Blue-emitting copper nanoparticles as a fluorescent probe for detection of cyanide ions

Nanoparticles Based Sensors for Cyanide Ion Sensing, Basic Principle, Mechanism and Applications

Rapidly detecting potentially toxic ions such as cyanide is paramount to maintaining a sustainable and environmentally friendly ecosystem for living organisms. In recent years, molecular sensors have been developed to detect cyanide ions, which provide a naked-eye or fluorometric response, making them an ideal choice for cyanide sensing. Nanosensors, on the other hand, have become increasingly popular over the last two decades due water solubility, quick reaction times, environmental friendliness, and straightforward synthesis. Researchers have designed many nanosensors and successfully utilized them for the detection of cyanide ions in various environmental samples. The majority of these sensors use gold and silver-based nanosensors because cyanide ions have a high affinity for these metals ions and coordinate through covalent bonds. These metal nanoparticles are typically combined or coated with fluorescent materials, which quench their fluorescence. However, adding cyanide ions etches out the metal nanoparticles, restoring their fluorescence/color. This principle has been followed by most nanosensors used for cyanide ion sensing. In this review, different nanosensors and their sensing mechanisms are discussed in relation to cyanide ions. The primary purpose is to compare the sensing abilities of these sensors, mainly their sensitivity, advantages, application and to find out research gaps for future work. In this review paper, the development made in nanosensors in the last thirteen years (2010-2023) was discussed and the nanosensors for cyanide ions were compared with molecular sensors while the nanosensors with the excellent limit of detection were highlighted.

2-Mercaptobenzimidazole Functionalized Copper Nanoparticles Fluorescence Probe for Sensitivity and Selectivity Detection of Cys in Serum

In this paper, a 2-mercaptobenzimidazole-copper nanoparticles (MBI-CuNPs) fluorescent probe with high performance based on 2-mercaptobenzimidazole functionalized copper nanoparticles was synthesized by a hydrothermal method and used for cysteine (Cys) detection in serum. The MBI-CuNPs probe exhibits strong fluorescence emission at 415 nm under the excitation at 200 nm, which is attributed to the metal-ligand charge transfer (MLCT) transition through the coordination of an MBI ligand and monovalent copper. Furthermore, the MBI-CuNPs probe has a high quenching fluorescence response to Cys, and shows a good linearity relationship with Cys in 0.05-65 µM, with a detection limit of 52 nM. Moreover, the MBI-CuNPs probe could eliminate the interference of biological mercaptan Hcy and GSH with a similar structure and reaction properties, due to the strong electron-donating ability of Cys, which can quench the fluorescence of the MBI-CuNPs probe. The MBI-CuNPs probe was applied to the analysis of Cys in real serum, and the absolute recovery rate was as high as 90.23-97.00%. Such a fluorescent probe with high sensitivity and selectivity has potential applications for the early prevention of various diseases caused by abnormal Cys levels.

A high-performance fluorescent probe for detection of cysteine in plasma constructed by combining Cu(I) and 2,5-dimercapto-1,3,4-thiadiazole

A high-performance fluorescent probe 2,5-dimercapto-1,3,4-thiadiazole copper nanoparticles (DMTD-CuNPs) was synthesized by hydrothermal method based on monovalent copper (Cu(I)) and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), and it can effectively detect cysteine (Cys) in plasma. Experiments show that DMTD can reduces band gap of Cu(I) in DMTD-CuNPs, promote charge transfer transition from DMTD to Cu(I) and significantly enhance fluorescence intensity of DMTD-CuNPs at 515 nm. The large Stokes shift of DMTD-CuNPs is 315 nm, which can reduce the self-quenching of probe fluorescence and improves detection accuracy of the probe. In the presence of Cys, fluorescence of DMTD-CuNPs at 515 nm is significantly quenched because Cys reacts with Cu(I) in DMTD-CuNPs through Cu-S bond to form reduced charge transfer, which can be successfully used for the detection of Cys. Linear range and detection limit for Cys detection are 25-65 µM and 50 nM, respectively. Furthermore, feasibility of detecting Cys in plasma using DMTD-CuNPs probe was evaluated by standard addition method, and the absolute recovery is 96-99%. Such a DMTD-CuNPs probe shows high sensitivity, good selectivity and low detection limit for Cys, which is expected to be used for the practical analysis of Cys in plasma.

