Oleyl group-functionalized insulating gate transistors for measuring extracellular pH of floating cells

Control of interface functions in solid-state biosensors for stable detection of molecular recognition

Significant progress has been achieved in the field of solid-state biosensors over the past 50 years. Various sensing devices with high-density integration and flexible configuration, as well as new applications for clinical diagnosis and healthcare, have been developed using blood, serum, and other body fluids such as sweat, tears, and saliva. A high-density array of ion-sensitive field effect transistors was developed by exploiting the advantages of advanced semiconductor technologies and commercialized in combination with an enzymatic primer extension reaction as a DNA sequencer in 2011. Different types of materials such as inorganic materials, metals, polymers, and biomolecules are mixed together on the surface of the gate while maintaining their own functions; therefore, compatibility among different materials has to be optimized so that the best detection performance of solid-state biosensors, including stability and reliability, is achieved as designed. Solid-state biosensors are suitable for the rapid, cost-effective, and noninvasive identification of biomarkers at various timepoints over the course of a disease.

Transepithelial delivery of insulin conjugated with phospholipid-mimicking polymers via biomembrane fusion-mediated transcellular pathways

Epithelial barriers that seal cell gaps by forming tight junctions to prevent the free permeation of nutrients, electrolytes, and drugs, are essential for maintaining homeostasis in multicellular organisms. The development of nanocarriers that can permeate epithelial tissues without compromising barrier function is key for establishing a safe and efficient drug delivery system (DDS). Previously, we have demonstrated that a water-soluble phospholipid-mimicking random copolymer, poly(2-methacryloyloxyethyl phosphorylcholine₃₀-random-n‑butyl methacrylate₇₀) (PMB30W), enters the cytoplasm of live cells by passive diffusion manners, without damaging the cell membranes. The internalization mechanism was confirmed to be amphiphilicity-induced membrane fusion. In the present study, we demonstrated energy-independent permeation of PMB30W through the model epithelial barriers of Madin-Darby canine kidney (MDCK) cell monolayers in vitro. The polymer penetrated epithelial MDCK monolayers via transcellular pathways without breaching the barrier functions. This was confirmed by our unique assay that can monitor the leakage of the proton as the smallest indicator across the epithelial barriers. Moreover, energy-independent transepithelial permeation was achieved when insulin was chemically conjugated with the phospholipid-mimicking nanocarrier. The bioactivity of insulin as a growth factor was found to be maintained even after translocation. These fundamental findings may aid the establishment of transepithelial DDS with advanced drug efficiency and safety. STATEMENT OF SIGNIFICANCE: A nanocarrier that can freely permeate epithelial tissues without compromising barrier function is key for successful DDS. Existing strategies mainly rely on paracellular transport associated with tight junction breakdown or transcellular transport via transporter recognition-mediated active uptake. These approaches raise concerns about efficiency and safety. In this study, we performed non-endocytic permeation of phospholipid-mimicking polymers through the model epithelial barriers in vitro. The polymer penetrated via transcytotic pathways without breaching the barriers of biomembrane and tight junction. Moreover, transepithelial permeation occurred when insulin was covalently attached to the nanocarrier. The bioactivity of insulin was maintained even after translocation. The biomimetic design of nanocarrier may realize safe and efficient transepithelial DDS.

Chemically Induced pH Perturbations for Analyzing Biological Barriers Using Ion-Sensitive Field-Effect Transistors

Potentiometric pH measurements have long been used for the bioanalysis of biofluids, tissues, and cells. A glass pH electrode and ion-sensitive field-effect transistor (ISFET) can measure the time course of pH changes in a microenvironment as a result of physiological and biological activities. However, the signal interpretation of passive pH sensing is difficult because many biological activities influence the spatiotemporal distribution of pH in the microenvironment. Moreover, time course measurement suffers from stability because of gradual drifts in signaling. To address these issues, an active method of pH sensing was developed for the analysis of the cell barrier in vitro. The microenvironmental pH is temporarily perturbed by introducing a low concentration of weak acid (NH₄⁺) or base (CH₃COO⁻) to cells cultured on the gate insulator of ISFET using a superfusion system. Considering the pH perturbation originates from the semi-permeability of lipid bilayer plasma membranes, induced proton dynamics are used for analyzing the biomembrane barriers against ions and hydrated species following interaction with exogenous reagents. The unique feature of the method is the sensitivity to the formation of transmembrane pores as small as a proton (H⁺), enabling the analysis of cell–nanomaterial interactions at the molecular level. The new modality of cell analysis using ISFET is expected to be applied to nanomedicine, drug screening, and tissue engineering.

