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This work illustrates the viability of optics ideas using a machine learning (ML) technique to choose the optimal SPR sensor for a particular set of structural parameters. Particle swarm optimization (PSO) algorithm is utilized in conjunction with an ML model to design a tunable surface plasmonic resonance (SPR) sensor. A trained ML model is applied to the PSO algorithm to develop the SPR sensor with the desired sensing performance. Using a learned ML model to forecast sensor performance rather than sophisticated electromagnetic calculation techniques allows the PSO algorithm to optimize solutions four orders of magnitude faster. This composite algorithm's implementation enabled us to rapidly and precisely create an SPR sensor with a sensitivity of 68.754 ᵒ/RIU and having an impressive figure of merit of 100. We anticipate that this effective and precise method will pave the way for the future development of plasmonic devices.

Graphene monolayer of sub-nanometer thickness shows strong metallic and plasmonic behavior in terahertz (THz) frequency range. This plasmonic effect varies considerably when graphene layer is placed under a magnetic field of appropriate strength. The strong adsorption characteristic of graphene layer is another advantage. In this work, a photonic spin Hall effect (PSHE)-based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz aiming at highly sensitive and reliable sensing under variable magnetic field. Modified Otto configuration and magneto-optic effect in graphene are considered. The sensor’s performance is examined in terms of sensitivity, limit of detection (LOD), and figure of merit (FOM). The analysis indicates that LOD of the order of 10−5 RIU for gas sensing is achievable, which is finer than recently reported gas sensors based on different techniques. Further, the FOM improves when a larger magnitude of magnetic field is applied. The FOM is even greater for rarer gaseous media, which can make the sensor extremely useful in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture. The results further indicate that the same sensor design can be used for magnetic field detection while the FOM of magnetic field detection is significantly greater for rarer gaseous medium (e.g., air), which may enable the probe to be used in early detection of radiation leakage in nuclear reactors. For larger magnitudes of magnetic field, the corresponding LOD becomes finer.

This paper deals with turning in different lubrication environment to study the effect of machining parameters on force, surface roughness and power. Turning operation is carried on AISI 1040 steel using carbide insert. Coconut oil is used as cutting fluid and applied to the cutting zone using minimum quantity lubrication. The design of experiment is done with the help of L9 orthogonal array whereas Taguchi’s experimental design and AHP-WASPAS is used to optimize the process parameters. The experimental results signify that machining with the use of coconut oil through MQL showed the reduction in forces is approximately 15.95% in surface roughness 13.92% and in case power it was 13.7% respectively.

We present herein the solvent and substituent dependent diverse spin crossover behaviours of molecular bis-(thiocyanato)iron(ii) complexes with smartly designed bidentate Schiff bases above room temperature.

In this work, we analyze the design of a graphene- and germanium-based plasmonic sensor with photonic spin Hall effect (PSHE) for detection of refractive index (RI) of a gas medium and magnetic field (B) applied to the graphene monolayer in THz frequency region. The PSHE phenomenon is studied in both conventional as well as modified weak measurements. The effect of gaseous medium thickness (d

Hallmarks of aging-associated osteoporosis include bone loss, bone marrow adipose tissue (BMAT) expansion, and impaired osteoblast function. Endogenous glucocorticoid levels increase with age, and elevated glucocorticoid signaling, associated with chronic stress and dysregulated metabolism, can have a deleterious effect on bone mass. Canonical glucocorticoid signaling through the glucocorticoid receptor (GR) was recently investigated as a mediator of osteoporosis during the stress of chronic caloric restriction. To address the role of the GR in an aging-associated osteoporotic phenotype, the current study utilized female GR conditional knockout (GR-CKO; GRfl/fl :Osx-Cre+) mice and control littermates on the C57BL/6 background aged to 21 months and studied in comparison to young (3- and 6-month-old) mice. GR deficiency in Osx-expressing cells led to low bone mass and BMAT accumulation that persisted with aging. Surprisingly, however, GR-CKO mice also exhibited alterations in muscle mass (reduced % lean mass and soleus fiber size), accompanied by reduced voluntary physical activity, and also exhibited higher whole-body metabolic rate and elevated blood pressure. Moreover, increased lipid storage was observed in GR-CKO osteoblastic cultures in a glucocorticoid-dependent fashion despite genetic deletion of the GR, and could be reversed via pharmacological inhibition of the mineralocorticoid receptor (MR). These findings provide evidence of a role for the GR (and possibly the MR) in facilitating healthy bone maintenance with aging in females. The effects of GR-deficient bone on whole-body physiology also demonstrate the importance of bone as an endocrine organ and suggest evidence for compensatory mechanisms that facilitate glucocorticoid signaling in the absence of osteoblastic GR function; these represent new avenues of research that may improve understanding of glucocorticoid signaling in bone toward the development of novel osteogenic agents. © 2021 American Society for Bone and Mineral Research (ASBMR).

