Specific Colorimetric Detection of Proteins Using Bidentate Aptamer‐Conjugated Polydiacetylene (PDA) Liposomes

Abstract

The development of a bidentate aptamer-functionalized polydiacetylene (PDA) liposome sensor that is capable of specifi c colorimetric detection of proteins, directly in complex mixtures (e.g., serum), at sub-micromolar concentrations within 15 min, is reported. In comparison to sensors fabricated with a single aptamer reagent, the conjugation of bidentate aptamer pairs that recognize two distinct exosites of the target protein (thrombin) to the liposome results in signifi cant enhancements of the sensitivity and the specifi city. To elucidate the mechanism behind this enhancement, experimental evidence is presented that suggests that the liposomic aggregation triggered by specifi c, multi-site binding to the target protein is responsible for the improved colorimetric response. Since the colorimetric protein sensor does not require any power or instrumentation, it offers a promising approach towards molecular diagnostics at point-of-care (POC), especially in low-resource settings.

Aptamer-based cell imaging reagents capable of fluorescence switching

“…6 We observed that in the absence of EpCAM, ACP probes are monodisperse and spherical in shape with an approximate diameter of ~364 nm (Fig. S4a and S4d † ).…”

Colorimetric detection of clinical DNA samples using an intercalator-conjugated polydiacetylene sensor

“…All measurements were carried out at 25°C in a cell with an optical path length of 1 cm. To quantify the blue-to-red color transition of PDA vesicles interacting with DNA, the colorimetric response (CR) was calculated as follows: CR (%) ¼[(PB 0 À PB 1 )/PB 0 ] Â 100%, where PB¼A blue /(A blue þA red ); A is the absorbance of the blue (∼645 nm) or red (∼541 nm) component in the UV-visible absorption spectrum; PB 0 is the blue/red ratio of the control sample in the absence of DNA; and PB 1 is the value of the sample after the color change in the presence of DNA (Jung et al, 2010). To determine the limit of detection (LOD) of our sensor with clinical dsDNA samples, various concentrations of 605-bp amplicons were mixed with 9AA-conjugated PDA vesicles.…”

“…Samples were incubated for 1 h and the relationship between dsDNA concentration and quantitative CR value was plotted to determine the LOD. Previous studies have suggested that a change in CR of 10% is readily discernible by the unaided human eye (Jung et al, 2010). Using this metric, we estimate the limit of visual detection of our sensor.…”

“…As predicted, the CR value increased as a function of target DNA concentration (0, 1, 5, 10, 20, 30, 60, 80, or 100 nΜ). Since the color change was readily discernible by naked eye for CR values 410% (Jung et al, 2010), we estimated the LOD of our sensor as ∼20 nM (Fig. 2c).…”

“…With regards to portable and more efficient analytic sensors for detecting dsDNA in clinical samples, conjugated polymer-based sensors (Ho et al, 2002(Ho et al, , 2005Jung et al, 2008Jung et al, , 2010Lee et al, 2007;Wang et al, 2006;Wang and Ma, 2005) have the important advantage of amplifying signals in response to external stimuli as compared to conventional sensors that are based on small molecules (Ali and Li, 2009;Du and Tang, 2011;Li et al, 2009;Li and Rothberg, 2004). The versatile and stable conjugated polydiacetylene (PDA) has useful structural and sensing properties when its head group is linked to ligands that can recognize external stressors such as pH, organic solvents, mechanical stress, and specific molecules.…”