title: A label-free G-quadruplex-based luminescent switch-on assay for the selective detection of histidine.
abstract: A label-free G-quadruplex-based luminescent switch-on assay has been developed for the selective detection of micromolar histidine in aqueous solution. In this study, an iridium(III) complex was employed as a G-quadruplex-specific luminescent probe while a guanine-rich oligonucleotide (Pu27, 5'-TG4AG3TG4AG3TG4A2G2-3')/cupric ion (Cu(2+)) ensemble was employed as a recognition unit for histidine. The initial luminescence of the iridium(III) complex in the presence of G-quadruplex DNA is effectively quenched by Cu(2+) ions due to the Cu(2+)-mediated unfolding of the G-quadruplex motif. The addition of histidine sequesters Cu(2+) ions from the ensemble, thereby restoring the luminescence of the system. The assay could detect down to 1 μM of histidine in aqueous media, and also exhibited good selectivity for histidine over other amino acids with the use of the cysteine, masking agent N-ethylmaleimide. Furthermore, the application of the assay for the detection of histidine in diluted urine samples was demonstrated.
authors.affiliation: Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China.
authors.forename: Hong-Zhang
authors.initials: HZ
authors.lastname: He
authors.forename: Modi
authors.initials: M
authors.lastname: Wang
authors.forename: Daniel Shiu-Hin
authors.initials: DS
authors.lastname: Chan
authors.forename: Chung-Hang
authors.initials: CH
authors.lastname: Leung
authors.forename: Jian-Wen
authors.initials: JW
authors.lastname: Qiu
authors.forename: Dik-Lung
authors.initials: DL
authors.lastname: Ma
mesh_terms: D015374:Biosensing Techniques; D002942:Circular Dichroism; D004277:DNA, Single-Stranded / Q000737:chemistry; D054856:G-Quadruplexes; D020862:GC Rich Sequence; D006639:Histidine / Q000032:analysis*; D008163:Luminescent Measurements; D011089:Polydeoxyribonucleotides / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012996:Solutions
chemical_list: D004277:DNA, Single-Stranded; D011089:Polydeoxyribonucleotides; D012996:Solutions; D006639:Histidine
keywords: CD; Cu(2+); G-quadruplex; Histidine; Iridium(III) complex; Label-free; Luminescence; N-ethylmaleimide; NEM; calf-thymus DNA; circular dichroism; ctDNA; double-stranded DNA; dsDNA; single-stranded DNA; ssDNA