Colorimetric determination of o-phenylenediamine in water samples based on the formation of silver nanoparticles as a colorimetric probe

A novel strategy for ratiometric determination of o-phenylenediamine via in-situ fluorogenic reaction and generation of metal nanoparticles

Herein, a novel ratiometric strategy for ultra-sensitive detection of o-phenylenediamine (OPD) was proposed based on combinatorial reactions of in-situ fluorogenic reaction and in-situ formation of red fluorescent dithiothreitol-copper nanoparticles (DTT-CuNPs). Here, Cu2+ is used both as an oxidant and as a precursor. Dehydroascorbic acid (DHAA) is formed via redox reaction of AA and Cu2+. Then, DHAA reacts with OPD to yield blue fluorescent quinoxaline (OXD) with emission peak at 434 nm through in-situ fluorogenic reaction. Red emitting DTT-CuNPs with emission peak at 666 nm is instantly generated due to the coordination reaction between DTT and the residual Cu2+ which is not consumed by AA. The fluorescence intensity (FI) of OXD at 434 nm is closely relied on the concentration of OPD, which can be used as a response signal for OPD detection. Meanwhile, FI of DTT-CuNPs at 666 nm has no significant change, which can be used as a reference signal for OPD detection. Thus, the ratio (F434/F666) of the Cu2+/AA/DTT sensing system is successfully employed to quantify OPD, exhibiting a wide linear range from 0.2 µM to 60 µM, with LOD of 0.09 µM.

Tartaric acid stabilized iridium nanoparticles with excellent laccase-like activity

Iridium nanoparticles with an average size of 1.7 nm (Tar-IrNPs) were synthesized by the reduction of IrCl₃ with NaBH₄ in the presence of tartaric acid. As prepared Tar-IrNPs showed not only oxidase, peroxidase and catalase activities but also exhibited unprecedented laccase-like activity, which can catalyze the oxidation of the substrates o-phenylenediamine (OPD) and p-phenylenediamine (PPD) accompanied by significant color changes. The superb catalytic performance is evidenced by the fact that Tar-IrNPs can achieve better laccase-like activity with only 2.5% of the dosage of natural laccase. Furthermore, they also exhibited superior thermal stability and broader pH adaptability (2.0-11) over that of natural laccase. Tar-IrNPs can retain more than 60% of their initial activity at 90 °C, while the natural laccase has totally lost its activity at 70 °C. At a prolonged reaction time, the oxidation products of OPD and PPD can form precipitates due to oxidation induced polymerization. Thus Tar-IrNPs have been successfully used for the determination and degradation of PPD and OPD.

Novel and Facile Colorimetric Detection of Reducing Sugars in Foods via In Situ Formed Gelatin-Capped Silver Nanoparticles

The evolution of green technology for the simple and ecological formation of silver nanoparticles (AgNPs) inspired the present work for simple and efficient detection of reducing sugars (RS) in foods. The proposed method relies on gelatin as the capping and stabilizing agent and the analyte (RS) as the reducing agent. This work may attract significant attention, especially in the industry, for testing the sugar content using gelatin-capped silver nanoparticles as it not only detects the sugar in food, but also determines the content (%), which could be an alternative technique to the conventionally used DNS colorimetric method. For this purpose, a certain amount of maltose was mixed with a gelatin-silver nitrate. Different conditions that may affect the color changes at 434 nm owing to the in situ formed AgNPs, such as gelatin-silver nitrate ratio, PH, time, and temperature, have been investigated. The 1:3 mg/mg ratio of gelatin-silver nitrate dissolved in 10 mL distilled water was most effective in color formation. The development of AgNPs color increases within 8-10 min at PH 8.5 as the selected optimum value and at the optimum temperature of 90 °C for the evolution of the gelatin-silver reagent's redox reaction. The gelatin-silver reagent showed a fast response (less than 10 min) with a detection limit for maltose at 46.67 µM. In addition, the selectivity of maltose was checked in the presence of starch and after its hydrolysis with α-amylase. Compared with the conventionally used dinitrosalicylic acid (DNS) colorimetric method, the proposed method could be applied to commercial fresh apple juice, watermelon, and honey to prove its viability for detecting RS in fruits; the total reducing sugar content was 287, 165, and 751 mg/g, respectively.

