Johan Hofkens

KU Leuven | ku leuven · Department of Chemistry

High‐entropy alloys (HEAs) made up of multiple metallic elements have gained attention for their excellent electrocatalytic performance. However, their application in the field of nitrogen (N2) oxidation reaction (NOR) remains underexplored. In this study, a “pomegranate‐like” carbon embedded with ultrafine AuPdPtRhIr HEA (HEA@C) is synthesized usi...

The resonance between an electronic transition of a micro/nanoscale object and an incident photon flux can modify the radiation force exerted on that object, especially at an interface. It has been theoretically proposed that a non-linear stimulated emission process can also induce an optical force, however its direction will be opposite to convent...

In recent years, there has been an impressively fast technological progress in the development of highly efficient lead halide perovskite solar cells. Nonetheless, the stability of perovskite films and associated solar cells remains a source of uncertainty and necessitates sophisticated characterization techniques. Here, we report low‐ to mid‐frequ...

Fluorescence lifetime imaging microscopy (FLIM) is a popular modality to create additional contrast in fluorescence images. By carefully analyzing pixel-based nanosecond lifetime patterns, FLIM allows studying complex molecular populations. At the single-molecule or single-particle level, however, image series often suffer from low signal intensiti...

Nanocrystals (NCs) of inorganic lead halide perovskites with narrow emission line widths hold great potential for next-generation color-saturated optoelectronic devices. However, their stability and electroluminescence performance are currently hindered by environment-dependent structure deterioration over time and inferior carrier transport. These...

Clathrin assembles at the cells’ plasma membrane in a multitude of clathrin-coated structures (CCSs). Among these are flat clathrin lattices (FCLs), alternative clathrin structures that have been found in specific cell types, including cancer cells. Here we show that these structures are also present in different colorectal cancer (CRC) cell lines,...

The frequency of reports utilizing synchrotron‐based grazing incident wide angle X‐ray scattering (GIWAXS) to study metal halide perovskite thin films has exploded recently, as this technique has proven invaluable for understanding several structure‐property relationships that fundamentally limit optoelectronic performance. The GIWAXS geometry and...

Synergically combining their respective ultrahigh charge mobility and strong light absorption, graphene (Gr)/semiconductor heterostructures are promising building blocks for efficient optoelectronics, particularly photodetectors. Charge transfer (CT) across the heterostructure interface crucially determines device efficiency and functionality. Here...

Solvatochromic compounds have emerged as valuable environment-sensitive probes for biological research, with the chromophore of the green fluorescent protein (GFP) being a well-studied example. In this study, we demonstrate that synthetic analogues of the GFP chromophore can be used to investigate ligand-induced conformational changes in proteins....

Fluorescence lifetime imaging microscopy (FLIM) is a popular modality to create additional contrast in fluorescence images. By carefully analyzing pixel-based nanosecond lifetime patterns, FLIM allows studying complex molecular populations. At the single molecule or single particle level, however, image series often suffer from low signal intensiti...

Die überwältigende Konkurrenz durch Wasserstoff/Sauerstoff‐Entwicklungsreaktionen und die geringe Löslichkeit von N 2 in wässrigen Systemen beeinträchtigen die Selektivität und Aktivität bei der Stickstofffixierungsreaktion. Hier entwerfen wir eine aerob‐hydrophobe Janus‐Struktur, indem wir eine fluorierte Modifikation auf porösen Kohlenstoff‐Nanof...

Expansion Microscopy (ExM) revolutionized the field of super-resolution microscopy by allowing for subdiffraction resolution fluorescence imaging on standard fluorescence microscopes. However, it has been found that it is hard to visualize actin filaments efficiently using ExM. To improve actin imaging, multifunctional molecules have been designed,...

Halide perovskite nanocrystals (PNCs) exhibit growing attention in optoelectronics due to their fascinating color purity and improved intrinsic properties. However, structural defects emerging in PNCs progressively hinder the radiative recombination and carrier transfer dynamics, limiting the performance of light-emitting devices. In this work, we...

G protein-coupled receptors (GPCRs) represent an important class of drug targets, and their structural studies facilitate rational drug discovery. However, atomic structures of only about 20% of human GPCRs have been solved to date. Recombinant production of GPCRs for structural studies at a large scale is challenging due to their low expression le...

