Addressing the use of PDIF-CN2 molecules in the development of n-type organic field-effect transistors for biosensing applications.

BACKGROUND: There is no doubt that future discoveries in the field of biochemistry will depend on the implementation of novel biosensing techniques, able to record biophysiological events with minimal biological interference. In this respect, organic electronics may represent an important new tool for the analysis of structures ranging from single molecules up to cellular events. Specifically, organic field-effect transistors (OFET) are potentially powerful devices for the real-time detection/transduction of bio-signals. Despite this interest, up to date, the experimental data useful to support the development of OFET-based biosensors are still few and, in particular, n-type (electron-transporting) devices, being fundamental to develop highly-performing circuits, have been scarcely investigated. METHODS: Here, films of N,N'-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide (PDIF-CN2) molecules, a recently-introduced and very promising n-type semiconductor, have been evaporated on glass and silicon dioxide substrates to test the biocompatibility of this compound and its capability to stay electrically-active even in liquid environments. RESULTS: We found that PDIF-CN2 transistors can work steadily in water for several hours. Biocompatibility tests, based on in-vitro cell cultivation, remark the need to functionalize the PDIF-CN2 hydrophobic surface by extra-coating layers (i.e. poly-l-lysine) to favor the growth of confluent cellular populations. CONCLUSIONS: Our experimental data demonstrate that PDIF-CN2 compound is an interesting organic semiconductor to develop electronic devices to be used in the biological field. GENERAL SIGNIFICANCE: This work contributes to define a possible strategy for the fabrication of low-cost and flexible biosensors, based on complex organic complementary metal-oxide-semiconductor (CMOS) circuitry including both p- (hole-transporting) and n-type transistors. This article is part of a Special Issue entitled Organic Bioelectronics-Novel Applications in Biomedicine.

Angular dependence of light transmittance through a polymer-dispersed liquid crystal above threshold.

The transmittance of polymer-dispersed liquid crystals (PDLC's) can be easily controlled by a low-frequency electric field. However, unlike glass, even in its transparent state a PDLC is an anisotropic material, so its transmittance has a characteristic angular dependence. We introduce a mathematical model to describe the angular dependence of the light transmittance through a PDLC sample above threshold. The accuracy of the model is tested and predictions compared with experimental measurements.

Vector formalism for circularly symmetric laser beams.

We present a finite dimensional vector formalism that describes the propagation of circularly symmetric beams in a simple and effective way. A propagation matrix operator is explicitly given that determines the amplitude as a function of the radius at any plane. Power transported to a circular or annular target is discussed in some detail. In particular, the problem of choosing a beam shape at the aperture that maximizes the power transported to a target has a simple solution in the new formalism.

Nonlinear total internal reflection through the thermoplastic effect.

We report on the observation of strong nonlinear optical behavior of SF59 Schott glass. An unfocused Ar' laser beam undergoing total internal reflection in this glass shows extremely strong selffocusing. This effect is ~ 1 order of magnitude higher than the usual thermal lensing, and, by means of an interferometric technique, we demonstrate that this effect is due to the thermoplastic effect. Focal lengths that are shorter than 10 cm are observed for the beam intensity I asymptotically equal to 30 W/cm(2). The use of this glass as a self-limiter is shown experimentally.

Diffraction field of a circularly symmetric beam through a sequence of apertures.

A method to compute the diffraction field of a circularly symmetric laser beam through a sequence of circular apertures is discussed. An explicit expression of the field is given as the linear combination of a set of values of the input beam. Comparisons with numerical integration and experimental data available in the literature show its accuracy even in the Fresnel region where approximate methods such as the beam mode expansion are less accurate.

Matrix representation of axisymmetric optical systems including spatial filters.

A matrix approach is presented that allows one to describe a complex optical system by a matrix relating the field at the output plane to the field at the input one. The elements of the optical system may be all those characterized by an ABCD ray-transfer matrix, as well as any kind of film which introduces a wavefront modulation that can be described by a complex radial transmittance function. These include, as particular cases, stops and limiting apertures. No integral has to be computed. The method holds only for circularly symmetric optical systems and laser beams.

Dielectric receivers for asymmetrical ideal concentrators.

Cylindrical asymmetrical nonimaging concentrators with receivers based on tin absorbers immersed in dielectric rhombuses are introduced and shown to be ideal. They have the same concentration factor as dielectric filled devices but require only a small amount of dielectric around the absorber. The asymmetric shape and nontracking property of the collectors allow their arrangement in flat panels that, integrated with a supporting thermal insulator, may be the roof or the wall of a small building situated in a remote locality. This would passively satisfy the electric requirements of the building.

Ideal nonfocusing concentrator with fin absorbers in dielectric rhombuses.

Two ideal concentrators with fin absorbers in dielectric rhombuses are described. Expressions for the design, height, and mirror length are derived. The devices have a concentration factor (n/sin ?(M)) that is clearly higher than the traditional air-filled ideal concentrators. They do not require more mirrors or space and, when such easily available dielectrics as glass and water are used, offer useful configurations for purposes such as the collection of solar energy.