Dependent Fluorescence Enhancement Research Articles

Green Synthesis of Ag2S Quantum Dots as Sensing Probe: An Optical Sensor for the Detection of Cholesterol

AbstractIn this study, an environmental‐friendly method of preparation is adopted for the synthesis of NIR emitted Ag2S quantum dots (QDs) with bovine serum albumin (BSA) as a functional capping agent. According to the experimental results, the QDs with an average size of 4.5 nm exhibit their emission peak at 820 nm when excited at 420 nm. Furthermore, these QDs are used for the easy and fast detection of cholesterol (Ch) using the fluorescence (FL) spectroscopic method. These Ag2S QDs show signs of Ch concentration dependent FL enhancement after Ch‐QD complexation and Ch concentration. These QDs are either unchanged or underwent FL quenching in the presence of other studied analytes. Under the optimal conditions, the selectivity and sensitivity of BSA capped QDs for Ch are found to be significantly higher compared with other bioanalytes. In this case, the limit of detection is determined as 50 × 10−9 m. Moreover, this assay demonstrated such advantages as cheap affordability, simplicity, and specificity in terms of Ch sensing.

Diverse interactions of aggregated insulin with selected coumarin dyes: Time dependent fluorogenicity, simulation studies and comparison with thioflavin T

In this study, we have compared neutral coumarin based well-known commercially available probes C6, C7 and C545T for fluorogenic response from the aggregated insulin. The immediate fluorogenic responses were comparatively poor from all the three probes with respect to the previously reported response from thioflavin T (ThT) in the presence of aggregated insulin. Interestingly C6 among the three neutral coumarin derivative showed a significant steady increase of fluorescence intensity with time up to 6 h before reaching the saturation limit. Similar time dependent fluorogenic experiment with C7, C545T and ThT showed comparatively fast saturation within few minutes to 2 h. The molecular docking and simulation studies showed that these neutral probes could be stabilized in the aggregated form of the insulin predominantly by non-covalent weak interactions such as hydrogen bonding, π-π and cation-π interactions. The probability distributions of the dihedral angles between two heterocyclic parts in C6 showed maximum probability of occurrence at 0° and 180°. These probability distributions of the dihedral angles between two heterocyclic parts within all the four fluorophores provided the justification of selective time dependent fluorescence enhancement from C6 in presence of insulin aggregate. The overall fluorogenic enhancement from C6 was comparable to the fluorogenic response from ThT and theoretical study confirmed distinctly different origin of this associated slow time dependent fluorogenic response.

Distance dependent fluorescence enhancement of silver nanowires deposited on AAO

Metal nanoparticls deposited on substrate are usually used for the enhancement of fluorescent molecules. In this article, AAO template was introduced into the reaction solution during the preparation of silver nanowires. Then the AAO template with deposited silver nanowires was suspended in RhB solution to study its fluorescence enhancement effect. The results showed that the uneven surface of AAO template caused a series of distances between silver nanowires and RhB molecules which were happen to be below 10 nm that can effectively enhance the fluorescence of RhB solution. Our research is helpful to the study of fluorescence enhancement of metal nanostructures deposited on substrate.

Fluorescence enhancement via varied long-chain thiol stabilized gold nanoparticles: A study of far-field effect

Metal enhanced fluorescence of carbon dots has been reported in aqueous solution. Moderately fluorescing carbon dots (λex=360nm and λem=440nm) of 6–8nm diameters (CDA) have been synthesized from freshly prepared aqueous ascorbic acid solution under modified hydrothermal treatment. The CDA fluorescence is quenched at the close proximity with gold nanoparticles (AuNPs). Here, a substrate specific near-field electric field distribution is pronounced. Anticipating distance dependent fluorescence enhancement phenomenon, long-chain aliphatic thiol capped AuNPs are introduced to improve fluorescence of moderately fluorescing CDAs. The long-chain aliphatic thiols act as spacers between CDA and AuNP. Interestingly, the fluorescence of CDA is observed to be enhanced successively as the chain lengths of aliphatic thiols are increased. Fluorescing CDA, upon excitation, transfers energy to the nearby AuNP and a plasmon is induced. This plasmon radiates in the far-field resulting in fluorescence enhancement of CDAs. Such an interesting enhancement in emission with metallic gold is termed as gold enhanced fluorescence. This far-field effect for fluorescence enhancement of CDA particles becomes a general consensus in solution with varied long-chain aliphatic amine ligand capped silver nanoparticles (AgNPs). Finally, consequence of far-field effect of fluorescence enhancement has been observed while derivatized AuNP and AgNP are introduced into the CDA solution simultaneously which is described as reinforced fluorescence enhancement due to coupled plasmonic radiation.

Size and distance dependent fluorescence enhancement of nanoporous gold.

