Dr. Eng. Daciana BOTTA

Paper-based devices hold great promise in biosensing, but the choice of electrode materials influences performance. Here, we report a paper-based electrochemical sensor developed for nucleic acid quantification, in a sandwich-type architecture integrating 3-electrode systems on metallized electrospun polymeric fibers. A 3D-printed hydrophobic barrier on the chromatographic paper defines injection and testing zones. Fluid diffusion through paper and concentration gradients are considered in the design. Electrochemical characterization is performed using 40 mu L of methylene blue solution, which interacts with double-stranded nucleic acids, reducing its redox activity. This interaction mechanism within the paper substrate is confirmed by spectroscopy. The sensor achieves detection of nucleic acids in 3 min with 2 mu L of solution. Real sample analysis is performed for the quantification of PCR-amplified genes with a limit of detection of 1.38 ng mu L-1. The device serves as a promising point-of-care diagnostics tool for the direct quantification of amplified genetic material.

This study investigates the development of electrochemical genosensors using gold-coated electrospun polymeric fibers electrodes, Au/PMMA/PET and immobilized phosphorothioated oligonucleotides. Scanning electron microscopy (SEM) with energy-dispersive X-rays spectroscopy (EDS) revealed a uniform distribution of oligonucleotides on the fibers, contrary to planar gold electrodes Au/Ti/SiO2/Si, where network-like films were observed. X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of the phosphorothioated oligonucleotides via strong covalent gold-sulfur bonds, while surface plasmon resonance (SPR) indicated superior binding affinity, with significantly lower equilibrium dissociation constants, when compared to unmodified probes. The detection of BCR/ABL fusion gene of chronic myeloid leukemia using differential pulse voltammetry and methylene blue as electroactive indicator, showed that the Au/PMMA/PET electrodes achieved a sensitivity of 379 +/- 12 mu A cm(-)(2) pM(-)(1) and a limit of detection of similar to 5.00 +/- 0.01 fM, outperforming the Au/Ti/SiO2/Si planar electrodes. Reduced non-specific adsorption was observed on the Au/PMMA/PET electrodes and attributed to the inherent charges introduced during the electrospinning process, which created localized electrostatic fields that repelled weakly adsorbing molecules. These findings demonstrate the potential of Au/PMMA/PET electrodes as a robust platform for further development of high-performance clinical diagnostic devices.

Flexible porous materials have gained a high interest due to their impact on the development of electrochemical point-ofcare devices for monitoring the state of health of individuals. Among the porous materials, paper and textiles are most commonly used due to their innate capillary action on fluids. In this article, attention is paid to the retention of analytes in paper and textile porous substrates, and possible procedures to overcome this effect are discussed. The patterning of hydrophilic and hydrophobic regions for sample flow manipulation, and the folding properties of the flexible substrates for 3D architectures capable of transfer of analytes, are considered in relation to current electrode materials and detection methodologies.

A numerical algorithm for interface analysis of wicking drops was developed. The code identifies the interface points and subsequently calculates the diameter, volume and contact angle of the drop. As the code can work with multiple frames, it can evaluate the evolution in time of these parameters and calculate the spreading velocity and the flow rate. The performance of the code was tested with solutions of poly(ethylene oxide) of 0.5% and 5% (w/v) concentration. The mean execution time was 0.5 seconds per frame. Therefore, the code can greatly improve the analysis of fluids wicking in porous media, where numerous frames are involved.

The current increasing interest in portable biosensing platforms led to their development on flexible porous substrates, such as filter paper. As these devices rely on fluid transport under capillary action, without the use of an external force, studies of the diffusion process can provide useful data for optimizing their working capabilities. We present here the results obtained by experimentally studying the radial diffusion of various fluids. The diffusion in filter paper has been recorded for six fluids with different viscosity. For each of them, the displacement of the fluid front has been measured along eight radial directions and then we investigated the possibility of describing this diffusion process using Gillespie's model.

The current increasing interest in portable biosensing platforms led to their development on flexible porous substrates, such as filter paper. As these devices rely on fluid transport under capillary action, without the use of an external force, studies of the diffusion process can provide useful data for optimizing their working capabilities. We present here the results obtained by experimentally studying the radial diffusion of various fluids. The diffusion in filter paper has been recorded for six fluids with different viscosity. For each of them, the displacement of the fluid front has been measured along eight radial directions and then we investigated the possibility of describing this diffusion process using Gillespie's model.