Glutathione­iron hybrid nanozyme-based colorimetric sensor for specific and stable detection of thiram pesticide on fruit juices.

Given the potential dangers of thiram to food safety, constructing a facile sensor is significantly critical. Herein, we presented a colorimetric sensor based on glutathione­iron hybrid (GSH-Fe) nanozyme for specific and stable detection of thiram. The GSH-Fe nanozyme exhibits good peroxidase-mimicking activity with comparable Michaelis constant (Km = 0.551 mM) to the natural enzyme. Thiram pesticides can specifically limit the catalytic activity of GSH-Fe nanozyme via surface passivation, causing the change of colorimetric signal. It is worth mentioning that the platform was used to prepare a portable hydrogel kit for rapid qualitative monitoring of thiram. Coupling with an image-processing algorithm, the colorimetric image of the hydrogel reactor is converted into the data information for accurate quantification of thiram with a detection limit of 0.3 µg mL-1. The sensing system has good selectivity and high stability, with recovery rates in fruit juice samples ranging from 92.4% to 106.9%.

A paper-based point-of-care device for the detection of cysteine using gold nanoparticles from whole blood.

We present a colorimetric probe based on polyvinylpyrrolidone-capped gold nanoparticles (PVP-AuNPs) that is sensitive and selective for cysteine (Cys). A microfluidic paper-based analytical device (µ-PAD) with embedded dried PVP-AuNPs at the polyethersulfone (PES) paper surface is used for Cys detection. When thiol molecules attach to PVP-AuNPs in the presence of Cys, they clump together, and this causes the solution's color to shift from red to blue within 5 minutes. The device is capable of detecting Cys levels between 1.0 µM and 50.0 µM with a limit of detection (LOD) of 0.2 µM under optimized conditions. The stability of the µ-PAD was tested for 100 days, demonstrating re-dispersibility to detect Cys levels in blood. Dried PVP-AuNP-µPADs were integrated with blood plasma separation modules for point-of-care (POC) Cys detection. Consequently, the device shows potential as a self-sustaining, quantification platform with a recovery percentage ranging from 98.44 to 111.9 in clinical samples.

Detection of Maize Mold Based on a Nanocomposite Colorimetric Sensor Array under Different Substrates.

This study developed a novel nanocomposite colorimetric sensor array (CSA) to distinguish between fresh and moldy maize. First, the headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC/MS) method was used to analyze volatile organic compounds (VOCs) in fresh and moldy maize samples. Then, principal component analysis and orthogonal partial least-squares discriminant analysis (OPLS-DA) were used to identify 2-methylbutyric acid and undecane as key VOCs associated with moldy maize. Furthermore, colorimetric sensitive dyes modified with different nanoparticles were employed to enhance the dye properties used in the nanocomposite CSA analysis of key VOCs. This study focused on synthesizing four types of nanoparticles: polystyrene acrylic (PSA), porous silica nanospheres (PSNs), zeolitic imidazolate framework-8 (ZIF-8), and ZIF-8 after etching. Additionally, three types of substrates, qualitative filter paper, polyvinylidene fluoride film, and thin-layer chromatography silica gel, were comparatively used to fabricate nanocomposite CSA combining with linear discriminant analysis (LDA) and K-nearest neighbor (KNN) models for real sample detection. All moldy maize samples were correctly identified and prepared to characterize the properties of the CSA. Through initial testing and nanoenhancement of the chosen dyes, four nanocomposite colorimetric sensitive dyes were confirmed. The accuracy rates for LDA and KNN models in this study reached 100%. This work shows great potential for grain quality control using CSA methods.

Asymmetrically split DNAzyme-based colorimetric and electrochemical dual-modal biosensor for detection of breast cancer exosomal surface proteins.

