Metal Site and Size-Controlled BTC-Based MOF as Cysteine Oxidase Mimic for Self-Cascade Detection of Cysteine and Hg2

Nanozyme-mediated strategy for sensing has been widely applied nowadays, in which the construction of a nanozyme cascade platform is an effective and challenging method to simulate the complexity and multifunctionality of natural systems. Herein, a simple and convenient self-cascade sensing platform was developed for the fluorescent detection of cysteine and Hg2+ by a BTC-based MOF through screening the metal sites and crystal sizes. By the introduction of polyvinylpyrrolidone, the as-prepared Cu-BTC possessed a metal center of Cu2+ and smaller size, which exhibited both cysteine oxidase- and peroxidase-like activities. The dual enzymic characters of Cu-BTC made a self-cascade reaction occur during which cysteine was first oxidized to cystine and generated H2O2 in the presence of O2, then H2O2 was decomposed into ·OH, and finally the ·OH triggered the turn-on fluorescence of Cu-BTC. Based on the self-cascade reactions and high affinity of Hg2+ and -SH within cysteine, a fluorescent method was developed to detect cysteine and Hg2+ with a range of 0-160/0-15 μM and a limit of detection of 0.04/0.09 μM, respectively. This work reveals the important role of the Cu2+ center for mimicking cysteine oxidase and gives a feasible strategy for constructing simple self-cascade reactions.

A novel biosensor based on tetrahedral DNA nanostructure and terminal deoxynucleotidyl transferase-assisted amplification strategy for fluorescence analysis of uracil-DNA glycosylase activity

Tetrahedral DNA nanostructure (TDN), as a classical bionanomaterial, which not only has excellent structural stability and rigidity, but also possesses high programmability due to strict base-pairs complementation, is widely used in various biosensing and bioanalysis fields. In this study, we first constructed a novel biosensor based on Uracil DNA glycosylase (UDG) -triggered collapse of TDN and terminal deoxynucleotidyl transferase (TDT)-induced insertion of copper nanoparticles (CuNPs) for fluorescence and visual analysis of UDG activity. In the presence of the target enzyme UDG, the uracil base modified on the TDN were specifically identified and removed to produce an abasic site (AP site). Endonuclease IV (Endo.IV) could cleave the AP site, making the TDN collapse and generating 3'-hydroxy (3'-OH), which were then elongated under the assistance of TDT to produce poly (T) sequences. Finally, Copper (II) sulfate (Cu²⁺) and l-Ascorbic acid (AA) were added to form CuNPs using poly (T) sequences as templates (T-CuNPs), resulting in a strong fluorescence signal. This method exhibited good selectivity and high sensitivity with a detection limit of 8.6 × 10^-5 U/mL. Moreover, the strategy has been successfully applied to the screening of UDG inhibitors and the detection of UDG activity in complex cell lysates, which means that it has promising applications in clinical diagnosis and biomedical research.

A fluorescent probe based on aptamer gold nanoclusters for rapid detection of mercury ions

The mercuric ion (Hg2+) is a hazardous pollutant that is widely distributed in living organisms, foods, and environments with highly toxic and bio-accumulative properties. In the present study, a fluorescent probe based on aptamer gold nanoclusters (apt-AuNCs) was prepared for the ultrasensitive detection of Hg2+ in food. The principle underlying the prepared probe was the quenching of the fluorescence of apt-AuNCs in the presence of Hg2+ due to the strong metallophilic interactions between the 5d10 centers of Hg2+ and Au+. Under optimal conditions, the proposed fluorescent probe exhibited a linear relationship with Hg2+ concentration within the range of 2-200 nM (R2 = 0.9960). In addition, the limit of detection (LOD) was 0.0158 nM, which is below the Chinese standard value of 25 nM for Hg2+ in food. Furthermore, the apt-AuNCs were applied to detect Hg2+ in spinach and crawfish samples, with recovery percentages of 91.99%∼108.06%, meaning that apt-AuNCs could be used as a promising probe to detect Hg2+ in complex food samples.

dsDNA-templated fluorescent copper nanoparticles for the detection of lipopolysaccharides

The introduction of lipopolysaccharides (LPS) or endotoxins that originate from Gram-negative bacteria into the human blood stream induces a severe immune response that can lead to septic shock, and even death. Hence, the accurate detection of LPS is of great importance in the medical and pharmaceutical sectors. This paper proposes a novel label-free fluorescence assay for the detection of LPS utilizing aptamers and the interference synthesis of dsDNA-templated copper nanoparticles. The assay can be performed at room temperature and does not require expensive reagents. The proposed assay has a limit of detection of 0.95 ng ml-1 of LPS, and the fluorescence emission from the copper nanoparticles was found to vary linearly with the concentration of LPS over a wide range (1 to 105 ng ml-1) with R2 = 0.9877.

