Heavy water detection using ultra-high-Q microcavities

Ultra-high-Q optical microcavities (Q>10(7)) provide one method for distinguishing chemically similar species. Resonators immersed in H(2)O have lower quality factors than those immersed in D(2)O due to the difference in optical absorption. This difference can be used to create a D(2)O detector. This effect is most noticeable at 1,300 nm, where the Q(H(2)O) is 106 and the Q(D(2)O) is 107. By monitoring Q, concentrations of 0.0001% [1 part in 106 per volume] of D(2)O in H(2)O have been detected. This sensitivity represents an order of magnitude improvement over previous techniques. Reversible detection was also demonstrated by cyclic introduction and flushing of D(2)O.     

Frequency-domain spectroscopic study of the PS I-CP43' supercomplex from the cyanobacterium Synechocystis PCC 6803 grown under iron stress conditions

Absorption, fluorescence excitation, emission, and hole-burning (HB) spectra were measured at liquid helium temperatures for the PS I-CP43' supercomplexes of Synechocystis PCC 6803 grown under iron stress conditions and for respective trimeric PS I cores. Results are compared with those of room temperature, time-domain experiments (Biochemistry 2003, 42, 3893) as well as with the low-temperature steady-state experiments on PS I-CP43' supercomplexes of Synechococcus PCC 7942 (Biochim. Biophys. Acta 2002, 1556, 265). In contrast to the CP43' of Synechococcus PCC 7942, CP43' of Synechocystis PCC 6803 possesses two low-energy states analogous to the quasidegenerate states A and B of CP43 of photosystem II (J. Phys. Chem. B 2000, 104, 11805). Energy transfer between the CP43' and the PS I core occurs, to a significant degree, through the state A, characterized with a broader site distribution function (SDF). It is demonstrated that the low temperature (T = 5 K) excitation energy transfer (EET) time between the state A of CP43' (IsiA) and the PS I core in PS I-CP43' supercomplexes from Synechocystis PCC 6803 is about 60 ps, which is significantly slower than the EET observed at room temperature. Our results are consistent with fast (< or =10 ps) energy transfer from state B to state A in CP43'. Energy absorbed by the CP43' manifold has, on average, a greater chance of being transferred to the reaction center (RC) and utilized for charge separation than energy absorbed by the PS I core antenna. This indicates that energy is likely transferred from the CP43' to the RC along a well-defined path and that the "red antenna states" of the PS I core are localized far away from that path, most likely on the B7-A32 and B37-B38 dimers in the vicinity of the PS I trimerization domain (near PsaL subunit). We argue that the A38-A39 dimer does not contribute to the red antenna region.     

A Microreactor with Thousands of Subcompartments: Enzyme‐Loaded Liposomes within Polymer Capsules

Fully loaded : Noncovalent anchoring of liposomes into polymer multilayered films with cholesterol‐modified polymers allows the preparation of capsosomes—liposome‐compartmentalized polymer capsules (see picture). A quantitative enzymatic reaction confirmed the presence of active cargo within the capsosomes and was used to determine the number of subcompartments within this novel biomedical carrier system.

     

Single molecule detection in nanofluidic digital array enables accurate measurement of DNA copy number

Digital polymerase chain reaction (PCR) is a promising technique for estimating target DNA copy number. PCR solution is distributed throughout numerous partitions, and following amplification, target DNA copy number is estimated based on the proportion of partitions containing amplified DNA. Here, we identify approaches for obtaining reliable digital PCR data. Single molecule amplification efficiency was significantly improved following fragmentation of total DNA and bias in copy number estimates reduced by analysis of short intact target DNA fragments. Random and independent distribution of target DNA molecules throughout partitions, which is critical to accurate digital PCR measurement, was demonstrated by spatial distribution analysis. The estimated relative uncertainty for target DNA concentration was under 6% when analyzing five digital panels comprising 765 partitions each, provided the panels contained an average of 212 to 3,365 template molecules. Partition volume was a major component of this uncertainty estimate. These findings can be applied to other digital PCR studies to improve confidence in such measurements. Figure Digital PCR amplification plot (left) and panel read out (right) of HindIII-digested pIRMM69. pIRMM69 contains one HindIII restriction enzyme site outside the hmg and transgene fragments used as targets in PCR. Red boxes with white shade denote positive hits containing one or more target DNA molecules, and white boxes with grey shade refer to no target being amplified.