In this work, we propose and analyze a plasmonic sensor with a three-layer waveguide structure. We consider the transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) in the waveguide at a given wavelength (1557 nm) for a TM (transverse magnetic or p-polarized) mode. The sensor structure is analyzed in two ways. First, under the normal methods, that is, angular and intensity interrogation methods, for which the results indicate that the maximum figure of merit (FOM) of 4007.0 RIU−1 is attained for an optimum thickness ( $d_{2}=51$ nm) of the gold layer and this FOM is significantly greater than the corresponding FOM (413.7 RIU−1) reported earlier (for a 50 nm thick gold layer). Also, the average sensitivity increases from 0.0005 to 0.002°/Oe when the volume fraction of Fe3O4 particles ( $c$ ) in the magnetic fluid is increased from 1.48% to 1.93%. Correspondingly, a considerably finer value of the resolution (0.046 Oe) is obtained when the volume fraction is increased to 1.93% (compared to 0.199 Oe at 1.48%). Second way is the proposed method of PSHE, for which the analysis indicates that transverse SDS of the horizontal PSHE is the maximum for $d_{2} = 51$ nm leads to the maximum sensitivity $6.25 \times 10^{7}~\mu$ m/RIU for an amplified angle $\Delta = 0.1^{\circ}$ and $1.09 \times 10^{6}~\mu$ m/RIU for $\Delta = 0.1$ rad in the conventional weak measurements. The corresponding finest possible resolution of magnetic field detection at 1.93% is $1.5 \times 10^{-6}$ Oe in the conventional weak measurements for $\Delta = 0.1^{\circ}$ and $7.8 \times 10^{-8}$ Oe in the modified weak measurements for $\Delta = 0.5$ rad, which are significantly finer than those existing in the related state of the art. The above resolution is also superior to those found under normal methods mentioned earlier. Furthermore, the effect of temperature (24.3 °C–60 °C) on PSHE-based magnetic field sensor’s performance is also analyzed which indicates that the proposed PSHE-based magnetic field sensor should be operated in a thermally controlled milieu.

This report describes the synthesis of two ruthenium(II) ENE pincer complexes (E = S, C1 and E = Se, C2) by the reaction of bis(2-(phenylchalcogenyl)ethyl)amine (L1, L2) with RuCl

Grating nanostructures play a crucial role for their application in plasmonic sensors. A comprehensive review on grating nanostructure based plasmonic sensor is presented in this article. The structural developments and sensing performance enhancements in last two decades are focused upon. Surface plasmon resonance (SPR) and localized SPR (LSPR) sensors have gained much popularity and are still flourishing due to advancements in nanofabrication technology. Refractive index change and field enhancement are the two phenomena that are responsible for qualitative and quantitative detection and analysis of a variety of samples. The future scenario and possibilities regarding the advancements in grating plasmonic sensors have also been discussed.

At present, the nanostructures consisting of tungsten metal are hardly explored for surface plasmon resonance–based applications in sensing and other photonic devices. In this view, a plasmonic nanostructure consisting of stacked tungsten gratings on aluminum nitride substrate with nickel interlayer is proposed and simulated for refractive index (RI) sensing in the visible and near infrared spectral regions. Rigorous coupled wave analysis (RCWA) with p-polarized light source is used for simulation and analysis. The sodium chloride (NaCl) concentration in water and gaseous medium is considered analyte. The performance of proposed plasmonic sensor is demonstrated in terms of sensitivity, resolution, and figure-of-merit values. In addition, a detailed analysis is also performed to study the effect of grating variable values on the sensor’s performance. The angle of light incidence emerges as an important parameter in significantly enhancing the sensor’s performance as well as in tuning the sensor’s applicability as per available light source. Further, it is shown that the same probe can be applied as a gas sensor with high sensitivity and accuracy. Moreover, the prominent absorbance characteristics of the proposed nanostructure leads to possible applications in spectral filtering as well as photodetection in both visible and NIR spectral regions. Owing to the advanced properties of tungsten, the proposed structure will be beneficial for bio- and gas-sensing applications along with other photonic devices operable in a wide spectral range.

