Uniform Synthesis of Bilayer Hydrogen Substituted Graphdiyne for Flexible Piezoresistive Applications.

Graphdiyne (GDY) has garnered significant attention as a cutting-edge 2D material owing to its distinctive electronic, optoelectronic, and mechanical properties, including high mobility, direct bandgap, and remarkable flexibility. One of the key challenges hindering the implementation of this material in flexible applications is its large area and uniform synthesis. The facile growth of centimeter-scale bilayer hydrogen substituted graphdiyne (Bi-HsGDY) on germanium (Ge) substrate is achieved using a low-temperature chemical vapor deposition (CVD) method. This material's field effect transistors (FET) showcase a high carrier mobility of 52.6 cm2 V-1 s-1 and an exceptionally low contact resistance of 10 Ω µm. By transferring the as-grown Bi-HsGDY onto a flexible substrate, a long-distance piezoresistive strain sensor is demonstrated, which exhibits a remarkable gauge factor of 43.34 with a fast response time of ≈275 ms. As a proof of concept, communication by means of Morse code is implemented using a Bi-HsGDY strain sensor. It is believed that these results are anticipated to open new horizons in realizing Bi-HsGDY for innovative flexible device applications.

All-optical modulation by continuous wave light using two-color excited-state absorption at visible wavelengths.

We demonstrated all-optical modulation with a nonlinear medium, i.e., indigo carmine, an aromatic conjugated structure with delocalized π-electrons, using non-high power continuous wave light for pump and probe of different visible wavelengths. Pump-induced probe transmission increase occurred through absorption saturation of probe light by pump-induced linear and nonlinear absorption including two-color excited-state absorption (ESA). The two-color ESA occurred only when both pump light and probe light co-propagated through a medium, leading to nearly pump power-independent increase in probe transmission for appropriately chosen wavelengths of pump and probe light, given the optical transition structure of electronic energy levels in the medium.

Ultrasensitive Monitoring of Cyanide Concentrations in Water Using a Aucore-Agshell Hybrid-Coating-Based Fiber Optical Sensor.

Cyanides, which are extremely toxic chemicals that are rapidly absorbed into the human body and interact with cytochrome oxidase, strongly inhibit cellular respiration to body death with convulsions. Cyanide ions that exist in many forms in nature such as those found in apricot kernels, cassava roots, and bamboo shoots as cyanogenic glycosides are inevitably used in various industries, including gold and silver mining as well as in dyes and plastic industries. In this study, for the sake of developing ultrahigh-sensitive sensors for cyanide monitoring in a simple manner, we chemically synthesize Aucore-Agshell hybrid nanomaterials of different core/shell thicknesses for colorimetric sensors and fiber optical sensors. Their sensing principle relies on the formation of the Ag/Au cyanocomplex upon cyanide injection. The generated metal cyanocomplex induced changes in refractive indices, causing changes in properties of localized surface plasmon resonance (LSPR), i.e., optical absorbance change for the colorimetric sensors. For fiber optical sensors, the hybrid metal nanoparticles were immobilized on the fiber core surface and the metal cyanocomplex formation induced changes in the fiber cladding refractive index, enabling quantitative cyanide detection with ultrahigh sensitivity. The LSPR-based colorimetric sensor provided the lowest detectable cyanide concentration of 5 × 10-6 M, whereas the value for the fiber-based sensor was 8 × 10-11 M.

Reproducible Enhancement of Fluorescence by Bimetal Mediated Surface Plasmon Coupled Emission for Highly Sensitive Quantitative Diagnosis of Double-Stranded DNA.

