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We have developed a simple and homogeneous fluorescence assay, comprised of 3-mercaptopropionic acid (MPA) and DNA-Cu/Ag nanoclusters (NCs) in aqueous solution, for the detection of [Cu.sup.2+] ions. The fluorescence of the DNA-Cu/Ag NCs was quenched by MPA, which was recovered in the presence of [Cu.sup.2+] ions. This MPA-induced fluorescence quenching arises through changes in the DNA conformation that occur after interactions between MPA and the Cu/Ag clusters. The MPA-induced fluorescence quenching displayed typical characteristics in Stern-Volmer plots; it followed a static quenching mechanism. The presence of [Cu.sup.2+] ions resulted in the oxidation of MPA to form a disulfide compound, leading to recovery of the fluorescence of the DNA-Cu/Ag NCs. The fluorescence of the DNA-Cu/Ag NCs in the presence of MPA increased upon increasing the concentration of [Cu.sup.2+] ions over the range from 5 to 200 nM. The DNA-Cu/Ag NC probe provided the limit of detection (at a signal-to-noise ratio of 3) for [Cu.sup.2+] ions of 2.7 nM, with high selectivity (by at least 2300-fold over other tested metal ions). We validated the practicality of using this probe for the detection of [Cu.sup.2+] ions in environmental samples through analyses of Montana soil and pond water samples. 10.1021/ac101659d

The presence of alkali cation adductions of oligonucleotides commonly deteriorates matrix-assisted laser desorption/ionization (MALDI) mass spectra. Thus, desalting is required for oligonucleotide samples prior to MALDI MS analysis in order to prevent the mass spectra from developing poor quality. In this paper, we demonstrate a new approach to extract traces of oligonucleotides from aqueous solutions containing high concentrations of salts using microwave-assisted extraction. The C18-presenting magnetite beads, capable of absorbing microwave irradiation, are used as affinity probes for oligonucleotides with the addition of triethylammonium acetate as the counterions. This new microwave-assisted extraction approach using magnetite beads as the trapping agents and as microwave-absorbers has been demonstrated to be very effective in the selective binding of oligonucleotides from aqueous solutions. The extraction of oligonucleotides from solutions onto the C18-presenting magnetite beads takes only 30 s to enrich oligonucleotides in sufficient quantities for MALDI MS analysis. After using this desalting approach, alkali cation adductions of oligonucleotides are dramatically reduced in the MALDI mass spectra. The presence of saturated NaCl (~6 M) in the oligonucleotide sample is tolerated without degrading the mass spectra. The detection limit for [d(A).sub.6] is ~2.8 fmol.

We herein demonstrate superparamagnetic [Fe.sub.3][O.sub.4] nanoparticles coated with nitrilotriacetic acid derivative (NTA) that can bind with different immobilized metal ions are capable of probing diverse target species. Immobilized Ni(II) on the surfaces of the NTA-magnetic nanoparticles have the capability of selectively trapping histidine (His)-tagged proteins such as a mutated streptopain tagged with 6 x His, i.e., C192S (MW ~42 kDa), from cell lysates. Enrichment was achieved by vigorously mixing the sample solution and the nanoparticles by pipetting in and out of a sample vial for only 30 s. After enrichment, the probe-target species could be readily isolated by magnetic separation. We also characterized the proteins enriched on the affinity probes using on-probe tryptic digestion under microwave irradiation for only 2 min, followed by matrix-assisted laser desorption/ionization mass spectrometry analysis. Using this enrichment and tryptic digestion, the target species can be rapidly enriched and characterized, reducing the time required for carrying out the complete analysis to less than 10 min. Furthermore, when either Zr(IV) or Ga (III) ions are immobilized on the surfaces of the NTA-magnetic nanoparticles, the nanoparticles have the capability of selectively enriching phosphorylated peptides from tryptic digests of [alpha]-, [beta]-caseins, and diluted milk. The detection limit for the tryptic digests of [alpha]- and [beta]-caseins is ~50 fmol.

Wireless systems offer a unique mixture of connectivity, flexibility, and freedom. It is therefore not surprising that wireless technology is being embraced with increasing vigor. For real-time applications, user satisfaction is closely linked to quantities such as queue length, packet loss probability, and delay. System performance is therefore related to, not only Shannon capacity, but also quality of service (QoS) requirements. This work studies the problem of resource allocation in the context of stringent QoS constraints. The joint impact of spectral bandwidth, power, and code rate is considered. Analytical expressions for the probability of buffer overflow, its associated exponential decay rate, and the effective capacity are obtained. Fundamental performance limits for Markov wireless channel models are identified. It is found that, even with an unlimited power and spectral bandwidth budget, only a finite arrival rate can be supported for a QoS constraint defined in terms of exponential decay rate. Index Terms--Communication systems, effective capacity, fluid models, quality of service (QoS), resource allocation, wireless networks, wireless systems.

In this study, we demonstrated that microwave-assisted enzymatic digestion could be greatly accelerated by multifunctional magnetite beads. The acceleration of microwave-assisted enzymatic digestion by the presence of the magnetite beads was attributable to several features of the beads. Their capacity to absorb microwave radiation leads to rapid heating of the beads. Furthermore, their negatively charged functionalities cause adsorption of proteins with opposite charges onto their surfaces by electrostatic interactions, leading to a concentration on the surfaces of the beads of proteins present in trace amounts in the solution. The adsorbed proteins are denatured and hence rendered vulnerable to enzymatic digestion and are digested on the beads. For microwave heating, 30 s was sufficient for carrying out the tryptic digestion of cytochrome c, in the presence of magnetite beads, while 1 min was adequate for tryptic digestion of myoglobin. The digestion products were characterized by MALDI-MS. This rapid enzymatic digestion allowed the entire time for identification of proteins to be greatly reduced. Furthermore, specific proteins present in trace quantities were enriched from the sample on the magnetite beads and could be rapidly isolated from the sample by employing an external magnetic field. These multiple roles of magnetite beads, as the absorber for microwave irradiation, the concentrating probe, and the agent for unfolding proteins, contributed to their capability of accelerating microwave-assisted enzymatic digestion. We also demonstrated that trypsin immobilized magnetite beads were suitable for use in microwave-assisted enzymatic digestion.