Enzymatic　manipulation　and　modulation　of　nucleic　acids　are　a　central　part　of　cellular　function,　protection,　and　reproduction,　while　rapid　and　accurate　detection　of　ultralow　amount　of　nucleic　acids　remains　a　major　challenge　in　molecular　biology　research　and　clinic　diagnosis　of　genetic　diseases.　Herein,　we　reported　that　exonuclease　III　can　degrade　the　G-quadruplex　structure,　indicating　the　new　exonuclease＇s　function.　Basing　on　the　function　of　exonuclease　III,　a　novel　G-quadruplex-hemin　DNAzyme-based　colorimetric　detection　of　tumor　suppressor　gene　p53　was　successfully　developed.　Although　only　one　oligonucleotide　probe　was　involved,　the　sensing　strategy　could　suppress　the　optical　background　and　achieve　an　efficient　G-quadruplex-hemin　DNAzyme-based　signal　amplification.　Specifically,　a　label-free　functional　nucleic　acid　probe　(called　THzyme　probe)　was　designed　via　introducing　target　DNA　probe-contained　hairpin　structure　into　G-quadruplex　DNAzyme.　Even　if　this　probe　can　fold　into　G-quadruplex　structure　in　the　presence　of　hemin　very　different　from　the　double-stranded　DNA,　it　is　easily　degraded　by　exonuclease　III.　Thus,　no　change　in　UV-vis　absorption　intensity　is　detected　in　the　absence　of　target　DNA.　However,　the　hybridization　of　target　DNA　can　protect　the　integrity　and　catalytic　activity　of　THzyme　probe,　producing　the　DNAzyme-amplified　colorimetric　signal.　As　a　result,　the　p53　gene　was　able　to　be　detected　down　to　1.0.　pM　(final　concentration　in　the　signal-generating　solution:　50.0.　fM)　and　mismatched　target　DNAs　were　easily　distinguished.　It　is　expected　that　this　simple　sensing　methodology　for　DNA　detection　can　find　its　utility　in　point-of-care　applications.　©　2015　Elsevier　B.V.