Despina Moschou

Amperometric IFN-γ immunosensors with commercially fabricated PCB sensing electrodes.

Lab-on-a-Chip (LoC) technology has the potential to revolutionize medical Point-of-Care diagnostics. Currently, considerable research efforts are focused on innovative production technologies that will make commercial upscaling of lab-on-chip products financially viable. Printed circuit board (PCB) manufacturing techniques have several advantages in this field. In this paper we focus on transferring a complete IFN-γ enzyme-linked immune-sorbent assay (ELISA) onto a commercial PCB electrochemical biosensing platform, We adapted a commercially available ELISA to detect the enzyme product TMB/H2O2 using amperometry, successfully reproducing the colorimetry-obtained ELISA standard curve. The results demonstrate the potential for the integration of these components into an automated, disposable, electronic ELISA Lab-on-PCB diagnostic platform.

Surface and electrical characterization of Ag/AgCl pseudo-reference electrodes manufactured with commercially available PCB technologies

Lab-on-Chip is a technology that could potentially revolutionize medical Point-of-Care diagnostics. Considerable research effort is focused towards innovating production technologies that will make commercial upscaling financially viable. Printed circuit board manufacturing techniques offer several prospects in this field. Here, we present a novel approach to manufacturing Printed Circuit Board (PCB)-based Ag/AgCl reference electrodes, an essential component of biosensors. Our prototypes were characterized both structurally and electrically. Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS) were employed to evaluate the electrode surface characteristics. Electrical characterization was performed to determine stability and pH dependency. Finally, we demonstrate utilization along with PCB pH sensors, as a step towards a fully integrated PCB platform, comparing performance with discrete commercial reference electrodes.

Integrated biochip for PCR-based DNA amplification and detection on capacitive biosensors

Responding to an increasing demand for LoC devices to perform bioanalytical protocols for disease diagnostics, the development of an integrated LoC device consisting of a μPCR module integrated with resistive microheaters and a biosensor array for disease diagnostics is presented. The LoC is built on a Printed Circuit Board (PCB) platform, implementing both the amplification of DNA samples and DNA detection/identification on-chip. The resistive microheaters for PCR and the wirings for the sensor read-out are fabricated by means of standard PCB technology. The microfluidic network is continuous-flow, designed to perform 30 PCR cycles with heated zones at constant temperatures, and is built onto the PCB utilizing commercial photopatternable polyimide layers. Following DNA amplification, the product is driven in a chamber where a Si-based biosensor array is placed for DNA detection through hybridization. The sensor array is tested for the detection of mutations of the KRAS gene, responsible for colon cancer.

Performance and reliability of SLS ELA polysilicon TFTs fabricated with novel crystallization techniques

SLS ELA polysilicon TFTs fabricated in films crystallized with several novel techniques, yielding different film microstructure and texture, were investigated. The parameter statistics indicate that the TFT performance depends on film quality and asperities, in conjunction with the grain boundary trap density. The drain current transients, upon TFT switch from OFF to ON state, showed gate oxide polarization, related to film asperities and also confirmed the presence of extended defects in the TFTs of small mobilities. DC hot carrier stress was applied, indicating a reliability dependence on polysilicon structure and differences in degradation mechanisms for the various TFT technologies.

Front and Back Channel Properties of Asymmetrical Double-Gate Polysilicon TFTs

Polycrystalline silicon thin-film transistors (TFTs) with different front- and back-gate lengths are investigated. In addition, the laser annealing process yields high-quality directional grains that enable us to orient TFT channels parallel or perpendicular to the grain boundaries. It is demonstrated that the turn-on voltage is not dependent on grain orientation, unlike the subthreshold swing and the maximum transconductance. Moreover, it is shown that double-gate TFTs are fully depleted and therefore back interface properties exert critical influence on the overall TFT electrical performance. From electrical measurements the back interface state density was estimated to reach values >6 X loll cm 2 eV -1 and it was shown that the electrical performance of the double-gate devices is highly dependent on the back-to-front gate-length ratio.

