Multivalent Interactions Regulate Signal Transduction in a Self-Assembled Hg2+ Sensor

In situ enzymatic control of colloidal phoresis and catalysis through hydrolysis of ATP

The ability to sense chemical gradients and respond with directional motility and chemical activity is a defining feature of complex living systems. There is a strong interest among scientists to design synthetic systems that emulate these properties. Here, we realize and control such behaviors in a synthetic system by tailoring multivalent interactions of adenosine nucleotides with catalytic microbeads. We first show that multivalent interactions of the bead with gradients of adenosine mono-, di- and trinucleotides (AM/D/TP) control both the phoretic motion and a proton-transfer catalytic reaction, and find that both effects are diminished greatly with increasing valence of phosphates. We exploit this behavior by using enzymatic hydrolysis of ATP to AMP, which downregulates multivalent interactivity in situ. This produces a sudden increase in transport of the catalytic microbeads (a phoretic jump), which is accompanied by increased catalytic activity. Finally, we show how this enzymatic activity can be systematically tuned, leading to simultaneous in situ spatial and temporal control of the location of the microbeads, as well as the products of the reaction that they catalyze. These findings open up new avenues for utilizing multivalent interaction-mediated programming of complex chemo-mechanical behaviors into active systems.

Luminescence Sensing of Biomacromolecules Heparin and Protamine in 100% Human Serum and Plasma by Supramolecular Polymeric Assemblies

Heparin, an anionic biomacromolecule, is routinely used as an anticoagulant during medical surgery to prevent blood clot formation and in the treatment of several heart, lung, and circulatory disorders having a higher risk of blood clotting. We herein report supramolecular polymeric nanoassemblies of cationic pyrene-tagged bis-imidazolium amphiphiles for heparin detection with high sensitivity and selectivity in aqueous buffer, plasma, and serum media. The nano-assemblies exhibited cyan-green excimeric emission in aqueous media, and their multivalent array of positive surface charges allowed them to form co-assemblies with heparin, resulting in significantly enhanced emission. This provided a convenient method for heparin detection in buffer at nanomolar concentrations, and most notably, a ratiometric fluorescence response was obtained even in highly competitive 100% human serum and 100% human plasma in a clinically relevant concentration range. Moreover, using the heparin-based luminescent co-assemblies, protamine sulfate, a clinically administered antidote to heparin, was also detected in 100% human serum and 100% human plasma at sub-micromolar concentrations.

Reversible detection of Hg(II) in pure water based on thymine modified nitrogen, sulfur co-doped carbon dots combined with antidote

Conventional Hg²⁺ visual sensors are unsustainable, hindering their practical application for improved water quality and health. In order to address this challenge, herein, N, S co-doped carbon nanodots (NS-CDs) were prepared and well characterized, presented the fluorescent monitoring for Hg²⁺ over other metal ions with the limit of detection (LOD) of 0.47 µM. Next, the CDs were successfully modified by thymine without any fluorescence labelling (referred to as T-NS-CDs). The sensitivity to Hg²⁺ cloud be noticeable enhanced due to the formation of T-Hg²⁺-T specific base pairs. Accordingly, the LOD was calculated with values as low as 1.56 nM. Furthermore, Hg²⁺ could be released and complexed with antidote (meso-2,3-dimercaptosuccinic acid) (DMSA-Hg²⁺), being the responsible for the reversible interconversion between T-Hg²⁺-T and DMSA-Hg²⁺. Interestingly, the proposed sensing system also applies to the fluorescent sensing for Hg²⁺ in tap water with satisfactory recoveries (96.97 %-101.38 %, RSD < 2 %). Thus, by simply combination of elemental doping and surface functionalization, the surface state and functionalities of CDs could be tailorable, endowing the fluorometric sensing towards Hg²⁺ in environmental system.

