Elisa Morganti

PDMS/Kapton Interface Plasma Treatment Effects on the Polymeric Package for a Wearable Thermoelectric Generator

The present work highlights the progress in the field of polymeric package reliability engineering for a flexible thermoelectric generator realized by thin-film technology on a Kapton substrate. The effects of different plasma treatments on the mechanical performance at the interface of a poly(dimethylsiloxane) (PDMS)/Kapton assembly were investigated. To increase the package mechanical stability of the realized wearable power source, the Kapton surface wettability after plasma exposure was investigated by static contact-angle measurements using deionized water and PDMS as test liquids. In fact, the well-known weak adhesion between PDMS and Kapton can lead to a delamination of the package with an unrecoverable damage of the generator. The plasma effect on the adhesion performances was evaluated by the scratch-test method. The best result was obtained by performing a nitrogen plasma treatment at a radio-frequency power of 20 W and a gas flow of 20 sccm, with a measured critical load of 1.45 N, which is 2.6 times greater than the value measured on an untreated Kapton substrate and 1.9 times greater than the one measured using a commercial primer.

Microfluidic Sample Preparation Methods for the Analysis of Milk Contaminants

In systems for food analysis, one of the major challenges is related to the quantification of specific species into the complex chemical and physical composition of foods, that is, the effect of “matrix”; the sample preparation is often the key to a successful application of biosensors to real measurements but little attention is traditionally paid to such aspects in sensor research. In this critical review, we discuss several microfluidic concepts that can play a significant role in sample preparation, highlighting the importance of sample preparation for efficient detection of food contamination. As a case study, we focus on the challenges related to the detection of aflatoxin in milk and we evaluate possible approaches based on inertial microfluidics, electrophoresis, and acoustic separation, compared with traditional laboratory and industrial methods for phase separation as a baseline of thrust and well-established techniques.

Super-Hydrophilic PDMS and PET Surfaces for Microfluidic Devices

In this work the effect of air plasmas on wettability of Polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET) was studied. These polymers are widely used materials in the fabrication of microfluidic devices. The microfluidic system fabricated from native PET and PDMS requires active pumping mechanism, due to a low hydrophilic surface behavior. To render hydrophilic and increase the capillary flow into the device, plasma treatments can be used. Air plasma treatment is an interesting technology for microfluidic fields due to simplicity of use and low cost. This study describes the effect of the working plasma pressure on wettability of polymers. The polymers were treated by RF plasma and the wettability was studied by means of sessile contact angle. The results established that the air plasma can increase the wettability of both polymers. Moreover we demonstrated that by optimizing the working pressure a superhydrophilic surface (with a contact angle less than 5°) can be obtained. The findings suggest that air plasma treatments are a suitable technology to enhance polymers surface wetting performance for microfluidic devices.

A Micro Polymerase Chain Reaction Module for Integrated and Portable DNA Analysis Systems

This work deals with the design, fabrication, and thermal characterization of a disposable miniaturized Polymerase Chain Reaction (PCR) module that will be integrated in a portable and fast DNA analysis system. It is composed of two independent parts: a silicon substrate with embedded heater and thermometers and a PDMS (PolyDiMethylSiloxane) chamber reactor as disposable element; the contact between the two parts is assured by a mechanical clamping obtained using a Plastic Leaded Chip Carrier (PLCC). This PLCC is also useful, avoid the PCR mix evaporation during the thermal cycles. Finite Element Analysis was used to evaluate the thermal requirements of the device. The thermal behaviour of the device was characterized revealing that the temperature can be controlled with a precision of ±0.5°C. Different concentrations of carbon nanopowder were mixed to the PDMS curing agent in order to increase the PDMS thermal conductivity and so the temperature control accuracy.

Structural reliability and thermal insulation performance of flexible thermoelectric generator for wearable sensors

Present work highlights the progress in the field of polymeric package reliability engineering for a flexible thermoelectric generator realized by thin film semiconductor technology on Kapton®. Together with mechanical enhancement, the thermal insulation performance of the realized 3D custom package was tested. The effect of different plasma treatments on the mechanical performance and interface of a Polydimethylsiloxane (PDMS)/Kapton® assembly were investigated; in order to increase the package mechanical stability of the realized wearable power source, Kapton® surface wettability was investigated by static contact angle measurements using deionized water and PDMS as liquid test. In fact, well known weak adhesion between PDMS and Kapton® leads to delamination of the package with unrecoverable damage of the generator. Plasma effect on adhesion performances was evaluated by scratch test method. By a numerical thermal analysis, the device packaging was optimized by coupling the module realized onto Kapton foil (by thin film PVD technology) to a PDMS layer opportunely molded to thermally insulate TEG cold junctions and enhance the thermal gradient useful for thermocouples operation. Fabrication process with optical lithography steps allows high resolution definition of thermoelectric semiconductors alloys. The main advances in wearable generator packaging technology is represented by increased structural robustness of PDMS/Kapton® assembly in terms of delamination and fatigue resistance.

