Sequential and cellular detection of copper and lactic acid by disaggregation and reaggregation of the fluorescent panchromatic fibres of an acylthiourea based sensor

Advancements in molecular disassembly of optical probes: a paradigm shift in sensing, bioimaging, and therapeutics

The majority of self-assembled fluorescent dyes suffer from aggregation-caused quenching (ACQ), which detrimentally affects their diagnostic and therapeutic effectiveness. While aggregation-induced emission (AIE) active dyes offer a promising solution to overcome this limitation, they may face significant challenges as the intracellular environment often prevents aggregation, leading to disassembly and posing challenges for AIE fluorogens. Recent progress in signal amplification through the disassembly of ACQ dyes has opened new avenues for creating ultrasensitive optical sensors and enhancing phototherapeutic outcomes. These advances are well-aligned with cutting-edge technologies such as single-molecule microscopy and targeted molecular therapies. This work explores the concept of disaggregation-induced emission (DIE), showcasing the revolutionary capabilities of DIE-based dyes from their design to their application in sensing, bioimaging, disease monitoring, and treatment in both cellular and animal models. Our objective is to provide an in-depth comparison of aggregation versus disaggregation mechanisms, aiming to stimulate further advancements in the design and utilization of ACQ fluorescent dyes through DIE technology. This initiative is poised to catalyze scientific progress across a broad spectrum of disciplines.

The Fluorescent Detection of Glucose and Lactic Acid Based on Fluorescent Iron Nanoclusters

In this paper, a novel fluorescent detection method for glucose and lactic acid was developed based on fluorescent iron nanoclusters (Fe NCs). The Fe NCs prepared using hemin as the main raw material exhibited excellent water solubility, bright red fluorescence, and super sensitive response to hydrogen peroxide (H2O2). This paper demonstrates that Fe NCs exhibit excellent peroxide-like activity, catalyzing H2O2 to produce hydroxyl radicals (•OH) that can quench the red fluorescence of Fe NCs. In this paper, a new type of glucose sensor was established by combining Fe NCs with glucose oxidase (GluOx). With the increase in glucose content, the fluorescence of Fe NCs decreases correspondingly, and the glucose content can be detected in the scope of 0-200 μmol·L-1 (μM). Similarly, the lactic acid sensor can also be established by combining Fe NCs with lactate oxidase (LacOx). With the increase in lactic acid concentration, the fluorescence of Fe NCs decreases correspondingly, and the lactic acid content can be detected in the range of 0-100 μM. Furthermore, Fe NCs were used in the preparation of gel test strip, which can be used to detect H2O2, glucose and lactic acid successfully by the changes of fluorescent intensity.

Critical Assessment of Micellar Surface Charge-Dependent Disaggregation and Reaggregation of a Bis-Indole Self-Aggregate: What Should Be Our Case-Dependent Choice?

"Aggregation-caused quenching" is a deep-seated mechanism and has been widely used by the researchers as the possible basis for new sensor development. Contrast to aggregation, its turn around process, disaggregation, has gained much less consideration so far. Unfortunately, study of the further scope for reaggregation of the disaggregated probe assembly in the same solution, as and when required, is still under the rare category. The central theme of the current study is focused on this aspect. For this purpose, the effects of headgroup charge (cationic, anionic, and nonionic) and polarity of the micelles on the degree of disaggregation and subsequent emission amelioration of a synthesized bis-indole derivative, 3,3'-bisindolyl(phenyl)methane (BIPM), are studied using steady-state and time-resolved spectroscopic techniques. The relative emission yield of BIPM (φf = 0.01) is significantly enhanced in the presence of cetyltrimethylammonium bromide (φf = 0.21) and polyoxyethylene (20) sorbitan monolaurate (φf = 0.24), whereas comparatively less emission enhancement is recorded within the sodium dodecyl sulfate system (φf = 0.07). In contrast, addition of an external biophilic agent, uric acid, causes requenching of the enhanced emission because of the reaggregation of the disaggregated probes. Detailed microscopic and calorimetric studies are also adopted to investigate the disaggregation-reaggregation mechanism of BIPM associations. The study will provide prior insights about the use of suitable micellar systems for the required degree of disaggregation as well as for the modulation of emission efficiency by controlled tuning of the disaggregation-reaggregation equilibrium for similar probe associations in pure aqueous medium avoiding any chemical transformation.