Alzheimer's disease (AD) is the most common neurodegenerative disorder, yet the cause and progression of this disorder are not completely understood. While the main hallmark of AD is the deposition of amyloid plaques consisting of the β-amyloid (Aβ) peptide, transition metal ions are also known to play a significant role in disease pathology by expediting the formation of neurotoxic soluble β-amyloid (Aβ) oligomers, reactive oxygen species (ROS), and oxidative stress. Thus, bifunctional metal chelators that can control these deleterious properties are highly desirable. Herein, we show that amentoflavone (AMF), a natural biflavonoid compound, exhibits good metal-chelating properties, especially for chelating Cu2+ with very high affinity (pCu7.4 = 10.44). In addition, AMF binds to Aβ fibrils with a high affinity (Ki = 287 ± 20 nM), as revealed by a competition thioflavin T (ThT) assay, and specifically labels the amyloid plaques ex vivo in the brain sections of transgenic AD mice, as confirmed via immunostaining with an Aβ antibody. The effect of AMF on Aβ42 aggregation and disaggregation of Aβ42 fibrils was also investigated and revealed that AMF can control the formation of neurotoxic soluble Aβ42 oligomers, both in the absence and presence of metal ions, as confirmed via cell toxicity studies. Furthermore, an ascorbate consumption assay shows that AMF exhibits potent antioxidant properties and can chelate Cu2+ and significantly diminish the Cu2+-ascorbate redox cycling and reactive oxygen species (ROS) formation. Overall, these studies strongly suggest that AMF acts as a bifunctional chelator that can interact with various Aβ aggregates and reduce their neurotoxicity and can also bind Cu2+ and mediate its deleterious redox properties. Thus AMF has the potential to be a lead compound for further therapeutic agent development for AD.

The synthesis, detailed characterization, and investigation of the DNA- and BSA-binding affinity and cytotoxicity of three half-sandwich Ru(II) arene chlorido complexes (1–3) are reported. Specifically, organometallic complexes [(η6-p-cymene)(L1)RuCl]Cl (1), [(η6-p-cymene)(L2)RuCl]Cl (2) and [(η6-p-cymene)(L3)RuCl]Cl (3) [L1 = 2-(1H-benzo[d]imidazol-2-yl)quinolone, L2 = 2-(quinolin-2-yl)benzo[d]oxazole, and L3 = 2-(quinolin-2-yl)benzo[d]thiazole] were synthesized using [((η6-p-cymene)Ru(μ-Cl)Cl)2] and L1–L3. All the complexes were characterized by various spectroscopic and analytical methods. Complex 1 was also characterized by single crystal X-ray diffraction analysis, the results of which are in-line with the piano-stool structure elucidated from the spectroscopic methods. Cyclic voltammetry of 1–3 showed good stability of the Ru(II) state. The interactions of 1–3 with CT-DNA were investigated by UV-Vis studies and competitive binding with ethidium bromide (EthBr) using emission spectroscopy. Steady-state fluorescence quenching and synchronous fluorescence studies were performed to understand the interactions between 1–3 and bovine serum albumin (BSA). The geometry optimization of 1–3 was performed using the density functional theory (DFT). Complexes 1 and 2 were investigated for DNA binding using theoretical calculations. Molecule complexes 1-DNA and 2-DNA were huge (482–483 atoms, 2442 electrons) for any level of quantum chemical analysis. The semi-empirical PM6 method, which is more accurate than the force-field methods, was used, and the result suggested that several strong and weak electrostatic and intermolecular hydrogen bonding interactions exist between the outer edge of DNA and complexes 1 and 2. In addition, the in vitro cytotoxicity of L1–L3 and complexes 1–3 against a breast cancer cell line (MCF-7) was investigated by MTT cytotoxicity analyses. The studies performed here show that these complexes exhibit a good binding behavior with DNA and BSA and show good anticancer potency towards MCF-7 cells.

