The employment of standard CMOS technology to produce semiconductor chips for recording neuronal activity or for its future use to link neurons and transistors under in vivo conditions, suffers from a low signal to noise ratio. Using Aplysia neurons cultured on CMOS floating gate field effect transistors, we report here that minor mechanical pressure applied to restricted neuronal compartment that face the sensing pad induces two independent alterations: (a) increase in the seal resistance formed between the neuron's membrane and the sensing pad, and (b) increase the conductance of the membrane patch that faces the sensing pad. These alterations (from ∼0.5 to ∼1.2 MΩ and 75 to ∼600 nS correspondingly), are sufficient to transform the low capacitive coupling between a neuron and a transistor to Ohmic coupling, which is manifested by semi-intracellular recordings of APs with amplitudes of up to 30 mV. The semi-intracellular recordings could be maintained for hours. As a number of compression and decompression cycles could be applied to a single cell without causing significant alterations in its excitable properties, we conclude that the mechanical damage inflicted to the neurons by local compression are reversible. Based on these observations, we suggest that the application of minimal local pressure or suction forces could be used to transform conventional extracellular field potential recordings into quasi-intracellular recording, and thereby dramatically improve both the signal to noise ratio and the quality of recordings from neurons cultured on CMOS semiconductors chips.

An inclusion complex between water-soluble p-sulfocalix[n]arene (Cn, n = 4, 6, 8) and the chromophore trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium-p-toluenesulfonate (D) formed the basis for a highly sensitive sensor for the selective detection of neurotransmitter acetylcholine (ACh). Formation of the [Cn·D] complex (Ka = ∼105 M-1) was accompanied by a drastic increase (up to 20−60-fold) in the chromophore relative quantum yield and by a large hypsochromic shift of the emission band maximum. The observed optical effects are fully reversible:  ACh displaces the chromophore molecules from the calixarene cavity as shown by the reappearance of the free chromophore emission band. Formation and dissociation of the complex were studied by fluorescence, 1H NMR, and UV−vis absorption spectroscopies. The [Cn·D] complex is capable of sensing ACh selectively in solution at sub-micromolar concentrations. Immobilization of monocarboxyl p-sulfocalix[4]arene (C4m) on an oxide-containing silicon surface is in keeping with its properties, such as chromophore binding and the ability of the immobilized inclusion complex to detect ACh. The unique [Cn·D] complex optical switching paves the way for application in ACh imaging and optoelectronic sensing.

We report the electropolymerization and characterization of polyaniline (PAN) on both DNA monolayer and single poly(dG)–poly(dC) DNA molecules serving as a template. The synthesis includes the formation of an electrostatic complex between the negatively charged DNA and positively charged anilinium ions followed by electrochemical oxidation and polymerization of the anilinium ions' monomers on the DNA template. The polymerization was carried out on a flame annealed gold substrate modified with positively charged self-assembled 4-aminothiophenol (4-ATPh) monolayer. The resulting monolayers and single macromolecular composites of DNA–PAN were characterized by atomic force microscopy (AFM), cyclic voltammetry (CV) impedance and UV–vis spectroscopy.

The interactions of the polymer poly(4-vinyl pyridine) moieties with free pyridine molecules in concentrated solution develop protonated and hydrogen-bonded species on the polymer backbone and turn the viscous solution to gel. Direct irradiation at proton transfer centre on the protonated polymer moiety promotes an amorphous-to-crystalline transition. The polymer crystals exhibit completely different optical properties when compared to the amorphous material. The proposed mechanism of the photoinduced crystallisation is the following: direct excitation to the proton transfer centre generates in abundance protonated polymer moieties, which have rigid quinone structure. Rigid quinone conformations stimulate the crystallisation of the polymer chains; in their turn, increasing polymer ordering stabilises the photoinduced protonated species. Photoinduced phase transition is reversible, meaning, that crystalline phase is metastable. To clarify the mechanism of the phase transition, in the present issue, using molecular modelling, we investigate the conformational behaviour of the polymer species depending on the state of protonation, interaction with adjacent solvent molecules and polymer side-chain units. The Density Functional Theory (DFT) calculations show the protonated pyridine moiety as a quinone structure that is clearly stable, thus emphasising the ability of such structure to play a key role as a ‘working’ species.

We describe a hydrogen-bonded poly(4-vinyl pyridine)-based dielectric material, in which conductivity can be induced due to the presence of side-chain protonated species that form spontaneously when the polymer is dissolved in pyridine. The conductivity of the proton conductive gel can be controlled by direct irradiation at the proton-transfer center:  a reversible change of conductivity was observed in response to the on/off switching of 385 nm wavelength radiation. Over most of the range of intensities used, the proton conductivity exhibited a bimolecular character. We present a model of the protonated pyridine side-chain unit in the ground and excited states (DFT level). In the ground state, the protonated pyridine moiety has a cyclic, conjugated structure.

