Polyamine-functionalized carbon quantum dots as fluorescent probes for selective and sensitive detection of copper ions

A novel sensing system has been designed for Cu(2+) ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu(2+) ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs' FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu(2+) with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu(2+) ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.     

Highly selective and sensitive magnetic silica nanoparticles based fluorescent sensor for detection of Zn ions

In this work, quinoline group modified multifunctional silica nanoparticles having high magnetization and excellent Zn²⁺ selectivity have been successfully prepared. These multifunctional nanoparticles were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The characterization data indicated that the organic ligand was successfully grafted on the surface of the magnetic silica nanoparticles. The fluorescent properties of the nanosensor were characterized and employed to detect Zn²⁺ with excellent selectivity and sensitivity (0.1 μM) toward Zn²⁺ over other cations even in trace amount.     

Oligonucleotide-based fluorescence probe for sensitive and selective detection of mercury(II) in aqueous solution

In this paper we unveil a new homogeneous assayusing TOTO-3 and the polythymine oligonucleotide T 33for the highly selective and sensitive detection of Hg (2+) in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T 33. After T 33 interacts specifically with Hg (2+) ions through T-Hg (2+)-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T 33 and TOTO-3 increases in the presence of Hg (2+). Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T 33-Hg (2+) complexes. Under optimum conditions, the TOTO-3/T 33 probe exhibited a high selectivity (>or=265-fold) toward Hg (2+) over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T 33 probe for the rapid determination of Hg (2+) levels in pond water and in batteries. This approach offers several advantages, including rapidity (<15 min), simplicity (label-free), and low cost.     

Sensitive detection of mercury (II) ion using water-soluble captopril-stabilized fluorescent gold nanoparticles

In our work, a simple, facile, and green method was developed for the synthesis of water-soluble and well-dispersed fluorescent gold nanoparticles (Au NPs) within 5 min, using captopril as a capping agent. The as-prepared Au NPs showed strong emission at 414 nm, with a quantum yield of 5.5%. The fluorescence of the Au NPs can be strongly quenched by mercury (II) ion (Hg^2 +) due to the stronger interactions between thiolates (RS^?) and Hg^2 +. It was applied to the detection of Hg^2 + in water samples in the linear ranges of 0.033–0.133 μM and 0.167–2.500 μM, with a detection limit of 0.017 μM. Therefore, the as-prepared Au NPs can meet the requirement for monitoring Hg^2 + in environmental samples.     

A fluorescent probe based on visible light-emitting functionalized Graphene Quantum dots for the sensitive and selective detection of Pb (II) ions

Journal of Materials Science - We demonstrate a functionalization strategy to improve the basic fluorescence properties and to systematically customize the bandgap properties of Graphene quantum...     

Quinolino-triazole linked gold nanoparticles as sensitive 'turn-on' fluorescent Cd(2+) probes

Quinoline derivatives were brought into the surface of gold nanoparticles (Au NPs) through click chemistry. The fluorescence was quenched by Au NPs because of electron transfer between Au NPs and quinoline. However, upon addition of Cd(2+) to the quinoline-triazole Au NP solution, it exhibited an effective switch-on fluorescence response, owing to the coordination between quinoline and Cd(2+) which can efficiently block the electron transfer. What's more, the fluorescent sensor can effectively detect Cd(2+) in aqueous solution with a detection limit of 1.0 × 10(-5) M.     

DOPA-mediated reduction allows the facile synthesis of fluorescent gold nanoclusters for use as sensing probes for ferric ions

In this paper, we describe a simple one-pot method, employing l-3,4-dihydroxyphenylalanine (L-DOPA) as a reducing/capping reagent, for the synthesis of fluorescent gold nanoclusters (AuNCs). Within a short reaction time of 15 min (excluding the time required for purification), this strategy allows the fabrication of homogeneous AuNCs having the capability to sense ferric ions (Fe(3+)). The as-prepared AuNCs exhibited a fluorescence emission at 525 nm and a quantum yield of 1.7%. On the basis of an aggregation-induced fluorescence quenching mechanism, these fluorescent AuNCs offer acceptable sensitivity, high selectivity, and a limit of detection of 3.5 μM for the determination of Fe(3+) ions, which is lower than the maximum level (0.3 mg L(-1), equivalent to 5.4 μM) of Fe(3+) permitted in drinking water by the U.S. Environmental Protection Agency.     