Regulating Spatial Localization and Reactivity Biasness of DNAzymes by Metal Ions and Oligonucleotides

Chemical gradient sensing behavior of catalytically active colloids and enzymes is an area of immense interest owing to their importance in understanding fundamental spatiotemporal complexity pattern in living systems and designing of dynamic materials. Herein, we have shown peroxidase activity of DNAzyme (G-quadruplex-hemin complex tagged in a micron-sized glass bead) can be modulated by metal ions and metal ion-binding oligonucleotides. Next we demonstrated both experimentally and theoretically that the localization and product formation ability of the DNAzyme containing particle remains biased to the more catalytically active zone where concentration of metal ion (Hg2+) inhibitor is low. Interestingly, this biased localization can be broken by introduction of Hg2+ binding oligonucleotide in the system. Additionally, macroscopically asymmetric catalytic product distributed zone has also been achieved on this process, showing possibility in regulation in autonomous spatially controlled chemical process. This demonstration of autonomous modulation of the localization pattern and spatially specific enhanced product forming ability of DNAzymes will further enable in designing of responsive nucleic acid-based motile materials and surfaces.

Biothiol-Functionalized Cuprous Oxide Sensor for Dual-Mode Sensitive Hg2+ Detection

Hg²⁺ ions are one of the highly poisonous heavy metal ions in the environment, so it is urgent to develop rapid and sensitive detection platforms for detecting Hg²⁺ ions. In this work, a novel electrochemical and photoelectrochemical dual-mode sensor (l-Cys-Cu₂O) was successfully fabricated, and the sensor exhibits a satisfactory detection limit (0.2 and 0.01 nM) for the detection of Hg²⁺, which is far below the dangerous limit of the U.S. Environmental Protection Agency. The linear ranges of dual-mode Hg²⁺ detections were 0.33-3.3 and 0.17-1.33 μM, respectively. Moreover, the sensor shows desirable stability, selectivity, and reproducibility for detecting Hg²⁺ ions. For river water samples, the recoveries of 96.6-101.4% (electrochemical data) and 93.0-105.6% (photoelectrochemical data) were obtained, indicating that the sensor could be successfully applied in the determination of Hg²⁺ ions in environmental water. Therefore, the designed sensor has a potential in the trace-level detection of Hg²⁺ ions.

Benchmark Acetylene Binding Affinity and Separation through Induced Fit in a Flexible Hybrid Ultramicroporous Material

Structural changes at the active site of an enzyme induced by binding to a substrate molecule can result in enhanced activity in biological systems. Herein, we report that the new hybrid ultramicroporous material sql-SIFSIX-bpe-Zn exhibits an induced fit binding mechanism when exposed to acetylene, C2 H2 . The resulting phase change affords exceptionally strong C2 H2 binding that in turn enables highly selective C2 H2 /C2 H4 and C2 H2 /CO2 separation demonstrated by dynamic breakthrough experiments. sql-SIFSIX-bpe-Zn was observed to exhibit at least four phases: as-synthesised (α); activated (β); and C2 H2 induced phases (β' and γ). sql-SIFSIX-bpe-Zn-β exhibited strong affinity for C2 H2 at ambient conditions as demonstrated by benchmark isosteric heat of adsorption (Qst ) of 67.5 kJ mol-1 validated through in situ pressure gradient differential scanning calorimetry (PG-DSC). Further, in situ characterisation and DFT calculations provide insight into the mechanism of the C2 H2 induced fit transformation, binding positions and the nature of host-guest and guest-guest interactions.

An asymmetric Schiff base-functionalized gold nanoparticle-based colorimetric sensor for Hg2+ ion determination: experimental and DFT studies

We report a colorimetric sensor for the detection of Hg²⁺ ions utilizing surface-modified gold nanoparticles. Gold nanoparticles (GNPs) were synthesized by direct reduction and were subsequently functionalized using Schiff base ligands. Schiff base ligands as electron transfer agents have been frequently used for the determination of heavy metal ions. From the spectroscopic analysis, it was found that the mechanism could be defined as coordination between azomethine nitrogen and the carbonyl oxygen of the ligand with Hg²⁺ ions. The affinity of Hg²⁺ ions towards the bidentate Schiff base on the GNPs result from their self-aggregation and investigated to be a powerful asset for the development of Hg²⁺ ion-selective sensors, which is accompanied by a visible color change from pink to purple or can be detect by UV-Vis spectroscopy. The optimized structures and binding mechanisms were supported with a high correlation and agreement via spectroscopy and DFT calculations. These simple colorimetric tests can be extended for the rapid pre-screening of a wide variety of heavy metal ions for onsite detection and mitigation.

