Fluorogenic response from DNA templated micrometer range self-assembled gold nanorod.

Plasmonic gold nanorod (AuNR) on a macromolecular matrix exhibits an end-to-end (ETE) long-range self-assembly (AuNR)n with n > 100. In the case of small molecules as a template, the pre-synthesized macromolecular matrix is missing and this brings a synthetic challenge in directed long-range assembly of AuNR. Self-assembly with thiol-modified small DNA and AuNR shows a much short-range ETE assembly with n < 25 via a simple evaporation technique on a solid surface. In this study, the introduction of two short amine modified probe DNAs (∼2.5 nm) and one 22-mer complementary single strand (ss)-DNA template (∼7 nm) show the long-range ETE self-assembly of (AuNR)n with n > 130. In the solution state, the zigzag arrangement within the assembled structure controls the typical change in the absorption behavior for (AuNR)n ETE assembly. The formation of this long-range ETE self-assembly in a solution state was verified from the combined effect of fluorescence resonance energy transfer (FRET) and hotspot-induced fluorescence enhancement. The probe DNAs and templated DNA concentration on fluorescence enhancement have been varied to monitor the effect of (AuNR)n with n = ∼5-130 in ETE self-assembly. Primarily quenched FRET acceptor in the presence of AuNR decisively exhibits remarkable fluorogenic response in ETE self-assembly with maximum n value. Although the FRET efficiencies among the fluorophores are comparable, the fluorogenic boost in ETE AuNR is due to the increased number of intrinsic navigated hotspots in these assemblies.

Seed free synthesis of polyethylene glycol stabilized gold nanoprisms exploiting manganese metal at low pH.

Manganese powder with a suitable potential (, -1.19 V) has never been investigated for the reduction of Au3+ (, 1.00 V). In this study, we have utilized and low pH dependent for the polyethylene glycol stabilized gold nanoprism synthesis by reducing AuCl-4 in the presence of thiol terminated polyethylene glycol as the stabilizing agent. The synthetic methodology for gold nanoprisms has been optimized by pH and Cl- ion combination. Time dependent absorbance studies have been conducted to demonstrate the role of various reaction parameters such as the stabilizing agent, HCl concentration, temperature, and Mn metal. The synthesized gold nanoprism has been further utilized as a seed for nucleic acid and selected amino acid mediated edge and surface growth, respectively.

Growth Reaction of Gold Nanorods in the Presence of Mutated Peptides and Amine-Modified Single-Stranded Nucleic Acids.

Conformation of biomolecules like DNA, peptides and amino acids play vital role during nanoparticle growth. Herein, we have experimentally explored the effect of different noncovalent interaction between a 5'-amine modified DNA sequence (NH2 -C6 H12 -5'-ACATCAGT-3', PMR) and arginine during the seed-mediated growth reaction of gold nanorods (GNRs). Amino acid-mediated growth reaction of GNRs results in a snowflake-like gold nanoarchitecture. However, in case of Arg, prior incubation of GNRs with PMR selectively produces sea urchin-like gold suprastructures, via strong hydrogen bonding and cation-π interaction between PMR and Arg. This distinctive structure formation strategy has been extended to study the structural modulation caused by two structurally close α-helical RRR (Ac-(AAAAR)3 A-NH2 ) peptide and the lysine mutated KKR (Ac-AAAAKAAAAKAAAARA-NH2 ) peptide with partial helix at the amino terminus. Simulation studies confirm that a greater number of hydrogen bonding and cation-π interaction between the Arg residues and PMR resulted in the gold sea urchin structure for RRR peptide against KKR peptide.

Methionine-Controlled Impediment of Secondary Nucleation Leading to Nonclassical Growth within Self-Assembled De Novo Gold Nanoparticles.

