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Nanocubes, nanopores and nanosheets have emerged as captivating entities in the realm of electrochemistry, offering unique properties for diverse applications. This comprehensive review explores recent strides in the applications of these novel nanomaterials. The pursuit of efficient and cost-effective energy storage devices has led to innovations like CuO/ZnO nanocubes, demonstrating enhanced properties for supercapacitors. Additionally, the study delves into the oxygen evolution reaction (OER) catalysts, presenting cost-effective alternatives like Ru-doped CoFeP nanocubes and Mn-containing catalysts with improved performance. Single entity electrochemistry techniques shed light on the intrinsic electrocatalytic activity of Co₃O₄ nanocubes in OER. The electrochemical reduction of carbon dioxide (CO₂RR) showcases the potential of nanocubes, such as In/ZnO@C hollow nanocubes and copper nanocubes, in synthesizing valuable chemicals like formate and ethylene. Furthermore, the exploration extends to the electrocatalytic reduction of nitrate and enantiorecognition, revealing the efficacy of metal-n–nonmetal alloyed mesoporous nanocubes. As nanocubes continue to unveil their potential, their integration into practical applications promises to revolutionize electrochemical technologies, paving the way for a sustainable future.

Nitrosourea (NU) and hydroxyurea (HU) are recognized as chemotherapeutic agents. Their efficiency is restricted by the risk of misuse and the release of trace amounts of un-metabolized chemicals into the environment. Numerous potential negative effects may arise from the use of these drugs. Nanomaterials for drug detection are essential in pharmaceutical research, particularly cancer therapeutic applications such as HU and NU. This study sought to investigate the sensitivity of the C${}_{24}$N${}_{24}$ nanocage in detecting HU and NU via density functional theory (DFT). The interactions between HU/NU drugs and the C${}_{24}$N${}_{24}$ nanocage were investigated using optimized geometries, adsorption energies, FMO, NCI, NBO and QTAIM analyses via DFT and TD-DFT at the B3LYP-D3/6-31G(d,p) theoretical level. The adsorption energy estimations of –24.47 kcal/mol for the NUG complex and –19.90 kcal/mol for the HUB complex indicate that the HU/NU medicines are strongly adsorbed onto the C${}_{24}$N${}_{24}$, and the process is exothermic. NCI and QTAIM analyses have shown noncovalent interactions, primarily van der Waals forces, between C${}_{24}$N${}_{24}$ and HU/NU drugs. When HU/NU interacts with the C${}_{24}$N${}_{24}$ surface, new energy levels are generated in the C${}_{24}$N${}_{24}$ PDOS. Upon evaluating the $E_{\text{g}}$ value, sensitivity and recovery time as parameters of the nanocage’s sensing efficacy, it was determined that the HUB complex exhibits the best conductivity (5.67 × 10${}^{12}$ S/m), fine sensitivity (0.2560) and most stability due to its small energy gap of 1.67 eV value. The complex NUG has the lowest recovery time with a value of 5.15 × 10${}^{-17}$ s. As a result of its recovery time, the C${}_{24}$N${}_{24}$ nanocage is highly desirable for its potential application as an HU/NU drug sensor. This demonstrates that HU/NU drugs can be efficiently identified by the C${}_{24}$N${}_{24}$ nanocage. Our findings indicate that the C24N24 nanocage may enhance drug detection (HU/NU), indicating possible pathways for further advancement.

The size of deterministic automata required for recognizing regular and $\omega$-regular languages is a well-studied measure for the complexity of languages. We introduce and study a new complexity measure, based on the sensing required for recognizing the language. Intuitively, the sensing cost quantifies the detail in which a random input word has to be read in order to decide its membership in the language. We study the sensing cost of regular and $\omega$-regular languages, as well as applications of the study in practice, especially in the monitoring and synthesis of reactive systems.

Terahertz (THz) radiation occupies part of the electromagnetic spectrum between the infrared and microwave bands. Until recently, technology at THz frequencies was under-developed compared to the rest of the electromagnetic spectrum, leaving a gap between millimeter waves and the far-infrared (FIR). In the past decade, interest in the THz gap has been increased by the development of ultrafast laser-based T-ray systems and their demonstration of diffraction-limited spatial resolution, picosecond temporal resolution, DC-THz spectral bandwidth and signal-to-noise ratios above 10⁴.

This chapter reviews the development, the state of the art and the applications of T-ray spectrometers. Continuous-wave (CW) THz-frequency sources and detectors are briefly introduced in comparison to ultrafast pulsed THz systems. An emphasis is placed on experimental applications of T-rays to sensing and imaging, with a view to the continuing advance of technologies and applications in the THz band.