Internalization Mechanisms of Pyridinium Sulfobetaine Polymers Evaluated by Induced Protic Perturbations on Cell Surfaces

Understanding the interactions of soft nanomatters with cell membranes is particularly important for research into nanocarrier-based drug delivery systems, cell engineering, and subcellular imaging. Most nanoparticles, vesicles, micelles, and polymeric aggregates are internalized into endosomes and, eventually, lysosomes in the cytosol because of energy-dependent endocytic processes. Endocytic uptake substantially limits the access to the cytoplasm where a cargo agent acts. Bypassing the endocytic pathways by direct penetration into plasma membrane barriers would enhance the efficacy of nanomedicines. Some zwitterionic polymer nanoaggregates have been shown to permeate into the cell interior in an energy-independent manner. We have elucidated this phenomenon by observing changes in the biomembrane barrier functions against protons as the smallest indicator and have used these results to further design and develop poly(betaines). In this work, we investigated the translocation mechanisms for a series of zwitterionic poly(methacrylamide) and poly(methacrylate) species bearing a pyridinium propane sulfonate moiety in the monomers. Minor differences in the monomer structures and functional groups were observed to have dramatic effects on the interaction with plasma membranes during translocation. The ability to cross the plasma membrane involves a balance among the betaine dipole-dipole interaction, NH-π interaction, π-π interaction, cation-π interaction, and amide hydrogen bonding. We found that the cell-penetrating polysulfobetaines had limited or no detrimental effect on cell proliferation. Our findings enhance the opportunity to design and synthesize soft nanomatters for cell manipulations by passing across biomembrane partitions.

Phospholipid-mimicking cell-penetrating polymers: principles and applications

Understanding the interactions of eukaryotic cellular membranes with nanomaterials is required to construct efficient and safe nanomedicines and molecular bioengineering. Intracellular uptake of nanocarriers by active endocytosis limits the intracellular distribution to the endosomal compartment, impairing the intended biological actions of the cargo molecules. Nonendocytic intracellular migration is another route for nanomaterials with cationic or amphiphilic properties to evade the barrier function of the lipid bilayer plasma membranes. Direct transport of nanomaterials into cells is efficient, but this may cause cytotoxic or biocidal effects by temporarily disrupting the biological membrane barrier. We have recently discovered that nonendocytic internalization of synthetic amphipathic polymer-based nanoaggregates that mimic the structure of natural phospholipids can occur without inducing cytotoxicity. Analysis using a proton leakage assay indicated that the polymer enters cells by amphiphilicity-induced membrane fusion rather than by transmembrane pore formation. These noncytotoxic cell-penetrating polymers may find applications in drug delivery systems, gene transfection, cell therapies, and biomolecular engineering.

Induced Proton Dynamics on Semiconductor Surfaces for Sensing Tight Junction Formation Enhanced by an Extracellular Matrix and Drug