Exosomal surface proteins are potentially useful for breast cancer diagnosis and awareness of risk. However, some detection techniques involving complex operations and expensive instrumentation are limited to advance to clinical applications. To solve this problem, we develop a dual-modal sensor combining naked-eye detection and electrochemical assay of exosomal surface proteins from breast cancer. Most of existing sensors rely on aptamers recognizing exosomes and generating amplified signals at the same time, which require well-designed aptamer probes to avoid difficulties in identifying exosomes. In our work, aptamers not bound by the exosomes can serve as complete templates to induce formation of G quadruplexes. The peroxidase activity of the G-quadruplex/hemin DNAzyme catalyze substrates can generate both color and electrochemical signals. The developed dual-modal sensor offers a remarkable capability to differentiate nonmetastatic, metastatic breast cancer patients, and healthy individuals through the analysis of exosomal surface proteins. The sensor's distinctive features, including its universality, simplicity, and cost-effectiveness, position it as a promising diagnostic tool in breast cancer research and clinical practice.

Colorimetric histology using plasmonically active microscope slides.

The human eye can distinguish as many as 10,000 different colours but is far less sensitive to variations in intensity1, meaning that colour is highly desirable when interpreting images. However, most biological samples are essentially transparent, and nearly invisible when viewed using a standard optical microscope2. It is therefore highly desirable to be able to produce coloured images without needing to add any stains or dyes, which can alter the sample properties. Here we demonstrate that colorimetric histology images can be generated using full-sized plasmonically active microscope slides. These slides translate subtle changes in the dielectric constant into striking colour contrast when samples are placed upon them. We demonstrate the biomedical potential of this technique, which we term histoplasmonics, by distinguishing neoplastic cells from normal breast epithelium during the earliest stages of tumorigenesis in the mouse MMTV-PyMT mammary tumour model. We then apply this method to human diagnostic tissue and validate its utility in distinguishing normal epithelium, usual ductal hyperplasia, and early-stage breast cancer (ductal carcinoma in situ). The colorimetric output of the image pixels is compared to conventional histopathology. The results we report here support the hypothesis that histoplasmonics can be used as a novel alternative or adjunct to general staining. The widespread availability of this technique and its incorporation into standard laboratory workflows may prove transformative for applications extending well beyond tissue diagnostics. This work also highlights opportunities for improvements to digital pathology that have yet to be explored.

A functional peptide-mediated colorimetric assay for mercury ion based on dual-modified gold nanoparticles.

In the work, a rapid and accurate biosensor for mercury ions (Hg2+) was constructed, with which aggregation of dual-modified (DGPFHR- and CALNN-) gold nanoparticles (D/C-AuNPs) could be triggered by the high specificity of peptides to Hg2+. The given peptide DGPFHR possesses great capability of capturing Hg2+, accompanied by the conformational folding. Under the circumstances, D/C-AuNPs were employed as the detection probes to accomplish the quantitative analysis of Hg2+. This is primarily because the specific Hg2+-induced folding of peptides reduces the electrostatic repulsion and steric hindrance, thus accelerating the AuNPs aggregation. The principle and application potential of this proposal was proved by evidence. And the results demonstrated that Hg2+ ions could be selectively detected as low as 28 nM with a linear range of 100-800 nM. In consideration of superior simplicity, selectivity, accuracy and stability, the protocol was advantageous over other projects in practical measurement of various water samples.

Reversible Ratiometric NADH Sensing Using Semiconducting Polymer Dots.

Reduced nicotinamide adenine dinucleotide (NADH) is a key coenzyme in living cells due to its role as an electron carrier in redox reactions, and its concentration is an important indicator of cell metabolic state. Abnormal NADH levels are associated with age-related metabolic diseases and neurodegenerative disorders, creating a demand for a simple, rapid analytical method for point-of-care NADH sensing. Here we develop a series of NADH-sensitive semiconducting polymer dots (Pdots) as nanoprobes for NADH measurement, and test their performance in vitro and in vivo. NADH sensing is based on electron transfer from semiconducting polymer chains in the Pdot to NADH upon UV excitation, quenching Pdot fluorescence emission. In polyfluorene-based Pdots, this mechanism resulted in an on-off NADH sensor; in DPA-CNPPV Pdots, UV excitation resulted in NADH-sensitive emission at two wavelengths, enabling ratiometric detection. Ratiometric NADH detection using DPA-CNPPV Pdots exhibits high sensitivity (3.1 µM limit of detection), excellent selectivity versus other analytes, reversibility, and a fast response (less than 5 s). We demonstrate applications of the ratiometric NADH-sensing Pdots including smartphone-based NADH imaging for point-of-care use.

