Time response and stability of porous silicon capacitive immunosensors

The time response of affinity sensors made with nanostructured materials is a topic of considerable interest, since affinity sensors made with nanostructured materials provide greater sensitivities than corresponding planar crystalline devices but at the cost of stability and drift. We present a study of the time response of capacitive immunosensors made using porous silicon and ultrathin room temperature anodic oxide. It was found that sensor drift can be substantial but can be reduced by subjecting the capacitive immunosensor in buffer to an anodic bias that is larger than the bias at which sensor capacitance is measured. By measuring sensor response before the addition of the analyte and using it for baseline correction after addition of the analyte, the effect of nonspecific sensor drift can be further reduced. We observed that after the addition of the analyte to the porous silicon immunocapacitor, there is a fast decrease in capacitance (order of tens of seconds) followed by a slow increase (order of tens of minutes), which models well as a sum of exponents with a fast exponential decay followed by a slow exponential rise. Possible processes that can give rise to such a response are perturbations of the double layer for the fast decay and column resistance switching for the slow rise.     

Evaluation of rayon swab surface sample collection method for Bacillus spores from nonporous surfaces

AIM: To evaluate US Centers for Disease Control and Prevention recommended swab surface sample collection method for recovery efficiency and limit of detection for powdered Bacillus spores from nonporous surfaces. METHODS AND RESULTS: Stainless steel and painted wallboard surface coupons were seeded with dry aerosolized Bacillus atrophaeus spores and surface concentrations determined. The observed mean rayon swab recovery efficiency from stainless steel was 0.41 with a standard deviation (SD) of +/-0.17 and for painted wallboard was 0.41 with an SD of +/-0.23. Evaluation of a sonication extraction method for the rayon swabs produced a mean extraction efficiency of 0.76 with an SD of +/-0.12. Swab recovery quantitative limits of detection were estimated at 25 colony forming units (CFU) per sample area for both stainless steel and painted wallboard. CONCLUSIONS: The swab sample collection method may be appropriate for small area sampling (10 -25 cm2) with a high agent concentration, but has limited value for large surface areas with a low agent concentration. The results of this study provide information necessary for the interpretation of swab environmental sample collection data, that is, positive swab samples are indicative of high surface concentrations and may imply a potential for exposure, whereas negative swab samples do not assure that organisms are absent from the surfaces sampled and may not assure the absence of the potential for exposure. SIGNIFICANCE AND IMPACT OF THE STUDY: It is critical from a public health perspective that the information obtained is accurate and reproducible. The consequence of an inappropriate public health response founded on information gathered using an ineffective or unreliable sample collection method has the potential for undesired social and economic impact.     

Functional Loss of Semaphorin 3C and/or Semaphorin 3D and Their Epistatic Interaction with Ret Are Critical to Hirschsprung Disease Liability

Innervation of the gut is segmentally lost in Hirschsprung disease (HSCR), a consequence of cell-autonomous and non-autonomous defects in enteric neuronal cell differentiation, proliferation, migration, or survival. Rare, high-penetrance coding variants and common, low-penetrance non-coding variants in 13 genes are known to underlie HSCR risk, with the most frequent variants in the ret proto-oncogene (RET). We used a genome-wide association (220 trios) and replication (429 trios) study to reveal a second non-coding variant distal to RET and a non-coding allele on chromosome 7 within the class 3 Semaphorin gene cluster. Analysis in Ret wild-type and Ret-null mice demonstrates specific expression of Sema3a, Sema3c, and Sema3d in the enteric nervous system (ENS). In zebrafish embryos, sema3 knockdowns show reduction of migratory ENS precursors with complete ablation under conjoint ret loss of function. Seven candidate receptors of Sema3 proteins are also expressed within the mouse ENS and their expression is also lost in the ENS of Ret-null embryos. Sequencing of SEMA3A, SEMA3C, and SEMA3D in 254 HSCR-affected subjects followed by in silico protein structure modeling and functional analyses identified five disease-associated alleles with loss-of-function defects in semaphorin dimerization and binding to their cognate neuropilin and plexin receptors. Thus, semaphorin 3C/3D signaling is an evolutionarily conserved regulator of ENS development whose dys-regulation is a cause of enteric aganglionosis.     

