Unraveling the Influence of the Carbon Skeleton Structure and Substituent Electronic Effects on the Nontraditional Intrinsic Luminescence Properties of Nonconjugated Polyolefins

Through-space conjugation (TSC) has gradually been proven to be a vital interaction in photophysical processes, especially with the recent observation of nontraditional intrinsic luminescence (NTIL) arising from cluster/aggregation-induced molecular-scale confinement. However, although the effect of the spatial distance between molecular chains has been understood, it is not clear how the distance between adjacent conjugated structures in a single chain affects the NTIL properties of polymers, and this has become a significant research focus. Herein, four nonconjugated polyolefins with different carbon skeletons (C5/C6/C7/C8, in which the repeat units contained 5, 6, 7, and 8 carbon atoms, respectively) were synthesized, and their photophysical properties were systematically studied. The experimental and theoretical results showed that although the carbon skeleton of the C5 polymer contained only one less carbon atom than that of the C6 polymer (but possessed the same conjugated structure in the chain), the C5 polymer (QY = 23.4%) exhibited a much greater luminescence efficiency than the C6 polymer (QY = 3.3%). Moreover, the distance to the neighboring conjugated structure in the C7/C8 polymer chains was the same as that in the C5/C6 polymers, whereas the conjugated structure in the C7/C8 polymers had a longer π conjugation region and more rigid polymer chains than the C5/C6 polymers; thus, the C7/C8 polymer had longer fluorescence emission wavelengths than the C5/C6 polymers. Moreover, simple and nonconjugated polymers of CPBB (PCPBB-C4) derivatives with electron-donating (methoxy) and electron-withdrawing (alkynyl) groups were also prepared, and the fluorescence spectra showed that both the electron-donating (increased electron density and stabilized TSC) and electron-withdrawing (increased through space electronic interactions) groups in PCPBB-C4 resulted in red-shifted luminescence and increased luminescence efficiency. Above all, these insights reveal that the carbon skeleton structure and substituent electronic effects strongly influence the NTIL properties and provide valuable strategies for optimizing the NTIL efficiency and tuning the emission colors of nonconjugated polymers

A Facile Method for Permanent and Functional Surface Modification of Poly(dimethylsiloxane)

An initiator integrated poly(dimethylsiloxane) (iPDMS) was prepared from a commercially available PDMS by simple mixing and curing, which was then used to realize permanent and functional surface modification via surface-initiated atom transfer radical polymerization

Label-Free Real-Time Detection of DNA Methylation Based on Quartz Crystal Microbalance Measurement

DNA methylation plays an important role in the regulation of gene transcription, chromatin compaction, genome imprinting, and X-chromosome inactivation. DNA methyltransferase is considered a potential target for anticancer drug design. It is important to locate aberrantly methylated sequences on the human genome that are linked to specific diseases and to discover new low-toxic methylation inhibitors for medical treatments. We developed a DNA methylation detection method using a quartz crystal microbalance (QCM). We applied this method to assay genes <i>p16</i> and <i>GALR2</i> in two cell lines. Methylation of <i>p16</i> was detected in both HT29 and HepG2 cell lines, whereas methylation of <i>GALR2</i> was detected only in the HT29 cell line. We also used this method to evaluate the effect of 5-aza-2′-deoxycytidine (decitabine), a methyltransferase inhibitor used in clinical treatment. We found methylation of genes <i>p16</i> and <i>GALR2</i> to be strongly inhibited. The results show that this method is sensitive to DNA methylation and is fit for evaluation of methyltransferase inhibitors

Convergence of Dissipation and Impedance Analysis of Quartz Crystal Microbalance Studies

A quartz crystal microbalance (QCM) consists of a resonator, which measures the resonance frequency of the quartz slab. When coupled with a network analyzer or coupled with impulse excitation technology, QCM gives additional impedance or dissipation information, respectively. This report provides a set of equations that bring the QCM community a convergence of the dissipation and impedance analysis. Equations derived from the complex frequency shift were applied to quantitatively analyze the dissipation data of polymer brushes obtained from QCM-D. The obtained viscoelastic properties of polymer brushes were then compared with those obtained by the Voigt model method. We believe that these equations will be useful in quantitative studies of interfacial phenomena accompanied with mass or viscoelasticity changes

Initiator Integrated Poly(dimethysiloxane)-Based Microarray as a Tool for Revealing the Relationship between Nonspecific Interactions and Irreproducibility