Amyloidogenic Propensity of Metabolites in the Uric Acid Pathway and Urea Cycle Critically Impacts the Etiology of Metabolic Disorders

Novel insights into the etiology of metabolic disorders have recently been uncovered through the study of metabolite amyloids. In particular, inborn errors of metabolism (IEMs), including gout, Lesch-Nyhan syndrome (LNS), xanthinuria, citrullinemia, and hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, are attributed to the dysfunction of the urea cycle and uric acid pathway. In this study, we endeavored to understand and mechanistically characterize the aggregative property exhibited by the principal metabolites of the urea cycle and uric acid pathway, specifically hypoxanthine, xanthine, citrulline, and ornithine. Employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), we studied the aggregation profiles of the metabolites. Insights obtained through molecular dynamics (MD) simulation underscore the vital roles of π-π stacking and hydrogen bonding interactions in the self-assembly process, and thioflavin T (ThT) assays further corroborate the amyloid nature of these metabolites. The in vitro MTT assay revealed the cytotoxic trait of these assemblies, a finding that was substantiated by in vivo assays employing the Caenorhabditis elegans (C. elegans) model, which revealed that the toxic effects were more pronounced and dose-specific in the case of metabolites that had aged via longer preincubation. We hence report a compelling phenomenon wherein these metabolites not only aggregate but transform into a soft, ordered assembly over time, eventually crystallizing upon extended incubation, leading to pathological implications. Our study suggests that the amyloidogenic nature of the involved metabolites could be a common etiological link in IEMs, potentially providing a unified perspective to study their pathophysiology, thus offering exciting insights into the development of targeted interventions for these metabolic disorders.

Triphenylamine-Functionalized Coordination Cage as a Supramolecular Fluorescence Sensor for Sequential Detection of Aluminum Ions and Nitrofurantoin

Coordination cages with a well-defined nanocavity are a class of promising supramolecular materials for molecular recognition and sensing. However, their applications in sequential sensing of multiple types of pollutants are highly desirable yet extremely limiting and challenging. Herein, we demonstrate a convenient strategy to develop a supramolecular fluorescence sensor for sequentially detecting environmental pollutants of aluminum ions and nitrofurantoin. A coordination cage (Ni-NTB), adopting an octahedral structure with triphenylamine chromophores occupying on the faces, is weakly emissive in solution due to the intramolecular rotations of the phenyl rings. Ni-NTB exhibits sensitive and selective fluorescence "off-on-off" processes during consecutive sensing of Al³⁺ and nitrofurantoin, an antibacterial drug. These sequential detection processes are highly interference-tolerant and visually observable with the naked eye. Mechanism studies reveal that the fluorescence switch is controllable by tuning the degree of intramolecular rotations of the phenyl rings and the pathway of intermolecular charge transfer, which is associated with the host-guest interaction. Moreover, the fabrication of Ni-NTB on test strips enabled a quick naked-eye sequential sensing of Al³⁺ and nitrofurantoin in seconds. Hence, this novel supramolecular fluorescence "off-on-off" sensing platform provides a new approach to developing supramolecular functional materials for monitoring environmental pollution.

Glucose-induced self-assembly and phase separation in hydrophilic triblock copolymers and the governing mechanism

Poly(ethylene oxide, EO)-poly(propylene oxide, PO)-poly(ethylene oxide, EO)-based triblock copolymers (BCPs) with 80% hydrophilicity stay molecularly dissolved as Gaussian chains at ambient temperature, even at fairly high concentrations (>5 %w/v). This study presents the plausible micellization behaviour of such very-hydrophilic Pluronics® - F38, F68, F88, F98, and F108 - incited upon the addition of glucose at low concentrations and temperatures. The outcomes obtained from phase behaviour and scattering studies are described. At temperatures near to ambient temperature, these BCPs form micelles with a central core made of a PO block, surrounded by a corona of highly hydrated EO chains. The phase transitions in these hydrophilic Pluronics® in the presence of glucose are demonstrated via the dehydration of the copolymer coil, leading to a decrease in the I₁/I₃ ratio, as determined using fluorescence spectroscopy. The temperature-dependent cloud point (CP) showed a marked decrease with an increase in the PO molecular weight and also in the presence of glucose. The change in solution relative viscosity (η_rel) caused by glucose is due to the enhanced dehydration of the EO block of the BCP amphiphile. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) investigations suggested that the dimensions of the hydrophobic core increase during the dehydration of the EO-PO blocks upon a temperature increase or after adding varying concentrations of glucose, thereby resulting in a micellar shape transition. It has been observed that added glucose influences the phase behaviour of BCPs in an analogous way to the influence of temperature. Also, plausible interactions between the EO-PO blocks and glucose were suggested based on the evaluated optimized descriptors obtained from a computational simulation approach. In addition, the core-shell blended micelles obtained using these BCPs are successfully utilized for drug (curcumin, Cur) solubilization based on the observed peak intensities from UV-visible spectroscopy. The loading of Cur into glucose-containing and glucose-free hydrophilic Pluronic® micelles shows how the radius of the micellar core (R_c) increases in the presence of glucose, thereby indicating Cur solubility enhancement for the Pluronic® micelles. Various kinetics models were employed, demonstrating a drug release profile that enables this approach to be used as an ideal platform for drug delivery.

