Styryl quinolinium/G-quadruplex complex for dual-channel fluorescent sensing of Ag+ and cysteine

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 μM 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 μM, 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.