RESUMEN
Förster resonance energy transfer (FRET) between lanthanide ion complexes (L) acting as donors and luminescent semiconductor quantum dots (QD) acting as acceptors is discussed in the terms of advantages and disadvantages for its application in immunoassay. L-QD-FRET is potentially a powerful tool that can be used to detect and confirm formation of immunocomplexes, but until now it had very limited practical analytical application. Therefore, the main aim of this review is to analyze all possibilities, advantages, and disadvantages of L-QD-FRET in immunoassay applications. Considering L and QD respectively applied as donor and acceptor, the most advantageous properties for analytical purposes are large decay time of L complexes and the high absorption of QD. L complexes' extremely long decay times make it possible to directly detect FRET through enhancement of QDs decay time as a result of energy transfer. Very high QD absorption predetermines extremely large Förster radii (ca. 10nm), which means that FRET can be utilized for proteins and protein complexes, such as antigen-antibody systems.
RESUMEN
CONTEXT: A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions. AIMS: To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216. METHODS: We used the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel to observe all rotational transitions up to the J = 3 level (three ortho- and six para-NH3 lines). We conducted non-LTE multilevel radiative transfer modelling, including the effects of near-infrared (NIR) radiative pumping through vibrational transitions. The computed emission line profiles are compared with the new HIFI data, the radio inversion transitions, and the MIR absorption lines in the ν2 band taken from the literature. RESULTS: We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3 abundances relative to molecular hydrogen were (2.8 ± 0.5) × 10-8 for ortho-NH3 and [Formula: see text] for para-NH3, consistent with an ortho/para ratio of 1. These values are in a rough agreement with abundances derived from the inversion transitions, as well as with the total abundance of NH3 inferred from the MIR absorption lines. To explain the observed rotational transitions, ammonia must be formed near to the central star at a radius close to the end of the wind acceleration region, but no larger than about 20 stellar radii (1σ confidence level).