Probing Multiscale Factors Affecting the Reactivity of Nanoparticle-Bound Molecules

The structures and physicochemical properties of surface-stabilizing molecules play a critical role in defining the properties, interactions, and functionality of hybrid nanomaterials such as monolayer-stabilized nanoparticles. Concurrently, the distinct surface-bound interfacial environment imposes very specific conditions on molecular reactivity and behavior in this setting. Our ability to probe hybrid nanoscale systems experimentally remains limited, yet understanding the consequences of surface confinement on molecular reactivity is crucial for enabling predictive nanoparticle synthon approaches for postsynthesis engineering of nanoparticle surface chemistry and construction of devices and materials from nanoparticle components. Here, we have undertaken an integrated experimental and computational study of the reaction kinetics for nanoparticle-bound hydrazones, which provide a prototypical platform for understanding chemical reactivity in a nanoconfined setting. Systematic variation of just one molecular-scale structural parameter-the distance between reactive site and nanoparticle surface-showed that the surface-bound reactivity is influenced by multiscale effects. Nanoparticle-bound reactions were tracked in situ using ¹⁹F NMR spectroscopy, allowing direct comparison to the reactions of analogous substrates in bulk solution. The surface-confined reactions proceed more slowly than their solution-phase counterparts, and kinetic inhibition becomes more significant for reactive sites positioned closer to the nanoparticle surface. Molecular dynamics simulations allowed us to identify distinct supramolecular architectures and unexpected dynamic features of the surface-bound molecules that underpin the experimentally observed trends in reactivity. This study allows us to draw general conclusions regarding interlinked structural and dynamical features across several length scales that influence interfacial reactivity in monolayer-confined environments.

Signaling in Systems Chemistry: Programing Gold Nanoparticles Formation and Assembly Using a Dynamic Bistable Network

Living cells exploit bistable and oscillatory behaviors as memory mechanisms, facilitating the integration of transient stimuli into sustained molecular responses that control downstream functions. Synthetic bistable networks have also been studied as memory entities, but have rarely been utilized to control orthogonal functions in coupled dynamic systems. We herein present a new cascade pathway, for which we have exploited a well-characterized switchable peptide-based replicating network, operating far from equilibrium, that yields two alternative steady-state outputs, which in turn serve as the input signals for consecutive processes that regulate various features of Au nanoparticle shape and assembly. This study further sheds light on how bridging together the fields of systems chemistry and nanotechnology may open up new opportunities for the dynamically controlled design of functional materials.

A Remarkable Fluorescence Quenching Based Amplification in ATP Detection through Signal Transduction in Self-Assembled Multivalent Aggregates

Signal transduction is essential for the survival of living organisms, because it allows them to respond to the changes in external environments. In artificial systems, signal transduction has been exploited for the highly sensitive detection of analytes. Herein, a remarkable signal transduction, upon ATP binding, in the multivalent fibrillar nanoaggregates of anthracene conjugated imidazolium receptors is reported. The aggregates of one particular amphiphilic receptor sensed ATP in high pm concentrations with one ATP molecule essentially quenching the emission of thousands of receptors. A cooperative merging of the multivalent binding and signal transduction led to this superquenching and translated to an outstanding enhancement of more than a millionfold in the sensitivity of ATP detection by the nanoaggregates; in comparison to the "molecular" imidazolium receptors. Furthermore, an exceptional selectivity to ATP over other nucleotides was demonstrated.

A novel pillar[5]arene-based emission enhanced supramolecular sensor for dual-channel selective detection and separation of Hg2+

We constructed a supramolecular sensor (APRA–G) via a host–guest inclusion interaction between a rhodamine hydrazide-functionalized pillar[5]arene (APRA) and a bipyridine salt guest (G), which formed a stable dimer.