Capsulation of red emission chromophore into the CoZn ZIF as nanozymes for on-site visual cascade detection of phosphate ions, o-phenylenediamine, and benzaldehyde

Accurate on-site profiling of the pollutants is of vital significance for estimating environmental pollution. Herein, we propose a paper-based fluorescence-sensing system to precisely report the level of multiple pollutants. A high-performance fluorescence-sensor for apparatus-free and visual on-site tandem precisely reporting phosphate ions (Pi), o-phenylenediamine (OPD), and benzaldehyde (BA) levels have been fabricated successfully by introducing synthesized red emission (>600 nm) fluorescent chromophore 10-(diethylamino)-3-hydroxy-5,6-dihydrobenzo [c]xanthen-12-ium (HTD) into the environment of CoZn zeolitic imidazolate framework (CoZn ZIF) by a simple stirring method. CoZn ZIF@HTD with the bimetallic nodes not merely provided main Zn²⁺ sites for specific recognition of Pi to generate an enhanced red fluorescent optical signal, Co³⁺/Co²⁺ exhibited excellent peroxidase-like activity for the catalytic oxidation of OPD substrate in the presence of H₂O₂ resulting in color changing from red to yellow. Subsequently, the obvious yellow fading of the OPDox species took place with the addition of BA. By virtue of the sensitively visual tandem detection of Pi, OPD, and BA, the sensor can be applied to real wastewater samples. Meanwhile, this fluorescent sensor was further adopted for practical application in confocal cell imaging and security inks. Overall, this work established a fluorescent sensing system with integrated multifunctional applications for environmental and biological samples, implying the great potential for simultaneous real-time cascade detection of various important pollutants with the merit of low-cost, time-saving, and easy-to-use.

Multicolor Nitrogen-Doped Carbon Quantum Dots for Environment-Dependent Emission Tuning

Carbon quantum dots (CQDs) have potential applications in many fields such as light-emitting devices, photocatalysis, and bioimaging due to their unique photoluminescence (PL) properties and environmental benignness. Here, we report the synthesis of nitrogen-doped carbon quantum dots (NCQDs) from citric acid and m-phenylenediamine using a one-pot hydrothermal approach. The environment-dependent emission changes of NCQDs were extensively investigated in various solvents, in the solid state, and in physically assembled PMMA-PnBA-PMMA copolymer gels in 2-ethyl-hexanol. NCQDs display bright emissions in various solvents as well as in the solid state. These NCQDs exhibit multicolor PL emission across the visible region upon changing the environment (solutions and polymer matrices). NCQDs also exhibit excitation-dependent PL and solvatochromism, which have not been frequently investigated in CQDs. Most CQDs are nonemissive in the aggregated or solid state due to the aggregation-caused quenching (ACQ) effect, limiting their solid-state applications. However, NCQDs synthesized here display a strong solid-state emission centered at 568 nm attributed to the presence of surface functional groups that restrict the π-π interaction between the NCQDs and assist in overcoming the ACQ effect in the solid state. NCQD-containing gels display significant fluorescence enhancement in comparison to the NCQDs in 2-ethyl hexanol, likely because of the interaction between the polar PMMA blocks and NCQDs. The application of NCQDs-Gel as a solid/gel state fluorescent display has been presented. This research facilitates the development of large-scale, low-cost multicolor phosphor for the fabrication of optoelectronic devices, sensing, and bioimaging applications.

Electroconductive and photoactive poly(phenylenediamine)s with antioxidant and antimicrobial activities for potential photothermal therapy

In recent years, polyaniline derivatives such as poly(phenylenediamine)s have attracted the attention of researchers due to their better solubility, good optical and electrical properties. In the current work, poly(ortho- phenylenediamine)...

Synthesis of two tetra-azolium salts and the recognition performance for guests

Two tetra-azolium salts 1 and 2 were synthesized and characterized, and their selective recognition of guests (o-phenylenediamine and F−) was investigated.