Developing fluorescent copper nanoclusters: Synthesis, properties, and applications

Metal nanoclusters exhibit strong fluorescence emission, providing immense potential for developments in biological labeling and imaging. Copper nanoclusters in particular, due to their unique optical properties such as molecular-like absorption and strong luminescence, represent a novel fluorescent nanomaterial for sensing and bioimaging applications. This review describes research progress on Cu nanoclusters in recent years, investigating the synthesis techniques, their properties, and their promising applications. A concluding summary provides an outlook on the future research challenges for Cu nanoclusters and their corresponding synthesis techniques.

Handheld fluorometer for in-situ melamine detection via interference synthesis of dsDNA-templated copper nanoparticles

Fluorescent copper nanoparticles templated by dsDNA have gained significant research interest as they are inexpensive and easy to synthesize, and have found applications in the detection of a wide range of analytes. The presence of the analyte in the reaction mixture interferes with the synthesis of the copper nanoparticles and the subsequent drop in fluorescence can be correlated to the concentration of the analyte present in the solution. Analyte detection using copper nanoparticle-based assays is amenable for in-situ applications as the test does not require expensive reagents and can be performed at room temperature. However, expensive and sophisticated detection systems are required for the detection of copper nanoparticles due to the low fluorescence emission signal from these nanoparticles. This restricts the use of the technology to centralized labs. Utilizing a recently developed chemical technique for fluorescence enhancement, this paper presents the first report of a handheld fluorometer capable of detecting DNA-templated copper nanoparticles. The fluorometer is portable and constructed with low-cost, off-the-shelf components like a UV-LED and a PIN photodiode. The performance of the developed system is demonstrated through the detection of melamine in milk samples via the interference synthesis of copper nanoparticles. Melamine is an adulterant used in dairy products that is harmful to human health if present in levels above 1 ppm. The developed system is capable of detecting up to 0.1 ppm of melamine in milk samples with a linear relationship observed between the detector output and concentration of melamine in the range from 0.1 ppm to 100 ppm (R² = 0.9979).

DNA-Templated Fluorescent Nanoclusters for Metal Ions Detection

DNA-templated fluorescent nanoclusters (NCs) have attracted increasing research interest on account of their prominent features, such as DNA sequence-dependent fluorescence, easy functionalization, wide availability, water solubility, and excellent biocompatibility. Coupling DNA templates with complementary DNA, aptamers, G-quadruplex, and so on has generated a large number of sensors. Additionally, the preparation and applications of DNA-templated fluorescent NCs in these sensing have been widely studied. This review firstly focuses on the properties of DNA-templated fluorescent NCs, and the synthesis of DNA-templated fluorescent NCs with different metals is then discussed. In the third part, we mainly introduce the applications of DNA-templated fluorescent NCs for sensing metal ions. At last, we further discuss the future perspectives of DNA-templated fluorescent NCs in the synthesis and sensing metal ions in the environmental and biological fields.

In situ formation of DNA-templated copper nanoparticles as fluorescent indicator for hydroxylamine detection

Herein, we develop a facile method for selective and sensitive detection of hydroxylamine (HA) based on the in situ formation of DNA templated copper nanoparticles (DNA-CuNPs) as fluorescent probes. It is firstly found that HA as a reducing agent can play a key role in the in situ formation of fluorescent DNA-CuNPs. This special optical property of DNA-CuNPs with (λ ex = 340 nm, λ em = 588 nm) with a mega-Stokes shifting (248 nm) makes it applicable for the turn-on detection of HA. In addition, this fluorescent method has several advantages such as being simple, rapid, and environmentally friendly, because it avoids the traditional organic dye molecules and complex procedures. Under optimized conditions, this platform achieves a fluorescent response for HA with a detection limit of 0.022 mM. Especially, successful detection capability in tap waters and ground waters exhibits its potential to be general method.

