Sample pre-concentration with high enrichment factors at a fixed location in paper-based microfluidic devices.

The lack of sensitivity is a major problem among microfluidic paper-based analytical devices (µPADs) for early disease detection and diagnosis. Accordingly, the present study presents a method for improving the enrichment factor of low-concentration biomarkers by using shallow paper-based channels realized through a double-sided wax-printing process. In addition, the enrichment factor is further enhanced by exploiting the ion concentration polarization (ICP) effect on the cathodic side of the nanoporous membrane, in which a stationary sample plug is obtained. The occurrence of ICP on the shallow-channel µPAD is confirmed by measuring the current-voltage response as the external voltage is increased from 0 to 210 V (or the field strength from 0 to 1.05 × 10(4) V m(-1)) over 600 s. In addition, to the best of our knowledge, the electroosmotic flow (EOF) speed on the µPAD fabricated with a wax-channel is measured for the first time using a current monitoring method. The experimental results show that for a fluorescein sample, the concentration factor is increased from 130-fold in a conventional full-thickness paper channel to 944-fold in the proposed shallow channel. Furthermore, for a fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) sample, the proposed shallow-channel µPAD achieves an 835-fold improvement in the concentration factor. The concentration technique presented here provides a novel strategy for enhancing the detection sensitivity of µPAD applications.

Effect of display size on visual attention.

Attention plays an important role in the design of human-machine interfaces. However, current knowledge about attention is largely based on data obtained when using devices of moderate display size. With advancement in display technology comes the need for understanding attention behavior over a wider range of viewing sizes. The effect of display size on test participants' visual search performance was studied. The participants (N = 12) performed two types of visual search tasks, that is, parallel and serial search, under three display-size conditions (16 degrees, 32 degrees, and 60 degrees). Serial, but not parallel, search was affected by display size. In the serial task, mean reaction time for detecting a target increased with the display size.

Charges in the cytoplasmic pore control intrinsic inward rectification and single-channel properties in Kir1.1 and Kir2.1 channels.

An E224G mutation of the Kir2.1 channel generates intrinsic inward rectification and single-channel fluctuations in the absence of intracellular blockers. In this study, we showed that positively charged residues H226, R228 and R260, near site 224, regulated the intrinsic inward rectification and single-channel properties of the E224G mutant. By carrying out systematic mutations, we found that the charge effect on the intrinsic inward rectification and single-channel conductance is consistent with a long-range electrostatic mechanism. A Kir1.1 channel where the site equivalent to E224 in the Kir2.1 channel is a glycine residue does not show inward rectification or single-channel fluctuations. The G223K and N259R mutations of the Kir1.1 channel induced intrinsic inward rectification and reduced the single-channel conductance but did not generate large open-channel fluctuations. Substituting the cytoplasmic pore of the E224G mutant into the Kir1.1 channel induced open-channel fluctuations and intrinsic inward rectification. The single-channel conductance of the E224G mutant showed inward rectification. Also, a voltage-dependent gating mechanism decreased open probability during depolarization and contributed to the intrinsic inward rectification in the E224G mutant. In addition to an electrostatic effect, a close interaction of K(+) with channel pore may be required for generating open-channel fluctuations in the E224G mutant.

Electrostatics in the cytoplasmic pore produce intrinsic inward rectification in kir2.1 channels.

Inward rectifier K+ channels are important in regulating membrane excitability in many cell types. The physiological functions of these channels are related to their unique inward rectification, which has been attributed to voltage-dependent block. Here, we show that inward rectification can also be induced by neutral and positively charged residues at site 224 in the internal vestibule of tetrameric Kir2.1 channels. The order of extent of inward rectification is E224K mutant > E224G mutant > wild type in the absence of internal blockers. Mutating the glycines at the equivalent sites to lysines also rendered weak inward rectifier Kir1.1 channels more inwardly rectifying. Also, conjugating positively charged methanethiosulfonate to the cysteines at site 224 induced strong inward rectification, whereas negatively charged methanethiosulfonate alleviated inward rectification in the E224C mutant. These results suggest that charges at site 224 may control inward rectification in the Kir2.1 channel. In a D172N mutant, spermine interacting with E224 and E299 induced channel inhibition during depolarization but did not occlude the pore, further suggesting that a mechanism other than channel block is involved in the inward rectification of the Kir2.1 channel. In this and our previous studies we showed that the M2 bundle crossing and selectivity filter were not involved in the inward rectification induced by spermine interacting with E224 and E299. We propose that neutral and positively charged residues at site 224 increase a local energy barrier, which reduces K+ efflux more than K+ influx, thereby producing inward rectification.

