Nicola Lovecchio

Electrowetting-on-dielectric system based on polydimethylsiloxane

In this paper we present a detailed characterization of an electro-wetting on dielectric (EWOD) system able to move drop of liquid and to detect its position over an array of electrodes covered with a 1μm thick polydimethylsiloxane (PDMS) layer. In the presented system, the PDMS layer acts as both insulation and hydrophobic material. An electronic board controls all the signals needed for the actuation and sensing functionalities of the EWOD system. Sessile drop experiments show the saturation of the contact angle at negative bias voltage applied to the droplet. This behavior is ascribed to trapped carrier in the PDMS layer and explains the movement of the droplet toward the grounded electrode found in EWOD experiment. The procedure chosen for the drop movement achieves speed around 5cm/s with applied voltages around 200V. Detection of drop position is successfully achieved implementing the time-constant method, which evaluates the variation of electrode capacitance induced by the droplet presence on the PDMS surface corresponding to the metal electrode.

Multifunctional System-on-Glass for Lab-on-Chip applications.

Lab-on-Chip are miniaturized systems able to perform biomolecular analysis in shorter time and with lower reagent consumption than a standard laboratory. Their miniaturization interferes with the multiple functions that the biochemical procedures require. In order to address this issue, our paper presents, for the first time, the integration on a single glass substrate of different thin film technologies in order to develop a multifunctional platform suitable for on-chip thermal treatments and on-chip detection of biomolecules. The proposed System on-Glass hosts thin metal films acting as heating sources; hydrogenated amorphous silicon diodes acting both as temperature sensors to monitor the temperature distribution and photosensors for the on-chip detection and a ground plane ensuring that the heater operation does not affect the photodiode currents. The sequence of the technological steps, the deposition temperatures of the thin films and the parameters of the photolithographic processes have been optimized in order to overcome all the issues of the technological integration. The device has been designed, fabricated and tested for the implementation of DNA amplification through the Polymerase Chain Reaction (PCR) with thermal cycling among three different temperatures on a single site. The glass has been connected to an electronic system that drives the heaters and controls the temperature and light sensors. It has been optically and thermally coupled with another glass hosting a microfluidic network made in polydimethylsiloxane that includes thermally actuated microvalves and a PCR process chamber. The successful DNA amplification has been verified off-chip by using a standard fluorometer.

Thermal characterization of thin film heater for lab-on-chip application

This paper presents the design, fabrication and characterization of a thin film heater functional for thermal treatments in lab-on-chip system. The spatial temperature distribution determined by different heater geometries has been studied through electro-thermal simulations by using COMSOL Multiphysics. The heater showing the more uniform temperature distribution has been subsequently fabricated and characterized. A very good agreement between modeled and measured data has been attained. Results show a spatial temperature distribution of about ±1°C over an area comparable to the heater area and a directly USB powered heater, demonstrating the suitability of the proposed device for lab-on-chip thermal applications.

Thermal control system based on thin film heaters and amorphous silicon diodes

In this paper we present a system able to perform thermal treatments on lab-on-chip devices fabricated on glass substrates. The system includes a thin film resistor acting as heater and thin film hydrogenated amorphous silicon diodes acting as temperature sensors. An electronic system controls the lab-on-chip temperature through a Proportional-IntegralDerivative algorithm. In particular, an electronic board infers the system temperature measuring the voltage across the amorphous silicon diodes and drives the heater to achieve the set-point temperature. Taking into account the 16-bit ADC resolution and the sensors sensitivity, which is around 3.6 mV/oC, we estimate that our system is able to detect temperature variation as low as 3.5·10-3oC. Furthermore, the experimental results show that the system is able to stabilize the system temperature with a precision better than 0.1 oC.

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.

