arXiv subjects

Joaquim B. S. Mendes

Publications and source records attributed to Joaquim B. S. Mendes.

7 recordsLinked to original sources

arXiv2026

PEDOT:PSS-Coated Magnetoelastic Sensors for Highly Sensitive Wireless Humidity Sensing

Magnetoelastic (ME) resonators provide an attractive platform for passive and wireless sensing, particularly for monitoring relative humidity (RH) in sealed or hard-to-access environments. In this work, we introduce ME humidity sensors functionalized with poly(3,4-ethylenedioxythiophene) sulfonate (PEDOT), marking the first application of this conductive polymer in ME-based humidity sensing. PEDOT films were deposited onto Metglas resonators via a simple drop-casting process, producing uniform and mechanically stable coatings. Comprehensive structural and morphological characterization by SEM, EDX, Raman spectroscopy, AFM/KPFM, and XRD confirmed the structural integrity of the polymer and revealed humidity-induced swelling of the PSS-rich domains, accompanied by enhanced polymer-chain mobility and an increase in the lamellar spacing from 23.5 Å to 24.2 Å at 95% RH. These structural changes directly affected the dynamic response of the resonators, leading to a systematic resonance-frequency downshift driven by the combined effects of water adsorption, mass loading, and viscoelastic damping. The optimized device achieved a sensitivity of 155 Hz/% RH in the 20 - 70% RH range, outperforming previously reported ME humidity sensors, while exhibiting a resolution better than 0.1% RH together with excellent response and recovery times. These results establish PEDOT as a highly effective functional coating for magnetoelastic humidity sensors and demonstrate a simple, low-cost, wireless sensing platform with high sensitivity and strong potential for practical environmental and industrial monitoring applications.

cond-mat.mtrl-sci↗

arXiv2025

Graphene-based magnetoelastic biosensor for COVID-19 serodiagnosis

This work presents an innovative magnetoelastic (ME) biosensor using graphene functionalized with the SARS-CoV-2 N protein for antibody detection via magnetoelastic resonance. Graphene was chosen for its biocompatibility and high surface area, enabling efficient antigen adsorption, validated by techniques such as energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and micro-Raman spectroscopy. Changes in Raman bands (a $\sim 10~\mathrm{cm}^{-1}$ shift in the 2D band and an increase in the $I_D/I_G$ ratio from 0.03 to 0.60) confirmed non-covalent interactions and enhanced surface coverage with ~100 $μ$g of N protein. Tests using human plasma (10 RT-PCR-positive and 10 negative samples) demonstrated a clear distinction between groups using graphene sensors functionalized with ~100 $μ$g of N protein. Enzyme-linked immunosorbent assay (ELISA) validation corroborated the results. Optimization of protein concentration and biofunctionalization time highlighted the importance of homogeneous surface coverage for reproducibility of the graphene-based ME biosensor. The platform combines graphene's advantages with the wireless, real-time detection capabilities of ME sensors, offering low cost, high sensitivity, and potential for automation, with applications in point-of-care diagnostics.

physics.bio-ph↗

arXiv2024

Development of an integrated device based on the gain/phase detector and Arduino platform for measuring magnetoelastic resonance

This study presents the development of an integrated device for measuring magnetoelastic resonance, utilizing a gain/phase detector and the Arduino platform. The device stands out for its simplicity, low cost, and efficiency. It employs the Arduino's ATmega328P microcontroller, coupled with the AD8302, and an intuitive graphical interface developed in Python, which facilitates the measurement of magnetoelastic signals in sensors. The device's validation is carried out through measurements of mass deposits on magnetoelastic sensors, confirming its accuracy and functionality. This advancement offers a practical and portable solution for detecting magnetoelastic resonances, promoting the use of these technologies in field environments and in diverse scientific applications. The integration of components into a compact, robust, and low-cost electronic circuit, along with an easy-to-operate graphical interface, significantly simplifies the complexity of the components, making the equipment complete and readily operational.

physics.ins-det↗

arXiv2024

A biosensor based on magnetoelastic waves for detection of antibodies in human plasma for COVID-19 serodiagnosis

The study proposes a new efficient wireless biosensor based on magnetoelastic waves for the detection of antibodies in human plasma, aiming at the serological diagnosis of COVID-19. The biosensor was functionalized with the N antigen - nucleocapsid phosphoprotein of the SARS-CoV-2 virus. Validation analyses, by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, atomic force microscopy (AFM), scanning electron microscopy (SEM), micro-Raman spectroscopy, confirmed the selectivity and effective surface functionalization of the biosensor. The research successfully obtained, expressed and purified the recombinant antigen, while plasma samples from COVID-19 positive and negative patients were used to test the performance of the biosensor. A comparison of performance with the ELISA method revealed equivalent diagnostic power. These results indicate the robustness of the biosensor in reliably differentiating between positive and negative samples, highlighting its potential as an efficient and low-cost tool for the serological diagnosis of COVID-19. In addition to being fast to execute and having the potential for automation in large-scale diagnostic studies, the biosensor fills a significant gap in existing SARS-CoV-2 detection approaches.