A poly(thymine)-templated fluorescent copper nanoparticle hydrogel-based visual and portable strategy for an organophosphorus pesticide assay

Since fluorescence assays with high sensitivity for organophosphorus pesticides (OPs) are urgently required to protect the ecosystem and prevent disease, an environmentally friendly and label-free fluorescent probe is desirable. Herein, a poly-thymine30 DNA-templated copper nanoparticle (poly T30-Cu NPs) hydrogel fluorescent probe was explored for the construction of an OPs sensing platform via tyrosinase (TYR) enzyme-controlled quenching. Initially, TYR can efficiently quench the fluorescence of poly T30-Cu NPs; however, when OPs are mixed with a certain amount of TYR, the fluorescence of poly T30-Cu NPs can be recovered. Based on this phenomenon, we designed a functionalized hydrogel based on poly T30-Cu NPs for portable and visible detection of OPs with high sensitivity and selectivity. This proposed fluorescent platform was demonstrated to enable rapid detection of OPs (paraoxon as the model analyte) and provide excellent sensitivity with a detection limit of 3.33 × 10-5 ng μL-1 and a linear range of 1.0 × 10-4-1.0 ng μL-1. The fluorescent probe does not require a sophisticated synthesis and labeling process; in addition, it is environmentally friendly because of the presence of a biotemplate of DNA and biocompatible copper. Moreover, the functional hydrogel combines the features of portability, visualization, fast signal response and environmental anti-interference that make the proposed strategy more feasible in complex practical detection.

Target-initiated synthesis of fluorescent copper nanoparticles for the sensitive and label-free detection of bleomycin

Fluorescent copper nanoparticles (CuNPs) have received great attention due to their distinct characteristics of facile synthesis, tunable fluorescence emission, high photostability, and biological compatibility, and they have been widely used for chemical and biological analyses. Bleomycins (BLMs) are widely used antitumor agents for the clinical treatment of various cancers. Here, we develop a sensitive and label-free fluorescence method for the quantitative detection of BLM on the basis of BLM-initiated enzymatic polymerization-mediated synthesis of fluorescent CuNPs. We design two hairpin DNAs: one (Hp1) for the recognition of BLM and the other (Hp2) for signal amplification. In the presence of BLM, it may recognize and cleave the 5'-GC-3' site of the Hp1 stem, releasing the 8-17 DNAzyme fragment. The resultant 8-17 DNAzyme fragments may bind with the loop of Hp2 to form a partial double-stranded DNA (dsDNA) duplex, initiating the cyclic cleavage of Hp2 in the presence of Zn2+-dependent DNAzymes and generating numerous new DNA fragments with the free 3'-OH terminal, which can induce the formation of a poly(thymine) (poly-T) sequence with the assistance of terminal deoxynucleotidyl transferase (TdTase). Subsequently, the ploy-T sequence may function as the template for the synthesis of CuNPs with strong fluorescence emission. This method shows good selectivity and high sensitivity with a detection limit as low as 8.1 × 10-16 M, and it exhibits good performance in serum samples. Moreover, this method has distinct advantages of simplicity and low cost, holding great potential in clinical diagnosis and biomedical research.

Label-free and sensitive assay for deoxyribonuclease I activity based on enzymatically-polymerized superlong poly(thymine)-hosted fluorescent copper nanoparticles

Deoxyribonuclease I (DNase I) is an important physiological indicator and diagnostic biomarker, but traditional methods for assessing its activity are time-consuming, laborious, and usually radioactive. Herein, by effectively combining the special functions of DNase I and terminal deoxynucleotidyl transferase (TdT), a simple, green, cost-effective, label-free and ultrasensitive assay for DNase I activity has been constructed based on superlong poly(thymine)-hosted copper nanoparticles (poly T-CuNPs). In this strategy, a 3'-phosphorylated DNA primer is designed to block TdT polymerization. After addition of DNase I, the primer could be digested to release 3'-hydroxylated fragments, which could further be tailed by TdT in dTTP pool with superlong poly T ssDNA for CuNPs formation. Fluorescence measurements and gel electrophoresis demonstrated its feasibility for DNase I analysis. The results indicated that with a size of 3-4nm, the CuNPs templated by TdT-polymerized superlong poly T (>500 mer) had several advantages such as short synthetic time (<5min), large Stokes shift (~275nm) and intense red fluorescence emission. Under the optimal conditions, quantitative detection of DNase I was realized, showing a good linear correlation between 0.02 and 2.0U/mL (R²=0.9928) and a detection limit of 0.02U/mL. By selecting six other nucleases or proteins as controls, an excellent specificity was also verified. Then, the strategy was successfully applied to detect DNase I in diluted serum with a standard addition method, thus implying its reliability and practicability for biological samples. The proposed strategy might be promising as a sensing platform for related molecular biology and disease studies.

