Sulfur-Phenolate Exchange: SuFEx-Derived Dynamic Covalent Reactions and Degradation of SuFEx Polymers.

The products of the SuFEx reaction between sulfonimidoyl fluorides and phenols, sulfonimidates, are shown to display dynamic covalent chemistry with other phenols. This reaction was shown to be enantiospecific, finished in minutes at room temperature in high yields, and useful for both asymmetric synthesis and sustainable polymer production. Its wide scope further extends the usefulness of SuFEx and related click chemistries.

Microsphere Peptide-Based Immunoassay for the Detection of Recombinant Bovine Somatotropin in Injection Preparations.

The use of peptides in immunoassays can be favored over the use of the full protein when more cost effective or less toxic approaches are needed, or when access to the full protein is lacking. Due to restricted access to recombinant bovine somatotropin (rbST), a protein enhancing growth and lactating performances of livestock, which use has been banned in the EU, Canada and Australia (amongst others), we developed a peptide-based biorecognition assay on an imaging planar array analyzer. For this, we identified the rbST epitope that is responsible for binding to the rbST-targeting monoclonal antibody 4H12 (MAb 4H12) to be 115DLEEGILALMR125. This linear peptide was synthesized and coupled to microspheres, after which it was tested in a biorecognition competitive inhibition assay format. We observed IC50 values of approximately 0.11 µg mL-1, which are lower than observed for the full rbST protein (IC50 = 0.20 µg mL-1). Importantly, there was no binding with the scrambled peptide. Preliminary results of directly coupled peptides in a microsphere biorecognition assay for detection of rbST are presented. Real-life applicability for detection of somatotropins (STs) in injection preparations of bovine-, porcine- and equine ST are shown. This newly developed immunoassay strongly supports future developments of peptide-based immunoassays to circumvent the limited access to the full protein.

Configurationally Chiral SuFEx-Based Polymers.

Novel methods to make synthetic chiral polymers are highly desirable given their potential in a rapidly increasing number of bio-inspired applications. The enantiospecific sulfur-fluorine exchange (SuFEx) reaction of chiral di-sulfonimidoyl fluorides (di-SFs) with diphenols, was used to produce high-molecular-weight chiral polymers with configurational backbone chirality. The resulting new class of polymers, polysulfonimidates, can be efficiently produced via this step-growth mechanism for a wide range of di-SFs and diphenols, yielding MnPS up to 283 kDa with a typical dispersity D around 1.6. The optical activity of the resulting chiral polymers is largely due to the intrinsic asymmetry of the S atoms (configurational chirality). Finally, the enantiospecificity (ee>98 %) of the polymerization reaction was demonstrated by the degradation of a disulfide-containing polysulfonimidate. This novel route towards configurational main-chain chirality opens up new approaches towards tailor-made chiral polymers with precisely defined properties.

Efficient Chemical Surface Modification Protocol on SiO2 Transducers Applied to MMP9 Biosensing.

The bioreceptor immobilization process (biofunctionalization) turns to be one of the bottlenecks when developing a competent and high sensitivity label-free biosensor. Classical approaches seem to be effective but not efficient. Although biosensing capacities are shown in many cases, the performance of the biosensor is truncated by the inefficacious biofunctionalization protocol and the lack of reproducibility. In this work, we describe a unique biofunctionalization protocol based on chemical surface modification through silane chemistry on SiO2 optical sensing transducers. Even though silane chemistry is commonly used for sensing applications, here we present a different mode of operation, applying an unusual silane compound used for this purpose (3-Ethoxydimethylsilyl)propylamine, APDMS, able to create ordered monolayers, and minimizing fouling events. To endorse this protocol as a feasible method for biofunctionalization, we performed multiple surface characterization techniques after all the process steps: Contact angle (CA), X-ray photoelectron spectroscopy (XPS), ellipsometry, and fluorescence microscopy. Finally, to evidence the outputs from the SiO2 surface characterization, we used those SiO2 surfaces as optical transducers for the label-free biosensing of matrix metalloproteinase 9 (MMP9). We found and demonstrated that the originally designed protocol is reproducible, stable, and suitable for SiO2-based optical sensing transducers.