A green synthesis of carbon nanoparticles from honey and their use in real-time photoacoustic imaging

Imaging sentinel lymph nodes (SLN) could provide us with critical information about the progression of a cancerous disease. Real-time high-resolution intraoperative photoacoustic imaging (PAI) in conjunction with a near-infrared (NIR) probe may offer opportunities for the immediate imaging for direct identification and resection of SLN or collecting tissue samples. In this work a commercially amenable synthetic methodology is revealed for fabricating luminescent carbon nanoparticles with rapid clearance properties. A one-pot “green” technique is pursued, which involved rapid surface passivation of carbon nanoparticles with organic macromolecules (e.g., polysorbate, polyethyleneglycol) in solvent-free conditions. Interestingly, the naked carbon nanoparticles are derived for the first time, from commercial food grade honey. Surface coated particles are markedly smaller (～7 nm) than previously explored particles (gold, single-walled carbon nanotubes, copper) for SLN imaging. The results indicate an exceptionally rapid signal enhancement (～2 min) of the SLN. Owing to their strong optical absorption in the NIR region, tiny size and rapid lymphatic transport, this platform offers great potential for faster resection of SLN and may lower complications caused in axillary investigation by mismarking with dyes or low-resolution imaging techniques.      

A synthesis of fluorescent starch based on carbon nanoparticles for fingerprints detection

A pyrolysis method for synthesizing carbon nanoparticles (CNPs) were developed by using malic acid and ammonium oxalate as raw materials. The incorporation of a minor amount of carbon nanoparticles into starch powder imparts remarkable color-tunability. Based on this phenomenon, an environment friendly fluorescent starch powder for detecting latent fingerprints in non-porous surfaces was prepared. The fingerprints on different non-porous surfaces developed with this powder showed very good fluorescent images under ultraviolet excitation. The method using fluorescent starch powder as fluorescent marks is simple, rapid and green. Experimental results illustrated the effectiveness of proposed methods, enabling its practical applications in forensic sciences.     

Green synthesis of nitrogen-doped fluorescent carbon quantum dots for selective detection of iron

Carbon quantum dots (CQDs) were synthesized by a simple and economic hydrothermal method using Lycium barbarum (LB-CQDs) as precursor. Ammonia was used as a dopant to prepare nitrogen modified LB-CQDs (N-LB-CQDs). The characterizations of atomic force microscope, transmission electron microscopy, X-ray photoelectron spectroscopy showed that N-LB-CQDs were spherical in shape with an average diameter of 2～5 nm. Its surface was rich in nitrogen-containing groups. The fluorescence spectrophotometer showed that N-LB-CQDs exhibited double peak emission. The two peak positions in photoluminescence were about 462 nm and 512 nm. The as-prepared N-LB-CQDs are high-fluorescent quantum yield and water soluble. In addition, iron selectively results in a strong fluorescence quenching of N-LB-CQDs. Theoretical research results verified that iron reduced energy gap between HOMO and LUMO of N-LB-CQDs greatly, which leads to its emission wavelength shift out of the visible range. Results from the study may shed light on the production of fluorescent and biocompatible CQDs with simple, economic and environmental benign strategy in which Lycium barbarum was used as a carbon source.     

Magnetic self-assembled zeolite clusters for sensitive detection and rapid removal of mercury(II)

We reported here the fabrication of a hierarchical mesoporous zeolite nanocomposite using 20 nm crystalline domins of zeolite L as building "bricks" by a simple and general one-step synthetic approach. By taking advantages of the large pore volumes, superparamagnetic iron oxide nanocrystals could be encapsulated into the nanocomposite conveniently for further facilitate separation and detection. In addition, by covalent coupling of fluorescent receptor (rhodamine-hydrazine), the combination of well-defined inorganic nanomaterials and organic receptors could be applied to selective detection of Hg(2+). Importantly, the unique adsorption capacity enabled by the hierarchical mesoporous zeolite and the efficient removal ability form complex multiphase systems by the magnetic characteristic made this multifunctional nanomaterial an excellent probe for detection, adsorption, and removal of Hg(2+) from waste aqueous solution.     

Sensitive and selective detection of mercury (II) based on the aggregation of gold nanoparticles stabilized by riboflavin

Gold nanoparticles (AuNPs) can be stabilized by riboflavin against tris buffer-induced aggregation. However, in the presence of mercury (II) (Hg2+), riboflavin can be released from the AuNPs surface and the riboflavin-Hg2+ complex formed, leading to the aggregation of AuNPs in tris buffer. The aggregation extent depends on the concentration of Hg2+. Based on the aggregation extent, a simple and sensitive method of determining Hg2+ is developed. The method enables the detection of Hg2+ over the concentration range of 0.02-0.8 microM, with a detection limit (3sigma) of 14 nM, and shows excellent selectivity for Hg2+ over other metal ions (Cu2+, Co2+, Cd2+, Pb2+, Mg2+, Zn2+, Ag+, Ce3+, Ca2+, Al3+, K+). More importantly, the method avoids complicated surface modifications and tedious separation processes.     

