Ratiometric fluorescence detection of bleomycin based on proximity-dependent fluorescence conversion of DNA-templated silver nanoclusters

Ratiometric sensor based on Ag+-mediated luminescence of Tb-DNA complexes for visual detection of 4-aminophenol

Development of accurate, convenient and portable methods for monitoring 4-aminophenol (4-AP) is extremely important because of its strong toxicity. Here, a ratiometric fluorescence sensor based on Ag+-enhanced luminescence of Tb-DNA complexes has been presented for the detection of 4-AP. The luminescence of Tb-DNA complexes is enhanced about 30 times by Ag+, which can trigger energy transfer from DNA to Tb3+ more efficiently. In the presence of 4-AP, Ag+ can be reduced into Ag0 owing to its strong reducibility, inducing the decrease of Tb-DNA complexes at 545 nm remarkably. Besides, 4-AP exhibits intrinsic fluorescence at 375 nm under the same conditions. Therefore, ratiometric detection of 4-AP can be achieved using F375/F545 as readout with a detection limit of 0.4 μM. Real water samples have been tsted to evaluate this method in practical application and satisfactory results have been obtained. Furthermore, the addition of 4-AP into Tb-DNA-Ag+ system induces a visible color variation from green to bluish violet, enabling visual detection of 4-AP under the assistance of a smartphone.

Recent Advances in Biosensors Based on Hybridization Chain Reaction and Silver Nanoclusters

Hybridization chain reaction (HCR) and DNA-templated silver nanoclusters (AgNCs) have emerged as powerful tools in biosensing. HCR enables cascade amplification through programmable DNA interactions, while DNA-AgNCs serve as transducing units with unique fluorogenic and electrochemical properties. Integrating these components into a hybrid sensor could significantly enhance sensing capabilities across various fields. Nonetheless, limited studies and the lack of systematic guidelines for HCR-AgNCs systems have hindered research progress, despite their potential. This review aims to address this gap by providing a comprehensive overview of HCR-AgNCs biosensors, facilitating further innovation in this field. The working principles, performance factors, and complementary features are discussed. Thereafter, reported HCR-AgNCs studies are assessed, emphasizing their distinct sensing mechanisms (e.g., fluorogenic, electrochemical), applications across various fields, and challenges in adopting the hybrid sensors. Drawing from the experience developing multiple HCR-AgNCs sensors, insights and guidelines for designing and developing HCR-AgNCs systems are provided for future researchers. Finally, prospective directions in HCR-AgNCs research, including multiplex assays and integration with emerging technologies, are explored to guide future advancements. The synergistic combination of HCR and AgNCs as a hybrid biosensor holds promise for addressing pressing challenges in healthcare, environmental monitoring, and beyond, paving the way for next-generation biosensing technologies.

Metal Nanocluster-Based Biosensors for DNA Detection

The early detection of genetic diseases is a critical need in modern medicine, underscoring the importance of developing deoxyribonucleic acid (DNA) biosensors. In recent years, metal nanoclusters (MNCs) have demonstrated significant potential as biosensors for DNA detection due to their ultra-small size, excellent photostability, bright photoluminescence, low toxicity and other outstanding properties. This review firstly discusses the characteristics of MNCs, which are effective in the early diagnosis of DNA diseases. Subsequently, different synthesis methods of MNCs are introduced. In the following section, DNA sensors based on different types of MNCs and their respective detection mechanisms are discussed in detail. Finally, the opportunities and challenges faced by DNA sensors based on MNCs are analyzed.