In the fields of tissue engineering and drug discovery, confirming the formation and maturation of epithelial cell tight junctions (TJs), which are necessary for blocking pathogenic invasion and absorption of nutrients and ions, at a high spatiotemporal resolution is essential. We previously developed a system of monitoring pH perturbation induced by weak acid exposure to cells cultured on an ion-sensitive field-effect transistor that enables a sensitive and specific detection of biomembrane injuries and TJ breakdowns caused by external stimuli such as nanomaterials and cytotoxins. In this study, we monitor time-lapse changes in the paracellular diffusion of growing epithelial cell monolayers using the pH perturbation assay as well as conventional permeability and trans-epithelial electrical resistance assays. The effects of the extracellular matrix and a TJ potentiator (KN-93) on epithelial TJ formation are evaluated. TJ formations were promoted on the substrate coated with Matrigel more than on the one coated with poly(l-lysine). KN-93 accelerated TJ formations in a dose-dependent manner. The pH perturbation assay denoted a longer incubation time for the completion of TJ formation compared with the conventional assays under the same conditions. Importantly, the pH perturbation assay is able to rigorously evaluate TJ formation, as the assay uses protons as the smallest indicator for detecting paracellular gaps, and the pH perturbation is specific to TJ alterations. These features for in vitro TJ evaluation using proton dynamics are advantageous for applications in tissue engineering and drug development.

Translocation Mechanisms of Cell-Penetrating Polymers Identified by Induced Proton Dynamics

Unlike the majority of nanomaterials designed for cellular uptake via endocytic pathways, some of the functional nanoparticles and nanospheres directly enter the cytoplasm without overt biomembrane injuries. Previously, we have shown that a water-soluble nanoaggregate composed of amphiphilic random copolymer of 2-methacryloyloxyethyl phosphorylcholine (MPC) and n-butyl methacrylate (BMA), poly(MPC- random-BMA) (PMB), passes live cell membranes in an endocytosis-free manner. Yet, details in its translocation mechanism remain elusive due to the lack of proper analytical methods. To understand this phenomenon experimentally, we elaborated the original pH perturbation assay that is extremely sensitive to the pore formation on cell membranes. The ultimate sensitivity originates from the detection of the smallest indicator H⁺ (H₃O⁺) passed through the molecularly sized transmembrane pores upon challenge by exogenous reagents. We revealed that water-soluble PMB at the 30 mol % MPC unit (i.e., PMB30W) penetrated into the cytosol of model mammalian cells without any proton leaks, in contrast to conventional cell-penetrating peptides, TAT and R8 as well as the surfactant, Triton X-100. While exposure of PMB30W permeabilized cytoplasmic lactate dehydrogenase out of the cells, indicating the alteration of cell membrane polarity by partitioning of amphiphilic PMB30W into the lipid bilayers. Nevertheless, the biomembrane alterations by PMB30W did not exhibit cytotoxicity. In summary, elucidating translocation mechanisms by proton dynamics will guide the design of nanomaterials with controlled permeabilization to cell membranes for bioengineering applications.

Self-assembly as a key player for materials nanoarchitectonics

The development of science and technology of advanced materials using nanoscale units can be conducted by a novel concept involving combination of nanotechnology methodology with various research disciplines, especially supramolecular chemistry. The novel concept is called 'nanoarchitectonics' where self-assembly processes are crucial in many cases involving a wide range of component materials. This review of self-assembly processes re-examines recent progress in materials nanoarchitectonics. It is composed of three main sections: (1) the first short section describes typical examples of self-assembly research to outline the matters discussed in this review; (2) the second section summarizes self-assemblies at interfaces from general viewpoints; and (3) the final section is focused on self-assembly processes at interfaces. The examples presented demonstrate the strikingly wide range of possibilities and future potential of self-assembly processes and their important contribution to materials nanoarchitectonics. The research examples described in this review cover variously structured objects including molecular machines, molecular receptors, molecular pliers, molecular rotors, nanoparticles, nanosheets, nanotubes, nanowires, nanoflakes, nanocubes, nanodisks, nanoring, block copolymers, hyperbranched polymers, supramolecular polymers, supramolecular gels, liquid crystals, Langmuir monolayers, Langmuir-Blodgett films, self-assembled monolayers, thin films, layer-by-layer structures, breath figure motif structures, two-dimensional molecular patterns, fullerene crystals, metal-organic frameworks, coordination polymers, coordination capsules, porous carbon spheres, mesoporous materials, polynuclear catalysts, DNA origamis, transmembrane channels, peptide conjugates, and vesicles, as well as functional materials for sensing, surface-enhanced Raman spectroscopy, photovoltaics, charge transport, excitation energy transfer, light-harvesting, photocatalysts, field effect transistors, logic gates, organic semiconductors, thin-film-based devices, drug delivery, cell culture, supramolecular differentiation, molecular recognition, molecular tuning, and hand-operating (hand-operated) nanotechnology.

