Substantial Spectral Changes Research Articles

Solvent optimization and fluorescein lasing for avidin biosensing

We report pulsed laser emission using fluorescein combined with avidin as an active medium matrix in a Littrow-like configuration system. The study covers testing several solvents and a range of excitation energies, aiming to get the narrowest bandwidth for stable peak emission wavelength. Initially, for 4 mM of fluorescein in 1:1 mixture of methanol-NSS, and excited with 20.80mJ of energy, a laser mission of 4.38 nm bandwidth is achieved. Then, different concentrations of thiolated avidin are mixed in the active medium, causing related red-shifts over the initial emission band. Substantial spectral changes are observed down to 0.3 μM of avidin, making apparent the stability conditions for this sort of laser system to work out as a biosensor.

Hyperspectral retrievals of suspended sediment using cluster-based machine learning regression in shallow waters

Remote sensing of suspended sediment in shallow waters is challenging because of the increased optical variability of the water, resulting from the influence of suspended matter in the water column and the heterogeneous bottom properties. To overcome this limitation, in this study, we developed a novel framework called cluster-based machine learning regression for optical variability (CMR-OV), using the Gaussian mixture model (GMM) clustering technique and a random forest regressor (RFR). We evaluated the model using an optically complex dataset from a field-scale experiment. This experiment was conducted with four sediment types injected into an experimental meandering channel divided into two reaches with submerged vegetation and a natural sand bottom. We obtained high-resolution hyperspectral images using unmanned aerial vehicles (UAVs) and measured the in situ suspended sediment concentration using laser diffraction sensors. Based on optical similarity, we used CMR-OV to divide the hyperspectral dataset into several clusters. Then, we built separate RFR models for each cluster using the corresponding spectral bands that were selected using recursive feature elimination (RFE). Thus, we found that the proposed CMR-OV yielded superior results compared to the conventional RFR model, decreasing the total error score by 10.81%. The optical spectral bands of each cluster were distinguished from each other, indicating that the datasets that were spectrally discriminated from clustering enhanced the performance of the estimator. By comparing the clustered spectral dataset and physical factors, we proved the bottom type was the most critical factor in separating the clusters, even though the variability in the sediment properties also induced substantial spectral changes. Our findings demonstrated that CMR-OV accurately reproduced the spatiotemporal distribution of suspended sediment under optically complex conditions by addressing the heterogeneity of bottom reflectance in shallow water.

A highly sensitive chemosensor for rapid recognition of Cu2+ and HSO3− in 100% aqueous solution

Dual-responsive chemosensors have garnered much research interests owing to the ability of recognizing two analytes simultaneously. Herein, the chemosensor BPIS composed of hemicyanine and 2, 2′-dipyridylamine (DPA) was facilely synthesized for sensitive and expeditious recognition of Cu2+ and HSO3− in 100% aqueous solution. By adding Cu2+, BPIS showed substantial spectral changes accompanied by a noticeable color change from pink to yellow under daylight. The absorbance and fluorescence intensity were linearly correlated to the Cu2+ concentration, enabling the quantitative recognition of Cu2+. The limit of detection (LOD) for Cu2+ was down to 4.02 × 10−9 M. The response time of BPIS towards Cu2+ was 10 s, imparting BPIS great potential in real-time detection of Cu2+. Meanwhile, BPIS manifested ratiometric fluorescence response by introducing HSO3− owing to the 1,4-addition between HSO3− and the unsaturated CC bond of BPIS. The color of the BPIS solution progressively faded from pink to colorless with increasing HSO3− concentration, and a LOD of 3.47 × 10−9 M was obtained. In addition, BPIS-coated test paper was found to be an efficient tool for fast, sensitive, portable detection of Cu2+ and HSO3− by naked eyes. More importantly, the precise detection of Cu2+ and HSO3− in real water and sugars were realized, respectively, by capitalizing on BPIS as the signal tool.