SuFExable polymers with helical structures derived from thionyl tetrafluoride.

Sulfur(VI) fluoride exchange (SuFEx) is a category of click chemistry that enables covalent linking of modular units through sulfur(VI) connective hubs. The efficiency of SuFEx and the stability of the resulting bonds have led to polymer chemistry applications. Now, we report the SuFEx click chemistry synthesis of several structurally diverse SOF4-derived copolymers based on the polymerization of bis(iminosulfur oxydifluorides) and bis(aryl silyl ethers). This polymer class presents two key characteristics. First, the [-N=S(=O)F-O-] polymer backbone linkages are themselves SuFExable and undergo precise SuFEx-based post-modification with phenols or amines to yield branched functional polymers. Second, studies of individual polymer chains of several of these new materials indicate helical polymer structures. The robust nature of SuFEx click chemistry offers the potential for post-polymerization modification, enabling the synthesis of materials with control over composition and conformation.

Organosilicon uptake by biological membranes.

Organosilicon compounds are ubiquitous in everyday use. Application of some of these compounds in food, cosmetics and pharmaceuticals is widespread on the assumption that these materials are not systemically absorbed. Here the interactions of various organosilicon compounds (simeticone, hexamethyldisilazane and polydimethylsiloxane) with cell membranes and models thereof were characterized with a range of analytical techniques, demonstrating that these compounds were retained in or on the cell membrane. The increasing application of organosilicon compounds as replacement of other plastics calls for a better awareness and understanding of these interactions. Moreover, with many developments in biotechnology relying on organosilicon materials, it becomes important to scrutinize the potential effect that silicone leaching may have on biological systems.

Change in Tetracene Polymorphism Facilitates Triplet Transfer in Singlet Fission-Sensitized Silicon Solar Cells.

Singlet fission in tetracene generates two triplet excitons per absorbed photon. If these triplet excitons can be effectively transferred into silicon (Si), then additional photocurrent can be generated from photons above the bandgap of Si. This could alleviate the thermalization loss and increase the efficiency of conventional Si solar cells. Here, we show that a change in the polymorphism of tetracene deposited on Si due to air exposure facilitates triplet transfer from tetracene into Si. Magnetic field-dependent photocurrent measurements confirm that triplet excitons contribute to the photocurrent. The decay of tetracene delayed photoluminescence was used to determine a transfer efficiency of ∼36% into Si. Our study suggests that control over the morphology of tetracene during the deposition will be of great importance to boost the triplet transfer yield further.

Surface Heterogeneous Nucleation-Mediated Release of Beta-Carotene from Porous Silicon.

We demonstrate that the release of a poorly soluble molecule from nanoporous carriers is a complex process that undergoes heterogeneous surface nucleation events even under significantly diluted release conditions, and that those events heavily affect the dynamics of release. Using beta-carotene and porous silicon as loaded molecule and carrier model, respectively, we show that the cargo easily nucleates at the pore surface during the release, forming micro- to macroscopic solid particles at the pores surface. These particles dissolve at a much slower pace, compared to the rate of dissolution of pure beta-carotene in the same solvent, and they negatively affect the reproducibility of the release experiments, possibly because their solubility depends on their size distribution. We propose to exploit this aspect to use release kinetics as a better alternative to the induction time method, and to thereby detect heterogenous nucleation during release experiments. In fact, release dynamics provide much higher sensitivity and reproducibility as they average over the entire sample surface instead of depending on statistical analysis over a small area to find clusters.

A method to detect triplet exciton transfer from singlet fission materials into silicon solar cells: Comparing different surface treatments.

