Nanoscale patterning controls inorganic-membrane interface structure

Numerical investigation of force and deflection of nanoneedle penetration into cell using finite element approach: Parameter study and experimental validation of results

This paper aims to develop a numerical methodology to investigate the penetration process of nanoneedles into cells and the corresponding force and indentation length. The finite element approach via the explicit dynamic method handles convergence difficulties in the nonlinear phenomenon. The cell is modeled as an isotropic elastic hemiellipsoidal shell with a thickness of 200 nm, which represents the lipid membrane and actin cortex, encapsulating cytoplasm that is regarded as an Eulerian body because of its fluid-type behavior. Nanoneedles with diameters 400, 200, and 50 nm are considered for model development based on available experimental data. The Von Mises strain failure criterion is used for rupture detection. A parameter study using 1, 2.5, 5, 7.5, and 10 kPa shows that Young's modulus of the HeLa cell membrane is about 5 kPa. Moreover, a failure strain of 1.2 chosen among 0.2, 0.4, 0.6, 0.8, 1, and 1.2 matches best the experimental data. In addition, a diameter study shows that the relations between force-diameter and indentation length-diameter are linear and polynomial, respectively. Furthermore, regarding the experimental data and by using contour of minimum principal stress around needle and an analytical equation for calculation of buckling force of a woven fabric, we proposed that for a given cell, membrane structural stability-a function of the coupled effect of Young's modulus and actin meshwork size-contributes directly to needle insertion success rate for that type of cell.

Cell penetration efficiency analysis of different atomic force microscopy nanoneedles into living cells

Over the last decade, nanoneedle-based systems have demonstrated to be extremely useful in cell biology. They can be used as nanotools for drug delivery, biosensing or biomolecular recognition inside cells; or they can be employed to select and sort in parallel a large number of living cells. When using these nanoprobes, the most important requirement is to minimize the cell damage, reducing the forces and indentation lengths needed to penetrate the cell membrane. This is normally achieved by reducing the diameter of the nanoneedles. However, several studies have shown that nanoneedles with a flat tip display lower penetration forces and indentation lengths. In this work, we have tested different nanoneedle shapes and diameters to reduce the force and the indentation length needed to penetrate the cell membrane, demonstrating that ultra-thin and sharp nanoprobes can further reduce them, consequently minimizing the cell damage.

Volcano-Shaped Scanning Probe Microscopy Probe for Combined Force-Electrogram Recordings from Excitable Cells

Atomic force microscopy based approaches have led to remarkable advances in the field of mechanobiology. However, linking the mechanical cues to biological responses requires complementary techniques capable of recording these physiological characteristics. In this study, we present an instrument for combined optical, force, and electrical measurements based on a novel type of scanning probe microscopy cantilever composed of a protruding volcano-shaped nanopatterned microelectrode (nanovolcano probe) at the tip of a suspended microcantilever. This probe enables simultaneous force and electrical recordings from single cells. Successful impedance measurements on mechanically stimulated neonatal rat cardiomyocytes in situ were achieved using these nanovolcano probes. Furthermore, proof of concept experiments demonstrated that extracellular field potentials (electrogram) together with contraction displacement curves could simultaneously be recorded. These features render the nanovolcano probe especially suited for mechanobiological studies aiming at linking mechanical stimuli to electrophysiological responses of single cells.

Poly(arylene ether sulfone) crosslinked networks with pillar[5]arene units grafted by multiple long-chain quaternary ammonium salts for anion exchange membranes

For the first time, high-molecular-weight pillar[5]arene-containing aromatic polymers were synthesized and further modified for application as anion exchange membranes.

Intracellular Recording of Cardiomyocyte Action Potentials with Nanopatterned Volcano-Shaped Microelectrode Arrays

Micronanotechnology-based multielectrode arrays have led to remarkable progress in the field of transmembrane voltage recording of excitable cells. However, providing long-term optoporation- or electroporation-free intracellular access remains a considerable challenge. In this study, a novel type of nanopatterned volcano-shaped microelectrode (nanovolcano) is described that spontaneously fuses with the cell membrane and permits stable intracellular access. The complex nanostructure was manufactured following a simple and scalable fabrication process based on ion beam etching redeposition. The resulting ring-shaped structure provided passive intracellular access to neonatal rat cardiomyocytes. Intracellular action potentials were successfully recorded in vitro from different devices, and continuous recording for more than 1 h was achieved. By reporting transmembrane action potentials at potentially high spatial resolution without the need to apply physical triggers, the nanovolcanoes show distinct advantages over multielectrode arrays for the assessment of electrophysiological characteristics of cardiomyocyte networks at the transmembrane voltage level over time.

Interfacial Contact is Required for Metal-Assisted Plasma Etching of Silicon

For decades, fabrication of semiconductor devices has utilized well-established etching techniques to create complex nanostructures in silicon. The most common dry process is reactive ion etching which fabricates nanostructures through the selective removal of unmasked silicon. Generalized enhancements of etching have been reported with mask-enhanced etching with Al, Cr, Cu, and Ag masks, but there is a lack of reports exploring the ability of metallic films to catalytically enhance the local etching of silicon in plasmas. Here, metal-assisted plasma etching (MAPE) is performed using patterned nanometers-thick gold films to catalyze the etching of silicon in an SF6/O2 mixed plasma, selectively increasing the rate of etching by over 1000%. The catalytic enhancement of etching requires direct Si-metal interfacial contact, similar to metal-assisted chemical etching (MACE), but is different in terms of the etching mechanism. The mechanism of MAPE is explored by characterizing the degree of enhancement as a function of Au catalyst configuration and relative oxygen feed concentration, along with the catalytic activities of other common MACE metals including Ag, Pt, and Cu.