Nanoporous gold (NPG) has been reported to provide remarkable fluorescence enhancement of adjacent fluorophores due to the metal-enhanced fluorescence phenomenon (MEF), and the enhancement is related with the characteristic length of nanoporosity. To fully understand the effect of NPG on nearby fluorophores, it is desirable to study systems with well-defined metal-fluorophore distances. In this study we investigated the distance effect by using silica as the spacing layer between fluorophores and NPG. Originating from competition between plasmonic amplifying and metallic quenching, the dye molecule rhodamine 6G was best enhanced by 20-nm SiO2 coated nanoporous gold with the pore size of 36 nm, while the protein phycoerythrin was best enhanced by 15-nm SiO2 coated nanoporous gold with the pore size of 42 nm and the quantum dots were best enhanced by 20-nm SiO2 coated nanoporous gold with the pore size of 42 nm.

Fluorescence emission of BDMO-PPV enhanced by different plasmon modes

Herein we report a symmetric study of metal surface plasmon-enhanced emission of conjugated polymer (poly[2,5-bis(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene], BDMO-PPV) in the process that silver metal substrates changed from isolated nano-particles to continuous metal film. It was found that photoluminescence (PL) enhancement was mainly raised from coupling of BDMO-PPV excitons with localized surface plasmon (LSP) of Ag nano-particles when the thickness of deposited Ag film was smaller than 15nm. However, surface plasmon polaritons (SPPs) dominated the PL enhancement when the thickness of deposited Ag film reached 20nm or thicker. Temperature dependent PL of BDMO-PPV on the silver substrates were also investigated in the range of 10–300K. Bose–Einstein statistical factors were calculated to reveal the mechanistic aspects of the observed temperature dependent fluorescence enhancement on Ag nano-films with variable thickness.

Enhanced quantum dot emission for luminescent solar concentrators using plasmonic interaction

Plasmonic excitation enhanced fluorescence of CdSe/ZnS core-shell quantum dots (QDs) in the presence of Au nanoparticles (NPs) has been studied for application in quantum dot solar concentrator (QDSC) devices. We observe that there is an optimal concentration of Au NPs that gives a maximum 53% fluorescence emission enhancement for the particular QD/Au NP composite studied. The optimal concentration depends on the coupling and spacing between neighboring QDs and Au NPs. We show the continuous transition from fluorescence enhancement to quenching, depending on Au NP concentration. The locally enhanced electromagnetic field induced by the surface plasmon resonance in the Au NPs leads to an increased excitation rate for the QDs. This is evidenced by excitation wavelength dependent fluorescence enhancement, where the locally enhanced field around the Au NPs is more pronounced close to the surface plasmon resonance (SPR) wavelength. However, at higher concentrations of Au NPs non-radiative energy transfer from the QDs to the Au NPs particles leads to a decrease of the emission, which is confirmed by detection of both a double exponential lifetime decay in, and a decrease in the lifetime of the QDs. The overall fluorescence emission enhancement depends on these competing effects; increased excitation rate and non-radiative energy transfer.

Fluorescence of 2-aminopurine reveals rapid conformational changes in the RB69 DNA polymerase-primer/template complexes upon binding and incorporation of matched deoxynucleoside triphosphates

We have used 2-aminopurine (2AP) as a fluorescent probe in the template strand of a 13/20mer primer/template (D) to detect deoxynucleoside triphosphates (N)-dependent conformational changes exhibited by RB69 DNA polymerase (ED) complexes. The rates and amplitudes of fluorescence quenching depend hyperbolically on the [dTTP] when a dideoxy-primer/template (ddP/T) with 2AP as the templating base (n position) is used. No detectable fluorescence changes occur when a ddP/T with 2AP positioned 5′ to the templating base (n + 1 position) is used. With a deoxy-primer/template (dP/T) with 2AP in the n position, a rapid fluorescence quenching occurs within 2 ms, followed by a second, slower fluorescence quenching with a rate constant similar to base incorporation as determined by chemical quench. With a dP/T having 2AP in the n + 1 position, there is a [dNTP]-dependent fluorescence enhancement that occurs at a rate comparable to dNMP incorporation. Collectively, the results favor a minimal kinetic scheme in which population of two distinct biochemical states of the ternary EDN complex precedes the nucleotidyl transfer reaction. Observed differences between dP/T and ddP/T ternary complexes indicate that the 3′ hydroxyl group of the primer plays a critical role in determining the rate constants of transitions that lead to strong deoxynucleoside triphosphate binding prior to chemistry.

Separation distance dependent fluorescence enhancement of fluorescein isothiocyanate by silver nanoparticles

Nanocomposites consisting of a metal core, a silica-spacer shell with controlled thickness, and a dye-labelled shell were synthesized and separation distance dependent fluorescence enhancement of fluorescein isothiocyanate by silver nanoparticles was studied; the results indicated an optimum enhancement of 4.8 times with a spacer shell thickness of 21 nm.

