Visible Detection Research Articles

Green and ligand-free gold nanoparticles in Padina australis extract for colorimetric detection of Cu2+ in water

The green and ligand-free gold nanoparticles (P-AuNPs) from Padina australis extract were easily and quickly prepared. A colorimetric probe based on P-AuNPs was designed for easy and visual detection of Cu2+ in domestic water with excellent sensitivity. The –OH and –NH2 in polysaccharides and proteins of Padina australis had played a reduced and protected role for AuNPs and also been easy to complex Cu2+ because of chelation. The complexed Cu2+ dragged P-AuNPs closely to aggregation, causing the red sol to turn blue. Also, the UV–vis spectrum was red-shifted, and a new peak developed. The limits of UV–vis detection are as low as 0.43 μM. The absorbance ratio (A630/A520) showed an excellent linear relationship with Cu2+ concentration (R2 = 0.9926) with a range of 20–60 μM by UV–vis.

Facile fabrication of Al nanoparticle arrays with continuous tunable diameter and plasmonic band for UV–visible SERS detection

Al-based nanostructures have a huge potential for surface-enhanced Raman scattering (SERS) in area of life science, chemical and food safety because of its excellent plasmonic characteristics from UV to near-infrared ranges. By only controlling the deposited Al thickness onto the parabola-shaped alumina nanopores template, the Al nanoparticle arrays with tunable diameter from 55 nm to 94 nm and plasmonic bands ranging from 285 nm to 717 nm were obtained. With excitation at UV and visible plasmon resonance wavelength (325 nm, 633 nm), the experimental SERS enhancement factor (EF) reached 103 and relative standard deviation (RSD) below 10% on a large scale. Finite-difference time-domain (FDTD) simulations reveal electric field intensity and charge distribution of dipolar and quadrupolar plasmon mode. The simple and controllable fabrication strategy and superior SERS performance in UV–visible range make the Al nanoparticle arrays promising candidates for SERS-based sensor applications. And the method provides a new approach for developing an inexpensive, efficient, and mass-produced Al-based SERS active substrate.

A smartphone-assisted ratiometric colorimetric and fluorescent probe for triple-mode determination of nitrite based on MnO2 nanoparticles and carbon quantum dots

A triple-mode colorimetric and fluorescent sensing scheme based on manganese dioxide nanoparticles (MnO2NPs) and carbon quantum dots (CQDs) were developed to determine nitrite. MnO2NPs can oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue oxidation product (TMBox), which is further oxidized into a yellow diimine derivative by nitrite. The ratio of absorbance at 652 nm to 452 nm was monitored as signal response for UV–vis detection mode. A “turn-off” CQDs fluorescence probe was also constructed for fluorescent detection mode. Smartphone tool kit was used to capture the color of sample for smartphone-based measurement. Various analytical performance under different detection modes were obtained and compared. The proposed methods were applied to food samples with satisfactory recoveries (83.3–106 %). The results were validated with AOAC standard spectrophotometric method. The current triple-mode detection were accurate, convenient, low-cost and fast for analyzing nitrite in foods and water samples on-site.

A fluorescent test paper fabricated by in situ growth of a functional Zn-MOG for fast and effective detection of Cr(VI) and Fe(III)

Heavy metals, like iron and chromium(Cr), have been proved to be a serious pollutant to environmental and biological systems. Long-term exposure to Cr(VI) ions through drinking water is harmful to human and will cause some serious diseases. Therefore, exploring new method for selective and rapid detection of such specific pollutants in water is crucial for environmental protection and human health. Herein, a novel functional metal organic gel(MOG) was successfully fabricated. Its detection limit of Cr(VI) was 2.4 × 10−8 mol·L−1 in aqueous solution, and 1.2 × 10−6 mol·L−1 for Fe(III) Based on the excellent deformability of MOG materials, a fluorescent test paper which could realize visible detection of Cr(VI) was fabricated by the in situ growth of Zn-MOGs onto the filter paper. To the best of our knowledge, it is the first sample of Zn-MOGs Based Test Paper (Zn-MOGs-FP) fabricated by in situ growth.

A flexible and stretchable photonic crystal film with sensitive structural color-changing properties for spoiled milk detection.