Singlet fission is one of the most promising routes to overcome the single-junction efficiency limit for solar cells. Singlet fission-enhanced silicon solar cells are the most desirable implementation, but transfer of triplet excitons, the product of singlet fission, into silicon solar cells has proved to be very challenging. Here, we report on an all optical measurement technique for the detection of triplet exciton quenching at semiconductor interfaces, a necessary requirement for triplet exciton or charge transfer. The method relies on the growth of individual, single-crystal islands of the singlet fission material on the silicon surface. The islands have different heights, and we correlate these heights to the quenching efficiency of triplet excitons. The quenching efficiency is measured by spatially resolved delayed fluorescence and compared to a diffusion-quenching model. Using silicon capped with a blocking thermal oxide and aromatic monolayers, we demonstrate that this technique can quickly screen different silicon surface treatments for triplet exciton quenching.

Fast room-temperature functionalization of silicon nanoparticles using alkyl silanols.

Silicon nanoparticles (Si NPs) are a good alternative to conventional heavy metal-containing quantum dots in many applications, due to their low toxicity, low cost, and the high natural abundance of the starting material. Recently, much synthetic progress has been made, and crystalline Si NPs can now be prepared in a matter of hours. However, the passivation of these particles is still a time-consuming and difficult process, usually requiring high temperatures and/or harsh reaction conditions. In this paper, we report an easy method for the room-temperature functionalization of hydrogen-terminated Si NPs. Using silanol compounds, a range of functionalized Si NPs could be produced in only 1 h reaction time at room temperature. The coated NPs were fully characterized to determine the efficiency of binding and the effects of coating on the optical properties of the NPs. It was found that Si NPs were effectively functionalized, and that coated NPs could be extracted from the reaction mixture in a straightforward manner. The silanol coating increases the quantum yield of fluorescence, decreases the spectral width and causes a small (∼50 nm) blue-shift in both the excitation and emission spectra of the Si NPs, compared to unfunctionalized particles.

Immuno-capture of extracellular vesicles for individual multi-modal characterization using AFM, SEM and Raman spectroscopy.

Tumor-derived extracellular vesicles (tdEVs) are promising blood biomarkers for cancer disease management. However, blood is a highly complex fluid that contains multiple objects in the same size range as tdEVs (30 nm-1 µm), which obscures an unimpeded analysis of tdEVs. Here, we report a multi-modal analysis platform for the specific capture of tdEVs on antibody-functionalized stainless steel substrates, followed by their analysis using SEM, Raman spectroscopy and AFM, at the single EV level in terms of size and size distribution, and chemical fingerprint. After covalent attachment of anti-EpCAM (epithelial cell adhesion molecule) antibodies on stainless steel substrates, EV samples derived from a prostate cancer cell line (LnCAP) were flushed into a microfluidic device assembled with this stainless steel substrate for capture. To track the captured objects between the different analytical instruments and subsequent correlative analysis, navigation markers were fabricated onto the substrate from a cyanoacrylate glue. Specific capture of tdEVs on the antibody-functionalized surface was demonstrated using SEM, AFM and Raman imaging, with excellent correlation between the data acquired by the individual techniques. The particle distribution was visualized with SEM. Furthermore, a characteristic lipid-protein band at 2850-2950 cm-1 was observed with Raman spectroscopy, and with AFM the size distribution and surface density of the captured EVs was assessed. Finally, correlation of SEM and Raman images enabled discrimination of tdEVs from cyanoacrylate glue particles, highlighting the capability of this multi-modal analysis platform for distinguishing tdEVs from contamination. The trans-instrumental compatibility of the stainless steel substrate and the possibility to spatially correlate the images of the different modalities with the help of the navigation markers open new avenues to a wide spectrum of combinations of different analytical and imaging techniques for the study of more complex EV samples.

Systematic Comparison of Zwitterionic and Non-Zwitterionic Antifouling Polymer Brushes on a Bead-Based Platform.

