Complementary bioconjugates based on antibody−antigen interactions were synthesized from luminescent CdTe nanoparticles (NPs). Antigen (bovine serum albumin) was conjugated to red-emitting CdTe NPs, while green-emitting NPs were attached to the corresponding anti-BSA antibody (IgG). The NP bioconjugates were characterized by native and SDS−PAGE electrophoresis, gel-permeation HPLC, and circular dichroism. Antigen−antibody binding affinity was evaluated by enzyme-linked immunosorbent assay (ELISA). The formation of BSA−IgG immunocomplex resulted in the Fo 1rster resonance energy transfer (FRET) between the two different NPs: the luminescence of green-emitting NPs was quenched whereas the emission of the red-emitting NPs was enhanced. The luminescence recovered when the immunocomplex was exposed to an unlabeled antigen. The immunocomplexes can be considered as a prototype of NP superstructures based on biospecific ligands, while the competitive FRET inhibition can be used in an immunoassay protocol.

Conjugates of bovine serum albumin and CdTe nanoparticles capped with l-cysteine have been synthesized via a one-pot glutaric dialdehyde cross-linking procedure. Diads (1:1) with some amount of 2:1 albumin−nanoparticle assemblies preferably form in this reaction, as evidenced by gel electrophoresis. Circular dichroism spectroscopy demonstrates that the tertiary structure of the protein remains largely intact after the conjugation. Attachment of protein moieties result in a significant increase of CdTe emission, which is attributed to the resonance energy transfer from the tryptophan moieties of albumin to CdTe nanoparticles acting as receptors for the protein antennae.

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The rapid Friedel-Crafts chromogenic acylation of alkene groups at ambient temperatures using a 25:1 mixture of 98% acetyl chloride and 70% perchloric acid is shown to have all the properties needed to serve as a potential quality control reagent that can be used to routinely discriminate among steroid analogs. Although ostensibly a non-selective reagent, from these and prior applications in terpenes and polyunsaturated acid esters, it is seen that the reaction is capable of discriminating bewteen geometric isomers and even enantiomers. The selectivity towards acylation of the alpha- over the beta-position at C-17 makes the method adaptable to screening for anabolic steroids. Reactions at that position produce the more unusual results, including a positive color reaction for alpha-methyltestosterone even though there is no alkene functional group in the vicinity of C-17. For molecules with more than one alkene, concurrent acylations are independent one from the other and, in the absence of any interferences, their spectral properties are found to be additive.

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