This study proposes a flexible and stretchable 3D polymer film with photonic crystals for the visible detection of spoiled milk. Thermoplastic polyurethane (TPU) was used as the substrate for the photonic crystal structure. The back barrier layer with a regular array of nanohemispheres of anodic aluminum oxide film was used as a template for electroforming a nickel mold. The nanohemisphere array was then nanoimprinted onto the TPU substrate to form a strain-controllable photonic crystal (SCPC) structure on it. Food spoilage can be easily detected by the structural color change caused by the gas it produces. Experimental results confirmed that the structural color change of the fabricated SCPC TPU film occurred when the elongation (ΔL) of the film reached 0.2mm (1.2%). Furthermore, spoiled milk detection experiments showed that the proposed SCPC TPU film is a highly intelligent and cost-effective biosensor for detecting spoiled food in a container.

Effect of purple sugarcane peel extracts on properties of films based on lemon peel waste pectin and the application in the visible detection of food freshness

In this work, the effect of purple sugarcane (Saccharum officinarum) peel anthocyanin extracts (PSPAEs) on the physical and functional properties of films based on lemon peel waste pectin (LPP) was investigated for the first time. PSPAEs have great compatibility with LPP matrix, and the LPP/PSPAEs composite film demonstrated a higher ultraviolet light barrier capacity. The incorporation of PSPAEs significantly improved the physical properties of LPP films confirmed by the enhanced mechanical properties and thermal stability, which might be associated with the more compact structure observed by scanning electron microscope images and possible intermolecular interaction such as hydrogen bond interactions between film components demonstrated via Fourier transform infrared spectra and X-ray diffraction analysis. Furthermore, PSPAEs imparted excellent functional properties on LPP films, including antioxidant properties and sensitive color response to the pH alternation and ammonia atmosphere, which favored the possible application in monitoring food freshness. Herein, LPP/PSPAEs films were employed to detect the freshness of shrimp and beef, and a visually discernible color change could be observed as the food turned from fresh to stale. In addition, the LPP/PSPAEs composite films displayed great biodegradability in the soil. The results showed that could impart excellent properties on LPP films, and LPP/PSPAEs composite film is a promising biodegradable film that can be used for intelligent detection of food freshness.

Visual Detection of Biomolecules Using Concentration Dependent Induced Aggregation of Plasmonic Gold Nanoparticles

Significant advancement has occurred in the detection methods of solution-based analytes. High-pressure liquid chromatography, gas chromatography, and other systems used for analyses are quite expensive. Therefore, there is a need for new methods and for the visible detection of analytes. Here, we demonstrate that 3-aminopropyl triethoxysilane (APTES) could impact the stability, optical, and morphology of gold nanoparticles (AuNps) in a colloidal solution. These impacts can be used to create a sensitive visual detection system. The strong impact of the APTES concentration on the ultraviolet–visible absorption spectra of the solutions is illustrated, which displays systematic and extensive red shifts. The presence of denatured proteins within a therapeutic drug product can induce a series of adverse effects. This report describes a fast, low cost, sensitive, and user-friendly platform where the plasmonic nanoparticles create visual biosensing of denatured proteins. Artificially heat stressed ferritin, glutathione, and insulin coupled to AuNps are exposed to ATES and upon denaturation of the protein or peptide, systematic blue or red shifts are observed in the absorbance spectra of the AuNps/biomolecules, and aminosilane solution. This serves as a proof-of-concept for a fast in-solution detection method for heat-stressed proteins or peptides.

Sensitive detection of acetaminophen in body fluids, pharmaceuticals and herbal medicines at un-doped mesoporous carbon nitride film electrode

Electrochemical sensing of acetaminophen (ACT) was made using un-doped mesoporous (average pore size 33.2 nm) carbon nitride (mGCN) modified glassy carbon electrode (GCE) in physiological buffer (PBS, pH 7.4). GCN was prepared by pyrolysis of agriculture urea precursor and characterized using XRD, UV–visible, FTIR, XPS and HRTEM techniques and observed 3D mesoporous structure. The electrochemical methods CV, EIS, and DPV were employed to explore the behaviour of mesoporous carbon nitride thin film modified electrode and its acetaminophen electrochemical sensing. The sensor showed a linear range from 0.1 to 1400 µM with sensitivity and limit of detection 0.0180 mA cm−2 mM−1 and 93.22 nM. Practical electrochemical sensing of ACT was demonstrated using unprocessed pharmaceutical tablet, body fluids (urine, blood serum), and herbal (ayurvedic Ocimumtenuifrum and Coleus amboinicus plants) samples. These electrochemical data were very well corroborated with results obtained from UV–Visible detection.

Pre-Folded G-Quadruplex as a Tunable Reporter to Facilitate CRISPR/Cas12a-Based Visual Nucleic Acid Diagnosis.

