Fluorescent Ensemble Based on Bispyrene Fluorophore and Surfactant Assemblies: Sensing and Discriminating Proteins in Aqueous Solution

Fluorescent Ensemble Sensors and Arrays Based on Surfactant Aggregates Encapsulating Pyrene-Derived Fluorophores for Differentiation Applications

Surfactant assemblies have drawn great attention in fabricating fluorescent sensors as they can provide advantages such as easy preparation, low cost, aqueous detection, high fluorescence stability, high sensitivity to external stimuli, etc. We have devoted the past few years to fluorescent cross-reactive sensors and arrays that are advantageous in differentiating similar analytes and analyzing mixed samples. In this Spotlight on Applications, we introduce our recent advances in developing surfactant assembly-based fluorescent sensors and arrays for discrimination applications. Besides using surfactant assemblies encapsulating fluorophores to fabricate multiple-element-based sensor arrays, we particularly proposed to take advantage of modulation effect of dynamic surfactant assemblies on the photophysical properties of encapsulated fluorophores to construct single-system-based discriminative sensors, which have been successfully applied in differentiation of multiple metal ions and various proteins. The applications of surfactant assembly-based sensors for the detection and discrimination of thiols, amino acids, and explosives are also introduced. Finally, the prospects of further efforts for improving surfactant ensemble sensors and their challenges are discussed.

Array-Based Discriminative Optical Biosensors for Identifying Multiple Proteins in Aqueous Solution and Biofluids

Identification of proteins is an important issue both in medical research and in clinical practice as a large number of proteins are closely related to various diseases. Optical sensor arrays with recognition ability have been flourished to apply for distinguishing multiple chemically or structurally similar analytes and analyzing unknown or mixed samples. This review gives an overview of the recent development of array-based discriminative optical biosensors for recognizing proteins and their applications in real samples. Based on the number of sensor elements and the complexity of constructing array-based discriminative systems, these biosensors can be divided into three categories, which include multi-element-based sensor arrays, environment-sensitive sensor arrays and multi-wavelength-based single sensing systems. For each strategy, the construction of sensing platform and detection mechanism are particularly introduced. Meanwhile, the differences and connections between different strategies were discussed. An understanding of these aspects may help to facilitate the development of novel discriminative biosensors and expand their application prospects.

Self-assembly of imidazolium/benzimidazolium cationic receptors: their environmental and biological applications

This review highlights the applications of imidazolium based cationic receptors for sensing of biomolecules and catalysis.

Single-system based discriminative optical sensors: different strategies and versatile applications

Discriminative optical sensors with pattern recognition properties and high-throughput ability have been widely developed as they can distinguish multiple chemically similar analytes. Compared to traditional sensor arrays composed of a series of sensor elements, single-system based discriminative sensors using an array of optical changes at different wavelengths to provide input signals have drawn intensive attention recently. On the one hand, they can provide discrimination ability that is lack in using selective sensors; on the other hand, they can simplify the complex data acquisition process accompanied by multiple-element-based sensor arrays and reduce consumption of sensor samples. This tutorial review gives an overview of the development of single-system based discriminative optical sensors. Different strategies for the construction of single-system based discriminative sensors including dynamic combinatorial libraries, cross-reactive conjugated polymers, DNA G-quadruplex ensembles, combinatorial fluorescent molecular sensors, and fluorophore/surfactant aggregate ensembles are particularly introduced.

Conformational and solution dynamics of hemoglobin (Hb) in presence of a cleavable gemini surfactant: Insights from spectroscopy, atomic force microscopy, molecular docking and density functional theory

Herein, we have explored the conformational alterations of hemoglobin (Hb) in presence of a cleavable gemini surfactant (C16-C4O2-C16). The concerned surfactant was found to induce significant structural perturbations in Hb. UV-vis spectroscopy, steady-state/time-resolved fluorescence, and other utilized techniques have authenticated the complexation of Hb with the gemini surfactant. CD has demonstrated the alterations in secondary structural elements (α-helicity, β-sheet, β-turn, and random coil) of Hb upon C16-C4O2-C16 addition. Atomic force microscopy (AFM) has revealed the existence of unique star-shaped gemini surfactant microstructures aligned to Hb in a necklace pattern. The ¹H NMR peak broadening and lower delta values hint at the binding of the concerned gemini surfactant to Hb. Molecular docking and DFT calculations have further substantiated the Hb-gemini complex formation and the involvement of electrostatic/hydrophobic forces therein. In future, these results might pave-the-way to construct self-assembled, sustainable, and green surfactant-protein mixtures for their end-use in industrial, engineering, biomedical, drug delivery, gene transfection, and other relevant excipient formulations.

