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We report herein five sensing platforms for the detection of five gastric cancer associated microRNAs (miRNAs). The sensing platforms are hybrids formed from a water-stable metal organic framework (MOF) {[Cu(dcbb)2(H2O)2]·10H2O}n (1, H2dcbbBr=1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide), respectively with five carboxyfluorescein (FAM) labeled probe single-stranded DNA (probe ss-DNA, denoted as P-DNA). Within the hybrid, MOF 1 tightly interacts with the P-DNA through electrostatic and/or π-stacking interactions and results in fluorescence quenching of FAM via a photo-induced electron transfer (PET) process. In the presence of the complementary target miRNAs miR-185, miR-20a, miR-92b, miR-25 and miR-210, which are expressed abnormally in the plasma of gastric carcinoma patients, P-DNA is released from the surface of MOF 1 ascribed to the stronger base pair matching, leading to the FAM fluorescence recovery. Each P-DNA@1 system is effective and reliable for the detection of its complementary target miRNA with the detection limits from 91 to 559pM, and is not interfered by other four miRNA sequences.

Coordination reaction of a known three-dimensional (3D) polymer precursor {Na3[Na9(Cbdcp)6(H2O)18]}n (A, Cbdcp = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium) with Zn(NO3)2·6H2O in H2O or H2O/DMF at 100 °C and in the presence of aspirin, 5-fluorouracil (5-FU) as modulators, trans-1,2-bis(4-pyridyl)ethylene (bpe) or 1,2-bis(4-pyridyl)ethane (bpea) as ancillary ligands afforded six novel Zn(II)-based metal-organic frameworks (MOFs), that is, {[Zn(Cbdcp)(H2O)3]·H2O}n (1, 1D zigzag chain), {[Zn(HCbdcp)2]·H2O}n (2, 2D sheet), {[Zn(Cbdcp)(bpe)1/2]·2H2O}n (3, 3D polymer), {[Zn(Cbdcp)(bpe)1/2]·2H2O}n (4, 2D network), {[Zn(Cbdcp)(bpea)1/2]·2H2O}n (5, 3D polymer) and {[Zn(Cbdcp)(bpea)1/2]·2H2O}n (6, 2D network). Among them, compound 2 contains aromatic rings, positively charged pyridinium, Zn2+ cation centers and carboxylic acid groups lined up on the 2D sheet structure with a certain extended surface exposure. The unique structure of 2 facilitates effective association with carboxyfluorescein (FAM) labeled probe single stranded DNA (probe ss-DNA, delineates as P-DNA) to yield a P-DNA@2 system, and leads to fluorescence quenching of FAM via a photoinduced electron transfer process. The P-DNA@2 system is effective and reliable for the detection of human immunodeficiency virus 1 ds-DNA (HIV ds-DNA) sequences and capable of distinguishing complementary HIV ds-DNA from mismatched target sequences with the detection limit as low as 10 pM (S/N = 3).

A water stable one-dimensional (1D) ladder-shaped coordination polymer (CP) has been synthesized and exhibits a strong affinity to two fluorescein-tagged single-stranded probe DNAs (P-DNAs), giving a sensing platform of P-DNAs@1. Such a hybrid sensing platform is capable of simultaneous detection of breast cancer related microRNA-221 (miRNA-221) and miRNA-222 in a specific and synchronous manner, without observable cross-reactions, as supported by experimental evidences. The interaction mode and the electronic energy between CP 1 with nucleic acid were confirmed by molecular simulation and the universal force field (UFF).