Marco Nardecchia

2-D digital microfluidic system for droplet handling using Printed Circuit Board technology

In this work, a digital microfluidic system for droplet handling using ElectroWetting-On-Dielectrics (EWOD) technique in closed configuration based on Printed Circuit Board (PCB) technology is presented. The proposed system features a bidimensional 24×24-electrodes array controlled by seven control signals that allow to move a droplet along the entire array. A stack of a dielectric layer (SU-8) and a hydrophobic layer (Teflon AF1600) deposited on the PCB complete the EWOD device. Technological processes have been refined and adapted in order to be compatible with the PCB substrate material while ensuring good adhesion as well satisfactory dielectric characteristics. Experimental results of contact angle measurements as a function of the applied voltage are in good agreement with the Lippmann-Young equation. The system has been tested in “closed” EWOD configuration by dispensing 1 μL of water and by driving the fluid over the array applying voltages in the range 15 V to 30 V to the control electrodes.

Lab-on-glass system for DNA treatments

This paper presents the fabrication and testing of a lab-on-chip system suitable for treatment of DNA. It includes two main modules: a system-on-glass (SoG) and a disposable microfuidic chip. The SoG integrates, on the same glass substrate, thin film metal heaters and amorphous silicon temperature sensors to achieve a uniform temperature distribution (within ±1°C) in the heated area. Two polydimethylsiloxane microfluidic chips have been developed: a PCR-Chip for DNA amplification and a dsDNA-Chip for separation and selective isolation of a ssDNA from a dsDNA. The proposed system aims therefore to develop compact, low-cost devices that can implement multiple functions in biochemical procedures. In particular, the tested bioanalytical procedures are well suited for carrying-out an on-chip SELEX process, a combinatorial chemistry technique for the selection of aptamers.

Integration of electrowetting technology inside an all-glass microfluidic network

This paper presents a low temperature technological process ahle to integrate an all-glass microfluidic network with an ElectroWetting On Dielectric (EWOD) structure for the digital handling of liquids. The fluidic channels result from the wet-etching of the glass, while the electrodes necessary for the droplet movement are deposited on the bottom and top surfaces of the microfluidic structure. The bottom electrodes are produced by a selective and sequential photolithographic pattern of a stack of metals, insulation layer and hydrophobic film. The top common electrode is made by a continuous transparent conductive oxide, covered by a hydrophobic layer. Compatibility of the technological steps and mechanical robustness of the proposed device have been tested designing and fabricating a microfluidic network integrating a central chamber, with a volume of about 9 μΐ, two reservoirs, two microfluidic channels and 26 EWOD electrodes. The maximum temperature reached during the device fabrication was 330°C, which is two times lower than the one used for the anodic bonding of glass-based microfluidic network.

Autonomous Microfluidic Capillary Network for on Chip Detection of Chemiluminescence

This work reports on the design, simulation and fabrication of an autonomous microfluidic network. It is a part of a highly integrated, new analytical platform for the multiparametric detection of bio-organic molecules in extra-terrestrial environment. The proposed microfluidic system, made in SU-8 3050, allows to obtain an autonomous microfluidic network able to have simultaneous capillary filling and fresh solution into each site of detection avoiding cross-contamination among different sites. Computational Fluid Dynamics (CFD) simulations have been carried in order to verify the proper operation of the designed microfluidic network and to optimize it. Technological processes have been refined and adapted in order to ensure good adhesion, using low-temperature and low-pressure bonding avoiding the risk of breaking the glass slides. Experiments have been conducted to verify the autonomous capillary filling of the entire network and its rinsing with buffer solution. The experimental results are in good agreement with the simulations.

Optoelectronic System-on-Glass for On-Chip Detection of Fluorescence

In this paper, we present an optoelectronic system-on-glass (SoG), suitable for detection of fluorescent molecule. It integrates, on the same glass substrate, an array of amorphous silicon (a-Si:H) photosensors and a thin film interferential filter. The system can be directly coupled with another glass substrate hosting a polydimethylsiloxane based microfluidic network where the fluorescent phenomena occur. The compatibility of the different technological steps to attain on the same glass substrate the photosensors and the filter determined the sequence, the selection of materials and the deposition parameters of the whole process. The electro-optical characterization of the photodiode, performed after the filter deposition, demonstrated the efficacy of the filter in reducing the excitation light. The system has been successfully tested using the ruthenium complex [Ru(phen)2(dppz)]2+, a fluorescent dye which works as DNA intercalating molecule.