Towards a high-precision, embedded system for versatile sensitive biosensing measurements

This paper demonstrates a versatile, high-accuracy, data-acquisition electronic platform for biosensing measurements, capable of collecting minute current and voltage input signals, stemming from various types of amperometric and potentiometric biosensors. The instrument is able to process the incoming analog signals in a digital manner and export them back to the user either as an amplified analog signal or in digital format through a USB 2.0 interface. The proposed system comprises off-the-shelf IC components and a commercially available FPGA-based DSP unit. The performance of the instrumentation platform has been tested initially by means of very small ideal current and voltage signals generated by precise electronic equipments and subsequently has been validated via proof-of-concept experiments with amperometric and potentiometric sensors. The results shown in this paper exhibit potential for integrating specific sections of the proposed instrumentation board with appropriate biosensors, towards developing affordable, yet reliable Point-Of-Care (POC) diagnostic tools for sensitive biochemical measurements.

On the importance of the Vg,max–Vth parameter on LTPS TFT stressing behavior

In this work we point out the importance of the device parameter Vg,max–Vth (the difference between the gate voltage at maximum transconductance and the threshold voltage obtained from linear extrapolation method) for LTPS TFTs under dc stress. The evolution of this parameter with stress time is monitored for the first time, along with the other typical device parameters (Vth, Gm,max, S) in order to further clarify the nature of the traps generated. In the first dc stress case considered, we observed very different S degradation of the two samples, but very similar Gm,max degradation, as well as similar Vg,max–Vth evolution. Therefore, Gm,max evolution with stress time was found to be related more strongly to tail state generation, probed through Vg,max–Vth, and not to midgap trap generation, probed through S. In the second case, no midgap state generation is observed, but only severe tail state generation. Hence, the nature of the created defects and the reason for the significant Gm,max reduction could only be probed through the observation of Vg,max–Vth, a parameter not utilized until now. Finally, stressing both n- and p-channel devices, we are able to explain the much more intense Gm,max degradation observed for n-channel devices, associating it to the larger tail state generation in n-channel TFTs, also pointed by Vg,max–Vth evolution with stress.

Short channel effects in double gate polycrystalline silicon SLS ELA TFTs

Short channel effects in double gate poly-Si SLS ELA TFTs are studied in this work by electrically characterizing devices with varying top gate length and constant bottom gate length. The electrical parameters were extracted for different bottom gate biases, observing a Vth increase with increasing channel length, attributed to more traps present within larger channels. This was also probed through the increase of Vg,max-Vth with increasing channel length. In order to distinguish between short channel effects and possible Ltop/Lbottom effects, devices with different bottom gate lengths and a constant top gate length were also studied. No similar trends as in the case of decreasing channel length were observed, thus supporting our case that the previously observed behavior is mainly an effect of channel shrinking and not of Ltop/Lbottom effects.

Reliability and defectivity comparison of n- and p-channel SLS ELA polysilicon TFTs fabricated with a novel crystallization technique

SLS ELA n- and p-channel polysilicon TFTs fabricated with a novel technique were investigated, oriented both along the preferential and the non-preferential direction. The degradation mechanisms proved very different between n- and p-channel devices, while the channel orientation had a larger effect on n-channel devices than on p-ones. In order to probe the reasons causing this effect we applied DLTS analysis to both n- and p-channel devices oriented along both directions, receiving valuable information about the defectivity differences in n- and p-polysilicon films.

A PNA-based Lab-on-PCB diagnostic platform for rapid and high sensitivity DNA quantification

We report the development of a Lab-on-PCB DNA diagnostic platform, exploiting peptide nucleic acid (PNA) sequences as probes. The study demonstrates the optimization and characterization of two commercial PCB manufacturing gold electroplating processes for biosensing applications. Using an optimized ratio of PNA with a spacer molecule (MCH), the lowest limit of detection (LoD) to date for PCB-based DNA biosensors of 57 fM is reported. The study also showcases a fully integrated Lab-on-PCB microsystem designed for rapid detection, which employs PCB-integrated sample delivery, achieving DNA quantification in the 0.1-100 pM range for 5 μL samples analyzed within 5 min under continuous flow. The demonstrated biosensor proves the capability of PCB-based DNA biosensors for high sensitivity and paves the way for their integration in Lab-on-PCB DNA diagnostic microsystems.