Discrimination of copper and silver ions based on the label-free quantum dots

Flexible silver-metal-organic framework probe for highly sensitive and visual detection of tetracycline hydrochloride in freshwater fish

Tetracycline hydrochloride (TCH) is commonly used in aquaculture to prevent bacterial infections, renders the detection of its residues highly crucial for ensuring the safety of aquatic products. In this study, an Ag-based metal-organic framework, Ag-dcp (H3dcp = 3-(3,5-dicarboxyphenyl)-6-carboxypyridine), was synthesized through hydrothermal method. The Ag-dcp framework offers environmental advantages, including a green synthesis process and potential for sustainable, eco-friendly applications. The uncoordinated carboxyl groups in Ag-dcp provide potential interaction sites for TCH, while the rhombic channels in the flexible structure of Ag-dcp that match the size of TCH effectively facilitate host-guest interactions. The Ag-dcp enables ratiometric fluorescence detection with high sensitivity via intramolecular charge transfer (ICT) triggered by TCH-induced ether bond rotation. The probe demonstrates a fluorescence color changes from blue to orange, achieving a detection limit as low as 0.14 μM and offering an ultrafast response time of just 10 s. Principal component analysis (PCA) was employed to effectively distinguish TCH from other tetracycline analogs (minocycline hydrochloride (MH) and doxycycline hydrochloride (DOX)), thereby enhancing the selectivity of the Ag-dcp probe. The fluorescence probe demonstrated performance comparable to HPLC in detecting TCH in freshwater fish. The detection strategy proposed here, based on the MOF structure, offers valuable insights for designing MOF materials and their specialized applications.

A novel fluorescent probe with large stokes shift based on naphthalimide and phenanthroline for specific detection of Ag+ and its application in living cells imaging

Silver ions (Ag+) are widely used in industry and daily life. To achieve the specific and sensitive detection of Ag+, a novel fluorescent probe NP based on naphthalimide-phenanthroline was developed in this study. NP has an emission wavelength of 580 nm and exhibits a large Stokes shift (190 nm), showing a quenching fluorescence response to Ag+. NP can sensitively detect Ag+ with a detection limit as low as 24.6 nM. The response time is only 110 s. In particular, NP demonstrates effective detection of Ag+ in real water samples. In addition, NP exhibits low toxicity and has been successfully applied for Ag+ imaging in Hela cells.

CdSe/ZnS QDs embedded polyethersulfone fluorescence composite membrane for sensitive detection of copper ions in various drinks

The copper ion was detected rapidly by a novel sensing membrane in this paper for its damage to health and the environment. CdSe/ZnS QDs modified polyethersulfone membrane (QDs@PESM) was made by phase-inversion method using a membrane separation technique and quantum dots (QDs). When the sample passed through the membrane, the copper ions in the sample caused the membrane's fluorescence to be quenched. The fluorescence quenching value of the membrane is used to calculate the concentration of copper ions. With R²= 0.9964, Cu²⁺could be quantitatively detected over a wide concentration range (10-1000 μg/L). The method's LOD and LOQ were 4.27 and 14.23 μg/L, respectively. When the CdSe/ZnS QDs@PESM was used to analyze Cu²⁺ in various real drinks, including well water, baijiu, orange juice, beer, and milk, the recovery ranged from 79.1 to 123.9%, indicating that the CdSe/ZnS QDs@PESM can be used as a rapid, simple and reliable method to determine Cu²⁺ in various matrices.

Sensitive detection and intracellular imaging of free copper ions based on DNA-templated silver nanoclusters aggregation-inducing fluorescence enhancement effect