High affinity heparin detection by multivalent supramolecular polymers through aggregation induced emission

Supramolecular polymers based on aggregation induced emission active cationic cyanostilbenes provide a highly sensitive “light-up” platform for heparin detection.

High-efficiency cathodic electrochemiluminescence of the tris(2,2′-bipyridine)ruthenium(ii)/N-hydroxy compound system and its use for sensitive “turn-on” detection of mercury(ii) and methyl blue

N-Hydroxysuccinimide (NHS) and N-hydroxysulfosuccinimide (NHSS) were exploited as efficient coreactants for cathodic Ru(bpy)₃²⁺ electrochemiluminescence (ECL) in neutral medium.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Induced-fit expansion and contraction of a self-assembled nanocube finely responding to neutral and anionic guests

Induced-fit or conformational selection is of profound significance in biological regulation. Biological receptors alter their conformation to respond to the shape and electrostatic surfaces of guest molecules. Here we report a water-soluble artificial molecular host that can sensitively respond to the size, shape, and charged state of guest molecules. The molecular host, i.e. nanocube, is an assembled structure consisting of six gear-shaped amphiphiles (GSAs). This nanocube can expand or contract its size upon the encapsulation of neutral and anionic guest molecules with a volume ranging from 74 to 535 Å3 by induced-fit. The responding property of this nanocube, reminiscent of a feature of biological molecules, arises from the fact that the GSAs in the nanocubes are connected to each other only through the hydrophobic effect and very weak intermolecular interactions such as van der Waals and cation-π interactions.

Electrostatic Modification for Promotion of Flavin-Mediated Oxidation of a Probe for Flavin Detection

Electrostatic effects on the redox photochemistry of synthetic probes (1, 2, and 1-Zn) are examined by adjusting the thermodynamic driving force of their oxidation reactions. The redox photochemistry was simply controlled by introducing a zinc binding site (2,2'-dipicolylamine (DPA)) on the coumarin moiety of probe 2. Zinc complexation produced a positively charged environment on the coumarin (1-Zn), which lowered the electron density of a nearby 9 H-xanthene ring, attenuating the auto-oxidation of 1-Zn by 45 % compared with that of probe 1 at 298 K. The positive net charge of 1-Zn also provided an attractive Coulombic force toward the phosphate of flavin mononucleotide and flavin adenine dinucleotide, which lowered the reduction potential of the electron acceptor (isoalloxazine) and improved intermolecular electron transfer from the 9 H-xanthene ring to isoalloxazine. The flavin-mediated oxidation rate of 1-Zn was increased to 1.5 times that of probe 2. Probe 1-Zn showed highly selective sensing behaviour toward flavins, producing an intense brightness (ϵΦ_F =2.80×10³  m^-1  cm^-1 ) in the long-wavelength regions (λ_max =588 nm) upon flavin-mediated oxidation. Furthermore, probes 1-Zn and 2 were successfully applied to eosinophil imaging and the differential diagnosis of eosinophilia; this demonstrates their use as diagnostic tools.

Photoswitchable Catalysis by a Nanozyme Mediated by a Light-Sensitive Cofactor

The activity of a gold nanoparticle-based catalyst can be reversibly up- and down-regulated by light. Light is used to switch a small molecule between cis- and trans-isomers, which inhibits the catalytic activity of the nanoparticles to different extent. The system is functional in aqueous buffer, which paves the way for integrating the system in biological networks.

