Successive and Specific Detection of Hg2+ and I- by a DNA@MOF Biosensor: Experimental and Simulation Studies.

A 2D metal-organic framework (MOF) of {[Cu(Dcbb)(Bpe)]·Cl} n (1, H2DcbbBr = 1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide, Bpe = trans-1,2-bis(4-pyridyl)ethylene)) has been prepared. MOF 1 associates with the thymine-rich (T-rich), single-stranded probe DNA (ss-DNA, denoted as P-DNA) labeled with fluorophore FAM (FAM = carboxyfluorescein) and quenches the FAM emission to give a nonemissive P-DNA@1 hybrid (off state). The P-DNA in the hybrid subsequently captures the Hg2+ to give a rigid double-stranded DNA featuring T-Hg2+-T motif (ds-DNA@Hg2+) and detach from MOF 1, triggering the recovery of the FAM fluorescence (on state). Upon subsequent addition of I-, Hg2+ was further sequestrated from the ds-DNA@Hg2+ duplex, driven by the stronger Hg-I coordination. The released P-DNA is resorbed by MOF 1 to regain the initial P-DNA@1 hybrid (off state). The P-DNA@1 sensor thus detects Hg2+ and I- sequentially via a fluorescence "off-on-off" mechanism. The sensor is highly selective and sensitive, yielding detection limits of 3.2 and 3.3 nM, respectively. The detection process was conformed by circular dichroism (CD) and the detection mechanism was verified by fluorescence anisotropy, binding constant, and simulation of the binding free energy at each stage.

Lanthanum-Based Metal-Organic Frameworks for Specific Detection of Sudan Virus RNA Conservative Sequences down to Single-Base Mismatch.

Reactions of La(NO3)3·6H2O with the polar, tritopic quaternized carboxylate ligands N-carboxymethyl-3,5-dicarboxylpyridinium bromide (H3CmdcpBr) and N-(4-carboxybenzyl)-3,5-dicarboxylpyridinium bromide (H3CbdcpBr) afford two water-stable metal-organic frameworks (MOFs) of {[La4(Cmdcp)6(H2O)9]}n (1, 3D) and {[La2(Cbdcp)3(H2O)10]}n (2, 2D). MOFs 1 and 2 absorb the carboxyfluorescein (FAM)-tagged probe DNA (P-DNA) and quench the fluorescence of FAM via a photoinduced electron transfer (PET) process. The nonemissive P-DNA@MOF hybrids thus formed in turn function as sensing platforms to distinguish conservative linear, single-stranded RNA sequences of Sudan virus with high selectivity and low detection limits of 112 and 67 pM, respectively (at a signal-to-noise ratio of 3). These hybrids also exhibit high specificity and discriminate down to single-base mismatch RNA sequences.

Compressive Strength Prediction of Rubber Concrete Based on Artificial Neural Network Model with Hybrid Particle Swarm Optimization Algorithm.

Conventional neural networks tend to fall into local extremum on large datasets, while the research on the strength of rubber concrete using intelligent algorithms to optimize artificial neural networks is limited. Therefore, to improve the prediction accuracy of rubber concrete strength, an artificial neural network model with hybrid algorithm optimization was developed in this study. The main strategy is to mix the simulated annealing (SA) algorithm with the particle swarm optimization (PSO) algorithm, using the SA algorithm to compensate for the weak global search capability of the PSO algorithm at a later stage while changing the inertia factor of the PSO algorithm to an adaptive state. For this purpose, data were first collected from the published literature to create a database. Next, ANN and PSO-ANN models are also built for comparison while four evaluation metrics, MSE, RMSE, MAE, and R2, were used to assess the model performance. Finally, compared with empirical formulations and other neural network models, the result shows that the proposed optimized artificial neural network model successfully improves the accuracy of predicting the strength of rubber concrete. This provides a new option for predicting the strength of rubber concrete.

Selective and recyclable tandem sensing of PO43- and Al3+ by a water-stable terbium-based metal-organic framework.