The conventional key steps for seed-mediated growth of noble metal nanostructures involve classical and nonclassical nucleation. Furthermore, the surface of the seed catalytically enhances the secondary nucleation involving Au+ to Au0 reduction, thus providing in-plane growth of the seed. In contrast to this well-established growth mechanism, herein, we report the unique case of a methionine (Met)-controlled seed-mediated growth reaction, which rather proceeds via impeding secondary nucleation in the presence of citrate-stabilized gold nanoparticles (AuNPs). The interaction between the freshly generated Au+ and the thioether group of Met in the medium restricts the secondary nucleation process of further seed-catalyzed Au+ reduction to Au0. This incomplete conversion of Au+, as confirmed by X-ray photoelectron spectroscopy, results in a significant enhancement of the zeta (ζ) potential even at low Met concentrations. Nucleation of in situ generated small-sized particles (nAuNPs) takes place on the parent seed surface followed by their segregation from the seed. The self-assembly process of these nAuNPs arises from the aurophilic interaction among the Au+. Furthermore, the time-dependent growth of smaller particles to larger-sized particles through assembly and merging within the same self-assembly validates the nonclassical growth. This strategy has been successfully extended toward the seed-mediated growth reaction of AuNPs in the presence of three bio-inspired decameric peptides having varying numbers of Met residues. The study confirms the nucleation strategy even in the presence of a single Met residue in the peptide and also the self-assembly of nucleated particles with increasing Met residues within the peptide.

Green Synthesis of Luminescent Gold-Zinc Oxide Nanocomposites: Cell Imaging and Visible Light-Induced Dye Degradation.

Green synthesis of gold-zinc oxide (Au-ZnO) nanocomposite was successfully attempted under organic solvent-free conditions at room temperature. Prolonged stirring of the reaction mixture introduced crystallinity in the ZnO phase of Au-ZnO nanocomposites. Luminescence properties were observed in these crystalline Au-ZnO nanocomposites due to in situ embedding of gold nanoparticles (AuNP) of 5-6 nm diameter on the surface. This efficient strategy involved the reduction of Au(III) by Zn(0) powder in aqueous medium, where sodium citrate (NaCt) was the stabilizing agent. Reaction time and variation of reagent concentrations were investigated to control the Au:Zn ratio within the nanocomposites. The reaction with the least amount of NaCt for a long duration resulted in Au-ZnO/Zn(OH)2 nanocomposite. X-ray photoelectron spectroscopy (XPS) confirmed the formation of Zn(OH)2 and ZnO in the same nanocomposite. These nanocomposites were reconnoitered as bioimaging materials in human cells and applied for visible light-induced photodegradation of rhodamine-B dye.

Selective Release of Doxorubicin from Cucurbit[8]uril Stabilized Gold Supra-Pyramid Host at pH of Small Intestine.

Gold supra-pyramid structures were obtained by the addition of acidic solution of cucurbit[8]uril (CB[8]) to an aqueous solution of citrate stabilized gold nanoparticles (AuNP). The reaction resulted in the precipitation of supra-pyramid from the solution after just 1 min of shaking. Microscopic images confirmed formation of the supra-pyramid. The stepwise structural transformation towards the supra-pyramid was examined with variable concentrations of CB[8] to AuNP solution. Anionic counter parts of these acids (Br- , NO3 - , SO4 2- and Cl- ) controlled the size of the synthesized supra-pyramids. These supra-pyramid hosts showed uptake of three anticancer drugs: oral drugs etoposide, prednisolone and intravenous drug doxorubicin. Releases of drugs from these hosts were emulated at acidic stomach pH, basic small intestinal pH and in the presence of human serum albumin (HSA). The specific release of doxorubicin was confirmed at small intestinal pH 7.4. Poor release of drugs in presence of CB[8] specific guest 1-adamantanamine confirmed the role of the supra-pyramid as the exclusive host. The release of doxorubicin from the supra-pyramid at pH 7.4 was confirmed by fluorescence microscopic imaging with prostate cancer DU-145 cell line.

Tryptophan-Stabilized Au-FexOy Nanocomposites as Electrocatalysts for Oxygen Evolution Reaction.

