Colorimetric Platform Research Articles

Covalent organic framework-loaded silver nanoparticles as robust mimetic oxidase for highly sensitive and selective colorimetric detection of mercury in blood.

Covalent organic frameworks (COFs) were fabricated with a hierarchical flower-like hollow structure, possessing a large specific surface area, high porosity, and excellent environmental stability. In situ growth of noble silver nanoparticles (AgNPs) onto COFs was conducted yielding COF-Ag nanozymes. The structural advantages of COFs can ensure the uniform dispersion and effective size control of AgNPs. More interestingly, the oxidase-like catalytic activity of the obtained COF-Ag nanozymes could be enhanced in the presence of Hg2+ ions, which could specifically interact with AgNPs to form Ag-Hg alloys. A COF-Ag catalysis-based colorimetric platform was thereby constructed for highly selective and sensitive analysis of Hg2+ ions, showing a linear concentration range from 0.050 to 10.0 μM, with a limit of detection of about 3.7 nM. Besides, the developed colorimetric strategy was successfully applied for detecting Hg2+ ions in human blood with favorable detection recoveries, indicating its potential for applications in the biomedical analysis, environmental monitoring, and food safety fields.

A colorimetric sensing platform for the determination of H2O2 using 2D-1D MoS2-CNT nanozymes.

A novel colorimetric platform based on nano-composites of two-dimensional (2D) molybdenum disulfide nanosheets (MoS2 NSs) and one-dimensional (1D) carbon nanotubes (CNTs), called 2D-1D MoS2-CNT nanozyme, was fabricated for the selective and sensitive determination of hydrogen peroxide (H2O2) in soda water. The MoS2-CNT nanozyme was synthesized through a one-step solvothermal reduction method. The introduced CNTs could effectively prevent the stacking of MoS2 nanosheets (NSs) and not only expanded the interlayer distance of MoS2 NSs from 0.620 nm to 0.710 nm but also improved their specific surface. Under acidic conditions, the as-prepared 2D-1D MoS2-CNT nanozymes could oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue-oxidized TMB (oxTMB) in the presence of H2O2, resulting in enhanced peroxidase-like (POD-like) activity. The kinetic study showed that MoS2-CNT nanozyme had stronger catalytic activity than natural horseradish peroxidase (HRP). The linear range for H2O2 colorimetric determination was 5.00-500 μmol L-1 with a limit of detection (LOD) of 1.40 μmol L-1. Furthermore, the established determination method was applied to actual samples and the recoveries of H2O2 spiked in soda water were in the range of 92.3-107%, showing feasibility for the analysis of food.

Simple smartphone merged rapid colorimetric platform for the environmental monitoring of toxic sulfide ions by cysteine functionalized silver nanoparticles

Herein, we have proposed a new, highly specific and simple colorimetric assay for the chemosensing of sulfide ions (S2−) in environmental water samples, by using cysteine-functionalized colloidal silver nanoparticles (Cys-AgNPs). As prepared Cys-AgNPs and their interface with S2− ions were demonstrated using absorption, high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS) and Zeta potential measurements. The colour of Cys-AgNPs altered from vivid-yellow to colourless in two minutes after the mixing of S2− ions, resulting the suppression of surface plasmon resonance (SPR) band. The relative absorption intensity was inversely proportional to the concentrations of S2− ions in the ranges from 4 × 10−7 mol dm−3 to 48 × 10−7 mol dm−3 and lowest detection limit was computed as 28 × 10−9 mol dm−3. Furthermore, the current tactic illustrates a highly specific towards S2− ions over fifteen other potentially interfering inorganic anions investigated. Furthermore, visually measurable colour changes of Cys-AgNPs have been well incorporated with a RGB colour value of smartphone to construct it consistent indicator for immediate testing of S2− ions with the limit of detection attributable to 90 × 10−9 mol dm−3. An analytical practicability of the present approaches were (colorimetric and RGB colour value based tactics) applied for the chemosensing of S2− ions in real samples including drinking, tap and sea water samples with reasonable recoveries (90.1–101.4%). Finally, the current colorimetric method is rapid, very simple, very sensitive with highly specific and this effortless nanosensor was practicable for environmental screening of toxic S2− ions.