Highly Sensitive Detection of Chymotrypsin Based on Metal Organic Frameworks with Peptides Sensors

In this study, peptides and composite nanomaterials based on copper nanoclusters (CuNCs) were used to detect chymotrypsin. The peptide was a chymotrypsin-specific cleavage peptide. The amino end of the peptide was covalently bound to CuNCs. The sulfhydryl group at the other end of the peptide can covalently combine with the composite nanomaterials. The fluorescence was quenched by fluorescence resonance energy transfer. The specific site of the peptide was cleaved by chymotrypsin. Therefore, the CuNCs were far away from the surface of the composite nanomaterials, and the intensity of fluorescence was restored. The limit of detection (LOD) using Porous Coordination Network (PCN)@graphene oxide (GO) @ gold nanoparticle (AuNP) sensor was lower than that of using PCN@AuNPs. The LOD based on PCN@GO@AuNPs was reduced from 9.57 pg mL^-1 to 3.91 pg mL^-1. This method was also used in a real sample. Therefore, it is a promising method in the biomedical field.

Optical Sensing of Toxic Cyanide Anions Using Noble Metal Nanomaterials

Water toxicity, one of the major concerns for ecosystems and the health of humanity, is usually attributed to inorganic anions-induced contamination. Particularly, cyanide ions are considered one of the most harmful elements required to be monitored in water. The need for cyanide sensing and monitoring has tempted the development of sensing technologies without highly sophisticated instruments or highly skilled operations for the objective of in-situ monitoring. Recent decades have witnessed the growth of noble metal nanomaterials-based sensors for detecting cyanide ions quantitatively as nanoscience and nanotechnologies advance to allow nanoscale-inherent physicochemical properties to be exploited for sensing performance. Particularly, noble metal nanostructure e-based optical sensors have permitted cyanide ions of nanomolar levels, or even lower, to be detectable. This capability lends itself to analytical application in the quantitative detection of harmful elements in environmental water samples. This review covers the noble metal nanomaterials-based sensors for cyanide ions detection developed in a variety of approaches, such as those based on colorimetry, fluorescence, Rayleigh scattering (RS), and surface-enhanced Raman scattering (SERS). Additionally, major challenges associated with these nano-platforms are also addressed, while future perspectives are given with directions towards resolving these issues.

Nitrogen-rich silicon quantum dots: facile synthesis and application as a fluorescent "on-off-on" probe for sensitive detection of Hg2+ and cyanide ions

The sensitive and reliable detection of Hg²⁺ and CN^- as harsh environmental contaminants are of great importance. In view of this, a novel "on-off-on" fluorescent probe based on nitrogen-rich silicon quantum dots (NR-SiQDs) has been designed for sensitive detecting Hg²⁺ and CN^- ions in aqueous media. NR-SiQDs were synthesized by a facile, one-step, and environment friendly procedure in the presence of 3-aminopropyl trimethoxysilane (APTMS) and ascorbic acid (AA) as precursors, with L-asparagine as a nitrogen source for surface modification. The NR-SiQDs exhibited strong fluorescence emission at 450 nm with 42.34% quantum yield, satisfactory salt tolerance, and superior photo- and pH-stability. The fluorescence emission was effectively quenched by Hg²⁺ (turn off) due to the formation of a non-fluorescent stable NR-SiQDs/Hg²⁺ complex while after the addition of cyanide ions (CN^- ), Hg²⁺ ions can be leached from the surface of the NR-SiQDs and the fluorescence emission intensity of the quenched NR-SiQDs fully recovered (turn on) due to the formation of highly stable [Hg (CN)₄ ]^2- species. After optimizing the response conditions, the obtained limits of detection were found to be 53 nM and 0.46 μM for Hg²⁺ and CN^- , respectively. Finally, the NR-SiQDs based fluorescence probe was utilized to detect Hg²⁺ and CN^- ions in water samples and satisfactory results were obtained, suggesting its potential application for environmental monitoring.

