Near-infrared Absorption Research Articles

Evaluation of the optical and electrical properties of (C8BTBT)(F4TCNQ) charge-transfer complexes according to film formation temperatures during solution-coating

Abstract This study focused on (C8BTBT)(F4TCNQ) charge-transfer complexes, where C8BTBT is 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and F4TCNQ represents fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane. These complexes exhibit excellent thermal and atmospheric stability and near-infrared absorption, serving as transparent thin films for photoelectric conversion. Here, we sought to improve the photoelectric conversion efficiency (and thus the quantum efficiency, QE) of (C8BTBT)(F4TCNQ) thin films by altering the film formation temperatures during solution-coating; we evaluated optical and electrical properties of the films. We found that increased film coverage of a substrate surface (leading to continuous film formation) enhanced optical absorption and improved the photocurrent extraction efficiency when such films were incorporated into devices. C8BTBT and its components, when present alone, negatively affected both the device fabrication yield and photocurrent extraction. It is thus important to maximize (C8BTBT)(F4TCNQ) formation when seeking to improve the QE.

Copper Versatility in Hydroxyapatite: Valence States, Clusters, and Optical Absorption Properties.

The solid-state reaction between a stoichiometric hydroxyapatite (HA) and CuO at temperatures above 1100 °C produces pure Cux-HA phases for x ≤ 0.7 with the general formula Ca10CuIx(PO4)6(OH)2-xOx. The Cu atoms are located at the center of the hexagonal tunnels between two hydroxyl ligands, as determined by Fourier analysis based on XRD data. During heat treatment, the reduction of Cu2+ ions into Cu+ is concomitant with the stabilization of copper in HA in the hexagonal tunnel. The incorporation of monovalent copper within the apatite, as revealed by XANES spectroscopy, explains the violet color of the samples. The incorporation of Cu+ ions, by substitution of a hydrogen atom by copper(I), results in the formation of linear O-Cu-O chains where the majority of which are isolated for x ≤ 0.3. In addition, the EXAFS investigation showed, thanks to the linear geometry of these clusters that results in multiple diffusion effects, the existence of [CuO]n chains with n ≥ 2, which only appear clearly for higher copper contents x ≥ 0.5. The strong covalency of the Cu-O bond in such a dumbbell configuration would lead to strong hybridization between the 3d and 4s orbitals of copper and the 2p orbitals of oxygen, as illustrated by ESR signals. In the case of Cu-doped HA prepared by coprecipitation and annealed at a lower temperature (T ≤ 600 °C), copper substitutes calcium according to the theoretical formula Ca10-xCux(PO4)6(OH)2, mainly at the Ca(2) site. This local environment is in line with the Jahn-Teller distortion induced by the Cu2+ ion (as evidenced by UV-vis-NIR, XPS, and XANES-EXAFS spectroscopy analyses) and also allows copper-copper interactions from one site to another, as observed by ESR spectroscopy. This versatility of copper in HA gives it optical properties that change from a violet color with near-IR absorption to a blue hue. In all cases, Cu-O-Cu interactions persist whatever the valence state, and heat treatment induces a redox phenomenon, with copper exchanging between two sites close to each other.

Structural Effect of N-7 Alkylation in 6-Chloropurine on Cu (II) Binding: Effect of Anions and Magnetic Studies.

This study investigates the anion-directed assembly of discrete copper (II) complexes. The ligands of choice are two N7-alkyl-purine-based neutral ligands. These ligands facilitate the exclusive coordination through the N3 and N9 positions, preventing polymeric chain formation. Perchlorate ions promoted the formation of discrete paddlewheel-like complexes with the general formula [Cu2(μ-Pur)4(CH3CN)2]4+, while chloride ions yielded chloride-bridged dimers of the form [Cu2(Pur)2(μ-Cl)2Cl2]. Copper-copper bond distances within these complexes ranged from 2.92 to 2.98 Å. Magnetic susceptibility measurement of chloride-bridged complexes exhibited antiferromagnetic coupling, whereas paddlewheel complexes displayed more complex alternating ferromagnetic and antiferromagnetic interactions. Chloride-bridged compounds exhibited strong near-infrared absorption.

Recent Advances in NIR-Switchable Multi-Redox Systems Based on Organic Molecules.

