Ultrasensitive detection of lead (II) based on fluorescent aptamer-functionalized carbon nanotubes

Lead contamination is a serious environmental problem with toxic effects in human. Here, we developed a simple and sensitive sensing method employing ATTO 647N/aptamer-SWNT ensemble for detection of Pb2+. This method is based on the super quenching capability of single-walled carbon nanotubes (SWNTs), high affinity of the aptamer toward Pb2+ and different propensities of ATTO 647N-aptamer and ATTO 647N-aptamer/Pb2+ complex for adsorption on SWNTs. In the absence of Pb2+, the fluorescence of ATTO 647N-aptamer is efficiently quenched by SWNTs. Upon addition of Pb2+, the aptamer binds to its target, leading to the formation of a G-quadruplex/Pb2+ complex and does not interact with SWNTs and ATTO 647N-aptamer starts fluorescing. This sensor exhibited a high selectivity toward Pb2+ and a limit of detection (LOD) as low as 0.42 nM was obtained. Also this sensor could be applied for detection of Pb2+ ions in tap water and biological sample like serum with high sensitivity.