DNAzyme-mediated fluorescence signal variation of DNA-Ag nanoclusters and construction of an aptasensor for ATP

DNA-templated silver nanoclusters (DNA-AgNCs) are novel nanomaterials with unique fluorescence characteristics. DNAzyme is a functional oligonucleotide that can catalyze the disruption of nucleic acid substrates. In this research, the effect of DNAzyme digestion on the fluorescence property of DNA-AgNCs was explored for the first time. A significant reduction in the fluorescence intensity of DNA-AgNCs after cleavage by DNAzyme was discovered. Further research found that the DNAzyme-catalyzed cleavage reduced the stability of DNA-AgNCs and led to their aggregation, accounting for a decline in fluorescence intensity up to 84%. Inspired by the above finding, a fluorescent aptasensor that integrates the benefits of DNA-AgNCs, exonuclease III (Exo III)-assisted signal amplification and DNAzyme was developed for sensitive detection of adenosine triphosphate (ATP). Under optimal conditions, the linear range was from 25 μM to 1000 μM and the detection limit was estimated to be 4.46 μM. Furthermore, this fluorescent aptasensor was effectively employed to quantify ATP levels in human serum samples, demonstrating its practicality in detecting ATP in biological matrices. The elucidation of DNAzyme-based fluorescence characteristic variation of DNA-AgNCs may provide insights into the interactions between DNAzyme and nanomaterials and has great prospects in the construction of fluorescent biosensors.

An ATMND/SGI based three-way junction ratiometric fluorescent probe for rapid and sensitive detection of bleomycin

In this work, we developed a rapid and sensitive label-free ratiometric fluorescent (FL) probe for the detection of bleomycin (BLM). The probe consists of a DNA sequence (D6) and two fluorophore groups, 2-amino-5,6,7-trimethyl-1,8-naphthalene (ATMND) and SYBR Green I (SGI). The D6 sequence could be folded into a three-way junction structure containing a C-C mismatch position in the junction pocket. The unique "Y" structure not only could entrap ATMND in the mismatch pocket with high affinity, leading to FL quenching at 408 nm, but also embed SGI in the grooves of the double-stranded portion, resulting in FL enhancement at 530 nm. In the presence of BLM-Fe(II), the "Y" structure of D6 was destroyed due to the specific cleavage of the BLM recognition site, the 5'-GT-3' site in D6. This caused the release of ATMND and SGI and thus the ratiometric signal change of FL enhancement by ATMND and FL quenching by SGI. Under optimal conditions, the ratiometric probe exhibited a linear correlation between the intensity ratio of F408/F530 and the concentration of BLM in the range of 0.5-1000 nM, with a detection limit of 0.2 nM. In addition, the probe was applied to detect BLM in human serum samples with satisfactory results, indicating its good clinical application potential.

Ratiometric fluorescence sensor based on europium-organic frameworks for selective and quantitative detection of cerium ions

BACKGROUND

Due to the unavoidable use of cerium in daily life, the accumulation of cerium in the environment increases health risks for humans. Therefore, it is crucial to develop a chemical sensing technology for the rapid, sensitive, and selective detection of cerium ions.

RESULTS

In this research work, a novel two-dimensional chain structure of a europium-based metal organic framework (Eu-MOF) [Eu2(tcpa)(Htcpa)2] was synthesized by using 3,4,5,6-tetrachloro-1,2-benzenedicarboxylic acid (H2TCPA) as the ligand and europium nitrate as the metal source. The results of powder X-ray diffraction and thermogravimetric analysis show that the synthesized Eu-MOF has excellent chemical and thermal stability. When the Eu-MOF suspension was excited by ultraviolet light at 292 nm, four fluorescence emissions were observed at 420, 595, 620 and 705 nm. It was particularly interesting that when cerium ions (Ce3+/Ce4+) were added to the Eu-MOF suspension, the fluorescence intensity at 420 nm was enhanced, while the fluorescence at 620 nm was quenched. On this basis, a ratiometric fluorescent sensor for detecting cerium ions was constructed, which has a good linear relationship in the range of 0.05-15 μM and a detection limit of 16 nM. The plausible mechanism of the change in the fluorescence characteristics of Eu-MOF caused by cerium ions was discussed in detail. Through the study of fluorescence lifetime and ultraviolet absorption, it was proven that the mechanism of Ce3+-quenching Eu-MOF fluorescence is the inner filter effect. Photoinduced electron transfer and internal filtering effects lead to fluorescence quenching at 620 nm, while redox reactions lead to fluorescence enhancement of the ligand at 420 nm.

