A novel near-infrared polymethine dye biosensor for rapid and selective detection of lithocholic acid

Lithocholic acid (LCA), a secondary bile acid, has emerged as a potential early diagnostic biomarker for various liver diseases. In this study, we introduce a novel near-infrared (NIR) polymethine dye-based biosensor, capable of sensitive and selective detection of LCA in phosphate buffer and artificial urine (AU) solutions. The detection mechanism relies on the formation of J-aggregates resulting from the interplay of 3,3-Diethylthiatricarbocyanine iodide (DiSC2(7)) dye molecules and LCA, which induces a distinctive red shift in both absorption and fluorescence spectra. The biosensor demonstrates a detection limit for LCA of 70 μM in PBS solution (pH 7.4), while in AU solution, it responds to an LCA concentration as low as ∼60 μM. Notably, the proposed biosensor exhibits outstanding selectivity for LCA, effectively distinguishing it from common interferents such as uric acid, ascorbic acid, and glucose. This rapid, straightforward, and cost-effective spectrometer-based method underscores its potential for early diagnosis of liver diseases by monitoring LCA concentrations.

Solution-based Supramolecular Hierarchical Assembly of Frenkel Excitonic Nanotubes Driven by Gold Nanoparticle Formation and Temperature

Translating nature's successful design principle of solution-based supramolecular self-assembling to broad applications─ranging from renewable energy and information technology to nanomedicine─requires a fundamental understanding of supramolecular hierarchical assembly. Though the forces behind self-assembly (e.g., hydrophobicity) are known, the specific mechanism by which monomers form the hierarchical assembly still remains an open question. A crucial step toward formulating a complete mechanism is understanding not only how the monomer's specific molecular structure but also how manifold environmental conditions impact the self-assembling process. Here, we elucidate the complex correlation between the environmental self-assembling conditions and the resulting structural properties by utilizing a well-characterized model system: well-defined supramolecular Frenkel excitonic nanotubes (NTs), self-assembled from cyanine dye molecules in aqueous solution, which further self-assemble into bundled nanotubes (b-NTs). The NTs and b-NTs inhabit distinct spectroscopic signatures, which allows the use of steady-state absorption spectroscopy to monitor the transition from NTs to b-NTs directly. Specifically, we investigate the impact of temperature (ranging from 23 °C, 55 °C, 70 °C, 85 °C, up to 100 °C) during in situ formation of gold nanoparticles to determine their role in the formation of b-NTs. The considered time regime for the self-assembling process ranges from 1 min to 8 days. With our work, we contribute to a basic understanding of how environmental conditions impact solution-based hierarchical supramolecular self-assembly in both the thermodynamic and the kinetic regime.

A Comparative Study on Cyanine Dyestuffs as Sensor Candidates for Macromolecular Crowding In Vitro and In Vivo

Pseudo isocyanine chloride (PIC) has been identified in a preceding work as a sensor suited to probe macromolecular crowding both in test tubes with solutions of synthetic crowding agents and in HeLa cells as a representative of living systems. The sensing is based on a delicate response of the self-assembly pattern of PIC towards a variation in macromolecular crowding. Based on a suitable selection of criteria established in the present study, four additional cyanine dyestuffs (TDBC, S071, S2275, and PCYN) were scrutinized for their ability to act as such a sensor, and the results were compared with the corresponding performance of PIC. UV-VIS and fluorescence spectroscopy were applied to investigate the photo-physical properties of the four candidates and, if possible, light scattering was used to characterize the self-assembly of the dyestuffs in solution. Finally, HeLa cells were exposed to solutions of the most promising candidates in order to analyze their ability to infiltrate the cells and to self-assemble therein. None of the dyestuff candidates turned out to be as similarly promising in probing crowding effects in cells as PIC turned out to be. S0271 and S2275 are at least stable enough and meet the photophysical requirements necessary to act as sensors responding to changes in macromolecular crowding.

Structurally Induced Chirality of an Achiral Chromophore on Self-Assembled Nanofibers: A Twist Makes It Chiral

The surface domains of self-assembled amphiphiles are well-organized and can perform many physical, chemical, and biological functions. Here, we present the significance of chiral surface domains of these self-assemblies in transferring chirality to achiral chromophores. These aspects are probed using l- and d-isomers of alkyl alanine amphiphiles which self-assemble in water as nanofibers, possessing a negative surface charge. When bound on these nanofibers, positively charged cyanine dyes (CY524 and CY600), each having two quinoline rings bridged by conjugated double bonds, show contrasting chiroptical features. Interestingly, CY600 displays a bisignated circular dichroic (CD) signal with mirror-image symmetry, while CY524 is CD silent. Molecular dynamics simulations reveal that the model cylindrical micelles (CM) derived from the two isomers exhibit surface chirality and the chromophores are buried as monomers in mirror-imaged pockets on their surfaces. The monomeric nature of template-bound chromophores and their binding reversibility are established by concentration- and temperature-dependent spectroscopies and calorimetry. On the CM, CY524 displays two equally populated conformers with opposite sense, whereas CY600 is present as two pairs of twisted conformers in each of which one is in excess, due to differences in weak dye-amphiphile hydrogen bonding interactions. Infrared and NMR spectroscopies support these findings. Reduction of electronic conjugation caused by the twist establishes the two quinoline rings as independent entities. On-resonance coupling between the transition dipoles of these units generates bisignated CD signals with mirror-image symmetry. The results presented herein provide insight on the little-known structurally induced chirality of achiral chromophores through transfer of chiral surface information.

