Multi-channel prismatic localized surface plasmon resonance biosensor for real-time competitive assay multiple COVID-19 characteristic miRNAs

A multi-channel prismatic localized surface plasmon resonance (LSPR) biosensor was developed for quantitative and real-time detection of multiple COVID-19 characteristic miRNAs. The well-dispersed and dense gold nanoparticles (AuNPs) arrays for LSPR biosensing were fabricated through a nano-thickness diblock copolymer template (BCPT). Both theoretical and experimental analyses were conducted to investigate the effects of particle size, interparticle spacing, and surface coverage on LSPR sensing spectrum and intensity sensitivity of varied AuNPs sizes. A competitive assay strategy was proposed and used for non-amplification miRNA detection with a low limit detection of 3.41 nM, while a four-channel prismatic LSPR system enables parallel detection of multiple miRNAs. Furthermore, this sensing strategy can effectively and specifically identify target miRNA, distinguish mismatched miRNA and interfering miRNA, and exhibit low non-specific adsorption. This BCPT-based LSPR biosensor demonstrates the practicality and potential of a multi-channel, adaptable, and integrated prismatic sensor in medical testing and diagnostic applications.

Aptamer-functionalized gold nanoparticles for mercury ion detection in a colorimetric assay based on color change time as signal readout

A universal strategy for a rapid colorimetric method for Hg2+ in an aqueous solution is described. The specific binding of Hg2+ (thymine-Hg2+-thymine) with thiolated DNA-functionalized gold nanoparticles (AuNPs) via Au-S bonds increases the spatial hindrance of the AuNP surface, resulting in a weakened catalytic ability of AuNPs to catalyze the reaction between p-nitrophenol and NaBH4. Therefore, the color change time (CCT) of the solution from yellow to colorless becomes longer. Based on the kinetic curve of absorbance over time measured by a UV spectrometer, the level of Hg2+ in aqueous solutions can be easily quantified. A linear relationship between CCT and Hg2+ concentration was obtained in the 10-600-nM range with a detection limit of 0.20 nM, which is much lower than the limit value (10 nM) defined by the US Environmental Protection Agency for Hg2+ in drinking water. The excellent sensitivity comes from CCT as the signal output of the probe, rather than the absorbance or wavelength change used in traditional colorimetric probes as the signal output.

Nanomaterials for fluorescent detection of vitamin B2: A review

Vitamin B2 plays vital roles in maintaining human health. It is of tremendous significance to construct sensitive sensors of VB2. In this review, we first briefly presented the sensing mechanisms of fluorescent nanomaterials for sensing VB2. Subsequently, the advances of nanomaterials for fluorescent determination of VB2 were highlighted. And sensing performance of traditional approaches and fluorescent nanosensors was further compared. In last section, the challenges and perspectives concerning the topic were discussed.

Colorimetric and Fluorescent Sensing of Copper Ions in Water through o-Phenylenediamine-Derived Carbon Dots

Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using a simple one-step hydrothermal method starting from o-phenylenediamine (OPD) and ammonium sulfide. The prepared NSCDs presented a selective dual optical response to Cu(II) in water through the arising of an absorption band at 660 nm and simultaneous fluorescence enhancement at 564 nm. The first effect was attributed to formation of cuprammonium complexes through coordination with amino functional groups of NSCDs. Alternatively, fluorescence enhancement can be explained by the oxidation of residual OPD bound to NSCDs. Both absorbance and fluorescence showed a linear increase with an increase of Cu(II) concentration in the range 1-100 µM, with the lowest detection limit of 100 nM and 1 µM, respectively. NSCDs were successfully incorporated in a hydrogel agarose matrix for easier handling and application to sensing. The formation of cuprammonium complexes was strongly hampered in an agarose matrix while oxidation of OPD was still effective. As a result, color variations could be perceived both under white light and UV light for concentrations as low as 10 µM. Since these color changes were similarly perceived in tap and lake water samples, the present method could be a promising candidate for simple, cost-effective visual monitoring of copper onsite.

