Colorimetric detection of DNA, small molecules, proteins, and ions using unmodified gold nanoparticles and conjugated polyelectrolytes.

We have demonstrated a novel sensing strategy employing single-stranded probe DNA, unmodified gold nanoparticles, and a positively charged, water-soluble conjugated polyelectrolyte to detect a broad range of targets including nucleic acid (DNA) sequences, proteins, small molecules, and inorganic ions. This nearly "universal" biosensor approach is based on the observation that, while the conjugated polyelectrolyte specifically inhibits the ability of single-stranded DNA to prevent the aggregation of gold-nanoparticles, no such inhibition is observed with double-stranded or otherwise "folded" DNA structures. Colorimetric assays employing this mechanism for the detection of hybridization are sensitive and convenient--picomolar concentrations of target DNA are readily detected with the naked eye, and the sensor works even when challenged with complex sample matrices such as blood serum. Likewise, by employing the binding-induced folding or association of aptamers we have generalized the approach to the specific and convenient detection of proteins, small molecules, and inorganic ions. Finally, this new biosensor approach is quite straightforward and can be completed in minutes without significant equipment or training overhead.

Insights into π-conjugated small molecule neat films and blends as determined through photoconductivity.

Spectrally dependent steady-state photoconductivity is a convenient method to gain insight into the charge generation and transport processes within a given material. In this work, we report on the photoconductive response of solution-processed neat films and blends of the fullerene, PC(71)BM, and the donor-acceptor small-molecule, p-DTS(PTTh(2))(2), as function of the processing additive, diiodooctance (DIO). The results, when considered in the context of their structural, optical, and electronic properties give insight into the dominant carrier generation and charge transport mechanisms in each of these molecular systems.