All‐inorganic lead‐free Cs 2 AgBiBr 6 double perovskites have gained significant attention due to their potential as stable and nontoxic photoactive semiconductors. Currently, it remains challenging to synthesize homogeneous microcrystals (MCs) exhibiting excellent properties, which are necessary for large‐area device integration. This work propose...

Inorganic chiral nanoparticles are attracting more and more attention due to their peculiar optical properties and potential biological applications, such as bioimaging, therapeutics, and diagnostics. Among inorganic chiral nanoparticles, gold chiral nanostructures were demonstrated to be very interesting in this context, with good physical chemica...

Metal-halide perovskites (MHPs) exhibit excellent properties for application in optoelectronic devices. The bottleneck for their incorporation is the lack of long-term stability such as degradation due to external conditions (heat, light, oxygen, moisture, and mechanical stress), but the occurrence of phase transitions also affects their performanc...

The complex pharmacology of G-protein-coupled receptors (GPCRs) is defined by their multi-state conformational dynamics. Single-molecule Förster Resonance Energy Transfer (smFRET) is well suited to quantify dynamics for individual protein molecules; however, its application to GPCRs is challenging. Therefore, smFRET has been limited to studies of i...

The fabrication of highly qualified patterns for photomasks using an electron beam writer is one of the key methods to achieve the requirements for high-end semiconductor devices manufacturing. We demonstrate in-situ examination of morphology changes in the electron-beam resist using super-resolution single-molecule fluorescence microscopy. An inte...

Expansion microscopy (ExM) is a newly developed super-resolution technique, allowing visualization of biological targets at nanoscale resolution on conventional fluorescence microscopes. Since its introduction in 2015, many efforts have been dedicated to broaden its application range or increase the resolution that can be achieved. As a consequence...

Surface passivation by post-treatment with methylammonium chloride (MACl) is regarded as a promising strategy to suppress surface defects in organic-inorganic lead halide perovskites and elevate the efficiency of solar cells based on these materials. However, traditional MACl post-treatment methods often impede the performance of the final device,...

Mapping of the spatial and temporal motion of particles inside an optical field is critical for understanding and further improvement of the 3D spatio-temporal control over their optical trapping dynamics. However, it is not trivial to capture the 3D motion, and most imaging systems only capture a 2D projection of the 3D motion, in which the inform...

Engineering crystal structure of Cs3BiBr6 and Cs3Bi2Br9 is theoretically and experimentally demonstrated to modulate their photocatalytic performance. This work offers insights into the structure-photoactivity relationships of metal halide perovskites (MHPs) and provides a guideline for exploiting MHPs toward efficient photocatalytic organic synthe...

Rechargeable aqueous zinc‐iodine batteries (ZIBs) are considered a promising newly‐developing energy‐storage system, but the corrosion and dendritic growth occurring on the anode seriously hinder their future application. Here, the corrosion mechanism of polyiodide is revealed in detail, showing that it can spontaneously react with zinc and cause r...

Lead halide perovskites are promising candidates for high-performance light-emitting diodes (LEDs); however, their applicability is limited by their structural instability toward moisture. Although a deliberate addition of water to the precursor solution has recently been shown to improve the crystallinity and optical properties of perovskites, the...

Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auge...

Optical trapping at interfaces has recently gained relevance due to the expansion of optical potential far away from the focus, especially for proteins where submillimeter structures have been described. Initially, lysozyme clusters are trapped as a shallow layer at the surface, becoming thicker with the irradiation time. Nonetheless, overcoming a...

Clathrin assembles at the cells' plasma membrane in a multitude of clathrin coated structures (CCSs). Among these are flat clathrin lattices (FCLs), alternative clathrin structures that have been found in specific cell types, including cancer cells. Here we show that these structures are also present in different colorectal cancer (CRC) cell lines,...

On-skin electronics based on impermeable elastomers and stacking structures often suffer from inferior sweat-repelling capabilities and severe mechanical mismatch between sub-layers employed, which significantly impedes their lengthy wearing comfort and functionality. Herein, inspired by the transpiration system of vascular plants and the water dio...

