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1.
Anal Bioanal Chem ; 411(21): 5481-5488, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31236648

RESUMO

The mechanism behind the variation in the photoluminescence (PL) of a MoS2 nanohybrid material with pH was investigated. Highly fluorescent MoS2 quantum dots dispersed across MoS2 nanosheets (MoS2 QDNS) were synthesized by a hydrothermal route in the presence of NaOH. Upon reducing the pH from 13 to 6.5, the PL intensity was markedly quenched. The removal of dangling sulfur atoms by adding mineral acids could be a plausible mechanism for this PL quenching, together with the inner filter effect and Förster resonance energy transfer due to the resulting species. A label-free turn-on fluorescence sensor for H2O2 was developed using this hybrid material. The PL of the acidified MoS2 QDNS at pH 6.5 increased (i.e., recovered) linearly with the concentration of H2O2. The dynamic range of the sensor was found to be 2-94 µM with a limit of detection (LOD) of 2 µM. This sensing strategy was also extended for the detection of glucose by appending glucose oxidase (GOx) as a catalyst. In the presence of GOx, glucose oxidizes to gluconic acid and H2O2, so the original level of glucose can be estimated by determining the H2O2 present. The absence of a complicated enzyme immobilization step is the prime advantage of the present glucose sensor. The current work exemplifies the utility of MoS2-based nanoparticle systems in the biological sensor domain. Graphical abstract.


Assuntos
Dissulfetos/química , Peróxido de Hidrogênio/análise , Concentração de Íons de Hidrogênio , Molibdênio/química , Transferência Ressonante de Energia de Fluorescência , Glucose Oxidase/análise , Limite de Detecção , Medições Luminescentes
2.
Analyst ; 143(7): 1691-1698, 2018 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-29532821

RESUMO

Fluorescence sensors for biologically active molecules are catching attention due to their good performance and simplicity. Herein, we report a fluorescence sensor for the selective and sensitive detection of dopamine (DA) in aqueous samples. MoS2 nanohybrid material composed of MoS2 quantum dots dispersed over MoS2 nanosheets (MoS2 QDNS) in alkaline medium was employed as the fluorescent probe. In the presence of DA, the photoluminescence intensity of MoS2 QDNS was quenched linearly with increasing concentration of the former. The quenching mechanism was found to operate via Förster resonance energy transfer (FRET), and the inner filter effect (IFE). The QDNS sensor demonstrates high selectivity towards DA, especially in the presence of ascorbic acid and uric acid, which are the most potential interference for DA in biological systems. The sensitivity of the system was as low as 0.9 nM and demonstrated two linear ranges from 2.5 nM to 5.0 µM and from 5.0 µM to 10.4 µM. The sensor demonstrated a remarkable ability in the analysis of real blood samples and showed excellent potential for visual detection.

3.
Chemphyschem ; 17(15): 2315-21, 2016 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-27159128

RESUMO

Doped fluorescent carbon dots (CDs) have drawn widespread attention because of their diverse applications and attractive properties. The present report focusses on the origin of photoluminescence in nitrogen-doped CDs (NCDs), which is unraveled by the interaction with Cu(2+) ions. Detailed spectroscopic and microscopic studies reveal that the broad steady-state photoluminescence emission of the NCDs originates from the direct recombination of excitons (high energy) and the involvement of defect states (low energy). In addition, highly selective detection of Cu(2+) is achieved, with a detection limit of 10 µm and a dynamic range of 10 µm-0.4 mm. The feasibility of the present sensor for the detection of Cu(2+) in real water samples is also presented.


Assuntos
Carbono/química , Cobre/análise , Substâncias Luminescentes/química , Nitrogênio/química , Pontos Quânticos/química , Cátions Bivalentes/análise , Limite de Detecção , Medições Luminescentes/métodos , Água/análise
4.
Anal Bioanal Chem ; 408(14): 3699-706, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-27023220

RESUMO

We present a Förster resonance energy transfer (FRET)-based fluorescence detection of vitamin C [ascorbic acid (AA)] using cadmium sulphide quantum dots (CdS QDs) and diphenylcarbazide (DPC). Initially, DPC was converted to diphenylcarbadiazone (DPCD) in the presence of CdS QDs to form QD-DPCD. This enabled excited-state energy transfer from the QDs to DPCD, which led to the fluorescence quenching of QDs. The QD-DPCD solution was used as the sensor solution. In the presence of AA, DPCD was converted back to DPC, resulting in the fluorescence recovery of CdS QDs. This fluorescence recovery can be used to detect and quantify AA. Dynamic range and detection limit of this sensing system were found to be 60-300 nM and 2 nM, respectively. We also performed fluorescence lifetime analyses to confirm existence of FRET. Finally, the sensor responded with equal accuracy to actual samples such as orange juice and vitamin C tablets. Graphical abstract Schematic showing the FRET based fluorescence detection of ascorbic acid.


