Carbon dots-based fluorescent probes for sensitive and selective detection of iodide

We report on a simple method for the determination of iodide in aqueous solution by exploiting the fluorescence enhancement that is observed if the complex formed between carbon dots and mercury ion is exposed to iodide. Fluorescent carbon dots (C-dots) were treated with Hg(II) ion which causes quenching of the emission of the C-dots. On addition of iodide, the Hg(II) ions are removed from the complex due to the strong interaction between Hg(II) and iodide. This causes the fluorescence to be restored and enables iodide to be determined in the 0.5 to 20 μM concentration range and with a detection limit of ~430 nM. The test is highly selective for iodide (over common other anions) and was used for the determination of iodide in urine.

Solid-phase extraction of mercury(II) with magnetic core-shell nanoparticles, followed by its determination with a rhodamine-based fluorescent probe

Magnetic Fe₃O₄@SiO₂ core shell nanoparticles containing diphenylcarbazide in the shell were utilized for solid phase extraction of Hg(II) from aqueous solutions. The Hg(II) loaded nanoparticles were then separated by applying an external magnetic field. Adsorbed Hg(II) was desorbed and its concentration determined with a rhodamine-based fluorescent probe. The calibration graph for Hg(II) is linear in the 60 nM to 7.0 μM concentration range, and the detection limit is at 23 nM. The method was applied, with satisfying results, to the determination of Hg(II) in industrial waste water.

Fluorescent probe for copper(II) ion based on a rhodamine spirolactame derivative, and its application to fluorescent imaging in living cells

A fluorescent probe for Cu(II) ion is presented. It is based on the rhodamine fluorophore and exhibits high selectivity and sensitivity for Cu(II) ion in aqueous methanol (2:8, v/v) at pH 7.0. The response is based on a ring opening reaction and formation of a strongly fluorescent 1:1 complex. The response is reversible and linear in the range between 50?nM and 900?nM, with a detection limit of 7.0?nM. The probe was successfully applied to fluorescent imaging of Cu(II) ions in HeLa cells.

Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots,and its application to the sensitive determination of dopamine

We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.

Dendrimer-based biosensor for chemiluminescent detection of DNA hybridization

We report on a highly sensitive chemiluminescent (CL) biosensor for the sequenc-specific detection of DNA using a novel bio barcode DNA probe modified with gold nanoparticles that were covered with a dendrimer. The modified probe is composed of gold nanoparticles, a dendrimer, the CL reagent, and the DNA. The capture probe DNA was immobilized on magnetic beads covered with gold. It first hybridizes with the target DNA and then with one terminal end of the signal DNA on the barcoded DNA probe. CL was generated by adding H₂O₂ and Co(II) ions as the catalyst. The immobilization of dendrimer onto the gold nanoparticles can significantly enhance sensitivity and gives a detection limit of 6 fmol L^-1 of target DNA.

A highly selective fluorescent probe for the detection of palladium(II) ion in cells and aqueous media

We report on a fluorescent probe for the optical (and even bare eye) detection of palladium(II) ion which causes the probe to undergo a strong increase in absorbance and fluorescence. The probe is easily synthesized from rhodamine B hydrazide and 9-anthraldehyde and displays high selectivity over other metal ions. Fluorescence intensity and absorbance are linearly proportional to the concentration of Pd(II) in the 0–7 μM and 0–1 μM concentration range, respectively, with detection limits of 0.21 μM and 0.03 μM. The probe can detect Pd(II) with virtually no interferences by other metal ions and anions. It was applied to intracellular imaging of Pd(II) in living cells and to its determination in a palladium-containing catalyst and in spiked water samples.