Surfactant Aggregates Encapsulating and Modulating: An Effective Way to Generate Selective and Discriminative Fluorescent Sensors

The heterogeneous structure and dynamic balancing nature of surfactant aggregates make them attractive in developing fluorescent sensors. They can provide a number of advantages, e.g., enhanced fluorescence stability and quantum yield, detection capability in aqueous solutions, and easy operation. Thus, various strategies have been used to construct surfactant aggregate-based fluorescent sensors. Surfactant aggregates play various roles in different strategies and realize multiple sensing behaviors. Many new functions have been discovered for surfactant aggregates in constructing fluorescent sensors. In this feature article, we briefly summarize the development of surfactant aggregate-based fluorescent sensors and their applications in three different types of sensing: selective sensing, multiple analyte sensing, and cross-reactive sensing. For each type of sensing, the design strategies and the roles of surfactant aggregates are particularly introduced. An understanding of these aspects will help to expand the applications of surfactant assemblies in the sensing field.

Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties

Alkyloxy modified 4,5,9,10-tetrasubstituted pyrenes display tunable photophysical and crystalline properties depending on the alkyl chains attached at the polyaromatic core.

Discrimination of proteins through interaction with pyrene-labelled polymer aggregates

A pyrene-labelled PDMAEMA (2-(dimethylamino)ethyl methacrylate) polymer was synthesized through a controlled radical RAFT polymerisation approach. An average pyrene content of 3.65% was determined by UV/Vis and ¹H NMR measurements. DLS measurements reveal the formation of polymer aggregates with an average size of 172 nm in aqueous phosphate buffer indicating the presence of hydrophobic interactions between pyrene and/or DMAEMA moieties of adjacent polymer chains. Furthermore, this aggregation results in the appearance of two characteristic emission bands at 394 and 488 nm analyzed by fluorescence measurements. Based on spectral changes of the so-called monomer and excimer emission intensity, the specific discrimination of various non-metallo- and metallo proteins was realized using an optical fingerprint approach. DLS and fluorescence measurements show a significant dependence of the structural characteristics of the analytes on the presence of different binding modes between the hydrophilic DMAEMA side groups of the polymer and the proteins, resulting in a molecular disassembly of the aggregates and/or fluorescence quenching. Furthermore, pH, temperature and ionic strength dependence of the sensor polymer with BSA was investigated to optimise the external parameters. Based on these results, the most specific discrimination of the analyzed proteins was obtained using a sodium chloride concentration of 50 mM and a pH of 7.0. This study gives fundamental insights into the sensing performance of a novel one-component pyrene-based polymer system and its application as a protein sensor.

A supramolecular assembly enables discrimination between metalloproteins and non-metalloproteins

A supramolecular assembly yields turn-on fluorescence response for non-metalloproteins and turn-off response for metalloproteins.

Supramolecular Dye Aggregate Assembly Enables Ratiometric Detection and Discrimination of Lysine and Arginine in Aqueous Solution

Constructing sensor systems for rapid and selective detection of small biomolecules such as amino acids is a major area of focus in bioanalytical chemistry. Considering the biological relevance of arginine and lysine, significant efforts have been directed to develop fluorescent sensors for their detection. However, these developed sensors suffer from certain disadvantages such as poor aqueous solubility, technically demanding and time-consuming synthetic protocols, and more importantly, most of them operate through single wavelength measurements, making their performance prone to small variations in experimental conditions. Herein, we report a ratiometric sensor that operates through lysine- and arginine-induced dissociation of a supramolecular assembly consisting of emissive H-aggregates of a molecular rotor dye, thioflavin-T (ThT), on the surface of a polyanionic supramolecular host, sulfated β-cyclodextrin. This disassembly brings out the modulation of monomer-aggregate equilibrium in the system which acts as an ideal scheme for the ratiometric detection of lysine and arginine in the aqueous solution. Besides facile framework of our sensor system, it employs a commercially available inexpensive probe molecule, ThT, which provides an added advantage over other sensor systems that employ synthetically demanding probe molecules. Importantly, the distinctive feature of the ratiometric detection of arginine and lysine provides an inherent advantage of increased accuracy in quantitative analysis. Interestingly, we have also demonstrated that arginine displays a multiwavelength distinctive recognition pattern which distinguishes it from lysine, using a single supramolecular ensemble. Furthermore, our sensor system also shows response in heterogeneous, biologically complex media of serum samples, thus extending its possible use in real-life applications.

Fluorescent Binary Ensemble Based on Pyrene Derivative and Sodium Dodecyl Sulfate Assemblies as a Chemical Tongue for Discriminating Metal Ions and Brand Water

Enormous effort has been put to the detection and recognition of various heavy metal ions due to their involvement in serious environmental pollution and many major diseases. The present work has developed a single fluorescent sensor ensemble that can distinguish and identify a variety of heavy metal ions. A pyrene-based fluorophore (PB) containing a metal ion receptor group was specially designed and synthesized. Anionic surfactant sodium dodecyl sulfate (SDS) assemblies can effectively adjust its fluorescence behavior. The selected binary ensemble based on PB/SDS assemblies can exhibit multiple emission bands and provide wavelength-based cross-reactive responses to a series of metal ions to realize pattern recognition ability. The combination of surfactant assembly modulation and the receptor for metal ions empowers the present sensor ensemble with strong discrimination power, which could well differentiate 13 metal ions, including Cu²⁺, Co²⁺, Ni²⁺, Cr³⁺, Hg²⁺, Fe³⁺, Zn²⁺, Cd²⁺, Al³⁺, Pb²⁺, Ca²⁺, Mg²⁺, and Ba²⁺. Moreover, this single sensing ensemble could be further applied for identifying different brands of drinking water.

