A　novel　electrochemical　biosensor　based　on　a　glassy　carbon　electrode　(GCE)　modified　with　aldehyde-agarose　hydrogel　films　was　developed　for　the　detection　of　PML/RARa　fusion　gene　in　acute　promyelocytic　leukemia　(APL).　To　generate　the　aldehyde　groups　that　will　react　with　probe,　the　diol　groups　in　the　activated　agarose　gels　were　transformed　into　aldehyde　groups　by　reaction　with　NaIO　4.　Immobilization　is　based　on　the　reaction　between　aldehyde　groups　in　aldehyde-agarose　and　primary　amino　groups　in　the　probe.　The　probe　was　covalently　immobilized　on　the　surface　of　the　GCE.　Cyclic　voltammetry　(CV)　and　differential　pulse　voltammetry　(DPV)　was　used　to　detect　PML/RARa　fusion　gene　in　APL　based　on　methylene　blue　(MB)　as　an　electrochemical　indicator.　The　electrochemical　behavior　and　the　determination　of　the　probe　in　APL　PML/RARa　fusion　gene　using　GCE　were　studied　by　DPV.　The　results　indicated　that　in　Tris-HCl　buffer　solution　(pH　7.0),　the　relationship　between　the　oxidation　peak　current　of　MB　and　the　concentration　of　complementary　strand　was　linear　in　the　range　of　4.0　×　10-12　to　1.2　×　10-11　M.　The　detection　limit　was　estimated　as　4.0　×　10-12　M.　The　presented　method　exhibited　excellent　specificity　for　complementary　and　single-mismatch　dsDNA　after　hybridization　and　will　be　applied　to　the　assay　of　PCR-amplified　DNA　extracted　from　real　sample　showing　the　potentialities　of　this　approach　for　routine　analysis.　©　2011　Elsevier　B.V.　All　rights　reserved.