SIGNIFICANCE

The proposed ratiometric fluorescence sensor was successfully employed for the detection of cerium ions in real water samples, confirming that it can be used as an alternative method for the detection of Ce3+ and Ce4+ in environmental samples.

Engineered DNA molecular machine for ultrasensitive detection of environmental lead pollution

Dynamic monitoring of environmental Pb2+ is of utmost importance for food safety and personal well-being. Herein, we report a novel, rapid, and practical fluorescence detection platform for Pb2+. The platform comprises two essential components: an engineered DNAzyme probe (EDP) and a responsive functionalized probe (RFP). The EDP demonstrates specific recognition of Pb2+ and the subsequent release of free DNA fragments. The released DNA fragments are then captured using the RFP to form DNA complexes, which undergo multiple cascade amplification reactions involving polymerases and nickases, resulting in the generation of a large number of fluorescence signals. These signals can detect Pb2+ at concentrations as low as 0.114 nmol/L, with a dynamic range spanning from 0.1 nmol/L to 50 nmol/L. Moreover, the platform exhibits excellent sensitivity and selectivity for Pb2+ detection. To further validate its effectiveness, we successfully quantitatively detected lead contamination in water from Chaohu Lake, and the results aligned closely with those obtained using inductively coupled plasma-mass spectrometry (ICP-MS). Moreover, this platform is suitable for detecting Pb2+ in seawater, soil, and fish samples. These findings confirm the suitability of the current detection platform for the dynamic assessment of Pb contamination in ecological environments, thereby contributing to environmental and food safety.

Graphene oxide-based colorimetric/fluorescence dual-mode immunochromatography assay for simultaneous ultrasensitive detection of respiratory virus and bacteria in complex samples

A point-of-care testing biosensor that supports direct, sensitive, and simultaneous identification of bacteria and virus is still lacking. In this study, an ultrasensitive immunochromatography assay (ICA) with colorimetric/fluorescence dual-signal output was proposed for flexible and accurate detection of respiratory virus and bacteria in complex samples. Colorimetric AuNPs of 16 nm and two layers of quantum dots (QDs) were coated onto the surface of monolayer graphene oxide (GO) layer by layer to form a multilayered dual-signal nanofilm. This material not only can generate strong colorimetric and fluorescence signals for ICA analysis but also can provide larger surface area, better stability, and superior dispersibility than conventional spherical nanomaterials. Two test lines were built onto the ICA strip to simultaneously detect common respiratory virus influenza A and respiratory bacteria Streptococcus pneumoniae. The dual-signal mode of assay greatly broadened the applied range of ICA method, in which the colorimetric mode allows for quick determination of virus/bacteria and the fluorescence mode ensures the highly sensitive and quantitative detection of target pathogens with detection limits down to 891 copies/mL and 17 cells/mL, respectively. The proposed dual-mode ICA can also be applied directly for real biological and environment samples, which suggests its great potential for field application.

Ratiometric fluorescence assay for sulfide ions with fluorescent MOF-based nanozyme

A novel ratiometric fluorescence strategy for sulfide ions (S^2-) analysis has been developed using metal-organic framework (MOF)-based nanozyme. NH₂-Cu-MOF displays blue fluorescence (λem = 435 nm) originating from 2-amino-1,4-benzenedicarboxylic acid ligand. Besides, it possesses oxidase-like activity due to Cu²⁺ node, which can trigger chromogenic reaction. o-Phenylenediamine (OPD), as a common enzyme substrate, can be oxidized by NH₂-Cu-MOF to form luminescent products (oxOPD) (λem = 570 nm). Inner filter effect occurs between oxOPD and MOF. Upon exposure to S^2-, oxidase-like activity of MOF is depressed significantly because of the generation of CuS. On one hand, the amount of free Cu²⁺ decreases, affecting the yielding of oxOPD. On the other hand, CuNPs with larger size are obtained during the oxidation-reduction reaction between Cu²⁺ and OPD, which show weaker autocatalytic ability for OPD oxidation. These result in the decrease and increase of intensities at 570 and 435 nm, respectively. This method exhibits sensitive and selective responses towards S^2- with LOD of 0.1 μM. Furthermore, such ratiometric strategy has been applied to detect S^2- in food samples.