Near Infrared Spectroscopy Enables Differentiation of Mechanically and Enzymatically Induced Cartilage Injuries

This study evaluates the feasibility of near infrared (NIR) spectroscopy to distinguish between different cartilage injury types associated with post-traumatic osteoarthritis and idiopathic osteoarthritis (OA) induced by mechanical and enzymatic damages. Bovine osteochondral samples (n = 72) were subjected to mechanical (n = 24) and enzymatic (n = 36) damage; NIR spectral measurements were acquired from each sample before and after damage, and from a separate control group (n = 12). Biomechanical measurements were then conducted to determine the functional integrity of the samples. NIR spectral variations resulting from different damage types were investigated and the samples classified using partial least squares discriminant analysis (PLS-DA). Partial least squares regression (PLSR) was then employed to investigate the relationship between the NIR spectra and biomechanical properties of the samples. Results of the study demonstrate that substantial spectral changes occur in the region of 1700–2200 nm due to tissue damages, while differences between enzymatically and mechanically induced damages can be observed mainly in the region of 1780–1810 nm. We conclude that NIR spectroscopy, combined with multivariate analysis, is capable of discriminating between cartilage injuries that mimic idiopathic OA and traumatic injuries based on specific spectral features. This information could be useful in determining the optimal treatment strategy during cartilage repair in arthroscopy.

Optical Absorption of Dye Molecules in a Spherical Shell Geometry

Dipole–dipole interactions between neighboring dye molecules can cause substantial spectral changes in optical absorption, with a strong dependence on near-neighbors’ relative distances and orientations. Such effects have been previously investigated in dimers, as well as planar arrangements of dipoles, but not to our knowledge in a three-dimensional spherical configuration. This work provides a comprehensive exploration of the effect of dipolar interactions in such a geometry, varying the dye concentration, orientations, and uniformity in coverage. We also contrast this coupled-dipole model to a simpler but often-used homogeneous effective-medium approximation, which ignores effects of orientation and nonuniformity. The results provide a first step toward the full description of light scattering in a complex anisotropic core–shell geometry, which is of strong relevance in surface-enhanced spectroscopy applications, as well as in the strong coupling between molecular emitters and optical nanoresonators.

Tautomerism of N-(3,4-dichlorophenyl)-1H-indazole-5-carboxamide – A new selective, highly potent and reversible MAO-B inhibitor

The tautomeric properties of an N-(3,4-dichlorophenyl)-1H-indazole-5-carboxamide (NTZ-1006, 2) derivative, developed as highly potent, reversible and selective MAO-B inhibitor useful for the treatment of Parkinson's disease (PD) and other neurological disorders, have been studied both experimentally and theoretically. The theoretical data (M06–2X, B3LYP and MP2-4 quantum chemical calculations) have shown that due to aromaticity reasons the 1H tautomer strongly dominates over the 2H form. There are no substantial spectral changes by changing the solvent and the concentration, which leads to a conclusion that compound 2 exists in solution as 1H tautomer and its tautomerism is not influenced by the solvents and the concentration. The results are in line with the understanding for the tautomerism of 1H-indazole and shows that substitution at the C5 position in the indazole unit does not influence the tautomeric state.The isolated crystal structure of 2 is in an excellent agreement with the computation in respect of the most stable tautomer. Combined single X-ray/molecular modeling studies including HYdrogen-DEsolvation (HYDE) analysis provided not only insights into the enzyme–inhibitor interaction within the binding site of the human MAO-B isoform, but also a valuable information regarding the most stable 1H-indazole tautomeric form of NTZ-1006 that contributes to its high potency against hMAO-B enzyme (IC50 0.586 nm) and selectivity (>17000-fold) over the hMAO-A isoenzyme.

Monitor Polyimide Production from Diamine and Dianhydride Reactions Using a Combination of In Situ Infrared and Raman Spectroscopy.

