Hamida Hallil

Breast cancer incidence is rising, particularly among younger populations, yet early detection remains a major challenge. Conventional diagnostics, including imaging and biopsies, provide only intermittent information and are limited by cost, invasiveness, and infrastructure requirements. Biosensors offer a promising complementary approach, enabling continuous, minimally invasive monitoring of blood, sweat, breath, or other biofluids. Despite advances in detecting circulating tumor DNA, proteins, RNA, metabolites, and extracellular vesicles, translating these signals into reliable, real-world devices has proven difficult. Could innovative sensor designs, multiplexed detection, or machine learning bridge the gap between laboratory promises and patient-centered monitoring?

MicroRNA-21 (miRNA-21) is a clinically relevant biomarker for cancer, cardiovascular, and inflammatory disorders. Conventional detection methods are laboratory-based, time-consuming, and poorly suited for point-of-care applications. Quartz Crystal Microbalance (QCM) sensors provide label-free, real-time detection, but conventional single-frequency analysis limits sensitivity and underestimates viscoelastic effects. Here, we present a multiharmonic and multivariate QCM framework combined with a gold nanoparticle (AuNP)–assisted sandwich assay to enhance miRNA detection. Frequency, amplitude, and phase features across multiple resonance modes were analyzed using a physics-informed feature selection and optimization strategy to identify the most discriminative parameters. The approach was validated experimentally for miRNA-21. Multivariate multimodal analysis reduced the detection limit from ~10 nM (single-frequency) to 100 pM. AuNP-mediated amplification further increased the effective signal by ~1.5×, yielding a final detection limit of 1 pM, corresponding to a two-order-of-magnitude improvement. Specificity assays with non-target miRNAs (miRNA-145 and miRNA-9) showed minimal cross-reactivity. These results demonstrate that combining multiharmonic signal analysis with nanoparticle-based amplification substantially enhances both sensitivity and selectivity of QCM-based miRNA detection, supporting its potential for sensitive biomarker monitoring in cancer and other pathologies.

Calibration transfer techniques aim to standardize secondary instruments to a primary instrument, enabling the utilization of the primary instrument’s calibration model with minimal additional experiments. While widely employed in spectroscopic datasets, their application in environmental sensors and sensor arrays is less common despite the pressing need due to issues like sensor batch variability and time drift. This study assesses 10 calibration transfer techniques on three experimental gas sensor datasets that have a small number of transfer standards. Model-based (linear regression) and model-free (K-nearest-neighbour) calibration methods are also compared. Results unexpectedly show that, despite the reduced data availability, direct recalibration of the secondary sensor (eg. without transfer) may be sufficient for the secondary sensor to reach the same performance as the primary one. In the other cases, Partial-Least-Square Standardization and Direct Standardization are the most robust transfer methods across the use cases, and they can outperform direct recalibration. Other methods, such as Single Sensor Standardization, Mean Correction, Principal Component Standardization, and Procrustes Transform, have consistently lower performance in this small data context.

In this study, a radio frequency (RF) humidity sensor for monitoring outdoor relative humidity (RH) was developed using polyethyleneimine as sensing material. The sensor’s performance was assessed in laboratory and outdoor conditions. The primary sensor demonstrated an exponential sensitivity in frequency and magnitude, approximately -3.65 MHz/%RH and -7.69 MHz/%RH, -0.051 dB/%RH and -0.12 dB/%RH, across the RH ranges of 30 – 50 %RH and 50 – 70 %RH respectively, with consistent results from 25 °C to 45 °C. The sensor exhibited a response and recovery time of 22 s/44 s, with minimal hysteresis and marginal cross-sensitivity to temperature. Following calibration using different calibration methods (analytical and machine-learning-based techniques), the RH prediction performance was gauged on a separate dataset. The exponential calibration law achieved mean absolute errors (MAE) as low as 0.8 %RH, while other methods like Gaussian Regression Process, k-nearest neighbour (KNN), and generalized linear regression (GLR) resulted in MAE of 0.9 %RH, 1 %RH, and 1.1 %RH. A secondary sensor, also exhibiting exponential sensitivity, underwent initial laboratory testing before transitioning to outdoor conditions. Applying laboratory calibration to outdoor data resulted in a MAE of 4.4%RH, showing remarkable transferability with only 0.8%RH increased MAE. Cross-sensitivity analysis revealed no dependency with temperature, NO ₂ , NO, CO, CO ₂ , and O ₃ in outdoor conditions. Finally, we confirmed the transferability of calibration between the two sensors under laboratory and outdoor conditions, utilizing output standardization with the slope-bias correction algorithm. This research underscores the potential of our RF humidity sensor for accurate outdoor RH monitoring.

