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

Abstract

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.biosensor | aptamer | visual detection | thrombin detection | cocaine detection G old nanoparticle colorimetric biosensors have seen significant applications in diagnostics, environmental monitoring, and antibioterrorism supporting unaided, visual readout (1-12). Commonly, the relevant nanoparticles are covalently modified with either a probe DNA or an aptamer such that hybridization (13-16) or aptamer-target interactions (17-27), for example the scanometric method developed by Mirkin (25), which is a very sensitive and specific tool, crosslink them, inducing aggregation. The second broad approach utilizes unmodified nanoparticles. (28-30) These two approaches, however, suffer from timeconsuming (20-40 h of assembly) and relatively poor (low nanomolar) detection limits, respectively. Here, a unique, colorimetric sensing strategy employing a simple but selective combination of a single-stranded DNA probe, a positively charged, water-soluble conjugated polyelectrolyte, and unmodified gold nanoparticles is demonstrated. The universality of this method allows detection of a broad range of targets, including nucleic acid (DNA) sequences, proteins, small molecules, and ino rganic ions. Our approach is rapid (turnaround time is 5-10 min) and sensitive (picomolar concentrations of target DNA are readily detected with the naked eye, even in complex sample matrices like blood serum). Hence, an operator with minimum scientific overhead can easily employ this technique.Generally, the gold nanoparticle applications typically rely on a quantitative coupling between target recognition and the aggregation of the nanoparticles, which, in turn, leads to a dramatic change in the photonic properties-and thus the color-of the nanoparticle solution. This colorimetric "readout" avoids the relative complexity inherent...

Tailoring Conformation-Induced Chromism of Polythiophene Copolymers for Nucleic Acid Assay at Resource Limited Settings

“…29 Naked eye detection of nucleic acids by using mixtures of CPEs and gold nanoparticles were successfully presented pending validation with clinical samples. 30 Electrochemical approaches on quantitative analysis of miRNA have claimed subnanomolar detection sensitivities. 31 Although detection at nanomolar concentration levels have been reported, most of the reported methodologies involve tedious synthesis procedures and sophisticated assay protocols and require trained personnel for interpretation of responses.…”

Properties and Customization of Sensor Materials for Biomedical Applications

“…The addition of sodium chloride caused aggregation and therefore a change in color from red to blue. Similarly, bare Au-NPs and cationic conjugated polyelectrolytes were employed for the detection of DNA, cocaine, and thrombin (228). Interestingly, the latter method provides a simple and rapid way to visually detect thrombin at a concentration as low as 10 nM.…”

Cancer cell sensing and therapy using affinity tag-conjugated gold nanorods

“…The colour of the nanoparticles also changes depending on the absorption maxima variations. This tuneability of the optical absorption facilitates various biomedical applications including, but not limited to, colorimetric detection assays for proteins [15][16][17][18], DNAs [18][19][20][21] and cancer cells [22] that operate in the visible range; photothermal therapy [23][24][25][26][27][28], photoacoustic imaging (PAI) [29][30][31][32][33][34] and heat-induced drug delivery [35] that operate in the NIR range.…”