Amplified fluorescence sensing of protease activity with conjugated polyelectrolytes

The multifaceted role of proteases and modern analytical methods for investigation of their catalytic activity

We discuss the diverse functions of proteases in the context of their biotechnological and medical significance, as well as analytical approaches used to determine the functional activity of these enzymes. An insight into modern approaches to studying the kinetics and specificity of proteases, based on spectral (absorption, fluorescence), mass spectrometric, immunological, calorimetric, and electrochemical methods of analysis is given. We also examine in detail electrochemical systems for determining the activity and specificity of proteases. Particular attention is given to exploring innovative electrochemical systems based on the detection of the electrochemical oxidation signal of amino acid residues, thereby eliminating the need for extra redox labels in the process of peptide synthesis. In the review, we highlight the main prospects for the further development of electrochemical systems for the study of biotechnologically and medically significant proteases, which will enable the miniaturization of the analytical process for determining the catalytic activity of these enzymes.

Literature Review on Conjugated Polymers as Light-Sensitive Materials for Photovoltaic and Light-Emitting Devices in Photonic Biomaterial Applications

Due to their extended p-orbital delocalization, conjugated polymers absorb light in the range of visible-NIR frequencies. We attempt to exploit this property to create materials that compete with inorganic semiconductors in photovoltaic and light-emitting materials. Beyond competing for applications in photonic devices, organic conjugated compounds, polymers, and small molecules have also been extended to biomedical applications like phototherapy and biodetection. Recent research on conjugated polymers has focused on bioapplications based on the absorbed light energy conversions in electric impulses, chemical energy, heat, and light emission. In this review, we describe the working principles of those photonic devices that have been applied and researched in the field of biomaterials.

A Perspective Looking Backward and Forward on the 25th Anniversary of Conjugated Polyelectrolytes

Conjugated polyelectrolytes are π-conjugated polymers that contain ionic charged groups such as sulfonate (R-SO3-), carboxylate (R-COO-), or ammonium (R-NR3+) combined with a π-conjugated backbone. This perspective provides a summary review of the key developments in the field, starting from the first reports of their synthesis and properties to application-focused developments. The applications include optical sensors for molecular and biomolecular targets, organic electronic applications, and specific biological applications including cellular imaging and photodynamic therapy. This perspective concludes with a discussion of where the field of conjugated polyelectrolytes is expected to lead in the coming years.

Induced Self-Assembly and Disassembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complexes with Charge Reversal Properties: "Proof-of-Principle" Demonstration of Ratiometric Förster Resonance Energy Transfer Sensing of pH

A series of pH-responsive alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complexes with charge-reversal properties was synthesized, and the supramolecular assemblies between conjugated polyelectrolyte, PFP-OSO₃^-, and [Pt{bzimpy(TEG)₂}{C≡C-C₆H₃-(COOH)₂-3,5}]Cl (1) have been studied using UV-vis absorption, emission, and resonance light scattering (RLS) spectroscopy. An efficient Förster resonance energy transfer (FRET) from PFP-OSO₃^- donor to the aggregated 1 as acceptor with the aid of Pt(II)···Pt(II) interactions has been presented, which leads to a growth of triplet metal-metal-to-ligand charge transfer (³MMLCT) emission in the low-energy red region. The two-component PFP-OSO₃^--1 ensemble was then exploited as a "proof-of-principle" concept strategy for pH sensing by tracking the ratiometric emission changes. With the aid of judicious molecular design on the pH-driven charge-reversal property, the polyelectrolyte-induced self-assembly and the FRET from PFP-OSO₃^- to the platinum(II) aggregates have been modulated. Together with its excellent reversibility and photostability, the extra stability provided by the Pt(II)···Pt(II) and π-π stacking interactions on top of the electrostatic and hydrophobic interactions existing in polyelectrolye-complex assemblies has led to a selective and sensitive pH sensing assay.