In recent years, near-infrared (NIR) dyes, exhibiting absorption in the NIR region (750-2500 nm), have been applied to various optical applications such as security marking, photovoltaic cells and chemotherapy of deep tissues in vivo. Electrochromic systems capable of switching NIR absorption are attractive from the viewpoint of applications for material and life science, and thus several examples have been reported to date. The development of organic-based materials is needed to reduce the environmental impact and improve biocompatibility, however, the switching of NIR absorption based on redox interconversion is still a challenging issue regarding reversibility and durability during interconversion. To overcome this potential instability, several studies on organic electrochromic systems that allow ON/OFF switching of NIR absorption have been developed in recent years. In this review, we focus on redox-active well-defined small molecules that enable ON/OFF switching of NIR absorption, and present recent studies on their intrinsic electrochemical and spectroscopic properties and/or structural characterization of their charged states. We also address more sophisticated electrochromic systems that can modulate their properties in response to external stimuli such as light, heat, and electric potential.

Synthesis of heavy-atom-free thienoisoindigo dye as near-infrared photosensitizer for type I photodynamic therapy and photoacoustic imaging

Thienoisoindigo (TIIG) has been extensively employed as promising building block of near-infrared (NIR) dyes and organic semiconductor materials. Herein, heavy-atom-free TIIG-based NIR dye TIIGTPA is reported as photosensitizer for combinational photodynamic and photothermal therapy and photoacoustic imaging (PAI). By introducing two methoxy-substituted triphenylamines as the rotors and electron donors at the periphery sites of the electron-deficient TIIG core, dye TIIGTPA featuring Donor-Acceptor-Donor (D-AD) structure is constructed with intensive NIR absorption. Through co-assembly with amphipathic F-127, water-soluble TIIGTPA NPs were prepared with good superoxide anion radical (O2-•) production and high photothermal conversion efficiency (PCE) of 59.0 % under 730 nm photoirradiation. Additionally, the excellent photothermal effect enabled a superior photoacoustic response for tumor blood vessel visualization through PAI. All results indicated the favorable potential of TIIGTPA NPs for PAI-mediated combinational phototherapy.

Bowl-Shaped Anthracene-Fused Antiaromatic Ni(II) Norcorrole: Synthesis, Structure, Assembly with C60, and Photothermal Conversion.

The synthesis of bowl-shaped antiaromatic molecules represents a formidable challenge, because the molecular distortion further destabilizes these already inherently reactive molecules. Here, we report the synthesis and properties of bowl-shaped fused anthrylnorcorroles that exhibit near-infrared (NIR) absorption reaching 1900 nm. The oxidation of meso-anthryldibromodipyrrin provides fused anthryldibromodipyrrin, which was converted to the fused mono- and bisanthrylnorcorroles through Ni(0)-mediated intramolecular coupling with a bis(dibromodipyrrin) Ni(II) complex. Single-crystal X-ray diffraction analyses revealed bowl-shaped structures for the fused mono- and bisanthrylnorcorroles, which enables them to act as suitable receptors for C60 with bonding constants of 2.89 × 103 M-1 and 1.59 × 103 M-1, respectively. The formation of a 1:1 complex between the fused monoanthrylnorcorrole and C60 was confirmed by single-crystal X-ray diffraction analysis. The effective expansion of the π-conjugation through the triple fusion of the norcorrole with the anthracene units substantially enhances the near-infrared absorption bands, which endows these anthrylnorcorroles with effective photothermal conversion.

Revealing the complexation of 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic acid (DPS) with cuprous ion and its contribution to Cu electrodeposition

An accelerator is an organic additive used in Cu electrodeposition, crucial for achieving superfilling during the fabrication of Cu interconnects in microelectronics. 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic acid (DPS) has been proposed and investigated as a substitute for SPS. However, its acceleration mechanism associated with its interaction with Cu ions has not been intensively investigated. In this study, the interaction between DPS and Cu+ was investigated using various spectroscopic analyses, including ultraviolet–visible–near-infrared absorption (UV–VIS–NIR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) spectroscopy. UV–VIS–NIR and EPR spectroscopy revealed that DPS forms a complex with Cu+, namely Cu(I)(DPS)2. The kinetic study on the complexation of DPS with Cu+ indicated second-order reaction characteristics. The structure of the complex was suggested using 1H and 13C NMR spectroscopy. Furthermore, electrochemical analyses, including cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were conducted to investigate the electrochemical behaviors of the Cu(I)(DPS)2 complex, demonstrating its acceleration effect on Cu electrodeposition. These results will provide valuable insights for understanding the acceleration mechanism of DPS in Cu electrodeposition.

Biodegradable ICG-Conjugated Germanium Nanoparticles for In Vivo Near-Infrared Dual-Modality Imaging and Photothermal Therapy.