Perspectives on weak interactions in complex materials at different length scales

Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties.

Multiple aggregates from multiple polymorphs: structural and mechanistic insight into organic dye aggregates

This case study provides evidence for the appearance of multiple aggregation forms of a single organic dye, arising from its packing polymorphs in the solid state. Each aggregate can be spectroscopically matched to one polymorph, acquiring nanoscopic structural information even in the absence of conventional H- or J-type aggregation spectral features. The conversion from one polymorphic aggregate to another supports the action of Ostwald's rule of stages in organic aggregates suspended in solution. Mechanistically, dye molecules from one aggregate dissociate then renucleate the more stable aggregate form, the first demonstration for an aggregation-induced emission-active organic dye.

Atomistic simulation studies of ionic cyanine dyes: self-assembly and aggregate formation in aqueous solution

Cyanine dyes are known to form large-scale aggregates of various morphologies via spontaneous self-assembly in aqueous solution, akin to chromonic liquid crystals. Atomistic molecular dynamics simulations have been performed on four cyanine dyes: pseudoisocyanine chloride (PIC), pinacyanol chloride (PCYN), 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine chloride (TTBC) and 1,1'-disulfopropyl-3,3'-diethyl-5,5',6,6'-tetrachloro-benzimidazolylcarbocyanine sodium salt (BIC). Simulations employed an optimised general AMBER force field and demonstrate the organisation of the dyes into stacked structures at dilute concentrations. The thermodynamics of self-assembly was studied by calculating potentials of mean force for n-mers (n = 2, 3 or 4), from which the free energies of association are determined. We report binding free energies in the range of 8 to 15k_BT for dimerisation, concordant with typical values for ionic chromonics (7 to 14k_BT), and examine the enthalpic and entropic contributions to the aggregation process. The self-assembly of these dyes yields two distinct classes of structures. We observe the formation of H-aggregate stacks for PCYN, with further complexity in these assemblies for PIC; where the aggregates contain shift and Y junction defects. TTBC and BIC associate into a J-aggregate sheet structure of unimolecular thickness, and is composed of a brickwork arrangement between molecules. These sheet structures are characteristic of the smectic chromonic mesophase, and such assemblies provide a route to the emergence of nanoscale tubular architectures.

Concurrent formation of H- and J-aggregates of dyes with chiralities individually determined by G-quadruplex handedness

DNA templated dye assemblies pave an easy way to regulate the optical properties of molecular aggregates. G-quadruplexes (G4s) provide versatile DNA platforms for the dye assemblies since their foldings can be easily tuned by cation ions and sequences. In this work, we found that the G4 handedness can be used to control the aggregate chirality of a dye of 3,3'-diethylthiacarbocyanine (DiSC₂(3)). The left-handed and right-handed G4s can template the concurrent formation of the J- and H-aggregates of DiSC₂(3) with emergence of the featured absorption spectra. However, the chiral J-aggregate of DiSC₂(3) can be formed only on the left-handed G4s, while the chiral H-aggregate is otherwise grown only on the right-handed G4s, as confirmed by the induced circular dichroism (ICD) spectra with the characteristic splitting bands. Additionally, these G4s even at tens of nM level are efficient to produce these chiral aggregates, demonstrating the high sensitivity of G4s in creating these optically active dye assemblies. The possible growth sites of the aggregates are proposed by the sequence length-dependent assemblies. Our work will provide a new way to control the chiral assemblies of dye aggregates via the G4 handedness.

Plexcitons: The Role of Oscillator Strengths and Spectral Widths in Determining Strong Coupling

Strong coupling interactions between plasmon and exciton-based excitations have been proposed to be useful in the design of optoelectronic systems. However, the role of various optical parameters dictating the plasmon-exciton (plexciton) interactions is less understood. Herein, we propose an inequality for achieving strong coupling between plasmons and excitons through appropriate variation of their oscillator strengths and spectral widths. These aspects are found to be consistent with experiments on two sets of free-standing plexcitonic systems obtained by (i) linking fluorescein isothiocyanate on Ag nanoparticles of varying sizes through silane coupling and (ii) electrostatic binding of cyanine dyes on polystyrenesulfonate-coated Au nanorods of varying aspect ratios. Being covalently linked on Ag nanoparticles, fluorescein isothiocyanate remains in monomeric state, and its high oscillator strength and narrow spectral width enable us to approach the strong coupling limit. In contrast, in the presence of polystyrenesulfonate, monomeric forms of cyanine dyes exist in equilibrium with their aggregates: Coupling is not observed for monomers and H-aggregates whose optical parameters are unfavorable. The large aggregation number, narrow spectral width, and extremely high oscillator strength of J-aggregates of cyanines permit effective delocalization of excitons along the linear assembly of chromophores, which in turn leads to efficient coupling with the plasmons. Further, the results obtained from experiments and theoretical models are jointly employed to describe the plexcitonic states, estimate the coupling strengths, and rationalize the dispersion curves. The experimental results and the theoretical analysis presented here portray a way forward to the rational design of plexcitonic systems attaining the strong coupling limits.