Large polarons are known to form in lead halide perovskites (LHPs). Photoinduced isolated polarons at low densities have been well-researched, but many-body interactions at elevated polaron densities, exceeding the Mott criterion (i.e., Mott polaron density), have remained elusive. Here, employing ultrafast terahertz spectroscopy, we identify a sta...

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into...

Metal–organic frameworks (MOFs) can provide a variety of nanocompartments for the confinement of guest molecules. Furthermore, the emissions of fluorescent molecules can be tuned by confinement. In this study, a solvent‐free “bottle‐around‐ship” method is used to encapsulate perylene and 9,10‐dimethylanthracene, two polycyclic aromatic hydrocarbons...

Expansion microscopy (ExM) has been widely used to detect biomolecules in cultured cells and tissue samples due to its enablement of super resolution imaging with conventional microscopes, via physical expansion of samples. However, reaction conditions inherent to the process bring about strong fluorescent signal loss during polymerization and dige...

Ambient electrocatalytic nitrogen fixation is an emerging technology for green ammonia synthesis, but the absence of optimized, stable and performant catalysts can render its practical application challenging. Herein, bimetallic NiCo boride nanoparticles confined in MXene are shown to accomplish high-performance nitrogen reduction electrolysis. Tak...

Optical binding has recently gained considerable attention because it enables the light-induced assembly of many-body systems; however, this phenomenon has only been described between directly irradiated particles. Here, we demonstrate that optical binding can occur outside the focal spot of a single tightly focused laser beam. By trapping at an in...

Cs3Bi2Br9 decorated with crystalline-amorphous Pd nanocubes as cocatalyst is reported to photocatalytically coproduce ca. 1400 μmol h−1 g−1 of H2 and benzaldehyde from the selective benzyl alcohol oxidation. This route...

Developing light‐harvesting materials with broad spectral response is of fundamental importance in full‐spectrum solar energy conversion. We found that, when a series of earth‐abundant metal (Cu, Co, Ni and Fe) salts are dissolved in coordinating solvents uniformly dispersed nanodots (NDs) are formed rather than fully dissolving as molecular specie...

Developing light‐harvesting materials with broad spectral response is of fundamental importance in full‐spectrum solar energy conversion. We found that, when a series of earth‐abundant metal (Cu, Co, Ni and Fe) salts are dissolved in coordinating solvents uniformly dispersed nanodots (NDs) are formed rather than fully dissolving as molecular specie...

Faradaic efficiency for the nitrogen reduction reaction (NRR) is often limited by the low N2 solubility in electrolyte while the large number of intimate contacts between the electrolyte and solid catalyst could also inevitably sacrifice many active sites for NRR. Here, we report that a “quasi‐gas‐solid” interface formed in donor‐acceptor based con...

Interactions between epigenetic readers and histone modifications play a pivotal role in gene expression regulation and aberrations can enact etiopathogenic roles in both developmental and acquired disorders like cancer. Typically, epigenetic interactions are studied by mass spectrometry or chromatin immunoprecipitation sequencing. However, in thes...

Structural analysis of metal clusters confined in nanoporous materials is typically performed by X-ray-driven techniques. Although X-ray analysis has proved its strength in the characterization of metal clusters, it provides averaged structural information. Therefore, we here present an alternative workflow for bringing the characterization of conf...

So far, the optical trapping potential is controlled by tuning the physical conditions of the system. Herein, for the first time, an approach, in which the induced optical force or optical potential is controlled, by an external chemical stimulus, is reported. The key to realize this is to design an optical trapping condition in conjunction with re...

Despite the intense research efforts directed to electrocatalytic nitrogen reduction reaction (eNRR), the NH3 yield and selectivity are still not up to the standard of practical application. Here, high-entropy perovskite oxides with composition Bax(FeCoNiZrY)0.2O3−δ (Bx(FCNZY)0.2 (x = 0.9, 1) are reported as eNRR catalysts. The eNRR activity of hig...

