The need for an accurate, rapid and affordable method for the determination of nitrite ions is due to its toxic effects on humans at elevated levels in wastewater and drinking water. The electrochemical determination is faster, cheaper and less labor intensive. It is based on the study of the electrochemical oxidation NO₂^- ion at different carbon electrodes. In this work, it was established by the cyclic voltammograms for the ISEM-3 graphite electrode has excellent limit of detection to nitrite ions: 5 × 10⁻⁶ М at pH 3, which makes it possible to determine the NO₂⁻ content below the maximum permissible concentration (6.5 × 10⁻⁵ M) in water.

A novel highly sensitive voltammetric sensor based on a glassy carbon electrode (GCE) modified with a mixture of cerium and tin dioxide nanoparticles (NPs) as a sensing layer was developed. Surfactants of various nature (anionic sodium dodecyl sulfate, cationic N-cetylpyridinium bromide, and non-ionic Triton X-100, Brij^® 35, and Tween-80) were used as dispersive agents for NPs. Complete suppression and a significant decrease in the dye oxidation peak occurred in the case of Tween-80 and sodium dodecyl sulfate, respectively. CeO₂–SnO₂ NPs in Brij^® 35 gave the best response to Acid Yellow 3 caused by its adsorption at the electrode surface. Linear dynamic ranges of 0.50–7.5 and 7.5–25 mg L⁻¹ with a detection limit of 0.13 mg L⁻¹ of Acid Yellow 3 were achieved using differential pulse mode in Britton-Robinson buffer pH 5.0.

Microdevices with dimensions comparable to a blood cell, i.e., tens of micrometers, show
great potential for use in the human body. They can be adopted to identify the source
of diseases, track their evolution and enhance the effectiveness of therapies, significantly
improving patients’ quality of life. A key challenge is how to power the devices, which
should ideally be obtained wireless from a remote source. Piezoelectric micromachined
ultrasonic transducers (pMUTs) offer a solution thanks to their ability to generate and
collect energy via acoustic waves. In this work, numerical simulations of transmitter pMUT
arrays are performed with the aim of generating an acoustic wave synchronized with a
single pMUT or pMUT array receiver. The latter is intended for insertion in the human body.
The characteristics required to switch on and power nano-electronics, in terms of generated
voltage and electrical power at the receiver, are studied in ballistic gel, a material that mimics
human organs. Focus is on a bio-compatible material for the piezoelectric layer, aluminum
nitride enriched with scandium. Coupled electromechanical and acoustic simulations
show that, of the considered pMUT devices, an 8 X 8 transmitter array combined with a
single-device receiver (with a 50 μm pitch) or a 2 X 2 receiver array provide alternative
options, with each offering advantages in terms of voltage amplitude or power at steady
state. The overall dimension of the receiver, at maximum only 100 X 100 μm2, is compatible
with a future proof-of-concept biosensing platform test chip.

Optical fiber sensors are recognized as a promising technology for detecting parameters such as temperature, biomolecules, and chemical substances. Among these, multimode interference (MMI) sensors stand out for their high sensitivity, ease of fabrication, and low cost. This work presents the design and analysis of an interferometric sensor based on a single-mode–multimode–single-mode (SMS) structure, in which the multimode section consists of a coreless fiber whose diameter was reduced from 125 µm to 20 µm. Numerical simulations using FIMMWAVE software were performed for external refractive indices (RI) between 1.33 and 1.43, evaluating sensitivity in two spectral ranges (600–800 nm and 900–1100 nm) and achieving a maximum value of 918.21 nm/RIU for the smallest diameter. The influence of the MMF length on resonance peak position and spectral selectivity was also studied. Experimental validation was carried out with a 125 µm coreless MMF of ≈15 mm length, using solutions of different refractive indices. The experimental results confirmed the sensor’s effective RI response and demonstrated the feasibility of the proposed configuration as a basis for developing low-cost, high-precision optical biosensors.

Bloch-like surface waves (BLSWs) are electromagnetic waves generated at the interface between a dielectric medium and a photonic crystal. BLSWs has significant potential for sensing applications, since their electromagnetic fields are tightly confined near the interface, reaching comparable sensitivities to those of surface plasmon polariton (SPP)-based devices, but with higher figures of merit (FOM). This work explores a sensor based on BLSW at the interface formed by a TiO2 thin film deposited on the flat surface of a laterally polished photonic crystal fiber (PCF). The performance of the sensor is studied when the TiO2 film is partially removed, transforming the nanolayer into a nanostrip. The results of this study contribute to the optimization of the sensing performance of the proposed structure.

