A novel signal amplification strategy based on the use of copper nanoclusters for ratiometric fluorimetric determination of o-phenylenediamine

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.

Ultra-small water-soluble fluorescent copper nanoclusters for p-nitrophenol detection

Due to the widespread application of p-nitrophenol (p-NP) across various industries, particularly in the pharmaceutical and chemical sectors, it has emerged as a significant environmental contaminant in both soil and water ecosystems. The development of swift and sensitive detection platforms for p-NP is therefore demanding. Herein, a fluorescence sensor based on ultra-small copper nanoclusters with exterior glutathione ligands determined by electrospray ionization mass spectrometry (ESI-MS) as [Cu14(SG)12]+ (denoted as Cu-SG NCs) has been prepared in high efficiency, and shown high selectivity for p-NP detection. The Cu-SG NCs, synthesized via a facile one-pot chemical reduction technique, exhibit emission maxima at 620 nm. Notably, the introduction of p-NP into the nanocluster system causes a significant quenching of the Cu-SG NCs fluorescence. The quenching phenomenon arises predominantly as a result of the inner filter effect (IFE), which stems from the substantial overlap between the UV-Vis absorption spectrum of p-NP and the excitation wavelength of Cu-SG NCs. The developed fluorescence sensor platform demonstrates a wide determination range for p-NP, ranging from 0.04 to 2000 µM, with a detection limit of 30 nM. Additionally, the sensor efficacy was successfully validated in the analysis of actual water samples. The ease of synthesis, excellent optical properties, and low toxicity of Cu-SG NCs represent significant advantages over the reported noble metal nanomaterials and is highly promising for future practical applications.

A Ratiometric Fluorescence Amplification Using Copper Nanoclusters with o-Phenylenediamine Sensor for Determination of Mercury (II) in Natural Water

A simple and rapid method for determining mercury (II) has been developed using L-cysteine-capped copper nanocluster (CuNCs) with o-phenylenediamine (OPD) as the sensor. The characteristic fluorescence peak of the synthesized CuNCs was observed at 460 nm. The fluorescence properties of CuNCs were strongly influenced by the addition of mercury (II). Upon addition, CuNCs were oxidized to form Cu²⁺. Then, the OPD were rapidly oxidized by Cu²⁺ to form o-phenylenediamine oxide (oxOPD), as evidenced by the strong fluorescence peak at 547 nm, resulting in a decrease in the fluorescence intensity at 460 nm and an increase in the fluorescence intensity at 547 nm. Under optimal conditions, a calibration curve between the fluorescence ratio (I547/I460) and mercury (II) concentration was constructed with a linearity of 0-1000 µg L^-1. The limit of detection (LOD) and limit of quantification (LOQ) were found at 18.0 µg L^-1 and 62.0 µg L^-1, respectively. The recovery percentage was in the range of 96.8-106.4%. The developed method was also compared with the standard ICP-OES method. The results were found to be not significantly different at a 95% confidence level (t_stat = 0.365 < t_crit = 2.262). This demonstrated that the developed method could be applied for detecting mercury (II) in natural water samples.

Chiral dual-emission composite material fluorescein/CCQDs @ZIF-8 for highly efficient recognition of phenylenediamine isomers and their oxidized product