physics.bio-ph↗

arXiv2024

Unraveling the Spin-to-Charge Current Conversion Mechanism and Charge Transfer Dynamics at Interface of Graphene/WS$_2$ Heterostructures at Room Temperature

We report experimental investigations of spin-to-charge current conversion and charge transfer dynamics (CT) at the interface of graphene/WS$_2$ van der Waals heterostructure. Pure spin current was produced by the spin precession in the microwave-driven ferromagnetic resonance of a permalloy film (Py-Ni$_{81}$Fe$_{19}$) and injected into the graphene/WS$_2$ heterostructure through the spin pumping process. The observed spin-to-charge current conversion in the heterostructure is attributed to inverse Rashba-Edelstein effect (IREE) at the graphene/WS$_2$ interface. Interfacial CT dynamics in this heterostructure was investigated based on the framework of core-hole-clock (CHC) approach. The results obtained from spin pumping and CHC studies show that the spin-to-charge current conversion and charge transfer process are more efficient in the graphene/WS$_2$ heterostructure compared to isolated WS2 and graphene films. The results show that the presence of WS$_2$ flakes improves the current conversion efficiency. These experimental results are corroborated by density functional theory (DFT) calculations, which reveal (i) Rashba spin-orbit splitting of graphene orbitals and (ii) electronic coupling between graphene and WS$_2$ orbitals. This study provides valuable insights for optimizing the design and performance of spintronic devices.

cond-mat.mes-hall↗

arXiv2024

Bulk and Interface Effects Based on Rashba-Like States in Ti and Ru Nanoscale-Thick Films: Implications for Orbital-Charge Conversion in Spintronic Devices

In this work, employing spin-pumping techniques driven by both ferromagnetic resonance (SP-FMR) and longitudinal spin Seebeck effect (LSSE) to manipulate and direct observe orbital currents, we investigated the volume conversion of spin-orbital currents into charge-current in YIG(100nm)/Pt(2nm)/NM2 structures, where NM2 represents Ti or Ru. While the YIG/Ti bilayer displayed a negligible SP-FMR signal, the YIG/Pt/Ti structure exhibited a significantly stronger signal attributed to the orbital Hall effect of Ti. Substituting the Ti layer with Ru revealed a similar phenomenon, wherein the effect is ascribed to the combined action of both spin and orbital Hall effects. Furthermore, we measured the SP-FMR signal in the YIG/Pt(2)/Ru(6)/Ti(6) and YIG/Pt(2)/Ti(6)/Ru(6) heterostructures by just altering the stack order of Ti and Ru layers, where the peak value of the spin pumping signal is larger for the first sample. To verify the influence on the oxidation of Ti and Ru films, we studied a series of thin films subjected to controlled and natural oxidation. As Cu and CuOx is a system that is already known to be highly influenced by oxidation, this metal was chosen to carry out this study. We investigated these samples using SP-FMR in YIG/Pt(2)/CuOx(tCu) and X-ray absorption spectroscopy and concluded that samples with natural oxidation of Cu exhibit more significant results than those when the CuOx is obtained by reactive sputtering. In particular, samples where the Cu layer is naturally oxidized exhibit a Cu2O-rich phase. Our findings help to elucidate the mechanisms underlying the inverse orbital Hall and inverse orbital Rashba-Edelstein-like effects. These insights indeed contribute to the advancement of devices that rely on orbital-charge conversion.

cond-mat.mtrl-sci↗

arXiv2023

On the use of organic semiconductors as handles for optical tweezers experiments: trapping and manipulating polyaniline (PANI) microparticles

Here we propose the use of the organic semiconductor polyaniline (PANI) for the preparation of spherical-shaped microparticles to serve as handles in optical tweezers (OT) experiments. The stable trapping and manipulation of PANI beads was demonstrated for the first time, using a Gaussian ($TEM_{00}$) beam optical tweezers. The trap stiffness was characterized for various different parameters such as the bead radius, the laser power and the distance between the bead and the coverslip of the sample chamber, attesting the viability of using such material for optical manipulation. Since the effective optical properties of PANI can be modulated by the synthesis process, new related applications are also proposed. The results of the present work therefore open the door for using semiconductor polymeric materials in OT applications.

physics.optics↗