A label-free and turn-off fluorescent method for the quantitative detection of kanamycin based on a funtional molecular beacon was developed. The molecular beacon consists of two hairpin structures with a split G-rich oligonucleotide in the middle. The kanamycin＇s aptamer formed the loops portion for recognizing kanamycin, and the G-quadruplex bound by Thioflavin T（ThT） was employed as the reporter. In the absence of target, the molecular beacon folded into double stem-loops and the splited G-rich oligonucleotid came close to form a G-quadruplex. When ThT bound to the G-quadruplex, the fluorescence intensity of the solution increased. Upon the addition of kanamycin, the function between kanamycin and aptamer unfolded the hairpin and disassembled the G-quadraplex structure, resulting in a significant decrease in the fluorescence intensity. A good linear relationship ranging from 0.7 nmol/L to 10 nmol/L was achieved and the limit of detection was 0.37 nmol/L. Besides, it could efficiently recognize kanamycin in real samples.
The title compound （2-iodo-5-nitrophenyl）-[1-（1-methylazepan-3-yl）-lH-indol-3- yl]methanone （C22H22IN303, Mr- 503.07 ） was synthesized by the reaction of 3-（2-iodo-5- nitrobenzoyl）indole with 2-chloromethyl-1-methylpiperidine. Its chemical structure was determined by 1H NMR, 13C NMR, DEPT, COSY, HMQC, HMBC, HRMS and X-ray single-crystal diffraction. The crystal belongs to the triclmic system, space group P1 with a = 9.153（4）, b = 10.409（3）, c = 11.882（4） A, a = 71.84（3）, β = 78.67（3）, ）, = 75.49（3）°, V = 1032.7（6） A3, Z = 2, Dc= 1.619 g/era3, = 1.579 mm-1, F（000） = 504, R = 0.0270 and wR = 0.0498 for 3634 observed reflections with I 〉 20（/）. X-ray analysis shows that the indole ring forms a dihedral angle of 84.57（12）° with the iodobenzene ring and the azepane ring adopts a twisted chair conformation. Weak C-H...O hydrogen bonding contributes to the stability and packing of the structure.
