargol and protargol was low. Depending on the microbial species, the bactericidal effect of the silver preparations was 12-235 times lower than that of decamethoxin. It was also shown that decamethoxin had a high disinfecting action on CPOM pathogens. It was noted that decamethoxin had a marked ability to increase the bactericidal action of poviargol (by 2-14 times) and its disinfecting action (by 2 times) on Proteus spp., E. coli and Ps. aeruginosa.     

Cytochemical duality of neurosecretory material in the hypothalamo-posthypophysial system of the rat as related to hormonal content

Summary Cytochemical methods using silver proteinate, silver methenamine and potassium ferrocyanide + OsO₄ for ultrastructural detection of glycoproteins allow, in the posthypophysis and the magnocellular nuclei of the rat, differentiation of two types of fibres and neurons: one type containing negative granules with a homogeneous content of low electron density, the second type containing granules which demonstrate a ring-shaped deposit either of silver or of potassium ferrocyanide-osmium complex, likely to be related to a glycoproteic component. The difference between these two types is increased by prestaining en bloc with uranyl acetate before the silver proteinate reaction. A similar investigation was carried out on the vasopressin deficient Brattleboro rat; the neurosecretory material, present in some endings and neurones only, is of the nonreactive type, so that it appears justified to correlate the reactivity of granules with vasopressin, and consequently to distinguish neurones and fibres containing vasopressin from those in which oxytocin is quantitatively the main hormonal peptide. This conclusion is strongly supported by the fact that percentages of reactive and negative endings, as determined on this basis in the posthypophysis of normal rats from two different strains, are in good agreement with biochemical data reported in the literature.     

方寸天地 世纪履痕——纪念国际昆虫学大会100周年

首届国际昆虫学大会1910年召开至今,已经100年了,本文通过邮票,回眸大会的发起与大会早期的情景;1910年到2008年间23届大会的概况,其中两次世界大战使大会受挫;在战后和平环境中,才获得日趋兴旺的发展。文章详细介绍了会期发行的邮票、邮戳、明信片和首日封。     

Pine cone-mediated green synthesis of silver nanoparticles and their antibacterial activity against agricultural pathogens

The medicinal and physicochemical properties of nanoscale materials are strong functions of the particle size and the materials used in their synthesis. The nanoparticle shape also contributes significantly to their medicinal properties. Several shapes ranging from oval, spherical, rods, to teardrop structures may be obtained by chemical methods. Triangular and hexagonal nanoparticles have been synthesized by using a pine cone extract (PCE). Here, we report the discovery that PCE, when reacted with silver nitrate ions, yields a high percentage of thin, flat, single-crystalline nanohexagonal and nanotriangular silver nanoparticles. The nanohexagonal and nanotriangular nanoparticles appear to grow by a process involving rapid reduction with assembly at room temperature at a high pH. The nanoparticles were characterized by UV–Vis absorption spectroscopy, SEM-EDS, TEM, FTIR, and X-ray diffraction analyses. The anisotropy of the nanoparticle shape results in large near-infrared absorption by the particles. Highly anisotropic particles are applicable in various fields, including agriculture and medicine. The obtained silver nanoparticles (Ag NPs) had significant antibacterial action on both Gram classes of bacteria associated with agriculture. Because the Ag NPs are encapsulated with functional group-rich PCE, they can be easily integrated in various applications.     

Metal complexes of 1,10-phenanthroline-5,6-dione alter the susceptibility of the yeast Candida albicans to Amphotericin B and Miconazole

Growth of the pathogenic yeast Candida albicans in sub-MIC (minimum inhibitory concentration) levels of Cu(ClO4)2 6H2O and [Cu(phendio)3](ClO4)2 4H2O (phendio = 1,10-phenanthroline-5,6-dione) increased the concentration of miconazole and amphotericin B required to achieve the MIC90 whereas pre-growth in AgClO4 and [Ag(phendio)2]ClO4 resulted in a small decrease in the relevant MIC90 values. The copper complexes reduce the oxygen consumption of C. albicans while the silver complexes increase oxygen consumption. In addition, pre-growth of cells in the copper complexes resulted in a lower ergosterol content while the silver complexes induced an elevation in ergosterol synthesis. The ability of copper and silver complexes to alter the susceptibility of C. albicans to miconazole and amphotericin B may be influenced by their action on respiration, since reduced respiration rates correlate with reduced cellular ergosterol which is the target for amphotericin B. Lower levels of ergosterol have previously been associated with elevated tolerance to this drug. In the case of reduced sensitivity to miconazole, tolerance may be mediated by lower ergosterol synthesis giving rise to fewer toxic side products once biosynthesis is inhibited by miconazole.     