Fluorescent Indicator Displacement Assay: Ultrasensitive Detection of Glutathione and Selective Cancer Cell Imaging

This Research Article reports the development of nanohybrid comprising of anionic carbon dots (ACD) protected gold nanoparticle (GNP). ACD directly cap GNP through its anionic surface functionalization leading to the formation of stable aqueous GNP dispersion. This newly developed ACD-GNP nanohybrid has been thoroughly characterized by different spectroscopic and microscopic techniques. This nanohybrid is successfully employed toward the selective sensing of glutathione (GSH). The mechanism of GSH sensing by this nanosensor is based on the GSH triggered displacement of fluorescent indicator ACD from the GNP surface. Upon capping GNP, intrinsic fluorescence of ACD gets quenched. Addition of GSH displaces the fluorescent indicator ACD from GNP surface and restores the fluorescence signal of ACD. This nanosensor exhibits very high selectivity as well as sensitivity toward glutathione over the other biothiols and can detect as low as 6 nM of GSH. More importantly, selective imaging of the cancer cells over the noncancerous cells was achieved by this ACD-GNP hybrid implying its potential applications in biosensing, as well as in cancer diagnosis.

Binding kinetics and multi-bond: Finding correlations by synthesizing interactions between ligand-coated bionanoparticles and receptor surfaces

The number of bonds formed between one single bionanoparticle and many surface receptors is an important subject to be studied but is seldom quantitatively investigated. A new evaluation of the correlation between binding kinetics and number of bonds is presented by varying ligand density and receptor density. An experimental system was developed using measurements with surface plasmon resonance spectroscopy. A corresponding multi-site adsorption model elucidated the correlation. The results show that with the increase of the receptor density, the adsorption rate first decreased when the number of bonds was below a maximum value and then increased when the number of bonds stayed at this maximum value. The investigation on ligand density variation suggests that the coating density on top of the bionanoparticle surface may have a particular value below which more ligand will accelerate the adsorption rate. The ratio of ligand amount bound by the receptors to the total ligand amount associated with a single bionanoparticle will remain constant even if one attaches more ligands to a bionanoparticle. We envision that the bionanoparticle desorption will not depend on density changes from either ligand or receptor when the number of bonds reaches a specific efficient value.

A Supramolecular Sensor Array Using Lanthanide-Doped Nanoparticles for Sensitive Detection of Glyphosate and Proteins

Lanthanide (Ln(3+))-doped nanoparticles (NPs) are an intensive area of research in chemical and materials sciences. Herein a sensor array of Ln(3+)-doped NPs was developed for the first time toward sensitive molecular sensing based on a novel strategy of the hybridized time-resolved Förster resonance energy transfer (TR-FRET) with the indicator displacement assay (IDA) concept (TR-FRET-IDA). The sensor platform was generated in situ by binding a series of negatively charged indicators on the surface of ligand-free LiYF4:Ce/Tb NPs. The TR-FRET between NPs and dyes resulted in indicator emission and was employed as a means of removing undesired short-lived background luminescence from the indicator effectively. Displacement of indicators from the NP/indicator ensembles by glyphosate, a common herbicide, led to turn-off of the indicator emission. The sensor array was able to successfully discriminate 11 biologically relevant anions with high accuracy and sensitivity in pure aqueous buffer both qualitatively and quantitatively. Furthermore, the differentiation of six model proteins in the nM range was achieved with 100% accuracy for the classification, thereby demonstrating the versatility of this simple sensor platform. The study of the mechanism of binding and signal modulation further verified TR-FRET-IDA as a reliable sensing paradigm.

Dynamic nanoproteins: self-assembled peptide surfaces on monolayer protected gold nanoparticles

Small peptides self-assemble on gold nanoparticles to form a dynamic multivalent peptide surface.

Two star-shaped tetranuclear Ru(II) complexes containing uncoordinated imidazole groups: synthesis, characterization, photophysical and pH sensing properties