Research continues to find a breakthrough for the treatment of Alzheimer's Disease (AD) due to its complicated pathology. Presented herein is a novel series of arydiazoquinoline molecules investigated for their multifunctional properties against the factors contributing to Alzheimer's disease (AD). The inhibitory properties of fourteen closely related aryldiazoquinoline derivatives have been evaluated for their inhibitory effect on Aβ42 peptide aggregation. Most of these molecules inhibited Aβ42 fibrillation by 50–80%. Selected molecules were also investigated for their binding behaviour to preformed Aβ40 aggregates indicating a nanomolar affinity. In addition, these compounds were further investigated as cholinesterase inhibitors. Interestingly, some of the compounds turned out to be moderate in vitro inhibitors for AChE activity with IC50 values in low micro molar range. The highest anti-AChE activity was shown by compound labelled as 2a with an IC50 value of 6.2 μM followed by 2b with IC50 value of 7.0 μM. In order to understand the inhibitory effect, binding of selected molecules to AChE enzyme was studied using molecular docking. In addition, cell toxicity studies using Neuro2a cells were performed to assess their effect on neuronal cell viability which suggests that these molecules possess a non-toxic molecular framework. Overall, the study identifies a family of molecules that show good in vitro anti-Aβ-aggregation properties and moderately inhibit cholinesterase activity.

In the current study, four novel mononuclear Cu(ii) complexes with terpyridine (L) and different co-ligands (phen, bipy, and imd) were synthesized and characterized in detail, where L is 4'-(3,4,5-trimethoxyphenyl)-2,2':6',2''-terpyridine. The identity and purity of all complexes were determined by elemental analysis, spectroscopic techniques (UV-vis, FTIR, ESI-MS, and EPR) and CV, including single crystal X-ray determination of three complexes ([Cu(L)(phen)](ClO4)2 (C-I), [Cu(L)2](ClO4)2 (C-II) and [Cu(L)(imd)(ClO4)](ClO4) (C-IV). DNA binding studies were performed using fluorescence assay and the binding constants were calculated using the Stern-Volmer equation and the modified Stern-Volmer equation. The magnitude of Kapp of all complexes was 105 M-1, indicating moderate intercalative binding between CT-DNA and the complexes. Agarose gel electrophoresis clearly reflected their ability to cleave a double stranded pET-28b plasmid in the presence of an external reducing agent (3-mercapto propionic acid). Steady-state fluorescence quenching was performed to understand their interactions with BSA. The studies suggested a mixed quenching mechanism with an initial static process. Furthermore, the antiproliferative activity of the complexes was evaluated against lung cancer A549 cells and primary mice splenocytes. Interestingly, the complexes show 25-200 fold greater toxicity towards the A549 cells than primary splenocytes, indicating their selectivity towards the former. The good binding behavior of all four complexes towards DNA and BSA and their cytotoxicity render these compounds promising potent anticancer drugs.

We present a high-throughput optogenetic illumination system capable of simultaneous closed-loop light delivery to specified targets in populations of moving Caenorhabditis elegans. The instrument addresses three technical challenges: It delivers targeted illumination to specified regions of the animal’s body such as its head or tail; it automatically delivers stimuli triggered upon the animal’s behavior; and it achieves high throughput by targeting many animals simultaneously. The instrument was used to optogenetically probe the animal’s behavioral response to competing mechanosensory stimuli in the the anterior and posterior gentle touch receptor neurons. Responses to more than 43,418 stimulus events from a range of anterior–posterior intensity combinations were measured. The animal’s probability of sprinting forward in response to a mechanosensory stimulus depended on both the anterior and posterior stimulation intensity, while the probability of reversing depended primarily on the anterior stimulation intensity. We also probed the animal’s response to mechanosensory stimulation during the onset of turning, a relatively rare behavioral event, by delivering stimuli automatically when the animal began to turn. Using this closed-loop approach, over 9,700 stimulus events were delivered during turning onset at a rate of 9.2 events per worm hour, a greater than 25-fold increase in throughput compared to previous investigations. These measurements validate with greater statistical power previous findings that turning acts to gate mechanosensory evoked reversals. Compared to previous approaches, the current system offers targeted optogenetic stimulation to specific body regions or behaviors with many fold increases in throughput to better constrain quantitative models of sensorimotor processing.