Plasmonic enhancement of fluorescence from SYBR Green I conjugated with a double-stranded DNA (dsDNA) amplicon is demonstrated on polymerase chain reaction (PCR) products. Theoretical computation leads to use of the bimetallic (Au 2 nm-Ag 50 nm) surface plasmons due to larger local fields (higher quality factors) than monometallic (Ag or Au) ones at both dye excitation and emission wavelengths simultaneously, optimizing fluorescence enhancement with surface plasmon coupled emission (SPCE). Two kinds of reverse Kretschmann configurations are used, which favor, in signal-to-noise ratio, a fluorescence assay that uses optically dense buffer such as blood plasma. The fluorescence enhancement (12.9 fold at maximum) with remarkably high reproducibility (coefficient of variation (CV) < 1%) is experimentally demonstrated. This facilitates credible quantitation of enhanced fluorescence, however unlikely to obtain by localized surface plasmons. The plasmon-induced optical gain of 46 dB due to SPCE-active dye molecules is also estimated. The fluorescence enhancement technologies with PCR enables LOD of the dsDNA template concentration of ≈400 fg µL-1 (CV < 1%), the lowest ever reported in DNA fluorescence assay to date. SPCE also reduces photobleaching significantly. These technologies can be extended for a highly reproducible and sufficiently sensitive fluorescence assay with small volumes of analytes in multiplexed diagnostics.

Diffraction effects incorporated design of a parallax barrier for a high-density multi-view autostereoscopic 3D display.

We present optical characteristics of view image provided by a high-density multi-view autostereoscopic 3D display (HD-MVA3D) with a parallax barrier (PB). Diffraction effects that become of great importance in such a display system that uses a PB, are considered in an one-dimensional model of the 3D display, in which the numerical simulation of light from display panel pixels through PB slits to viewing zone is performed. The simulation results are then compared to the corresponding experimental measurements with discussion. We demonstrate that, as a main parameter for view image quality evaluation, the Fresnel number can be used to determine the PB slit aperture for the best performance of the display system. It is revealed that a set of the display parameters, which gives the Fresnel number of ∼ 0.7 offers maximized brightness of the view images while that corresponding to the Fresnel number of 0.4 ∼ 0.5 offers minimized image crosstalk. The compromise between the brightness and crosstalk enables optimization of the relative magnitude of the brightness to the crosstalk and lead to the choice of display parameter set for the HD-MVA3D with a PB, which satisfies the condition where the Fresnel number lies between 0.4 and 0.7.

Parallax barrier engineering for image quality improvement in an autostereoscopic 3D display.

We present a image quality improvement in a parallax barrier (PB)-based multiview autostereoscopic 3D display system under a real-time tracking of positions of a viewer's eyes. The system presented exploits a parallax barrier engineered to offer significantly improved quality of three-dimensional images for a moving viewer without an eyewear under the dynamic eye tracking. The improved image quality includes enhanced uniformity of image brightness, reduced point crosstalk, and no pseudoscopic effects. We control the relative ratio between two parameters i.e., a pixel size and the aperture of a parallax barrier slit to improve uniformity of image brightness at a viewing zone. The eye tracking that monitors positions of a viewer's eyes enables pixel data control software to turn on only pixels for view images near the viewer's eyes (the other pixels turned off), thus reducing point crosstalk. The eye tracking combined software provides right images for the respective eyes, therefore producing no pseudoscopic effects at its zone boundaries. The viewing zone can be spanned over area larger than the central viewing zone offered by a conventional PB-based multiview autostereoscopic 3D display (no eye tracking). Our 3D display system also provides multiviews for motion parallax under eye tracking. More importantly, we demonstrate substantial reduction of point crosstalk of images at the viewing zone, its level being comparable to that of a commercialized eyewear-assisted 3D display system. The multiview autostereoscopic 3D display presented can greatly resolve the point crosstalk problem, which is one of the critical factors that make it difficult for previous technologies for a multiview autostereoscopic 3D display to replace an eyewear-assisted counterpart.

Bimetal coated optical fiber sensors based on surface plasmon resonance induced change in birefringence and intensity.