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a-based detection strategies with a fluorophore quencher-labeled ssDNA reporter or gold nanoparticle ssDNA reporter have been widely used in point-of-care (POC) molecular diagnostics. However, the potential of these CRISPR/Cas12a strategies for POC molecular diagnostics is often compromised due to the complex labeling, high cost, and low signal-to-noise ratio. Herein, we show a pre-folded G-quadruplex (G4) structure with tunable tolerance to CRISPR/Cas12a trans-cleavage and explore its mechanism. Two G4 structures (i.e., Tel22-10 and G16C) sensitive or tolerant to CRISPR/Cas12a trans-cleavage are designed and used as signal elements to fabricate a label-free visible fluorescent strategy or "signal-on" colorimetric strategy, respectively. These two strategies facilitate an ultrasensitive visual nucleic acid determination of Group B Streptococci with a naked-eye limit of detection of 1 aM. The feasibility of the developed G4-assisted CRISPR/Cas12a strategies for real-world applications is demonstrated in clinical vaginal/anal specimens and further verified by a commercial qPCR assay. This work suggests that the proposed G4 structures with tunable tolerance can act as promising signal reporters in the CRISPR/Cas12a system to enable ultrasensitive visible nucleic acid detection.

VALIDATED RP-HPLC METHOD AND STABILITY STUDIES FOR SIMULTANEOUS ESTIMATION OF OFLOXACIN AND RACECADOTRIL IN BULK AND PHARMACEUTICAL FORMULATION

A simple, accurate and precise stability indicating method for simultaneous estimation of ofloxacin and racecadotril in bulk and marketed formulation was developed and validated by RP-HPLC. The chromatographic separation of this method was carried out by Waters X Bridge Stainless steel C18 column (250 mm × 4.6 mm, 5 μm) packed with ODS using methanol: acetonitrile and water (40:40:20 V/V/V) as mobile phase. The pH of the mobile phase was 2.7, adjusted by orthophosphoric acid. The flow rate of the instrument was set at 0.8 mL min-1 and wavelength of UV visible detector was set at 210 nm at room temperature. The method showed good linearity and the correlation coefficients of ofloxacin and racecadotril were found to be 0.9966 and 0.9991, respectively. The mean recovery values were calculated to be 99.1 and 100.03, respectively. This method could be applied successfully for the estimation of both the drugs in bulk and pharmaceutical formulation. The stress studies for this method were performed to confirm that the specificity and stability was achieved.

A light-responsive, highly sensitive probe to perceive mercuric ions in both water and biological samples using fluorescence, colorimetric & electrochemical techniques

Given the increasing levels of Hg2+ in the environment and ecosystem, a simple highly fluorescent, colorimetric, and electroactive probe based on benzothiazolinic salt was developed to monitor its presence in environmental and biological samples. An abrupt change in fluorescence signal in solid-state was also observed caused by Hg2+ ions. Cyclic voltammetry was successfully used to investigate the redox response of the probe for Hg2+ ions. Due to the superior colorimetric/fluorometric properties of the probe, a simple, cost-effective paper strip was developed aided by a smartphone to enable visible, quick, reliable, and practical detection of Hg2+ in environmental analysis. For the probe, a LOD value of 55 nM was witnessed for Hg2+ ions in water using the electrochemical method, while the colorimetric method aided by a smartphone yielded an 80 nM LOD value. The probe exhibited low cytotoxicity for Hg2+ detection in HeLa cells enhancing its potential application in biological and environmental science.

STD-Yolov5: a ship-type detection model based on improved Yolov5

ABSTRACT Ship visible images detection based on computer vision plays an important role in the field of intelligent ship. To increase the model speed, accuracy, and reduce the parameters of the model to facilitate the deployment on hardware devices in practical applications, this study proposed a new model named STD-Yolov5. Firstly, the attention mechanism module of ECA was embedded in backbone to enhance the feature extraction capability of the network. Secondly, GAFPN was designed to reduce the parameters and GFLOPs. Thirdly, to solve the problem of ship-type false detection and missing detection, this paper presented a new receptive field amplification module named GSPP. Finally, replaced the GIoU bounding box regression loss function with a simpler generalisation of α-GIoU to improve the accuracy of the model. Compared to Yolov5, the mAP@.5:.95 of STD-Yolov5 increased by 1.2%, the parameters decreased by 24.85%, and the GFLOPs decreased by 14.46%.

