| Abstract
| - The combination of high metal selectivity of DNAzymes with the strong distance-dependent opticalproperties of metallic nanoparticles has presented considerable opportunities for designing colorimetricsensors for metal ions. We previously communicated a design for a colorimetric lead sensor based on theassembly of gold nanoparticles by a Pb2+-dependent DNAzyme. However, heating to 50 °C followed by acooling process of ∼2 h was required to observe the color change. Herein we report a new improveddesign that allows fast (<10 min) detection of Pb2+ at ambient temperature. This improvement of sensorperformance is a result of detailed studies of the DNAzyme and nanoparticles, which identified “tail-to-tail”nanoparticle alignment, and large (42 nm diameter) nanoparticle size as the major determining factors inallowing fast color changes. The optimal conditions for other factors such as temperature (35 °C) andconcentrations of the DNAzyme (2 μM), its substrate (3 nM), and NaCl (300 mM) have also been determined.These results demonstrate that fundamental understanding of the DNAzyme biochemistry and nanoparticlescience can lead to dramatically improved colorimetric sensors.
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