I. A. Grimaldi

Printing of polymer microlenses by a pyroelectrohydrodynamic dispensing approach.

The investigation of a method for fabricating microlenses by a nozzle-free inkjet printing approach is reported. The new method, based on a pyroelectrohydrodynamic mechanism, is also able to dispense viscous liquids and to draw liquid phase drops directly from the reservoir. Specifically, by dispensing optical grade polymer dissolved in different solvent mixtures, microlenses were printed with a pattern defined directly through this deposition method. The reliability of the microlenses and the tunability of their focal properties were demonstrated through profilometric and inteferometric analyses.

Graded-size microlens array by the pyro-electrohydrodynamic continuous printing method.

In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.

Flow through ring resonator sensing platform

This paper presents a novel sensing polymeric platform based on microring resonators with a direct microfluidic addressing scheme employing a flow-through approach. The fabrication of a hole placed in the centre of the ring allows precise analyte dispensing with an efficient transfer rate to the ring surface. The devices are exploited for biosensing experiments with bovine serum albumin (BSA) based solutions. The measured resonance peak shift shows a linear behaviour up to 200 nM. The sensor response time is measured by flowing 20 nM BSA solution at two different flow rates and in two different flow-through configurations. A reduction of more than one order of magnitude of the sensor response time, as compared with the standard flow-over approach, is obtained with the proposed flow-through approach thanks to improved transport kinetics of the analyte. The proposed device architecture, in its intrinsic simplicity, gives numerous advantages related to time responses and multiplexing of different analytes, selectively addressed to the ring resonators, for label-free biosensing.

Polymer based planar coupling of self-assembled bottle microresonators

The investigation of a simple and self-assembling method for realizing polymeric micro-bottle resonators is reported. By dispensing precise amounts of SU-8 onto a cleaved optical fiber, employed as mechanical support, bottle microcavities with different shapes and diameters are fabricated. The balancing of surface energy between glass fiber and polymeric microresonator with surface tension of SU-8 confers different shape to these microstructures. Planar single-mode SU-8 based waveguide, realized on polymethylmethacrylate, is chosen for exciting the micro-bottle resonators by evanescent wave. The reliability of the fabrication process and the shape of the bottle microcavities are investigated through optical analysis. We observe whispering gallery modes in these resonant microstructures by a robust coupling with single mode planar waveguides around 1.5 μm wavelength. The resonance spectra of micro-bottle resonators and the spectral characteristics, such as Quality-factor (Q factor) and free spectral range, are evaluated for all the realized microstructures. SU-8 micro-bottle resonators show high Q-factors up to 3.8 × 104 and present a good mechanical stability. These features make these microcavities attractive for sensing and/or lasing applications in a planar platform.

Study of the interference effects in an optical cavity for organic light-emitting diode applications

The interference effects generated in a bottom-emitting electroluminescent device fabricated on a polymer underlayer introduced with the aim of improving the anode roughness have been studied. The analysis of the interference fringes at different detection angles and the spatial coherence demonstrates that this phenomenon is due to multiple internal reflections that propagate in the polymer layer. This effect can be eliminated by modifying the polymer thickness and the incidence angle of the electromagnetic radiation at the anode-polymer interface. Inkjet etching technology is adopted for microcavities-shaped polymer structuring to destroy the resonator effect of the optical cavity.

Plasma functionalization procedure for antibody immobilization for SU-8 based sensor.

In this paper, we report the study on a new protocol for the immobilization process of antigen/antibody assay on SU-8 layers by oxygen plasma treatment. Plasma treatments, at different plasma powers and for different duration times, are performed and their effects on immobilization efficiency are studied. The chemical properties and the surface morphology of SU-8 before and after the functionalization and immobilization of (IgG) are then verified by Raman spectroscopy and atomic force microscopy (AFM). An increase of the surface roughness of SU-8 layers is observed after the oxygen plasma treatment and an intensity variation of functional groups is also evidenced. To demonstrate the validity of the process the distribution of IgG immobilized on SU-8 surfaces is detected by fluorescence microscopy measurement after incubation with fluorescein isothiocyanate (FITC)-tagged anti-human IgG. An increase of the amount of the adsorbed protein of about 20% and a good repeatability on antigen/antibody distribution on the surface are detected for IgG on plasma treated substrates. Finally, label free measurements are performed by SU-8 optical ring resonators reaching detection limits of 0.86ngcm(-2). The proposed approach offers a smart protocol for IgG immobilization on SU-8 substrate that can be easily extended to different antigen/antibody assay and polymeric materials for the realization of high performance immunosensors.