Ratiometric fluorescence probe of Cu2+ and biothiols by using carbon dots and copper nanoclusters

A novel dual-emission ratiometric fluorescent probe based on N-doped yellow fluorescent carbon dots (y-CDs) and blue fluorescent copper nanoclusters (CuNCs) was established for quantitative determination of Cu2+ and biothiols. In this work, the Cu2+-(y-CDs) complexes formed by the chelation of y-CDs with Cu2+, showed an absorption peak at 430 nm that not only enhanced the fluorescence of y-CDs through inhibiting photoinduced electron transfer (PET) but also effectively quenched the fluorescence of CuNCs due to Förster resonance energy transfer (FRET). In addition, the chelation of y-CDs with Cu2+ could be inhibited by biothiols that prevented the fluorescence of y-CDs from being enhanced and the fluorescence of CuNCs from being quenched. On account of the changes of ratiometric signal, a dual-emission fluorescence probe for Cu2+ and biothiols determination was achieved. The proposed method exhibited high sensitivity for Cu2+ and biothiols in the ranges of 0.5-100 μM and 0.8-50 μM and the limits of detection (LODs) of Cu2+, glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) were 0.21 μM, 0.33 μM, 0.39 μM and 0.46 μM, respectively. Subsequently, the established strategy presented an application prospect for the detection of Cu2+ and biothiols in real samples.

A smartphone-integrated ratiometric fluorescence sensor for visual detection of cadmium ions

A novel fluorescence sensing platform was fabricated for visual detection of cadmium ions (Cd²⁺) with excellent stability and portability. In this protocol, dual-emission ratiometric fluorescence probe were constructed based on silicon oxide-coated copper nanoclusters (CuNCs@SiO₂) as a signal reference and cadmium telluride quantum dots (CdTe QDs) as signal response, thereby greatly improving the accuracy of test results. The level of Cd²⁺ can be reported within a wide linear range from 0.010 mg·L^-1 to 2.0 mg·L^-1 with a sensitive detection limit of 1.1 μg·L^-1 (2.75 μg·kg^-1) and a quick sample-to-answer monitoring time of 6 min, which was quite qualified for regularly monitoring Cd²⁺. Moreover, aiming to attain portable analysis, the smartphone as colorimetric reader and analyzer were also utilized for rapidly analyzing Cd²⁺ by capturing the change in fluorescence color. Additionally, benefiting from the strong combination of 1, 10-phenanthroline (Phen) and Cd²⁺, the fluorescence probe showed excellent anti-interference activities for Cd²⁺ assay in complex oyster matrix. Overall, the sensing platform had significant stability, specificity and sensitivity, offering a promising potential for conveniently evaluating the quality of marine bivalves polluted with Cd²⁺.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg²⁺, [Formula: see text]Co²⁺, and CN^- in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed 'on-off' fluorescence responses at the addition of Hg²⁺ and [Formula: see text] under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC-SA at 500 nm was found to be exclusively turned off by Co²⁺ and enhanced by CN^-. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.

Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH 3 -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg2+ are better than to other metal ions (Ag+, Al3+, Ba2+, Cd2+, Co3+, Cu2+, Cr3+, Fe3+, Ga2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+). According to the standard curve diagram, the detection limits of CH 3 -R6G and CN-R6G were determined to be 1.34 × 10-8 and 1.56 × 10-8 M, respectively. Reaction of the probes with Hg2+ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH 3 -R6G and CN-R6G have been successfully used for imaging Hg2+ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg2+ in vivo.