Facile immobilization of glucose oxidase with Cu3(PO4)2·3H2O for glucose biosensing via smartphone

A smartphone-based colorimetric platform for facile glucose detection was constructed below. First, glucose oxidase-Cu3(PO4)2·3H2O hybrid microflowers (GOx-HMFs) were facilely synthesized via biomineralization, which can react with glucose and 3,3′,5,5′-tetramethylbenzidine to generate colored product. Next, the color information of product was real-time collected and processed via smartphone to realize accurate glucose detection. The as-constructed colorimetric platform based on GOx-HMFs and smartphone had wide linear range, high sensitivity and good selectivity for glucose detection, moreover, the detection process was convenient and efficient, which provided a new idea for glucose detection.

Portable on-chip colorimetric biosensing platform integrated with a smartphone for label/PCR-free detection of Cryptosporidium RNA

Cryptosporidium, a protozoan pathogen, is a leading threat to public health and the economy. Herein, we report the development of a portable, colorimetric biosensing platform for the sensitive, selective and label/PCR-free detection of Cryptosporidium RNA using oligonucleotides modified gold nanoparticles (AuNPs). A pair of specific thiolated oligonucleotides, complementary to adjacent sequences on Cryptosporidium RNA, were attached to AuNPs. The need for expensive laboratory-based equipment was eliminated by performing the colorimetric assay on a micro-fabricated chip in a 3D-printed holder assembly. A smartphone camera was used to capture an image of the color change for quantitative analysis. The detection was based on the aggregation of the gold nanoparticles due to the hybridization between the complementary Cryptosporidium RNA and the oligonucleotides immobilized on the AuNPs surface. In the complementary RNA’s presence, a distinctive color change of the AuNPs (from red to blue) was observed by the naked eye. However, in the presence of non-complementary RNA, no color change was observed. The sensing platform showed wide linear responses between 5 and 100 µM with a low detection limit of 5 µM of Cryptosporidium RNA. Additionally, the sensor developed here can provide information about different Cryptosporidium species present in water resources. This cost-effective, easy-to-use, portable and smartphone integrated on-chip colorimetric biosensor has great potential to be used for real-time and portable POC pathogen monitoring and molecular diagnostics.

Smartphone-Based Device for Colorimetric Detection of MicroRNA Biomarkers Using Nanoparticle-Based Assay

The detection of microRNAs (miRNAs) is emerging as a clinically important tool for the non-invasive detection of a wide variety of diseases ranging from cancers and cardiovascular illnesses to infectious diseases. Over the years, miRNA detection schemes have become accessible to clinicians, but they still require sophisticated and bulky laboratory equipment and trained personnel to operate. The exceptional computing ability and ease of use of modern smartphones coupled with fieldable optical detection technologies can provide a useful and portable alternative to these laboratory systems. Herein, we present the development of a smartphone-based device called Krometriks, which is capable of simple and rapid colorimetric detection of microRNA (miRNAs) using a nanoparticle-based assay. The device consists of a smartphone, a 3D printed accessory, and a custom-built dedicated mobile app. We illustrate the utility of Krometriks for the detection of an important miRNA disease biomarker, miR-21, using a nanoplasmonics-based assay developed by our group. We show that Krometriks can detect miRNA down to nanomolar concentrations with detection results comparable to a laboratory-based benchtop spectrophotometer. With slight changes to the accessory design, Krometriks can be made compatible with different types of smartphone models and specifications. Thus, the Krometriks device offers a practical colorimetric platform that has the potential to provide accessible and affordable miRNA diagnostics for point-of-care and field applications in low-resource settings.