Colorimetric detection of lead (II) based on silver nanoparticles capped with iminodiacetic acid

We report on a colorimetric probe for the determination of Pb(II). It is based on the use of silver nanoparticles that have been functionalizd with iminodiacetic acid (IDA-Ag NPs). The absorption spectrum and solution color of IDA-Ag NPs undergo dramatic changes on exposure to Pb(II) with a new absorption peak appearing at 650 nm and a concomitant color change from yellow to green. This is assumed to result from the aggregation of IDA-Ag NPs induced by Pb(II). Under optimum conditions, there is a linear relationship between the ratio of the absorbances at 650 and 396 nm, respectively, and the concentration of Pb(II) in the 0.4 to 8.0 μM concentration range, with a detection limit of 13 nM. The method was applied to the determination of Pb(II) in tap water and urea samples, and recoveries ranged from 93.7 % to 98.6 %.

Colorimetric and bare-eye detection of alkaline earth metal ions based on the aggregation of silver nanoparticles functionalized with thioglycolic acid

We describe a simple and rapid method for colorimetric and bare-eye detection of the alkaline earth metal ions Mg(II), Ca(II), Sr(II) and Ba(II) based on the use of silver nanoparticles (AgNPs) functionalized with thioglycolic acid (TGA). The TGA ligand was self-assembled onto the AgNPs to form a probe that undergoes a color change from yellow to orange or red on exposure to the alkaline earth ions. It is presumed that the color change is a result of the aggregation of the AgNPs caused by the interaction of the bivalent ions with the carboxy groups on the AgNPs. The color change can be used for bare-eye and colorimetric determination of the alkaline earth metal ions, for example to rapidly determine water hardness.

A lanthanide nanoparticle-based luminescent probe for folic acid

We report on a novel luminescent method for the detection of folic acid (FA), a member of the vitamin B family. Y₂O₃ nanoparticles were doped with europium(III) ions and surface-modified with captopril. Their fluorescence is quenched by FA, and intensity is a function of folic acid concentration in the 0.1 – 40 μM concentration range. The detection limit is 83 nM of FA at pH 7 and room temperature.

Functionalized manganese-doped zinc sulfide quantum dot-based fluorescent probe for zinc ion

We report on a simple strategy for the determination of zinc ion by using surface-modified quantum dots. The probe consists of manganese-doped quantum dots made from zinc sulfide and capped N-acetyl-L-cysteine. The particles exhibit bright yellow-orange emission with a peak at 598?nm which can be attributed to the ⁴T₁→⁶A₁ transition of Mn(II). This bright fluorescence is effectively quenched by modifying the sulfur anion which suppresses the radiative recombination process. The emission of the probe can then be restored by adding Zn(II) which causes the formation of a ZnS passivation layer around the QDs. The fluorescence enhancement caused is linear in the 1.25 to 30?μM zinc concentration range, and the limit of detection is 0.67?μM.

Highly sensitive SERS probe for mercury(II) using cyclodextrin-protected silver nanoparticles functionalized with methimazole

We have developed a surface-enhanced Raman scattering (SERS) probe for the determination of mercury(II) using methimazole-functionalized and cyclodextrin-coated silver nanoparticles (AgNPs). These AgNPs in pH 10 solution containing sodium chloride exhibit strong SERS at 502 cm^?1. Its intensity strongly decreases in the presence of Hg(II). This effect serves as the basis for a new method for the rapid, fast and selective determination of trace Hg(II). The analytical range is from 0.50 μg L^?1 to 150 μg L^?1, and the limit of detection is 0.10 μg L^?1. The influence of 11 metal ions commonly encountered in environmental water samples was found to be quite small. The method was applied to the determination of Hg(II) in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and with relative standard deviations of <3.5 % (n?=?5). The total analysis time is <10 min for a single sample.