Terahertz (THz) sensing technology enables 6G communication, detection of biological and chemical hazardous agents, cancer detection, monitoring of industrial processes and products, and detection of mines and explosives. THz sensors support security in buildings, airports, and other public spaces. They found important applications in radioastronomy and space research and, more recently, in Artificial Intelligence-driven THz sensing of MMICs and VLSI. Exploding demand for data transfers will require using the 300 GHz band after 2028 or even before and will make the deployment of THz sensing electronics inevitable. This paper discusses the new physics of THz sensing and THz sensing devices. It also reviews the THz sensing market, and key THz sensor companies.

The latest addition to the nanocarbon family, graphene, has been proclaimed to be the material of the century. Its peculiar band structure, extraordinary thermal and electronic conductance and room temperature quantum Hall effect have all been used for various applications in diverse fields ranging from catalysis to electronics. The difficulty to synthesize graphene in bulk quantities was a limiting factor of it being utilized in several fields. Advent of chemical processes and self-assembly approaches for the synthesis of graphene analogues have opened-up new avenues for graphene based materials. The high surface area and rich abundance of functional groups present make chemically synthesized graphene (generally known as graphene oxide (GO) and reduced graphene oxide (RGO) or chemically converted graphene) an attracting candidate in biotechnology and environmental remediation. By functionalizing graphene with specific molecules, the properties of graphene can be tuned to suite applications such as sensing, drug delivery or cellular imaging. Graphene with its high surface area can act as a good adsorbent for pollutant removal. Graphene either alone or in combination with other materials can be used for the degradation or removal of a large variety of contaminants through several methods. In this review some of the relevant efforts undertaken to utilize graphene in biology, sensing and water purification are described. Most recent efforts have been given precedence over older works, although certain specific important examples of the past are also mentioned.

The VO₂ thin film has the advantage of thermally controlled insulator-metal phase transition. Based on this, we presented a thermally reconfigurable metamaterial with switchable wideband absorption and sensing at THz band in this paper. At low temperature (${\sigma }_{{\mathrm{\text{VO}}}_2}=20$S/m), the metamaterial can realize nearly perfect absorption at the range of 6.88–9THz. When the temperature rises to a certain extent (${\sigma }_{{\mathrm{\text{VO}}}_2}=2\times 10^5$S/m), an absorption peak which can be used to sensing appears at 4.08THz with the permittivity sensitivity of 0.5THz/PU. The metamaterial has the advantages of simple structure and switchable wideband absorption/sensing functions with potential application value on terahertz stealth, detection, sensing, and so on.

Pulsed laser-assisted etching is a simple but effective method for fabricating small regular structures directly onto a surface. We have successfully fabricated submicro- or nano-meter sized spikes on a solid surface immersed in liquids with femtosecond laser pulse irradiations. This method is applicable to different metals such as stainless steel, copper, titanium, cobalt, as well as different semiconductors, such as Si and GaAs. The femtosecond laser method is much faster than other methods. We can control the experimental conditions to design and fabricate nanostructures in different materials and on the surfaces with different morphologies. Here, we discuss the nanostructures formation with femtosecond pulse laser irradiations, and introduce our results of the nanostructure for applications in sensing, biology and artificial photosynthesis. The femtosecond laser irradiation technique can efficiently integrate metal, semiconductor and polymer nanostructures in various small devices to leverage the expertise in other research fields and applications.

In this paper, a plasmonic analogue of electromagnetically induced transparency (EIT) is demonstrated theoretically in a T-shaped silver nanohole array. A sharply narrow reflectance transparency window is clearly observed within the background spectrum of the broad dipole-like resonance at optical frequencies when structural asymmetry is introduced. Furthermore, the transparency peak exhibits highly sensitive response to the refractive index of surrounding medium and yield a sensitivity of 725 nm/refractive index unit (RIU), which ensures our proposed nanohole array as an excellent plasmonic sensor. In addition, the dependence of figure of merit (FOM) on structural asymmetry is investigated numerically to optimize the sensing performance of the EIT-based sensor.