Si doping and perylene diimide modification contributed to enhancement of peroxidase-like activity of ceria for constructing colorimetric sensing platform of hydroquinone

Exploring nanoenzymes with higher peroxidase-like activity is an important task to construct a fast sensing platform. In this work, Si doping together with organic functional molecule, N, N-dicarboxymethyl Perylene-diimide (PDI) modification were employed as effective strategies to promote the peroxidase-like activity of ceria nanoenzymes. Compared with pure CeO2 and Si-CeO2, PDI/Si-CeO2 exhibits the highest peroxidase-like activity together with oxidase-like activity. The catalytic activity of PDI/Si-CeO2 remained more than 90% of its initial activity in pH range of 4.0~5.0 and higher temperature between 45 °C and 60 °C. The catalytic mechanism of PDI/Si-CeO2 NCs was from the active species including superoxide free radicals (•O2-) and holes (h+). The practical application of the proposed colorimetric platform was validated by detecting HQ in real water samples.

Sensitive colorimetric aptasensor based on stimuli-responsive metal-organic framework nano-container and trivalent DNAzyme for zearalenone determination in food samples

Zearalenone (ZEN) poses a serious threat to human and animal health. The development of sensitive determination methods for ZEN is of great significance for ensuring the quality and safety of food. Herein, based on a stimuli-responsive aptamer-functionalized metal–organic framework (MOF) nano-container and trivalent DNA peroxidase mimicking enzyme (DNAzyme), an efficient aptasensor was constructed initially for the colorimetric determination of ZEN. The proposed aptasensor only required simple operations but exhibited outstanding specificity, reproducibility, storage stability and reusability simultaneously. Under the optimal conditions, there was a good linear relationship between the changed absorbance and logarithm concentration of ZEN within 0.01–100 ng mL−1, and the limit of detection (LOD) could reach 0.36 pg mL−1. Moreover, the proposed aptasensor was reliable in quantifying ZEN in spiked food samples. The current bioassay provides a promising scheme for constructing stable, specific and rapid colorimetric platforms with potential applications in the fields of food safety.

Cr2O3-TiO2-Modified Filter Paper-Based Portable Nanosensors for Optical and Colorimetric Detection of Hydrogen Peroxide.

In the present approach, a Cr2O3–TiO2-modified, portable, and biomimetic nanosensor was designed to meet the requirement of a robust and colorimetric sensing of hydrogen peroxide. Cr2O3–TiO2 nanocomposites prepared via the hydrothermal method were fabricated as a transducer surface on the filter paper using the sol–gel matrix. The color on the filter paper sensor changed from green to blue upon the addition of hydrogen peroxide in the presence of TMB. This change in the color intensity was linear with the concentration of H2O2. RGB software was used as a color analyzing model to evaluate the optical signals. This paper-based colorimetric platform provided us with an improved analytical figure of merit with a linear range of 0.005–100 μM with 0.003 μM limit of detection. The real sample analysis and excellent anti-interference potential results proved the good analytical performance of the proposed design, providing a more promising tool for colorimetric H2O2 detection. Introducing Cr2O3–TiO2 nanocomposite-based paper sensors, being a novel method for optical and colorimetric detection, can pave the way for the development of other sensing devices for the detection of different analytes.

Assessment of Iodate in Food-grade Salt Based on a Smartphone Colorimetric Platform

The regular monitoring of iodized salt available in the household and marketplace is necessary for the effective implementation of the national program of salt iodization to control iodine deficiency and its associated diseases. This study describes a colorimetric measurement of iodate in table salt using a smartphone equipped with applications for color analysis and direct readout of iodate levels. The method involved the measurement of the blue component of the colored solution under controlled lighting conditions. The parameters for colorimetric reactions were optimized using a univariate approach – including KI concentration, pH, type and volume of acid, and order of addition of reagents. The effect of NaCl and sample size on the B signal was also investigated. Under optimum conditions, a linear response was observed from 10 to 175 mg iodate per kg of salt (r = 0.9959) with a coefficient of variation of 1.9% over this range and a detection limit of 2.7 mg kg–1 salt. The method was applied for real samples, and the results agreed well with the reference method at the 95% confidence level. The simplicity of operation, compactness, and wide availability of smartphones offer a convenient colorimetric platform for the iodate assessment in table salt.

