RESUMEN
Low-frequency ionic current noise in solid-state nanopores imposes a limitation on the time resolution achieved in translocation experiments. Recently, this 1/f noise was described as obeying Hooge's phenomenological relation, where the noise scales inversely with the number of charge carriers present. Here, we consider an alternative model in which the low-frequency noise originates from surface charge fluctuations. We compare the models and show that Hooge's relation gives the best description for the low-frequency noise in solid-state nanopores over the entire salt regime from 10(-3) to 1.6 M KCl.
Asunto(s)
Canales Iónicos/química , Modelos Químicos , Modelos Estadísticos , Nanoestructuras/química , Nanoestructuras/ultraestructura , Simulación por Computador , Tamaño de la Partícula , Porosidad , Electricidad EstáticaRESUMEN
We report translocation of double-stranded DNA (dsDNA) molecules that are coated with RecA protein through solid-state nanopores. Translocation measurements show current-blockade events with a wide variety in time duration (10-4-10-1 s) and conductance blockade values (3-14 nS). Large blockades (11.4+/-0.7 nS) are identified as being caused by translocations of RecA-dsDNA filaments. We confirm these results through a variety of methods, including changing molecular length and using an optical tweezer system to deliver bead-functionalized molecules to the nanopore. We further distinguish two different regimes of translocation: a low-voltage regime (<150 mV) in which the event rate increases exponentially with voltage, and a high-voltage regime in which it remains constant. Our results open possibilities for a variety of future experiments with (partly) protein-coated DNA molecules, which is interesting for both fundamental science and genomic screening applications.
Asunto(s)
ADN/metabolismo , Nanoestructuras/química , Nanotecnología/métodos , Rec A Recombinasas/metabolismo , ADN/análisis , Membranas Artificiales , Nanotecnología/instrumentación , Tamaño de la Partícula , Propiedades de Superficie , Factores de TiempoRESUMEN
We study ionic current fluctuations in solid-state nanopores over a wide frequency range and present a complete description of the noise characteristics. At low frequencies (f approximately < 100 Hz) we observe 1/f-type of noise. We analyze this low-frequency noise at different salt concentrations and find that the noise power remarkably scales linearly with the inverse number of charge carriers, in agreement with Hooge's relation. We find a Hooge parameter alpha = (1.1 +/- 0.1) x 10(-4). In the high-frequency regime (f approximately > 1 kHz), we can model the increase in current power spectral density with frequency through a calculation of the Johnson noise. Finally, we use these results to compute the signal-to-noise ratio for DNA translocation for different salt concentrations and nanopore diameters, yielding the parameters for optimal detection efficiency.
Asunto(s)
Iones , Nanopartículas/química , Nanotecnología/métodos , Algoritmos , Transporte Biológico , ADN/química , ADN/metabolismo , Concentración de Iones de Hidrógeno , Microscopía Electrónica de Transmisión , Modelos Químicos , Oxígeno/química , ARN/química , Reproducibilidad de los Resultados , Sales (Química)/farmacología , Dióxido de Silicio/química , Programas Informáticos , TemperaturaRESUMEN
From conductance and noise studies, we infer that nanometer-sized gaseous bubbles (nanobubbles) are the dominant noise source in solid-state nanopores. We study the ionic conductance through solid-state nanopores as they are moved through the focus of an infrared laser beam. The resulting conductance profiles show strong variations in both the magnitude of the conductance and in the low-frequency noise when a single nanopore is measured multiple times. Differences up to 5 orders of magnitude are found in the current power spectral density. In addition, we measure an unexpected double-peak ionic conductance profile. A simple model of a cylindrical nanopore that contains a nanobubble explains the measured profile and accounts for the observed variations in the magnitude of the conductance.
Asunto(s)
Modelos Teóricos , Nanoestructuras/química , Conductividad Eléctrica , Rayos Láser , Microscopía Electrónica de TransmisiónRESUMEN
UNLABELLED: This study was conducted to gain insight into the attitudes of medical staff towards life-support of newborns with life-threatening problems, seen against the background of these children's expected morbidity and quality of life. The opinions about the mode of life-support were determined by questionnaires and the demographic characteristics of the respondents were noted. Each patient's risk of mortality was scored by means of the standardized Paediatric Risk of Mortality Score (PRISM). Attitudes towards support were unanimous for 39 of the 46 patients. For the other 7 patients at least one of the respondents preferred a different support mode than that given at the time. The attitudes were influenced by the patient's risk of mortality. CONCLUSION: Decisions about life-support of newborns with life-threatening problems should include all the disciplines involved in patient care and should be made at an early stage.
Asunto(s)
Actitud del Personal de Salud , Anomalías Congénitas/terapia , Ética Médica , Cuidado Intensivo Neonatal , Cuidados para Prolongación de la Vida , Toma de Decisiones , Humanos , Recién Nacido , Países Bajos , PronósticoRESUMEN
The component structure of the expanded Brief Psychiatric Rating Scale (BPRS-E) was analyzed in a sample (n = 150) of consecutively admitted general psychiatric inpatients and compared with a group (n = 97) of adolescent patients with schizophrenia spectrum diagnoses. A stable five-component solution, of which four were interpretable, was found across groups. The component scales of the 24-item version of the BPRS had good internal consistency, allowed better coverage of schizophrenia and affective symptoms than the 18-item version but did not distinguish the schizophrenia diagnostic subgroups. The implications of the findings are discussed.
Asunto(s)
Escalas de Valoración Psiquiátrica Breve , Trastornos del Humor/diagnóstico , Esquizofrenia/diagnóstico , Adolescente , Adulto , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
133 patients in whom a Wilms' tumour had been diagnosed between 1971 and 1986 were evaluated retrospectively for presence of congenital anomalies of the genitourinary tract. These were detected in 51 patients, 38.3%. A comparison was made between the incidence of each detected malformation in the patient group and in the general population. Some anomalies seemed to have a high association with the nephroblastoma; sharing the same basic embryological disorder is suggested as a possible explanation for this association.