Light-induced Assembly Research Articles

The interplay of chromophore-spacer length in light-induced gold nanocluster self-assembly.

The light-induced self-assembly of chromophore-tethered precision nanoclusters (NCs) has recently received significant attention due to their facile control over structure, function, and reversibility under ambient conditions. However, the magnitude of assembly depends on the photoswitching efficiency, chemical structure, and proximity of the chromophore to the NC surface. Herein, using azobenzene alkyl monothiol (AMT)-capped gold NCs with two different spacer lengths (denoted as C3-NC and C9-NC), we show that reversible cis ↔ trans isomerization efficiency can be readily tuned to control the self-assembly kinetics of NCs. Irrespective of the chain length, the time required for trans-to-cis (140 s) and cis-to-trans (260 s) isomerization of individual C3-AMT and C9-AMT is identical in dichloromethane solution. When a similar experiment was performed using a solution of C3-NCs and C9-NCs, it resulted in self-assembled disc-like superstructures. Notably, the trans-to-cis photoswitching in C3-NC could reach only 65% even after 460 seconds of irradiation. On the other hand, C9-NC completed this process within 160 seconds of irradiation. The low photoswitching efficiency of the C3-NC analog is due to the short and rigid spacer length of C3-AMT ligands, which are in close proximity to the NC surface, resulting in steric hindrance experienced at the NC-chromophore interface. Importantly, the slow photoswitching in C3-NCs helps isolate and investigate the intermediates of assembly. Using high-resolution electron microscopy, atomic force microscopy, and 3D reconstruction, we show that the discs are made up of densely packed arrays of NCs. The prolonged illumination of C9-NCs results in a chain-like assembly due to the dipolar attraction between the previously assembled superstructures. The efficient photoisomerization of chromophores located away from the nanocluster surface has been identified as the key element to speed up the light-induced assembly in chromophore-tethered nanoclusters. Such information will be useful while developing nanoscale photoswitches for electrochemistry, biosensors, and electronic devices.

Synthesis of bisindolyl diphenylene from its ketone derivatives by infrared irradiation supported on a natural clay

We examined the near-infrared (NIR) light-induced assembly efficiency to obtain light-sensitive 3,3′-(9H-fluorene-9,9-diyl) bis(1H-indole) derivatives using natural clay as metal-free Brønsted–Löwry catalyst (bentonitic Tonsil–Actisil FF (TAFF) clay) and an adduct of aluminum (III) chloride with 9-fluorenone. Their mixtures in solventless and aprotic solvent conditions were also explored. Among all the modified reactions tested, the combined effects of TAFF natural clay with NIR light, specifically in the λ1.1 µm spectral region, result especially efficient to achieve the formation of C–Cπ bonds between π-excessive azaheteroaromatic reagents and functionalized polycyclic aromatic hydrocarbon to give the title compound in good yields within reasonable reaction times. The reaction coordinate was obtained using quantum chemical calculations. All the reactants, products, intermediates, and transition states were obtained for four systems. Natural orbital analysis allowed us to rationalize the transformations. Overall, this approach represents a greener and equally efficient alternative for conducting C–Cπ bond construction reactions in organic chemistry, and it is especially useful for protecting photosensitive compounds from abrupt decomposition.

Light-Induced Wavelength Dependent Self Assembly Process for Targeted Synthesis of Phase Stable 1D Nanobelts and 2D Nanoplatelets of CsPbI3 Perovskites.

