A transistor based sensing platform and a microfluidic chip for a scaled-up simulation of controlled drug release

The framework of my thesis are Biomedical (or Biological) Microelectromechanical Systems (BioMEMSs). Two fields in which this discipline is involved are sensors and fluidics. Functionalized organic materials are under investigation to be the means for target biological sensing, and sensors are evolving to be integrated in fluidics platforms in order to produce in the future new small portable diagnostic devices. On the other hand one of the challenges of micro and nanofluidic technology is the fabrication of drug release devices, in order to control the amount of drug present in an organism. In this thesis these two arguments are considered. First we will discuss the implementation of a process oriented to the fabrication of an hybrid Organic Field Effect Transistor (OFET) with sensing capabilities from the semiconductive layer. In the second part we will show the fabrication process of a silicon based structure for the scaled-up characterization of drugs in nanochannels for controlled drug release. The characterization will consider charged microspheres playing the role of drugs to be tracked with a microscope. We will highlight also the possibility of implementing the transistor related technology in nanofluidic systems for the electronic controlled drug release

Development of a Flexible Lead-Free Piezoelectric Transducer for Health Monitoring in the Space Environment

In this work we report on the fabrication process for the development of a flexible piezopolymeric transducer for health monitoring applications, based on lead-free, piezoelectric zinc oxide (ZnO) thin films. All the selected materials are compatible with the space environment and were deposited by the RF magnetron sputtering technique at room temperature, in view of preserving the total flexibility of the structures, which is an important requirement to guarantee coupling with cylindrical fuel tanks whose integrity we want to monitor. The overall transducer architecture was made of a c-axis-oriented ZnO thin film coupled to a pair of flexible Polyimide foils coated with gold (Au) electrodes. The fabrication process started with the deposition of the bottom electrode on Polyimide foils. The ZnO thin film and the top electrode were then deposited onto the Au/Polyimide substrates. Both the electrodes and ZnO layer were properly patterned by wet-chemical etching and optical lithography. The assembly of the final structure was then obtained by gluing the upper and lower Polyimide foils with an epoxy resin capable of guaranteeing low outgassing levels, as well as adequate thermal and electrical insulation of the transducers. The piezoelectric behavior of the prototypes was confirmed and evaluated by measuring the mechanical displacement induced from the application of an external voltage

Lift-off assisted patterning of few layers graphene

Graphene and 2D materials have been exploited in a growing number of applications and the quality of the deposited layer has been found to be a critical issue for the functionality of the developed devices. Particularly, Chemical Vapor Deposition (CVD) of high quality graphene should be preserved without defects also in the subsequent processes of transferring and patterning. In this work, a lift-off assisted patterning process of Few Layer Graphene (FLG) has been developed to obtain a significant simplification of the whole transferring method and a conformal growth on micrometre size features. The process is based on the lift-off of the catalyst seed layer prior to the FLG deposition. Starting from a SiO2 finished Silicon substrate, a photolithographic step has been carried out to define the micro patterns, then an evaporation of Pt thin film on Al2O3 adhesion layer has been performed. Subsequently, the Pt/Al2O3 lift-off step has been attained using a dimethyl sulfoxide (DMSO) bath. The FLG was grown directly on the patterned Pt seed layer by Chemical Vapor Deposition (CVD). Raman spectroscopy was applied on the patterned area in order to investigate the quality of the obtained graphene. Following the novel lift-off assisted patterning technique a minimization of the de-wetting phenomenon for temperatures up to 1000 °C was achieved and micropatterns, down to 10 µm, were easily covered with a high quality FL

P3HT Processing Study for In-Liquid EGOFET Biosensors: Effects of the Solvent and the Surface

In-liquid biosensing is the new frontier of health and environment monitoring. A growing number of analytes and biomarkers of interest correlated to different diseases have been found, and the miniaturized devices belonging to the class of biosensors represent an accurate and cost-effective solution to obtaining their recognition. In this study, we investigate the effect of the solvent and of the substrate modification on thin films of organic semiconductor Poly(3-hexylthiophene) (P3HT) in order to improve the stability and electrical properties of an Electrolyte Gated Organic Field Effect Transistor (EGOFET) biosensor. The studied surface is the relevant interface between the P3HT and the electrolyte acting as gate dielectric for in-liquid detection of an analyte. Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) characterizations were employed to study the effect of two solvents (toluene and 1,2-dichlorobenzene) and of a commercial adhesion promoter (Ti Prime) on the morphological structure and electronic properties of P3HT film. Combining the results from these surface characterizations with electrical measurements, we investigate the changes on the EGOFET performances and stability in deionized (DI) water with an Ag/AgCl gate electrode

The fabrication of Schottky photodiode by monolayer graphene direct-transfer-on-silicon

A two-step hot embossing process was used to transfer graphene and to fabricate Gr/Si Schottky photodiodes. As a direct graphene transfer technique through a hot embossing system, chemical vapor deposition Gr monolayer was transferred from copper foil to cyclic olefin copolymer foil without a poly(methylmethacrylate) sacrificial layer. Then, hot embossing was employed once again to bond graphene with the prepared Si substrate to form Schottky contact. Electrical and photoelectrical characterizations have been performed to evaluate the Schottky photodiode. The photocurrent increases linearly with light intensity under 633 nm illumination. With an appropriate bias voltage, the maximum responsivity reaches 0.73 A/W. Extracted from I–V characteristics by Cheung’s function, the Schottky barrier height and ideality factor are 1.01 eV and 2.66, respectively. The experimental result shows the feasibility and effectiveness of this hot embossing fabrication process, which demonstrates the opportunity for large scale production and provides a new approach for graphene optoelectronics

Layered Double Hydroxide-Based Gas Sensors for VOC Detection at Room Temperature

Miniaturized low-cost sensors for volatile organic compounds (VOCs) have the potentiality to become a fundamental tool for indoor and outdoor air quality monitoring, to significantly improve everyday life. Layered double hydroxides (LDHs) belong to the class of anionic clays and are largely employed for NOx detection, while few results are reported on VOCs. In this work, a novel LDH coprecipitation method is proposed. For the first time, a study comparing four LDHs (ZnAl−Cl, ZnFe−Cl, ZnAl−NO3, and MgAl−NO3) is carried out to investigate the sensing performances. As explored through several microscopy and spectroscopy analyses, LDHs show a morphology characterized by a large surface area and a three-dimensional hierarchical flowerlike architecture with micro- and nanopores that induce a fast diffusion and highly effective surface interaction of the target gases. The fabricated sensors, operating at room temperature, are able to reversibly and selectively detect acetone, ethanol, ammonia, and chlorine vapors, reaching significant sensing response values up to 6% at 21 °C. The results demonstrate that by changing the LDHs’ composition, it is possible to modulate the sensitivity and selectivity of the sensor, helping the discrimination of different analytes, and the consequent integration on a sensor array paves the way for electronic nose development

A programmable culture platform for stimulation and in situ sensing of lung epithelial cells

A programmable dynamic cell culture chamber compatible with a standard multi-well plate was designed and characterized. The system is integrated with an array of OECT biosensors, in view of an in-situ monitoring of the dynamic cultures