A ring of negative charges in the intracellular vestibule of Kir2.1 channel modulates K+ permeation.

The glutamate at site 224 of a Kir2.1 channel plays an important role in K+ permeation. The single-channel inward current flickers with reduced conductance in an E224G mutant. We show that open-channel fluctuations can also be observed in E224C, E224K, and E224Q mutants. Yet, open-channel fluctuations were not observed in either the wild-type or an E224D mutant. Introducing a negatively charged methanethiosulfonate reagent to the E224C mutant irreversibly increased channel conductance and eliminated open-channel fluctuations. These results suggest that although the negatively charged residue 224 is located at the internal vestibule, it is important for smooth inward K+ conduction. We identified a substate in the E224G mutant and showed that open-channel fluctuations are mainly attributed to rapid transitions between the substate and the main state. Also, we characterized the voltage- and ion-dependence of the substate kinetics. The open-channel fluctuations decreased in internal NH4+ or Tl+ as compared to internal K+. These results suggest that NH4+ and Tl+ gate the E224G mutant in a more stable state. Based on an ion-conduction model, we propose that the appearance of the substate in the E224G mutant is due to changes of ion gating in association with variations of ion-ion interaction in the permeation pathway.

The effects of spermine on the accessibility of residues in the M2 segment of Kir2.1 channels expressed in Xenopus oocytes.

We examined the effects of spermine binding to aspartate at site 172 on the accessibility of internal trimethylammonioethylmethane thiosulphonate (MTSET) to substituted cysteines within the pore of a Kir2.1 channel. Spermine prevented MTSET modification in Q164C and G168C mutants, indicating that sites 164 and 168 are located externally to the spermine binding site. The rates of MTSET modification were significantly reduced by spermine in I176C mutants, indicating that site 176 is located internally to D172 and that the bound spermine hinders the reaction of MTSET with cysteine at site 176. Spermidine, putrescine and Mg2+ also decreased MTSET modification at site 176. The order of effect is putrescine > spermidine approximately = spermine approximately = Mg2+. To account for the electrostatic and physical repulsion between MTSET and polyamines, possible locations of polyamines in the pore are discussed. In D172C mutants, the spermine that bound to sites 224 and 299 completely inhibited channels at +40 mV, yet MTSET remained accessible to site 172. In addition, in the D172C mutant, spermine did not affect the exit rate of Ba2+ bound to the threonine at the site 141. These results indicate that spermine bound at the cytoplasmic pore induces channel closure at positions 141-172. The effects of spermine on the accessibility of amino acids in the pore may shed light on the structural and functional relationships of the Kir2.1 channels during inward rectification.

Sonography for monitoring closed reduction of displaced extra-articular distal radial fractures.

BACKGROUND: Closed reduction and cast immobilization are employed in the primary treatment of most distal radial fractures, and conventional radiographic techniques have been essential and effective in monitoring these reductions. Radiation-free ultrasonography, however, can provide both real-time and dynamic multiple-plane images with a small and simple-to-use transducer that can be operated with only one hand. We therefore wanted to see if the real-time and dynamic multiple-plane observation capabilities of ultrasonography would allow an orthopaedic surgeon to perform a closed reduction without multiple attempts, as are frequently required when only conventional radiographic techniques are used. METHODS: Sonographically guided closed reduction was performed in twenty-seven consecutive wrists with an acute distal radial fracture. The efficacy of this method was evaluated and compared with that of conventional radiographic techniques. RESULTS: The sonographic images delineated the fractures as accurately as did the conventional radiographs. All parameters measured on the sonograms and radiographs showed substantial restoration of anatomic alignment after reduction, and all measurements were similar on the two types of images. CONCLUSIONS: Sonographically guided monitoring compared well with conventional radiographic techniques during closed reduction of extra-articular distal radial fractures. Sonography is an accurate, simple, and radiation-free tool that provides the substantial benefits of dynamic multiple-plane and real-time observation.