A microfluidic colorimetric biosensor for in-field detection of Salmonella in fresh-cut vegetables using thiolated polystyrene microspheres, hose-based microvalve and smartphone imaging APP.

A microfluidic colorimetric biosensor was developed using thiolated polystyrene microspheres (SH-PSs) for aggregating of gold nanoparticles (AuNPs), a novel hose-based microvalve for controlling the flow direction, and a smartphone imaging APP for monitoring colorimetric signals. Aptamer-PS-cysteamine conjugates were used as detection probes and reacted with Salmonella in samples. Complementary DNA - magnetic nanoparticle (cDNA - MNP) conjugates were used as capture probes, reacted with the free aptamer-PS-cysteamine conjugates. AuNPs were aggregated on the surface of Salmonella-aptamer-PS-cysteamine conjugates, resulting in a visible color change in the detection chamber, which indicating different concentrations of Salmonella. The limit of detection was low to 6.0 × 101 cfu/mL. The microfluidic biosensor exhibited a good specificity. It was evaluated by analyzing salad samples spiked with Salmonella. The recoveries ranged from 91.68% to 113.76%, which indicated its potential application in real samples.

Laser engraved microapillary pump paper-based microfluidic device for colorimetric and electrochemical detection of salivary thiocyanate.

A microcapillary grooved paper-based analytical device capable of dual-mode sensing (colorimetric and electrochemical detection) was demonstrated for analysis of viscous samples (e.g., human saliva). Herein, a hollow capillary channel was constructed via laser engraved micropatterning functions as a micropump to facilitate viscous fluidic transport, which would otherwise impede analysis on paper devices. Using salivary thiocyanate as a model analyte, the proposed device was found to exhibit a promising sensing ability on paper devices without the need for sample pretreatment or bulky instrumentation, as normally required in conventional methods used for saliva analysis. An extensive linear dynamic range covering detection of salivary thiocyanate for both high and trace level regimes (5 orders of magnitude working range) was collectively achieved using the dual-sensing modes. Under optimal conditions, the limit of detection was 6 µmol L-1 with a RSD of less than 5%. An excellent stability for the µpumpPAD was also observed for over 30 days. Real sample analysis using the proposed device was found to be in line with the standard chromatographic method. Benefitting from simple fabrication and operation, portability, disposability, low sample volume (20 µL), and low cost (< 1 USD), the µpumpPAD is an exceptional alternative tool for the detection of various biomarkers in saliva specimens.

Smartphone digital image colorimetry combined with solidification of floating organic drop-dispersive liquid-liquid microextraction for the determination of iodate in table salt.

Smartphone digital image colorimetry (SDIC), combined with solidification of floating organic drop-dispersive liquid-liquid microextraction (SFOD-DLLME), was proposed for the determination of iodate ions. A colorimetric box was designed to capture images of sample solutions. Factors affecting the efficiency of SDIC included type of phone, region of interest, position of camera, and distance between camera and sample solution. Optimum SFOD-DLLME conditions were achieved with 1-undecanol (500 µL) as the extraction solvent, ethanol (1.5 mL) as the disperser solvent within 20 s extraction time. Limit of detection (LOD) was found as 0.1 µM (0.2 µg g-1) and enrichment factors ranged between 17.4 and 25.0. Calibration graphs showed good linearity with coefficients of determination higher than 0.9954 and relative standard deviations lower than 5.6%. The proposed method was efficiently applied to determine iodate in table salt samples with percentage relative recoveries ranging between 89.3 and 109.3%.

Identification of Chinese teas by a colorimetric sensor array based on tea polyphenol induced indicator displacement assay.