As a new type of fluorescent nanomaterial, chiral carbon quantum dots (CCQDs) have the advantages of wide source, good water solubility and high chemical stability, and have been widely used in drug detection, bioimaging and chemical sensing. In this work, a chiral dual-emission hybrid material fluorescein/CCQDs@ZIF-8 (1) was synthesized by in-situ encapsulation strategy. Luminescence emission position of CCQDs and fluorescein are almost unchanged after the encapsulation into ZIF-8. The luminescent emissions of CCQDs and fluorescein can be observed to be located at 430 nm and 513 nm, respectively. When 1 is soaked in pure water, ethanol, dimethylsulfoxide, DMF, DMA and targeted substances solution for 24 h, 1 can maintain its structural stability. Photo-luminescent (PL) studies show that 1 can discriminate p-phenylenediamine (PPD) from m-phenylenediamine (MPD) and o-phenylenediamine (OPD), which can detect the presence of PPD with high sensitivity and selectivity (ratiomeric fluorescent probe with K_BH: 1.85 × 10³ M^-1 and detection limit: 8.51 μM). Further, 1 also effectively distinguish the oxidized product of these phenylenediamine(PD) isomers. 1 can be used as a "turn-off" fluorescent probe to detect oxidized product of PPD (ratiomeric fluorescent probe with K_SV: 6.82 × 10² M^-1 and detection limit: 0.112 mM) and a "turn-on" fluorescent probe to detect oxidized product of MPD (ratiomeric fluorescent probe: K_BH: 1.65 × 10³ M^-1 and detection limit: 35.03 μM) and oxidized product of OPD (ratiomeric fluorescent probe: K_BH: 2.40 × 10⁶ M^-1 and detection limit: 0.105 μM). Further, for the convenience of practical application, 1 can be developed as fluorescence ink and be prepared into a mixed matrix membrane. When the target substances are gradually added to the membrane, significant luminescence change with obvious color change can be observed.

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.

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.

Energy Security in Danger? A Comparative Analysis of Oil and Copper Supply

This study aims to examine energy security in terms of crude oil and copper supply. While oil remains the leading energy commodity globally, copper is crucial for many new technologies, foremost for RES. Therefore, both oil and copper are extremely important for current and future energy security. This article contains a bivariate methodological approach to a comparative analysis of oil and copper supply: determining supply security with an Index of security of supply, and examines price stability with generalized autoregressive conditional heteroscedasticity (GARCH) models. This research provides evidence that there are many differences but also significant similarities between these two completely different commodities in terms of both supply security and price stability. Facing the future for RES, significant demand may cause a threat to energy security on a previously unknown scale. Therefore this instability, both supply- and price-related, appears to be the main threat to future energy security.

Synthesis of Copper Nanocluster and Its Application in Pollutant Analysis

Copper nanoclusters (Cu NCs) with their inherent optical and chemical advantages have gained increasing attention as a kind of novel material that possesses great potential, primarily in the use of contaminants sensing and bio-imaging. With a focus on environmental safety, this article comprehensively reviews the recent advances of Cu NCs in the application of various contaminants, including pesticide residues, heavy metal ions, sulfide ions and nitroaromatics. The common preparation methods and sensing mechanisms are summarized. The typical high-quality sensing probes based on Cu NCs towards various target contaminants are presented; additionally, the challenges and future perspectives in the development and application of Cu NCs in monitoring and analyzing environmental pollutants are discussed.

Ratiometric fluorescence and smartphone dual-mode detection of glutathione using carbon dots coupled with Ag+-triggered oxidation of o-phenylenediamine

Developing ratiometric fluorescence and smartphone dual-mode bioanalysis methods is important but challenging. A ratiometric fluorescence method for determining glutathione (GSH) using carbon dots (CDs) and Ag⁺-triggered o-phenylenediamine (OPD) oxidation is described here. Ag⁺oxidizes OPD to give 2,3-diaminophenazine (oxOPD), which effectively quenches CD fluorescence at 436 nm through the inner filter effect and causes a new emission peak at 561 nm. GSH chelates with Ag⁺and prevents the Ag⁺oxidizing OPD and therefore effectively preserves CD emission at 436 nm (blue) and allows only weak oxOPD fluorescence at 561 nm (orange) to occur. The oxOPD to CD fluorescence intensity ratio decreased linearly as the GSH concentration increased in the range 0-150 nM, and the detection limit was 15 nM. The ratiometric fluorescence probe lit with an ultraviolet lamp clearly changed color from orange to blue as the GSH concentration increased. An image was acquired using a smartphone camera and converted into digital values. The blue and red channel ratio was calculated and used to quantify GSH. The method therefore allows dual-mode detection of GSH.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Simple assay for colorimetric quantification of unamplified bacterial 16S rRNA in activated sludge using gold nanoprobes