Surface-modified CdS nanoparticles as a fluorescent probe for the selective detection of cysteine

We present a novel method for the selective detection of cysteine, a sulfur-containing amino acid, which plays a crucial role in many important biological functions such as protein folding. Surface-modified colloidal CdS nanoparticles have been used as a fluorescent probe to selectively detect cysteine in the presence of other amino acids in the micromolar concentration range. Cysteine quenches the emission of CdS in the 0.5-10?μM concentration range, whereas the other amino acids do not affect its emission. Among the other amino acids, histidine is most efficient in quenching the emission of the CdS nanoparticles. The sulfur atom of cysteine plays a crucial role in the quenching process in the 0.5-10?μM concentration range. Cysteine is believed to quench the emission of the CdS nanoparticles by binding to their surface via its negatively charged sulfur atom. This method can potentially be applied for its detection in biological samples.     

Hydrothermal synthesis of nitrogen-containing carbon nanodots as the high-efficient sensor for copper(II) ions

Preparing high photoluminescent carbon nanodots (CNDs) by facile and low-cost processes have received considerable research interest. In this paper, high photoluminescent nitrogen-containing CNDs have been synthesized by one-step hydrothermal treatment of the pipe tobacco. The dispersion of these CNDs shows a strong blue luminescent emission with a max peak at 450 nm when it is excited at 369 nm. The as-made CNDs can sensitively and selectively detect Cu²⁺ ions compared with Ca²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Pb²⁺ ions, which offers a novel sensing platform for the detection of Cu²⁺ ions.     

Optically tunable fluorescent carbon nanoparticles and their application in fluorometric sensing of copper ions

Nano Research - A series of carbon nanoparticles (CNPs) with emission wavelength ranging from 483 to 525 nm were prepared by hydrothermal treatment of poly-3-thiopheneacetic acid (PTA) and NaOH....     

Highly sensitive, colorimetric detection of mercury(II) in aqueous media by quaternary ammonium group-capped gold nanoparticles at room temperature

We provide a highly sensitive and selective assay to detect Hg(2+) in aqueous solutions using gold nanoparticles modified with quaternary ammonium group-terminated thiols at room temperature. The mechanism is the abstraction of thiols by Hg(2+) that led to the aggregation of nanoparticles. With the assistance of solar light irradiation, the detection limit can be as low as 30 nM, which satisfies the guideline concentration of Hg(2+) in drinking water set by the WHO. In addition, the dynamic range of detection is wide (3 × 10(-8)-1 × 10(-2) M). This range, to our best knowledge, is the widest one that has been reported so far in gold nanoparticle (AuNP)-based assays for Hg(2+).     

Preparation and use of chemically modified MCM-41 and silica gel as selective adsorbents for Hg(II) ions

Adsorbents for Hg(II) ion extraction were prepared using amorphous silica gel and ordered MCM-41. Grafting with 2-(3-(2-aminoethylthio)propylthio)ethanamine was used to functionalize the silica. The functionalized adsorbents were characterized by nitrogen adsorption, X-ray diffraction, 13C MAS NMR spectroscopy and thermogravimetric analysis. The adsorption properties of the modified silica gel and MCM-41 were compared using batch method. The effect of pH, stirring time, ionic strength and foreign ions were studied. The extraction of Hg(II) ions occurred rapidly with the modified MCM-41 and the optimal pH range for the extraction by the modified materials was pH 4-7. Foreign ions, especially Cl- had some effect on the extraction efficiency of the modified silica gel and the modified MCM-41. The adsorption behavior of both adsorbents could be described by a Langmuir model at 298 K, and the maximum adsorption capacity of the modified silica gel and MCM-41 at pH 3 was 0.79 and 0.70 mmol g(-1), respectively. The modified MCM-41 showed a larger Langmuir constant than that of the modified silica gel, indicating a better ability for Hg(II) ion adsorption. The results indicate that the structure of the materials affects the adsorption behavior. These materials show a potential for the application as effective and selective adsorbents for Hg(II) removal from water.     

Sensitive and selective detection of adenine using fluorescent ZnS nanoparticles

We have used fluorescent ZnS nanoparticles as a probe for the determination of adenine. A typical 2 × 10(-7) M concentration of adenine quenches 39.3% of the ZnS fluorescence. The decrease in ZnS fluorescence as a function of adenine concentration was found to be linear in the concentration range 5 × 10(-9)-2 × 10(-7) M. The limit of detection (LOD) of adenine by this method is 3 nM. Among the DNA bases, only adenine quenched the fluorescence of ZnS nanoparticles in the submicromolar concentration range, thus adding selectivity to the method. The amino group of adenine was important in determining the quenching efficiency. Steady-state fluorescence experiments suggest that one molecule of adenine is sufficient to quench the emission arising from a cluster of ZnS consisting of about 20 molecules. Time-resolved fluorescence measurements indicate that the adenine molecules block the sites on the surface of ZnS responsible for emission with the longest lifetime component. This method may be applied for the determination of adenine in biological samples since the measurements have been carried out at pH 7.