Hemostatic properties of in situ gels composed of hydrophobically modified biopolymers

Hemorrhaging often occurs during cardiac surgery, and postoperative bleeding is associated with medical complications or even death. Medical complications resulting from hemorrhaging can lead to longer hospital stays, thus increasing costs. Hemostatic agents are the main treatment for bleeding. In the present study, hemostatic agents composed of aldehyde groups and hydrophobically modified with hyaluronic acid (ald-hm-HyA) and hydrophobically modified gelatin (hm-ApGltn) were developed and their hemostatic effects were evaluated. These modified hemostatic agents formed more stable blood clots compared with the nonhydrophobically modified HyA-based hemostatic agent. The bulk strength of the whole blood clot using the aldehyde and stearoyl group-modified hyaluronic acid (ald-C18-HyA)/hm-ApGltn-based hemostatic agent was higher than that of the aldehyde group only modified HyA (ald-HyA)/hm-ApGltn-based hemostatic agent. Rheological experiments using α-cyclodextrin showed that hydrophobic modification of HyA with C18 groups effectively enhanced anchoring to the red blood cell surface. Therefore, the ald-hm-HyA/hm-ApGltn-based hemostatic agent has potential applications in cardiac surgery.

Proton-sensing transistor systems for detecting ion leakage from plasma membranes under chemical stimuli

The membrane integrity of live cells is routinely evaluated for cytotoxicity induced by chemical or physical stimuli. Recent progress in bioengineering means that high-quality toxicity validation is required. Here, we report a pH-sensitive transistor system developed for the continuous monitoring of ion leakage from cell membranes upon challenge by toxic compounds. Temporal changes in pH were generated with high reproducibility via periodic flushing of HepG2 cells on a gate insulator of a proton-sensitive field-effect transistor with isotonic buffer solutions with/without NH₄Cl. The pH transients at the point of NH₄Cl addition/withdrawal originated from the free permeation of NH₃ across the semi-permeable plasma membranes, and the proton sponge effect produced by the ammonia equilibrium. Irreversible attenuation of the pH transient was observed when the cells were subjected to a membrane-toxic reagent. Experiments and simulations proved that the decrease in the pH transient was proportional to the area of the ion-permeable pores on the damaged plasma membranes. The pH signal was correlated with the degree of hemolysis produced by the model reagents. The pH assay was sensitive to the formation of molecularly sized pores that were otherwise not measurable via detection of the leakage of hemoglobin, because the hydrodynamic radius of hemoglobin was greater than 3.1nm in the hemolysis assay. The pH transient was not disturbed by inherent ion-transporter activity. The ISFET assay was applied to a wide variety of cell types. The system presented here is fast, sensitive, practical and scalable, and will be useful for validating cytotoxins and nanomaterials.

STATEMENT OF SIGNIFICANCE

The plasma membrane toxicity and hemolysis are widely and routinely evaluated in biomaterials science and biomedical engineering. Despite the recent development of a variety of methods/materials for efficient gene/drug delivery systems to the cytosol, the methodologies for safety validation remain unchanged in many years while leaving some major issues such as sensitivity, accuracy, and fast response. The paper describes a new way of measuring the plasma membrane leakage in real time upon challenge by toxic reagents using a solid-state transistor that is sensitive to proton as the smallest indicator. Our system was reliable and was correlated to the results from hemolysis assay with advanced features in sensitivity, fast response, and wide applicability to chemical species. The downsizing and integration features of semiconductor fabrication technologies may realize cytotoxicity assays at the single-cell level in multi-parallel.

Identification of types of membrane injuries and cell death using whole cell-based proton-sensitive field-effect transistor systems

Membrane injury and apoptosis of mammalian cells by chemical stimuli were distinguished using ammonia-perfused continuous pH-sensing systems.