CoO Nanotubes Loaded on Graphene and Modified with Porphyrin Moieties for Colorimetric Sensing of Dopamine

In this paper, CoO nanotubes loaded on the surface of graphene oxide (GO) have been first modified by 5,10,15,20-tetrakis(4-carboxyl phenyl)porphyrin (Por) by a hydrothermal method. Por/CoO/GO exhibits excellent peroxidase-like activity, which is evaluated by virtue of the chromogenic substrate 3,3,5,5-tetramethylbenzidine (TMB). In the presence of H2O2, Por/CoO/GO nanoperoxidase can rapidly catalyze colorless TMB to be oxidized into blue oxTMB, which is distinguished visually in 1 min. The experimental data including fluorescence and electrochemistry data and radical scavengers confirm that the catalytic mechanism of Por/CoO/GO is ascribed to electron transfer between substrates, as well as produced active species (h+ and •O2–). Based on Por/CoO/GO nanoperoxidase, a fast colorimetric sensor for H2O2 has been established for a wide range of concentrations (0.1–3 mM) with a lower limit of detection (LOD = 0.2942 mM). Notably, the blue color of oxTMB can be gradually faded in the presence of dopamine (DA) with various concentrations. Thus, a fast, cheap, and convenient colorimetric sensor has been designed to monitor DA in a wide range (0.2–10 μM) with a much lower LOD (0.1391 μM). The Por/CoO/GO-based colorimetric platform has been validated by determining DA in real serum samples.

An innovative colorimetric platform for the low-cost and selective identification of Cu(II), Fe(III), and Hg(II) using GQDs-DPA supported amino acids by microfluidic paper-based (µPADs) device: Multicolor plasmonic patterns

This study reports the synthesis of functional graphene quantum dots (GQDs) through the thermal pyrolysis of D-penicillamine (DPA) and citric acid towards water treatment. For the first time, a novel type of highly fluorescent probe for selective Cu2+ detection among 26 types of metal ions which considerably enhance the fluorescence intensity of GQD. Furthermore, the recognition effects can be strengthen addition of amino acids owing to raise the electron density of the system and boos the accumulation profile of the sensing molecules. This simple fluorescent probe was applied for facile metal ions recognition in human urine samples, as well as environmental fluids. The proposed DPA-GQDs supported amino acids respond to Cu2+, Hg2+, and Fe3+, with high sensitivity. The intensity of the fluorescence histogram of this probe significantly diminished in exposure to metal ions such as, Cu(II), Hg(II), and Fe(III). Moreover, in our work, microfluidic paper-based (µPADs) was fabricated through a facile and a cost-effective method. Cu2+ can selectively be recognized by GQD-DPA on the paper-based sensors by naked-eye. The functionalized DPA-GQDs is an excellent alternative to previously reported fluorescent probes for sensing, bio-labeling, and other biological usages in aqueous solution. Its nitrogen and oxygen-rich groups can coordinate with Cu2+ and cause to an apparent fluorescence quenching by the non-radiative electron-transmission. The technique presented in this paper is economical and simple in design, and provides a "mix-and-sense" protocol with no need to chemical- or dye-modifications. Our proposed Cu2+ sensing probe exhibits linear response in the concentrations ranging from 0.001 ppm to 5 ppm, with a lower limit of quantitation (LLOQ) of 0.1 ppm in both environmental fluids, and human urine samples. The enhanced color uniformity, the low instrumental needs of the stamp, and disposability of μPADs enable the application of the suggested paper-based device for the commercial diagnostics biosensor.