Luminescence of ferrocene-modified pyrene derivatives for turn-on sensing of Cu2+ and anions

Detection and identification of metal ions by fluorescent turn-on sensors are challenging due to the quenching effect of most of the tested metal ions. In the present work, three ferrocene-modified pyrene-based probes 2-4 were synthesized to act as turn-on fluorescent sensors for Cu²⁺. The measurements of fluorescence quantum yield and fluorescence lifetime reveal that ferrocenyl unit can efficiently reduce the fluorescence emission of pyrene moiety. Steady-state fluorescence measurements find that the three ferrocene-modified fluorophores exhibit selective turn-on responses to Cu²⁺. Moreover, this turn-on effect to Cu²⁺ is highly influenced by the type of the counter ion. It is found that the presence of Cl^- or NO₃^- could realize the turn-on response to Cu²⁺, whereas, the presence of SO₄^2- or Ac^- could not induce any fluorescence enhancement to Cu²⁺. Control experiments with ferrocene-free pyrene-based probe 1 reveal that the ferrocenyl unit plays the key role in the turn-on response to Cu²⁺. The possible mechanism for the turn-on responses is attributed to the oxidation behavior of Cu²⁺ to the ferrocene unit, which is confirmed by the control experiments with sodium ascorbate. Cyclic voltammetry measurements show that Cu²⁺ can influence the redox behaviors of ferrocenyl derivatives, which is also highly dependent on the anion of the copper salts. The influence of anion on the turn-on responses to Cu²⁺ was further used for anion detection and fluorescent logic gate.

Fluorescent binary ensemble with pattern recognition ability for identifying multiple metalloproteins with applications in serum and urine

A fluorescent binary ensemble with multiple-wavelength cross-reactivity functioning as a discriminative sensor to identify different metalloproteins in serum or urine solution.

Discrimination of Metalloproteins by a Mini Sensor Array Based on Bispyrene Fluorophore/Surfactant Aggregate Ensembles

Fluorescent sensor arrays with pattern recognition ability have been widely used to detect and identify multiple chemically similar analytes. In the present work, two particular bispyrene fluorophores containing hydrophilic oligo(oxyethylene) spacer, 6 and 4, were synthesized, but one is with and the other is without cholesterol unit. Their ensembles with cationic surfactant (CTAB) assemblies realize multiple fluorescence responses to different metalloproteins, including hemoglobin, myoglobin, ferritin, cytochrome c, and alcohol dehydrogenase. The combination of fluorescence variation at monomer and excimer emission of the two binary sensor ensembles enables the mini sensor array to provide a specific fingerprint pattern to each metalloprotein. Linear discriminant analysis shows that the two-ensemble-sensor-based array could well discriminate the five tested metalloproteins. The present work realizes using a mini sensor array to accomplish discrimination of complex analytes like proteins. They also display a very high sensitivity to the tested metalloproteins with detection limits in the range of picomolar concentration.

Benzimidazolium-Based Self-Assembled Fluorescent Aggregates for Sensing and Catalytic Degradation of Diethylchlorophosphate

The unregulated use of chemical weapons has aroused researchers to develop sensors for chemical warfare agents (CWA) and likewise to abolish their harmful effects, the degradation through catalysis has great advantage. Chemically, the CWAs are versatile; however, mostly they contain organophosphates that act on inhibition of acetyl cholinesterase. In this work, we have designed and synthesized some novel benzimidazolium based fluorescent cations and their fluorescent aggregates were fabricated using anionic surfactants (SDS and SDBS) in aqueous medium. The prepared fluorescent aggregates have shown aggregation induced emission enhancement, which was further used as detection of chemical warfare agent in aqueous medium. The aggregates (Benz-2/SDBS and Benz-3/SDBS) have shown significant changes in emission profile upon interaction with diethylchlorophosphate. Contrarily, the pure dipodal receptor Benz-4 has not shown any response in emission after interaction with organophosphate, and consequently, it was concluded that benzimidazolium cation plays a decisive role in sensing. The mechanism of sensing was fully validated using ³¹P NMR spectroscopy as well as GC-MS, which highlights the transformation of diethylchlorophosphate into diethylhydrogen phosphate. The aggregates selectively interact with diethylchlorophosphate over other biological important phosphates.

Aggregation induced emission enhancement and growth of naphthalimide nanoribbons via J-aggregation: insight into disaggregation induced unfolding and detection of ferritin at the nanomolar level

A core substituted naphthalimide AIEEgen displays unusual nanoribbon growth in aqueous media with ultra-sensitivity towards non-heme protein ferritin at physiological conditions.