Facile preparation of Cu-doped carbon dots for naked-eye discrimination of phenylenediamine isomers and highly sensitive ratiometric fluorescent detection of H2O2

Changing a detection analyte into a colored material is a key challenge for visual discrimination of isomers. In this work, a novel fluorescent probe incorporating Cu-doped carbon dots (Cu-CDs), for the first time, was developed for naked-eye discrimination of phenylenediamine isomers and highly sensitive ratiometric fluorescence detection of H₂O₂. In this strategy, Cu-CDs were synthesized by a facile hydrothermal approach using citric acid, formamide, and CuCl₂ as reactants. The prepared Cu-CDs exhibited outstanding peroxidase-like activity and stability. Consequently, a chemosensor platform based on Cu-CDs was constructed to enable naked-eye discrimination of phenylenediamine isomers through the H₂O₂-mediated oxidation reaction. Moreover, a Cu-CDs-based ratiometric fluorescence sensor was proposed as a means to sensitively detect H₂O₂ with a detection limit of 5.0 nM. The sensor was further employed for monitoring H₂O₂ in human serum, indicating its potential applications in other biologically related study.

Rapid and sensitive detection of selective 1,2-diaminobenzene based on facile hydrothermally prepared doped Co3O4/Yb2O3 nanoparticles

In this approach, the performance of a newly developed sensor probe coated with low-dimensional Co₃O₄/Yb₂O₃ nanoparticles (NPs) in rapidly detecting 1,2-diaminobenzene was evaluated by an electrochemical technique. The sensor probe was fabricated by depositing a very thin layer consisting of synthesized Co₃O₄/Yb₂O₃ NPs using a 5% Nafion conducting binder onto a glassy carbon electrode (GCE). The facile hydrothermally prepared Co₃O₄/Yb₂O₃ NPs were totally characterized by conventional methods such as FTIR, UV-vis, TEM, XPS, EDS, and XRD analyses. The fabricated chemical sensor probe was found to exhibit long-term activity, stability in electrochemical response, good sensitivity (5.6962 μAμM^-1cm^-2), lowest detection limit (0.02±0.001 pM), and broad linear dynamic range (0.1 pM to 0.01 mM). The observed performances suggest that the newly introduced sensor could play an efficient role in detecting 1,2-diaminobenzene especially in healthcare and environmental applications on a broad scale.

Separation of phenylenediamine isomers by using decamethylcucurbit[5]uril

This work investigated the binding interactions between decamethylcucurbit[5]uril (Me₁₀Q[5]) and phenylenediamine isomers, and developed a strategy to isolate phenylenediamine isomers.

The fabrication of a chemical sensor with PANI-TiO2 nanocomposites

In this study, conjugated conducting polyaniline was fabricated onto titania nanoparticles (PANI-TiO₂ NPs) using a microwave-accelerated reaction system. The synthesized nanoparticles were characterized using the techniques of electron microscopy (e.g., FE-SEM and TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and ultraviolet-visible (UV-Vis) spectrometry. An ultrasensitive sensor using the electrochemical (I–V) approach was fabricated using a thin film of PANI-TiO₂ NPs on a glassy carbon electrode (GCE), and it was found to be selective towards 1,2-diaminobenzene (1,2-DAB) in a buffer phase. From current versus concentration studies, the calibration curve was plotted to estimate the sensor's analytical parameters. The highest sensitivity (19.8165 μA μM⁻¹ cm⁻²) and lowest detection limit (0.93 ± 0.05 pM) were obtained from the electrochemical assessment by applying a signal-to-noise ratio of 3. A linear calibration plot was attained over a large range of concentration (LDR: 1.0 pM to 0.01 mM). The selective 1,2-DAB sensor was found to be efficient and reproducible in performance, yielding significant results with a fast response time (12.0 s). Therefore, the overall results of the 1,2-DAB chemical sensor suggest that this detection approach might be an easy way to develop an efficient electrochemical sensor for the protection of the environment as well as for use in the healthcare field on a broad scale.

The conjugated conducting polyaniline was fabricated onto PANI-TiO₂ nanoparticles prepared by microwave-accelerated reaction system for the development an efficient and sensitive electrochemical sensor to protect the environment and healthcare fields in a broad scale.