Porous polymers from octa(amino-phenyl)silsesquioxane and metalloporphyrin as peroxidase-mimicking enzyme for malathion colorimetric sensor

Rapid and efficient pesticide detection methods are particularly important due to the growing problems of pesticide residues. Here, a new azo-based porous organic polymer, Azo(Fe)PPOP, was prepared from octa(amino-phenyl)silsesquioxane (OAPS) and iron(III) 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin (FeTPP(NO2)4) via a simple coupling reaction without the participation of metal catalysts. The inorganic cage units of OAPS endowed Azo(Fe)PPOP a porous framework, high surface area, favorably thermal and chemical stability. In Azo(Fe)PPOP, iron(III) porphyrin units were individually isolated in a fixed location, which could effectively avoid dimerization or self-oxidation as happens as in the case of porphyrin monomers. Such a unique structure made Azo(Fe)PPOP exhibit an excellent peroxidase-like catalytic performance in the presence of H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB). Because of these advantages, we established a selective, facile, and sensitive colorimetric platform for direct detection of malathion within a very short time (3 min) with a low detection limit (8.5 nM). In addition, the recognition mechanism between Azo(Fe)PPOP and malathion was verified using X-ray photoelectron spectroscopy spectra. The practicality of the constructed platform was further executed by the detection of the pesticide in soil and food samples.

Early-warning and semi-quantitative colorimetric detection of Hg(II) with lysine-bis-Schiff base cellulose membranes designed by simple interfacial covalent bonding

It is of great significance to develop efficient platforms for the detection of hypertoxic Hg2+ in water. In previous decades, colorimetric sensors have received much attention for the early-warning detection of Hg2+. In this work, lysine-bis-Schiff base cellulose membranes (SCMs) were prepared by a simple interfacial covalent bonding method between lysine and high-purity cellulose membranes (CMs). SCMs, as immobilized probe colorimetric platforms, provides an efficient solution for Hg2+ early-warning detection, making it simple and convenient Hg2+ chemical colorimetric sensors. The morphology and structure were analyzed by SEM, EDS, FT-IR, and XPS. As per results, the unique high-loose interpenetrating porous morphology and easy chemically modified structure of CMs, not only improved the interface covalent bonding ability but also provided many channels and sites to chelate Hg2+. Selective Hg2+ chelation with N, O bidentate ligands formed on SCMs prompted the immediate colorimetric sensing. Further performance experiments were designed to study the Hg2+ colorimetric sensing ability of SCMs under real aqueous system. The results showed that SCMs had high selectivity, high sensitivity, robust reusability, and a wide response range without external interference. Qualitative and semi-quantitative detection of Hg2+ with a visual limit of detection (VLOD) of 5 × 10−8 mol/L was fast as 2 and 30 min, respectively. Notably, the capture-based dynamic colorimetry was first designed and used to detect the lower concentrations of Hg2+ (0.1 nM). All experimental results indicated that CM was an excellent material for the design of chemical colorimetric sensors, which held good promise for early-warning and semi-quantitative application.

High-performance cascade nanoreactor based on halloysite nanotubes-integrated enzyme-nanozyme microsystem

Various enzymatic reactions or enzymatic cascade reactions occur efficiently in biological microsystems due to space constraints or orderly transfer of intermediate products. Inspired by this, the horseradish peroxidase (HRP)-like nanozyme (Fe-aminoclay) was in situ synthesized on the surface of alkali-activated halloysite nanotubes and the natural enzyme (glucose oxidase, GOx) was immobilized on it to construct a high-efficiency GOx-FeAC@AHNTs cascade nanoreactor. In which, FeAC@AHNTs can not only be used as a carrier for immobilized enzymes, but also help its catalytic activity to cooperate with glucose oxidase in a cascade reaction. The microcompartments and substrate channel effect of this enzyme-nanozyme microsystem exhibit a superior catalytic performance than that of natural enzyme system, and exhibits excellent long-term stability and recyclability. Subsequently, the GOx-FeAC@AHNTs cascade nanoreactor was employed as a glucose colorimetric platform, which displayed a low detection limit (0.47 µmol/L) in glucose detection. This enzyme-nanoenzyme nanoreactor provides a simple and effective example for constructing a multi-enzyme system with limited space, and lays the foundation for subsequent research in the fields of biological analysis and catalysis.