A Glycine-Hcl-Formalin Fixative for Improved Staining of Neuroglia

The pH of fixatives as well as the components of the fixative mixture exert a displacing action on the isoelectric point of tissue proteins, which influences the intensity of staining. Studies of these effects showed that ammonium nitrate, sulfate or chloride could be substituted successfully for ammonium bromide in Cajal's formalin-ammonium bromide fixative. However, the best results from staining with Rio Hortega's silver carbonate and with Cajal's gold-sublimate methods were obtained after fixation in a mixture consisting of: glycine, 1.05 gm; 12V HCl, 14.8 ml; concentrated formalin, 15 ml and distilled water to make 100 ml.     

Bacterial Resistance to Nanosilver: Molecular Mechanisms and Possible Ways to Overcome them

This review contains the results of experimental studies of recent years dedicated to the resistance of bacteria to the action of nanosized silver and describes the putative molecular mechanisms of its development. Emphasis is placed on the study of works devoted to the investigation of the mechanisms of the resistance of bacteria to silver ions, which are the main factor of the bactericidal action of nanoparticles. The review also contains suggestions for further research aimed at developing of ways to overcome the problem of resistance of individual bacterial strains to the action of nanosilver and methods preventing its further spread.

     

Role of alpha-tocopherol in oxidative stress of rat thymocytes induced by hydrogen peroxide and menadione

T paper deals with studying the effect of alpha-tocopherol and its analogues (alpha-tocopheryl acetate and alpha-tocopheryl quinine) showing no antioxidant properties on rat thymocytes survival and intracellular content of reactive oxygen species (ROS) at H2O2 and menadione-induced oxidative stress. It is established, that the ability of alpha-tocopherol to inhibit the thymocytes destruction induced by the development of oxidative stress is insignificant. It does not depend on the presence of free OH-group in the structure of alpha-tocopherol molecule responsible for development of antioxidant properties, and does not correlate with its influence on intracellular ROS content. The efficiency of the glutathione synthesis predecessor N-acetyl-L-cysteine in the given model testifies to the involving of other systems of antioxidative protection in these processes. The obtained data allow to conclude, that alpha-tocopherol does not play the main role in the protection of cells against ROS damaging action that calls into question its ability to prevent the oxidative stress.     

A Method of Obtaining Silver–Succinyl Chitosan Nanocomposites and their Antimicrobial Activity

To form silver nanoparticles by reduction from metal ions in the presence of a reducing agent, D-glucose, a water-soluble derivative of chitosan, succinyl-chitosan, was used as a polymer matrix at room temperature. The synthesis of silver nanoparticles can also be carried out without a reducing agent by thermal activation of the system using an alkali (NaOH) as an accelerator. The presence of silver nanoparticles in the obtained colloidal solutions was judged by the appearance of an absorption band in the electron plasmon resonance spectra (?_max = 417 nm). It has been shown that the use of an additional component, polyethylene oxide, in a macromolecular system makes it possible to obtain small silver nanoparticles (1–3 nm). The results of in vitro studies of the antimicrobial activity of the obtained colloidal solutions containing silver nanoparticles confirm that a decrease in the size of silver nanoparticles leads to an expansion of the spectrum of antibacterial activity of strains of gram-positive and gram-negative bacteria (B. subtilis ATCC 6633, S. aureus 209P, E. coli ATCC 25922) and to the manifestation of a pronounced antifungal action in relation to A. niger INA 00760.

     

Bassam和Sanguinetti银染方法在SRAP和TRAP标记中的比较研究

银染作为一种重要的DNA染色方法,对分子标记检测有重要影响.SRAP标记和TRAP标记是两种较为新型的分子标记,近年来得到了广泛应用,尤其在缺少遗传图谱的物种中应用价值更大.以普通烟草种(Nicotiana tabacum L.)烤烟和香料烟品种作为供试材料,对Bassam和Sanguinetti两种银染方法,在标记检测效率、成本及染色效果等方面进行了研究,并对其在SRAP标记和TRAP标记中的应用进行了探讨.结果表明,Sanguinetti银染法比Bassam银染更为简便、经济,染色照片的色阶图说明Sanguinetti染色方法的背景与扩增带区分明显,能够清楚地读带;且该方法能够扩增出很好的SRAP和TRAP标记谱带.因此,推荐在SRAP和TRAP标记检测中采用Sanguinetti银染方法.     