Assuntos
Ácido Ascórbico/análise , Compostos de Cádmio/química , Pontos Quânticos , Sulfetos/química , Transferência Ressonante de Energia de Fluorescência , Limite de Detecção , Espectrometria de Fluorescência , Espectrofotometria Ultravioleta
5.
Chem Rev ; 112(10): 5356-411, 2012 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-22913366
6.
Analyst ; 137(6): 1363-9, 2012 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-22318214

RESUMO

The design and characterization of a system for in situ Raman analysis of surfaces prepared by ion soft landing (SL) is described. The performance of the new high vacuum compatible, low cost, surface analysis capability is demonstrated with surface enhanced Raman spectroscopy (SERS) of surfaces prepared by soft landing of ions of crystal violet, Rhodamine 6G, methyl orange and copper phthalocyanine. Complementary in situ mass spectrometric information is recorded for the same surfaces using a previously implemented secondary ion mass spectrometer (SIMS). Imaging of the modified surfaces is achieved using 2D Raman imaging as demonstrated for the case of Rhodamine 6G soft landing. The combination of the powerful molecular characterization tools of SERS and SIMS in a single instrument fitted with in-vacuum sample transport capabilities, facilitates in situ analysis of surfaces prepared by ion SL. In particular, information is provided on the charge state of the soft landed species. In the case of crystal violet the SERS data suggest that the positively charged ions being landed retain their charge state on the surface under vacuum. By contrast, in the case of methyl orange which is landed as an anion, the SERS spectra suggest that the SL species has been neutralized.

7.
J Am Soc Mass Spectrom ; 23(5): 842-9, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22290484

RESUMO

Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.

8.
Anal Chem ; 83(13): 5114-21, 2011 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-21634371

RESUMO

We report implementation of two powerful characterization tools, in situ secondary ion mass spectrometry (SIMS) and ex situ surface enhanced Raman spectroscopy (SERS), in analyzing surfaces modified by ion soft landing (SL). Cations derived from Rhodamine 6G are soft landed onto Raman-active silver colloidal substrates and detected using SERS. Alternatively and more conveniently, high-quality SERS data are obtained by spin coating a silver colloidal solution over the modified surface once SL is complete. Well-defined SERS features are observed for Rhodamine 6G in as little as 15 min of ion deposition. Deposition of ~3 pmo1 gave high-quality SERS spectra with characteristic spectroscopic responses being derived from just ~0.5 fmol of material. Confocal SERS imaging allowed the enhancement to be followed in different parts of deposited dried droplets on surfaces. Characteristic changes in Raman spectral features occur when Rhodamine 6G is deposited under conditions that favor gas-phase ion fragmentation. Simultaneous deposition of both the intact dye and its fragment ion occurs and is confirmed by SIMS analysis. The study was extended to other Raman active surfaces, including Au nanostar and Au coated Ni nanocarpet surfaces and to SL of other molecules including fluorescein and methyl red. Overall, the results suggest that combination of SERS and SIMS measurements are effective in the characterization of surfaces produced by ion SL with significantly enhanced molecular specificity.


Assuntos
Espectrometria de Massas/métodos , Rodaminas/química , Vibração
9.
Nanoscale ; 3(3): 1066-72, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21161103

RESUMO

Mercaptosuccinic acid protected gold nanoparticles (Au@MSA) self assemble to form superlattice (SL) crystals at the air-water interface. These have been used for gas adsorption. The current-voltage (I-V) characteristics of the SL film with embedded SL crystals, obtained by four probe measurements, show Ohmic conduction. The conductance observed was proportional to the polarizability of the adsorbed gases. The current through the SL decreases on adsorption of the gas along with decrease in the SERS intensity of a probe molecule from the crystals. We rationalise our observation of the linear dependence of the conductance on the polarizability of the adsorbed gas using a simple model calculation. Variation of the conductance may be useful in designing electrical switches operating at the nanometre length scales.


Assuntos
Ouro/química , Modelos Químicos , Nanoestruturas/química , Ressonância de Plasmônio de Superfície/métodos , Simulação por Computador , Condutividade Elétrica , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Nanoestruturas/ultraestrutura , Tamanho da Partícula , Propriedades de Superfície
10.
J Am Soc Mass Spectrom ; 20(6): 949-56, 2009 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-19318277

RESUMO

Mass-selected polyatomic cations and anions, produced by electrosonic spray ionization (ESSI), were deposited onto polycrystalline Au or fluorinated self-assembled monolayer (FSAM) surfaces by soft landing (SL), using a rectilinear ion trap (RIT) mass spectrometer. Protonated and deprotonated molecules, as well as intact cations and anions generated from such molecules as peptides, inorganic catalysts, and fluorescent dyes, were soft-landed onto the surfaces. Analysis of the modified surfaces was performed in situ by Cs(+) secondary ion mass spectrometry (SIMS) using the same RIT mass analyzer to characterize the sputtered ions as that used to mass select the primary ions for SL. Soft-landing times as short as 30 s provided surfaces that yielded good quality SIMS spectra. Chemical reactions of the surfaces modified by SL were generated in an attached reaction chamber into which the surface was transferred under vacuum. For example, a surface on which protonated triethanolamine had been soft landed was silylated using vapor-phase chlorotrimethylsilane before being returned still under vacuum to the preparation chamber where SIMS analysis revealed the silyloxy functionalization. SL and vapor-phase reactions are complementary methods of surface modification and in situ surface analysis by SIMS is a simple way to characterize the products produced by either technique.

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