We investigated a reversibly-propagational metamaterial perfect absorber (MPA) for X band using two separated identically-patterned copper layers, which were deposited on continuous dielectric FR-4 layers. By adjusting oblique incidence, two separated resonances are excited, then come close to each other and is finally merged to be a perfect absorption peak at 10.1 GHz. The nature of resonance is the quadrupole mode instead of the fundamental resonances in common MPAs. The mechanism of perfect absorption is the coupling of two quadrupole resonances at their superposition, leading to an enhancement of energy absorption. Finally, we numerically presented the capability of sensing thin resonant substance using the proposed MPA. The characteristic resonance of substance, which does not appear on the absorption spectrum at the limited thickness of bare substance layer, is detected with a great magnitude of signal by exploiting the absorption resonance of MPA. Our work provides another way to obtain the reversibly-propagational absorption by controlling the incident angle instead of the geometrical structure, and might be useful for the potential devices based on MPA such as detectors and sensors.

It is well known that Fano effect usually requires the introduction of asymmetric (or breaking) in their structure designs. The smaller the degree of breaking, the more obvious the Fano effect. However, the small degree of breaking demands extremely precise manufacturing capabilities and levels. This paper proposes a novel robust metallic array structure that can achieve a Fano-like effect with a high $Q$-factor as 73, consisting of a square patch and a closed-ring resonator. This distinct Fano-like resonance originates from the interactions of quadrupole resonance mode and dipole resonance mode. Moreover, the effect of the size and conductivity of the square patch on the Fano effect are discussed, and the sensing performance of this structure is also discussed. These results will pave the way for designing practical sensors and optical switches in the terahertz frequency range.

We present an algorithm for a single pursuer with one flashlight searching for an unpredictable, moving target in a 2D environment. The algorithm decides whether a simple polygon with n edges and m concave regions can be cleared by the pursuer, and if so, constructs a search schedule of length O(m) in time O(m²+mlogn+n). The key ideas in this algorithm include a representation called "visibility obstruction diagram" and its "skeleton": a combinatorial decomposition based on a number of critical visibility events. An implementation is presented along with a computed example.

We present an algorithm for a pair of pursuers, each with one flashlight, searching for an unpredictable, moving target in a 2D environment (simple polygon). Given a polygon with n edges and m concave regions, the algorithm decides in time O(n² + nm² + m⁴) whether the polygon can be cleared by the two 1-searchers, and if so, constructs a search schedule. The pursuers are allowed to move on the boundary and in the interior of the polygon. They are not required to maintain mutual visibility throughout the pursuit.

The problem of recovering the initial temperature of a body from discrete temperature measurements made at later times is studied. While this problem has a general formulation, the results of this paper are only given in the simplest setting of a finite (one-dimensional), constant coefficient, linear rod. It is shown that with a judicious placement of a thermometer on this rod, the initial temperature profile of the rod can be completely determined by later time measurements. The paper then studies the number of measurements that are needed to recover the initial profile to a prescribed accuracy and provides an optimal reconstruction algorithm under the assumption that the initial profile is in a Sobolev class.

Bifurcation morphing created by means of nonlinear feedback excitation is a vibration-based method for sensing. In this work, several new studies are presented to connect previously demonstrated theory to increasingly more practical applications. In particular, in the process of designing nonlinear feedback auxiliary signals, time delays in the circuitry are unavoidable. Advantages as well as possible side effects and disadvantages of time delays are discussed. Furthermore, additional time delay is considered as a new design parameter. Increasing the time delay has advantages such as enhanced robustness and sensitivity, which are demonstrated computationally. Moreover, calibration using multiple sensor locations is discussed. A clamped-free cantilever beam structure is modeled and used for computational validation. The beam model resembles cantilever-based resonant sensor systems. Thus, potential applications of the new algorithm are discussed and the results stress the importance of nonlinear features for enhancing sensing performance in mechanical sensors without structural modifications.

There are many schemes to increase energy efficiency in wireless sensor network as energy is a precious resource. We focus on improving energy efficiency in sensing module while most of the previous works focus on the energy saving in communication module. When a sensor network continuously senses wide area, energy consumption is needed largely in the sensing module. We consider a change rate of sensed data and adjust sensing period to reduce energy consumption while minimizing average delay between change of field and detection. Additionally, cooperation among neighbor nodes is essential to reduce energy consumption and the delay. Our dynamic sensing algorithm reduces the energy consumption and delay between change of field and detection. Our scheme controls sensing cycle based on change of sensing data and information of neighbor nodes such as sensing cycle and number of cooperative nodes. It improves energy efficiency up to 90% comparing with the static sensing method, and reduces the delay up to 84% comparing to the previous works.