Ag/n–Si/p–MgSe/(Ag, C, Au, Pt) devices designed as current rectifiers, photodetectors and as ac signal filters suitable for VLC, IR and 6G technologies

Herein the fabrication and practical applications of MgSe thin films as active layer of electronic devices are reported. MgSe films are prepared by a vacuum evaporation technique onto Si substrates under a vacuum pressure of 10–5 mbar. The films are morphologically, structurally, electrically and opto-electronically investigated. Having identified the work function of MgSe as 6.74 eV, the role of Ag, C, Au and Pt metal contacts on the performance of the Si/MgSe (SM) diodes are studied. It is observed that high rectification ratios of ∼104 and 102 are achieved at an applied voltage of 3.0 V for the Ag/SM/C and Ag/SM/Ag diode structures, respectively. In addition, a current responsivity to visible and infrared light of ∼0.70 A W−1 is observed for the Ag/SM/Ag channels. The noise equivalent ratios, the external quantum efficiency and the detectivity of the Ag/SM/Ag diodes suit requirements of visible light and infrared communication detectors. Moreover, studies of the capacitance-voltage characteristics showed capacitor characteristics. The depleting of the Ag/SM/Ag capacitors is possible up to 50 MHz. Furthermore, analyzing the capacitance, resistance and cutoff frequency spectra have shown that the Ag/SM/Ag device channels can perform as negative resistance sources with cutoff frequency values that suits 6G technology requirements.

Deep learning-based dot and globule segmentation with pixel and blob-based metrics for evaluation

Deep learning (DL) applied to whole dermoscopic images has shown unprecedented accuracy in differentiating images of melanoma from benign lesions. We hypothesize that accuracy in whole-image deep learning suffers because whole lesion analysis lacks an evaluation of dermoscopic structures. DL also suffers a “black box” characterization because it offers only probabilities to the physician and no visible structures. We propose the detection of structures called dots and globules as a means to improve precision in melanoma detection. We compare two encoder-decoder architectures to detect dots and globules: UNET vs. UNET++. For each of these architectures, we compare three pipelines: with test-time augmentation (TTA), without TTA, and without TTA but with checkpoint ensembles. We use an SE-RESNEXT encoder and a symmetric decoder. The pixel-based F1-scores for globule and dot detection based on UNET++ and UNET techniques with checkpoint ensembles were found to be 0.632 and 0.628, respectively. The blob-based UNET++ and UNET F1-scores (50 percent inter-section) were 0.696 and 0.685, respectively. This agreement score is over twice the statistical correlation score measured among specialists. We propose UNET++ globule and dot detection as a technique that offers two potential advantages: increased diagnostic accuracy and visible structure detection to better explain DL results and mitigate deep learning's black-box problem. We present a public globule and dot database to aid progress in automatic detection of these structures.

“On Water” Effect for Green Click Reaction: Spontaneous Polymerization of Activated Alkyne with “Inert” Aromatic Amine in Aqueous Media

“On Water” Effect for Green Click Reaction: Spontaneous Polymerization of Activated Alkyne with “Inert” Aromatic Amine in Aqueous Media

Determination of Astaxanthin in Trout by High Performance Liquid Chromatography Coupled with Visible Detection

Background: Astaxanthin is widely and naturally distributed in marine animals including, crustaceans, such as shrimp, crabs, and fish, such as salmon and trout.
 Methods: A total of 20 trout samples were collected from local market and were analyzed for astaxanthin via HPLC-UV. Analyte extraction was done by water, methanol, dichloromethane, and acetonitrile 4.5:85:5:45.5, v/v/v/v.
 Results: Despite the optimal conditions, analytical property of the method containing lower limit of quantitation (2.00 ng g-1) and upper limit of quantitation (1000 ng g-1), linearity (r2=0.992), and recovery (103%) were acceptable. The results showed the range of 105 ± 0.09 - 875 ± 0.020 ng g-1.
 Conclusion: The method was successfully used to quantify the target analytes in all trout samples.