Free copper ions (Cu⁺ and Cu²⁺) have critical toxicity to cells, although copper is an essential element for human body. Hence, sensitive monitoring is crucial to avoid over intake of Cu⁺/Cu²⁺. We herein designed a ssDNA sequence (A₃₁) for synthetizing A₃₁-templated silver nanoclusters (AgNCs), and demonstrated that Cu⁺/Cu²⁺ can induce the aggregation of A₃₁-templated AgNCs and thus greatly enhanced the fluorescence emission of A₃₁-templated AgNCs. Based on Cu⁺/Cu²⁺-induced fluorescence enhancement effect of A₃₁-templated AgNCs, a label-free and signal-on fluorescent sensing platform was developed for the specific and sensitive detection of Cu⁺/Cu²⁺ in biological samples and intracellular imaging of Cu⁺/Cu²⁺ in cells. The signal-on fluorescent sensing platform could be used to rapidly detect Cu⁺ and Cu²⁺ with a detection limit of 0.1 µM within 30 min., and to perform the intracellular imaging of Cu⁺ and Cu²⁺ in cells with good cell permeability and biocompatibility. By using the signal-on fluorescent sensing platform, we have successfully detected Cu⁺ and Cu²⁺ in cells fluids and human serum with a recovery of 90-104% and a RSD (n = 5) < 5%, and performed the imaging of Cu⁺/Cu²⁺ in Hela cells. The developed fluorescent sensing platform has obvious analytical and imaging advantages such as signal-on, simple operation, short analysis time, both Cu⁺ and Cu²⁺ detection, similar or higher sensitivity, good cell permeability and biocompatibility, which promising a reliable approach for the rapid and on-site detection or imaging of free copper ions in biological samples in clinical diagnosis.

Recent Advances of Optical Sensors for Copper Ion Detection

A trace element copper (Cu2+) ion is the third most plentiful metal ion that necessary for all living organisms and playing a critical role in several processes. Nonetheless, according to cellular needs, deficient or excess Cu2+ ion cause various diseases. For all these reasons, optical sensors have been focused rapid Cu2+ ion detection in real-time with high selectivity and sensitivity. Optical sensors can measure fluorescence in the refractive index-adsorption from the relationships between light and matter. They have gained great attention in recent years due to the excellent advantages of simple and naked eye recognition, real-time detection, low cost, high specificity against analytes, a quick response, and the need for less complex equipment in analysis. This review aims to show the significance of Cu2+ ion detection and electively current trends in optical sensors. The integration of optical sensors with different systems, such as microfluidic systems, is mentioned, and their latest studies in medical and environmental applications also are depicted. Conclusions and future perspectives on these advances is added at the end of the review.

Ratiometric fluorescent nanoprobes based on carbon dots and multicolor CdTe quantum dots for multiplexed determination of heavy metal ions

Owing to the high risk to human and environmental health, heavy metal pollution has become a global problem. Rapid, accurate and multiplexed determination of heavy metal ions is critical. In this work, we reported a promising approach to designing ratiometric fluorescent nanoprobes for multiplexed determination of Hg²⁺, Cu²⁺, and Ag⁺ ions. The nanoprobes (CDs-QDx) were designed by mixing the CDs and multicolor CdTe QDs without the involvement of recognition elements. The CDs were insensitive to heavy metal ions while CdTe QDs showed the size-dependent fluorescence response to different heavy metal ions, thereby establishing a ratiometric detection scheme by measuring the fluorescence intensity ratios of CDs-QDx systems. By evaluating the detection performance, the CDs-QDx (x = 570, 650, and 702) were successfully used for differentiation and quantification of Hg²⁺, Cu²⁺, and Ag⁺ ions. In addition, we also carried out the detection of heavy metal ions in actual samples with acceptable results. We believed that this work offers new insight into the design of ratiometric fluorescent nanoprobe for multiplexed determination of not only heavy metals but also some other analytes by combining the CDs with CdTe QDs with fine-tuned sizes.