Enhancement in PDMS-Based Microfluidic Network for On-Chip Thermal Treatment of Biomolecules

In this paper, we present an improved microfluidic network based on polydimethylsiloxane (PDMS) and thin film heaters for thermal treatment of biomolecules in lab-on-chip systems. It relies on the series connection of two thermally actuated valves, at both inlet and outlet of the network, in order to reduce leakage of sample when its process temperature approaches 100 °C. The spatial arrangement of valves and microfluidic channels in between has been optimized using COMSOL Multiphysics, through the investigation of the system thermal behavior. Taking into account the simulation results, the geometries of the heaters have been defined following standard microelectronic technologies and the microfluidic network has been fabricated by soft lithography. The experiments demonstrate that with the proposed configuration the liquid evaporation is strongly reduced since more than 80% of the sample is recovered after a practical thermal treatment experiment.

Integrated System Based on Thin Film Technologies for Cell-Based Bioluminescence Assays

This work presents a miniaturized lab-on-chip system suitable for monitoring the activity of living cells through the on-chip detection of their bioluminescence emission. The system integrates amorphous silicon diodes, acting as temperature and light sensors, and indium tin oxide film, acting as heater, on a single glass substrate. During its operation, the glass is thermally and optically coupled to the investigated cells and electrically connected to an electronic board, which controls the lab-on-chip temperature and monitors the sensor photocurrents. The proposed lab-on-chip is particularly attractive for the development of portable cell-based biosensors useful for biological activity monitoring as well as for cell cytotoxicity evaluation.

An All-Glass Microfluidic Network with Integrated Amorphous Silicon Photosensors for on-Chip Monitoring of Enzymatic Biochemical Assay

A lab-on-chip system, integrating an all-glass microfluidics and on-chip optical detection, was developed and tested. The microfluidic network is etched in a glass substrate, which is then sealed with a glass cover by direct bonding. Thin film amorphous silicon photosensors have been fabricated on the sealed microfluidic substrate preventing the contamination of the micro-channels. The microfluidic network is then made accessible by opening inlets and outlets just prior to the use, ensuring the sterility of the device. The entire fabrication process relies on conventional photolithographic microfabrication techniques and is suitable for low-cost mass production of the device. The lab-on-chip system has been tested by implementing a chemiluminescent biochemical reaction. The inner channel walls of the microfluidic network are chemically functionalized with a layer of polymer brushes and horseradish peroxidase is immobilized into the coated channel. The results demonstrate the successful on-chip detection of hydrogen peroxide down to 18 μM by using luminol and 4-iodophenol as enhancer agent.

Amorphous Silicon Temperature Sensors Integrated with Thin Film Heaters for Thermal Treatments of Biomolecules

This work combines a lab-on-chip device with an electronic system for the achievement of a small-scale and low-cost thermal treatment of biomolecules. The lab-on-chip is a 1.2 mm-thick glass substrate hosting thin film resistor acting as heater and, on the other glass side, amorphous silicon diodes acting as temperature sensors. The electronic system controls the lab-on-chip temperature through a Proportional-Integral-Derivative algorithm. In particular, an electronic board infers the temperature measuring the voltage across the amorphous silicon diodes, which are biased with a constant forward current of 50 nA, and drives the heater to achieve the set-point temperature. The characterization of the whole system has been carried out implementing the thermal cycles necessary in the polymerase chain reaction technique for amplification of DNA. To this purpose, the lab-on-chip has been thermally coupled with another glass hosting a microfluidic network made in polydimethilsiloxane, and the time evolution of temperature has been carefully monitored. The measured performances in terms of heating rate, cooling rate and settling time demonstrate that the proposed system completely fulfills the requirements of the investigated biological application.

Design, Fabrication and Testing of a Capillary Microfluidic System with Stop-and-Go Valves Using EWOD Technology

This article presents the successful design, fabrication and testing of a miniaturized system integrating capillarity and electrowetting-on-dielectric (EWOD) technology in a microfluidic network. In particular, the change in hydrophobicity occurring at the interphase between a capillary channel and a hydrophobic layer has been exploited using EWOD as a stop-go fluid valve. The combination of capillary forces and EWOD technology to control the fluid movement opens the possibility to implement a wide variety of microfluidic configurations to perform different biomedical assays with a low-power consumption process. These assays could be easily and inexpensively integrated in lab-on-chip systems featuring small size and high-throughput characteristics.