Turn on fluorescence strip based sensor for recognition of Sr2+ and CN- via lowerrim substituted calix[4]arene and its computational investigation

Fluorescence sensor L designed around a calix[4]arene scaffold, bearing two fluorogenic aminoquinoline moities, has been synthesized. It is found to be selective and sensitive towards Sr²⁺ and CN^- over a wide range of cations and anions in a spectrofluorometric study in acetonitrile. The ion-binding property of L was monitored by fluorescence spectroscopy, UV-vis spectroscopy, ESI-MS, ¹H NMR, FT-IR investigation and PXRD study. The host L shows a minimum detection limit which is 1.36 nM for Sr²⁺ and 1.23 nM for CN^- having concentration range 5-120 nM and 5-115 nM respectively. The calculated binding constants for L:Sr²⁺ and L: CN^- are respectively 8.859 × 10⁸ M^-1 and 8.574 × 10⁸ M^-1. Our host L has been utilised in formation of a user-friendly, affordable, and disposable paper-based analytical device (PAD) for rapid chemical screening of Sr²⁺ and CN^- ion via single strip. Moreover, the optimization of probe L has also been done by the MOPAC-2016 software package using NM7 popular method resulting -21.71 kcals/mol heat of formation and also determined the HOMO-LUMO energy band gap for L, L:Sr²⁺ and L: CN^-. Further, molecular docking score has been calculated using HEX software. The applicability of our probe in real samples containing Sr²⁺ and CN^- has also been checked by emission study with 94-99% recovery.

Computational design and clinical demonstration of a copper nanocluster based universal immunosensor for sensitive diagnostics

Nanoparticle based sensors are good alternatives for non-enzymatic sensing applications due to their high stability, superior photoluminescence, biocompatibility and ease of fabrication, with the only disadvantage being the cost of the synthesis process (owing to the expensive precursors and infrastructure). For the first time, we report the design of an immunosensor employing streptavidin conjugated copper nanocluster, developed at a much lower cost compared to other nanomaterials like noble metal nanoparticles and quantum dots. Using in silico tools, we have tried to establish the dynamics of conjugation of nanocluster to the streptavidin protein, based on EDC-NHS coupling. The computational simulations have successfully explained the crucial role played by the components of the immunosensor leading to an efficient design capable of high sensitivity. In order to demonstrate the functioning of the Copper Nanocluster ImmunoSensor (CuNIS), HIV-1 p24 biomarker test was chosen as the model assay. The immunosensor was able to achieve an analytical limit of detection of 23.8 pg mL-1 for HIV-1 p24 with a linear dynamic range of 27-1000 pg mL-1. When tested with clinical plasma samples, CuNIS based p24 assay showed 100% specificity towards HIV-1 p24. With the capability of multiplexed detection and a cost of fabrication 100 times lower than that of the conventional metal nanoclusters, CuNIS has the potential to be an essential low-cost diagnostic tool in resource-limited settings.

Colorimetric and visual detection of cyanide ions based on the morphological transformation of gold nanobipyramids into gold nanoparticles

In this study, we developed a facile, rapid, selective and sensitive colorimetric method for the detection of cyanide ions (CN⁻) by using gold nanobipyramids (Au NBPs).

The presence of a single-nucleotide mismatch in linker increases the fluorescence of guanine-enhanced DNA-templated Ag nanoclusters and their application for highly sensitive detection of cyanide

Fluorescence of DNA-templated silver nanoclusters can be enhanced by more than 100-fold by placing the nanoclusters in proximity to guanine-rich DNA sequences after hybridization. We found that the fluorescence of the guanine-enhanced silver nanoclusters is not increased with the guanine-rich DNA sequence closer to the silver nanoclusters. By studying the different numbers of mismatches in the linker sequences, we found that the presence of a single-nucleotide mismatch in the linker increases fluorescence more than the complementary nucleotide. Further study indicated the mismatch position of the linker sequence also affects the fluorescence of the hybridized DNA-Ag NCs. The evidence reported here indicated that the mismatch of the linker sequence affects the fluorescence enhancement of guanine-enhanced silver nanoclusters. We also found that DNA-Ag NCs is an excellent fluorescence sensor for cyanide, as cyanide effectively quenches the fluorescence of NCs at a very low concentration with high selectivity. Cyanide in the range from 0.10 μM to 0.35 μM could be linearly detected, with a detection limit of 25.6 nM.