Purification and sequencing of multiple forms of Brassica napus seed napin large chains that are calmodulin antagonists and substrates for plant calcium-dependent protein kinase

Six napin large (L) chains (as well as six napin small chains) were resolved from the seeds of kohlrabi ( Brassica napus var. rapifera) by a procedure involving extraction, batchwise elution from carboxymethylcellulose (CM52) and reversed-phase HPLC after treatment with guanidine hydrochloride and 2-mercaptoethanol. The precise average molecular masses of the circa 4.5 kDa small subunits and the circa 10 kDa large subunits were detern ined by electrospray ionisation mass spectrometry (ESMS). Of six large subunits resolved (LIA, L1B, L1C, L2A, L2B and L2C), the complete amino acid sequences of four (LIA, L2A, L2B and L2C) and the near-complete sequences of two (LIB and LIC) were deduced from the ESMS-based masses of tryptic fragments, Edman sequencing and previously published data. The deduced structures are precisely consistent with this data and with the ESMS-based average molecular masses of these polypeptides. ESMS analysis of unreduced napin extract revealed only seven circa 14.5 kDa complexes, the observed masses being in close agreement with those calculated for 1:1 complexes of particular small and large subunits assuming four disulfides in each napin complex. The structures of the napin large subunits (86–91 residues) are very similar and all amino acid differences observed are confined to only 25 positions. The L2A, L2B and L2C large chains (but not the L1 A, LIB and LIC large chains) are phosphorylated well by plant Ca 2+-dependent protein kinase (CDPK). The CDPK-catalyzed phosphorylation site on the large chain L2A is inferred to be S 57 within the sequence LQQVIS17RIYQT (the site being S 60 within the same sequence in L2B and L2C). The napin-containing basic protein fraction from B. napus seeds largely abolishes the Ca 2+-dependent fluorescence enhancement of dansyl-calmodulin and also inhibits calmodulin (CaM)-dependent myosin light chain kinase (MLCK). The resolved napin long chains also inhibit MLCK. Each kohlrabi large chain contains 2 sequences (corresponding to L1 10-Q 20 and Q 51-L 64 of LIA) which have the potential to form amphipathic α-helices. Each large chain also contains a Q-rich 19 amino acid sequence (corresponding to L 30-Q 48 of LIA) which has the potential to form a ‘2-sided’ α-helix with basic residues confined to one side. These structural elements may be involved in the inferred interaction of these proteins with CaM and may be relevant to the biological activity of antifungal proteins of this kind.

Purification and sequencing of multiple forms of Brassica napus seed napin small chains that are calmodulin antagonists and substrates for plant calcium-dependent protein kinase

Six napin small (S) subunits and six napin large (L) subunits were resolved from the seeds of kohlrabi ( Brassica napus var. rapifera) by a procedure involving extraction, batchwise elution from carboxymethylcellulose (CM52) and reverse-phase HPLC after treatment with guanidine hydrochloride and 2-mercaptoethanol. The precise average molecular masses of the ca. 4.5 kDa small subunits and the ca. 10 kDa large subunits were determined by electrospray ionisation mass spectrometry (ESMS). The amino-acid sequences of six small subunits (SIA, SIB, S2, SM., S3B and S4) were deduced from the ESMS-based masses of tryptic fragments, Edman sequencing and previously published data. The deduced structures were precisely consistent with this data and with the ESMS-based average molecular masses of these polypeptides. The structures of the small subunits (39–41 residues) are very similar with variations involving single substitutions at or near the N-terminus and 1 to 3 changes within the last 7 amino acids. Particular B. napus small and large chains are phosphorylated by plant Ca 2+-dependent protein kinase (CDPK). The best site of phosphorylation on small chains is inferred to be either S 34 or S 39 of SIB. The napin-containing basic protein fraction from B. napus seeds largely abolishes the Ca 2+-dependent fluorescence enhancement of dansyl-calmodulin and also inhibits calmodulin (CaM)-dependent myosin light chain kinase (MLCK). The resolved napin small chains also inhibit MLCK. All of the kohlrabi napin small chains, as well as homologous Brassicaceae small chains, have a central 23 amino-acid sequence that can potentially form an α-helix in which all the basic residues are located on one side. This structural element may be involved in the interaction of these proteins with CaM and the biological activity of antifungal proteins of this kind.

Kinetics of chlorotetracycline uptake in [formula omitted] by a fluorescence technique

The antibiotic chlorotetracycline (CTC) is used as a fluorescent chelate probe to investigate the kinetics of its uptake into Staphylococcus aureus . CTC binds to divalent cations in an aqueous solution with enhanced fluorescence. This fluorescence is polarity dependent, being higher in apolar solutions. Upon addition of CTC to dispersions of S. aureus , a time dependent fluorescence enhancement is detected demonstrating that the CTC-divalent cation complex migrates into the apolar regions of the membrane. This uptake, which follows saturation kinetics, is energy dependent. A K m of 162 μ M was obtained for CTC concentration ranges of 0.2–100 μgm/ml.