Electrochemical biosensors employing an internal electrode attachment site and achieving reversible, high gain detection of specific nucleic acid sequences

Electrochemical DNA (E-DNA) sensors, which are rapid, reagentless, and readily integrated into microelectronics and microfluidics, appear to be a promising alternative to optical methods for the detection of specific nucleic acid sequences. Keeping with this, a large number of distinct E-DNA architectures have been reported to date. Most, however, suffer from one or more drawbacks, including low signal gain (the relative signal change in the presence of complementary target), signal-off behavior (target binding reduces the signaling current, leading to poor gain and raising the possibility that sensor fouling or degradation can lead to false positives), or instability (degradation of the sensor during regeneration or storage). To remedy these problems, we report here the development of a signal-on E-DNA architecture that achieves both high signal gain and good stability. This new sensor employs a commercially synthesized, asymmetric hairpin DNA as its recognition and signaling probe, the shorter arm of which is labeled with a redox reporting methylene blue at its free end. Unlike all prior E-DNA architectures, in which the recognition probe is attached via a terminal functional group to its underlying electrode, the probe employed here is affixed using a thiol group located internally, in the turn region of the hairpin. Hybridization of a target DNA to the longer arm of the hairpin displaces the shorter arm, allowing the reporter to approach the electrode surface and transfer electrons. The resulting device achieves signal increases of ～800% at saturating target, a detection limit of just 50 pM, and ready discrimination between perfectly matched sequences and those with single nucleotide polymorphisms. Moreover, because the hairpin probe is a single, fully covalent strand of DNA, it is robust to the high stringency washes necessary to remove the target, and thus, these devices are fully reusable.     

Comparison of the effects of acebutolol (Sectral) and practolol (Eraldin) on airways obstruction in asthmatics

The effects of oral practolol (Eraldin, I.C.I. Ltd) (300 mg) and acebutolol (Sectral, May & Baker Ltd) (300 mg) were compared in a placebo-controlled, crossover study in ten asthmatics. 2. Pulse rate, forced expiratory volume in one second (FEV1) and specific airways conductance were measured before and after a bronchodilator and the same procedure was repeated after taking acebutolol, practolol or placebo. 3. A mean increase in resting airways obstruction and reduction in bronchodilator response were evident with both drugs. The differences were statistically significant only after acebutolol for the logarithm of specific conductance. Mean plasma levels of the two drugs were similar. The response to both drugs was similar in the same patient and unrelated to severity of asthma. Mean reduction in resting pulse rate was statisitcally greater after acebutolol compared with placebo but not after practolol compared with placebo. 4. In any individual the beta-adrenoceptor blocking response is unpredictable and any beta-adrenoceptor blocking drug must be used with extreme caution in asthmatics.