邮票图说达尔文和他的昆虫情缘

今年是伟大的进化论创建者达尔文诞生200周年,本文通过邮票介绍达尔文的昆虫情缘。其中主要内容有:(1)有关纪念达尔文的邮票;(2)他青少年时代是个甲虫迷;(3)在南美和昆虫打交道;(4)昆虫成为进化论的重要元素;(5)他睿智预测马达加斯加存在长喙天蛾,足以为花冠长300mm的兰花授粉。     

Human nucleolar organizer chromosomes: satellite associations

The D and G group chromosomes from cultured human lymphocytes exhibit single and multiple satellite associations when stained with silver. Unlike earlier methods this simple and highly repeatable procedure shows physical attachments between satellited regions of various acrocentric autosomes. After studying 1,000 satellite associations from 118 normal individuals, it was found that both single and multiple associations occur with frequencies that correlate with random expectancies.     

Micropatterned agarose gels for stamping arrays of proteins and gradients of proteins

We describe a method for repetitive and rapid formation of planar microarrays and gradients of proteins using patterned agarose stamps. It demonstrates: (i) micropatterning of agarose gels with feature sizes as small as 2 microm; (ii) inking of posts (diameter 50-1000 microm) on patterned agarose stamps with one or multiple (here, eight) proteins and repetitive stamping of patterns (>100 times in the case of one protein) and arrays (20 times in the case of eight proteins) without the need for intermediate re-inking; (iii) transferring spots of proteins with good homogeneity in surface coverage to glass slides; (iv) applying this technique to surface-based immunoassays; (v) stamping that requires only sub-nanomolar amounts of protein (typically approximately 3 microg in approximately 0.6 microL of solution); (vi) stamping without the need for drying of the proteins, as opposed to stamping with stamps made of poly(dimethylsiloxane); and (vii) patterning gradients of proteins by allowing two proteins to diffuse toward each other in an agarose stamp, followed by printing the protein gradients onto a surface.     

Luminescence Enhancement and SERS by Self-Assembled Plasmonic Silver Nanostructures in Nanoporous Glasses

It was shown experimentally that the action of continuous electric field on nanoporous silicate glasses with interconnecting pores, containing silver nanoparticles, leads to the spatial redistribution of nanoparticles. The concentration of nanoparticles near the negative electrode increases and results in silver nano- and microdendrite structure growth. The main mechanisms of the described effects are the field emission of silver ions from silver nanoparticles near negative electrode, migration of silver ions in the external electric field to the negative electrode, reduction of silver ions by free electrons, and new silver nanoparticle formation. The experiments have shown that at the ends of microdendrites, local field enhancement appears, which results in luminescence enhancement and in SERS.

     

Factors affecting the formation of metallic silver and the binding of silver ions by tissue components

Summary The rate of formation of metallic silver has a maximum when plotted as a function of pH. The site of this maximum on a pH scale differs noticeably for various tissue elements. By contrast, the amount of silver ions bound to the tissue is a monotonously increasing function of the pH. A temperature rise decreases the length of the induction period and increases the gradient of the ascending section of the kinetic curve representing the formation of metallic silver. It also increases the maximum amount of silver ions bound to the tissue. An increase in the concentration (activity) of the silver ions in the impregnating bath has the same effect. Chemical composition and concentration of the complexing agent, as well as special ions in the impregnating bath to which earlier some definitive role has been attributed in the silver staining methods, proved to be ineffective when both pH and activity of silver ions were kept constant. Illumination of the reaction was also ineffective. The kinetic curves obtained in nonaqueous but polar media (e.g., acetone) exhibited the same qualitative characteristics as those obtained in aqueous solutions. No reaction between silver ions and tissue was observed in apolar solvents.     

Sensitive colloidal metal (gold or silver) staining of protein blots on nitrocellulose membranes

A sensitive staining method for protein blots on nitrocellulose membranes is described and compared with commonly used dye staining methods. It uses colloidal metal sols (gold or silver) stabilized with Tween 20 and adjusted to pH 3. It is based on the selective high-affinity binding of colloidal metal particles to the proteins and produces a red-purplish color (gold) or dark grey (silver). The sensitivity of this new staining method is in the same range as silver staining of polyacrylamide gels and matches the sensitivity of overlay assays. It will therefore be a useful tool for correlating the position of bands or spots of proteins detected with overlay assays with the complete electropherogram in a duplicate protein blot.