Tetrapodal ligands H4L(1) and H4L(2) containing imidazole groups have been synthesized by the reaction of 1,10-phenanthroline-5,6-dione with 1,2,4,5-tetrakis[(4-formylphenoxy)methyl]benzene and 1,2,4,5-tetrakis[(3-formylphenoxy)methyl]benzene, respectively, in presence of NH4OAc. Two star-shaped complexes [{Ru(bpy)2}4(μ4-H4L(1))](PF6)8 and [{Ru(bpy)2}4(μ4-H4L(2))](PF6)8 (bpy = 2,2'-bipyridine) have been prepared by refluxing Ru(bpy)2Cl2 ·2H2O and each ligand in ethylene glycol. The deprotonated complexes [{Ru(bpy)2}4(μ4-L(1))](PF6)4 and [{Ru(bpy)2}4(μ4-L(2))](PF6)4 have been obtained by the reaction of sodium methoxide with [{Ru(bpy)2}4(μ4-H4L(1))](PF6)8 and [{Ru(bpy)2}4(μ4-H4L(2))](PF6)8, respectively, in methanol. The pH effects on the UV-vis light absorption and emission spectra of both complexes have been studied, and ground- and excited-state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as proton-induced off-on-off luminescent sensors through two successive deprotonation processes of imidazole groups, with a maximum on-off ratio of 8 in buffer solution at room temperature. Theoretical calculations for the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LOMO) orbitals of bridging ligand are also presented for plausible explanations of the fluorescence changes.

N-(3-Imidazolyl)propyl dansylamide as a selective Hg(2+) sensor in aqueous media through electron transfer

N-Imidazolylpropyl dansylamide 1 was synthesized for the sensing of metal ions and found to be selective and sensitive toward Hg(2+) ions in a PBS-EtOH (1:4, pH=7.4) solution. The sensing ability of probe 1 was examined by UV-Vis, fluorescence, and (1)H NMR spectroscopy. The sensing of Hg(2+) exhibited a quenching of emission band at λmax=515 nm of probe 1, which was associated with quenching of green fluorescence emission under 365 nm illumination. Probe 1 showed a good association constant with Hg(2+) (Ka=6.48×10(4) M(-1)) with a stoichiometry of 1:1 in PBS-EtOH (1:4, pH=7.4) having the lowest detection limit of 1 μM for Hg(2+); on the other hand, probe 2, which has no imidazole moiety, was not able to detect any metal ion. In the case of probe 1, electrons on the imidazole nitrogen are available for electron transfer (ET), which was responsible for its green emission band that was quenched on addition of Hg(2+); this clearly indicates that these electrons were used for the formation of a coordinate bond with Hg(2+) and that ET was switched off.

Transient signal generation in a self-assembled nanosystem fueled by ATP

A fundamental difference exists in the way signal generation is dealt with in natural and synthetic systems. While nature uses the transient activation of signalling pathways to regulate all cellular functions, chemists rely on sensory devices that convert the presence of an analyte into a steady output signal. The development of chemical systems that bear a closer analogy to living ones (that is, require energy for functioning, are transient in nature and operate out-of-equilibrium) requires a paradigm shift in the design of such systems. Here we report a straightforward strategy that enables transient signal generation in a self-assembled system and show that it can be used to mimic key features of natural signalling pathways, which are control over the output signal intensity and decay rate, the concentration-dependent activation of different signalling pathways and the transient downregulation of catalytic activity. Overall, the reported methodology provides temporal control over supramolecular processes.

Natural and synthetic systems have fundamentally different approaches to signal generation. Here, the authors report a strategy that enables transient signal generation in a self-assembled system and show that it can be used to mimic several key features of natural signalling pathways.