A new aggregation induced emission enhancement (AIEE) dye which self-assembles to panchromatic fluorescent flowers and has application in sensing dichromate ions

We report for the very first time the crystal structure and self-assembly of a new aggregation-induced emission enhancement (AIEE) dye 4-(5-methoxythiazolo[4,5-b]pyridin-2-yl)-N,N-dimethylaniline (TPA) and its application in sensing dichromate ions. TPA reveals cyan blue emission under UV and visible light. The self-assembly properties of TPA were studied extensively by scanning electron microscopy (SEM) which revealed the formation of beautiful flower-like morphologies. These structures revealed both green and red fluorescence under FITC and rhodamine filters respectively when observed through fluorescence microscopy connoting the panchromatic emission properties of TPA from blue to red. The interactions which cause self-assembled structure formation in TPA were also validated theoretically using density functional theory (DFT) calculations. Crystal and molecular structure analysis of TPA was carried out via single-crystal X-ray diffraction to visualize the intermolecular interactions occurring in the solid-state and to study the structure-photophysical property relationship in the aggregated state. The photophysical properties of TPA were also studied extensively by UV-visible and fluorescence spectroscopy and its quantum yield and fluorescence lifetime were calculated by time-correlated single-photon counting (TCSPC). Interestingly, TPA could efficiently sense dichromate (Cr₂O₇^2-) ions in an acidic medium and an interesting morphological transition from a fluorescent flower to non-fluorescent disassembled structures could also be observed. The limit of detection of TPA for Cr₂O₇^2- ions was found to be as low as 5.5 nM, suggesting its exceptional sensitivity. More importantly, TPA could selectively sense Cr₂O₇^2- ions in real water samples even in the presence of other metal ions routinely present in polluted water, hence making it practically useful for water quality monitoring.

Controlled aggregation properties of single amino acids modified with protecting groups

The self-assembling properties of single amino acids modified with protecting groups under controlled conditions of temperature and concentration are illustrated.

Unusual Aggregates Formed by the Self-Assembly of Proline, Hydroxyproline, and Lysine

There is a plethora of significant research that illustrates toxic self-assemblies formed by the aggregation of single amino acids, such as phenylalanine, tyrosine, tryptophan, cysteine, and methionine, and their implication on the etiology of inborn errors of metabolisms (IEMs), such as phenylketonuria, tyrosinemia, hypertryptophanemia, cystinuria, and hypermethioninemia, respectively. Hence, studying the aggregation behavior of single amino acids is very crucial from the chemical neuroscience perspective to understanding the common etiology between single amino acid metabolite disorders and amyloid diseases like Alzheimer's and Parkinson's. Herein we report the aggregation properties of nonaromatic single amino acids l-proline (Pro), l-hydroxyproline (Hyp), and l-lysine hydrochloride (Lys). The morphologies of the self-assembled structures formed by Pro, Hyp, and Lys were extensively studied by various microscopic techniques, and controlled morphological transitions were observed under varied concentrations and aging times. The mechanism of structure formation was deciphered by concentration-dependent ¹H NMR analysis, which revealed the crucial role of hydrogen bonding and hydrophobic interactions in the structure formation of Pro, Hyp, and Lys. MTT assays on neural (SHSY5Y) cell lines revealed that aggregates formed by Pro, Hyp, and Lys reduced cell viability in a dose-dependent manner. These results may have important implications in the understanding of the patho-physiology of disorders such as hyperprolinemia, hyperhydroxyprolinemia, and hyperlysinemia since all these IEMs are associated with severe neurodegenerative symptoms, including intellectual disability, seizures, and psychiatric problems. Our future studies will endeavor to study these biomolecular assemblies in greater detail by immuno-histochemical analysis and advanced biophysical assays.

Chemical Perspective of the Mechanism of Action of Antiamyloidogenic Compounds Using a Minimalistic Peptide as a Reductionist Model

The diphenylalanine (FF) residue which is present at the 19 and 20 positions of the amyloid beta (1-42) (Aβ42) peptide sequence is considered as a reductionist model for studying Aβ42 aggregation. FF self-assembles into well-ordered tubular structures via aromatic π-π stacking. Herein the manuscript, we have presented a chemical perspective on the mechanism of action of antiamyloid compounds by assessing their interaction with FF. Therefore, we first coincubated FF fibers with single amino acids, since they are constituted of different R side chains yet have a common structural unit. This study revealed a crucial role of aromatic rings and functional groups like thiol (-SH) in causing destabilization of FF assembly via their interaction with π-electrons participating in π-π stacking present in FF. We further studied the interaction of different nonsteroidal anti-inflammatory drugs (NSAIDs), other known antiamyloidogenic compounds, and host-guest inclusion compounds like cyclodextrin (CD) to assess their mechanism of action and to decipher the functional moiety present in these compounds which could cause destabilization of π-π stacking. From the coincubation experiments, we could surmise a crucial role of aromatic rings present in these compounds for causing interference in aromatic stacking. We further consolidated our observations through microscopy analysis by various spectroscopic methods such as aggregation-induced emission enhancement (AIEE), fluorescence spectroscopy, solution-state ¹H NMR, FTIR, and circular dichroism. The studies presented in the manuscript thus provide significant insights into the role of functional groups in imparting antiamyloid action and open new avenues for an efficient design of antiamyloid drugs in the future.

Self-assembly of a benzothiazolone conjugate into panchromatic fluorescent fibres and their application in cellular imaging

We report self assembly of a benzothiazolone conjugate (CBT) into fluorescent panchromatic fibres and their application as a panchromatic dye in bioimaging.