In this work, we developed an optical colorimetric sensor array for the discrimination of Chinese teas. The sensor array was carefully designed based on tea polyphenol induced indicators displacement assay (IDA), using phenylboronic acids with different substituents as the receptors to polyphenols. The accurate identification for polyphenols with different species or concentrations proved the potential of the sensor array. The sensor array successfully distinguished tea samples within different categories, grades and origins, coupling with PLS-DA. This work offered an efficient and rapid method to distinguish teas and tea-related products. Besides, the assay is supposed to be suitable for the identification of other polyphenol-related natural products.

Fast, Precise, and Reliable Multiplex Detection of Potato Viruses by Loop-Mediated Isothermal Amplification.

Potato is an important staple food crop in both developed and developing countries. However, potato plants are susceptible to several economically important viruses that reduce yields by up to 50% and affect tuber quality. One of the major threats is corky ringspot, which is a tuber necrosis caused by tobacco rattle virus (TRV). The appearance of corky ringspot symptoms on tubers prior to commercialization results in ≈ 45% of the tubers being downgraded in quality and value, while ≈ 55% are declared unsaleable. To improve current disease management practices, we have developed simple diagnostic methods for the reliable detection of TRV without RNA purification, involving minimalized sample handling (mini), subsequent improved colorimetric loop-mediated isothermal amplification (LAMP), and final verification by lateral-flow dipstick (LFD) analysis. Having optimized the mini-LAMP-LFD approach for the sensitive and specific detection of TRV, we confirmed the reliability and robustness of this approach by the simultaneous detection of TRV and other harmful viruses in duplex LAMP reactions. Therefore, our new approach offers breeders, producers, and farmers an inexpensive and efficient new platform for disease management in potato breeding and cultivation.

Colorimetric and fluorescent dual-identification of glutathione based on its inhibition on the 3D ball-flower shaped Cu-hemin-MOF's peroxidase-like activity.

Hemin as the organic linker ligand and Cu (II) as the metal center were applied to prepare a copper-metal-organic framework (Cu-hemin-MOF) via one-step hydrothermal method. Characterization using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) demonstrate that the acquired Cu-hemin-MOF possesses the appearance of 3D ball-flower shape with the existence of C, N, O, Fe, and Cu on the surface. Further study found that this 3D ball-flower shaped Cu-hemin-MOF exhibits peroxidase-like activity, which can catalyze the peroxidase substrate of o-phenylenediamine (OPD) to generate 2,3-diaminophenazine (DAP) in the presence of H2O2. DAP has a yellow color and also emits a strong fluorescence when excited by ultraviolet light. Interestingly, Cu-hemin-MOF's peroxidase-like activity can be strongly inhibited by glutathione (GSH). In view of this, a dual readout (fluorescence and colorimetry) was proposed to detect GSH for the first time. Under optimal conditions, the proposed method exhibits good linear relationship between the signal response (fluorescence and colorimetry) and the concentration of GSH, and low limits of detection (LOD) of 2.3 and 26.6 nM, respectively.Graphical abstract.

A paper-based colorimetric sensor array for discrimination and simultaneous determination of organophosphate and carbamate pesticides in tap water, apple juice, and rice.

A colorimetric paper-based sensor is proposed for the rapid monitoring of six major organophosphate and carbamate pesticides. The assay was constructed by dropping gold and silver nanoparticles on the hydrophilic zones of a paper substrate. The nanoparticles were modified by L-arginine, quercetin, and polyglutamic acid. The mechanism of sensing is based on the interaction between the pesticide and the nanoparticles. The color of nanoparticles changed during the interactions. A digital camera recorded these changes. The assay provided a unique response for each studied pesticide. This method can determine six individual pesticides including carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos. The limit of detection for these pesticides were 29.0, 22.0, 32.0, 17.0, 45.0, and 36.0 ng mL-1, respectively. The assay was applied to simultaneously determine the six studied pesticides in a mixture using the partial least square method (PLS). The root mean square errors of prediction were 11, 8.7, 9.2, 10, 12, and 11 for carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos, respectively. The paper-based device can differentiate two types of studied pesticide (organophosphate and carbamate) as well as two types of organophosphate structures (oxon and thion). Furthermore, this sensor showed high selectivity to the pesticides in the presence of other potential species (e.g., metal ions, anions, amino acids, sugar, and vitamins). This assay is capable of determining the pesticide compounds in tap water, apple juice, and rice samples.Graphical abstract.