Despite black cubic phase α-CsPbI3 nanocrystals having an ideal bandgap of 1.73 eV for optoelectronic applications, the phase transition from α-CsPbI3 to non-perovskite yellow δ-CsPbI3 phase at room temperature remains a major obstacle for commercial applications. Since γ-CsPbI3 is thermodynamically stable with a bandgap of 1.75 eV, which has great potential for photovoltaic applications, herein we report a conceptually new method for the targeted design of phase stable and near unity photoluminescence quantum yield (PLQY) two-dimensional (2D) γ-CsPbI3 nanoplatelets (NPLs) and one-dimensional (1D) γ-CsPbI3 nanobelts (NBs) by wavelength dependent light-induced assembly of CsPbI3 cubic nanocrystals. This article demonstrates for the first time that by varying the excitation wavelengths, one can design air stable desired 2D nanoplatelets or 1D nanobelts selectively. Our experimental finding indicates that 532 nm green light-driven self-assembly produces phase stable and highly luminescent γ-CsPbI3 NBs from CsPbI3 nanocrystals. Moreover, we show that a 670 nm red light-driven self-assembly process produces stable and near unity PLQY γ-CsPbI3 NPLs. Systematic time-dependent microscopy and spectroscopy studies on the morphological evolution indicates that the electromagnetic field of light triggered the desorption of surface ligands from the nanocrystal surface and transformation of crystallographic phase from α to γ. Detached ligands played an important role in determining the morphologies of final structures of NBs and NPLs from nanocrystals via oriented attachment along the [110] direction initially and then the [001] direction. In addition, XRD and fluorescence imaging data indicates that both NBs and NPLs exhibit phase stability for more than 60 days in ambient conditions, whereas the cubic phase α-CsPbI3 nanocrystals are not stable for even 3 days. The reported light driven synthesis provides a simple and versatile approach to obtain phase pure CsPbI3 for possible optoelectronic applications.

Light-Induced Condensation of Biofunctional Molecules around Targeted Living Cells to Accelerate Cytosolic Delivery.

The light-induced force and convection can be enhanced by the collective effect of electrons (superradiance and red shift) in high-density metallic nanoparticles, leading to macroscopic assembly of target molecules. We here demonstrate application of the light-induced assembly for drug delivery system with enhancement of cell membrane accumulation and penetration of biofunctional molecules including cell-penetrating peptides (CPPs) with superradiance-mediated photothermal convection. For induction of photothermal assembly around targeted living cells in cell culture medium, infrared continuous-wave laser light was focused onto high-density gold-particle-bound glass bottom dishes exhibiting plasmonic superradiance or thin gold-film-coated glass bottom dishes. In this system, the biofunctional molecules can be concentrated around the targeted living cells and internalized into them only by 100 s laser irradiation. Using this simple approach, we successfully achieved enhanced cytosolic release of the CPPs and apoptosis induction using a pro-apoptotic domain with a very low peptide concentration (nM level) by light-induced condensation.

Raw data for 'Light-induced assembly and disassembly of polymers with PdnL2n-type network junctions'

raw data for 'Light-induced assembly and disassembly of polymers with PdnL2n-type network junctions'

The primeval optical evolving matter by optical binding inside and outside the photon beam

Optical binding has recently gained considerable attention because it enables the light-induced assembly of many-body systems; however, this phenomenon has only been described between directly irradiated particles. Here, we demonstrate that optical binding can occur outside the focal spot of a single tightly focused laser beam. By trapping at an interface, we assemble up to three gold nanoparticles with a linear arrangement which fully-occupies the laser focus. The trapping laser is efficiently scattered by this linear alignment and interacts with particles outside the focus area, generating several discrete arc-shape potential wells with a half-wavelength periodicity. Those external nanoparticles inside the arcs show a correlated motion not only with the linear aligned particles, but also between themselves even both are not directly illuminated. We propose that the particles are optically bound outside the focal spot by the back-scattered light and multi-channel light scattering, forming a dynamic optical binding network.