Thermally actuated microfluidic system for lab on chip applications

In this paper, we present the design and fabrication of Polydimethylsiloxane based Lab-on-Chip system useful for polymerase chain reaction (PCR) application. The proposed system is fabricated on glass substrate, taking advantage of thermally conductive and electrically insulating substrate. On one side of glass microfluidic system having reaction chamber for PCR, microchannel for fluid handling and two thermally actuated valves for fluid control has been made. On the other side of glass three thin film heaters are integrated, two heaters located under valves actuate the valves membrane and allow the chamber isolation and the middle heater is dedicated to PCR thermal cycle. The design of the system, carried out by using COMSOL Multiphysics, involved the optimization of the system dimensions and the shape of microchannel used to completely close the channel. We have also study the thermal interaction between three heaters and optimize the design to minimize the interference. The system was fabricated and an experiment actuating the valves was performed verifying the closing of the microfluidic channel.

Array of differential photodiodes for thermal effects minimization in biomolecular analysis

In this paper, we present a device that minimizes the effects of the temperature on light detection in lab-on-chip systems. The device is based on hydrogenated amorphous silicon p-type/intrinsic/n-type junction, fabricated on a glass substrate using thin-film technologies. The device structure is constituted by two series-connected amorphous silicon diodes: a blind one acting as dark reference and a photosensitive one. The signal measured at the output node of each element is equal to the difference of the current of the two diodes. This allows to minimize the temperature-dependent dark current contribution. The design of the photolithographic masks has been carefully carried out to pursue a perfect technological symmetry between the two diodes of the differential structure. Experimental data obtained by current-voltage characteristics show the correct operation of the individual diodes as well as the effectiveness of the differential structure to reject the common-mode signal induced by temperature variations. This feature makes the device a suitable candidate for analytical systems based on optical detection that involve thermal treatments.

Drop position sensing in digital microfluidics based on capacitance measurement

In this work, we present an electronic circuit able to sense the droplet position in Electro-Wetting On Dielectric (EWOD) systems. The drop position is determined measuring the equivalent capacitance of the EWOD electrode, whose value varies according to the presence of the fluid over the pad. In the presented system, the capacitance measurement is achieved through the “Frequency Shift Oscillator” method: the EWOD electrode is inserted in an oscillator circuit, whose operating frequency is inversely proportional to the electrode capacitance value. A microcontroller, included in the system, counts the number of rising edges at the output of the circuit determining the oscillation frequency. The oscillator has been simulated and subsequently fabricated on a double layer printed circuit board. A very good agreement between simulations and experiments has been achieved. The value of obtained sensitivity is not lower than 1.2 kHz/pF that corresponds to a minimum detectable capacitance variation of 0.167 pF. This value is well below the variation of capacitance due to the presence of the droplet above the EWOD electrode and demonstrates the suitability of our circuit as a successful drop position sensor.

Integrated chemiluminescence-based lab-on-chip for detection of life markers in extraterrestrial environments

The detection of life markers is a high priority task in the exploration of the Solar System. Biochips performing in-situ multiplex immunoassays are a very promising approach alternative to gas chromatography coupled with mass spectrometry. As part of the PLEIADES project, we present the development of a chemiluminescence-based, highly integrated analytical platform for the detection of biomarkers outside of the Earth. The PLEIADES device goes beyond the current lab-on-chip approaches that still require bulky external instrumentation for their operation. It exploits an autonomous capillary force-driven microfluidic network, an array of thin-film hydrogenated amorphous silicon photosensors, and chemiluminescence bioassays to provide highly sensitive analyte detection in a very simple and compact configuration. Adenosine triphosphate was selected as the target life marker. Three bioassay formats have been developed, namely (a) a bioluminescence assay exploiting a luciferase mutant with enhanced thermal and pH stability and (b and c) binding assays exploiting antibodies or functional nucleic acids (aptamers) as biospecific recognition elements and peroxidase or DNAzymes as chemiluminescence reporters. Preliminary results, showing limits of detection in the nanomolar range, confirm the validity of the proposed approach.

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.