Theranostics, by integrating diagnosis and therapy on a single platform, enables real-time monitoring of tumors during treatment. To improve the accuracy of tumor diagnosis, the fluorescence and photoacoustic imaging modalities can complement each other to achieve high resolution and a deep penetration depth. Despite the superior performance, the biodegradability of theranostic agents plays a critical role in enhancing nanoparticle excretion and reducing chronic toxicity, which is essential for clinical applications. Herein, we synthesize biocompatible and biodegradable indocyanine green (ICG)-conjugated germanium nanoparticles (GeNPs) and investigate their biodistributions in nude mice and 4T1 tumor models after intravenous injections using near-infrared (NIR) dual-modality fluorescence and photoacoustic imaging. The ICG-conjugated GeNPs have strong NIR absorption due to the NIR-absorbing ICG and Ge in combination, emit strong NIR fluorescence due to the multilayered ICG coatings, and exhibit very low in vitro and in vivo toxicity. After tail vein injections, the ICG-conjugated GeNPs mainly accumulate in the liver and spleen as well as the tumor with the help of the enhanced permeability and retention effect. The tumor's fluorescence signal is much stronger than that of the control group injected with pure ICG solution, as the GeNPs can function as biodegradable carriers for efficiently delivering the ICG molecules to the tumor. Lastly, the ICG-conjugated GeNPs accumulated in the tumor can also be utilized for photothermal treatment under NIR laser irradiation, after which the tumor volume almost diminishes after 14 days. The experimental findings in this work demonstrate that the ICG-conjugated GeNPs are promising theranostic agents with exceptional biodegradability for in vivo NIR dual-modality imaging and photothermal therapy.

Diradicaloid-Loaded Polypeptide Nanoparticles for Two-Photon NIR Phototheranostics.

Stable organic radicals, with unique electronic transitions from the ground state (D0) to the doublet excited state (D1), show promise as high-fluorescence quantum yield dyes. While organic small-molecule photosensitizers (PSs) have advanced for tumor photodynamic therapy (PDT), opportunities exist to enhance their performance and functionality. Herein, we synthesized Thiele's fluorocarbon derivative diradicaloid TFC-I with nearly 100% PLQY and integrated it into amphiphilic polypeptide nanoparticles, P-TI, using a precursor-doping approach. P-TI demonstrated notable features including high photostability, aggregation-induced emission, bright near-infrared fluorescence, substantial quantum yield (37% PLQY), robust near-infrared two-photon absorption (∼400 GM cross section), and superior ROS generation compared to commercial PSs. In vitro and in vivo experiments confirmed that P-TI performed well in mitochondria-targeted PDT, two-photon fluorescence imaging, and biosafety. This work highlights the use of organic stable radicals with precursor-doping for efficient PDT and deep tumor tissue imaging.

Molecular Engineering of a Tumor-Targeting Thione-Derived Diketopyrrolopyrrole Photosensitizer to Attain NIR Excitation Over 850 nm for Efficient Dual Phototherapy.

Photosensitizers with near-infrared (NIR) excitation, especially above 800 nm which is highly desired for phototherapy, remain rare due to the fast nonradiative relaxation process induced by exciton-vibration coupling. Here, a diketopyrrolopyrrole-derived photosensitizer (DTPA-S) is developed via thionation of carbonyl groups within the diketopyrrolopyrrole skeleton, which results in a large bathochromic shift of 81 nm, endowing the photosensitizer with strong NIR absorption at 712 nm. DTPA-S is then introduced with a functional biomolecule (N3-PEG2000-RGD) via click reaction for the construction of integrin αvβ3 receptor-targeted nano-micelles (NanoDTPA-S/RGD), which endows the photosensitizer with a further superlarge absorption redshift of 138 nm, thus extending the absorption maxima to ≈850 nm. Remarkably, thiocarbonyl substitution increases the nonbonding characters in frontier molecular orbitals, which can effectively suppress the nonradiative vibrational relaxation process via reducing the reorganization energy, enabling efficient reactive oxygen species (ROS) generation under 880 nm excitation. Screened by in vitro and in vivo assays, NanoDTPA-S/RGD with high water solubility, excellent tumor-targeting ability, and photodynamic/photothermal therapy synergistic effect exhibits satisfactory phototherapeutic performance. Overall, this study demonstrates a new design of efficient NIR-triggered diketopyrrolopyrrole photosensitizer with facile installation of functional biomolecules for potential clinical applications.