Guava leaf volatiles and dimethyl disulphide inhibit response of Diaphorina citri Kuwayama to host plant volatiles

The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors the causal pathogen of huanglongbing (HLB), which is likely the most important disease affecting worldwide citrus production. Interplanting citrus with guava, Psidium guajava L., was reported to reduce D. citri populations and incidence of HLB. We describe a series of investigations on the response of D. citri to citrus volatiles with and without guava leaf volatiles and to synthetic dimethyl disulphide (DMDS), in laboratory olfactometers and in the field. Volatiles from guava leaves significantly inhibited attraction of D. citri to normally attractive host‐plant (citrus) volatiles. A similar level of inhibition was recorded when synthetic DMDS was co‐released with volatiles from citrus leaves. In addition, the volatile mixture emanating from a combination of intact citrus and intact guava leaves induced a knock‐down effect on adult D. citri. Compounds similar to DMDS including dipropyl disulphide, ethyl‐1‐propyl disulphide, and diethyl disulphide did not affect the behavioural response of D. citri to attractive citrus host plant volatiles. Head‐space volatile analyses were conducted to compare sulphur volatile profiles of citrus and guava, used in our behavioural assays, with a gas chromatography‐pulsed flame photometric detector. DMDS, produced by wounded guava in our olfactometer assays, was not produced by similarly wounded citrus. The airborne concentration of DMDS that induced the behavioural effect in the 4‐choice olfactometer was 107 pg/ml. In a small plot field experiment, populations of D. citri were significantly reduced by deployment of synthetic DMDS from polyethylene vials compared with untreated control plots. Our results verify that guava leaf volatiles inhibit the response of D. citri to citrus host plant volatiles and suggest that the induced compound, DMDS, may be partially responsible for this effect. Also, we show that field deployment of DMDS reduces densities of D. citri and thus may have potential as a novel control strategy.     

Refractory seizures with global developmental delay: A rare cause

Aicardi syndrome is a genetic disorder characterized by the triad of infantile spasm in flexion, callosal agenesis and ocular abnormalities (chorioretinal lacunae, coloboma of optic disc). We report a typical case of Aicardi syndrome with all the classical features.     

Interplay between structure and dynamics in chitosan films investigated with solid-state NMR, dynamic mechanical analysis, and X-ray diffraction

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl(-)) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl(-) counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.     

Development of a chitosan nanofibrillar scaffold for skin repair and regeneration

The final goal of the present study was the development of a 3-D chitosan dressing that would shorten the healing time of skin wounds by stimulating migration, invasion, and proliferation of the relevant cutaneous resident cells. Three-dimensional chitosan nanofibrillar scaffolds produced by electrospinning were compared with evaporated films and freeze-dried sponges for their biological properties. The nanofibrillar structure strongly improved cell adhesion and proliferation in vitro. When implanted in mice, the nanofibrillar scaffold was colonized by mesenchymal cells and blood vessels. Accumulation of collagen fibrils was also observed. In contrast, sponges induced a foreign body granuloma. When used as a dressing covering full-thickness skin wounds in mice, chitosan nanofibrils induced a faster regeneration of both the epidermis and dermis compartments. Altogether our data illustrate the critical importance of the nanofibrillar structure of chitosan devices for their full biocompatibility and demonstrate the significant beneficial effect of chitosan as a wound-healing biomaterial.     

Complex recombination patterns arising during geminivirus coinfections preserve and demarcate biologically important intra-genome interaction networks

Genetic recombination is an important process during the evolution of many virus species and occurs particularly frequently amongst begomoviruses in the single stranded DNA virus family, Geminiviridae. As in many other recombining viruses it is apparent that non-random recombination breakpoint distributions observable within begomovirus genomes sampled from nature are the product of variations both in basal recombination rates across genomes and in the over-all viability of different recombinant genomes. Whereas factors influencing basal recombination rates might include local degrees of sequence similarity between recombining genomes, nucleic acid secondary structures and genomic sensitivity to nuclease attack or breakage, the viability of recombinant genomes could be influenced by the degree to which their co-evolved protein-protein and protein-nucleotide and nucleotide-nucleotide interactions are disreputable by recombination. Here we investigate patterns of recombination that occur over 120 day long experimental infections of tomato plants with the begomoviruses Tomato yellow leaf curl virus and Tomato leaf curl Comoros virus. We show that patterns of sequence exchange between these viruses can be extraordinarily complex and present clear evidence that factors such as local degrees of sequence similarity but not genomic secondary structure strongly influence where recombination breakpoints occur. It is also apparent from our experiment that over-all patterns of recombination are strongly influenced by selection against individual recombinants displaying disrupted intra-genomic interactions such as those required for proper protein and nucleic acid folding. Crucially, we find that selection favoring the preservation of co-evolved longer-range protein-protein and protein DNA interactions is so strong that its imprint can even be used to identify the exact sequence tracts involved in these interactions.