Multi-excitation wavelength of gold nanocluster-based fluorescence sensor array for sulfonamides discrimination

Sulfonamides (SAs) are widely used in many fields because of their advantages, including low price, wide antibacterial spectrum, and high stability. However, their accumulation in the human body leads to a variety of serious diseases. Therefore, it is necessary to design a convenient, effective, and sensitive method to detect SAs. Moreover, the fluorescence excitation spectrum has rich information characteristics, especially for the interaction between fluorophore and quencher via various mechanisms. However, the excitation wavelength-guided sensor array construction does not draw proper attention. To address these issues, we used BSA-AuNCs as a single probe to construct a sensor array for the detection of five SAs. The selected SAs showed different quenching effects on the fluorescence intensities of BSA-AuNCs. The changes in the fluorescence intensity at different excitation wavelengths (λ = 230, 250, and 280 nm) have been applied to construct our sensor array and address the distinguishability between the selected SAs. With helping of pattern recognition methods, five different SAs have been identified at three different concentrations. Additionally, qualitative analysis at different moral ratios and quantitative analysis at nanogram concentrations have been considered. Moreover, the proposed sensor array was successfully used to distinguish between different SAs in commercial milk with an accuracy of 100 %. This study provides a simple and powerful approach to SAs detection. Also, it shows a broad application prospect in the field of food and drug monitoring.

Surface modifications of Gold Nanoparticles: Stabilization and Recent Applications in Cancer Therapy

Gold nanoparticles (GNP) are noble metal nanocarriers that have been recently researched upon for pharmaceutical applications, imaging, and diagnosis. These metallic nanocarriers are easy to synthesize using chemical reduction techniques as their surface can be easily modified. Also, the properties of GNP are significantly affected by its size and shape which mandates its stabilization using suitable techniques of surface modification. Over the past decade, research has focused on surface modification of GNP and its stabilization using polymers, polysaccharides, proteins, dendrimers, and phase-stabilizers like gel phase or ionic liquid phase. The use of GNP for pharmaceutical applications requires its surface modification using biocompatible and inert surface modifiers. The stabilizers used, interact with the surface of GNP to provide either electrostatic stabilization or steric stabilization. This review extensively discusses the surface modification techniques for GNP and the related molecular level interactions involved in the same. The influence of various factors like the concentration of stabilizers used their characteristics like chain length and thickness, pH of the surrounding media, etc., on the surface of GNP and resulting to stability have been discussed in detail. Further, this review highlights the recent applications of surface-modified GNP in the management of tumor microenvironment and cancer therapy.

One-Step Green Synthesis of Water-Soluble Fluorescent Carbon Dots and Its Application in the Detection of Cu2

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu²⁺ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu²⁺ ions, with a low detection limit of 0.005 μg/mL; this was largely ascribed to Cu²⁺ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu²⁺ metal ions in wastewater.

Nanomaterials for fluorescent detection of curcumin

Owing to the attractive biological and pharmacological activities, sensitive and selective detection of curcumin is of great significance. Nanomaterials possessing unique optical properties exhibit potential applications in the fluorescent detection of curcumin. This review first discussed the detection strategies of fluorescent nanosensors. In the subsequent section, we highlighted the recent advances of different nanomaterials for fluorescent detection of curcumin, including semiconductor QDs, lanthanide upconversion nanoparticles, fluorescent metal nanoclusters, and carbon quantum dots. And we further provided the merits of fluorescent nanosensors for curcumin. Lastly, the challenges and further directions were presented.

Paper-based plasmonic nanosensor monitors environmental lead pollution in real field

Development of a low-cost portable colorimetric nanosensor for real field pollution monitoring.

Multiple ions detection by field-effect transistor sensors based on ZnO@GO and ZnO@rGO nanomaterials: Application to trace detection of Cr (III) and Cu (II)