We present a surface plasmon resonance (SPR) based multimode fiber sensor with non-golden bimetallic coating. Our detection scheme used, which is capable of measuring the combined effects of SPR-induced birefringence and intensity changes, supported the minimum resolvable refractive index (RI) of 5.8 × 10(-6) RIU with the operating RI range of 0.05 to be experimentally obtained at a single wavelength (632.8 nm) without non-spectroscopic techniques. The asymmetric profile of the thickness of the bimetal coating on the fiber core together with the inherent range of incidence angle for multimode propagation also contributed to the wide operating range. The SPR fiber device with the detection scheme demonstrated will be likely to be developed as a real-time label-free and highly sensitive diagnostic device of a wide operating range for biomedical and biochemical applications in a portable format.

Determination of the optimum viewing distance for a multi-view auto-stereoscopic 3D display.

We present methodologies for determining the optimum viewing distance (OVD) for a multi-view auto-stereoscopic 3D display system with a parallax barrier. The OVD can be efficiently determined as the viewing distance where statistical deviation of centers of quasi-linear distributions of illuminance at central viewing zones is minimized using local areas of a display panel. This method can offer reduced computation time because it does not use the entire area of the display panel during a simulation, but still secures considerable accuracy. The method is verified in experiments, showing its applicability for efficient optical characterization.

Anomalous spectral shift of localized surface plasmon resonance.

We report the first observation of spectral blue shift of plasmon resonance of synthesized silver nanoparticles (AgNPs) due to a negative optical nonlinearity of a local ambient medium, i.e., indigo carmine (IC) solution at around 420 nm wavelength. The blue shift occurred at a larger concentration of AgNPs or at a larger concentration of IC solution, being in obvious contrast to spectral red shift which was widely witnessed in plasmon spectral shift in a linear regime. Plasmon-enhanced local fields could excite the third-order optical nonlinearity for blue shift even under continuous (non-pulsed) light illumination. We also found that the plasmon-excited nonlinearity could allow for differential nonlinear response of the IC solution to be even greater than its differential linear response, though appearing to be somewhat inconsistent with what was generally known in light-matter interaction. The demonstrated properties of such anomalous shift of plasmon spectral peaks and its accompanying properties indicated that plasmon technologies could be exploited not only in linear but also in nonlinear aspects for critical optimization in plasmon-energy harvesting systems such as in surface enhanced spectroscopy/microscopy, biomedical imaging/sensing, laser frequency conversion, ultrashort pulse generation, and all-optical switching.

Smartphone-enabled colorimetric visual quantification of highly hazardous trivalent chromium ions in environmental waters and catalytic reduction of p-nitroaniline by thiol-functionalized gold nanoparticles.

High-efficiency sensing systems for extremely hazardous chromium (Cr(III)) ions are important due to their detrimental effects on human health and the environment. We employed a spectrophotometric method combined with a smartphone (red, green, and blue (RGB) color ratio)-based detection platform to realize the quick, visually quantifiable in situ detection of Cr(III) ions using surface plasmon resonance (SPR)-aided colorimetry. For optical sensing nanoprobes, we synthesized the 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMT)-modified gold nanoparticles (MMT-AuNPs) using a wet chemical method. By way of a coordination reaction, the Cr(III) ions induce the as-prepared MMT-AuNPs to aggregate and subsequently change the SPR wavelength band. The freshly synthesized MMT-AuNPs exhibited a wine-red color. While Cr(III) ions interact with the MMT-AuNPs, the color of the latter evolved from wine red to purple, thus facilitating visual monitoring. The SPR-relevant color change allowed the quantitative sensing of Cr(III) ions in the range of 40-128 nM, with the limit of detection of 6.93 nM when employing the spectrophotometric method and 12.4 nM when using the smartphone RGB color ratio. Furthermore, we developed the spectrophotometric technique that used the smartphone RGB color ratio for on-site analysis of Cr(III) ions in environmental water samples, indicating the possibility of its chemo-sensing applications for portable quantitative detection devices. Additionally, the catalytic performance of the MMT-AuNPs was demonstrated by the reduction of p-nitroaniline in the presence of sodium borohydride. It was interestingly unveiled that the MMT-AuNPs showed outstanding catalytic performance with a catalytic rate constant of 6.31 × 10-3 s-1.

