A single-cell drug efflux assay in bacteria by using a directly accessible femtoliter droplet array

Active efflux of drugs, such as antibiotics, from a cell is one of the major mechanisms that cause multi-drug resistance in bacteria. Here we report a method to assess drug efflux activity in individual Escherichia coli cells enclosed and isolated in a directly accessible femtoliter droplet array with a fluorogenic compound. The inhibitory effect of a chemical compound on an exogenously expressed efflux pump system from pathogenic bacteria was easily detected at the single-cell level. We also present a proof-of-principle experiment to screen for the gene encoding a drug efflux pump by collecting individual droplets containing single cells in which the drug efflux activity was restored after introduction of the exogenous gene from pathogenic bacteria. Our approach will be a useful tool to screen novel pump inhibitors and efflux pump genes, and to overcome infectious diseases caused by multi-drug-resistant bacteria.     

An optical waveguide bend with enhanced curvature and the optimization of its structure

We have investigated a waveguide bend having enhanced curvature with reduced loss. The waveguide width is made wider toward the inner side of the bend. The numerical analysis, by means of the beam propagation method, showed that the loss of the proposed bend is lower than that of an abrupt bend or a smooth bend of constant curvature. For a typical waveguide, we have optimized the structure of the bend and achieved one order of loss reduction in comparison with an abrupt bend of the same angle.     

Effects of Small Signal Injection on Laser Diode Pumped Hybrid Bistable System with Large Delay

Effects of small signal injection on an electro-optical bistable system with a very large delay are theoretically and experimentally investigated from the viewpoint of linear stability analysis. The resonance phenomena and frequency locking are observed when sinusoidal and rectangular small signals are additively injected into the system. Experiments confirm that theoretical results obtained by linear stability analysis are good predictions of the effects of both resonance and frequency-locking phenomena and show the dependence of these phenomena on the system parameters. As an application of the frequency locking phenomenon to the dynamical memory, the phase identification of the memory oscillation using the frame pulse externally injected is successfully executed.     

Determination of cadmium and bismuth in high-purity zinc metal by inductively coupled plasma mass spectrometry with on-line matrix separation

Traces of cadmium and bismuth in high-purity zinc metal were determined by inductively coupled plasma mass spectrometry (ICP-MS) in combination with flow injection (FI) on-line matrix separation (FI-ICP-MS). The anion-exchange separation method of the potassium iodide (KI) system was applied to the separation of the analytes from the matrix zinc. The analytes, cadmium and bismuth, were adsorbed on the anion-exchange (BIO. RAD AG1-X8) mini-column (1.0 mm i.d.x 100 mm bed length), while the matrix zinc can be completely removed from the anion-exchange resin. The analytes were eluted by 2 mol/l HNO(3) and directly introduced into the ICP-MS. The detection limits (D.L.) obtained by using a single injection (350 microl) were 0.81 and 0.075 ng g(-1) for cadmium and bismuth, respectively. In the case of multi-injection concentration onto the anion-exchange mini-column (five injections 350 microl each), the detection limits could be improved to 0.16 and 0.014 ng g(-1) for cadmium and bismuth, respectively. The reproducibilities of the single injection and the multi-injection method were satisfactory with a relative standard deviation of less than 5% (at the 10 and 1 ng ml(-1) level for the single injection and the multi-injection method, respectively). The method was successfully applied to the determination of trace impurities in four samples of high-purity zinc metal (7 nines grade) and three standard reference materials of high-purity unalloyed zinc samples (from NIST).     

Interaction between dyes and polyelectrolytes. I. Effect of polyelectrolytes on the reaction of methylene blue with 1-benzyl-1,4-dihydronicotinamide

The effect of polyelectrolytes on the reaction of methylene blue with 1-benzyl-1,4-dihydronicotinamide was investigated. An accelerating effect was observed on addition of sodium polystyrenesulfonate of poly(potassium p-styrenesulfonate). On the other hand, deceleration was observed on addition of potassium polyvinylsulfate. No appreciable effect was observed when sodium p-toluenesulfonate or potassium chloride was used as an electrolyte. An obvious color change was observed when methylene blue is bound to these anionic polyelectrolytes. Some correlations with spectral change of methylene blue and acceleration or deceleration effect are discussed.