A synergetic effect of light and anion: near-infrared colorimetric monitoring of nitric oxide (NO) release from fluoride/cyanide anions and a water responsive ruthenium nitrosyl complex.

Near-infrared (NIR) spectral-responsive multitasking chemical systems are always advantageous in biological and environmental systems. Although ruthenium complexes are highly attractive compounds for many applications, studies on NIR optical responsive sensors are very limited because of their synthetic difficulties. The sensing of fluoride and cyanide ions using ruthenium nitrosyl complexes is not known. In this study, we report the synthesis and characterization of a new terpyridine-based ruthenium nitrosyl complex [Ru(Cl)2NO(terpy-C6H4OH)] 1·Ru-OH. The complex exhibited distinct NIR absorptions at 680 nm, as well as a visible color change with the fluoride ion in DMSO-CH3CN medium. However, when the solvent is changed to DMSO-H2O, it responds only with a cyanide ion with a distinct colorimetric change. Binding of the F- ion leads to deprotonation of 1·Ru-OH; the deprotonated complex is also used for the colorimetric detection of a trace amount of water in DMSO and acetonitrile with a limit of detection (LOD) of 0.034 wt% and 0.007 wt%, respectively. Ruthenium nitrosyl complexes have appeared as promising platforms for light-controlled release of nitric oxide (NO), which can be beneficial for therapeutic application. NO release studies of 1·Ru-OH by UV-vis and FT-IR spectroscopy confirm that it can release NO in a light-controlled manner. In addition, the NO release could be monitored by the naked eye with a color change and spectral change in the NIR region. Importantly, NO release studies revealed that the rate of NO release could be modulated in the presence of the F- ion. Here, the fluoride ion acts as an allosteric regulator. These results demonstrate that 1·Ru-OH is both a promising multitasking colorimetric and NIR sensor and a colorimetric responsive NO-releasing agent.

A Near-Infrared Retinomorphic Device with High Dimensionality Reservoir Expression.

Physical reservoir-based reservoir computing (RC) systems for intelligent perception have recently gained attention because they require fewer computing resources. However, the system remains limited in infrared (IR) machine vision, including materials and physical reservoir expression power. Inspired by biological visual perception systems, the study proposes a near-infrared (NIR) retinomorphic device that simultaneously perceives and encodes narrow IR spectral information (at ≈980nm). The proposed device, featuring core-shell upconversion nanoparticle/poly (3-hexylthiophene) (P3HT) nanocomposite channels, enables the absorption and conversion of NIR into high-energy photons to excite more photo carriers in P3HT. The photon-electron-coupled dynamics under the synergy of photovoltaic and photogating effects influence the nonlinearity and high dimensionality of the RC system under narrow-band NIR irradiation. The device also exhibits multilevel data storage capability (≥8 levels), excellent stability (≥2000 s), and durability (≥100 cycles). The system accurately identifies NIR static and dynamic handwritten digit images, achieving recognition accuracies of 91.13% and 90.07%, respectively. Thus, the device tackles intricate computations like solving second-order nonlinear dynamic equations with minimal errors (normalized mean squared errorof 1.06 × 10⁻3 during prediction).

Resonant Cell-Based 1f Photoacoustic Gas Analyzer Immune to Light Power Fluctuation and Frequency Mismatch.

To overcome the light power fluctuation and frequency mismatch in photoacoustic spectroscopy (PAS), we proposed a self-corrected 1f-only resonant cell-based PAS (1f-RCPAS) gas analyzer. Based on the theoretical analysis of the 1f signal, a signal processing algorithm considering laser power-current nonlinearity is proposed. The 1f-only algorithm is well-tailored for the resonant systems, requiring no time-division multiplexing. The algorithm is further improved to extend the dynamic range. The T-type resonant cell incorporating a graphene sticker is utilized for effectively amplifying the acoustic signals from both the gas and solid to achieve normalization. No optical path alignment is needed. For the low resonance frequency, a digital orthogonal-vector lock-in amplifier is used, further simplifying the system setup. The gas analyzer is used to measure methane (CH4) with the near-infrared absorption peak at 1651 nm. The experiments demonstrated immunity to fiber coupling loss, laser power drift over time, and frequency mismatch caused by property differences between air and standard gases. The R2 value in the concentration calibration reaches 0.99995, and the minimum detection limit given by the Allan variance reaches 3.5 ppb at an average time of 105 s.

Magneto-Chiral Dichroism of Chiral Lanthanide Complexes in the Context of Richardson's Theory of Optical Activity.

