Fluorogenic nanocrystals for highly sensitive detection of C-reactive protein.

A solid-phase sandwich fluorescence immunoassay using nanocrystals of a fluorogenic precursor, fluorescein diacetate (FDA), conjugated with monoclonal antibodies for the detection of C-reactive protein (CRP), is described. FDA nanocrystals were coated with distearoylglycerophosphoethanolamine (DSPE), modified with amino(poly(ethylene glycol))(PEG(2000)-Amine) as an interface for coupling biomolecules. CRP was chosen as a model analyte because of its widely accepted role as a marker for acute inflammation and prospective heart failure. A low limit of detection (1.10 microg l(-1)) and high precision (CV = 2.72-9.48%) were achieved. Following the immunoreaction, the monoclonal anti-CRP conjugated nanocrystals were released by hydrolysis and dissolution instigated by the addition of a large volume of organic solvent-sodium hydroxide mixture. Using human serum samples from 66 patients with high heart attack risk and 19 healthy blood donors, this CRP fluorescence immunoassay showed a good correlation to the commercially available, turbidimetric immunoassay for CRP. This result was corroborated by the Bland-Altman plot that showed a mean difference between the two methods of only 0.36+/-1.46 mg l(-1). The study demonstrates that the organic fluorogenic FDA nanocrystals can be applied for the detection of CRP, which is a clinically interesting plasma protein with a low limit of detection.

Molecular signal transduction by conformational transmission: use of tetrasubstituted perhydroanthracenes as transducers.

2,3,6,7-Tetrasubstituted cis-anti-cis perhydroanthracenes have been studied as conformational transducers for molecular signal transduction. 2,2'-Bipyridine groups attached to the perhydroanthracene through ether linkages were chosen as receptor substituents, while pyrene groups were selected as effectors. A chelation-induced triple ring flip of the perhydroanthracene could be achieved by the complexation of zinc(II) ions at the bipyridine sites of ligands 13 and 15. It was found that two pyrene substituents attached to the perhydroanthracene via a linker with an E double bond and an ester group could be used to monitor the triple ring flip. In the equatorial positions, the pyrenes are sufficiently close to form an excimer in the excited state, giving a fluorescence signal at 480 nm. In the axial positions, they are far away from each other and give mainly a monomer fluorescence signal at 380 nm. Both the bipyridine receptor and the pyrene effector are present in compound 33. The conformational switching 34-->35 (the two conformers of 33) has successfully been used for a signal transduction over a signal distance of 2 nm.