Nonspecific adsorption of biomolecules to solid surfaces, a process called biofouling, is a major concern in many biomedical applications. Great effort has been made in the development of antifouling polymer coatings that are capable of repelling the nonspecific adsorption of proteins, cells, and micro-organisms. In this respect, we herein contribute to understanding the factors that determine which polymer brush results in the best antifouling coating. To this end, we compared five different monomers: two sulfobetaines, a carboxybetaine, a phosphocholine, and a hydroxyl acrylamide. The antifouling coatings were analyzed using our previously described bead-based method with flow cytometry as the read-out system. This method allows for the quick and automated analysis of thousands of beads per second, enabling fast analysis and good statistics. We report the first direct comparison made between a sulfobetaine with opposite charges separated by two and three methylene groups and a carboxybetaine bearing two separating methylene groups. It was concluded that both the distance between opposite charges and the nature of the anionic groups have a distinct effect on the antifouling performance. Phosphocholines and simple hydroxyl acrylamides are not often compared with the betaines. However, here we found that they perform equally well or even better, yielding the following overall antifouling ranking: HPMAA ≥ PCMA-2 ≈ CBMAA-2 > SBMAA-2 > SBMAA-3 ≫ nonmodified beads (HPMAA being the best).

High electrical conductivity and high porosity in a Guest@MOF material: evidence of TCNQ ordering within Cu3BTC2 micropores.

The host-guest system TCNQ@Cu3BTC2 (TCNQ = 7,7,8,8-tetracyanoquinodimethane, BTC = 1,3,5-benzenetricarboxylate) is a striking example of how semiconductivity can be introduced by guest incorporation in an otherwise insulating parent material. Exhibiting both microporosity and semiconducting behavior such materials offer exciting opportunities as next-generation sensor materials. Here, we apply a solvent-free vapor phase loading under rigorous exclusion of moisture, obtaining a series of the general formula xTCNQ@Cu3BTC2 (0 ≤ x ≤ 1.0). By using powder X-ray diffraction, infrared and X-ray absorption spectroscopy together with scanning electron microscopy and porosimetry, we provide the first structural evidence for a systematic preferential arrangement of TCNQ along the (111) lattice plane and the bridging coordination motif to two neighbouring Cu-paddlewheels, as was predicted by theory. For 1.0TCNQ@Cu3BTC2 we find a specific electrical conductivity of up to 1.5 × 10-4 S cm-1 whilst maintaining a high BET surface area of 573.7 m2 g-1. These values are unmatched by MOFs with equally high electrical conductivity, making the material attractive for applications such as super capacitors and chemiresistors. Our results represent the crucial missing link needed to firmly establish the structure-property relationship revealed in TCNQ@Cu3BTC2, thereby creating a sound basis for using this as a design principle for electrically conducting MOFs.

One-Step Generation of Reactive Superhydrophobic Surfaces via SiHCl3-Based Silicone Nanofilaments.

Superhydrophobic surfaces gain ever-growing attention because of their applicability in many (consumer) products/materials as they often display, among others, antifouling, anti-icing, and/or self-cleaning properties. A simple way to achieve superhydrophobicity is through the growth of silicone nanofilaments. These nanofilaments, however, are very often nonreactive and thus difficult to utilize in subsequent chemistries. In response, we have developed a single-step procedure to grow (SiHCl3-based) silicone nanofilaments with selective reactivity that are intrinsically superhydrophobic. The silicone nanofilaments could be further functionalized via Pt-catalyzed hydrosilylation of exposed Si-H moieties. These surfaces are easily obtained using mild conditions and are stable under hydrolytic conditions (neutral water, 24 h at 80 °C) while remaining highly transparent, which makes them well suited for optical and photochemical experiments.

One-Pot Gram-Scale Synthesis of Hydrogen-Terminated Silicon Nanoparticles.

Silicon nanoparticles (Si NPs) are highly attractive materials for typical quantum dots functions, such as in light-emitting and bioimaging applications, owing to silicon's intrinsic merits of minimal toxicity, low cost, high abundance, and easy and highly stable functionalization. Especially nonoxidized Si NPs with a covalently bound coating serve well in these respects, given the minimization of surface defects upon hydrosilylation of H-terminated Si NPs. However, to date, methods to obtain such H-terminated Si NPs are still not easy. Herein, we report a new synthetic method to produce size-tunable robust, highly crystalline H-terminated Si NPs (4-9 nm) using microwave irradiation within 5 min at temperatures between 25 and 200 °C and their further covalent functionalization. The key step to obtain highly fluorescent (quantum yield of 7-16%) green-red Si NPs in one simple step is the reduction of triethoxysilane and (+)-sodium l-ascorbate, yielding routinely ∼1 g of H-Si NPs via a highly scalable route in 5-15 min. Subsequent functionalization via hydrosilylation yielded Si NPs with an emission quantum yield of 12-14%. This approach can be used to easily produce high-quality H-Si NPs in gram-scale quantities, which brings the application of functionalized Si NPs significantly closer.

