Energy Transfer-Based Recognition of Membrane Cholesterol by Controlling Intradistance of Linker

Gold nanoparticles (AuNPs) are good candidates for donor material in energy transfer systems and can easily be functionalized with various ligands on the surface with Au-S bonding. Cyclodextrin (CD) forms inclusion complexes with fluorophores due to its unique structure for host-guest interaction. In this study, we fabricated βCD-functionalized AuNPs using different lengths of thiol ligands and recognized cholesterol to confirm the energy-transfer-based turn-on fluorescence mechanism. AuNP-βCD conjugated with various thiol ligands and quenched the fluorescein (Fl) dye, forming βCD-Fl inclusion complexes. As the distance between AuNPs and βCD decreased, the quenching efficiency became higher. The quenched fluorescence was recovered when the cholesterol replaced the Fl because of the stronger binding affinity of the cholesterol with βCD. The efficiency of cholesterol recognition was also affected by the energy transfer effect because the shorter βCD ligand had a higher fluorescence recovery. Furthermore, we fabricated a liposome with cholesterol embedded in the lipid bilayer membrane to mimic the cholesterol coexisting with lipids in human serum. These cellular cholesterols accelerated the replacement of the Fl molecules, resulting in a fluorescence recovery higher than that of pure lipid. These discoveries are expected to give guidance towards cholesterol sensors or energy-transfer-based biosensors using AuNPs.

Exploiting a Multi-Responsive Oxadiazole Moiety in One Three-Dimensional Metal-Organic Framework for Remedies to Three Environmental Issues

Multifunctional metal-organic frameworks (MOFs) rely on the properties of metal centers (nodes) and/or linkers (struts) for their diverse applications in the emerging field of research. Currently, there is a huge demand for MOF materials in the field of capture/fixation/sensing of air pollutants, harmful chemical effluents, and nuclear waste. However, it is a challenging task to utilize one MOF for providing remedies to all these issues. On the basis of our current research activities, we have identified that an oxadiazole moiety-a five-membered ring with two different heteroatoms (O and N)-in a carboxylate linker can be the key to generating such MOF materials for its (a) inherent polarizable nature and molecular docking ability and (b) photoluminescence properties. In this work, we report a 3D MOF {[Co₂(oxdz)₂(tpbn)(H₂O)₂]·4H₂O}_n (1), self-assembled at room temperature from a three-component reaction, with an oxadiazole moiety (where H₂oxdz = 4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoic acid and tpbn = N,N',N,"N″'-tetrakis(2-pyridylmethyl)-1,4-diaminobutane). The inherent polarizable nature of the oxadiazole moiety in 1 has been efficiently exploited for (i) multimedia iodine capture and (ii) fixation of CO₂ under solvent-free and ambient conditions. On the other hand, the luminescent nature of the framework is found to be an efficient, highly preferred turn-on sensor for the ultra-fast detection of ketones with a limit as low as parts-per-trillion (mesitylene oxide: 447 ppt; cycloheptanone: 4.7 ppb; cyclohexanone: 17.2 ppb; acetylacetone: 18 ppb).

Stable Eu3+/Cu2+-Functionalized Supramolecular Zinc(II) Complexes as Fluorescent Probes for Turn-On and Ratiometric Detection of Hydrogen Sulfide

Fabrication of dual-emitting materials for H₂S sensing under environmental and biological conditions is currently of great interest. In this work, a new chemically stable metal supramolecular complex [Zn₂(pda)₂(H₂O)₃]·(H₂O)_0.5 (Znpda, pda = 1,10-phenanthroline-2,9-dicarboxylic acid), with accessible uncoordinated carboxylic oxygen sites, is solvothermally synthesized. It can serve as a host in luminescent hybrid composites. By incorporating Eu³⁺ and Cu²⁺ in the supramolecular coordination network, we obtained the dual-emitting hybrid material Eu³⁺/Cu²⁺@Znpda, which simultaneously shows intense ligand and weak Eu³⁺ emissions in HEPES buffer solution. Since H₂S can easily chelate with Cu²⁺ and recover the blocked "antenna effect" between the ligand and Eu³⁺, Eu³⁺/Cu²⁺@Znpda possesses both the turn-on and ratiomectric fluorescence response to H₂S. Accordingly, we designed an IMPLICATION logic gate for H₂S recognition by employing the fluorescence intensity ratio between the ligand and Eu³⁺ as the output signal. In addition, Eu³⁺/Cu²⁺@Znpda shows a fast response (<1 min) and high sensitivity (1.45 μM) to H₂S over other interfering species in the HEPES buffer solution, highlighting its potential use for H₂S sensing under environmental and biological conditions.