Here we report on the Magneto-Chiral Dichroism (MChD) detected through visible and near-infrared light absorption of two enantiomeric pairs of ErIII and TmIII chiral complexes featuring a propeller-like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with 4I15/2 and 3H6 ground state terms. MChD spectroscopy shows high gMChD dissymmetry factors of ca. 0.12 T-1 and 0.05 T-1 (T = 4.0 K and B = 1.0 T) for ErIII and TmIII, respectively, associated with their magnetic-dipole allowed 4I13/2 ← 4I15/2 and 3H5 ← 3H6 transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results reported here are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD-active electronic transitions of lanthanide complexes.

Dual-Activated Photoacoustic Probe for Reliably Detecting Hydroxyl Radical in Ischemic Cardiovascular Disease in Mouse and Human Samples.

Cardiovascular disease (CVD) is a chronic disease characterized by the accumulation of lipids and fibrous tissue within the arterial walls, potentially leading to vascular obstruction and an increased risk of heart disease and stroke. Hydroxyl radicals play a significant role in the formation and progression of CVD as they can instigate lipid peroxidation, resulting in cellular damage and inflammatory responses. However, precisely detecting hydroxyl radicals in CVD lesions presents significant challenges due to their high reactivity and short lifespan. Herein, we present the development and application of a novel activatable optical probe, Cy-OH-LP, designed to detect hydroxyl radicals in lipid-rich environments specifically. Built on the Cy7 molecular skeleton, Cy-OH-LP exhibits near-infrared absorption and fluorescence characteristics, and its specific response to hydroxyl radicals enables a turn-on signal in both photoacoustic and fluorescence spectra. The probe demonstrated excellent selectivity and stability in various tests. Furthermore, Cy-OH-LP was successfully applied in an in vivo model to detect hydroxyl radicals in mouse models, providing a potential tool for diagnosing and monitoring AS. The biosafety of Cy-OH-LP was also verified, showing low cytotoxicity and no significant organ damage in mice. The findings suggest that Cy-OH-LP is a promising tool for the specific detection of hydroxyl radicals in lipid-rich environments, providing new possibilities for research and clinical applications in the field of oxidative stress-related diseases.

Thionation of conjugated porphyrin with enhanced photodynamic and photothermal effects for cancer therapy

Phototherapy has emerged as a promising modality for cancer treatment in recent years, owing to its precise temporal control and minimally invasive nature. Here, two new organic porphyrin molecules, denoted as ONP and SNP, were designed and synthesized with an acceptor–donor–acceptor (A-D-A) architecture. The donor–acceptor (D-A) pairs in molecules facilitated the intermolecular charge transfer (ICT), thereby amplifying near-infrared (NIR) absorbance and promoting nonradiative heat generation. Notably, the substitution of oxygen atoms with sulfur in naphthalimides (NI) led to significant change of their photophysical and photochemical properties. Specifically, the sulfur atoms exhibited pronounced spin–orbit coupling (SOC) effect, leading to efficient photoinduced intersystem crossing (ISC) processes, thus facilitating the generation of reactive oxygen species (ROS). Upon self-assembly, the formed nanomaterials (ONP NPs and SNP NPs) exhibited spherical morphology with average size about 150 nm. The biocompatibility and photocytotoxicity of nanoparticles against Hepa1-6 cells were evaluated using the CCK-8 assay. Additionally, the synergistic effects (photodynamic therapy and photothermal therapy) of SNP NPs were confirmed through diverse in vitro experiment under 690 nm laser irradiation. The generation of intracellular ROS by SNP NPs was confirmed with DCFH-DA as probe. This study provides an ingenious strategy for developing organic nanomaterials with high treatment efficiency through synergistic photodynamic/photothermal effects.