Two positively charged amphiphilic benzothiadiazoles (2–3), functionalized with 2,3-dimethylbenzo[d]thiazol-3-ium and 2,3-dimethylnaphtho[2,1-d]thiazol-3-ium acceptor moieties, synthesized earlier in our research group, from 7-(4-methoxyphenyl)benzo[c][1,2,5]thiadiazole-4-carbaldehyde (1), were evaluated concerning their optical chemosensory capabilities towards different anions in DMSO and in a DMSO/water (75:25). Spectrophotometric and spectrofluorimetric titrations were performed demonstrating that both compounds were highly sensitive to cyanide in DMSO. Compound 2 showed fluorescence quenching at 657 nm with 5 equivalents of CN⁻, while compound 3 displayed a decrease in absorption at 480 nm and emission at 666 nm with 7 equivalents of CN⁻ in DMSO solution. Nevertheless, in DMSO/water mixture, the sensitivity decreased, requiring 50–70 equivalents of cyanide for fluorescence quenching.

Herein we first attempt to compare catalytic and electrocatalytic properties of the most commonly used peroxidase mimicking nanozymes based on transition metal ions, including magnetite, cerium oxide, and Prussian Blue. For the nanomaterials under consideration, the catalytic rate constant for reducing substrate increases upon decreasing its redox potential and reaches the ultimate values for Prussian Blue in the presence of ferrocyanide (k_cat = 3.8 s⁻¹ per single redox-active site). In addition to the highest k_cat, Prussian Blue nanoparticles in electrochemical sensors exhibit sensitivity to H₂O₂ by more than 3 orders of magnitude higher than other nanomaterials. Sensing properties of the electrodes modified with Prussian Blue nanoparticles appear to be dependent on their diameter; particles with diameter of 140 nm provide optimal sensitivity and lifespan of the corresponding sensor. The achieved exceptional (electro)catalytic properties of Prussian Blue nanoparticles open the prospects for their application as universal labels for personal analyzers with either optical or electrochemical readout.

This study investigates the influence of morphology on the photocatalytic and gas-sensing properties of copper oxide (CuO) nanomaterials, comparing spherical nanoparticles (NPs) and nanowhiskers (NWs). CuO NWs were synthesized via thermal oxidation of electrodeposited copper, exhibiting a polycrystalline structure with an average diameter of 68 nm, while NPs were obtained by ball-milling NWs, resulting in spherical particles (220 nm). Photocatalytic tests using methylene blue degradation under UV and visible light revealed that NWs exhibited superior. Kinetic analysis indicated pseudo-first-order behavior under visible light, while UV-driven reactions deviated due to surface-limited processes. In gas-sensing experiments, CuO NPs demonstrated higher sensitivity to acetone than NWs.

This paper presents a checkerboard-patterned terahertz (THz) metamaterial absorber en-gineered for wideband dual-band absorption. The absorber consists of a gold metal layer patterned on a polyimide substrate, forming a unit cell structure with dimensions of 85 µm × 85 µm. At the core of the design is a square metal patch of 67 µm × 67 µm, which is di-vided into a 5 × 5 grid of 25 smaller cells. An integer-coded Particle Swarm Optimization (PSO) algorithm is employed to generate the pattern, where an input value of ‘1’ retains the metal in a cell, and a ‘0’ results in the removal of metal from that cell, resulting in a digi-tally optimized checkerboard pattern. The substrate height is also optimized and fixed at 7 µm to enhance resonance characteristics. The PSO algorithm is run for 50 iterations, with the fitness function defined as the number of frequency points at which the absorption ex-ceeds 90%. The finalized design achieves two distinct absorption peaks with high effi-ciency: 99.53% at 3.434 THz with a 90% absorption bandwidth of 212 GHz and 99.35% at 3.823 THz with a bandwidth of 177 GHz. While the absorption performance is already significant, it can be further improved by increasing the number of PSO iterations, albeit at the cost of higher computational complexity. The proposed absorber demonstrates strong potential for biomedical sensing, as validated through its ability to differentiate between cancerous and non-cancerous breast and blood cells. This work paves the way for fully automated, algorithm-driven metamaterial design strategies in the THz regime, particu-larly for applications in non-invasive biomedical diagnostics.

Magnetic Resonance Relaxometry is a powerful technique which reveals a sample’s mo-lecular dynamics thanks to the dependence of the T1 relaxation time on field strength. With applications in protein research, food systems, materials development and environ-mental science, relaxometry measurements are typically undertaken using a technique known as fast field cycling where T1 is measured a given detection field, but the sample experiences relaxation in a variable field without the challenges associated with retuning a probe to each of the necessary frequencies of interest. This technique is limited by a maximum relaxation time since the measurement and relaxation fields are typically ap-plied using a fluid cooled electromagnet which ultimately will overheat for very long ex-perimental times. In this work we propose an alternative approach to permit measure-ments of samples with inherently long T1. We utilise a broadband spectrometer alongside a solenoid transmit-receive coil and custom tuning and matching boards whilst two sets of magnets are moved around the coil to achieve a range of different fields. By collecting a reduced number of points and utilising this method, we show it is still possible to make useful measurements on samples at a range of frequencies which has great potential in quality assurance applications. We find a similar trend for food samples of corn oil while Manganese Chloride, a common contrast agent, has a more than 100% difference when compared to traditional fast field cycling measurements.