Light-induced assembly of colloidal nanoparticles based on photo-controlled metal–ligand coordination

Self-assembly of colloidal nanoparticles is a promising approach for the fabrication of functional materials. Zeta potential strongly influences the self-assembly processes of nanoparticles. Light-induced zeta potential manipulation provides spatiotemporal resolution. However, current studies on photo-controllable zeta potential are based on ultraviolet (UV) light. In comparison with UV light, visible light is better suited to control the zeta potential of colloidal nanoparticles. In the present study, we applied visible light-responsive ruthenium (Ru) complexes, grafted onto the surface of silica nanoparticles (Ru-SNPs), to control their assembly. The Ru complexes were photoresponsive. Irradiation of Ru-SNPs induced the release of Ru complexes from the nanoparticle surface. The released Ru caused a decrease in the zeta potential of colloidal Ru-SNPs that further changed the assembly behavior and led to the aggregation of Ru-SNPs.

Damage-free light-induced assembly of intestinal bacteria with a bubble-mimetic substrate

Rapid evaluation of functions in densely assembled bacteria is a crucial issue in the efficient study of symbiotic mechanisms. If the interaction between many living microbes can be controlled and accelerated via remote assembly, a cultivation process requiring a few days can be ommitted, thus leading to a reduction in the time needed to analyze the bacterial functions. Here, we show the rapid, damage-free, and extremely dense light-induced assembly of microbes over a submillimeter area with the “bubble-mimetic substrate (BMS)”. In particular, we successfully assembled 104–105 cells of lactic acid bacteria (Lactobacillus casei), achieving a survival rate higher than 95% within a few minutes without cultivation process. This type of light-induced assembly on substrates like BMS, with the maintenance of the inherent functions of various biological samples, can pave the way for the development of innovative methods for rapid and highly efficient analysis of functions in a variety of microbes.

Light-induced assembly and disassembly of polymers with Pd n L2n -type network junctions.

Polymers containing PdnL2n complexes as network junctions were obtained by reaction of poly(ethylene glycol)-linked N-donor ligands with Pd2+. The addition of a metastable state photoacid renders the networks light sensitive, and gel–sol transitions can be achieved by irradiation with light. The inverse process, a light-induced sol–gel transition, was realized by using a molecularly defined Pd complex as an acid-sensitive reservoir for Pd2+. Upon irradiation, Pd2+ ions are released, allowing the formation of an acid-resistant polymer network. Both the gel–sol and the sol–gel transitions are reversed in the dark.

Light-induced assembly of living bacteria with honeycomb substrate.

Some bacteria are recognized to produce useful substances and electric currents, offering a promising solution to environmental and energy problems. However, applications of high-performance microbial devices require a method to accumulate living bacteria into a higher-density condition in larger substrates. Here, we propose a method for the high-density assembly of bacteria (106 to 107 cells/cm2) with a high survival rate of 80 to 90% using laser-induced convection onto a self-organized honeycomb-like photothermal film. Furthermore, the electricity-producing bacteria can be optically assembled, and the electrical current can be increased by one to two orders of magnitude simply by increasing the number of laser irradiations. This concept can facilitate the development of high-density microbial energy conversion devices and provide new platforms for unconventional environmental technology.

Electrical detection of DNA via nanoparticles under light-induced assembly

Rapid, simple, and label-free detection of DNA without fluorescent dyes is desired in the fields of medical diagnosis and food inspection. Electrical measurement using microelectrodes is a promising method for the detection of DNA, whereas it requires multiple pre-treatment processes. In this study, omitting these processes, we demonstrated the possibility of rapid electrical detection of DNA-modified gold nanoparticles and target DNA transported and accumulated between electrodes by photothermal assembly (PTA) under the laser irradiation to a microelectrode. Two types of target DNA molecules with different base sequences were detected within 10 min through the change of electric resistance before and after PTA. The obtained results will be a foundation of a rapid and simple genetic screening method and the detection of various biological nanomaterials based on the electrical measurement mediated by a light-induced assembly.

Improving the Photoresponse Properties of CdSe Quantum Wires by Alignment and Ligand Exchange.