Herein, a luminescent water-stable terbium-based metal-organic framework (MOF) {[Tb(Cmdcp)(H2O)3]2(NO3)2·5H2O}n (1, H3CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and used for the recyclable sensing of PO43- and Al3+ in tandem. MOF 1 acts as a fluorescent sensor for PO43- by the luminescence "turn-off" mechanism with high selectivity over other anions, such as F-, Cl-, Br-, I-, NO3-, H2PO4-, HSO4-, HCO3-, HSO3-, SO42-, CO32- and HPO42-. The formed PO43-@1 complex further acts as the Al3+ sensor with the luminescence "turn-on" mechanism, also with high selectivity over diverse inorganic cations of Fe2+, Mn2+, Co2+, Ni2+, Hg2+, Na+, K+, Li+, Ag+, Mg2+, Ca2+, Cd2+, Pb2+, Cu2+, and Zn2+. The detection process for both PO43- and Al3+ can be directly observed with naked eyes under the UV light at 365 nm. The detection limits for PO43- and Al3+ are 1.1 µM and 6.6 µM, respectively. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.

Facile and recyclable dopamine sensing by a label-free terbium(III) metal-organic framework.

Herein, we present a facile strategy for dopamine (DA) sensing by a water-stable MOF of {[Tb(Cmdcp)(H2O)3]2(NO3)2·5H2O}n (1, H3CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide). Without any post-modification, MOF 1 functions as an effective fluorescent sensor for the label-free detection of DA with the detection limit of 0.41 µM (S/N = 3). Under the optimum condition of 80 °C, pH 9 for 80 min in Tris-HCl with natural ambient oxygen, DA polymerizes to give polydopamine (pDA), which adheres to the surface of MOF 1 and quenched its green luminescence thoroughly. The sensing process is visible to naked eyes under 365 nm UV light irradiation due to the partial overlap of its excitation spectrum with the absorption spectrum of pDA. The sensing process is not interfered by coexisting of bio-related organic substances, such as glucose (Glu), 5-hydroxytryptamine (5-HT), homocysteine (Hcy), ascorbic acid (AA), uric acid (UA), cysteine (Cys), glutathione (GSH), as well as the presence of metal ions, including Zn2+, Ca2+, Mg2+, Ni2+ and Co2+. The sensing process is also adaptable in biological fluids of serum and urine with satisfactory recoveries ranging from 96.14% to 104.32%.

Experimental and theoretical validations of a one-pot sequential sensing of Hg2+ and biothiols by a 3D Cu-based zwitterionic metal-organic framework.

A zwitterionic three-dimensional (3D) metal-organic framework (MOF) of {[Cu(Cdcbp)(bipy)]·4H2O}n (1) has been synthesized and characterized (H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide; bipy = 4,4'-bipyridine). MOF 1 exhibits a variety of structural traits, such as ligand conjugated, positively charged pyridinium center, and Cu(II) cations that collectively enable its efficient hybridization with the flexible, negatively charged, single-stranded, and thymine-rich (T-rich) DNA. The T-rich DNA is labeled with carboxyfluorescein (FAM) fluorescent probe (characterized as P-DNA), but the resultant MOF 1 - P-DNA hybrid (characterized as P-DNA@1) is non-emissive (off-state) because of the fluorescent quenching by MOF 1. The P-DNA@1 hybrid functions as an effective and selective sensor for Hg2+ due to the formation of rigid hairpin-like T-Hg2+-T double-stranded DNA (ds-DNA@Hg2+) which is subsequently ejected by MOF 1, triggering a recovery of the P-DNA fluorescence (on-state). Subsequent addition of biothiols further sequestrates Hg2+ from the ds-DNA@Hg2+ duplex driven by the stronger Hg-S coordination, thus release the P-DNA and, in turn, resorbed by MOF 1 to regain the initial hybrid (off-state). P-DNA@1 hybrid thus detects Hg2+ and biothiols sequentially via a fluorescence "off-on-off" mechanism. The limits of detection (LOD) for Hg2+, biothiols, including cysteine (Cys), glutathione (GSH) and homocysteine (Hcy) are 3.0, 14.2, 15.1 and 8.0 nM, respectively, with the detection time of 60 min for Hg2+, and instantaneous detection for all the three biothiols. The detection mechanism is further confirmed by circular dichroism (CD), fluorescence anisotropy (FA), binding constant and molecular simulation. This sequential detection of Hg2+ and biothiols counter-proofs the presence of each other and may shed light to the occurrence of related diseases, such as neurodegenerative disorders of Parkinson's disease (PD), and Alzheimer's disease (AD).

Rapid sequential detection of Hg2+ and biothiols by a probe DNA-MOF hybrid sensory system.