Photosensing Properties of Pentacene OFETs Based on a Novel PMMA Copolymer Gate Dielectric

In the present work, bottom-gate top-contact organic field effect transistors (OFETs) were fabricated by evaporating a pentacene semiconductor film on top of a new insulating poly(methyl methacrylate) (PMMA) copolymer containing methacrylate units. The PMMA copolymer was synthesized in order to combine the well-known insulating properties of PMMA with the possibility to be efficiently photocured enabling photopatterning-based organic circuitry integration processes. The properties of the pentacene layer deposited on ITO/PMMA copolymer stack were studied through morphological and structural analyses. Device photoresponses and photoexcitated transients were investigated and compared to reference devices based on standard PMMA gate dielectric.

ITO-free polymer solar cells with inkjet-printed highly-conductive PEDOT:PSS anode

Actually the most promising polymer solar cell architecture utilizes ITO as transparent conductve anodic electrode. The limited flexibility of ITO and the increasing cost of indium make this kind of electrode not desirable for realizations of low-cost and flexible solar cells. For this reason, it is necessary to develop low-cost, highly flexible and transparent electrodes that can replace the widely used ITO. In this paper, we investigated a new commercial dispersion of PEDOT:PSS suitably modified with dimethyl sulfoxide in solution in order to obtain a highly transparent and conductive manufactured film (HC-PEDOT:PSS) by inkjet printing.

Inkjet Etching of Polymer Surfaces to Manufacture Microstructures for OLED Applications

A soluble polymer layer can be structured by means of solvent drops etching. The inkjet etching (IJE), innovative technique that consists of ejecting liquid material in controlled manner in terms of both volume amount (10–100 pL) and positioning on the substrate (μm resolution), allows to manufacture suitable shaped microstructures on top of polymer surfaces. In the present work we fabricated IJ etched polymer microstructures whose shape varies from concave to convex by employing a pure solvent or solvent mixtures with suitable mixing ratio of the solvents. The manufactured structure profile has been analyzed and the related geometrical parameters, i.e. depth, diameter and height, have been valuated as function of the drops number. Preliminary tests have been performed in order to employ the IJ etched polymer microstructures with the aim to improve the out‐coupling efficiency of organic light‐emitting diodes.

Ring resonator for biosensing via flow-through approach (Conference Presentation)

The realization of a simple real time biosensor, in which antibodies are immobilized onto surfaces, represents a promising application in the immunoassay development. Among the various sensing approaches, one of the most promising is based on microring resonators, offering a lot of advantages such as mass production, reduced dimensions, label-free and real time detection. The use of the evanescent field as optical transduction principle allows the development of label-free biosensors, in which the antibody is usually immobilized on the sensor surface and the binding of the antigen can be controlled and followed in real-time. The overall performances of immunosensors are strongly related to the optimization of the immobilization process and the integration between the microfluidic parts and the optical detection system. The combination of these two aspects makes the biosensing process very efficient, with a consequent reduction of the response time and improvement of the immobilization process efficiency. In this work we explore the working mechanism of a flow-through microresonator platform. A drilled hole, in the center of the ring, allows the active transport mechanism of the analyte toward the sensing surface with a consequent reduction of the response time. Moreover, we study the effects of oxygen plasma, in terms of duration times and plasma power, on immobilization efficiency of immunoglobulin G (IgG). An improvement of about 20% of the protein adsorption is ascribed to chemico-physical modification of SU-8. The measured sensor response time in flow-through configuration is about five times shorter respect to standard flow-over configuration.