Counting single native biomolecules and intact viruses with color-coded nanoparticles

Nanometer-sized particles such as semiconductor quantum dots and energy-transfer nanoparticles have novel optical properties such as tunable light emission, signal brightness, and multicolor excitation that are not available from traditional organic dyes and fluorescent proteins. Here we report the use of color-coded nanoparticles and dual-color fluorescence coincidence for real-time detection of single native biomolecules and viruses in a microfluidic channel. Using green and red nanoparticles to simultaneously recognize two binding sites on a single target, we demonstrate that individual molecules of genes, proteins, and intact viruses can be detected and identified in complex mixtures without target amplification or probe/target separation. Real-time coincidence analysis of single-photon events allows rapid detection of bound targets and efficient discrimination of excess unbound probes. Quantitative studies indicate that the counting results are remarkably precise when the total numbers of counted molecules are more than 10. The use of bioconjugated nanoparticle probes for single-molecule detection is expected to have important applications in ultrasensitive molecular diagnostics, bioterrorism agent detection, and real-time imaging and tracking of single-molecule processes inside living cells.     

A deterministic study of delta modulation

Delta modulation has often been viewed as a type of PCM and has been analyzed by probabilistic methods. This paper views delta modulation as a hybrid PDM/PAM system. A nonlinear feedback model is constructed and subjected to digital computation on an IBM 650. Computation is enabled by trapezoidal convolution, an approximateZ-transform method for solving dynamical systems. Responses to various steps and ramp inputs for unity and nonunity feedback are considered. Dead space is also introduced into the nonlinearity in the forward link. A series of computer runs is condensed and observations are reported. A typical observation is that a trade-off exists between average error and noise and that both may not be minimized by any one of two versions of the delta modulator.     

Circadian neuroendocrine physiology and electromagnetic field studies: precautions and complexities

The suppression of melatonin by exposure to low frequency electromagnetic fields (EMFs) 'the melatonin hypothesis'. has been invoked as a possible mechanism through which exposure to these fields may result in an increased incidence of cancer. While the effect of light on melatonin is well established, data showing a similar effect due to EMF exposure are sparse and, where present, are often poorly controlled. The current review focuses on the complexities associated with using melatonin as a marker and the dynamic nature of normal melatonin regulation by the circadian neuroendocrine axis. These are issues which the authors believe contribute significantly to the lack of consistency of results in the current literature. Recommendations on protocol design are also made which, if followed, should enable researchers to eliminate or control for many of the confounding factors associated with melatonin being an output from the circadian clock.     

Estimate of treatment plant effluent impact on chloride concentrations and oyster environment within the murderkill river estuary

The Murderkill River is a partially tidal body of water with summer-time 50-percentile freshwater flows ranging from 17.9 to 27.6ft³s⁻¹ (0.5 to 0.77m³s⁻¹) at a point coincident with the effluent discharge from the Kent County Regional Wastewater Treatment Plant (start-up late 1972). Chloride concentrations were determined over six summers to characterize river conditions prior to start-up of the 10-million gal day⁻¹ (37.850 m³ day⁻¹) (design) plant. Use of a one-dimensional steadystate model for a conservative substance shows that chloride values would be reduced by up to 20% at low water slack (LWS) periods for wastewater flows of 10 million gal day⁻¹ (37,850 m³ day⁻¹). The LWS chloride concentrations in the area of oyster production would be reduced to 3–6 ppt (5.9–10.8 ppt salinity) for wastewater loadings greater than 10 million gal day⁻¹ (37,850 m³ day⁻¹) . It is suggested that chloride additions in the treatment plant effluent be implemented to maintain minimum summertime low-water-slack levels of 5.6 ppt chloride (10 ppt salinity), consistent with a proper environment for oyster development.     

Asynchronous multiuser detection for sparse code multiple access with unknown delays: A compressed sensing approach

Despite being the subject of a growing body of research, nonorthogonal multiple access has failed to garner sufficient support to be included in modern standards. One of the more promising approaches to nonorthogonal multiple access is sparse code multiple access, which seeks to utilize nonorthogonal, sparse spreading codes to share bandwidth among users more efficiently than traditional orthogonal methods. Nearly all of the studies regarding sparse code multiple access assume synchronization at the receiver, which may not always be a practical assumption. In this work, we aim to bring this promising technology closer to a practical realization by dropping the assumption of synchronization. We therefore propose a compressed sensing-based delay estimation technique developed specifically for an uplink sparse code multiple access system. The proposed technique can be used with nearly all of the numerous decoding algorithms proposed in the existing literature, including the popular message passing approach. Furthermore, we derive a theoretical bound regarding the recovery performance of the proposed technique and use simulations to demonstrate its viability in a practical uplink system.     

Optimal survey design using focused resistivity arrays

The first problem which needs to be solved when planning any geoelectrical survey is a choice of a particular electrode configuration that can give the maximal response from a target inhomogeneity. The authors formulate a problem of maximizing the response as an optimization problem for an applied current intensity distribution on the surface. The solution of this problem is the optimal intensity distribution of the current, which maximizes the response from the inclusion. This problem is solved numerically with singular value decomposition of an impedance matrix. The optimal current array is modeled as a current of varying optimal intensity injected at different electrodes. The problem does not need any information about the inclusion but its measured impedance matrix. Thus an optimal current array can be designed for every particular resistivity distribution. The optimal current patterns are found for a number of models of a conductive inclusion, and responses due to the optimal current are compared with responses due to conventional arrays. This method can be applied to any background and inclusion resistivity distribution     

Investigation of the `switch-epitope' concept with random peptide libraries displayed as thioredoxin loop fusions

The `FLITRX' random peptide library, consisting of dodecamerloop peptides displayed on a thioredoxin-flagellin scaffoldon Escherichia coli, was used to select peptide sequences withaffinity for a monoclonal antibody. These peptides were furtherscreened for pH- and metal-sensitive antibody binding. Severalzinc-sensitive peptides were identified, termed `switch epitopes'.A soluble, monomeric thioredoxin loop (`Trxloop') insertionanalog of a FLITRX switch epitope was constructed and its antibodybinding properties were characterized by Western blots. Zinc-dependentantibody recognition was maintained in the Trxloop protein althoughthe apparent antibody affinity was lower. This Trxloop proteinbound to an immobilized metal affinity chromatography matrix,similar to a `histidine-patch' thioredoxin variant, and wasreversibly precipitated by 1 mM Zn²⁺ or Cu²⁺ ions. Residuesimportant for zinc and antibody binding were determined by site-directedmutagenesis. The Trxloop antibody affinity was increased bysaturation mutagenesis. Biotinylated Trxloop (`Biotrxloop')variants of the original and improved affinity Trxloop proteinswere constructed and characterized by surface plasmon resonancemeasurements. Increased antibody affinity was partially dueto a slower antibody desorption rate, although the relativeadsorption rates were dependent on the amount of immobilizedBiotrxloop protein, indicating an influence of avidity on theapparent affinity.