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples.

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0-29.7 µM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner.

Cysteamine-decorated gold nanoparticles for plasmon-based colorimetric on-site sensors for detecting cyanide ions using the smart-phone color ratio and for catalytic reduction of 4-nitrophenol.

In this paper, we have reported the cyanide ions (CN-) sensing in environmental water samples using cysteamine-capped gold nanoparticles (Cyst-AuNPs) by spectrophotometric, colorimetric, and smartphone-based RGB color detection. The surface plasmon resonance shift at around 525 nm for the Cyst-AuNPs could be used to detect quantitatively the amounts of CN- with concomitant alteration of their color from wine red to purple visualized by the naked eye. For the first time, the Cyst-AuNPs-based visual sensing of CN- was performed using smartphone-based detection with its detection limit of 159 × 10-9 M, ten times lower than that of the highest tolerance level (2 × 10-6 M) permitted by the world health organization. The Cyst-AuNPs displayed excellent specificity for detecting the concentration of 30 × 10-6 M even amid the presence of other interfering inorganic anions with their concentrations about five times higher than it. Environmental real water samples were used to arrange the three different CN- concentrations for plasmon-based colorimetric detection and smartphone-based method. Additionally, the catalytic performance of Cyst-AuNPs was demonstrated for the fast catalytic conversion of hazardous 4-nitrophenol (selected environmental contaminant) to the analogous amino aromatic compounds. A chemical kinetic study showed the conversion rate to be estimated as 1.65 × 10-2 s-1. Cyst-AuNPs can find an application in colorimetric sensing of CN- while being able to be utilized as a catalytic nanomaterial for ecological remedies associated with health care.

Optical Sensing of Toxic Cyanide Anions Using Noble Metal Nanomaterials.

Water toxicity, one of the major concerns for ecosystems and the health of humanity, is usually attributed to inorganic anions-induced contamination. Particularly, cyanide ions are considered one of the most harmful elements required to be monitored in water. The need for cyanide sensing and monitoring has tempted the development of sensing technologies without highly sophisticated instruments or highly skilled operations for the objective of in-situ monitoring. Recent decades have witnessed the growth of noble metal nanomaterials-based sensors for detecting cyanide ions quantitatively as nanoscience and nanotechnologies advance to allow nanoscale-inherent physicochemical properties to be exploited for sensing performance. Particularly, noble metal nanostructure e-based optical sensors have permitted cyanide ions of nanomolar levels, or even lower, to be detectable. This capability lends itself to analytical application in the quantitative detection of harmful elements in environmental water samples. This review covers the noble metal nanomaterials-based sensors for cyanide ions detection developed in a variety of approaches, such as those based on colorimetry, fluorescence, Rayleigh scattering (RS), and surface-enhanced Raman scattering (SERS). Additionally, major challenges associated with these nano-platforms are also addressed, while future perspectives are given with directions towards resolving these issues.

Quantum Dot-Induced Blue Shift of Surface Plasmon Spectroscopy.