Swollen polymer networks exhibit multiscale pores filled with solvent. Such porosity, inherent to cross-linked polymers, determines some of their most relevant physical properties and applications. In this research, several samples of chemically crosslinked poly(N-vinylimidazole) were synthesized with the same permanent crosslinking density at two different conversions, and their inherent porosity was characterized on freeze-dried specimens by SEM, TEM and nitrogen physisorption. It was thus found that all of the samples showed pores, both on the nanometer and the micrometer scales, whose dimensions were mostly equal to or larger than the mesh size of the primary polymer network (22 nm) and whose volume and specific surface decreased with increasing conversion. Micropores have, in all cases, a very minor contribution. Samples synthesized with the largest comonomer concentrations show quasi-spherical mesopores (90 nm average diameter at any conversion) and macropores (from 5 to 10 μm with increasing conversion), whereas the mesopores of samples synthesized with the largest crosslinker ratios were channel-like (150 nm) and the macropores were interconnected contiguous voids (3 μm). Samples with intermediate compositions exhibit the lowest porosity due, mostly, to interconnected mesopores. The differences in shape were ascribed to the mechanism of phase separation, taking place during polymerization, even for samples that are transparent following polymerization. The inherent porosity is a significant source of spatial inhomogeneity, which contributes to the increase in turbidity. Light scattering decreases with increasing ionization when the degree of protonation is greater than 10%. An important consequence of the inherent porosity is that the degrees of swelling determined either gravimetrically or through size measurements are not equivalent.

Electronic structures at the silicon/molecule interface were studied by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, inverse photoemission spectroscopy, and Kelvin probe techniques. The heterojunctions were fabricated by direct covalent grafting of a series of molecules (−C6H4−X, with X = NMe2, NH2, NO2, and Mo6 oxide cluster) onto the surface of four types of silicon substrates (both n- and p-type with different dopant densities). The electronic structures at the interfaces were thus systematically tuned in accordance with the electron-donating ability, redox capability, and/or dipole moment of the grafted molecules. The work function of each grafted surface is determined by a combination of the surface band bending and electron affinity. The surface band bending is dependent on the charge transfer between the silicon substrate and the grafted molecules, whereas electron affinity is dependent on the dipole moment of the grafted molecules. The contribution of each to the work function can be separated by a combination of the aforementioned analytical techniques. In addition, because of the relatively low molecular coverage on the surface, the contribution from the unreacted H-terminated surface to the work function was considered. The charge-transfer barrier of silicon substrates attached to different molecules exhibits a trend analogous to surface band bending effects, whereas the surface potential step exhibits properties analogous to electron affinity effects. These results provide a foundation for the utilization of organic molecule surface grafting as a means to tune the electronic properties of semiconductors and, consequently, to achieve controllable modulation of electronic characteristics in small semiconductor devices at future technology nodes.

Electronic structures at the Si/SiO2/molecule interfaces were studied by Kelvin probe techniques (contact potential difference) and compared to theoretical values derived by the Helmholtz equation. Two parameters influencing the electronic properties of n-type <100> Si/SiO2substrates were systematically tuned:  the molecular dipole of coupling agent molecules comprising the layer and the surface coverage of the chromophoric layer. The first parameter was checked using direct covalent grafting of a series of trichlorosilane-containing coupling agent molecules with various end groups causing a different dipole with the same surface number density. It was found that the change in band bending (ΔBB) clearly indicated a major effect of passivation due to two-dimensional polysiloxane network formation, with minor differences resulting from the differences in the end groups' capacity to act as “electron traps”. The change in electron affinity (ΔEA) parameter increased upon increasing the dipole of the end group comprising the monolayer, resulting in a range of 600 mV. Moreover, a shielding effect of the aromatic spacer compared with the aliphatic spacer was found and estimated to be about 200 mV. The density effect was examined using the 4-[4-(N,N-dimethylamino phenyl)azo]pyridinium halide chromophore which has a calculated dipole of more than 10 D. It was clearly shown that upon increasing surface chromophoric coverage an increase in the electronic effects on the Si substrate was observed. However, a major consequence of depolarization was also detected while comparing the experimental and calculated values.

Hybrid integration of living cells and electronic circuits on a chip requires a high-density matrix of sensors and actuators. This matrix must be processable on top of CMOS devices and must be bio-compatible in order to support living cells. Recent studies have shown that the use of nail structures combined with a phagocytosis-like event of the cell can be exploited to improve the electrical coupling between a cell and a sensor.

In this paper, two CMOS-compatible fabrication methods for sub-micron nails will be presented. The biocompatibility and proof-of-concept is demonstrated by the culturing of PC12 neuroblastoma cells. Electrical functionality is shown by simultaneous stimulation and recording of pig cardiomyocyte cells. Biocompatibility aspects for more demanding cortical cell cultures have been addressed in a preliminary assessment.