Interface-Engineered 2D Heterojunction with Photoelectric Dual Gain: Mxene@MOF-Enhanced SPR Spectroscopy for Direct Sensing of Exosomes

MXene is widely used in the construction of optoelectronic interfaces due to its excellent properties. However, the hydrophilicity and metastable surface of MXene lead to its oxidation behavior, resulting in the degradation of its various properties, which seriously limits its practical application. In this work, a 2D metal-organic framework (2D MOF) with matching 2D morphology, excellent stability performance, and outstanding optoelectronic performance is grown in situ on the MXene surface through heterojunction engineering to suppress the direct contact between reactive molecules and the inner layer material without affecting the original advantages of MXene. The photoelectric dual gain MXene@MOF heterojunction is confirmed. As a photoelectric material, its properties are highly suitable for the demand of interface sensitization layer materials of surface plasmon resonance (SPR). Therefore, using SPR as a platform for the application of this interface material, the performance of MXene@MOF and its potential mechanism to enhance SPR are analyzed in depth using experiments combined with simulation calculations (FDTD/DFT). Finally, the MXene@MOF/peptides-SPR sensor is constructed for rapid and sensitive detection of the cancer marker exosomes to explore its potential in practical applications. This work offers a forward-looking strategy for the design of interface materials with excellent photoelectric performance.

2D MOF-enhanced SPR detector based on tunable supramolecular probes for direct and sensitive detection of DOX in serum

Therapeutic drug monitoring of doxorubicin (DOX) is important to study pharmacokinetics in patients undergoing chemotherapy for reduction of side effects and improve patient survival by rationally controlling the dose of DOX. A fast and ultra-sensitive surface plasmon resonance (SPR) detector without sample pre-handling was developed for DOX monitoring. First, the two-dimensional metal-organic framework was modified on the Au film to enhance SPR, and then, the supramolecular probes with tunable cavity structure were self-assembled at the sensing interface for direct detection of DOX through specific host-guest interactions with a low detection limit of 60.24 pM. The precise monitoring of DOX in serum proved the possibility of clinical application with recoveries in the range 102.86-109.47%. The mechanisms of host-guest interactions between supramolecular and small-molecule drugs were explored in depth through first-principles calculations combined with SPR experiments. The study paves the way for designing facile and sensitive detectors and provides theoretical support and a new methodology for the specific detection of small molecules through calixarene cavity modulation.

Rapid and sensitive detection of PD-L1 exosomes using Cu-TCPP 2D MOF as a SPR sensitizer

Two-dimensional metal organic framework (2D MOF Cu-TCPP) with significantly enhanced photoelectric properties was synthesized by a simple hydrothermal method. The π-stacked electroactive porphyrin molecules of TCPP-based 2D MOF carry out charge transport in the MOF structure. The d-d band transition of Cu²⁺ and its 2D ultra-thin characteristics can produce excellent near-infrared light absorption to couple with SPR. Three key parameters including the refractive index sensitivity, detection accuracy and quality factor were improved significantly for 2D MOF modified gold chips. Especially, the refractive index sensitivity was increased from 98 to 137.67°/RIU after modified with 2D MOF. Thus, for the first time, we applied it as a signal enhancer to improve direct SPR assay for the Programmed death ligand-1 (PD-L1) exosomes. Owning to its large specific surface area, excellent photoelectric properties, highly ordered structure, good dispersion and biocompatibility, the LOD of the SPR sensor was 16.7 particles/mL. The reliability and practicability were further validated by analysis of PD-L1 exosomes in human serum samples. The recovery rate was 93.43 %-102.35%, with RSD of 5.79 %-14.6%. Given their excellent signal amplification ability, 2D MOF Cu-TCPP could serve as an ideal SPR sensitizer for rapid and sensitive detection of trace disease markers.

