Three-dimensionally two-photon lithography realized vascular grafts.

Generation of artificial vascular grafts as blood vessel substitutes is a primary challenge in biomaterial and tissue-engineering research. Ideally, these grafts should be able to recapitulate physiological and mechanical properties of natural vessels and guide the assembly of an endothelial cell lining to ensure hemo-compatibility. In this paper, we advance on this challenging task by designing and fabricating 3D vessel analogues by two-photon laser lithography using a synthetic photoresist. These scaffolds guarantee human endothelial cell adhesion and proliferation, and proper elastic behavior to withstand the pressure exerted by blood flow.

Optoelectrochemical biorecognition by optically transparent highly conductive graphene-modified fluorine-doped tin oxide substrates.

Both optical and electrochemical graphene-based sensors have gone through rapid development, reaching high sensitivity at low cost and with fast response time. However, the complex validating biochemical operations, needed for their consistent use, currently limits their effective application. We propose an integration strategy for optoelectrochemical detection that overcomes previous limitations of these sensors used separately. We develop an optoelectrochemical sensor for aptamer-mediated protein detection based on few-layer graphene immobilization on selectively modified fluorine-doped tin oxide (FTO) substrates. Our results show that the electrochemical properties of graphene-modified FTO samples are suitable for complex biological detection due to the stability and inertness of the engineered electrodic interface. In addition, few-layer immobilization of graphene sheets through electrostatic linkage with an electrochemically grafted FTO surface allows obtaining an optically accessible and highly conductive platform. As a proof of concept, we used insulin as the target molecule to reveal in solution. Because of its transparency and low sampling volume (a few microliters), our sensing unit can be easily integrated in lab-on-a-chip cell culture systems for effectively monitoring subnanomolar concentrations of proteins relevant for biomedical applications.

Short and long range surface plasmon polariton waveguides for xylene sensing.

Nanostructured plasmonic sensors are fabricated as sinusoidal surface plasmon metallic gratings (SPGs) embedded in a functional and porous hybrid sol-gel material, phenyl-bridged polysilsesquioxane (ph-PSQ). The metal layer is in contact with the environment through the sol-gel film, which works as sensitive element, changing its dielectric properties upon interaction with aromatic hydrocarbons. The combination of sensitivity, transparency and patternability offered by ph-PSQs gives the exceptional possibility to fabricate innovative optical sensors with straightforward processes. An embedded SPG is a thin metal slab waveguide, in which the surface plasmon polaritons (SPPs) at the two metal-dielectric interfaces superpose, resulting in two physical coupled modes: the long range SPPs (LRSPPs) and the short range SPPs (SRSPPs). An extended experimental and theoretical characterization of the optical properties of the plasmonic device was performed. The sensor performance was tested against the detection of 30 ppm xylene, monitoring the influence of the target gas on the SPPs modes. A reversible red-shift of the reflectance dips of both LRSPP and SRSPP resonances in the 1.9-2.9 nm range was observed and correlated to the interaction with the analyte. An enhancement in sensitivity associated with the rotation of the grating grooves with respect to the scattering plane (azimuthal rotation) was verified within the experimental errors. Collected data are compatible with theoretical predictions assuming a variation of the film refractive index of 0.011 ± 0.005.

Phenyl-bridged polysilsesquioxane positive and negative resist for electron beam lithography.

We present and characterize an organic-inorganic hybrid sol-gel material, phenyl-bridged polysilsesquioxane (ph-PSQ), for use as a new high resolution resist for electron beam lithography (EBL). The resist has a unique characteristic as the only positive tone silica-based resist available for EBL. Exploring the processing parameters has revealed that it is possible to switch the behaviour from negative to positive tone by application of a post-exposure bake (PEB). Based on the results from micro-FTIR spectroscopy, a description of the tone switching mechanisms is proposed. The negative tone behaviour is explained by the etch rate difference between silanol groups and cross-linked silica, present in unexposed and in exposed areas of the films, respectively. In the case of positive tone, after a PEB, the etch rate difference between a thermally densified cross-linked silica network and cage-like silica structures allows us to reveal the pattern. Contrast and sensitivity are estimated under different processing conditions, and the significant parameters for line edge roughness minimization are pointed out. Dense patterns down to 25 nm half-pitch and isolated structures down to 30 nm are demonstrated, exploiting the positive tone, and dense patterns down to 60 nm half-pitch are demonstrated in the negative tone. Etching selectivities in fluorinated gases for ph-PSQ nanostructures on silicon substrates are 1-9 for the positive tone and 1-12 for the negative tone.

Active diffraction gratings: development and tests.

We present the realization and characterization of an active spherical diffraction grating with variable radius of curvature to be used in grazing-incidence monochromators. The device consists of a bimorph deformable mirror on the top of which a diffraction grating with laminar profile is realized by UV lithography. The experimental results show that the active grating can optimize the beam focalization of visible wavelengths through its rotation and focus accommodation.