Transition-metal-based (Zn2+ and Cd2+) metal-organic frameworks as fluorescence “turn-off” sensors for highly sensitive and selective detection of hydrogen sulfide

A wearable flexible electrochemical biosensor with CuNi-MOF@rGO modification for simultaneous detection of uric acid and dopamine in sweat

BACKGROUND

In health assessment and personalized medical services, accurate detection of biological markers such as dopamine (DA) and uric acid (UA) in sweat is crucial for providing valuable physiological information. However, there are challenges in detecting sweat biomarkers due to their low concentrations, variations in sweat yield among individuals, and the need for efficient sweat collection.

RESULTS

We synthesized CuNi-MOF@rGO as a high-activity electrocatalyst and investigated its feasibility and electrochemical mechanism for simultaneously detecting low-concentration biomarkers UA and DA. Interaction between the non-coordinating carboxylate group and the sample produces effective separation signals for DA and UA. The wearable biomimetic biosensor has a wide linear range of 1-500 μM, with a detection limit of 9.41 μM and sensitivity of 0.019 μA μM-1 cm-2 for DA, and 10-1000 μM, with a detection limit of 9.09 μM and sensitivity of 0.026 μA μM-1 cm-2 for UA. Thus, our sensor performs excellently in detecting low-concentration biomarkers. To improve sweat collection, we designed a microfluidic-controlled device with hydrophilic modification in the microchannel. Experimental results show optimal ink flow at 2% concentration. Overall, we developed an innovative and highly active electrocatalyst, successfully enabling simultaneous detection of low-concentration biomarkers UA and DA.

SIGNIFICANCE

This study provides a strategy for sweat analysis and health monitoring. Moreover, the sensor also showed good performance in detecting real sweat samples. This study has shown great potential in future advances in sweat analysis and health monitoring.

Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure

In this study, the ability of the highly scalable metal-organic framework (MOF) CALF-20 to adsorb polar and non-polar gases at low pressure was investigated using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results from the simulated adsorption isotherms revealed that the highest loading was achieved for SO₂ and Cl₂, while the lowest loading was found for F₂ molecules. The analysis of interaction energies indicated that SO₂ molecules were able to form the strongest adsorbent-adsorbate interactions and had a tight molecular packing due to their polarity and angular structure. Additionally, Cl₂ gas was found to be highly adsorbed due to its large van der Waals surface and strong chemical affinity in CALF-20 pores. MD simulations showed that SO₂ and Cl₂ had the lowest mobility inside CALF-20 pores. The values of the Henry coefficient and isosteric heat of adsorption confirmed that CALF-20 could selectively adsorb SO₂ and Cl₂. Based on the results, it was concluded that CALF-20 is a suitable adsorbent for SO₂ and Cl₂ but not for F₂. This research emphasizes the importance of molecular size, geometry, and polarity in determining the suitability of a porous material as an adsorbent for specific adsorbates.

A novel phenanthridine and terpyridine based D-π-A fluorescent probe for the ratiometric detection of Cd2+ in environmental water samples and living cells

A "turn-on" Donor-π-Acceptor (D-π-A) containing phenanthridine-functionalized extended π-conjugate terpyridine, 5-(4'-([2,2':6',2''-terpyridin]-4'-yl)-[1,1'-biphenyl]4-yl)7,8,13,14-tetrahydrodibenzo [a, i] phenanthridine (TBTP) was synthesised. It shows strong selectivity for the detection of toxic Cd²⁺ without interference from other metal ions. In the presence of Cd²⁺, the absorption of the TBTP changes dramatically along with the fluorescent emission with the large Stokes shift of 6300 cm^-1. When the compound TBTP is exposed to UV light, its colour changes from blue to orange over the addition of Cd²⁺. Adding other transition metal ions has no effect. This is based on the mechanism of intramolecular charge transfer. The detection limit for Cd²⁺ was found to be around 1.181 × 10^-8 M. An investigation of the sensing mechanism includes job plot, NMR titration, DFT calculation, and HRMS analyses. Excitingly, the recognition of Cd²⁺ in CH₃CN: H₂O (8:2, v/v) medium is quantitative without interference from Zn^2+, which is a common interferent for Cd²⁺. Furthermore, the probe was used for detecting Cd²⁺ in real water samples and cell imaging in living cells was also performed.