This work narrates the preparation of efficient nanomaterials framework of zinc oxide (ZnO) nanoglobules (NGs) with graphene oxide (GO) and reduced graphene oxide (rGO) for the fabrication of rapid multiple ion field-effect transistor (MI-FET) sensors. Prepared ZnO-NGs@GO and ZnO-NGs@rGO nanocomposites were broadly analyzed by different analytical techniques to study their morphological, structural, compositional, and electrochemical properties. As electrode materials, ZnO-NGs@GO and ZnO-NGs@rGO were used to fabricate MI-FETs sensor for the detection of multiple ions such as Ni (II), Co (II), Cu (II), Cr (III), Fe (II), and Bi (II) ions. ZnO-NGs@GO and ZnO-NGs@rGO modified MI-FETs sensor exhibited excellent responses towards Cr (III) and Cu (II) ions, which presented the remarkable sensitivities of ~49.28 mA μM^-1. cm^-2 (Cr (III) ions) and ~185.32 mA μM^-1. cm^-2 (Cu (II) ions), respectively. The fabricated MI-FETs sensor displayed good dynamic linear detection of ions with low limit of detection (LOD) values of ~7.05 μM and ~14.9 μM for ZnO-NGs@GO and ZnO-NGs@rGO electrodes, respectively. Efficient charge transfer over electrode considerably enhanced the trace detection of Cr (III) and Cu (II) ions. The fabricated MI-FETs sensor platform exhibited extraordinary reproducibility and excellent stability of sensing performance and thus, confirmed delightful potential to sprout a useful tool for water maintaining system.

Molecular reactivity of thiolate-protected noble metal nanoclusters: synthesis, self-assembly, and applications

Thiolate-protected noble metal (e.g., Au and Ag) nanoclusters (NCs) are ultra-small particles with a core size of less than 3 nm. Due to the strong quantum confinement effects and diverse atomic packing modes in this ultra-small size regime, noble metal NCs exhibit numerous molecule-like optical, magnetic, and electronic properties, making them an emerging family of "metallic molecules". Based on such molecule-like structures and properties, an individual noble metal NC behaves as a molecular entity in many chemical reactions, and exhibits structurally sensitive molecular reactivity to various ions, molecules, and other metal NCs. Although this molecular reactivity determines the application of NCs in various fields such as sensors, biomedicine, and catalysis, there is still a lack of systematic summary of the molecular interaction/reaction fundamentals of noble metal NCs at the molecular and atomic levels in the current literature. Here, we discuss the latest progress in understanding and exploiting the molecular interactions/reactions of noble metal NCs in their synthesis, self-assembly and application scenarios, based on the typical M(0)@M(i)-SR core-shell structure scheme, where M and SR are the metal atom and thiolate ligand, respectively. In particular, the continuous development of synthesis and characterization techniques has enabled noble metal NCs to be produced with molecular purity and atomically precise structural resolution. Such molecular purity and atomically precise structure, coupled with the great help of theoretical calculations, have revealed the active sites in various structural hierarchies of noble metal NCs (e.g., M(0) core, M-S interface, and SR ligand) for their molecular interactions/reactions. The anatomy of such molecular interactions/reactions of noble metal NCs in synthesis, self-assembly, and applications (e.g., sensors, biomedicine, and catalysis) constitutes another center of our discussion. The basis and practicality of the molecular interactions/reactions of noble metal NCs exemplified in this Review may increase the acceptance of metal NCs in various fields.

A novel iron quantum cluster confined in hemoglobin as fluorescent sensor for rapid detection of Escherichia coli

A new method based on fluorescent probe of iron quantum cluster has been proposed for rapid detection of Escherichia coli (E. coli). The iron quantum cluster was synthesized using hemoglobin as both a source of iron and a protective agent (Hb-FeQCs). The investigation of the sensitivity of Hb-FeQCs towards metal ions showed a highly selective turn off fluorescence for Cu²⁺. It suggests that Cu²⁺ can induce fluorescence quenching by binding to amino acids of Hb. The ability of E. coli bacteria to capture and reduce of Cu ions caused to efficient recovery of the fluorescence of Hb-FeQCs from Cu²⁺-caused quenching. This probe has a satisfactorily linear range of 0.35-35 μM for Cu²⁺ under the optimal iron quantum cluster concentration (500 μg/mL) with an 85 nM detection limit. Rapid and facile detection of E.coli bacteria with the limit of detection around 8.3 × 10³ CFU/mL was successfully achieved in the artificially contaminated urine, tap water, and DMEM samples within 30 min. The fluorescence recovery was investigated by different types of bacteria and only E. coli revealed 56% recovery which related to its capability to Cu²⁺ reduction and the great potential of the fluorescent probe for rapid detection of pathogenic E. coli bacteria. Furthermore, the Hb-FeQCs can detect E. coli bacteria in an infected urine sample by retrieving up to 74% of its fluorescence which is helpful to accelerate the diagnosis and treatment of urinary tract infection (UTI).