Domestic and industrial wastewater treatment systems are vital in the protection of natural ecosystems and human health. Identification of microbial communities in the systems is essential to stable treatment performance. However, the current tools of microbial community analysis are labor intensive and time consuming, and require expensive equipment. Therefore, we developed a simple assay for colorimetric quantification of bacterial 16S rRNA extracted from environmental samples. The assay is based on RNA extraction with commercial kits, mixing the unamplified RNA sample with Au-nanoprobes and NaCl, and analyzing the absorbance spectra. Our experimental results confirmed that the assay format was valid. By analyzing the synthesized DNA, we optimized the operational parameters affecting the assay. We achieved adequate capture DNA density by setting the capture DNA probe concentration at 10 μM during the functionalization step. The required incubation time after NaCl addition was 30 min. The binding site of the target had negligible effect on DNA detection. Under the optimized condition, a calibration curve was created using 16S rRNA extracted from activated sludge. The curve was linear above 5.0 × 10⁷ copies/μL of bacterial 16S rRNA concentration, and the limit of detection was 1.17 × 10⁸ copies/μL. Using the calibration curve, the bacterial 16S rRNA concentration in activated sludge samples could be quantified with deviations between 48% and 208% against those determined by RT-qPCR. The findings of our study introduce an innovative tool for the quantification of 16S rRNA concentration as the activity of key bacteria in wastewater treatment processes, achieving stable treatment performance.

A fluorescence "off-on-off" sensing platform based on bimetallic gold/silver nanoclusters for ascorbate oxidase activity monitoring

Herein, papain-protected bimetallic gold/silver nanoclusters (Au/Ag NCs) were successfully synthesized and applied for the detection of ascorbate oxidase (AAO). The doping of papain-protected Au nanoclusters with Ag enhanced the fluorescence intensity with an intense red fluorescence peak at 617 nm, and the red-emitting Au/Ag nanoclusters were further used to monitor the AAO activity. The fluorescence of Au/Ag NCs could be quenched by hydrogen peroxide (H2O2) due to the generation of hydroxyl radicals (˙OH) from the reaction of Ag/Au nanoclusters and H2O2. However, the addition of ascorbic acid (AA) effectively reacted with the free radicals and caused the fluorescence recovery of the Au/Ag NCs. Furthermore, AAO could catalyze the oxidation of AA to form dehydro-ascorbate (DHA). As a result, there was not enough AA to consume the hydroxyl radicals, which resulted in a decrease in the fluorescence of the papain-capped Au/Ag NCs. Therefore, the AAO activity can be monitored by measuring the fluorescence intensity of the red-emitting Au/Ag NCs. Moreover, the developed method for AAO detection displayed a good linear relationship from 5 to 80 mU mL-1 and the detection limit was 1.72 mU mL-1. Thus, a simple and selective method for the determination of the AAO activity was constructed and satisfactory results were obtained in real sample detection.

Recent progress in copper nanocluster-based fluorescent probing: a review

Copper nanoclusters (CuNCs) are an attractive alternative to other metal nanoclusters. The synthesis of CuNCs is highly efficient and fast, with low-cost and without any complicated manipulation. Because of their tunable fluorescence and low toxicity, CuNCs have been highly exploited for biochemical sensing. This review (with 172 refs.) summarizes the progress that has been made in the field in the past years. Following an introduction into the fundamentals of CuNCs, the review first focuses on synthetic methods and the fluorescence properties of CuNCs (with subsections on the use of proteins, peptides, DNA and other molecules as templates). This is followed by a section on the use of CuNCs in fluorometric assays, with subsections on the detection of small molecules, proteins, nucleic acids, various other biomolecules including drugs, and of pH values. A further large chapter summarizes the work related to environmental analyses, specifically on determination of metal ions, anions and pollutants. Graphical abstract Schematic representation of the synthesis and potential applications of copper nanocluster (CuNCs) in biochemical analysis, emphatically reflected in some vital areas such as small molecule analysis, biomacromolecule monitoring, cell imaging, ions detection, toxic pollutant, etc.