A two-step synthesis of polyimide reaction from dianhydride and diamine was followed by both infrared (IR) and Raman spectroscopy in situ in this case study. In the first step, the two reactants form poly(amide acid), which resulted in substantial spectral changes easily detected by both spectroscopic techniques. The reaction was found to occur rapidly and reached completion within tens of minutes at room temperature. In the second step, trimethylamine (catalyst) and acetic anhydride (dehydration agent) were added to form the five-member imide ring. Interestingly, different spectral changes were observed using IR and Raman spectroscopic methods due to their different responses toward the various functional groups involved. Conclusive evidence was also obtained based on the Raman results to demonstrate a long-lived intermediate species, which was harder to observe in the IR results. This work provides a good case study of the combined use of different vibrational spectroscopy techniques to extract maximum information from a reaction system.

Emission characteristics of Er 3+ in vapor-transport-equilibrated Er/Zn-codoped LiNbO 3 crystals

Polarized visible and infrared emission characteristics of Er 3+ ions in vapor-transport-equilibration (VTE)-treated LiNbO 3 crystals codoped with different concentrations of Zn and Er were investigated in comparison with corresponding as-grown crystals. The results show that the VTE treatment leads to substantial spectral changes of Er 3+ emissions at 0.65, 0.98 and 1.5 μm regions, and the spectral changes in the 0.98 and 1.5 μm regions appear to be Zn-concentration-dependent. It is concluded in combination with X-ray powder diffraction results and optical absorption characteristics reported previously that the VTE treatment resulted in crystalline phase transformation with respect to Er 3+ ions from original LiNbO 3 to ErNbO 4 phase in all crystals studied. The formation of the ErNbO 4 phase and the Zn 2+ codopants are responsible for the VTE-induced substantial spectral changes. The emission characteristics of the ErNbO 4 precipitates in the Zn/Er-codoped crystals are found to be very different from those of the ErNbO 4 precipitates in the only Er-doped crystal in the infrared region, and the difference is attributed to the influence of the Zn 2+ codopant on the Er 3+ ion environment. The mechanism of the crystalline phase transformation is qualitatively explained from the viewpoint of the declined solubility of Er 3+ ion in a Li-rich LiNbO 3 crystal and from the phase diagram of Li 2O–Nb 2O 5 system.

X‐Ray, Micro‐Raman, Optical Absorption/Emission Studies of ErNbO4 Grown by Vapor Transport Equilibration

Vapor transport equilibration (VTE) treatments were performed on a Y‐cut bulk Er (1.6 mol%)‐doped congruent LiNbO3 crystal and an X‐cut pure congruent crystal, on one surface of which a 40 nm‐thick film of erbium metal was coated before the VTE treatment. Scanning electron microscope, powder or single‐crystal X‐ray diffraction (XRD), polarized infrared absorption/emission of Er3+ as well as micro‐Raman spectroscopy were used to study the two VTE crystals. The results are discussed in comparison with a corresponding as‐grown bulk Er‐doped crystal, calcined ErNbO4 powder, and a locally Er‐doped congruent LiNbO3 crystal prepared by using the standard Er‐diffusion technique. The experimental results show that the VTE treatment induces the formation of micrometer‐sized ErNbO4 precipitates with the crystallographic morphology of a flat polyhedron not only on the surfaces of both crystals but also in the bulk of the homogeneously Er‐doped one. The optical absorption and emission studies show that the formation of the precipitates results in substantial spectral changes in both the 0.98 and 1.5 μm regions. The micro‐Raman studies allow to resolve four additional Raman peaks around 800 cm−1 in the E(TO) spectra of the two VTE crystals. These additional Raman peaks are associated with the characteristic vibrations with respect to the NbO43− group. Characteristic XRD, optical absorption, and emission and Raman peaks for identifying the ErNbO4 phase are proposed. Finally, the formation mechanism and light‐scattering effect of the precipitates are discussed.