Distance-based quantification of miRNA-21 by the coffee-ring effect using paper devices.

Enabled by the coffee-ring effect, a paper-based signal transduce method is employed for catalytic hairpin assembly (CHA) amplification and hybridization chain reaction (HCR) to achieve miRNA quantification. Once the target miRNAs appeared, it was circularly used by CHA to initiate HCR amplification to produce a large number of G-quadruplex, which is combined with hemin to form a hemin/G-quadruplex DNAzyme. The DNAzyme catalyzes a colorimetric reaction to produce colored nanoparticles, which were converted to the end edge of the paper by evaporation-driven flow, forming a visible colored band. Higher concentration of miRNA led to more colored nanoparticles and thus a longer colored band that can simply be measured by a ruler. The results of determination of miRNA in samples demonstrate that the relative standard deviation of the proposed approach is 5.2%, highly sensitive and repeatable, with a working range 1.0 to 1000 pM and a LOD of 0.2 pM. The paper-based analytical device as a novel platform offers a new signal transduce pathway toward the detection of low-abundance biomarkers for diagnosis.Graphical abstract Schematic representation of the principle for quantification of miRNA on paper based on the coffee-ring effect.

Oxidase-mimicking activity of ultrathin MnO2 nanosheets in a colorimetric assay of chlorothalonil in food samples.

Chlorothalonil is a class of 2B carcinogen which is widely used in the prevention and treatment of fungal diseases in food samples. Its residual problem has been increasingly concerned by society. In this paper, a fast and simple colorimetric assay based on Manganese dioxide nanosheets (MnO2 NSs)-oxidize 3,3',5,5'-tetramethylbenzidine (TMB) platform was used to detect residual pesticide chlorothalonil in food samples. Under optimal conditions, the half maximal inhibitory concentration and the limit of detection of chlorothalonil were 3.27 and 0.024 ng/mL. There were no obvious cross-reactivity between chlorothalonil and interference substances. The recoveries shown the satisfactory results. The results of colorimetric assay for the authentic samples were largely consistent with gas chromatography. Therefore, the proposed method would be convenient and satisfactory analytical methods for the monitoring of chlorothalonil. Furthermore, the MnO2 - TMB system was used to produce test strips for quick and convenient visual detection of chlorothalonil with good performance.

A portable microfluidic device-based Fe3O4-urease nanoprobe-enhanced colorimetric sensor for the detection of heavy metals in fish tissue.

A portable microfluidic device with highly sensitive enzyme nanoprobe (Fe3O4 MNPs-urease, average size 34.6 nm) was demonstrated for the analysis of heavy metals ions (Hg2+, Cd2+ and Pb2+) in fish gill and muscle tissue. The immobilized urease nanoprobe (Km = 0.05 mM) exhibited twofold sensitivity over the free enzyme assay (apparent Km = 0.1 mM). The nanoprobe was characterized using SEM, EDAX, PSA and FT-IR. The inhibition measurements were carried out for individual as well as the mixture of metal ions (CRM standards of 9 elements (CRMmix-9)). The lower limit of quantification (LOQ) (0.5, 0.1, and 0.1 ng L-1 for Hg2+, Cd2+, and Pb2+) and lower limit of detection (LOD) was achieved at 0.1 ng L-1 with sensitivity 8-14% per decade for Hg2+, Cd2+, and Pb2+ ions. A visual result can be observed by the naked eye through the microfluidic device as well as with 96 transparent microwell plates. The order of relative inhibition was found to be CRMmix-9 > (Hg2+ + Cd2+ + Pb2+) > (Cd2+ + Pb2+) > (Pb2+ + Hg2+) > (Hg2+ + Cd2+) > Pb2+ > Cd2+ > Hg2+, respectively. The recovery % in fish tissues were found to be 88-98% for Hg2+, Cd2+ and Pb2+ ions.