Determination of copper ions in herbal medicine based on click chemistry using an electronic balance as a readout

The amount of copper affects the quality of herbal medicine greatly, it is necessary to develop some simple and sensitive methods to detect copper for the remote or resource-limited area. An electronic balance is one of the most familiar equipment that can be found nearly in all laboratories. The presence of Cu(i) can catalyze azide-alkyne cycloaddition reaction (called as click chemistry) with high efficiency. In this study, a simple method had been developed to detect copper ions in herbal medicine using an electronic balance as a readout device based on click chemistry. Cu(ii) is reduced to Cu(i) by sodium ascorbate in situ, which induces the "click" reaction between azido-DNA modified magnetic beads (MB-DNA) and alkynyl-DNA modified platinum nanoparticles (Pt NP-DNA) and results in the fixing of the platinum nanoparticles on the beads (called as MB-Pt NPs). MB-Pt NPs can be separated by a magnetic frame easily and transferred into a drainage reaction device containing hydrogen peroxide. Then, hydrogen peroxide can be decomposed by Pt NPs modified on MB to generate oxygen, which increases the pressure in the drainage reaction device and forces the water in the system to be discharged. The weight of the discharged water can be easily and accurately measured by an electronic balance. The weight of the water has a linear relationship with Cu(ii) in the range of 2.0-200 μM and a detection limit of 0.83 μM under 30 min of collected time. This method does not need complicated and expensive instruments, skilled technicians, and a complex data processing process. The proposed method had been applied to detect copper ions in herbal medicine with satisfactory results.

γ-Aminobutyric acid-modified graphene oxide as a highly selective and low-toxic fluorescent nanoprobe for relay recognition of copper(II) and cysteine

A sensitive and selective graphene oxide (GO)-based fluorescent nanoprobe has been developed for the relay recognition of Cu²⁺ and cysteine (Cys) by covalently grafting γ-aminobutyric acid (GABA) onto GO. The fluorescence of the probe (with excitation/emission maxima at 360/445 nm) is selectively quenched by Cu²⁺ via static fluorescence quenching. Fluorescence drops linearly as the concentration of Cu²⁺ is increased from 50 nM to 1.0 µM, and the detection limit for Cu²⁺ is calculated as 15 nM. By virtue of the strong interaction between Cys and Cu²⁺, the GO-GABA/Cu²⁺ complex can further sensitively recognize Cys in a "switch-on" mode. The linear range for Cys detection is from 50 nM to 1.0 µM, and the detection limit is 38 nM. The probe has low cytotoxicity, and it works well inside living cells, which is verified by the successful application in imaging of LLC-PK1 cells. Graphical abstract Gamma-Aminobutyric Acid (GABA) modified graphene oxide (GO) is a highly selective nanoprobe for the fluorometric relay recognition of Cu²⁺ and Cys.

A label-free ratiometric fluorescence nanoprobe for ascorbic acid based on redox-modulated dual-emission signals

In this paper, we constructed a label-free ratiometric fluorescence nanoprobe for ascorbic acid (AA) on the basis of the change in dual-emission signals by the specific reaction between cobalt oxyhydroxide (CoOOH) and AA. CoOOH nanoflakes were used as the recognition unit while polymer dots (PFO dots) and gold nanoclusters (AuNCs) served as luminescent units of the nanoprobe. After electrostatic assembly of PFO dots and AuNCs on the surface of CoOOH nanoflakes, the energy transfer between the PFO dots and CoOOH could occur and thereby quench the fluorescence of the PFO dots. When AA was present, CoOOH nanoflakes were reduced to Co²⁺, resulting in a recovery of the fluorescence of the PFO dots. In the meantime, the generated Co²⁺ could combine with the surface ligands of AuNCs, accompanied by a reduction in the luminescence intensity of the AuNCs. Therefore, the fluorescence intensity ratio of PFO dots to AuNCs would be related to the concentration of AA. The nanoprobe enabled highly sensitive analysis of AA with a detection limit of 1.9 μM and showed great performance in human serum samples and living cells. This report may not only endow a CoOOH-based nanoprobe with improved ability but also offer a novel strategy for the construction of ratiometric nanoprobes for AA and have potential applications in research into and clinical diagnosis of AA-related diseases.

