A fluorescent probe sensitive to differences at the single-base-level of DNA has been created by researchers in Japan. 

Hiroshi Abe and colleagues at the Riken Advanced Science Institute, Saitama, Japan developed a system for detecting specific nucleotide sequences in DNA. 

Many fluorescent probes use a pair of quencher and fluorescence dyes, but a detection method with a higher sensitivity is still required to monitor gene expression, explains Abe. 

Abe's method uses two probe DNA molecules, one is attached to a coumarin dye and the other to a nucleophilic group. The two probes bind to adjacent sequences on target DNA or RNA strands, bringing the coumarin and the nucleophile together. 'The two groups form an intermediate complex, which quickly decomposes to give an unmasked amino group on the coumarin accompanied by the transfer of a dinitrobenzene. Thereby, the probe emits a fluorescence signal,' explains Abe. 

Reaction-triggered fluorescent compounds for nucleotide sensing have been described before. But Abe's system offers high signal and very low background fluorescence under biological conditions and is able to discriminate even single base differences. '[The previous methods] have drawbacks, such as the instability of probes in biological conditions, the requirement for a catalyst and the toxicity of the compounds used,' he notes.

'Our future aim is the detection of RNA species in living cells and simple gene diagnosis that is carried out by simply mixing the probe with cells,' concludes Abe. 

Michael Spencelayh 

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