Au-FexOy nanocomposites with a variable gold-to-iron ratio were stabilized with l-tryptophan. The synthetic methodology is based on the facile redox reaction between Au(III) and Fe(0) in the presence of gold nanoparticle as a seed at room temperature in an aqueous medium. The synthesis results in the deposition of Au nanoparticles on the surface of iron oxide layers. Composition variation in the nanocomposites was obtained by controlling the seed amount and reducing agent. These nanocomposites are used as electrocatalysts for the thermodynamically unfavorable oxygen evolution reaction (OER) from water. Among the nanocomposites, the most efficient OER activity was observed from the nanocomposite 12. The content of iron with respect to gold is at the maximum in the nanocomposite, which was obtained from the reaction with a minimum seed concentration and maximum reducing agent.

Gold Nanoflower for Selective Detection of Single Arginine Effect in α-Helix Conformational Change over Lysine in 310-Helix Peptide.

Hydroxylamine-based growth reaction in the presence of natural l-amino acids (9 mM) and gold nanoparticle seed mostly produce aggregated or nonaggregated gold nanostructures except the cases of immediate precipitation with aspartic acid, glutamic acid, cysteine, and tyrosine. Among the other amino acids, arginine shows the control growth reaction to form gold nanoflower from gold nanoparticle seeds, which were preincubated with amine-modified DNA (NH2-oln). The absorbance trend with NH2-oln in the presence of arginine is similar to the aggregation behavior in the presence of histidine and methionine. The formations of gold nanoflower with arginine and aggregation due to histidine and methionine in the presence of NH2-oln were sorted out with lower concentration (50 µM) of these amino acids. This observation was successfully transferred to differentiate 310-helical Ac-(AAAAK)3A-NH2 from α-helical Ac-(AAAAR)3A-NH2. The concept was further applied for the detection of single arginine modification closest to the carboxy terminus of 310-helical Ac-(AAAAK)3A-NH2 peptide for maximum conformational change toward α-helix.

Formation of Growth-Mediated Gold Nanoflowers: Roles of the Reducing Agent and Amine-Modified, Single-Strand DNA Sequences.

The formation of growth-mediated structures from gold nanoparticle seeds was studied in the presence of amine-modified single-strand DNA sequences and reducing agents such as hydroxylamine and hydroquinone. In the case of hydroxylamine, spherical gold nanoparticle seeds (0.45 nM) were incubated with amine-modified single-strand DNA probes PMR (amine-5'-ACATCAGT-3') and PML (amine-5'-GATAAGCT-3'), which resulted in gold nanoflowers and nanospheres, respectively. When the concentration of the nanoparticle seeds was varied (0.15-0.45 nM), only the PMR sequence showed growth-mediated development of gold nanoflowers. The size of the gold nanoparticles obtained is independent of the seed concentration for both PMR and PML sequences. In contrast, in the presence of the reducing agent hydroquinone, the growth processes are identical in for both the sequences. At a lower seed concentrations (0.15 nM), gold nanoflowers of larger size were observed for both sequences, whereas at higher seed concentrations (0.45 nM), much smaller gold nanospheres resulted. The formation and stability of nanoflowers and nanospheres for PMR and PML with hydroxylamine-based reduction were further studied in detail with diverse controlled amine-modified (5'-, 3'- and both end-modified) and non-modified DNA sequences with other mutants of these two sequences.

Regioisomeric cryptand stabilized gold supraspheres and elongated dodecahedron supraparticles for reversible host-guest chemistry.

Addition of bis-pyrazole based cryptand regioisomers (1 and 2) to citrate stabilized gold nanoparticles (AuNPs) led to gold supraspheres (AuSSL) and elongated dodecahedron (AuEDL) supraparticles, respectively. These supraparticles as heterogenous hosts show a high uptake of a small fluorophore SEA-SC1 in an aqueous medium and reversible release in organic solvents.

Highly selective tridentate fluorescent probes for visualizing intracellular Mg2+ dynamics without interference from Ca2+ fluctuation.

We developed highly selective fluorescent Mg2+ probes based on a novel tridentate Mg2+-selective chelator. The superior selectivity for Mg2+ over Ca2+ enabled the detection of intracellular Mg2+ concentration changes without any response to Ca2+ influx. The new probes are potential keys to elucidating intracellular Mg2+ dynamics under conditions of extremely sharp Ca2+ fluctuation.

Fluorogen-free aggregation induced NIR emission from gold nanoparticles.