Tubular J-aggregates of a new thiacarbocyanine Cy5 dye for the far-red spectral region – a spectroscopic and cryo-transmission electron microscopy study

A new phenol-substituted Cy5 dye forms tubular J-aggregates that are active in the far-red spectral region.

Molecular Origin and Self-Assembly of Fluorescent Carbon Nanodots in Polar Solvents

Despite numerous efforts, there are several fundamental ambiguities regarding the photoluminescence of carbon dots (CDs). Spectral shift measurements display characteristic of both π-π* and n-π* transitions for the main absorption or excitation band at ∼350 nm, contrary to common assignment of exclusive n-π* transition. Additionally, the generally perceived core-state transition at ∼250 nm, involving sp²-networked carbogenic domains shielded from external environments, needs to be reassessed because it fails to explain the observed fluorescence quenching and spectral shift. These results have been explained based on the molecular origin of PL in CDs invoking the similarity between CD and citrazinic acid. Fluorescent derivatives of the latter are recognized to be produced during citric-acid-based CD synthesis. Concentration-dependent spectral splitting of the main excitation band in combination with the temperature-dependent PL results has been envisioned assuming self-assembly of CDs into various H-aggregates.

Amplified Fluorescence from Polyfluorene Nanoparticles with Dual State Emission and Aggregation Caused Red Shifted Emission for Live Cell Imaging and Cancer Theranostics

A newly synthesized polyfluorene derivative with pendant di(2-picolyl)amine (PF-DPA) shows dual state emission and aggregation caused red shifted emission that was utilized for cell imaging and cancer theranostics. PF-DPA was nontoxic to normal cells but showed cytotoxicity against cancer cells, suggesting its utility for cancer therapy. PF-DPA exhibits a large and unique red shifted emission at 556 nm at higher water ratio of THF:H₂O (10:90) due to the formation of polymer nanoparticles or PDots spontaneously by intra- and intermolecular self-assembly induced aggregation. Dual state emission and aggregation caused red shifted emission (>100 nm) in PF-DPA homopolymer nanoparticles is very unique and attributed to the combined effect of intramolecular planarization and J-type aggregate formation in the PDots (25 ± 5 nm). The PF-DPA PDots exhibit bright green and orange fluorescence with exceptional live cell imaging properties and potential applications in cancer theranostics due to their selective cytotoxic nature toward cancer cells.

Association behaviors of carbazole-labeled polyacrylamide in water studied by fluorescence spectroscopy

Spectroscopic signatures in aggregation process of carbazole-labeled copolymers in water.

Two-photon absorption of polyfluorene aggregates stabilized by insulin amyloid fibrils

We report on the photophysical and optical properties of a polyfluorene derivative (PFO) and its binding to the amyloid-forming protein insulin.

Co-intercalation of Acid Red 337 and a UV absorbent into layered double hydroxides: enhancement of photostability

Organic-inorganic hybrid pigments with enhanced thermo- and photostability have been prepared by co-intercalating C.I. Acid Red 337 (AR337) and a UV absorbent (BP-4) into the interlayer of ZnAl layered double hydroxides through a coprecipitation method. The obtained compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric-differential thermogravimetric-differential thermal analysis, UV-visible spectroscopy, and the International Commission on Illumination (CIE) 1976 L*a*b* color scales. The results show the successful co-intercalation of AR337 and BP-4 into the interlayer region of layered double hydroxides (LDHs) and reveal the presence of host-guest interactions between LDH host layers and guest anions of AR337 and BP-4 and guest-guest interactions between AR337 and BP-4. The intercalation can improve the thermostability of AR337 due to the protection of LDH layers. Moreover, the co-intercalation of AR337 and BP-4 not only markedly enhances the photostability of AR337 but also significantly influences the color of the hybrid pigment.

Cooperativity of the assembly process in a low concentration chromonic liquid crystal

IR-806 is a near-infrared cyanine dye that undergoes a two-step assembly process in aqueous solutions. The final assemblies orientationally order into a liquid crystal at a very low concentration (∼0.6 wt % at room temperature). While the first step of the assembly process is continuous as the dye concentration or temperature is varied (isodesmic), the second step is more abrupt (cooperative). Because the absorption spectrum of IR-806 changes dramatically during the assembly process, careful equilibrium and kinetic absorption experiments are utilized to examine the details of the cooperative second step. These experiments involve changes in both concentration and temperature, allowing a close thermodynamic analysis of the assembly process. Both equilibrium and kinetic investigations reveal that the assembly process is highly cooperative and can be described by multiple models (for example, nucleation and growth) in the highly cooperative limit. The enthalpy associated with the growth process and the activation energy of the rate-limiting step during disassembly are determined. These findings have significant implications for the structure of the assemblies that form the liquid crystal phase in IR-806.