Nonspecific interactions (NSIs) and irreproducibility greatly reduce the accuracy of antigen–antibody screening, which is key to the discovery of monoclonal antibody drugs and biomarkers identification. We previously developed a solid supporting material, polymer-coated initiator integrated poly­(dimethysiloxane) (iPDMS), which is able to provide near-zero background for microarray screening. Here, we applied two monoclonal antibodies (mAbs), namely, anti-FLAG and HM1, to screen an iPDMS-based peptide microarray with 2083 peptides from 62 proteins to evaluate NSIs and irreproducibility. In addition to recognizing their cognate epitopes, the two mAbs also cross-reacted with random sequences, especially when they were used at high concentrations. At 50 μg mL^–1, 295 peptides (14.2% of the peptide library) had positive reactions to anti-FLAG and only 39 peptides (1.9%) reacted positively to HM1. Virtually all cross-reactions disappeared when the [mAbs] reached 0.01 μg mL^–1. Reproducible experiments of 404 peptides at various [mAbs] showed that only specific interactions, molecular mimicry, and mimotope were reproducible between different experiments. These findings suggest that irreproducibility was at least partially caused by NSIs. We also demonstrated that repeating tests and mAb dilution could effectively avoid NSI-related irreproducibility in serological screening. This will not only largely simplify the data analysis, but will also make immunoassays more reliable for clinical research

In Vitro Hemocompatibility and Toxic Mechanism of Graphene Oxide on Human Peripheral Blood T Lymphocytes and Serum Albumin

Graphene oxide (GO) has shown tremendous application potential as a biomedical material. However, its interactions with blood components are not yet well understood. In this work, we assess the toxicity of pristine GO (<i>p</i>-GO) and functionalized GO (GO-COOH and GO-PEI) to primary human peripheral blood T lymphocytes and human serum albumin (HSA), and also study the underlying toxic mechanism. Our results indicate that <i>p</i>-GO and GO-COOH have good biocompatibility to T lymphocytes at the concentration below 25 μg mL^–1, but notable cytotoxicity above 50 μg mL^–1. By contrast, GO-PEI exhibits significant toxicity even at 1.6 μg mL^–1. Further investigations show that although <i>p</i>-GO does not enter into the cell or damage the membrane, its presence leads to the increase in reactive oxygen species (ROS), moderate DNA damage, and T lymphocyte apoptosis. Interestingly, little effect on T lymphocyte immune response suppression is observed in this process despite <i>p</i>-GO inflicting cell apoptosis. The toxic mechanism is that <i>p</i>-GO interacts directly with the protein receptors to inhibit their ligand-binding ability, leading to ROS-dependent passive apoptosis through the B-cell lymphoma-2 (Bcl-2) pathway. Compared with <i>p</i>-GO, GO-COOH exhibits a similar toxic effect on T lymphocytes except keeping a normal ROS level. A proposed toxic mechanism is that GO-COOH inhibits protein receptor–ligand binding, and passes the passive apoptosis signal to nucleus DNA through a ROS-independent mechanism. On the other hand, GO-PEI shows severe hematotoxicity to T lymphocytes by inducing membrane damage. For plasma protein HSA, the binding of GO-COOH results in minimal conformational change and HSA’s binding capacity to bilirubin remains unaffected, while the binding of <i>p</i>-GO and GO-PEI exhibits strong toxicity on HSA. These findings on the interactions of two-dimensional nanomaterials and biological systems, along with the enquiry of the mechanisms, would provide essential support for further safety evaluation of the biomedical applications of GO

Superhydrophobic Poly(dimethylsiloxane) via Surface-Initiated Polymerization with Ultralow Initiator Density