A universal approach for synthesis of copper nanoclusters templated by G-rich oligonucleotide sequences and their applications in sensing

Herein, five common G4 sequences have been selected, including three different length of telomere DNA, hemin aptamer, and thrombin aptamer, to synthesize Cu nanoclusters (Cu NCs) in-situ. All G4s are proper templates for Cu NCs with low temperature treatment. The particles (G4-Cu NCs) smaller than 3 nm in diameter were obtained and showed light green fluorescence. This is the first report of metal clusters templated by G4s in-situ. As proof of the concept, hemin and alkaline phosphatase (ALP) were used as the targets to test whether the system can monitor the interaction between G4s and its substrate. The results suggest that G4-Cu NCs can indicate the behavior of G4 and its interaction with hemin, and sensing ALP is achieved with the aid of ATP. The linear ranges of hemin and ALP are 300-4000 nM and 10-500 U/L, respectively, and the corresponding limits of detection as low as 97 nM for hemin and 2.8 U/L for ALP. Moreover, this present system has been successfully applied for the detection of ALP in human serum samples with satisfactory recoveries. This synthesis approach is universal, and it can be easily extended to evaluating the formation of G4, or monitoring the interaction between G4 and its substrate, or selective targeting individual G4, or sensitive detection of other important biomarkers by changing template G4 sequence.

Ratiometric fluorescence detection of artemisinin based on photoluminescent Zn-MOF combined with hemin as catalyst

Artemisinin (ART) is a type of frontline drug to treat drug-resistant falciparum malaria. Simple, accurate and selective determination of ART is significant to monitor its clinical pharmaceutical efficacy. Herein, a new ratiometric fluorescence method has been designed for the determination of ART with Zn-MOF as fluorescence reference and hemin as catalyst, respectively. Zn-MOF possesses intrinsic fluorescence at 443 nm owing to 2-aminoterephthalic acid ligand. When o-phenylenediamine (OPD) is mixed with hemin, a weak fluorescent signal at 570 nm ascribed to oxidized product of OPD (oxOPD) is observed. In the presence of ART, hemin can catalyze ART to break its peroxide bridge and release a large number of reactive oxygen species, which effectively oxidize OPD into luminescent oxOPD. Therefore, the fluorescence at 570 nm is enhanced significantly while the fluorescence of Zn-MOF remains basically unchanged. Thus, a ratiometric fluorescence sensing platform has been constructed for the detection of ART. This method exhibits wider linear range (0.15 μM-150 μM) with detection limit of 50 nM. This novel and selective method has been used to detect ART in compound naphthoquinone phosphate tablets.

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.

Ratiometric fluorescence sensing of formaldehyde in food samples based on bifunctional MOF

A new fluorescence strategy was described for ratiometric sensing of formaldehyde (FA) with bifunctional MOF, which acted as a fluorescence reporter as well as biomimetic peroxidase. With the assistance of H₂O₂, NH₂-MIL-101 (Fe) catalyzes the oxidation of non-luminescent substrate o-phenylenediamine (OPD) to produce fluorescent product (oxOPD) with the maximum emission at 570 nm. Besides, intrinsic fluorescence of MOF (λem = 445 nm) was quenched by oxOPD through inner filter effect (IFE). However, FA and OPD reacted to generate Schiff bases, which competitively consumed OPD inhibiting the generation of oxOPD. Under the excitation wavelength of 375 nm, a ratiometric strategy was designed to detect FA with the fluorescence intensity ratio at 445 nm and 570 nm (F₄₄₅/F₅₇₀) as readout signal. This strategy exhibited a wide linear range (0.1-50 μM) and low detection limit of 0.03 μM. This method was confirmed for FA detection in food samples. In addition to establishing a new method to detect FA, this work will open new applications of MOF in food safety.