In this study, a highly angular sensitive surface plasmon resonance (SPR) biosensor has been designed for cancer cell detection. The proposed surface plasmon resonance biosensor structure is based on Kretschmann configuration, which works on an angular interrogation technique. The proposed SPR biosensor has enormous possibility to detect the various kind of cancer cells. The refractive index alteration of different cancerous (skin, cervical and blood) cells is 1.360–1.390. The proposed SPR biosensor is stacked with multilayers having CaF2 prism, silver metal, bismuth telluride (Bi2Te3) and MXene (Ti3C2Tx) layers. The performance parameters like angular sensitivity, quality factor, detection accuracy, and electric field intensity distribution have been optimized in this article. Here, various kind of cancer cells (skin, cervical and blood) have been also analyzed and corresponding angular sensitives are 252.20, 305.70 and 319.46 deg R−1IU−1 respectively. The proposed SPR biosensor shows best results for blood cancer cell detection. Some other important performance parameters like detection accuracy, quality factor, and electric field intensity distribution have also been calculated for proposed SPR biosensor device. The simulation results have been performed by MATLAB 2019a software. The proposed SPR biosensor design may open a new way for the medical industry.

Graphene monolayer of sub-nanometer thickness possesses strong metallic and plasmonic behavior in a broad terahertz (THz) frequency range. This plasmonic effect can be considerably manipulated when graphene layer is subjected to a variable chemical potential (EThe online version contains supplementary material available at 10.1007/s11082-022-03626-7.

The enormous use of cutting fluid in machining leads to an increase in machining costs, along with different health hazards. Cutting fluid can be used efficiently using the MQL (minimum quantity lubrication) method, which aids in improving the machining performance. This paper contains multiple responses, namely, force, surface roughness, and temperature, so there arises a need for a multicriteria optimization technique. Therefore, in this paper, multiobjective optimization based on ratio analysis (MOORA), VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and technique for order of preference by similarity to ideal solution (TOPSIS) are used to solve different multiobjective problems, and response surface methodology is also used for optimization and to validate the results obtained by multicriterion decision-making technique (MCDM) techniques. The design of the experiment is based on the Box–Behnken technique, which used four input parameters: feed rate, depth of cut, cutting speed, and nanofluid concentration, respectively. The experiments were performed on AISI 304 steel in turning with minimum quantity lubrication (MQL) and found that the use of hybrid nanofluid (Alumina–Graphene) reduces response parameters by approximately 13% in forces, 31% in surface roughness, and 14% in temperature, as compared to Alumina nanofluid. The response parameters are analyzed using analysis of variance (ANOVA), where the depth of cut and feed rate showed a major impact on response parameters. After using all three MCDM techniques, it was found that, at fixed weight factor with each MCDM technique, a similar process parameter was achieved (velocity of 90 m/min, feed of 0.08 mm/min, depth of cut of 0.6 mm, and nanoparticle concentration of 1.5%, respectively) for optimum response. The above stated multicriterion techniques employed in this work aid decision makers in selecting optimum parameters depending upon the desired targets. Thus, this work is a novel approach to studying the effectiveness of hybrid nanofluids in the machining of AISI 304 steel using MCDM techniques.

The machining process is widely used to manufacture various machine elements for its innumerable application in manufacturing industry. The cutting fluid imparts an essential duty to the machining processes as a coolant and lubricant. With the advancement and innovations in the machining processes, the cutting fluid is under progression, and many novel cutting fluids are developed in last two decades. In recent years, the metal-oxide and non-metal-oxide particle-based nanofluids have drawn attention of the researchers due to their enhanced thermophysical and tribological properties and capabilities as efficient coolant and lubricants. This article reviews the work on potential use of the metal-oxide-based nanofluids for sustainable machining processes reported in the scientific literature over years.