Recent Advances in Conjugated Polymer-Based Biosensors for Virus Detection

Nowadays, virus pandemics have become a major burden seriously affecting human health and social and economic development. Thus, the design and fabrication of effective and low-cost techniques for early and accurate virus detection have been given priority for prevention and control of such pandemics. Biosensors and bioelectronic devices have been demonstrated as promising technology to resolve the major drawbacks and problems of the current detection methods. Discovering and applying advanced materials have offered opportunities to develop and commercialize biosensor devices for effectively controlling pandemics. Along with various well-known materials such as gold and silver nanoparticles, carbon-based materials, metal oxide-based materials, and graphene, conjugated polymer (CPs) have become one of the most promising candidates for preparation and construction of excellent biosensors with high sensitivity and specificity to different virus analytes owing to their unique π orbital structure and chain conformation alterations, solution processability, and flexibility. Therefore, CP-based biosensors have been regarded as innovative technologies attracting great interest from the community for early diagnosis of COVID-19 as well as other virus pandemics. For providing precious scientific evidence of CP-based biosensor technologies in virus detection, this review aims to give a critical overview of the recent research related to use of CPs in fabrication of virus biosensors. We emphasize structures and interesting characteristics of different CPs and discuss the state-of-the-art applications of CP-based biosensors as well. In addition, different types of biosensors such as optical biosensors, organic thin film transistors (OTFT), and conjugated polymer hydrogels (CPHs) based on CPs are also summarized and presented.

Simple Nano-Luciferase-Based Assay for the Rapid and High-Throughput Detection of SARS-CoV-2 3C-Like Protease

In this study, we described an easy-to-perform nano-luciferase (nLuc) sensor for the rapid detection of 3-chymotrypsin-like protease (3CLpro) encoded by SARS-CoV-2. The technology is based on the cleavage reaction of recombinant-nLuc via 3CLpro. The nLuc-based assay is a general, one-step method and is naturally specific in detection. The stability, sensitivity, detection range, and response time are fully characterized. The application of 3CLpro detection in artificial and human saliva as well as antiviral drug screening demonstrates that the method can quantify 3CLpro with high sensitivity in one step. With its unique features, the nLuc-based assay may find broad applications in the auxiliary diagnosis of SARS-CoV-2, as well as other types of coronavirus infection.

A Novel Fluorescent Probe for the Detection of Cyanide Ions in Solutions and Studies on Its Biophysical Interactions with ctDNA and Proteases

A new cationic indolium based styryl dye (Ci) as a fluorescent probe was synthesized and its anions selectivity/sensitivity properties/molecular interactions with protease enzymes (pepsin/trypsin) and ctDNA has been studied by spectroscopic and computational methods. The fluorescence measurements at different temperatures indicated that quenching mechanism of enzymes by Ci was static. ΔH and ΔS data pointed out electrostatic/hydrophobic interactions with pepsin, and also hydrogen bonds/van der Waals forces with trypsin of Ci. According to Förster's non-radiative energy transfer, binding distances (r) were calculated as 3.53/3.27 nm for pepsin/trypsin. It was also investigated that groove binding is effective in interaction with ctDNA. The results were supported with molecular docking analyzes which have same tendency. Ci has been demonstrated hypsochromic effect with a decrease in polarity of solvents and it showed highly selective colorimetric and fluorometric sensing behavior for cyanide in organic solvent and in aqueous solution. ¹H NMR titration was performed to examine the interaction mechanism between Ci and cyanide. The LOD values of cyanide ion were reported as 4.87 × 10^-9 M and 9.70 × 10^-7 M in DMSO and DMSO/H₂O binary mixture, respectively. In addition, sensitivity of Ci as a chemosensor to cyanide was investigated in bitter almond samples.

Semiconducting Polymers for Neural Applications

Electronically interfacing with the nervous system for the purposes of health diagnostics and therapy, sports performance monitoring, or device control has been a subject of intense academic and industrial research for decades. This trend has only increased in recent years, with numerous high-profile research initiatives and commercial endeavors. An important research theme has emerged as a result, which is the incorporation of semiconducting polymers in various devices that communicate with the nervous system—from wearable brain-monitoring caps to penetrating implantable microelectrodes. This has been driven by the potential of this broad class of materials to improve the electrical and mechanical properties of the tissue–device interface, along with possibilities for increased biocompatibility. In this review we first begin with a tutorial on neural interfacing, by reviewing the basics of nervous system function, device physics, and neuroelectrophysiological techniques and their demands, and finally we give a brief perspective on how material improvements can address current deficiencies in this system. The second part is a detailed review of past work on semiconducting polymers, covering electrical properties, structure, synthesis, and processing.