Cascade amplification strategy combined with analyte-triggered fluorescence switching of dual-quenching system for highly sensitive detection of isoniazide

A sensitive fluorescence sensing platform consisting of manganese dioxide nanosheets (MnO₂) and gold nanoparticles (AuNPs) as dual nanoquenchers has been constructed to detect isoniazid combined with analyte-triggered cascade reactions. The fluorescence of 2,3-diaminophenazine (DAP) is quenched simultaneously by MnO₂ and AuNPs via inner filter effect. MnO₂ is decomposed by isoniazid to generate Mn²⁺, which makes AuNPs aggregated. The quenching abilities of both the decomposed MnO₂ and aggregated AuNPs are inhibited, causing remarkable fluorescence recovery. The usage of dual nanoquenchers enhances the quenching efficiency and reduces the fluorescence background. Moreover, the isoniazid-triggered cascade reaction further amplifies the readout signal. Thus, this strategy exhibits higher sensitivity towards the detection of isoniazid. Compared with MnO₂-based fluorescence assay, this strategy possesses lower limit of detection. This strategy has been successfully used to detect isoniazid in pharmaceutical preparations, which is of great significance for drug analysis.

A ratiometric fluorescence-scattering sensor for rapid, sensitive and selective detection of doxycycline in animal foodstuffs

The residue problem of tetracycline antibiotics, especially doxycycline (DC), in animal foodstuffs has attracted much attention. This paper reported ZIF-8 and bovine serum albumin (BSA) as a ratiometric fluorescence-scattering sensor for DC. The mechanism relied on the disassembly of ZIF-8 caused by DC, bringing weakened second-order scattering, and the double fluorescence amplification of DC under ZIF-8 with BSA, inducing enhanced fluorescence. The response of the sensor was completed within 1 min, and the detection limit for DC (3.4 nM) was 1-2 orders of magnitude lower than the reported ones. The distinguishment of DC from other tetracycline antibiotics was also achieved by the sensor. The sensor was applied to detecting DC in animal foodstuffs with satisfactory recoveries (80.0-104.0%). Hence, this work develops a rapid, sensitive and selective ratiometric sensor to monitor the DC residue in animal foodstuffs, also opens the window to construct ratiometric DC sensors with the fluorescence-scattering strategy.

Copper nanocluster composites for analytical (bio)-sensing and imaging: a review

As an ideal substitute for traditional organic fluorescent dyes or up-conversion nanomaterials, copper nanoclusters (CuNCs) have developed rapidly and have been involved in exciting achievements in versatile applications. The emergence of novel CuNCs composites improves the poor stability and fluorescence intensity of CuNCs. With this in mind, great efforts have been made to develop a wide variety of CuNCs composites, and impressive progress has been made in the past few years. In this review, we systematically summarize absorption, fluorescence, electrochemiluminescence, and catalytic properties and focus on the multiple factors that affect the fluorescence properties of CuNCs. The fluorescence properties of CuNCs are discussed from the point of view of core size, surface ligands, self-assembly, metal defects, pH, solvent, ions, metal doping, and confinement effect. Especially, we illustrate the research progress and representative applications of CuNCs composites in bio-related fields, which have received considerable interests in the past years. Additionally, the sensing mechanism of CuNCs composites is highlighted. Finally, we summarize current challenges and look forward to the future development of CuNCs composites. Schematic diagram of the categories, possible sensing mechanisms, and bio-related applications of copper nanoclusters composites.