Recent progress in nanomaterial-based assay for the detection of phytotoxins in foods

Phytotoxins refers to toxic chemicals derived from plants. They include both secondary metabolites that are dose-dependently toxic and allergens that can cause anaphylactic shock in sensitive individuals. Detecting phytotoxins in foods is increasingly important. Conventional methods for detecting phytotoxins lack sufficient sensitivity and operational convenience. Nanomaterial-based determination assays show great competence in fast and accurate sensing of trace substances. In the present review, representative phytotoxin categories of alkaloids, cyanides, and proteins are discussed. Application of notable nanomaterials, e.g. carbon nanotubes, graphene oxide, magnetic nanoparticles, metal-based nanotools, and quantum dots, in specific sensing strategies to fit the physiochemical properties of the target toxins are summarized. Nanomaterials mainly play four roles in phytotoxin detection: 1) analyte enricher; 2) sensor structure mediator; 3) target recognizer or reactant; 4) signaling agent. Great achievements have been made in the detection of trace plant-derived toxins in food matrices, yet there are still challenges awaiting further investigation.

Fast synthesis of porous copper nanoclusters for fluorescence detection of iron ions in water samples

Copper nanoclusters (Cu NCs) have attracted great research interest in recent years owing to its unique physical, electrical and optical properties. Macromolecules have been widely used as templates to synthesize fluorescent Cu NCs. In this study, a simple method for synthesis of albumin chicken egg capped porous copper nanoclusters (p-Cu NCs) was developed for the first time. The obtained p-Cu NCs exhibited intense emission and excitation peaks at 280 nm and 340 nm, respectively. Besides, the p-Cu NCs fluorescence probe could be quenched by Fe³⁺ ions in aqueous solutions. Therefore, the p-Cu NCs can be excellently candidated as fluorescent probe for the detection of Fe³⁺ ions. Under optimized conditions, this fluorescent probe exhibited a wide linear response concentration range (0.2 to 100 μM) to Fe³⁺ with a detection limit of 0.0234 μM. In addition, the fluorescent probe has been successfully used for the detection of Fe³⁺ in natural water samples with satisfactory result.

Copper nanoclusters as fluorescence-quenching probes for the quantitative analysis of total iodine

Tannic acid-coated copper nanoclusters (CuNCs@TA) were synthesized and used quantitatively to analyze iodine in kelp. Compared with other methods for iodine detection, the proposed method showed excellent performance. The iodine-induced linear decrease in the fluorescence intensity of CuNCs@TA allowed the quantitative detection of iodine in the range 20-100 μM, and the limit of detection for iodine was 18 nM. The probe can be used for the determination of iodine in real samples with reliable and accurate results. Modified Stern-Volmer equation and thermodynamic calculation studies were used to discuss the quenching mechanism.

Analysis of malondialdehyde in human plasma samples through derivatization with 2,4-dinitrophenylhydrazine by ultrasound-assisted dispersive liquid-liquid microextraction-GC-FID approach

A sensitive and reliable ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) procedure was developed and validated for extraction and analysis of malondialdehyde (MDA) as an important lipids-peroxidation biomarker in human plasma. In this methodology, to achieve an applicable extraction procedure, the whole optimization processes were performed in human plasma. To convert MDA into readily extractable species, it was derivatized to hydrazone structure-base by 2,4-dinitrophenylhydrazine (DNPH) at 40 °C within 60 min. Influences of experimental variables on the extraction process including type and volume of extraction and disperser solvents, amount of derivatization agent, temperature, pH, ionic strength, sonication and centrifugation times were evaluated. Under the optimal experimental conditions, the enhancement factor and extraction recovery were 79.8 and 95.8%, respectively. The analytical signal linearly (R² = 0.9988) responded over a concentration range of 5.00-4000 ng mL^-1 with a limit of detection of 0.75 ng mL^-1 (S/N = 3) in the plasma sample. To validate the developed procedure, the recommend guidelines of Food and Drug Administration for bioanalytical analysis have been employed.