As the threshold for stimulated emission is significantly reduced at cryogenic temperatures, cooling of perovskite light emitting diodes (PeLEDs) is considered an essential strategy for reaching injection lasing in perovskite diodes. In this work, we demonstrate the intense electrical pulsing of a PeLED stack up to a few kA cm−2 at cryogenic condit...

Gaining control on particle–particle interactions and in this way on their (self)‐assembled structures is essentialfor colloidal and material sciences. Currently, different strategies are described to achieve such control, however, all of them lack the spatiotemporal resolution required at the microscale. In this work, the potential of combining op...

We demonstrate a new case of materials‐gene engineering to precisely design photocatalysts with the prescribed properties. Based on theoretical calculations, a phase‐doping strategy was proposed to regulate the pathways of CO2 conversion over Au nanoparticles (NPs) loaded TiO2 photocatalysts. As a result, the thermodynamic bottleneck of CO2‐to‐CO c...

We demonstrate a new case of materials‐gene engineering to precisely design photocatalysts with the prescribed properties. Based on theoretical calculations, a phase‐doping strategy was proposed to regulate the pathways of CO2 conversion over Au nanoparticles (NPs) loaded TiO2 photocatalysts. As a result, the thermodynamic bottleneck of CO2‐to‐CO c...

Genetically-encoded biosensors based on a single fluorescent protein are widely used to visualize analyte levels or enzymatic activities in cells, though usually to monitor relative changes rather than absolute values. We report photochromism-enabled absolute quantification (PEAQ) biosensing, a method that leverages the photochromic properties of b...

With fascinating photophysical properties and strong potential to utilize solar energy, metal halide perovskites (MHPs) have become a prominent feature within photocatalysis research. However, the effectiveness of single MHP photocatalysts is relatively poor. The introduction of a second component to form a heterojunction represents a well‐establis...

Inverted perovskite solar cells (PSCs) prepared by anti‐solvent method have achieved power conversion efficiencies (PCEs) of over 23%, but they are not ideal for device upscaling. Conversely, gas‐quenched PSCs offer great potential for upscaling, but their performance still lags behind. Herein, we seek to upgrade the gas‐quenched films through both...

Background: Liver metastasis is the primary cause of colorectal cancer (CRC)-associated death. Aryl-hydrocarbon receptor-interacting protein (AIP), a putative positive intermediary in aryl-hydrocarbon receptor-mediated signalling, is overexpressed in highly metastatic human KM12SM CRC cells and other highly metastatic CRC cells. Methods: Meta-an...

With fascinating photophysical properties and strong potential to utilize solar energy, metal halide perovskites (MHPs) have become a prominent feature within photocatalysis research. However, the effectiveness of single MHP photocatalysts is relatively poor. The introduction of a second component to form a heterojunction represents a well‐establis...

We report a porous metal-organic framework loaded with single Pt atoms, namely PCN-222(Pt) nanorods, which are prepared by the self-assembly of Pt-metalized tetrakis(4-carboxyphenyl)porphyrin ligand with a Zr6 cluster. The mass-loading of Pt in the synthesized PCN-222(Pt) is up to 4.67%, and can be accurately controlled by using an in-situ reaction...

The optoelectronic properties of a series of p-phenylene vinylene derivatives are studied herein to scrutinize their relationship with the molecular flexibility of the peripheral groups induced by the hybridization of the presented nitrogen atoms. All the molecules share a model fluorophore in the core, 1,3,5-tristyrylbenzene, as a structural leitm...

Ruddlesden–Popper perovskite is a class of layered halide perovskite which gained much attention over the past few years in the field of photovoltaics. Herein, we have presented a compendious sketch of third-order nonlinear optical (NLO) properties of (PEA)2Cs4Pb5Br16, a quasi-two-dimensional (2D) perovskite using femtosecond Z-scan technique at 80...

Recently, the detection and quantification of humidity has attracted great interest, but for fluorescence sensing of humidity, it is still a challenge to achieve high-performance. Here, we report an ultrasensitive...

Population growth, depletion of world resources and persistent toxic chemical production underline the need to seek new smart materials from inexpensive, biodegradable, and renewable feedstocks. Hence, "metal-free" ring-opening copolymerization to convert biomass carvone-based monomers into non-conventional luminescent biopolymers is considered a s...