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We report the synthesis of four oligothiophene-5-labeled deoxyuridines. These modified fluorescent nucleosides have been incorporated into oligodeoxynucleotides designed to be used as probes to discriminate, through changes in fluorescence emission, between hybridization with a perfectly complementary strand and that with a single nucleotide mismatch facing the modified uridines. Upon hybridization, remarkable differences (up to 47%) of the emitted light, depending on the uridine facing base, were observed.

Bovine serum albumin (BSA) was reacted with linear and newly synthesized branched oligothiophene N-hydroxysuccinimidyl ester fluorophores (TSEs) in moderately basic carbonate buffer solution. Optically stable BSA-TSE conjugates were obtained with a degree of labeling depending on experimental conditions. Conjugates with high fluorophore to BSA ratios (F/BSA = 8) displayed fluorescence quantum yields in the range of 10-30% in water at pH = 7.2, comparable to the quantum yield (25%) of the BSA-FITC conjugate prepared under the same conditions and with the same degree of labeling.

Oligomers of thiophene are widely studied compounds for their electronic and optoelectronic properties. Despite their strong fluorescence, their use as markers for biomolecules, especially for oligonucleotides (ONs), is still largely unexplored. Here, we describe the synthesis of a series of ON molecular beacons employing different oligothiophenes as fluorescent probes and discuss their fluorescence emissions in comparative experiments with and without dabcyl as a quencher, in their hairpin and linear conformations, and as duplexes after hybridization with a complementary target.

The synthesis of multicolor fluorescent oligothiophene N-succinimidyl esters (TSEs) is reported, and their optical properties are discussed with the aid of ab initio calculations. The esters were coupled to proteins and to 3'-amino-modified oligonucleotides in mild conditions and with similar modalities. A comparative study of the bioconjugate of IgG1 anti-CD3 antibody labeled with a blue fluorescent TSE and with fluorescein isothiocyanate (FITC) is reported, showing that the former achieves higher photoluminescence intensity and optical stability than the latter. Fluorescence resonance energy transfer experiments with TSE-labeled oligonucleotides and examples of cellular imaging via TSE-labeled proteins are reported.