The activity of an animal’s brain contains information about that animal’s actions and movements. We investigated the neural representation of locomotion in the nematode C. elegans by recording population calcium activity during unrestrained movement. We report that a neural population more accurately decodes locomotion than any single neuron. Relevant signals are distributed across neurons with diverse tunings to locomotion. Two distinct subpopulations are informative for decoding velocity and body curvature, and different neurons’ activities contribute features relevant for different instances of behavioral motifs. We labeled neurons AVAL and AVAR and found their activity was highly correlated with one another. They exhibited expected transients during backward locomotion, although they were not always the most informative neurons for decoding velocity. Finally, we compared population neural activity during movement and immobilization. Immobilization alters the correlation structure of neural activity and its dynamics. Some neurons previously correlated with AVA become anti-correlated and vice versa.The activity of an animal’s brain contains information about that animal’s actions and movements. We investigated the neural representation of locomotion in the nematode C. elegans by recording brain-wide neural dynamics in freely moving animals. We report that a population of neurons more accurately decodes the animal’s locomotion than any single neuron. Neural signals are distributed across neurons in the population with a diversity of tuning to locomotion. Two distinct subpopulations are most informative for decoding velocity and body curvature, and different neurons’ activities contribute features relevant for different instances of behavioral motifs within these subpopulations. We additionally labeled the AVA neurons within our population recordings. AVAL and AVAR exhibit activity that is highly correlated with one another, and they exhibit the expected responses to locomotion, although we find that AVA is not always the most informative neuron for decoding velocity. Finally, we compared brain-wide neural activity during movement and immobilization and observe that immobilization alters the correlation structure of neural activity and its dynamics. Some neurons that were previously correlated with AVA become anti-correlated and vice versa during immobilization. We conclude that neural population codes are important for understanding neural dynamics of behavior in moving animals.

The development of adiposity in the bone marrow, known as marrow adipose tissue (MAT), is often associated with musculoskeletal frailty. Glucocorticoids, which are a key component of the biological response to stress, affect both bone and MAT. These molecules signal through receptors such as the glucocorticoid receptor (GR), but the role of the GR in regulation of MAT is not yet clear from previous studies. The purpose of this review is to establish and determine the role of GR-mediated signaling in marrow adiposity by comparing and contrasting what is known against other energy-storing tissues like adipose tissue, liver, and muscle, to provide better insight into the regulation of MAT during times of metabolic stress (e.g., dietary challenges, aging). GR-mediated glucocorticoid signaling is critical for proper storage and utilization of lipids in cells such as adipocytes and hepatocytes and proteolysis in muscle, impacting whole-body composition, energy utilization, and homeostasis through a complex network of tissue cross talk between these systems. Loss of GR signaling in bone promotes increased MAT and decreased bone mass. GR-mediated signaling in the liver, adipose tissue, and muscle is critical for whole-body energy and metabolic homeostasis, and both similarities and differences in GR-mediated GC signaling in MAT as compared with these tissues are readily apparent. It is clear that GC-induced pathways work together through these tissues to affect systemic biology, and understanding the role of bone in these patterns of tissue cross talk may lead to a better understanding of MAT-bone biology that improves treatment strategies for frailty-associated diseases.

Surface plasmon resonance-based fiber optic sensor with multilayer heterojunction is simulated and analyzed. The constituent materials are ZBLAN fluoride core, NaF clad, amorphous Si layer, Ag layer, Al2O3 interlayer, and graphene monolayer. The main idea behind the study is to optimize the radiative damping ( i.e. , optimum radiative damping, ORD) at the Ag–Al2O3–graphene heterojunction in order to enhance the sensor's figure of merit (FOM) as much as possible. The effect of graphene monolayer's presence on sensor's FOM is also examined. Multiple occurrences of ORD may be achieved by coordinated variation of Ag and Al2O3 layer thicknesses along with light wavelength. Among the several prominent ORD conditions, the combination of 45.3-nm-thick Ag layer, 11-nm-thick Al2O3 layer, and 938.7-nm wavelength leads to a massively large FOM of 31806.65 RIU–1. The above FOM of the FOSPR sensor is nearly six times that for the corresponding prism-based SPR sensor ( i.e. , 5500 RIU–1) reported earlier with Al2O3 interlayer and MoS2 monolayer at λ = 1200 nm. Further, the proposed sensor provides substantially greater FOM compared to existing prism-based and FOSPR sensors.