Electronic-Tongue Colorimetric-Sensor Array for Discrimination and Quantitation of Metal Ions Based on Gold-Nanoparticle Aggregation

Sensor arrays, called "electronic tongues", provide an alternative to time-consuming detection approaches. In this work, a colorimetric-sensor array composed of three recognition receptors (cysteine, l-glutathione, and melamine) was developed for fast discrimination of toxic metal ions. Different recognition receptors exhibited different binding affinities toward metal ions, causing diverse gold-nanoparticle (AuNP)-aggregation behaviors and generating distinct colorimetric response patterns. As "fingerprints", these response patterns can be quantitatively analyzed by linear-discriminant analysis (LDA). The sensor array achieved good discrimination of six kinds of metal ions (Ti⁴⁺, Cr³⁺, Mn²⁺, Fe³⁺, Pb²⁺, and Sn⁴⁺) in deionized water and real samples. It possessed good reproducibility and exhibited a linear range of 100-900 nM ( R² = 0.97) for Ti⁴⁺, 100-900 nM ( R² = 0.97) for Cr³⁺, 100-900 nM ( R² = 0.98) for Mn²⁺, 100-1000 nM ( R² = 0.92) for Sn⁴⁺, 100-800 nM ( R² = 0.94) for Fe³⁺, and 100-900 nM ( R² = 0.97) for Pb²⁺. The sensor array shows feasible potential in environmental monitoring and simplification of water-quality analysis.

Influence of doping ion, capping agent and pH on the fluorescence properties of zinc sulfide quantum dots: Sensing of Cu2+ and Hg2+ ions and their biocompatibility with cancer and fungal cells

Herein, a facile one-pot synthetic method was explored for the fabrication of glutathione capped Mn²⁺ doped‑zinc sulphide quantum dots (GSH-Mn²⁺-ZnS QDs) for both fluorescent detection of Cu²⁺ and Hg²⁺ ions and for fluorescence imaging of two cancer (RIN5F and MDAMB231) and fungal (Rhizopus oryzae) cells. Particularly, doping of Mn²⁺ into ZnS QDs nanocrystal structure resulted a great improvement in the fluorescence properties of ZnS QDs. The emission peak of undoped ZnS QDs was found at 447 nm, which is due to the large number of surface defects in the ZnS QDs nanostructures. Under identical conditions, there is a good linear relationship between the quenching of fluorescence intensity and analytes (Cu²⁺ and Hg²⁺ ions) concentration in the range of 0.005 to 0.2 mM and of 0.025 to 0.4 mM for Cu²⁺ and Hg²⁺ ions, respectively. The GSH-Mn²⁺-ZnS QDs exhibit least cytotoxicity against RIN5F and MDAMB231 cells, demonstrating the multifunctional applications in sensing of metal ions and biocompatibility towards cancer (RIN5F and MDAMB231) and fungal (Rhizopus oryzae) cells.

Ratiometric fluorescent sensor for visual determination of copper ions and alkaline phosphatase based on carbon quantum dots and gold nanoclusters

In this work, a novel ratiometric fluorescent sensor, based on carbon dots (CDs) and gold nanoclusters (AuNCs), is developed for highly sensitive and selective visual colorimetric detection of Cu²⁺ and alkaline phosphatase (ALP). The ratiometric fluorescent sensor was synthesized by covalently linking 11-mercaptoundecanoic acid (11-MUA)-stabilized AuNCs to the surface of amino-functionalized CD/SiO₂ nanoparticles. The red fluorescence of the AuNCs can be quenched by Cu²⁺ owing to coordination between Cu²⁺ and 11-MUA; however, the blue emission of the CDs was insensitive to Cu²⁺ owing to the protective silica shell. The quenching of the AuNCs' fluorescence returned when PPi was added because of the higher affinity between Cu²⁺ and PPi than that between Cu²⁺ and 11-MUA. In the presence of ALP, PPi was catalytically hydrolyzed into phosphate (Pi), which showed a much weaker affinity for Cu²⁺. Thus, Cu²⁺ ions were released, and the fluorescence of the AuNCs was quenched once more. Based on this principle, Cu²⁺ and ALP could be simultaneously detected. The developed ratiometric fluorescent sensor could detect Cu²⁺ over a range from 0.025 to 4 μM with a detection limit of 0.013 μM and ALP over a range from 0.12 to 15 U/L with a detection limit of 0.05 U/L. The present method was successfully applied for the detection of Cu²⁺ and ALP in real water samples and in human serum samples, respectively. This ratiometric fluorescent approach may provide a highly sensitive and accurate platform for visual Cu²⁺ and ALP sensing in environmental monitoring and medical diagnosis.