New application of old methods: Development of colorimetric sensor array based on Tollen's reagent for the discrimination of aldehydes based on Tollen's reagent

Qualitative and quantitative testing of aldehydes is meaningful for chemical toxin detection, food inspection, and disease monitoring. Herein, we reported a simple, accurate, and selective Tollen's reagent-based colorimetric sensor array for determination and detection of aldehydes. Three kinds of negatively charged gold nanoparticles (Au NPs) with different sizes (13, 22, and 40 nm) were synthesized and characterized by transmission electron microscopy and zeta potential measurement. In the presence of aldehydes, Ag+ from Tollen's reagent was attracted by the negative charge on the surface of Au NPs. Ag+ was reduced into Ag0 in situ, forming Au@Ag core-shell nanostructure and resulting in a significant color change. Detailed morphological and dimensional changes were observed by transmission electron microscopy. ΔRGB values (the value changes in the red, green, and blue color model) of Au NPs were captured as the optical signal for further data processing. Results of pattern recognition indicated the outstanding discrimination performance of the system for identification of aldehydes. Moreover, the array possessed quantitative detection capability for formaldehyde, selectivity, and reproducibility and thus has great potential in practical detection.

Silver Nanoparticle Formation-Based Colorimetric Determination of Reducing Sugars in Food Extracts via Tollens' Reagent

A simple, sensitive, and nonenzymatic nanospectrophotometric method was developed for the determination of reducing sugars. The silver mirror reaction-assisted method is based on the in situ formation of silver nanoparticles in the presence of reducing sugars. All simple reducing sugars (glucose, galactose, fructose, mannose, maltose, and lactose) examined had perfectly linear regression equations. The detection limit for glucose was 40 nM. The proposed method could be selectively applied to various synthetic mixtures of reducing sugars with polyphenolic compounds, and to honey, milk, and commercial fruit juice as real samples using solid phase extraction as a clean-up process. The developed method was also statistically validated against conventional alkaline CUPRAC (cupric-neocuproine, Cu(II)-Nc) spectrophotometric method using Student's t- and F-tests.

Facilely prepared Fe3O4/nitrogen-doped graphene quantum dot hybrids as a robust nonenzymatic catalyst for visual discrimination of phenylenediamine isomers

In this work, we report a reducing agent-free strategy for the synthesis of Fe3O4 nanoparticle/nitrogen-doped graphene quantum dot (Fe3O4/N-GQD) hybrids, and constructed a sensing platform based on Fe3O4/N-GQDs for the visual discrimination of phenylenediamine isomers. Fe3O4/N-GQDs were facilely prepared by hydrothermal treatment of Fe(3+)/N-GQD solutions under alkaline conditions without other reagents. The prepared Fe3O4/N-GQDs exhibited outstanding peroxidase-like activity and were stable under a wide range of pH values and temperatures. The phenylenediamine isomers (o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine) were discriminated through the H2O2-mediated oxidation reaction using Fe3O4/N-GQDs as novel peroxidase mimics, which resulted in appreciable color changes. The proposed method is simple, economical, and effective for discrimination of isomers, and can be used for sensitive and selective quantitative analysis of o-phenylenediamine and p-phenylenediamine. A good linear relationship from 1 to 90 μM and a detection limit of 230 nM for o-phenylenediamine were achieved, and the linear relationship for p-phenylenediamine was from 2 to 70 μM with a detection limit of 530 nM. The proposed method may open new applications of Fe3O4/N-GQDs in biomedicine and environmental chemistry.

Microwave-assisted ultrafast synthesis of silver nanoparticles for detection of Hg²⁺

Silver nanoparticles (AgNPs) were successfully prepared in aqueous solution by a one-pot procedure based on a rapid microwave-assisted green approach. L-Cysteine acted as a capping agent in the process of AgNP formation. The structural and morphological characteristics of the L-cysteine-capped AgNPs were investigated by the UV-vis, CD, FL, FTIR, XRD, TEM and EDX analysis. It was found that the well-dispersed crystalline AgNPs were formed after irradiation for 90 s and had sphere-like morphology. Such strategy may facilitate new ways to the synthesis of other metal nanoparticles, such as Au, Pt and Pd. In addition, the synthesized AgNPs were developed as a platform for the detection of Hg(2+) and showed a high sensitivity on the order of 1×10(-8) M. This sensing system could discriminate Hg(2+) from a wide range of cations (Ca(2+), Ba(2+), Mn(2+), etc.). The selectivity and sensitivity of AgNPs indicated its potential use as a sensor for Hg(2+) detection in the ecosystems.