The performance of multiple variants of fluoride fiber plasmonic sensor is simulated and analyzed under optimum radiation damping (ORD) in terms of coordinated tuning of Ag layer thickness ( $\text{d}_{\mathbf {Ag}}$ ) and near infrared (NIR) wavelength ( $\lambda $ ). The sensor variants are in terms of number of monolayers (N: 1 – 5) of graphene and MoS2. The dispersion relations of all constituent layers along with the transfer matrix method are utilized for sensor simulation. The sensor’s performance is evaluated in terms of figure of merit (FOM) that takes into account the shift and width of fiber power loss resonance curves originating under the plasmonic modulation. Further totality is added to performance evaluation by combining the FOM with signal scattering and power loss ratio factors. The simulation results and their comprehensive analysis indicate that a combination of $\lambda =925.3$ nm, $\text{d}_{\mathbf {Ag}} =48.4$ nm, and MoS2 monolayer can provide considerably enhanced performance in terms of maximum FOM, small light signal scattering (and analyte photodamage), and large power loss ratio (with respect to the reference resonance curve). The FOM achievable with this sensor is 4.5 times better than the previously reported chalcogenide fiber plasmonic sensor under its corresponding ORD. A deeper analysis of the proposed fluoride sensor predicts that even smaller signal scattering (and photodamage) along with nearly identical power loss ratio and FOM can be achieved with the sensor variant based on MoS2 bilayer.

This paper presents a sharp review of the current state-of-the-art related to the fiber optic sensors with (i) gratings (namely, fiber Bragg gratings, i.e., FBG and long period fiber gratings, i.e., LPG) and (ii) plasmonic nanostructures (metallic/non-metallic gratings, corrugations, and arrays). The objective of this review is to highlight the importance of these areas in terms of their high sensing performance and the great potential they possess for developing plasmonics-based fiber optic chemical and biosensors with even higher levels of performance in the future. In line with the above objectives, the selected salient works are revisited while beginning with the earliest works on general fiber SPR sensors as well as both the above-mentioned areas. In this process, the review makes a thoughtful attempt to spot the possible future scope and emergent themes in these research areas. The review will be able to provide adequate directives to the researchers willing to take up these areas as their future endeavors.

Evanescent wave (EW) based fiber optic sensor is simulated and analyzed aiming at highly sensitive and precise detection of cancerous human liver tissues in near infrared (NIR). Various parameters such as combinations of fiber core (fluoride glass) and clad (fluoride and silica-based) materials, 2D materials (graphene and MoS 2 ), absorptive amorphous silicon layer with different thicknesses, change of reference analyte, and variation in clad thickness are explored. Spectral interrogation method is utilized and the sensor’s performance is evaluated in terms of sensitivity and resolution. The analysis indicates that for detection of malignant (HCC) liver tissue, the 5-layer sensor design, i.e. , ZBLA fluoride glass core – 19.3% GeO 2 doped silica clad (10 nm) – MoS 2 monolayer (0.71 nm) – amorphous silicon layer (10 nm) – analyte (H 2 O as reference) leads to the maximum possible sensitivity of 234.2 mW/RIU (real index) and 1228.8 mW/RIU (imaginary index), and resolution of the order of 10 −10 RIU (real index) and 10 −11 RIU (imaginary index) at 0.954 µm wavelength. The proposed sensor has the capability of providing significantly finer resolution than previously reported fiber sensors based on various techniques (such as SPR, LMR, etc. ).

The dynamic nature of radiation damping is exploited in a fluoride fiber–based plasmonic sensor in terms of variable temperature (T) and Ag layer thickness (dm) at certain near-infrared wavelengths. The optimum point of radiation damping, which is stimulated by the presence of a graphene monolayer and its dynamic dispersive and thermo-optic properties as per Kubo formulation, causes extremely huge enhancement in sensor’s performance (analyzed in terms of its figure of merit, i.e., FOM). The simulation indicates that at λ = 1550 nm, the optimum radiation damping is achieved at dm = 35 nm and T = 322.7 K leading to a peak FOM value of 27,086 RIU−1. At λ = 1310 nm, the peak FOM is 16,736.65 RIU−1 for dm = 35.4 nm and T = 315.6 K. The above peak FOM values are significantly greater than those presently available with plasmonic sensors.