Tetrazine as a general phototrigger to turn on fluorophores

Light-activated fluorescence affords a powerful tool for monitoring subcellular structures and dynamics with enhanced temporal and spatial control of the fluorescence signal. Here, we demonstrate a general and straightforward strategy for using a tetrazine phototrigger to design photoactivatable fluorophores that emit across the visible spectrum. Tetrazine is known to efficiently quench the fluorescence of various fluorophores via a mechanism referred to as through-bond energy transfer. Upon light irradiation, restricted tetrazine moieties undergo a photolysis reaction that generates two nitriles and molecular nitrogen, thus restoring the fluorescence of fluorophores. Significantly, we find that this strategy can be successfully translated and generalized to a wide range of fluorophore scaffolds. Based on these results, we have used this mechanism to design photoactivatable fluorophores targeting cellular organelles and proteins. Compared to widely used phototriggers (e.g., o-nitrobenzyl and nitrophenethyl groups), this study affords a new photoactivation mechanism, in which the quencher is photodecomposed to restore the fluorescence upon light irradiation. Because of the exclusive use of tetrazine as a photoquencher in the design of fluorogenic probes, we anticipate that our current study will significantly facilitate the development of novel photoactivatable fluorophores.

Ultrafast dynamics of differently aligned COOH-DTE-BODIPY conjugates linked to the surface of TiO2

The photoinduced dynamics of two DTE-BODIPY conjugates A, B with carboxylic acid anchoring groups coupled to the surface of TiO2 were studied by ultrafast transient absorption spectroscopy. For compound A, with an orthogonal orientation of the BODIPY chromophore and the photoswitchable DTE unit, a charge separated state could not be reliably detected. Nevertheless, besides the energy transfer from the BODIPY to the ring-closed DTE-c, indications for an electron transfer reaction were found by analyzing fluorescence quenching on TiO2 in steady state fluorescence measurements. For compound B with a parallel orientation of chromophore and photoswitch, a charge separated state was conclusively identified for the coupled dyad (TiO2) via the observation of a positive absorption signal (at λ pr  >  610 nm) at later delay times. An electron transfer rate of 7  ×  1010 s-1 can be extracted, indicating slower processes in the dyads in comparison to previously published electron transfer reactions of DTE compounds coupled to TiO2.

Phase partitioning, solvent-switchable BODIPY probes for high contrast cellular imaging and FCS

Lipophilic BODIPY fluorphores, in which the BODIPY core bears pendant dipyrido[3,2-a:2′,3′-c]phenazine (Dppz) or naphthyridyl and cholesterol substituents were designed and prepared as lipid probes for both liposomes and live cell imaging.

Acid-Sensitive BODIPY Dyes: Synthesis through Pd-Catalyzed Direct C(sp3 )-H Arylation and Photophysics

A novel palladium-catalyzed direct C(sp³ )-H arylation of the methyl group at the 8-position of BODIPY by bromoarenes was established. A deprotonative cross-coupling process was supposed to be involved in the reaction. This approach allowed us to attach electron-donating/withdrawing, halogen substituted aryls and a heteroaryl with a yield running from 55 to 99 %. Novel pH sensors, which in the absence of acid showed the occurrence of photoinduced electron transfer, were synthesized by attaching dimethylaniline to the methyl at the C8-position of BODIPY. The reference compounds with dimethylaniline directly attached to the C8-position were also synthesized and besides photoinduced electron transfer also showed a charge-transfer emission. Their photophysical properties were investigated by steady-state fluorescence, time-correlated single-photon counting and femtosecond fluorescence up-conversion. Time-dependent density functional (TD-DFT) electronic-structure calculations on the properties of the excited states corresponding to local excitation of the BODIPY core and to charge transfer were conducted. Upon addition of trifluoroacetic acid in toluene and ethanol, the partial fluorescence intensity recovery was at least an order of magnitude more efficient with the newly synthesized sensors compared to the traditional reference sensors. The improved sensitivity of these novel BODIPY-based pH sensors was attributed to less efficient proton-coupled electron transfer of the protonated species.

Demonstrating the role of anchoring functionality in interfacial electron transfer dynamics in the newly synthesized BODIPY–TiO2 nanostructure composite

Scheme illustrating the extent of coupling and charge recombination dynamics between BODIPY and NS-TiO₂ anchoring through the catechol and resorcinol binding group.

Synthesis, characterization, and photocurrent generation of a new nanocomposite based Cu–TCPP MOF and ZnO nanorod

Schematic representation of the Cu–TCPP MOF/ZnO (15%) nanocomposite on an FTO substrate in the photoelectrochemical cell and the mechanism of the photocurrent generation (the chemical potentials were calculated by cyclic voltammetry measurement).

Interfacial charge transfer events of BODIPY molecules: single molecule spectroelectrochemistry and substrate effects

BODIPY dye single molecules on nanostructured substrates are studied with a single molecule spectroelectrochemistry technique to reveal the heterogeneous charge transfer mechanism.