Yb3+-activated phosphate glasses melted with MnCO3 for solar spectral conversion

This paper reports on the physical and optical properties of phosphate glasses containing red-emitting Mn2+ and near-infrared (NIR)-emitting Yb3+ ions of interest for solar spectral conversion. The glasses were prepared by melting with 50P2O5-(48 – x)BaCO3-2Yb2O3-xMnCO3 (x = 0, 1, 2, 3, 4 mol%) formulas, and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), UV-Vis-NIR spectrophotometry, and photoluminescence (PL) spectroscopy. The glasses were X-ray amorphous with the various characteristic features of phosphate glasses being evident in the FT-IR spectra. The thermal properties of the co-doped glasses assessed by DSC appeared similar despite the variation in manganese content. The optical absorption spectra supported the occurrence of Mn2+ ions while Mn3+ was detected at high MnCO3 content. The NIR absorption due to Yb3+ ions was nonetheless consistent with the fixed Yb2O3 content. The PL evaluation showed that sensitized Yb3+ PL was attained under Mn2+ excitation at 410 nm where the NIR emission increased with MnCO3 content in connection with Mn2+ → Yb3+ energy transfer. However, the NIR emission output realized with 4 mol% MnCO3 was just marginally higher than the obtained with 3 mol% MnCO3. On the other hand, the red Mn2+ emission was highest for 3 mol% MnCO3. Thus, considering the optimized red and NIR emissions while minimizing absorption by Mn3+, the Yb-containing glass melted with 3 mol% MnCO3 was put in perspective with the concept of solar spectral conversion.

Common structural features in some of the sequentially distant neurotransmitter transporters N-termini

The N-terminal regions of SLC6 transporters are sequentially unrelated, and the majority of such transporters contain only relatively short peptide N-terminal extensions. Currently, it is not clear if a diversity of N-terminal sequences represents diverse functions among the transporters or if there are common functions hidden behind similar, as yet unidentified, structures. Using alignment of amino acid sequences with the hydropathy plot, disorder prediction, and calpain recognition sites, we show that common structural features among the N-termini of some transporters might exist.We previously showed that polymeric neurotransmitter transporter N-termini exhibit very similar profiles of dynamic, time-dependent 465 nm-595 nm-750 nm absorbance metachromasia in the Bradford assay. Here we report that under certain mild denaturing conditions, filamentous aggregation of glutathione S-transferase (GST) protein results in similar near-infrared metachromasia. This effect was eliminated by further GST protein denaturation and solubilization. The results suggest that aggregation of partially denatured GST stabilizes Coomassie dye docking sites, producing a near-infrared absorbance shift similar to that observed in the polymeric unstructured N-termini of transporters.

Novel Synthesis Route of Plasmonic CuS Quantum Dots as Efficient Co-Catalysts to TiO2/Ti for Light-Assisted Water Splitting.

Self-doped CuS nanoparticles (NPs) were successfully synthesized via microwave-assisted polyol process to act as co-catalysts to TiO2 nanofiber (NF)-based photoanodes to achieve higher photocurrents on visible light-assisted water electrolysis. The strategy adopted to perform the copper cation sulfidation in polyol allowed us to overcome the challenges associated with the copper cation reactivity and particle size control. The impregnation of the CuS NPs on TiO2 NFs synthesized via hydrothermal corrosion of a metallic Ti support resulted in composites with increased visible and near-infrared light absorption compared to the pristine support. This allows an improved overall efficiency of water oxidation (and consequently hydrogen generation at the Pt counter electrode) in passive electrolyte (pH = 7) even at 0 V bias. These low-cost and easy-to-achieve composite materials represent a promising alternative to those involving highly toxic co-catalysts.

Feature Selection and Spectral Indices for Identifying Maize Stress Types

This study aims to identify different types of stress on maize leaves using feature selection and spectral index methods. Spectral data were collected from leaves under heavy metal, water, fertilizer stress, as well as under normal healthy conditions. Preprocessing steps such as continuum removal (CR), standard normal variable (SNV) transformation, multiple scattering correction (MSC), detrend correction (DT), and first-order derivative (FOD) were applied to the raw spectra. Various feature selection methods including ReliefF, chi-square test, recursive feature elimination (FRE), mutual information (MI), random forest (RF), and gradient boosting tree (GBT) were employed to determine the importance scores of different spectral bands, thus identifying sensitive spectral features capable of distinguishing various stress types. Spectral indices for stress type differentiation were constructed using label correlation method. Classification models were built using support vector machine (SVM), K-nearest neighbors (KNN), Gaussian naive Bayes (GNB), extreme gradient boosting (XGBoost), RF, and adaptive boosting (AdaBoost) algorithms. Results indicate that the characteristic spectral bands for differentiating stress types are primarily distributed around the red edge (near 700–800 nm) and water absorption valley (near 1900 nm). Spectral indices constructed using combinations of spectral bands around the near-infrared plateau absorption valley (near 1185 nm) and water absorption valley (near 1460 nm) effectively differentiate maize stress types. Among the modeling classification algorithms, RF and AdaBoost algorithms exhibited optimal performance, demonstrating high classification accuracy on both training and validation sets. These findings hold promise for providing new technical support for maize stress monitoring and diagnosis in agricultural production.