A fluorescent nanoprobe based on cellulose nanocrystals with porphyrin pendants for selective quantitative trace detection of Hg2+

A well-dispersed chemosensor based on cellulose nanocrystals with porphyrin pendants presented high sensitivity and selectivity for trace Hg²⁺ in aqueous solution.

Hydrothermal synthesis of nitrogen and boron doped carbon quantum dots with yellow-green emission for sensing Cr(vi), anti-counterfeiting and cell imaging

Nitrogen and boron co-doped carbon quantum dots with great stability in high-salt conditions and good photostability are prepared through hydrothermal method and utilized for fluorometric detection of Cr(vi), anti-counterfeiting and cell imaging.

TTE DNA–Cu NPs: enhanced fluorescence and application in a target DNA triggered dual-cycle amplification biosensor

A crowded TTE DNA structure for the preparation of Cu NPs with enhanced fluorescence was prepared and applied for the ultrasensitive detection of target DNA.

Fluorescent copper nanoparticles: recent advances in synthesis and applications for sensing metal ions

Fluorescent copper nanoparticles (F-CuNPs) have received great attention due to their attractive features, such as water solubility, wide availability, ease of functionalization and good biocompatibility, and considerable efforts have been devoted to the preparation and applications of F-CuNPs. This review article comprises three main parts. In the first part, we briefly present the fluorescence properties of F-CuNPs. Then we cover the fabrication strategies of various F-CuNPs functionalized by different ligands. In the third part, we focus on the applications of F-CuNPs for sensing metal ions, including Hg(2+), Pb(2+), Cu(2+), Fe(3+) and other metal ions. Lastly, we further discuss the opportunities and challenges of F-CuNPs in the synthetic strategies and applications for sensing metal ions.

Ce (III) - Porphyrin Sandwich Complex Ce2(TPP)3: A Rod-Like Nanoparticle as a Fluorescence Turn-Off Probe for Detection of Hg (II) and Cu (II)

In this study the researcher reports a novel, one step synthesized rod-like nanoparticles of cerium (III)-tetraphenylporphyrin sandwich complex as a spectrofluorometric sensor to measure trace amount of Hg (II) and Cu (II) metal ions. Moreover, the synthesized fluorescent probe was able to detect higher amounts (>10(-4) M) of Hg (II) in aqueous media by changing the color which can also be used as a selective mercury naked-eye sensor. The selectivity and sensitivity of the sensor based on its fluorescence quenching in the presence of Hg (II) and Cu (II) were studied according to the Stern-Volmer equation. The detection limit of the sensor was 16 nM for Hg (II) and about 2.34 μM for Cu (II) ions. Graphical Abstract Ce2(TPP)3 sandwich complex application as a fluorescent probe for measuring trace amounts of mercury and copper in real samples.

Cascade Signal Amplification Based on Copper Nanoparticle-Reported Rolling Circle Amplification for Ultrasensitive Electrochemical Detection of the Prostate Cancer Biomarker

An ultrasensitive and highly selective electrochemical assay was first attempted by combining the rolling circle amplification (RCA) reaction with poly(thymine)-templated copper nanoparticles (CuNPs) for cascade signal amplification. As proof of concept, prostate specific antigen (PSA) was selected as a model target. Using a gold nanoparticle (AuNP) as a carrier, we synthesized the primer-AuNP-aptamer bioconjugate for signal amplification by increasing the primer/aptamer ratio. The specific construction of primer-AuNP-aptamer/PSA/anti-PSA sandwich structure triggered the effective RCA reaction, in which thousands of tandem poly(thymine) repeats were generated and directly served as the specific templates for the subsequent CuNP formation. The signal readout was easily achieved by dissolving the RCA product-templated CuNPs and detecting the released copper ions with differential pulse stripping voltammetry. Because of the designed cascade signal amplification strategy, the newly developed method achieved a linear range of 0.05-500 fg/mL, with a remarkable detection limit of 0.020 ± 0.001 fg/mL PSA. Finally, the feasibility of the developed method for practical application was investigated by analyzing PSA in the real clinical human serum samples. The ultrasensitivity, specificity, convenience, and capability for analyzing the clinical samples demonstrate that this method has great potential for practical disease diagnosis applications.

A sensitive fluorescence sensor for glutathione detection based on MnO2 nanosheets–copper nanoclusters composites

A sensitive fluorescence sensor has been developed for glutathione detection based on MnO₂ nanosheets–Cu NCs composites.

Label-free biosensor based on dsDNA-templated copper nanoparticles for highly sensitive and selective detection of NAD+

A novel label-free biosensor for high sensing of NAD⁺ based on dsDNA-templated CuNPs and DNA ligation reaction.