This report describes the selective fluorometric detection of pyrophosphate in water with a simple Al${}^{\text{III}}$-salen complex. The Al-based probe is synthesized in two steps in 30% yield and disassembled in the presence of pyrophosphate into its molecular building blocks. The released 3-chlorosalicylaldehyde signaling unit leads to a detectable signal with a 29-fold increase in fluorescence (${\lambda }_{\text{em}}$ = 513 nm; ${\lambda }_{\text{ex}}$ = 388 nm). At this emission wavelength, we did not observe a response from the Al${}^{\text{III}}$-salen probe despite its intrinsic blue fluorescence (${\lambda }_{\text{em}}$ = 460 nm;${\lambda }_{\text{ex}}$ = 347 nm). The Al${}^{\text{III}}$-complex shows excellent discrimination of pyrophosphate over other ions including phosphate containing adenosine triphosphate, phytic acid, or glyphosate and only fluoride inhibits the pyrophosphate-triggered disassembly process. Related salen-based probes with the same hydrophobic ligand framework but either Zn${}^{\text{II}}$ or Fe${}^{\text{III}}$ ions instead of Al${}^{\text{III}}$ were not sufficiently robust and therefore not suitable for analytical applications in pure water at pH 7.4.

In this work, water-soluble and blue-emitting carbon nanodots (CDs) were synthesized from apple peels for the first time via one-step hydrothermal method. The synthetic route is facile, green, economical and viable. The as-prepared CDs were characterized thoroughly by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, Fourier transform infrared (FT-IR), X-ray photoelectron (XPS), fluorescence and UV–Vis absorption spectroscopy in terms of their morphology, surface functional groups and optical properties. The results show that these CDs possessed ultrasmall size, good dispersivity, and high tolerance to pH, ionic strength and continuous UV irradiation. Significantly, the CDs had fast and reversible response towards temperature, and the accurate linear relationship between fluorescence intensity and temperature was used to design a novel nanothermometer in a broad temperature range from 5 to 65${}^{\circ }$C facilely. In addition, the fluorescence intensity of CDs was observed to be quenched immediately by Cr(VI) ions based on the inner filter effect. A low-cost Cr(VI) ions sensor was proposed employing CDs as fluorescent probe, and it displayed a wide linear range from 0.5 to 200$\mu$M with a detection limit of 0.73$\mu$M. The practicability of the developed Cr(VI) sensor for real water sample assay was also validated with satisfactory recoveries.

Cantilever-based piezoelectric has been the most preferred technique for energy harvesting and sensing application due to its simple design. The energy conversion efficiency has been continuously improved by exploring alternative cantilever geometries by increasing the stress distribution on the beam surface. In this paper, we have introduced half elliptical and full elliptical profile modification in the cantilever structure to improve and uniformly distribute the stress at the beam surface. Stress distribution characteristics of the modified cantilever beams were investigated and compared using finite element analysis. Based on the theoretical and finite element analysis, cantilever beams were fabricated using 3D print technology. Fabricated cantilever beams were then used to investigate the piezoelectric performances of polyvinylidene fluoride (PVDF) in composite of barium titanate (BaTiO₃) nanoparticles in the form of electrospun composite nanofibers. FTIR analysis shows successful conversion of alpha phase to beta phase of PVDF and PVDF/BaTiO₃ nanocomposites. During 6Hz cyclic actuating experiment, maximum voltage output of 0.15V and 1.5nA current output were observed. The concept was proposed to replace MEMS-based sensor in hand tremor quantification to assist Parkinson disease management.

We present theoretical modeling of the local surface plasmon resonance (LSPR) induced by hollow nanoshell spheres assisted with a graphene shell, aiming to examine their potential for use as efficient narrowband absorbers in the infrared wavelength region. We investigate two designs of hollow nanoparticles; namely, a hollow graphene nanosphere with a single graphene shell, and a hollow nanosphere with double shells comprising a graphene shell wrapped around a silver shell. The electric field in each region of the nanoshell is determined by solving the Laplace equation of the potential within the electrostatic approximation (the nanoshell radius $<$50nm). Using the calculated polarizability of nanoshells, we derive analytical expressions for the absorption and scattering cross-sections. We show that in both proposed nanocomposite models, the graphene shell affords an ultra-narrow LSPR with an absorption efficiency significantly higher than the scattering efficiency. In addition, the graphene-assisted LSPR can be tuned through the visible and infrared regions by changing the Fermi energy and thickness of the graphene layer. Another exciting finding is that the use of a silver shell in the hollow bi-shell nanoparticles provides another LSPR peak besides that induced by the graphene shell. Both LSPRs of graphene and silver shells can be overlapped by changing the optical properties of graphene and/or the geometrical parameters of the silver shell. The resulting LSPR is characterized by a dominant absorption cross-section and a significant narrowband. In both proposed nanoshell designs, the properties of LSPRs are promising for use in various optical imaging and phototherapy applications.