We experimentally demonstrate the spectral blue shift of surface plasmon resonance through the resonant coupling between quantum dots (QDs) and surface plasmons, surprisingly in contrast to the conventionally observed red shift of plasmon spectroscopy. Multimode optical fibers are used for extended resonant coupling of surface plasmons with excited states of QDs adsorbed to the plasmonic metal surface. The long-lived nature of excited QDs permits QD-induced negative change in the local refractive index near the plasmonic metal surface to cause such a blue shift. The analysis utilizes the physical causality-driven optical dispersion relation, the Kramers-Kronig (KK) relation, attempting to understand the abnormal behavior of the QDs-induced index dispersion extracted from blue shift measurement. Properties of QDs' gain spectrally resonating with plasmons can account for such blue shift, though their absorbance properties never allow the negative index change for the blue shift observed according to the KK relation. We also discuss the limited applicability of the KK relation and possible QDs gain saturation for the experiment-theory disagreement. This work may contribute to the understanding of the photophysical properties critical for plasmonic applications, such as plasmonic local index engineering required in analyte labeling QDs coupled with plasmons for biomedical imaging or assay.

Corrigendum to: GSK-3 Inhibitors in the Regulation and Control of Colon Carcinoma.

The author requested to add a co-author after the publication of the original article [1]. In this correction, the author has been added in the article entitled "GSK-3 Inhibitors in the Regulation and Control of Colon Carcinoma" in the journal "Current Drug Targets" 2021; 22(13), 1485-1495. Details of the error and a correction are provided here. The original editorial can be found online at 10.2174/1389450122666210204203950 We regret any errors and apologize to the readers. Original: Sitansu S. Nanda1, Md Imran Hossain1, Heongkyu Ju2 and Dong Kee Yi1,* 1Department of Chemistry, Myongji University, Yongin, 03674, South Korea; 2Department of Physics, Gachon University, Seongnam-si, Gyeonggi-do, South Korea Corrected: Sitansu S. Nanda1, Md Imran Hossain1, Heongkyu Ju2, Georgia C. Papaefthymiou3 and Dong Kee Yi1,* 1Department of Chemistry, Myongji University, Yongin, 03674, South Korea; 2Department of Physics, Gachon University, Seongnam-si, Gyeonggi-do, South Korea 3Department of Physics, Villanova University, Villanova, Pennsylvania19085, USA.

Functionalized silver nanoparticles for SERS amplification with enhanced reproducibility and for ultrasensitive optical fiber sensing in environmental and biochemical assays.

Plasmonic sensors have broad application potential in many fields and are promising to replace most bulky sensors in the future. There are various method-based chemical reduction processes for silver nanoparticle production with flexible structural shapes due to their simplicity and rapidity in nanoparticle fabrication. In this study, self-assembled silver nanoparticles (Ag NPs) with a plasmon peak at 424 nm were successfully coated onto -NH2-functionalized glass and optical fiber sensors. These coatings were rapidly produced via two denaturation reactions in plasma oxygen, respectively, and an APTES ((3-aminopropyl)triethoxysilane) solution was shown to have high strength and uniformity. With the use of Ag NPs for surface-enhanced Raman scattering (SERS), excellent results and good stability with the detection limit up to 10-10 M for rhodamine B and 10-8 M for methylene blue, and a signal degradation of only ∼20% after storing for 30 days were achieved. In addition, the optical fiber sensor with Ag NP coatings exhibited a higher sensitivity value of 250 times than without coatings to the glycerol solution. Therefore, significant enhancement of these ultrasensitive sensors demonstrates promising alternatives to cumbersome tests of dye chemicals and biomolecules without any complicated process.

Kramers-Kronig Relation for Attenuated Total Reflection from a Metal-Dielectric Interface Where Surface Plasmon Polaritons Are Excited.

The applicability of the Kramers-Kronig relation for attenuated total reflection (ATR) from a metal-dielectric interface that can excite surface plasmon polaritons (SPP) is theoretically investigated. The plasmon-induced attenuation of reflected light can be taken as the resonant absorption of light through a virtual absorptive medium. The optical phase shift of light reflected from the SPP-generating interface is calculated using the KK relation, for which the spectral dependence of ATR is used at around the plasmonic resonance. The KK relation-calculated phase shift shows good agreement with that directly obtained from the reflection coefficient, calculated by a field transfer matrix formula at around the resonance. This indicates that physical causality also produces the spectral dependence of the phase of the leakage field radiated by surface plasmons that would interfere with the reflected part of light incident to the interface. This is analogous with optical dispersion in an absorptive medium where the phase of the secondary field induced by a medium polarization, which interferes with a polarization-stimulating incident field, has a spectral dependence that stems from physical causality.