Emergence of complex chemistry on an organic monolayer

In many origin-of-life scenarios, inorganic materials, such as FeS or mineral clays, play an important role owing to their ability to concentrate and select small organic molecules on their surface and facilitate their chemical transformations into new molecules. However, considering that life is made up of organic matter, at a certain stage during the evolution the role of the inorganic material must have been taken over by organic molecules. How this exactly happened is unclear, and, indeed, a big gap separates the rudimentary level of organization involving inorganic materials and the complex organization of cells, which are the building blocks of life. Over the past years, we have extensively studied the interaction of small molecules with monolayer-protected gold nanoparticles (Au NPs) for the purpose of developing innovative sensing and catalytic systems. During the course of these studies, we realized that the functional role of this system is very similar to that typically attributed to inorganic surfaces in the early stages of life, with the important being difference that the functional properties (molecular recognition, catalysis, signaling, adaptation) originate entirely from the organic monolayer rather than the inorganic support. This led us to the proposition that this system may serve as a model that illustrates how the important role of inorganic surfaces in dictating chemical processes in the early stages of life may have been taken over by organic matter. Here, we reframe our previously obtained results in the context of the origin-of-life question. The following functional roles of Au NPs will be discussed: the ability to concentrate small molecules and create different local populations, the ability to catalyze the chemical transformation of bound molecules, and, finally, the ability to install rudimentary signaling pathways and display primitive adaptive behavior. In particular, we will show that many of the functional properties of the system originate from two features: the presence of metal ions that are complexed in the organic monolayer and the multivalent nature of the system. Complexed metal ions play an important role in determining the affinity and selectivity of the interaction with small molecules, but serve also as regulatory elements for determining how many molecules are bound simultaneously. Importantly, neighboring metal ion complexes also create catalytic pockets in which two metal ions cooperatively catalyze the cleavage of an RNA-model compound. The multivalent nature of the system permits multiple noncovalent interactions with small molecules that enhances the affinity, but is also at the basis of simple signal transduction pathways and adaptive behavior.

Thymine Functionalized Graphene Oxide for Fluorescence "Turn-off-on" Sensing of Hg2+ and I- in Aqueous Medium

Selective detection of either mercury (Hg2+) or iodide (I-) ion using fluorescence turn-on or turn-off processes is an important area of research. In spite of intensive research, simultaneous detection of both mercury and iodide using fluorescence turn-off-on processes, high sensitivity and theoretical support concerning the mechanisms are still lacking. In the present work, graphene oxide is functionalized by thymine to realize simultaneous detection of both Hg2+ and I- selectively using fluorescence turn-off-on mechanism. Ultra high sensitivity to the extent of ppb level exploiting large surface area of graphene is achieved. DFT calculations also assist to realize the detailed mechanisms involving this PL quenching and also its regain during sensing of these ions in aqueous solution.

Dynamic combinatorial chemistry on a monolayer protected gold nanoparticle

Here, we show that the addition of Hg(2+) or Ag(+) metal ions to a dynamic system composed of monolayer protected gold nanoparticles (Au NPs) and a mixture of four nucleotides (dGMP, dAMP, TMP, and dCMP) leads to the self-selection of TMP or dGMP, respectively, on the monolayer surface.

Sunlight induced unique morphological transformation in graphene based nanohybrids: appearance of a new tetra-nanohybrid and tuning of functional property of these nanohybrids

In this study, sunlight was used for in situ preparation of gel-based various nanohybrid systems. A naturally occurring amino acid, l-phenylalanine derivative formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at physiological pH. This hydrogel was then used in the presence of silver ions and diffuse sunlight to form initially a tri-nanohybrid system consisting of six atom silver nanoclusters, nanosheets, and nanofibers. Interestingly, a time-dependent morphological transformation occurs in this nanohybrid system to form one tri-nanohybrid to another tri-nanohybrid with the appearance of a novel, nanoscopic intermediate tetra-nanohybrid system consisting of four distinctly different nanomaterials (nanofibers, nanosheets, nanospheres, and nanoparticles). UV-Vis and fluorescence spectroscopic analyses, transmission electron microscopic, X-ray photo electron spectroscopic and MALDI-TOF mass spectral analyses with time were applied to characterise these morphological transformations in gel based nanohybrids. Time-dependent X-ray photo electron spectroscopic (XPS) analysis was used to uncover the mechanism for the transformation of silver nanoclusters to silver nanoparticles in the hydrogel matrix. Sunlight was used to trigger time-dependent structural transformation in the nanohybrid systems. Interestingly, one of these tri-nanohybrid systems (silver nanoparticles containing rGO based hydrogel) shows a catalytic property of reducing nitroarenes to aminoarenes and the catalytic efficiency can be modulated by changing the size of the silver nanoparticles with time in diffuse sunlight. The mechanism for different catalytic activities for different hybrids with varying size of silver nanoparticles has also been deciphered.