Semiconductor nanowires are the ideal building blocks to construct various thin-film electronic and optoelectronic devices, the performance of which is largely determined by their ensemble geometry and surface chemistry in addition to the chemical composition. Here, we report the large-scale and oriented assembly of CdSe nanowires on the basis of a light-induced assembly approach under an external electric field. To further increase the electrical conductivity of nanowire films, the original surface-capping organic ligands are exchanged with small ionic species through a solid-state ligand-exchange process. The resulting surface-modified CdSe nanowire films exhibit markedly enhanced photoresponse properties including high on/off ratios and fast response. This work establishes a simple yet scalable method to fabricate aligned nanowire films with a desired surface chemistry, which can be broadly used in various electronic and optoelectronic devices.

Light-Induced Assembly of Metal Nanoparticles on ZnO Enhances the Generation of Charge Carriers, Reactive Oxygen Species, and Antibacterial Activity

Increasing the photocatalytic activity of semiconductors by forming heterojunctions with metal improves their energy transfer efficiency and environmental remediation capabilities. However, our knowledge regarding the structure–activity relationship of semiconductor/metal hybrid nanostructures is lacking due to poor control over their physicochemical properties. Here, we report a facile way to make ZnO/metal hetero-nanoparticles by the mixing/irradiation process of ZnO and metal nanoparticles. The resultant products provide an expedient model to explore the effects of various metal NPs on light-induced electron/hole separation, reactive oxygen species (ROS) production, and antibacterial activities of ZnO NPs. Electron spin resonance spectroscopy was used to compare the effect of mixing Pt, Au, or Ag NPs at different sizes and concentrations with ZnO NPs on light-induced electron–hole separation and ROS production. The enhancing effect of metal NPs depends on particle size, composition, and mass ratio of t...

Light induced assembly and self-sorting of silica microparticles

To tailor the properties of colloidal materials, precise control over the self-assembly of their constituents is a prerequisite. Here, we govern the assembly of silica particles by functionalization with supramolecular moieties which interact with each other via directional and reversible hydrogen bonding. Through a generally applicable synthesis protocol, two different types of self-complementary hydrogen bonding moieties, BTA- and UPy-derivatives, are anchored to silica particles. Their self-assembly is initiated by the UV-induced removal of a photolabile protecting group, allowing the formation of hydrogen bonds between tethered molecules. The light-induced assembly of BTA- and UPy-decorated colloids in single-component dispersions and colloidal self-sorting in mixed dispersions is studied. Furthermore, we demonstrate that UPy-colloids can dissasemble upon addition of traces of a competitive binder (NaPy). This work provides further insight into the utility of supramolecular handles to orchestrate the assembly of micron-sized colloids via non-oligonucleotide hydrogen-bonding units.

2C05 液晶エマルションにおけるマイクロドロップレットの光組織化(フォトニクス・光デバイス)

2C05 液晶エマルションにおけるマイクロドロップレットの光組織化(フォトニクス・光デバイス)

Three-dimensional nano-optical assembly of antenna structures with collective near-field coupling

Metallic nanostructures are used for various applications because of their characteristic optical responses that generate strong near-fields. We have theoretically clarified that the configuration of nanoparticles (NPs) and their optical properties can be controlled by optical manipulation. In this study, we greatly improved our previously reported simulation method, and this improvement enables investigation of the stable states of optically trapped NPs in a three-dimensional system. On the basis of this method, the assembly process of rod-shaped silver NPs is concisely clarified, where NPs of a specific shape are selectively assembled even in a mixture of NPs of different shapes. In particular, our simulation method clarifies how a light-induced force drives assembly processes, which is an important subject to consider for extending the degree of freedom of an optical manipulation. Furthermore, as reported in our previous studies, an assembled structure inherits the properties of light used for the optical trapping; e.g., rod-shaped silver NPs are radially connected to each other and assembled into a ring-shaped structure under the irradiation of a radially polarized vector beam with a ring-shaped intensity distribution. The assembled structure is an artificial light-harvesting antenna because it theoretically exhibits an enhancement of near-field and extinction in a broader wavelength range than that of the original NPs composing the antenna and also a response to the non-polarized light such as the sunlight. On the basis of an optically manipulated configuration of NPs and their optical properties, we discuss the selective optical assembly in a three-dimensional simulation.