Controlled diluted aqua regia addition leads to NIR (near infrared) luminescence from aggregated gold nanoparticles at 916 nm. This turn-on luminescence has been observed for gold nanoparticles, regardless of reductants used in their preparation. These aggregated nanoparticles are nontoxic and have been used for bioimaging in human liver carcinoma cells.

Nucleic Acid Templated Chemical Reaction in a Live Vertebrate.

Nucleic acid templated reactions are enabled by the hybridization of probe-reagent conjugates resulting in high effective reagent concentration and fast chemical transformation. We have developed a reaction that harnesses cellular microRNA (miRNA) to yield the cleavage of a linker releasing fluorogenic rhodamine in a live vertebrate. The reaction is based on the catalytic photoreduction of an azide by a ruthenium complex. We showed that this system reports specific expression of miRNA in living tissues of a vertebrate.

In cellulo protein labelling with Ru-conjugate for luminescence imaging and bioorthogonal photocatalysis.

Labelling of proteins with a luminescent ruthenium complex enables the direct visualization and photocatalytic reduction of aryl azide in live cells. The confinement of catalysis to the labeled proteins was visualized using an azide-based immolative linker releasing a precipitating dye.

Detection of miRNA in live cells by using templated RuII-catalyzed unmasking of a fluorophore.

Reactions templated by cellular nucleic acids are attractive for nucleic acid sensing or responsive systems. Herein we report the use of a photocatalyzed reductive cleavage of an immolative linker to unmask a rhodamine fluorophore, and its application to miRNA imaging. The reaction was found to proceed with a very high turnover (>4000) and provided reliable detection down to 5 pM of template by using γ-serine-modified peptide nucleic acid (PNA) probes. The reaction was used for the selective detection of miR-21 in BT474 cells and miR-31 in HeLa cells following irradiation for 30 min. The probes were introduced by using reversible permeation with streptolysin-O (SLO) or a transfection technique.

Nucleic acid-tagged peptides: encoding libraries and controlling dimerization and conformation.

Recent progress in the synthesis, screening, and self-assembly of nucleic acid-tagged peptidic libraries is reviewed.

pH induced dual "OFF-ON-OFF" switch: influence of a suitably placed carboxylic acid.

The design and synthesis of molecular probes competent for pH signaling within or beyond a certain range is a complicated matter. Herein a new mechanism for ''OFF-ON-OFF'' absorbance and fluorescence intensities vs. pH behaviour is described. The probe design is based on the connection of carboxylic acid derivatized benzoxazole and 7-hydroxycoumarin/iminocoumarin parts. The protonation/deprotonation of the carboxylic acid (-COOH), N atom of benzoxazole ring and hydroxy part of the coumarin ring have been used for this mechanistic study. We have designed the molecule in such a fashion that deprotonation of the hydroxy part takes place at a lower pK(a) compared to deprotonation of the -COOH. The dual ''OFF-ON-OFF'' properties of our probes depend on the C-C bond between the two different heterocyclic parts. Quantum mechanical calculations showed that the particular 'C-C' bond has an additional π-character. The twisting around this bond in different forms is responsible for such an ''OFF-ON-OFF'' property. This mechanism is new in fluorescence alteration processes. The delocalization of charge from one heterocyclic part to the other heterocyclic part in the mono- and dianionic forms controls the ''OFF-ON-OFF'' properties. The role of the carboxylic acid group was examined using an acetyl substituted derivative. One of our probes was successfully applied in live cell imaging studies in media at different pH.

Photoreductive uncaging of fluorophore in response to protein oligomers by templated reaction in vitro and in cellulo.

The photoreduction of azide-based immolative linker by Ru(II) conjugates to uncage rhodamine was achieved using different oligomeric protein templates. The generality of the approach was validated with three sets of ligand having varying affinity to their target (biotin, desthiobiotin and raloxifene). The reaction rates of the templated reaction was found to be at least 30-fold faster than the untemplated reaction providing a clear fluorescent signal in response to the protein oligomer within 30 min. The templated reaction was found to also proceed in cellulo and could be used to identify acetyl coenzyme A carboxylase (ACC) in Pseudomonas aeruginosa and human cell lines as well the and estrogen receptor (ER).