CdTe-CdSe nanocrystals capped with dimethylaminoethanethiol as ultrasensitive fluorescent probes for chromium(VI)

We report on the synthesis of water-soluble luminescent colloidal CdTe nanocrystals capped with various stabilizers (mercaptopropanol, thioglycolic acid, mercaptosuccinic acid, mercaptopropionic acid, L-cysteine, reduced L-glutathione, mercaptoethanol and dimethylaminoethanethiol), and their use as fluorescent probes for chromium(VI) ions. The results show that Cr(VI) ions can be ultrasensitively detected with CdTe NCs capped with dimethylaminoethanethiol (DMAET), with high selectivity over Cr(III) and other ions. Synchronous fluorescence spectroscopy was applied to quantify trace levels of Cr(VI) ions with this probe in the 3.0 nM to 0.2 μM concentration range, with a detection limit as low as 0.57 nM. The interaction between the nanocrystals and Cr(VI) ions was investigated in a study on the zeta potentials, UV-Vis absorption spectroscopy and time-resolved luminescence spectroscopy. Electron transfer process occurred and the decay times of the probe remain constant (about 14 ns). This simple and ultrasensitive analytical method was successfully applied to the direct determination of Cr(VI) in spiked samples of environmental waters.

Water-soluble homo-oligonucleotide stabilized fluorescent silver nanoclusters as fluorescent probes for mercury ion

Water–soluble fluorescent silver nanoclusters (Ag NCs) were prepared with the assistance of commercially available polyinosinic acid (PI) or polycytidylic acid (PC). The fluorescence of the Ag NCs is effectively quenched by trace mercury(II) ions, which can be applied for their detection. The response of the Ag NCs prepared with PI to Hg(II) ion is linear in the Hg(II) concentration range from 0.05 to 1.0 μM (R²?=?0.9873), and from 0.5 to 10 μM of Hg(II) (R²?=?0.9971) for Ag NCs prepared with PC. The detection limits are 3.0 nM and 9.0 nM (at an S/N of 3), respectively. The method is simple, sensitive and fairly selective.

Silicon-hybrid carbon dots strongly enhance the chemiluminescence of luminol

We report on a 4-min microwave pyrolytic method for the preparation of fluorescent and water-soluble silicon-hybrid carbon dots (C-dots) with high fluorescent quantum yield. The material is prepared by preheating aminopropyltriethoxysilane and ethylene diamine tetraacetic acid for 1 min, then adding a mixture of poly(ethylene glycol) and glycerin to the solution and heating for another 3 min. It is found that the hybrid carbon dots strongly enhance the chemiluminescence (CL) of the luminol/N-bromosuccinimide system. A study on the enhancement mechanism via CL, fluorescence and electron paramagnetic resonance spectroscopy showed that the effect most probably is due to electrostatic interaction between the C-dots and the luminol anion which facilitates electron transfer from luminol anion to the N-bromosuccinimide oxidant. CL intensity is linearly related to the concentration of the C-dots in the range between 1.25 and 20 μg mL^?1. The detection limit is 0.6 μg mL^?1 (at an S/N of 3).

Fluorometric determination of paraoxon in human serum using a gold nanoparticle-immobilized organophosphorus hydrolase and coumarin 1 as a competitive inhibitor

A dimeric organophosphorus hydrolase (OPH; EC 3.1.8.1; 72 kDa) was isolated from wild-type bacteria, analyzed for its 16s rRNA sequence, purified, and immobilized on gold nanoparticles (AuNPs) to form the transducer part of a biosensor. The isolated strain was identified as Pseudomonas aeruginosa. The AuNPs were characterized by transmission electron microscopy and localized surface plasmon resonance. Covalent binding of OPH to the AuNPs was confirmed by spectrophotometry, enzymatic activity assays, and FTIR spectroscopy. Coumarin 1, a competitive inhibitor of OPH, was used as a fluorogenic probe. The bioconjugates quench the emission of coumarin 1 upon binding, but the addition of paraoxon results in an enhancement of fluorescence that is directly proportional to the concentration of paraoxon. The gold-OPH conjugates were then used to determine paraoxon in serum samples spiked with varying levels of paraoxon. The method works in the 50 to 1,050 nM concentration range, has a low standard deviation (with a CV of 5.7–11 %), and a detection limit as low as 5?×?10^?11 M.