We reported herein a facile method that utilized surface-initiated polymerization (SIP) alone to produce superhydrophobic poly(dimethylsiloxane) (PDMS) surfaces, either flat or as the wall of microfluidic channels. In this so-called relayed SIP strategy, the first SIP was conducted from the initiator integrated PDMS (iPDMS) of varied initiator density, i.e., from 0.5iPDMS to 10−6iPDMS, corresponding to surface density of 3.7 × 10−2 and 1.0 × 10−9 chains nm−2, respectively, an estimation based on uniform distribution of feed initiator molecules. The monomer in use was oligo(ethylene glycol) methacrylate, resulting in poly(OEGMA) chains with terminal hydroxyl groups. The iPDMS substrates were then treated with bromoisobutyryl bromide as the initiation moiety, followed by the second SIP using monomer 1H,1H,2H,2H-perfluorodecyl methacrylate (FMA). The resulting surface was covered with polymeric trees that had poly(FMA) as the branches and poly(OEGMA) as the central trunk. Only the iPDMS of ultralow initiator density, i.e., 10−3iPDMS (1.0 × 10−5 chains nm−2), produced a superhydrophobic surface with a contact angle of water at 155°. The impact of SIP duration and monomer in use was also studied. The results demonstrated that SIP from substrates of ultralow initiator density could also produce functional surfaces. Furthermore, because this method is compatible with the in situ modification of microfluidic channels, it also provides new opportunities for the field of microfluidics

Fibronectin and Bone Morphogenetic Protein-2-Decorated Poly(OEGMA-<i>r</i>-HEMA) Brushes Promote Osseointegration of Titanium Surfaces

To be better used as medical implants in orthopedic and dental clinical applications, titanium and titanium-based alloys need to be capable of inducing osteogenesis. Here we describe a method that allows the facile decoration of titanium surfaces to impart an osteogenesis capacity. A Ti surface was first deposited on a poly(OEGMA-r-HEMA) film using surface-initiated atom-transfer radical polymerization (SI-ATRP) with the further step of carboxylation. The modified surfaces were resistant to cell adhesion. Fibronectin (FN) and recombinant human bone morphogenetic protein-2 (rhBMP-2) were further immobilized onto p(OEGMA-r-HEMA) matrices. Our results demonstrate that the FN- and rhBMP-2-conjugated polymer surfaces could induce the adhesion of MC3T3 cells on Ti surfaces. Moreover, the protein-tethered surface exhibited enhanced cell differentiation in terms of alkaline phosphatase activity compared to that of the pristine Ti surface at similar cell proliferation rates. This research establishes a simple modification method of Ti surfaces via Ti-thiolate self-assembled monolayers (SAMs) and SI-ATRP and identifies a dual-functional Ti surface that combines antifouling and osseointegration promotion

Study Viscoelasticity of Ultrathin Poly(oligo(ethylene glycol) methacrylate) Brushes by a Quartz Crystal Microbalance with Dissipation

Ultrathin polymer brushes play important roles in natural and artificial systems. To better understand and utilize their unique behaviors, characterization is a fundamental, but not trivial, task. In this paper, we demonstrated that the quartz crystal microbalance with dissipation (QCM-D) could be applied to study ultrathin poly(oligo(ethylene glycol) methacrylate) brushes. First, we identified four linear relations between dissipation/frequency changes and thickness changes, which were measured by QCM-D and ellipsometry, respectively. Next, we derived a set of equations starting from the Voigt model to further extract viscoelasticity of poly(OEGMA) brushes (≤30 nm) under high-frequency vibration in contact with water. The viscosity was ∼10−3 N s m−2 and the elasticity was ∼105 N m−2. Both were frequency dependent. Also discussed were other quantities such as the density (both the dry and wet film) and the working range of linear relations. These equations and quantitative information are important in advancing our understanding of ultrathin polymer brushes, which consequently promote our ability in designing functional surface coatings (i.e., in biosensor applications) and studying related interfacial phenomena

Single-Chain Polymers Achieved from Radical Polymerization under Single-Initiator Conditions

Radical polymerization from a single initiator molecule in a microenvironment is a nearly ideal system in which bimolecular termination, solution concentration, and viscosity changes could be neglected. In this study, we provide two facile methods of preparing polymers via atom-transfer radical polymerization (ATRP) under single-initiator conditions: tether initiators on planar substrates at superlow density through mixed self-assembled monolayers (SAMs) and encapsulated single initiators in microfluidic droplets. The molecular weight (MW) of the resultant polymers characterized by atomic force microscope-based single-molecule force spectroscopy (AFM-based SMFS) showed that the single-chain ATRP had an extraordinarily faster chain propagation rate (2 unit/s) on planar substrates and gave polymers with much higher MWs (105–106 g/mol) than those obtained from traditional ATRP (103–105 g/mol). The former method offered a general platform for single-chain polymer synthesis and investigation, and the latter could be amplified to obtain abundant single-chain polymers with ultrahigh molecular weight (UHMW) for commercial applications