Fluorescent DNA-templated silver nanoclusters for highly sensitive detection of D-penicillamine

Herein, fluorescent DNA-templated silver nanoclusters (DNA-AgNCs) with red emission were synthesized and utilized as novel probe to detect D-penicillamine (D-Pen) for the first time. D-Pen molecules contain a thiol which can combine with Ag to form a non-fluorescent ground state complex, inducing the aggregation of DNA-AgNCs followed by the fluorescence quenching. The quenching mechanism is well-studied and found to be a static quenching process. This method can detect D-Pen in the range of 0.025-0.7 μM with the detection limit as low as 8 nM, which is 1-3 orders of magnitude more sensitive than those based on other fluorescent nanoprobes. More importantly, the preparation procedure for DNA-AgNCs is fast and without the requirement of heavy metal ions. Thus, this detection strategy is time-saving and eco-friendly. Satisfactory recoveries have been acquired for monitoring D-Pen in human serum samples and pharmaceutical samples owing to the high sensitivity.

MOF@MnO2nanocomposites prepared usingin situmethod and recyclable cholesterol oxidase-inorganic hybrid nanoflowers for cholesterol determination

In this work, through thein situgrowth of MnO₂nanosheets on the surface of terbium metal-organic frameworks (Tb-MOFs), MOF@MnO₂nanocomposites are prepared and the fluorescence of Tb-MOFs is quenched significantly by MnO₂. Additionally, the hybrid nanoflowers are self-assembled by cholesterol oxidase (ChOx) and copper phosphate (Cu₃(PO₄)₂·3H₂O). Then a new strategy for cholesterol determination is developed based on MOF@MnO₂nanocomposites and hybrid nanoflowers. Cholesterol is oxidized under the catalysis of hybrid nanoflowers to yield H₂O₂, which further reduces MnO₂nanosheets into Mn²⁺. Hence, the fluorescence recovery of Tb-MOFs is positively correlated to the concentration of cholesterol in the range of 10 to 360μM. The limit of detection (LOD) of cholesterol is 1.57μM. On the other hand, the hierarchical and confined structure of ChOx-inorganic hybrid nanoflowers greatly improve the stability of the enzyme. The activity of hybrid nanoflowers remains at a high level for one week when stored at room temperature. Moreover, the hybrid nanoflowers can be collected by centrifugation and reused. The activity of hybrid nanoflowers can continue at a high level for five cycles of determination. Therefore, it can be concluded that the hybrid nanoflowers are more stable and more economic than free enzymes, and they show a similar sensitivity and specificity to cholesterol compared with free ChOx. Finally, this strategy has been further validated for the determination of cholesterol in serum samples with satisfactory recoveries.

A ratiometric fluorescence assay for bleomycin based on dual-emissive chameleon DNA-templated silver nanoclusters

The authors design dual-emissive DNA-templated silver nanoclusters (DNA-AgNCs) for ratiometric fluorescence sensing bleomycin (BLM) for the first time. A hairpin probe containing two different C-rich DNA templates at two terminals is used to synthesize chameleon DNA-AgNCs, which possess two emission peaks when they are in close proximity. A strong emission is founded at 622 nm (λex = 570 nm) while a weak one is located at 572 nm (λex = 504 nm). Meanwhile, the loop of this probe contains the scission site (5'-GC-3') of BLM. The loop can be cleaved into two parts by BLM-Fe(II) complex, inducing the two DNA-AgNCs away from each other. The fluorescence intensity at 572 nm and 622 nm increases and decreases, respectively. Such chameleon DNA-AgNCs exhibit an obvious fluorescence discoloration from orange to yellow. Therefore, a sensitive ratiometric fluorescent strategy for BLM detection has been proposed with the detection limit of 67 pM. Finally, this ratiometric method is used to detect BLM in serum samples.

Ce4+-triggered cascade reaction for ratiometric fluorescence detection of alendronate