Threading plasmonic nanoparticle strings with light.

Nanomaterials find increasing application in communications, renewable energies, electronics and sensing. Because of its unsurpassed speed and highly tuneable interaction with matter, using light to guide the self-assembly of nanomaterials can open up novel technological frontiers. However, large-scale light-induced assembly remains challenging. Here we demonstrate an efficient route to nano-assembly through plasmon-induced laser threading of gold nanoparticle strings, producing conducting threads 12±2 nm wide. This precision is achieved because the nanoparticles are first chemically assembled into chains with rigidly controlled separations of 0.9 nm primed for re-sculpting. Laser-induced threading occurs on a large scale in water, tracked via a new optical resonance in the near-infrared corresponding to a hybrid chain/rod-like charge transfer plasmon. The nano-thread width depends on the chain mode resonances, the nanoparticle size, the chain length and the peak laser power, enabling nanometre-scale tuning of the optical and conducting properties of such nanomaterials.

Atomic Force Microscopy Adhesion Mapping: Revealing Assembly Process in Inorganic Systems

There are still many unknowns regarding assembly processes. In this work, we demonstrate the capability of atomic force microscopy (AFM) adhesion mapping in revealing the conditions that promote the light-induced assembly of nanoparticles (NPs) on nanostructured surfaces in inorganic systems, both in macro- and nanodomains. Gold (Au) NPs and zinc oxide (ZnO) nanostructures are employed as the model materials, and different characterization techniques are used for extracting the relationship between the materials’ crystallinity, stoichiometry, and morphology as well as surface adhesion mapping information. The light-induced assembly of Au NPs is associated with the attraction forces between the opposite surface charges of the NPs and preferential ZnO sites, which can be identified by adhesion mapping. We show that the yield of Au nanoclusters assembled onto the ZnO surface depends on the crystallinity and stoichiometry of ZnO and is not due to the roughness of the surface. The presented experiments demonstrate that AFM adhesion mapping can be used as an invaluable tool for predicting the strength and directions of assembly processes.

Light-induced phase transitions of colloidal monolayers with crystalline order

We experimentally study the phase behavior of a charge-stabilized two-dimensional colloidal crystal which is subjected to a one-dimensional periodic light field. Such light fields are created by a scanned optical line tweezer which allows the variation of the periodicity without optical realignments. In order to realize a wide range of line spacings relative to the lattice constant, we use a suspension of silica particles in bromobenzene. This colloidal system has a Debye screening length of about 4.6 μm which results in the formation of crystals with lattice constants up to 20 μm. Because the refractive index of bromobenzene is larger than that of the colloids, optical gradient forces lead to the attraction of particles at regions where the intensity is smallest. Depending on the depth and periodicity of the optical potential, we observe the light-induced assembly of colloids into triangular, rhombic and square phases.

Assembly of sol–gel-grown Li x CoO2 nanocrystals through electromagnetic irradiation

We report the fabrication of assembled nanostructures from the pre-synthesized nanocrystals building blocks through optical means of exciton formation and dissociation. We demonstrate that LixCoO2 nanocrystals assemble to an acicular architecture, upon prolonged exposure to ultraviolet–visible radiation emitted from a 125 W mercury vapor lamp, through intermediate excitation of excitons. The results obtained in the present study clearly show how nanocrystals of various materials with band gaps appropriate for excitations of excitons at given optical wavelengths can be assembled to unusual nanoarchitectures through illumination with incoherent light sources. The disappearance of exciton bands due to LixCoO2 phase in the optical spectrum of the irradiated film comprising acicular structure is consistent with the proposed mechanism of exciton dissociation in the observed light-induced assembly process. The assembly process occurs through attractive Coulomb interactions between charged dots created upon exciton dissociation. Our work presents a new type of nanocrystal assembly process that is driven by light and exciton directed.