A colorimetric sensing platform for azodicarbonamide detection in flour based on MnO2 nanosheets oxidative system.

Azodicarbonamide (ADA), as a dough conditioner food additive in flour, can be turned into toxic biurea and semicarbazide after high temperature processing. Hence, the using of ADA in food material should be strictly controlled, and the detection of ADA is very important for consumers' safety and health. Herein, a simple and fast colorimetric strategy has been developed for ADA detection based on the MnO2 nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO2-TMB-GSH). Since the ADA can selectively react with GSH via oxidizing the sulfydryl (-SH) group of GSH to disulfide bond (S-S), which makes GSH unable to reduce MnO2 nanosheets and restore its oxidase-like activity. The absorbance changes of the TMB solution depended on ADA content. The MnO2-TMB-GSH colorimetric platform can detect the ADA with a linear range of 10μmolL-1 (11.6ppm) to 400μmolL-1 (464ppm), and the limit of detection (LOD) is 3.3μmolL-1 (3.51ppm). Some potential interferences in real sample were tested and did not affect the MnO2-TMB-GSH colorimetric platform for ADA detection. Furthermore, the sensing platform was applied for detecting ADA in real flour sample with a recovery of 96%-105% (RSD < 5%). This colorimetric method can effectively and rapidly detect ADA additives in flour less than the prescribed standard (45mgkg-1), which shows a great potential for visualization analysis and on-site detection of ADA in flour. A simple and fast colorimetric strategy has been developed for azodicarbonamide (ADA) detection based on the MnO2 nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO2-TMB-GSH).

Ultrafine Platinum Nanoparticles Supported on Covalent Organic Frameworks As Stable and Reusable Oxidase-Like Catalysts for Cellular Glutathione Detection

Nanozymes have been widely developed as supplements of natural enzymes owing to their relatively low cost, high mass production, easy storage, good stability, and reusability. By controlling the particle size, nanozymes’ catalytic activities can distinctly be improved. The porous materials such as covalent organic frameworks (COFs) are definitely considered as promising supports for in situ preparation of high dispersity and small-size nanozymes. Herein, we designed and synthesized COF supported ultrafine platinum nanoparticles (Pt NPs/COF-300-AR) by controlling the growth of Pt NPs by using uniformly distributed nitrogen atoms of well-organized framework structures of 3D COFs. Pt NPs/COF-300-AR nanohybrids catalyzed the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) solution to turn blue, displaying excellent oxidase-like activity, good stability, and high reusability, which should be owed to the uniform size and high dispersity of ultrafine Pt NPs. By virtue of those advantages, the TMB-Pt NPs/COF-300-AR colorimetric platform was successfully applied to cellular glutathione detection. Similarly, other COFs with good acid resistance and abundant functional groups can also be used as the supports of a nanozyme, which will greatly expand the members of the nanoenzyme family. KEYWORDS: oxidase mimic, in situ preparation, ultrafine Pt nanoparticles, COF support, glutathione, nanohybrids, colorimetry, cell lysate

Oxidase-like Nanozyme-Mediated Altering of the Aspect Ratio of Gold Nanorods for Breaking through H2O2-Supported Multicolor Colorimetric Assay: Application in the Detection of Acetylcholinesterase Activity and Its Inhibitors