Colorimetric determination of cysteine by a paper-based assay system using aspartic acid modified gold nanoparticles.

A method is described for cysteine (Cys) determination on paper-based analytical devices using aspartic acid modified gold nanoparticles (Asp-AuNPs). The Asp-AuNPs were characterized by their size, zeta potential, and UV-visible absorption spectrum. After the addition of Cys, it will interact with Asp-AuNPs selectively and leads to the aggregation of Asp-AuNPs. A color change from red to blue can be observed on the paper-based analytical devices. The results were recorded using a cell phone and subsequently analyzed using the Photoshop software. The ratiometric color intensity at red channel and blue channel (Red/Blue) increased linearly in the range 99.9-998.7 µM for Cys (R = 0.9984), and the limit of detection was 1.0 µM. The effects of assay conditions have been investigated and are discussed. The Cys concentration was determined as (0.27 ± 0.02 mM) in human plasma, and the recovery was from 99.2 to 101.1%. Graphical abstract Schematic representation of the paper-based assay system using aspartic acid modified gold nanoparticles (Asp-AuNPs). The ratiometric color intensity method was used for the cysteine (Cys) determination.

Plasmonic gel nanocomposites for detection of high energy electrons.

Radiation therapy is a common treatment modality employed in the treatment of cancer. High energy photons are the primary source of radiation but when administered, they leave an exit dose resulting in radiation damage to the adjacent healthy tissues. To overcome this, high energy electrons are employed in cases of skin cancer to minimize radiation induced toxicity. Despite these advances, measurement of delivered radiation remains a challenge due to limitations with existing dosimeters including labor intensive fabrication, complex read-out techniques and post-irradiation instability. To overcome these limitations, we have developed a novel colorimetric plasmonic gel nanocomposite for the detection of therapeutic levels of radiation delivered in electron beam therapy. The plasmonic nanocomposite consists of an agarose gel matrix encapsulating precursor gold ions, which are reduced to gold nanoparticles as a result of exposure to high energy electrons. The formation of gold nanoparticles renders a change in color to the agarose matrix, resulting in the formation of plasmonic gel nanocomposites. The intensity of the color formed exhibits a linear relation with the delivered electron dose, which can be quantified using absorbance spectroscopy. The plasmonic gel nanocomposites were able to detect doses employed in fractionated electron therapy, including in an anthropomorphic phantom used for planning radiation treatments in the clinic. Furthermore, the use of glutathione as a quenching agent facilitated qualitative and quantitative spatial mapping of the delivered dose. Our results indicate that the ease of fabrication, simplicity of detection and quantification using absorbance spectroscopy, determination of spatial dose profiles, and relatively low cost make the plasmonic gel nanocomposite technology attractive for detecting electron doses in the clinic.

Dual-Color Plasmonic Nanosensor for Radiation Dosimetry.

Radiation dosimeters are critical for accurately assessing the levels of radiation exposure of tumor sites and surrounding tissues and for optimizing therapeutic interventions as well as for monitoring environmental exposure. To fill the need for a simple, user-friendly, and inexpensive dosimeter, we designed an innovative colorimetric nanosensor-based assay for detecting ionizing radiation. We show that hydroxyl radicals generated by ionizing radiation can be used to etch gold nanorods (AuNRs) and silver nanoprisms (AgNPRs), yielding reproducible color changes for radiation dose detection in the range of 50-2000 rad, broad enough to cover doses used in hyperfractionated, conventional, and hypofractionated radiotherapy. This range of doses detected by this assay correlates with radiation-induced DNA damage response in mammalian cells. Furthermore, this AuNR- and AgNPR-based sensing platform has been established in a paper format that can be readily adopted for a wide range of applications and translation.