Based　on　the　disruption　and　recovery　of　fluorescence　of　styryl　quinolinium　(SQ)　dye/G-quadruplex　complex,　a　label-free　method　for　dual-channel　detection　of　Ag+　and　cysteine　is　developed.　The　above　sensing　system　exhibits　high　sensitivity　and　good　selectivity　for　Ag+,　even　in　the　presence　of　other　metal　ions　(such　as　Na+,　Mg2+,　Mn2+,　Ba2+,　Ca2+,　Pb2+,　Zn2+,　Cd2+,　Hg2+　and　Cu2+).　Due　to　cysteine　(Cys)　is　a　strong　Ag+-binder　and　competes　with　quadruplex-forming　G-rich　oligonucleotides　for　Ag+　binding,　and　results　in　the　reformation　of　G-quadruplex　structure　and　the　recovery　of　fluorescence.　Thus　SQ　dye/G-quadruplex　complexes　are　not　only　a　potential　primary　sensor　toward　Ag+,　but　also　a　secondary　sensor　toward　Cys.　Neither　the　Ag+-sensing　nor　the　Cys-sensing　systems　required　labeled　oligonucleotides.　Under　the　optimal　conditions,　this　method　is　capable　of　detection　of　Ag+　in　the　range　of　0.1-15.0　mu　M　with　a　detection　limit　of　26.0　nM.　In　addition,　the　proposed　method　allows　a　good　response　to　cysteine　with　a　linear　range　of　0.008-10　mu　M,　and　the　limit　of　detection　is　found　to　be　2.0　nM.　Moreover,　this　method　has　been　applied　successfully　to　the　sensing　of　cysteine　in　human　urine　with　satisfactory　recovery.　(C)　2012　Elsevier　B.V.　All　rights　reserved.