A sensitive colorimetric hydrogen sulfide detection approach based on copper-metal-organic frameworks and a smartphone

In this study, we demonstrate a colorimetric approach for the detection of hydrogen sulfide (H₂S) in water samples with high sensitivity. Firstly, copper-metal-organic frameworks (Cu-MOFs) were synthesized by ultrasonic-assisted hydrothermal method, presenting a maximum absorption peak at 700 nm. It was found that Cu-MOFs could react with H₂S to form a copper-sulfur complex along with a decrease of the absorption peak at 700 nm and a visible color change from blue to tan. Under the optimal reaction conditions, the absorption intensity at 700 nm was linear with H₂S concentration in a range of 0.05-2 mM (R² = 0.9928), providing a detection limit of 22 μM. Furthermore, the method was successfully applied to the detection of H₂S in lake water samples with a recovery rate between 94.4% and 112.6%. In addition, a practical and portable device for on-site H₂S detection was designed by using agarose hydrogels, and a simple colorimetric detection method based on a smartphone was developed. This analytical method showed good selectivity for H₂S compared to other interfering substances, and the feasibility of the agarose hydrogel-based device was proved by the determination of H₂S in real lake water samples.

Comparative Study of Nitro and Azide Functionalized Zn(II) based Coordination Polymers as Fluorescent Turn-on Probes for Rapid and Selective Detection of H2S in Living Cells

Selective Detection of H 2 S in cellular system using fluorescent CPs/MOFs is of great scientific interest due to their outstanding aqueous stability, biocompatibility and real-time detection ability.  Fabrication of such materials using complete biologically essential elements and applying them as an efficient biosensors is still quite challenging.  In this context, we present two newly synthesized CPs containing biologically essential metal ion (Zn) and nitro/azido functional group on the framework to sense extracellular and intracellular H 2 S by reducing into respective amines.  The CP- 1 containing the azide group acted as an efficient fluorencent turn-on probe with lowest detection limit (7.2 µM) and shortest response time (30 sec) among the Zn-based probes reported till date.  Moreover, CP-1 exhibited green luminescence in live cells after imaging very low concentration of H 2 S, while the nitro analogue, CP-2, couldn't detect the target analyte due to it's framework disruption.

A Metallosupramolecular Coordination Polymer for the 'Turn-on' Fluorescence Detection of Hydrogen Sulfide

A coumarin based probe for the efficient detection of hydrogen sulfide in aqueous medium is reported. The investigated coumarine-based derivative forms spherical nanoparticles in aqueous media. In presence of Pd2+, a metallosupramolecular coordination polymer is formed, which is accompanied by quenching of the coumarin emission at 390 nm. Its Pd2+ complex could be used as a probe for chemoselective detection of monohydrogensulfide (HS-). Presence of HS- leads to a'turn-on' fluorescence signal, resulting from decomplexation of Pd2+ from the metallosupramolecular probe. The probe was successfully applied for qualitative and quantitative detection of HS- in different sources of water directly collected from sea, river, tap and laboratory drain water, as well as in growth media for aquatic species.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.

Designing an "Off-On" Fluorescence Sensor Based on Cluster-Based CaII-Metal-Organic Frameworks for Detection of l-Cysteine in Biological Fluids

Recently, luminescent metal-organic framework (MOF) materials have attracted considerable attention in fluorescence sensing. In this essay, we prepared a new cluster-based Ca^II-MOFs {[Ca_1.5(μ₈-HL₁)(DMF)₂]·DMF}_n (1) with good water dispersibility, excellent photoluminescence properties (FL quantum yield of 20.37%) and great fluorescence stability. Further, it was employed to design as an "off-on" fluorescence sensor for sensitive detection of l-cysteine. This proposed strategy was that fluorescence of Ca^II-MOFs 1 was quenched for providing a low fluorescence background by the introduction of Pb²⁺ forming the Ca^II-MOFs 1/Pb²⁺ hybrid system. The quenching effect could be ascribed to the static quenching mechanism because of the formation of ground-state complexes and coordination interactions between the free carboxyl of H₄L₁ ligands of Ca^II-MOFs 1 and Pb²⁺. Then, with the addition of l-cysteine into the Ca^II-MOFs 1/Pb²⁺ hybrid system, the fluorescence signal was immediately restored. This result was because the Pb²⁺ was gradually released from the hybrid system by chelation interactions between the -SH groups of l-cysteine and Pb²⁺. This method received a relative wide linear range varying from 0.05 to 40 μM and a low detection limit of 15 nM for detection of l-cysteine. This proposed strategy was also successfully applied to detect l-cysteine in human serum samples with satisfactory recoveries from 95.9 to 101.5%.

A silver nanoparticle-anchored UiO-66(Zr) metal–organic framework (MOF)-based capacitive H2S gas sensor

Metal–organic frameworks anchored with metal oxide nanoparticles for the detection of H₂S gas with enhanced sensitivity.