Overuse of antibiotics has spawned strains of bacteria whose cell walls are impervious to the crippling blows once delivered by penicillin and its derivatives. One such so-called superbug, methicillin-resistant staphylococcus aureus, although found primarily in prisons and hospitals, has now spread beyond those confines. Despite the controlled use of the drug vancomycin, a last line of defense against MRSA, the latest threat are vancomycin-resistant bacteria, which mutate by deleting a key hydrogen bond that allows the drug to bind and inhibit cell wall growth, thereby mechanically weakening the bacteria . Rachel McKendry at University College London and her collaborators recently demonstrated a nanoscale cantilever system that is sensitive enough to detect the difference between the native drug-sensitive bacteria and the mutated resistant form with the missing hydrogen bond. The researchers coated silicon cantilevers with vancomycin-resistant (DLac in the schematic) and vancomycin-sensitive (DAla ) bacterial cell-wall analogues, then immersed them in a solution containing free vancomycin molecules. As expected, the molecules preferentially bound to the cantilevers coated with the drug-sensitive analogue; those cantilevers experienced a marked deflection—as measured by an optical detector—that equated to an 800-fold difference in binding compared with the cantilevers coated with the drug-resistant analogue. The researchers believe their system will lead to sensitive, nondestructive, and rapid nanomechanical biosensors for high-throughput drug– target interaction studies and will aid in the design of more effective drugs. (J.W. Ndieyira et al., Nat. Nanotechnol., doi: 10.1038/nnano.2008.275 .) — Jermey N.A. Matthews
Recently in Metrology and fundamental constants Category
In the pursuit of a quantum computer, the photon is a leading candidate for the quantum bit, or qubit. Working models of photonic circuits, however, have been unscalable arrangements of bulky mirrors and beamsplitters sitting atop a square-meter-sized table. Now scientists at the Center for Quantum Photonics at the University of Bristol in the UK have printed several dozen photonic circuits onto a silicon wafer. The research team created waveguides by first depositing a doped layer of silica onto the wafer, then patterning 3.5-micron-wide ridges into the silica. Two waveguides are coupled when they approach each other and then diverge, as shown in the figure, allowing evanescent waves to overlap. Using such directional couplers, the researchers not only fabricated on-chip beamsplitters, interferometers, and even a controlled-NOT gate, but combined those devices into photonic circuits. Among their demonstrated results is a high-fidelity, path entangled state of two photons, an important element for quantum computation. The silica-on-silicon photonic circuits may also be applied to quantum metrology and communication technologies. (A. Politi et al., Science 320, 646, 2008 [MEDLINE].) — Jermey N.A. Matthews