Development of MEMS-based liquid chromatography modules for agrofood applications

This work presents the realization of a MEMS-based miniaturized system for liquid chromatography focused on agrofood applications, and in particular on the detection of wine defects. The main modules of the systems are: i.) a Si-based separation column with inlet/outlet for fluidic connections; ii.) a three-microelectrode voltammetric sensor. Moreover, a Platinum heater has been realized on the back side of the chip containing the Si column in order to operate at temperatures greater than the room temperature. The realized device consists of a Silicon/Pyrex structure realised by anodic bonding. Microchannels and inlet/outlet have been fabricated by Deep Reactive Ion Etching (DRIE) and Tetra Methyl Ammonium Hydroxide (TMAH) wet etching respectively. The column has been functionalised with n-octyltriethoxysilane (C8-TEOS). A lift-off technique has been developed for realizing the Pt heater and the Pt microelectrodes on-chip. In order to separately characterize the main modules of the device, a package of the system has been realized following a modular approach; appropriate tubing and nanovolume connections have been used in order to minimize dead volumes. Then other packages approaches have been considered in order to minimize dead volumes and to avoid leakage issues. Preliminary characterization tests of the two main modules have been performed. The capability of the system to correctly retain and detect Acetic acid has been tested.

The e-cardiac rehabilitation service: An integrated system for Home-Care Cardiac Rehabilitation

The production of devices for remote monitoring of cardiac activity and other physiological parameters in cardiovascular patients, and the adoption of tele-monitoring services, tele-consultation and online reporting are taking place in different public and private contexts. This paper aims to present the concept of Home Care Rehabilitation and the technological platform to enable it. The e-cardiac rehabilitation service is a telemedicine service directed to cardiac patients, who need a structured rehabilitation in Phase 3 to be performed at home or at local clinics, with scheduled sessions of exercise remotely monitored.

Protein detection system based on 32x32 SPAD pixel array

In this work, a compact low-cost system designed to detect low amounts of proteins in biological fluids is presented. The system, based on time-gated fluorescence detection principle, is composed by a Single-Photon Avalanche Diode (SPAD) pixel array, a LED excitation light source and a micro-machined reaction chamber coupled to a microfluidic network. A dual-site binding strategy based on DNA aptamers is used for target protein recognition. The microreactor, composed of an array of microwells covered with a transparent membrane, is functionalized with a primary aptamer, while a fluorescent-tagged secondary aptamer is used for the detection. Preliminary measurements demonstrate the feasibility of fluorescence lifetime detection to discriminate between different fluorophores. The detection of human thrombin protein in 300nM concentration is reported as a biological proof of principle of the biosensor.

CMOS single-photon detector for advanced fluorescence sensing applications

Fluorescence lifetime measurement is used in biological research to enhance the contrast of fluorescence images. The outstanding sensitivity that can be achieved with this method is obtained at the expense of a high data throughput. A substantial data reduction can be achieved using the time-gated technique, which consists in counting the number of photons occurring inside different time windows. Thanks to the recent developments in the realization of Single Photon Avalanche Diodes (SPAD) in standard CMOS technologies, this technique can be monolithically implemented on-chip. In this work, three different detectors fabricated within a 0.35 ▪m High Voltage CMOS technology will be described, focusing onto their use in lifetime imaging. The sensors have been designed for different optical setups and for different applications, ranging from Fluorescence Lifetime Imaging Microscopy to miniaturized Lab-on-Chip. The advantages and limitation of the proposed sensors will be pointed out and a case study of a specific application will be presented.

Design and simulation of interdigitated micro-electrode arrays for tumor cells separation and detection

This work presents the design and simulations of an interdigitated micro-electrode array aimed to discriminate cancer cells, with potential applications in predictive oncology, diagnostics and anti-tumor drug research. The device has been designed and a technological fabrication process has been defined. The microsystem consists of a quartz substrate with gold electrodes and a microfabricated three-dimensional structure (glass/SU8) for cells confinement. The designed device consists of three separated part: two circular areas for confinement, detection and moving and a narrow channel between those areas for the transportation of the cells. The detection can be done by measuring the charge variations associated to the different membrane capacitances and conductivities of tumor and normal cells. Alternating electric field over the electrodes is used for moving the cells between the circular areas (Travelling Wave Dielectrophoresis TwDEP) as well as for levitating and trapping cells on the electrodes (positive-negative Dielectrophoresis p-nDEP). Analytical and Finite Elements simulations have been performed in order to verify the system reliability and to estimate the parameters in use, like operative frequency, voltage, expected velocity.