A one-dimensional (1D) metal-organic framework (MOF) of [Cu(Cdcbp)(H2O)2·2H2O]n (1, H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide) has been synthesized and characterized. MOF 1 features a cationic Cu2+ center, conjugated tricarboxylate ligand bearing positively charged pyridinium and uncoordinated carboxylate groups within its skeleton. These features enable MOF 1 to tightly adsorb thymine rich (T-rich) single-stranded DNA (ss-DNA) probe labeled with carboxyfluorescein (FAM) (denote as P-DNA) through π-stacking, electrostatic interactions and/or hydrogen bonding to give a hybrid complex (denote as P-DNA@1), and quenches its fluorescence via a photo-induced electron transfer (PET) process. The formed P-DNA@1 hybrid can thus function as a sensing platform for the detection of Hg2+, driven by the formation of hairpin-like double-stranded DNA (ds-DNA@Hg2+) with a T-Hg-T coordination motif, and subsequently dissociated into the solution due to its more rigid nature than ss-DNA, leading to the recovery of FAM fluorescence. In the presence of biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), the strong coordination interaction between Hg2+ and the mercapto function serves to sequestrate the Hg2+ from the ds-DNA@Hg2+ duplex. The released ss-DNA, in turn, are re-adsorbed by MOF 1, leading to the formation of the initial P-DNA@1 state with fluorescence quenching. As such, P-DNA@1 detects Hg2+ and biothiols Cys/Hcy/GSH in sequence with detection limits of (2.3 ±â€¯0.8) nM and (29.6 ±â€¯0.1) nM/(19.8 ±â€¯0.5) nM/(10.2 ±â€¯0.1) nM. The sensing process is efficient and selective with instantaneous response time. The detection mechanism was further validated by circular dichroism (CD), and simulation studies using Molecular Operating Environment (MOE) package.

Phenanthroline-linked berberine dimer and fluorophore-tagged DNA conjugate for the selective detection of microRNA-185: Experimental and molecular docking studies.

A phenanthroline (phen) tethered berberine dimer 1 is synthesized and further conjugated with carboxyfluorescein (FAM)-labeled single-stranded probe DNA (P-DNA) to give P-DNA@1. The mutual interaction of these two components triggers the fluorescence quenching of FAM, and the non-emissive P-DNA@1, in turn, functions as a sensor to detect cancer-associated microRNA-185 (miRNA-185), characterized by the FAM fluorescence recovery. The results show that P-DNA@1 is capable of detecting miRNA-185 in 2 min with the detection limit of 0.2 nM. The detection mechanism was supported by fluorescence anisotropy, binding constant and molecular docking study. Competing experiments further indicate that P-DNA@1 exhibits a high selectivity for miRNA-185 thus has a good potential in the diagnosis of related cancer at the early stage.

Experimental and computational investigation of a DNA-shielded 3D metal-organic framework for the prompt dual sensing of Ag+ and S2.

We herein report an efficient Ag+ and S2- dual sensing scenario by a three-dimensional (3D) Cu-based metal-organic framework [Cu(Cdcbp)(bpea)] n (MOF 1, H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide, bpea = 1,2-di(4-pyridinyl)ethane) shielded with a 5-carboxytetramethylrhodamine (TAMRA)-labeled C-rich single-stranded DNA (ss-probe DNA, P-DNA) as a fluorescent probe. The formed MOF-DNA probe, denoted as P-DNA@1, is able to sequentially detect Ag+ and S2- in one pot, with detection limits of 3.8 nM (for Ag+) and 5.5 nM (for S2-), which are much more lower than the allowable Ag+ (0.5 µM) and S2- (0.6 µM) concentration in drinking water as regulated by World Health Organization (WHO). The detection method has been successfully applied to sense Ag+ and S2- in domestic, lake, and mineral water with satisfactory recoveries ranging from 98.2 to 107.3%. The detection mechanism was further confirmed by molecular simulation studies.

Sequential and recyclable sensing of Fe3+ and ascorbic acid in water with a terbium(iii)-based metal-organic framework.

A water-stable three-dimensional (3D) metal-organic framework (MOF) of {[Tb(Cmdcp)(H2O)3]2(NO3)2·5H2O}n (1, H3CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and characterized. MOF 1 is highly emissive, giving rise to green luminescence that can be quenched by Fe3+ due to the partial overlap of its excitation spectrum with the absorption spectrum of Fe3+. The subsequent introduction of ascorbic acid (AA) leads to the reduction of Fe3+ into Fe2+, accompanied by the near-entire recovery of MOF 1 emission. The density functional theory (DFT) calculation results support the proposed mechanism. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.