Grating coupled nanostructures are integral part of advanced plasmonic sensors for bio-sensing applications. In this work, gold gratings on dielectric substrate (e.g., GaN, AlN, and Si3N4) based plasmonic sensor is simulated and analyzed in optical communication band for refractive index sensing with spectral interrogation. The sensor simulation is carried out with rigorous coupled wave analysis (RCWA). The influence of grating variables on resonance behavior and sensing performance of the grating structure is also studied. A significantly large sensitivity of 1140 nm/RIU is achieved with a very high precision (in terms of as small curve width as 4.20 nm). The results indicate that Au grating on GaN substrate can provide a high sensing performance for a broad range of analyte refractive indices. The sensor provides comparatively better performance than the existing grating based plasmonic sensors. The possibility of self-referenced sensing is also explored.

The dynamic nature of radiation damping in plasmonic structures can have immense potential in relation to significant improvement in plasmonic sensor performance. In this paper, we have explored the careful tuning of dynamic radiation damping in Si-Ag-graphene-Al2O3 heterojunction-based fiber optic plasmonic sensor structure. Low-refractive index rare-earth doped chalcogenide glass is considered as fiber material in near infrared spectral region. The simultaneous tuning of Ag and Al2O3 layer thicknesses with wavelength in appropriate broad ranges is investigated to enhance the sensor’s performance as much as possible. As another interesting step, the presence/absence of graphene layer on sensor’s performance is also examined. The results indicate that significantly large figure of merit (FOM) of magnitude 19212.67 RIU $^{-1}$ at $\lambda = 969$ nm for 5.2-nm-thick Al2O3 layer, and 36.6-nm-thick Ag layer is achievable from the proposed sensor with graphene. The above FOM is substantially larger than the existing (reported) plasmonic sensors claiming large FOM values. The findings of this paper can be crucial for developing surface plasmon reasonance biosensors with highly enhanced performance.

Dicationic cobalt(II) complexes of the type [Co(fterpy)2]c(X)2·nH2O·mCH3OH (fterpy = 4′-(2-furyl)-2,2′:6′,2″-terpyridine; 1: X = PF6−, n = 1.5, m = 0; 2: X = ClO4−, n = 1, m = 1) have been isolated using self-assembly method and characterized by various spectroscopic techniques. In crystalline states both compounds exhibit gradual and incomplete spin crossover (SCO) behaviour in the temperature range 2–320 K. Various spin states of cobalt(II) in 1 have been confirmed by crystallographic evidences at 150 K and 293 K. A variation in counter anions and solvent molecules from 1 to 2 substantially improves the cooperativity among the spin active metal centres and thereby changing the nature of SCO behaviour.

The present work reports the synthesis, spectroscopic and structural characterizations of Fe(III) complexes of types [Fe(L)(H2O)(NCS)] (1), [Fe(L)(1-methylimidazole)2]ClO4 (2) and [(L)Fe(μ-O)Fe(L)]·3H2O·MeOH (3) containing a known planar N2O2-donor salphen Schiff base, H2L (N,N′-bis(3-methoxysalicylidene)phenylene-1,2-diamine). In mononuclear complexes 1 and 2, iron(III) centre adopts a distorted octahedral geometry where planar N2O2-donor L2− ligand forms equatorial plane and varied co-ligands (aqua and thiocyanate in 1 and 1-methylimidazole in 2) occupy the axial sites. The μ-oxo-bridged dinuclear complex 3 is a new solvatomorph of [(μ-O)(Fe(vanophen))2]·2H2O [vanophen = N,N′-bis(3-methoxysalicylidene)phenylene-1,2-diamine] reported by Jana et al. where a marked difference in Fe–O–Fe bond angle is noticed. The electrochemical behaviours of H2L and complexes 1–3 have been examined to ascertain the nature of electron transfer processes. The binding interactions of 1–3 with ct-DNA as well as with Bovine serum albumin (BSA) have been investigated using fluorescence spectroscopy in T10E1 buffer (pH = 7.8). All the complexes show good binding propensity with ct-DNA probably via partial intercalation mode. Furthermore, the complexes quench the intrinsic fluorescence of BSA by a static quenching mechanism.