Influence of vapor transport equilibration on spectroscopic properties of Er:LiNbO3 crystal heavily codoped with MgO

Z -cut MgO heavily codoped (6mol%) Er(0.4mol%):LiNbO3 crystals were thermally treated at 1110 and 1120°C over 100, 120, and 220h using vapor transport equilibration (VTE) technique. Visible and infrared-absorption and x-ray powder diffraction have been used to characterize their spectral, spectroscopic, and crystalline phase characteristics in comparison with the as-grown crystal. The experimental results show that VTE treatment results in the reduction of background absorption and 4–5-nm blueshift of the optical-absorption edge, qualitatively showing that these crystals have been brought closer to stoichiometric composition. The VTE procedure also results in remarkable Er3+ absorption changes. These spectroscopic changes imply that the VTE treatment may result in the formation of ErNbO4 precipitates in all VTE crystals. In addition, the VTE treatment also results in substantial spectral changes with respect to OH− absorption. These OH− spectral changes are explained from the viewpoint of VTE-induced site-occupancy alterations of intrinsic and extrinsic defects. Based upon the measured absorption spectra, the influences of VTE treatment on the Er3+ spectroscopic parameters were studied by using the Judd–Ofelt (JO) theory. The theoretical results show that VTE treatment has a little influence on the branch ratio, and a substantial influence on JO parameters and electron transition probability because of the phase transformation with respect to Er3+. The VTE treatment results in the increase of the JO parameters by more than 50% and theoretical radiative lifetime by 50%–120%.

Absorption characteristics of vapor transport equilibrated Er:LiNbO3 crystals

The visible and infrared transmission spectra of vapor transport equilibration (VTE) treated Er:LiNbO3 crystals, which have different doping levels (0.2%, 0.4%, and 2.0% Er per cation site), different cut orientation (X and Z cut) and different VTE duration (80, 120, 150, and 180 h), were recorded at room temperature in the wavelength range of 250–3700 nm. All of 2.0 mol % doped VTE crystals have precipitated whether X cut or Z cut, while the others have not. Their absorption characteristics were summarized and discussed in contrast to those of corresponding as-grown crystals. The OH− absorption feature of VTE treated Er:LiNbO3 is found to be different from that of pure VTE LiNbO3 crystal. The significant reduction of OH− absorption band implies that the hydrogen content in the VTE crystals has been reduced substantially whether the crystal precipitates or not. The electron transition absorption characteristics of the lower-doped, not precipitated crystals mainly include the higher transmittance, slight shift of peak or band position, slight absorption intensity change, the appearance of some additional peaks or bands, the narrowing of the peak width (full width at half maximum), and the definite blueshift of the optical absorption edge. The spectral changes are associated with the redistribution of Er3+ spectroscopic sites induced by the VTE procedure. In comparison with those lower-doped VTE crystals, the highly doped VTE crystals display more significant absorption characteristics: the significant enhancement of 1480 nm pumping band and the obvious weakening of 1531 nm peak, the appearance of many additional peaks in the infrared region, and the interesting evolution of the transmittance with the wavelength. These substantial spectral changes are unambiguously conducted with the formation of a precipitate ErNbO4 induced by the VTE treatment in these crystals. The mechanism for the formation of the precipitate has been tentatively explained from the viewpoint of both microscopic and macroscopic domains. The higher transmittance, the narrowing of the peak width, the blueshift of the optical absorption edge, as well as the significant reduction of the OH band are the indicatives of the VTE treatment having brought these crystals closer to stoichiometric composition.

Photophysical investigation of the degree of dispersion of aqueous colloidal clay

The photophysical properties of water-soluble tetrakis(N-methylpyridyl)porphyrin (TMPyP) are altered upon adsorption to the surface of a smectite clay mineral in an aqueous dispersion. In particular, the Soret absorption band shifts from 421 nm in aqueous solution to 452 nm when the molecule is adsorbed on the external face of a clay sheet in contact with the bulk solution. Upon intercalation between clay sheets, the Soret band further shifts in 488 nm. The net Soret absorption band observed in a particular clay sample is a superposition of contributions from intercalated versus externally adsorbed porphyrin and provides a convenient method to monitor the degree of dispersion or extent of deflocculation of a clay dispersion to produce primary particles or single sheets. Further, the spectral changes can be utilized to assess the effect of chemical and physical modification to the clay dispersion on the extent of face-to-face particle aggregation. Shifts in the fluorescence spectrum parallel those of the Soret band. A mechanism which could account for the substantial spectral changes observed is proposed.