Sensitive and selective detection of Cu2+ ions based on fluorescent Ag nanoparticles synthesized by R-phycoerythrin from marine algae Porphyra yezoensis

In this study, using a natural and green protein R-phycoerythrin (R-PE) extracted from marine Porphyra yezoensis as the stabilizer and reducer, silver nanoparticles (AgNPs) were synthesized. Based on this, a highly sensitive and selective method for the detection of Cu²⁺ ions was developed using R-PE-AgNPs as fluorescent probe. The interactions between R-PE-AgNPs and Cu²⁺ ions were systematically characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), elemental mapping and Fourier transform infrared (FTIR). It was found that Cu²⁺ ions could cause aggregation of the R-PE-AgNPs, accompanied by the greatly increased particle size. Importantly, the method offered a wide linear detection range from 0 μM to 100.0 μM with a detection limit of 0.0190 μM. Moreover, the proposed method was successfully applied to analyze Cu²⁺ ions in tap water and lake water samples, acquiring satisfactory recovery between 91.6% and 102.2%. Such a green, fast and cost-effective fluorimetric method of the R-PE-AgNPs probe has great potential for tracing Cu²⁺ ions in diverse aqueous media.

Shape-Controlled Synthesis of Luminescent Hemoglobin Capped Hollow Porous Platinum Nanoclusters and their Application to Catalytic Oxygen Reduction and Cancer Imaging

Engineering hollow and porous platinum nanostructures using biomolecular templates is currently a significant focus for the enhancement of their facet-dependent optical, electronic, and electrocatalytic properties. However, remains a formidable challenge due to lack of appropriate biomolecules to have a structure-function relationship with nanocrystal facet development. Herein, human hemoglobin found to have facet-binding abilities that can control the morphology and optical properties of the platinum nanoclusters (Pt NCs) by regulation of the growth kinetics in alkaline media. Observations revealed the growth of unusual polyhedra by shape-directed nanocluster attachment along a certain orientation accompanied by Ostwald ripening and, in turn, yield well-dispersed hollow single-crystal nanotetrahedrons, which can easily self-aggregated and crystallized into porous and polycrystalline microspheres. The spontaneous, biobased organization of Pt NCs allow the intrinsic aggregation-induced emission (AIE) features in terms of the platinophilic interactions between Pt(II)-Hb complexes on the Pt(0) cores, thereby controlling the degree of aggregation and the luminescent intensity of Pt(0)@Pt(II)−Hb core−shell NCs. The Hb-Pt NCs exhibited high-performance electrocatalytic oxygen reduction providing a fundamental basis for outstanding catalytic enhancement of Hb-Pt catalysts based on morphology dependent and active site concentration for the four-electron reduction of oxygen. The as-prepared Hb-Pt NCs also exhibited high potential to use in cellular labeling and imaging thanks to the excellent photostability, chemical stability, and low cytotoxicity.

Penicillamine-protected Ag20 nanoclusters and fluorescence chemosensing for trace detection of copper ions

We report the synthesis of penicillamine-protected Ag₂₀ nanoclusters (NCs), with properties of high monodispersity, red fluorescence and water solubility. Full characterization of the Ag₂₀ NCs is addressed, along with first-principles optimization calculations, revealing the chemical composition and structure of the as-prepared Ag NCs within a molecular formula [Ag₂₀(DPA)₁₈-H]^-. Moreover, natural bond orbital (NBO) analysis demonstrates the charge-transfer interactions between the ligand and Ag atoms, and helps in understanding the origins of fluorescence of Ag₂₀ NCs related to the ligand-to-metal charge transfer (LMCT) mechanism. Further, fluorescence chemosensing of the Ag₂₀ NCs is demonstrated for tracing copper ions with high sensitivity and selectivity in aqueous solution.