A ratiometric fluorescence assay for alendronate (ALDS) has been designed with Ce⁴⁺-triggered cascade chromogenic reaction. This strategy involves three processes: (1) Ce⁴⁺ oxidizes ascorbic acid (AA) into dehydroascorbic acid (DHAA), which then condenses with o-phenlenediamine (OPD) to generate fluorescent 3-(dihydroxyethyl)furo[3,4-b] quinoxaline-1-one (DFQ), presenting the maximum emission at 434 nm; (2) As oxidase-mimics, Ce⁴⁺ can oxidize OPD into fluorescent 2,3-diaminophenazine (DAP) which shows a strong emission at 568 nm; (3) ALDS inhibits the oxidation ability of Ce⁴⁺ towards OPD, thus inhibiting the generation of DAP. Accordingly, a homogeneous ratiometric fluorescence system with dual emission comes into being and the presence of ALDS can change the fluorescence intensity ratio obviously. With F₄₃₄/F₅₆₈ as readout, ALDS can be detected sensitively with the detection limit of 30 nM. Moreover, this ratiometric method was used to analyze ALDS in both human serum and pharmaceutical samples.

Lead halide perovskites with aggregation-induced emission feature coupled with gold nanoparticles for fluorescence detection of heparin

Herein, a new kind of lead halide perovskite (LHP, (C₁₂H₂₅NH₃)₂PbI₄) with aggregation-induced emission (AIE) feature is developed as a fluorescent probe for heparin (Hep). The LHPs exhibit high emission when they aggregate in water. Interestingly, a few picomoles of dispersed gold nanoparticles (AuNPs) can quench the emission of LHPs, but the aggregated AuNPs are invalid. When protamine (Pro) is mixed with AuNPs at first, the negatively charged AuNPs aggregate through electrostatic interaction, producing the AIE recovery. Nevertheless, Hep disturbs the interaction between AuNPs and Pro due to its strong electrostatic interaction with Pro. Therefore, the dispersed AuNPs quench the fluorescence of LHPs again. A response linear range of Hep of 0.8-4.2 ng ml^-1is obtained, and the detection limit is 0.29 ng ml^-1. Compared with other probes for determination of Hep with AuNPs, this strategy exhibits better sensitivity due to the small quantity of AuNPs used. Finally, it is also successfully applied to detect Hep in human serum samples with satisfactory recoveries.

pH-modulated aggregation-induced emission of Au/Cu nanoclusters and its application to the determination of urea and dissolved ammonia

A fluorescence platform is designed based on aggregation-induced emission of Au/Cu nanoclusters (Au/Cu NCs) driven by pH value. When pH increases from 6.0 to 7.0, Au/Cu NCs change from aggregation to dispersion, accompanied by the oxidation of Cu cores. Under the catalysis of urease, urea is hydrolysed to release ammonia, which further undergoes a hydrolysis reaction to produce OH^-, causing the pH to increase. The fluorescence of Au/Cu NCs quenches linearly at 590 nm with the excitation wavelength at 320 nm when the concentration of urea varies from 5.0 to 100 μM. The limit of detection (LOD) and limit of quantification (LOQ) of urea are 2.23 and 7.45 μM, respectively. Combined with headspace single-drop microextraction technology, Au/Cu NCs are employed to monitor dissolved ammonia with low-cost and simple operation. The linear range of dissolved ammonia is from 20 to 300 μM. The LOD and LOQ of dissolved ammonia are 7.04 and 23.4 μM, respectively. The relative standard deviation (RSD) values of the intra-day and inter-day precision of urea are 2.4-3.0% and 3.0-3.7%, respectively, and those of dissolved ammonia are in the range 3.4-5.1% (intra-day precision) and 4.2-5.8% (inter-day precision). No interferences have been indentified in the determination of urea and dissolved ammonia. Finally, the proposed method has been applied to determine urea in human urine samples and dissolved ammonia in water samples with satisfactory results.Graphical abstract The pH increase produces the dispersion and decomposition of Au/Cu NCs, leading to the fluorescence quenching. Both urea and dissolved ammonia are detected successfully because they cause the pH change to alkaline.

A ratiometric fluorescence assay for bleomycin based on Cu2+-triggered cascade reactions and nanoparticle-mediated autocatalytic reactions

A new and facile method has been proposed for ratiometric fluorescence sensing of BLM based on the Cu²⁺-induced formation of two fluorescent probes (DFQ and DAP) with OPD as the precursor coupled with nanoparticle-mediated autocatalytic reactions.