Rapid fluorescent color analysis of copper ions on a smart phone via ratiometric fluorescence sensor

A smartphone-assisted fluorescence color sensing system for rapid, convenient, and on-site detection of copper ions was developed. The ratiometric fluorescence sensor was fabricated by using silica-coated blue-light-emitting carbon dots and surface-grafted red-light-emitting cadmium-telluride quantum dots. After exposure to Cu²⁺ in 20 s, the red fluorescence was quenched obviously, while the blue fluorescence remained unchanged, and the sensor color changes continuously from red to blue under the ultraviolet lamp. The concentration (50-1200 nM) of copper ions could be measured by the fluorescence spectrum (excitation at 360 nm, dual-emission at 441 and 640 nm) with a detection limit of 7.7 nM. The fluorescence colors were converted to digital RGB values to calculate the concentration of copper ions by a smartphone with a detection limit of 9.6 nM. The method was applied to detecting copper ions spiked in real samples with recovery from 97.9 to 108.0% and RSD from 3.8 to 8.9%. Thus, this convenient and practical fluorescence color sensing system presents a new strategy for rapid, sensitive, and on-site determination of copper ions in environmental or biological samples.

Metal-organic gel as a fluorescence sensing platform to trace copper(II)

Metal-organic gel (MOG), as a novel type of metallic organic hybrid material, exhibits diverse properties. However, its application in fluorescence detection for specific metal ions has rarely been exploited. In this work, we have designed and synthesized a MOG based on Al-carboxylate coordination assemblies (denoted as MOG-Al). The resultant MOG-Al shows good specific fluorescence signal response to trace Cu²⁺. Under optimal conditions, the fluorescence quenching degrees (F₀ - F) of the MOG-Al have a linear correlation with Cu²⁺ concentration ranging from 0.05 to 100 μM, and the limit of detection (LOD) is 45.00 nM. The proposed sensing platform was also applied for the detection of Cu²⁺ in real samples. Satisfactory recoveries (92-116%) for Cu²⁺ in rice, soybean milk powder and pork liver were obtained. These results indicate that MOG-Al is a promising material for the specific and sensitive sensing of Cu²⁺.

A Highly Sensitive and Selective Fluorescent Probe Using MPA-InP/ZnS QDs for Detection of Trace Amounts of Cu2+ in Water

Detection of copper (II) ions (Cu²⁺) in water is important for preventing them from entering the human body to preserve human health. Here, a highly sensitive and selective fluorescence probe that uses mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) was proposed for the detection of trace amounts of Cu²⁺ in water. The fluorescence of MPA-InP/ZnS QDs can be quenched significantly in the presence of Cu²⁺, and the fluorescence intensity shows excellent linearity when the concentration of Cu²⁺ varies from 0–1000 nM; this probe also exhibits an extremely low limit of detection of 0.22 nM. Furthermore, a possible fluorescence-quenching mechanism was proposed. The MPA-InP/ZnS QDs probes were further applied to the detection of trace Cu²⁺ in real water samples and drink samples, showing good feasibility.

Deacetylation-activated construction of single quantum dot-based nanosensor for sirtuin 1 assay

Sirtuin 1 (SIRT1) is an important histone deacetylase that regulates biological functions ranging from DNA repair to metabolism. The alteration of SIRT1 is associated with a variety of diseases including diabetes, inflammation, aging-related diseases, and cancers. Consequently, the detection of SIRT1 activity is of great therapeutic importance. Herein, we demonstrate for the first time the deacetylation-activated construction of single quantum dot (QD)-based nanosensor for sensitive SIRT1 assay. This nanosensor is composed of a Cy5-labeled peptide substrate and a streptavidin-coated QD. The peptide with one lysine acetyl group acts as both the Cy5 fluorophore carrier and the substrate for sensing SIRT1. In the presence of SIRT1, it removes the acetyl group in the acetylated peptide, and the resultant deacetylated peptide can react with the NHS-activated biotin reagent (sulfo-NHS-biotin) to form the biotinylated peptide. The multiple biotinylated peptides can assemble on single QD surface via biotin-streptavidin interaction, inducing efficient fluorescence resonance energy transfer (FRET) from the QD to Cy5, generating distinct Cy5 signal which can be simply quantified by total internal reflection fluorescence-based single-molecule detection. This single QD-based nanosensor can sensitively detect SIRT1 with a detection limit of as low as 3.91 pM, and it can be applied for the measurement of enzyme kinetic parameters and the screening of SIRT1 inhibitors. Moreover, this nanosensor can be used to detect the SIRT1 activity in cancer cells, providing a powerful platform for epigenetic research and SIRT1-targeted drug discovery.