Biomimetic surface patterning for long-term transmembrane access

Here we present a planar patch clamp chip based on biomimetic cell membrane fusion. This architecture uses nanometer length-scale surface patterning to replicate the structure and function of membrane proteins, creating a gigaohm seal between the cell and a planar electrode array. The seal is generated passively during cell spreading, without the application of a vacuum to the cell surface. This interface can enable cell-attached and whole-cell recordings that are stable to 72 hours, and generates no visible damage to the cell. The electrodes can be very small (<5 μm) and closely packed, offering a high density platform for cellular measurement.

Nano-Bioelectronics

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

Penetration of cell membranes and synthetic lipid bilayers by nanoprobes

Nanoscale devices have been proposed as tools for measuring and controlling intracellular activity by providing electrical and/or chemical access to the cytosol. Unfortunately, nanostructures with diameters of 50-500 nm do not readily penetrate the cell membrane, and rationally optimizing nanoprobes for cell penetration requires real-time characterization methods that are capable of following the process of membrane penetration with nanometer resolution. Although extensive work has examined the rupture of supported synthetic lipid bilayers, little is known about the applicability of these model systems to living cell membranes with complex lipid compositions, cytoskeletal attachment, and membrane proteins. Here, we describe atomic force microscopy (AFM) membrane penetration experiments in two parallel systems: live HEK293 cells and stacks of synthetic lipid bilayers. By using the same probes in both systems, we were able to clearly identify membrane penetration in synthetic bilayers and compare these events with putative membrane penetration events in cells. We examined membrane penetration forces for three tip geometries and 18 chemical modifications of the probe surface, and in all cases the median forces required to penetrate cellular and synthetic lipid bilayers with nanoprobes were greater than 1 nN. The penetration force was sensitive to the probe's sharpness, but not its surface chemistry, and the force did not depend on cell surface or cytoskeletal properties, with cells and lipid stacks yielding similar forces. This systematic assessment of penetration under various mechanical and chemical conditions provides insights into nanoprobe-cell interactions and informs the design of future intracellular nanoprobes.

Nanotechnology and neurophysiology

Neuroscience would be revolutionized by a technique to measure intracellular electrical potentials that would not disrupt cellular physiology and could be massively parallelized. Though such a technology does not yet exist, the technical hurdles for fabricating minimally disruptive, solid-state electrical probes have arguably been overcome in the field of nanotechnology. Nanoscale devices can be patterned with features on the same length scale as biological components, and several groups have demonstrated that nanoscale electrical probes can measure the transmembrane potential of electrogenic cells. Developing these nascent technologies into robust intracellular recording tools will now require a better understanding of device-cell interactions, especially the membrane-inorganic interface. Here we review the state-of-the art in nanobioelectronics, emphasizing the characterization and design of stable interfaces between nanoscale devices and cells.

Analysis of nanoprobe penetration through a lipid bilayer

With the rapid development of nanotechnology and biotechnology, nanoscale structures are increasingly used in cellular biology. However, the interface between artificial materials and a biological membrane is not well understood, and the harm caused by the interaction is poorly controlled. Here, we utilize the dissipative particle dynamics simulation method to study the interface when a nanoscale probe penetrates the cell membrane, and propose that an appropriate surface architecture can reduce the harm experienced by a cell membrane. The simulation shows that a hydrophilic probe generates a hydrophilic hole around the probe while a hydrophobic probe leads to a 'T-junction' state as some lipid molecules move toward the two ends of the probe. Both types of probe significantly disrupt lipid bilayer organization as reflected by the large variations in free energy associated with penetration of the membrane. Considering the hydrophilic/hydrophobic nature of the lipid bilayer, three other hydrophilic/hydrophobic patterns - band pattern, axial pattern and random pattern - are discussed to reduce the damage to the lipid membrane. Both the free energy analysis and simulation studies show that the axial pattern and the random pattern can both minimize the variations in free energy with correspondingly smaller adverse effects on membrane function. These results suggest that the axial pattern or random pattern nanoprobe generates a mild interaction with the biological membrane, which should be considered when designing nondestructive nanoscale structures.

Multi-electrode array technologies for neuroscience and cardiology

At present, the prime methodology for studying neuronal circuit-connectivity, physiology and pathology under in vitro or in vivo conditions is by using substrate-integrated microelectrode arrays. Although this methodology permits simultaneous, cell-non-invasive, long-term recordings of extracellular field potentials generated by action potentials, it is 'blind' to subthreshold synaptic potentials generated by single cells. On the other hand, intracellular recordings of the full electrophysiological repertoire (subthreshold synaptic potentials, membrane oscillations and action potentials) are, at present, obtained only by sharp or patch microelectrodes. These, however, are limited to single cells at a time and for short durations. Recently a number of laboratories began to merge the advantages of extracellular microelectrode arrays and intracellular microelectrodes. This Review describes the novel approaches, identifying their strengths and limitations from the point of view of the end users--with the intention to help steer the bioengineering efforts towards the needs of brain-circuit research.

Molecular structure influences the stability of membrane penetrating biointerfaces

Nanoscale patterning of hydrophobic bands on otherwise hydrophilic surfaces allows integration of inorganic structures through biological membranes, reminiscent of transmembrane proteins. Here we show that a set of innate molecular properties of the self-assembling hydrophobic band determine the resulting interface stability. Surprisingly, hydrophobicity is found to be a secondary factor with monolayer crystallinity the major determinate of interface strength. These results begin to establish guidelines for seamless bioinorganic integration of nanoscale probes with lipid membranes.