Application of QDs for Probing Biorecognition Processes

DNA-QD conjugates have also been used as luminescent labels in fluorescence in situ hybridization (FISH) assays. The FISH assay is based on the denaturation of genomic DNA and the consecutive hybridization with a fluorescent-labeled DNA sequence, in order to visualize the presence or absence of specific DNA sequences in the chromosomes. For example, a QDs-based FISH labeling method was used to detect the Y chromosome in human sperm cells [74], and also the human metaphase chromosome [150]. The FISH technique was also used for the multiplex cellular detection of different mRNA targets [151], and to visualize a pUClS plasmid inside the Escherichia coli HBlOl bacterium [152]. 

Aptamers are nucleic acid sequences that specifically bind proteins or low molecular-weight substrates. Aptamers are selected from a combinatorial library of lO -lO DNAs, using the Systematic Evolution of Ligands by Exponential Enrichment Process (SELEX). Numerous aptamers that specifically bind proteins or low molecular-weight substrates have been elicited in recent years. Also, their recognition properties have been used extensively to develop electrochemical [162,163] or optical 

QD-based aptamer sensors for the detection of low-molecular-weight substrates have been similarly developed [168]. The aptamer against adenosine monophosphate 

Upon analysis of AMP, the aggregate is separated, and the fluorescence of the QDs is switched on (b) Fluorescence intensity changes as a function ofthe concentration ofAMP. Inset enlargement of the calibration curve in the region 0.0-0.4mM AMP. (Reproduced with permission from ref. [168]. Copyright 2007 American Chemical Society). 

This permitted the detection of cocaine with a detection limit corresponding to 1 X 10 M [169]. The main advantage of this sensing platform over the use of an 

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