A convenient, fast, and colorful colorimetric platform with high resolution for acetylcholinesterase (AChE) activity and its inhibitors detection based on the regulation of oxidase-like nanozyme-mediated etching of gold nanorods (AuNRs) has been proposed in this work. MnO2 nanosheets are selected as the nanozyme. Their excellent oxidase-like activity enables the etching process to proceed smoothly without the usage of unstable H2O2. When AChE is present, it catalytically hydrolyzes acetylthiocholine (ATCh) to thiocholine (TCh). With high reducing ability, TCh induces the decomposition of MnO2 nanosheets, causing them to lose their oxidase-like activity. Thus, the etching of AuNRs is hampered. Consequently, with the increasing concentration of AChE, an apparent change in the AuNRs solution color is observed. The proposed platform achieves high-sensitivity detection of AChE (limit of detection = 0.18 mU/mL). Furthermore, the proposed platform also has been demonstrated its applicability for its inhibitors detection. Benefiting from the advantages of convenient and high resolution of visual readout, the proposed platform holds great potential for the detection of AChE and its inhibitors in clinical diagnosis.

Functionalized silver nanoparticles-based efficient colorimetric platform: Effects of surface capping agents on the sensing response of thiram pesticide in environmental water samples

An efficient colorimetric probe based on surface-functionalized silver nanoparticles (AgNPs) was prepared for sensitive thiram pesticide detection in water samples. The influence of various surface capping agents including polyhexamethylene biguanide hydrochloride (PHMB), polyvinylpyrrolidone (PVP) and anion BH4− on the performance of colorimetric probe in the detection of thiram was evaluated. Among the investigated capping agents, the amine-functionalized AgNPs exhibited higher stability and sensitivity response in thiram detection. The higher performance of the amine-functionalized AgNPs was hypothesized due to the synergistic effect of formation Ag-S bonds and hydrogen interactions of amine groups with electronegative atoms in thiram which craving the proton. The calibration curve for thiram determination through amine-functionalized AgNPs probe showed a linear range from 0.1−100 μM with a detection limit of about 0.036 μM (8.64 μg.kg-1). Along with that, the excellent stability and highly selective sensing of thiram, amine-functionalized AgNPs could be seen as the most promising platform for colorimetric probes in the highly efficient detection of thiram in environmental water solutions.

Design of a dual-signal sensing platform for d-penicillamine based on UiO-66-NH2 MOFs and APBA@Alizarin Red.

Herein, we designed a diversified sensing platform for d-penicillamine based on amino-functionalized Zr-based metal-organic frameworks (UiO-66-NH2 MOFs) and 3-aminophenylboronic acid (APBA)@Alizarin Red (ARS). The boronic acid group of 3-aminophenylboronic acid could react with Alizarin Red to form an APBA@ARS complex with a yellow fluorescence emission at 580 nm and ultraviolet absorption at 435 nm. APBA@ARS can greatly quench the fluorescence of UiO-66-NH2 MOFs at 450 nm via fluorescence resonance energy transfer (FRET). When copper ions were present in the reaction system of APBA and Alizarin Red, the copper ions could complex with Alizarin Red to prevent the generation of APBA@ARS, and the absorption of Cu@ARS at 530 nm occurred. Thus, the absorbance of APBA@ARS at 435 nm declined, restoring the fluorescence of UiO-66-NH2 MOFs. Nevertheless, when d-penicillamine and copper ions coexist in the APBA and Alizarin Red reaction system, the copper ions would complex with the sulfhydryl group of d-penicillamine and no longer hinder the generation of APBA@ARS, and the fluorescence of UiO-66-NH2 MOFs is quenched again. Meanwhile, the absorbance of APBA@ARS at 435 nm enhanced and the absorbance at 530 nm decreased. Thus, a fluorescence and colorimetric dual-signal sensing platform was constructed for d-penicillamine detection, which could detect d-penicillamine in the 1-20 μM and 2-50 μM ranges with the limit of detection (LOD) values of 0.46 μM and 1.38 μM, respectively. Furthermore, this sensing platform could also realize the intelligent RGB detection via mobile phones due to the obvious color change of the reaction system.