Magnetic Control of Optical Reflectance from Metallic Thin Film Using Surface Plasmon Resonance and Faraday Rotation.

We demonstrate magnetic control of optical reflectance with no ferromagnetic material via combining the Faraday rotation and the surface plasmon resonance (SPR) in a Kretschman configuration under magnetic fields < 0.5 T. The SPR produces the polarization sensitive reflectance from the Au or Ag thin film coated on a N-BK7 prism in which the Faraday rotation occurs. The gold (Au) or silver (Ag) metal film as a plasmonic film somewhat acts as an incident angle-dependent reflection polarizer that can sensitively sense the polarization change induced by the Faraday rotation that occurs in a prism. We find that combination of Faraday rotation and the surface plasmon can induce a significant magnetic modulation of reflectance normalized with respect to that obtained with no magnetic fields at a specific incident angle of light. The magnetic control of optical reflectance presented may find an application in polarizer-free photonic devices with no ferromagnetic material for magneto-optical modulation.

Solution Synthesis of Cubic Spinel Mn-Ni-Cu-O Thermistor Powder.

Toward the development of NTCR thermistors, nanocrystalline Mn-Ni-Cu-O powder was synthesized from a mixed chloride aqueous solution by a simple co-precipitation method.The introduction of an oxidizing agent (H2O2) into the solution led to the partial oxidation of Mn2+ ions into Mn3+ ions, which enabled the collected powder to be well crystallized at 650 °C. Such a low calcining temperature resulted in fine particles with a mean size of 60 nm, which significantly promoted densification of the resulting ceramics. As a result, a dense and homogenous microstructure with a relative density up to 97.2% was achieved for pellets sintered at 1100 °C. Furthermore, these sintered ceramics exhibited a room temperature resistivity (ρ25) of 67 Ω·cmand a thermistor constant (B25/85) of 2843 K, which make them suitable for use in industrial thermistors. In addition, electrical stability was greatly improved when the ceramics were prepared by a new two-step sintering method. The results suggest that the co-precipitation route with the introduction of H2O2 is suitable for the fabrication of cubic spinel thermistor nanopowders.

Fluorescence Based on Surface Plasmon Coupled Emission for Ultrahigh Sensitivity Immunoassay of Cardiac Troponin I.

This work demonstrates the quantitative assay of cardiac Troponin I (cTnI), one of the key biomarkers for acute cardiovascular diseases (the leading cause of death worldwide) using the fluorescence-based sandwich immune reaction. Surface plasmon coupled emission (SPCE) produced by non-radiative coupling of dye molecules with surface plasmons being excitable via the reverse Kretschmann format is exploited for fluorescence-based sandwich immunoassay for quantitative detection of cTnI. The SPCE fluorescence chip utilizes the gold (2 nm)-silver (50 nm) bimetallic thin film, with which molecules of the dye Alexa 488 (conjugated with detection antibodies) make a near field coupling with the plasmonic film for SPCE. The experimental results find that the SPCE greatly improves the sensitivity via enhancing the fluorescence signal (up to 50-fold) while suppressing the photo-bleaching, permitting markedly enhanced signal-to-noise ratio. The limit of detection of 21.2 ag mL-1 (atto-gram mL-1) is obtained, the lowest ever reported to date amid those achieved by optical technologies such as luminescence and label-free optical sensing techniques. The features discovered such as ultrahigh sensitivity may prompt the presented technologies to be applied for early diagnosis of cTnI in blood, particularly for emergency medical centers overloaded with patients with acute myocardial infarction who would suffer from time-delayed diagnosis due to insufficient assay device sensitivity.