Core-shell fluorescent silica nanoparticles for sensing near-neutral pH values

pH-responsive fluorescent core-shell silica nanoparticles (SiNPs) were prepared by encapsulating the pH-sensitive fluorophore 8-hydroxypyrene-1,3, 6-trisulfonate into their silica shell via a facile reverse microemulsion method. The resulting SiNPs were characterized by SEM, TEM, fluorescence lifetime spectroscopy, photobleaching experiments, and photoluminescence. The core-shell structure endows the SiNPs with reduced photobleaching, excellent photostability, minimized solvatachromic shift, and increased fluorescence efficiency compared to the free fluorophore in aqueous solution. The dynamic range for sensing pH ranges from 5.5 to 9.0. The nanosensors show excellent stability, are highly reproducible, and enable rapid detection of pH. The results obtained with the SiNPs are in good agreement with data obtained with a glass electrode.

A novel magnetic metal organic framework nanocomposite for extraction and preconcentration of heavy metal ions, and its optimization via experimental design methodology

We describe a novel magnetic metal-organic framework (MOF) prepared from dithizone-modified Fe₃O₄ nanoparticles and a copper-(benzene-1,3,5-tricarboxylate) MOF and its use in the preconcentration of Cd(II), Pb(II), Ni(II), and Zn(II) ions. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Three variables (extraction time, amount of the magnetic sorbent, and pH value) were selected as the main factors affecting adsorption, while four variables (type, volume and concentration of the eluent; desorption time) were selected for desorption in the optimization study. Following preconcentration and elution, the ions were quantified by FAAS. The limits of detection are 0.12, 0.39, 0.98, and 1.2 ng mL^?1 for Cd(II), Zn(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations were <4.5 % for five separate batch determinations of 50 ng mL^?1 of Cd(II), Zn(II), Ni(II), and Pb(II) ions. The adsorption capacities (in mg g^?1) of this new MOF are 188 for Cd(II), 104 for Pb(II), 98 Ni(II), and 206 for Zn(II). The magnetic MOF nanocomposite has a higher capacity than the Fe₃O₄/dithizone conjugate. This magnetic MOF nanocomposite was successfully applied to the rapid extraction of trace quantities of heavy metal ions in fish, sediment, soil, and water samples.

Fluorometric sensing of DNA using curcumin encapsulated in nanoparticle-assembled microcapsules prepared from poly(diallylammonium chloride-co-sulfur dioxide)

We report on the synthesis of microcapsules (MCs) containing self-assembled nanoparticles formed from poly[diallylammonium chloride-co-(sulfur dioxide)] in the presence of citrate and silica sol nanoparticles. The MCs are spherical, and SEM and optical microscopy reveal them to have micrometer size. The fluorescent probe curcumin was encapsulated in the MCs and found to be located in the shell. The fluorescence of curcumin in the MCs is altered depending on their microenvironment. Effects of pH and ammonia on the fluorescence of curcumin in the MCs also were studied. The brightness of the probe in the MCs increases on addition of DNA. The effect was used to determine DNA from fish sperm by fluorometry. The association constant (K) is 4?000 mL.g^?1, and the number of binding sites is ~1.0.

FAAS slurry analysis of lead and copper ions preconcentrated on titanium dioxide nanoparticles coated with a silver shell and modified with cysteamine

We report on the separation and preconcentration of lead(II) and copper(II) ions using silver-coated titanium dioxide nanoparticles modified with cysteamine, and their determination by slurry analysis via flame atomic absorption spectrometry. The ions were adsorbed via a conventional batch technique, and the ion-loaded slurry was separated and directly introduced into the spectrometer, thereby eliminating a number of drawbacks. The effects of pH, amount of sorbent, slurry volume, sample volume and other ions on the recovery were investigated. Under optimized experimental conditions, copper and lead can be recovered within the 95% confidence level in certificated waste water, but also in spiked sea water samples. The technique is fast, simple, and leads to complete elution. The limit of detection (3δ, at n?=?10) was 0.37 μg L^?1 for Cu(II), and 0.38 μg L^?1 for Pb(II).