Lipid-Modified Graphene-Transistor Biosensor for Monitoring Amyloid-β Aggregation.

A graphene field-effect transistor (G-FET) with the spacious planar graphene surface can provide a large-area interface with cell membranes to serve as a platform for the study of cell membrane-related protein interactions. In this study, a G-FET device paved with a supported lipid bilayer (referred to as SLB/G-FET) was first used to monitor the catalytic hydrolysis of the SLB by phospholipase D. With excellent detection sensitivity, this G-FET was also modified with a ganglioside G-enriched SLB (G-SLB/G-FET) to detect cholera toxin B.

One-Step Synthesis of Antioxidative Graphene-Wrapped Copper Nanoparticles on Flexible Substrates for Electronic and Electrocatalytic Applications.

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)).

Site-specific covalent modifications of human insulin by catechol estrogens: Reactivity and induced structural and functional changes.

Proteins, covalently modified by catechol estrogens (CEs), were identified recently from the blood serum of diabetic patients and referred to as estrogenized proteins. Estrogenization of circulating insulin may occur and affect its molecular functioning. Here, the chemical reactivity of CEs towards specific amino acid residues of proteins and the structural and functional changes induced by the estrogenization of insulin were studied using cyclic voltammetry, liquid chromatography-mass spectrometry, circular dichroism spectroscopy, molecular modeling, and bioassays.

Potentiometric-scanning ion conductance microscopy.

We detail the operation mechanism and instrumental limitations for potentiometric-scanning ion conductance microscopy (P-SICM). P-SICM makes use of a dual-barrel probe, where probe position is controlled by the current measured in one barrel and the potential is measured in a second barrel. Here we determine the interaction of these two barrels and resultant effects in quantitation of signals.

Potentiometric-scanning ion conductance microscopy for measurement at tight junctions.

Scanning Ion Conductance Microscopy (SICM) has been developed originally for high-resolution imaging of topographic features. Recently, we have described a hybrid voltage scanning mode of SICM, termed Potentiometric-SICM (P-SICM) for recording transmembrane ionic conductance at specific nanostructures of synthetic and biological interfaces. With this technique, paracellular conductance through tight junctions - a subcellular structure that has been difficult to interrogate previously - has been realized.

Advances in nanowire transistors for biological analysis and cellular investigation.

Electrical biosensors based on silicon nanowire field-effect transistors (SiNW-FETs) have attracted enormous interest in the biosensing field. SiNW-FETs have proven to be significant and efficient in detecting diverse biomolecular species with the advantages of high probing sensitivity, target selectivity, real-time recording and label-free detection. In recent years, significant advances in biosensors have been achieved, particularly for cellular investigation and biomedical diagnosis.

Scanning ion conductance microscopy measurement of paracellular channel conductance in tight junctions.

Elucidation of epithelial transport across transcellular or paracellular pathways promises to advance the present understanding of ion transport and enables regulation of cell junctions critical to the cell and molecular biology of the epithelium. Here, we demonstrate a new instrumental technique, potentiometric scanning ion conductance microscopy (P-SICM), that utilizes a nanoscale pipet to differentiate paracellular and transcellular transport processes at high spatial resolution. The technique is validated for well-defined polymer membranes and then employed to study wild type and claudin-deficient mutants of Madin-Darby Canine Kidney strain II (MDCKII) cells.

Scanning ion conductance microscopy.

Scanning ion conductance microscopy (SICM) is a versatile type of scanning probe microscopy for studies in molecular biology and materials science. Recent advances in feedback and probe fabrication have greatly increased the resolution, stability, and speed of imaging. Noncontact imaging and the ability to deliver materials to localized areas have made SICM especially fruitful for studies of molecular biology, and many examples of such use have been reported.

Heterogeneity of multiple-pore membranes investigated with ion conductance microscopy.

Heterogeneous conductance of individual pores on a porous membrane was studied with a four-electrode scanning ion conductance microscope (SICM). Application of a potential difference across the membrane resulted in migration of ions through nanopores, where subsequent conductance changes were measured by a nanopipet positioned above the nanopore as a change in pipet current. Current responses of single-pore membranes and individual pores within a multipore membrane were examined and demonstrated variations in ion current rectification (ICR) ratios due to the small differences in pore geometries.

Transport of redox probes through single pores measured by scanning electrochemical-scanning ion conductance microscopy (SECM-SICM).

We report scanning electrochemical microscopy-scanning ion conductance microscopy (SECM-SICM) experiments that describe transport of redox active molecules which emanate from single pores of a track-etch membrane. Experiments are performed with electrodes which consist of a thin gold layer deposited on one side of a nanopipet. Subsequent insulation of the electrode with parylene results in a hybrid electrode for SECM-SICM measurements.

Single-nanopore investigations with ion conductance microscopy.

A three-electrode scanning ion conductance microscope (SICM) was used to investigate the local current-voltage properties of a single nanopore. In this experimental configuration, the response measured is a function of changes in the resistances involved in the pathways of ion migration. Single-nanopore membranes utilized in this study were prepared with an epoxy painting procedure to isolate a single nanopore from a track-etch multipore membrane.

Effects of pipette modulation and imaging distances on ion currents measured with scanning ion conductance microscopy (SICM).

Local conductance variations can be estimated by measuring ion current magnitudes with scanning ion conductance microscopy (SICM). Factors which influence image quality and quantitation of ion currents measured with SICM have been evaluated. Specifically, effects of probe-sample separation and pipette modulation have been systematically studied for the case of imaging conductance variations at pores in a polymer membrane under transmembrane concentration gradients.

Measurement of ion currents through porous membranes with scanning ion conductance microscopy.

Scanning ion conductance microscopy (SICM) was used to interrogate ion currents emanating from nanometer-scale pores of a polymer membrane. The transport activity of individual pores was measured by examining ion current images and corresponding topographic images recorded simultaneously. Localized ion currents over individual nanopores were generated by introducing a concentration difference between the upper and lower chambers of a diffusion cell.