Conventional bulk and thin piezoelectric materials based film bulk acoustic resonators (FBARs) are facing an insurmountable challenge for millimetric frequency applications due to the poor piezoelectric properties of the materials when their thickness reaches the sub‐micron regime. Novel FBARs for ultra‐high working frequencies are in urgent demand to meet the requirements of the fast‐growing 5/6G telecommunication techniques. Recent advances in 2D piezoelectric nanomaterials create an opportunity in this perspective. Here, the first FBAR chip based on 2D 3R‐MoS₂ ultrathin piezoelectric flakes with a solidly mounted resonator (SMR) architecture is reported. The typical resonant frequency for an SMR device based on ≈200 nm 3R‐MoS₂ flake reaches over 25 GHz with high reproducibility. Theoretical and finite element analysis suggest that the observed resonance is of longitudinal acoustic modes. This study demonstrates for the first time that the access to 2D piezoelectric nanomaterials makes high performance piezoelectric devices feasible for various promising applications including high‐speed telecommunication, acousto‐optic, and sensor fields,etc.

The past few decades have witnessed the ultra-fast development of wireless telecommunication systems, such as mobile communication, global positioning, and data transmission systems. In these applications, radio frequency (RF) acoustic devices, such as bulk acoustic waves (BAW) and surface acoustic waves (SAW) devices, play an important role. As the integration technology of BAW and SAW devices is becoming more mature day by day, their application in the physical and biochemical sensing and actuating fields has also gradually expanded. This has led to a profusion of associated literature, and this article particularly aims to help young professionals and students obtain a comprehensive overview of such acoustic technologies. In this perspective, we report and discuss the key basic principles of SAW and BAW devices and their typical geometries and electrical characterization methodology. Regarding BAW devices, we give particular attention to film bulk acoustic resonators (FBARs), due to their advantages in terms of high frequency operation and integrability. Examples illustrating their application as RF filters, physical sensors and actuators, and biochemical sensors are presented. We then discuss recent promising studies that pave the way for the exploitation of these elastic wave devices for new applications that fit into current challenges, especially in quantum acoustics (single-electron probe/control and coherent coupling between magnons and phonons) or in other fields.

The rise of gas-sensing applications and markets has led to microwave sensors associated to polymer-based sensitive materials gaining a lot of attention, as they offer the possibility to target a large variety of gases (as polymers can be easily functionalised) at ultra-low power and wirelessly (which is a major concern in the Internet of Things). A two-channel microstrip sensor with one resonator coated with 1,2 epoxybutane-functionalised poly(ethyleneimine) (EB-PEI) and the other left bare was designed and fabricated for humidity sensing. The sensor, characterised under controlled laboratory conditions, showed exponential response to RH between 0 and 100%, which is approximated to −1.88 MHz/RH% (−0.03 dB/RH%) and −8.24 MHz/RH% (−0.171 dB/RH%) in the RH ranges of 30–80% and 80–100%, respectively. This is the first reported use of EB-PEI for humidity sensing, and performances, especially at high humidity level (RH > 80%), as compared with transducer working frequencies, are better than the state of the art. When further tested in real outdoor conditions, the sensor shows satisfying performances, with 4.2 %RH mean absolute error. Most importantly, we demonstrate that the sensor is selective to relative humidity alone, irrespective of the other environmental variables acquired during the campaign (O₃, NO, NO₂, CO, CO₂, and Temperature). The sensitivities obtained outdoors in the ranges of 50–70% and 70–100% RH (−0.61 MHz/%RH and −3.68 MHz/%RH, respectively) were close to lab results (−0.95 MHz/%RH and −3.51 MHz/%RH, respectively).

Distinct from conventional 2H‐MoS₂, recently synthesized 3R‐MoS₂ exhibits a noncentrosymmetric atomic structure of the trigonal “building blocks” and, thus, remarkable piezoelectric characteristics of ultrathin 3R‐MoS₂ flakes are predicated theoretically. This paper reveals, for the first time, very high piezoelectricity in 3R‐MoS₂ flakes experimentally. Through applying mechanical stress to a 48 nm 3R‐MoS₂ flake, a high output power density of 65 mW m^‐2 is obtained and is at least one order larger than those from the corresponding monolayer MoS₂ flake. With out‐of‐plane lateral piezoresponse force microscopy technique, the two piezoelectric coefficients d₃₃ and d₁₃ are analyzed to be ≈0.9 and ≈1.6 pm V^‐1, respectively. These piezoelectric coefficients are not apparently dependent on the flake thickness. The findings suggest that 3R‐MoS₂ is of excellent piezoelectric properties and it can be an excellent material for novel piezoelectric devices.

This paper elaborates on an instrumental scheme for translating electrochemical reactions occurring at an electrode under potentiostatic control into fluorescent signals. We examine the performance enhancement of this device using recently introduced water‐soluble fluorescent reporter systems, either the pH‐sensitive 8‐hydroxypyrene‐1,3,6‐trisulfonic acid (HPTS) system or the electrofluorogenic Amplex Red species. The conversion of stationary and transient, cathodic and anodic electrochemical currents into fluorescence is demonstrated. We show that pure capacitive currents can also be converted to fluorescence by our setup, highlighting the rarely observed coupling between a faradaic reaction at one electrode and capacitive charging at another.