Quantitative and Orthogonal Formation and Reactivity of SuFEx Platforms.

The constraints of minute reactant amounts and the impossibility to remove any undesired surface-bound products during monolayer functionalization of a surface necessitate the selection of efficient, modular and orthogonal reactions that lead to quantitative conversions. Herein, we explore the character of sulfur-fluoride exchange (SuFEx) reactions on a surface, and explore the applicability for quantitative and orthogonal surface functionalization. To this end, we demonstrate the use of ethenesulfonyl fluoride (ESF) as an efficient SuFEx linker for creating "SuFEx-able" monolayer surfaces, enabling three distinct approaches to utilize SuFEx chemistry on a surface. The first approach relies on a di-SuFEx loading allowing dual functionalization with a nucleophile, while the two latter approaches focus on dual (CuAAC-SuFEx/SPOCQ-SuFEx) click platforms. The resultant strategies allow facile attachment of two different substrates sequentially on the same platform. Along the way we also demonstrate the Michael addition of ethenesulfonyl fluoride to be a quantitative surface-bound reaction, indicating significant promise in materials science for this reaction.

High-Density Modification of H-Terminated Si(111) Surfaces Using Short-Chain Alkynes.

H-Si(111)-terminated surfaces were alkenylated via two routes: through a novel one-step gas-phase hydrosilylation reaction with short alkynes (C3 to C6) and for comparison via a two-step chlorination and Grignard alkenylation process. All modified surfaces were characterized by static water contact angles and X-ray photoelectron spectroscopy (XPS). Propenyl- and butenyl-coated Si(111) surfaces display a significantly higher packing density than conventional C10-C18 alkyne-derived monolayers, showing the potential of this approach. In addition, propyne chemisorption proceeds via either of two approaches: the standard hydrosilylation at the terminal carbon (lin) at temperatures above 90 °C and an unprecedented reaction at the second carbon (iso) at temperatures below 90 °C. Molecular modeling revealed that the packing energy of a monolayer bonded at the second carbon is significantly more favorable, which drives iso-attachment, with a dense packing of surface-bound iso-propenyl chains at 40% surface coverage, in line with the experiments at <90 °C. The highest density monolayers are obtained at 130 °C and show a linear attachment of 1-propenyl chains with 92% surface coverage.

Universal Calibration of Computationally Predicted N 1s Binding Energies for Interpretation of XPS Experimental Measurements.

Computationally predicted N 1s core level energies are commonly used to interpret the experimental measurements obtained with X-ray photoelectron spectroscopy. This work compares the application of Koopmans' theorem to core electrons using the B3LYP functional with two commonly used basis sets, analyzes the factors relevant to the comparison of the computational with experimental data, and presents several correlations that allow an accurate prediction of the N 1s binding energy. The first correlation is obtained with a series of known nitrogen-containing functional groups on well-characterized organic monolayers. This approach can then be reliably extended to a number of nitrogen-containing chemical systems on silicon surfaces in which the nature of the chemical environment of nitrogen atoms had only been proposed based on a number of analytical techniques. In most of those cases, the XPS analysis is consistent with the proposed structures, but is not always sufficient for conclusive assignments. Third, it was attempted to also include N-containing systems on metals. Despite the admittedly oversimplified approach taken in this case (the metal surface is approximated by a single atom), the observed correlations are still experimentally useful, although in this case significant outliers are found. Finally, previously published correlations between experimental and theoretical C 1s data were reexamined, yielding a set of correlations that allow experimentalists to predict C 1s and N 1s XPS spectra with high accuracy.