Ultra-low-power photodetector based on a high-photoresponse, plasmonic-effect-induced gateless quasi-freestanding graphene device

Large-area metal-graphene-metal UV–Visible photodetectors fabricated on quasifreestanding graphene (QFSG)/vicinal SiC (8° off-axis) wafers are applicable to future low-power consumption systems. They demonstrate effective photoresponse under 365 nm (UV) and 405 nm (Visible) light irradiation upon the application of a built-in electric field (self-biased) and ultra-low bias (−10 mV). Photocurrent gain and responsivity under UV–Visible light are more significant on QFSG/vicinal SiC than on epitaxial graphene (EG)/SiC(0 0 0 1) because of the freestanding nature of the topmost layer, absence of a buffer layer, and primary carrier scattering/trapping centers. Further, they are tuned by localized surface plasmon resonance using gold nanoparticles (AuNPs). In the self-power mode and low-bias mode in QFSG/vicinal SiC, the photocurrent is enhanced by 9-fold and 120-fold, respectively, compared to the photocurrent in EG/SiC(0 0 0 1). The responsivity of QFSG/vicinal SiC after AuNP treatment is ≈1.65 mA/W (at zero bias) and ≈20 mA/W (at −10 mV) under 365 nm light illumination (intensity = 18 mW/cm−2), significantly higher than that of EG/SiC (0 0 0 1). This device shows a similar trend of photoresponse under 405 nm light illumination. These results confirm that this QFSG/vicinal SiC combined with AuNPs possesses potential for application in UV–Visible detection with minimum power consumption.

New family of Type V eutectic solvents based on 1,10-phenanthroline and their application in metal extraction

Although a theoretically extensive number of hydrophobic eutectic mixtures suitable for solvent extraction are obtainable, to date reported mixtures rely on a limited number of chelating groups, namely phosphine oxide, carboxylic acid, and ketones. Herein, a new family of Type V Deep Eutectic Solvents (DES) based on the polypyridyl ligand 1,10-phenanthroline (phen) is presented with the aim of facilitating the extrapolation of the disclosed findings to other potential systems based on phen or bipyridine derivatives. The hydrophobic eutectic solvent composed of the natural phenolic extract thymol with phen exhibits a solid-liquid phase diagram with a useable liquidus compositional range on the thymol-rich side. The physical properties of the mixture are dependent on the presence of solutes liable to change the nature of the existing hydrogen-bonded network, most notably through the protonation of phen. The metal chelating ability of phen are retained when included as a DES component. Quantitative extraction of various transition metals cations (Cd(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)) as well as the platinum group metal Pd(II) was obtained across a range of solvent compositions. The extraction of Li(I), Mn(II), Co(II) and Ni(II) was further studied as a function of the aqueous phase pH, with the extent of metal partition decreasing with the protonation of phen at pH values below 1.0. Building upon the luminescent properties of phen, the eutectic solvent was further applied as a simultaneous pre-concentration and quantification medium for Fe(II/III), allowing for the facile UV–vis detection of Fe up to 12 μg L−1.

Programmable Photovoltaics of Metal‐Oxide‐Semiconductor Junction

AbstractProgrammability, fundamental to the computing of electronic systems, is traditionally achieved in processing and memory modules. Recently, the emergence of in‐sensor computing allows the programmability of the sensing modules and the process of raw data upon the sensor edge, which reduces data transport and energy consumption. Here, a programmable photodetector module with a tunable photoelectric response based on molybdenum sulfide (MoS2) metal‐oxide‐semiconductor (MOS) junction for visible detection is reported. The sensor takes advantage of the tunable band alignment at the MOS junction and generates an adjustable or even reversible out‐of‐plane photovoltaic effect with high efficiency. This work provides new device configurations to architect the programmability of the photodetectors, and pave the way toward in‐sensor computing at the application edge.

Biomimetic 3D Recognition with 2D Flexible Nanoarchitectures for Ultrasensitive and Visual Extracellular Vesicle Detection.

Despite increasing recognition of extracellular vesicles being important circulating biomarkers in disease diagnosis and prognosis, current strategies for extracellular vesicle detection remain limited due to the compromised sample purification and extensive labeling procedures in complex body fluids. Here, we developed a 2D magnetic platform that greatly improves capture efficiency and readily realizes visible signal conversion for extracellular vesicle detection. The technology, termed high-affinity recognition and visual extracellular vesicle testing (HARVEST), leverages 2D flexible Fe3O4-MoS2 nanostructures to recognize extracellular vesicles through multidentate affinity binding and feasible magnetic separation, thus enhancing the extracellular vesicle capture performance with both yield and separation time, affording high sensitivity with the detection limit of 20 extracellular vesicle particles/μL. Through integration with lipid labeling chemistry and the fluorescence visualization system, the platform enables rapid and visible detection. The number of extracellular vesicles can be feasibly determined by smart mobile phones, readily adapted for point-of-care diagnosis. When clinically evaluated, the strategy accurately differentiates melanoma samples from the normal cohort with an AUC of 0.98, demonstrating the efficient extracellular vesicle detection strategy with 2D flexible platforms for cancer diagnosis.