摘要： Recently a few RNA-cleaving DNAzymes have been isolated with excellent specificity for Na+, and some of them contain a Na+ binding aptamer. This metal recognition mechanism is different from most previously reported DNAzymes. Previous studies using 2-aminopurine (2AP) as a probe have indicated interesting local folding by Na+. In this work, fluorescence resonance energy transfer (FRET) was used to probe the global folding of the Ce13d DNAzyme, one of the Na+-specific DNAzymes. FRET pairs were at different locations yielding a total of five constructs to probe its three-way junction structure with a large loop. With end-labelled DNAzymes, the global structure appears quite rigid with little folding by adding up to 200 mM monovalent metal ions, although some minor differences were observed between Li+, Na+ and K+. This lack of large conformational change is also consistent with CD spectroscopy data. The loop was then labelled with an internal TMR fluorophore at the G14 position, and its cleavage activity was partially retained. A clear Na+-dependent folding was observed with spectral crossover. From a biosensing standpoint, global folding based sensors are unlikely to work due to the overall rigid structure of the DNAzyme. Therefore, the best way using this DNAzyme to discriminate Na+ from K+ is based on cleavage activity, followed by probing local folding, while global folding is the least effective for metal discrimination.