Dimitra Dimotikali

Biocompatible photolithographic process for the patterning of biomolecules.

A new approach for the patterning of biomolecule layers is introduced based on the design of a new photoresist material with biocompatible lithographic processing requirements. The photoresist is based on poly(t-butyl acrylate), which allows positive imaging with very dilute basic solutions, tolerable by selected biomolecules used in immunoanalysis. Sensitivity at lambda>300 nm is obtained using a suitable sulfonium salt photoacid generator. Thermal steps also take place under conditions tolerable by biomolecules. Lithographic results on Si wafer substrates show resolution capabilities for equal lines/spaces, down to the range of 5-10 microm under biocompatible conditions. The process is also used on substrates of different geometries, including inner capillary surfaces. The patterning of the inner surface of a polystyrene capillary with mouse IgG is reported to demonstrate the principles of the above approach.

Photolithographic patterning of proteins with photoresists processable under biocompatible conditions

The microlithographic patterning of proteins on solid substrates using photoresists, which can be processed in the presence of biomolecules without affecting their bioactivity, is reported. Chemically amplified resist materials based on poly(t-butyl acrylate) and a newly synthesized copolymer of t-butyl methacrylate, 2-hydroxyethyl methacrylate, isobornyl methacrylate, and acrylic acid designed for this application, are evaluated regarding capabilities for processing under biocompatible conditions (processing temperatures at about 50 °C or lower and development with dilute aqueous base developers). The photoresist formulations based on the newly synthesized (meth)acrylate copolymer had higher sensitivity and contrast allowing lithographic processing even without postexposure bake. Patterns down to 3.75 μm lines/spaces of two different protein molecules, rabbit Immunoglobulin G and bovine serum albumin, on aminosilane-treated silicon surfaces, were obtained with a photoresist formulation based on the new c...

Luminescent Methods in the Analysis of Untreated Edible Oils: A Review

The present review describes the application of luminescent methods in the analysis of edible oils without any pretreatment such as extraction prior to analysis. Emphasis has been given to applications of chemiluminescence and fluorescence assays for determining quality parameters of edible oils, such as oxidative stability, antioxidant activity, and lipid hydroperoxides content, as well as classification or adulteration of vegetable oils.

Protein-Resistant Cross-Linked Poly(vinyl alcohol) Micropatterns via Photolithography Using Removable Polyoxometalate Photocatalyst

In the last years, there has been an increasing interest in controlling the protein adsorption properties of surfaces because this control is crucial for the design of biomaterials. On the other hand, controlled immobilization of proteins is also important for their application as solid surfaces in immunodiagnostics and biosensors. Herein we report a new protein patterning method where regions of the substrate are covered by a hydrophilic film that minimizes protein adsorption. Particularly, poly(vinyl alcohol) (PVA) cross-linked structures created by an especially developed photolithographic process are proved to prevent protein physisorption and they are used as a guide for selective protein adsorption on the uncovered areas of a protein adsorbing substrate such as polystyrene. The PVA cross-linking is induced by photo-oxidation using, as a catalyst, polyoxometalate (H3PW12O40 or α-(NH4)6P2W18O62), which is removed using a methyl alcohol/water mixed solvent as the developer. We demonstrate that the polystyrene and the cross-linked PVA exhibit dramatically different performances in terms of protein physisorption. In particular, the polystyrene areas presented up to 130 times higher protein binding capacity than the PVA ones, whereas the patterning resolution could easily reach dimensions of a few micrometers. The proposed approach can be applied on any substrate where PVA films can be coated for controlling protein adsorption onto surface areas custom defined by the user.

Effect of triphenylsulfonium triflate addition in wide band-gap polymer light-emitting diodes: improved charge injection, transport and electroplex-induced emission tuning

The presence of mobile anions in the emitting layer of polymer-based OLEDs has been proven to influence substantially the injection characteristics of the diode. In this work we report on the improvement of both injection and transport of charge carriers in blue emitting poly[2-(6-cyano-6-methyl-heptyloxy)-1,4-phenylene] (CN-PPP) based OLEDs upon insertion of the all-organic triphenylsulfonium (TPS) triflate salt in the emitting layer. On one hand, the anion displacement influences the energetics at the polymer/anode interface facilitating hole injection, whereas, on the other hand, the triphenylsulfonium cations act as electron transporting sites. The OLEDs exhibit significantly reduced turn-on voltage to half their initial value and increased luminance at low operating voltage. Moreover, the large energetic mismatch of the polymer and the triphenylsulfonium salt as well as the polarity induced by the ions result in simultaneous dual emission originating from the polymer exciton and from an electroplex, which is proposed to be formed at the triphenylsulfonium salt/polymer interfaces in the bulk. These results show that triphenylsulfonium salts represent an attractive class of materials that can be blended with conjugated polymers and can modify their electrical and/or emissive characteristics.

Dehydration of molybdenum oxide hole extraction layers via microwave annealing for the improvement of efficiency and lifetime in organic solar cells

A significant contribution to the improvement of efficiency and lifetime of organic solar cells is due to the successful engineering of the metal contact/organic interface by introducing appropriate interlayers. In the current work we show that a short microwave post-annealing treatment in air of an under-stoichiometric molybdenum oxide (MoOx) hole transport layer significantly enhanced the performance and lifetime of an organic solar cell based on a poly(3-hexylthiophene):[6,6]-phenyl-C71-butyric acid methyl ester (P3HT:PC71BM) blend. The enhanced performance is mainly driven by improvement in the short circuit current (Jsc) and the fill factor (FF), caused by, except for an increase of the anode work function, reduced series resistance, and increased shunt resistance and also higher charge generation efficiency, reduced recombination losses and improved hole transport towards the anode contact. In addition, the lifetime of the devices with microwave annealed MoOx interlayers was also significantly improved compared to those with as-deposited MoOx and, especially, those with the PEDOT-PSS interlayer. The above were attributed to effective dehydration which was also followed by structural transformation and crystallization of the MoOx layer during microwave annealing. The removal of absorbed water molecules led to alterations of the structure and microstructure of the MoOx films, visible in the X-ray diffraction patterns, infrared and Raman spectra and atomic force microscopy images recorded on their surface without influencing the oxides chemical composition as evidenced by X-ray photoelectron spectroscopy. During microwave annealing the substrate remains practically at room temperature, so the method is applicable for films deposited on plastics or other temperature-sensitive substrates.