Calf thymus DNA-stabilized polythiophene fluorescence probe for label-free detection of spermine.

It is a challenge to detect molecules lacking a chromophore, such as polyamines, by optical methods since they are insensitive to light. In order to detect the optical signals, it is compulsory to derive these molecules with optical labels, which, however, is complicated, time-consuming and may be expensive. In this work, a highly specific strategy for spermine detection is developed on the basis of the iodide-induced conformational change of polythiophene. By using the triplex complex of negatively charged double-stranded calf thymus DNA (ctDNA)-stabilized cationic polythiophene as a fluorescent probe, the highly specific detection of spermine could be realized since polythiophene, which will be released from the triplex complex owing to the condensation and aggregation of ctDNA with spermine, undergoes a conformational change from the random-coiled non-planar state to the highly conjugated planar form in the presence of iodide, resulting in a yellow-to-red color conversion and fluorescence quenching. The quenched fluorescence was found to be proportional to the spermine concentrations in the range of 1.2-50 µM with the limit of detection (LOD) being 0.5 µM (3σ/k).

Enhanced plasmon resonance light scattering signals of colloidal gold resulted from its interactions with organic small molecules using captopril as an example.

Gold nanoparticles are known for their plasmon resonance absorption (PRA) depending on their size. Our this investigation shows that plasma resonance light scattering (PRLS) signals in the corresponding PRA region could be measured using a common spectrofluorometer, and be enhanced when aggregation of gold nanoparticles occurs due to their interaction with organic small molecules (OSMs). Using captopril (Cap) as an example, we investigated the interactions of gold nanoparticles with OSMs in order to propose a general method of OSMs such as typical clinic organic drugs. In aqueous medium of pH 2.09, there are about 2.2 x 10(3) Cap molecules covalently binding to the surface of a 10-nm diameter gold nanoparticle through the thiol functional group of Cap, and thus forms a core-shell assembly of [(Au)(31000)]@[(Cap)(2200)], displaying strong enhanced PRLS signals in the PRA region of gold colloid. The PRLS intensities characterized at 553.0 nm were found to be proportional to the concentration of Cap over the range of 0.1-1.7 mg L(-1) with the determination limit (3sigma) of 32.0 microg L(-1). With that, Cap in pharmaceutical preparations could be determined with the recovery of 97.0-104.5% and R.S.D. of less than 2.4%.