Synthesis of highly fluorescent gold nanoclusters and their use in sensitive analysis of metal ions

The fluorescence properties, including emission peak and quantum yield, of Au clusters are dependent upon the ligands capping the core.

Gold–platinum bimetallic nanoclusters with enhanced peroxidase-like activity and their integrated agarose hydrogel-based sensing platform for the colorimetric analysis of glucose levels in serum

Bimetallic Au–PtNCs with enhanced peroxidase-like activity were integrated into agarose hydrogels for direct visualization of glucose in human serum.

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.

Integration of nanomaterials for colorimetric immunoassays with improved performance: a functional perspective

The boom of nanotechnology has yielded exciting developments in designing new kinds of colorimetric immunoassays.

Dual ligand co-functionalized fluorescent gold nanoclusters for the “turn on” sensing of glutathione in tumor cells

A “turn on” approach was established for GSH sensing in tumor cells based on dual ligand co-functionalized fluorescent Au NCs.

Sensitive detection of mercury and copper ions by fluorescent DNA/Ag nanoclusters in guanine-rich DNA hybridization

In this work, we designed a new fluorescent oligonucleotides-stabilized silver nanoclusters (DNA/AgNCs) probe for sensitive detection of mercury and copper ions. This probe contains two tailored DNA sequence. One is a signal probe contains a cytosine-rich sequence template for AgNCs synthesis and link sequence at both ends. The other is a guanine-rich sequence for signal enhancement and link sequence complementary to the link sequence of the signal probe. After hybridization, the fluorescence of hybridized double-strand DNA/AgNCs is 200-fold enhanced based on the fluorescence enhancement effect of DNA/AgNCs in proximity of guanine-rich DNA sequence. The double-strand DNA/AgNCs probe is brighter and stable than that of single-strand DNA/AgNCs, and more importantly, can be used as novel fluorescent probes for detecting mercury and copper ions. Mercury and copper ions in the range of 6.0-160.0 and 6-240 nM, can be linearly detected with the detection limits of 2.1 and 3.4 nM, respectively. Our results indicated that the analytical parameters of the method for mercury and copper ions detection are much better than which using a single-strand DNA/AgNCs.

Furthering the chemosensing of silver nanoclusters for ion detection

An eco-friendly silver nanocluster chemosensor for Mn²⁺and I⁻ion detection, differentiation and bioimaging was synthesized. The chemosensing mechanisms were elucidated by microscopic characterization and spectral analyses.

Rapid detection of Cu2+ by a paper-based microfluidic device coated with bovine serum albumin (BSA)–Au nanoclusters

In this work, bovine serum albumin (BSA)–Au nanoclusters were used to coat a paper-based microfluidic device.

Fluorescent small Au nanodots prepared from large Ag nanoparticles for targeting and imaging cancer cells

The fluorescent gold nanodots are conjugated with folic acid, which provides them with potential applications in targeted imaging of cancer cells.

Water-soluble, nitrogen-doped fluorescent carbon dots for highly sensitive and selective detection of Hg2+ in aqueous solution

Highly fluorescent water-soluble and nitrogen-doped carbon dots (NCDs) were synthesized by a simple one-pot hydrothermal method using citric acid as carbon source and urea as nitrogen source.

Highly Sensitive Simultaneous Detection of Mercury and Copper Ions by Ultrasmall Fluorescent DNA-Ag Nanoclusters

Fluorescent metal nanoclusters (NCs) have given rise to a new class of fluorescent nanomaterials for the detection of heavy metals. Here, we design a simple, rapid and highly sensitive sensing nanosystem for the detection of Hg2+ and Cu2+ based on fluorescence quenching of ultrasmall DNA-Ag NCs. The fluorescence intensity of DNA-Ag NCs was selectively quenched by Hg2+ and Cu2+, and the limit of detection (LOD) was found to be 5 nM and 10 nM, respectively. The technique was renewable employment by EDTA addition and successfully applied to detection of Hg2+ and Cu2+ in domestic water samples. The quantum yield (QY) of DNA-Ag NCs was significantly higher to ~30% compared to traditional water-soluble fluorescent metal NCs. The DNA-Ag NC detection system make it potentially suitable for detecting Hg2+ and Cu2+ and monitoring water quality in a wide range of samples regulated under the Environmental Protection Agency.