A Portrait of the OPE as a Biological Agent

Oligophenylene ethynylenes, known as OPEs, are a sequence of aromatic rings linked by triple bonds, the properties of which can be modulated by varying the length of the rigid main chain or/and the nature and position of the substituents on the aromatic units. They are luminescent molecules with high quantum yields and can be designed to enter a cell and act as antimicrobial and antiviral compounds, as biocompatible fluorescent probes directed towards target organelles in living cells, as labelling agents, as selective sensors for the detection of fibrillar and prefibrillar amyloid in the proteic field and in a fluorescence turn-on system for the detection of saccharides, as photosensitizers in photodynamic therapy (due to their capacity to highly induce toxicity after light activation), and as drug delivery systems. The antibacterial properties of OPEs have been the most studied against very popular and resistant pathogens, and in this paper the achievements of these studies are reviewed, together with almost all the other roles held by such oligomers. In the recent decade, their antifungal and antiviral effects have attracted the attention of researchers who believe OPEs to be possible biocides of the future. The review describes, for instance, the preliminary results obtained with OPEs against severe acute respiratory syndrome coronavirus 2, the virus responsible for the COVID-19 pandemic.

Biological Sensing and Imaging Using Conjugated Polymers and Peptide Substrates

Peptides have been widely applied as targeting elements or enzyme-substrates in biological sensing and imaging. Conjugated Polymers (CPs) have emerged as a novel biosensing material and received considerable attention due to their excellent light absorption, strong fluorescence emission, as well as amplified quenching properties. In this review, we summarize the recent advances of using CPs and peptide substrates in biosensing and bioimaging. After a brief introduction of the advantages of CPs and peptide substrates, different sensing designs and mechanisms are discussed based on peptides' structures and functions, including targeting recognition elements, enzyme-substrates, and cell-penetrating elements. Applications of CPs and peptides in fluorescent imaging and Raman imaging in living cells are subsequently reviewed.

Different Surface Interactions between Fluorescent Conjugated Polymers and Biological Targets

Fluorescent conjugated polymers (CPs) have attracted considerable interest in biosensing owing to their high fluorescence, tunable bandgap, and good biocompatibility. Aiming at acquiring the desired optical responses of CPs for bioapplications, it is essential that the CPs bind to biological targets with high efficacy and affinity. However, the efficient binding of CPs is largely driven by their effective interaction with target surfaces. In this Review, we will focus on the different surface interactions that pervade between CPs and biological targets. The multiple surface interactions can lead to changes in spatial conformation and distribution of CPs, which manifest alterable optical properties of CPs based on accumulation of target-directed CPs, Förster resonance energy transfer mechanism, and metal-enhanced fluorescence mechanism. Then, we display diverse bioapplications applying CPs-based surface interactions, such as cell imaging, imaging-guided detection, and photodynamic therapy. Finally, the challenges and future developments to control the efficient attachment of CPs to biological targets are discussed. We expect that the understanding of surface interactions between CPs and biological targets benefits the CPs-based system design and expands their applications in biological detections and therapies.

Novel Method for the Quantitative Analysis of Protease Activity: The Casein Plate Method and Its Applications

No simple methods are used for the quantitative analysis of the protease activity in colored food up till now. Thus, this study aims to establish a new and simple method for the quantitative detection of protease activity, especially in colored food. The detection accuracy, detection limit, and repeatability of the casein plate method were analyzed. Then, the application of the casein plate method in sample detection and recovery was further evaluated. The results showed that the casein plate method for the quantitative detection of protease activity has high accuracy, high precision, and low detection limit. The recoveries of eight kinds of colored samples were in the range of 92.26-97.84%, and the relative standard deviation (RSD) was in the range of 3.56-10.88%. The results of the casein plate method exhibited high accuracy. This indicated that the method was suitable for the detection of colored samples. The casein plate method for the quantitative detection of protease activity is simple. The newly constructed casein plate method has broad potential application value in food industry, especially for the detection of dark food.

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu2+ , and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through "intra"- and "inter"-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.

Exploring the potential of a urea derivative: an AIE-luminogen and its interaction with human serum albumin in aqueous medium

A simple AIE active urea molecule (L1) can selectively interact with HSAviaturn-on fluorescence response in aqueous medium.

Peptide-based nanoprobes for molecular imaging and disease diagnostics

Pathological changes in a diseased site are often accompanied by abnormal activities of various biomolecules in and around the involved cells. Identifying the location and expression levels of these biomolecules could enable early-stage diagnosis of the related disease, the design of an appropriate treatment strategy, and the accurate assessment of the treatment outcomes. Over the past two decades, a great diversity of peptide-based nanoprobes (PBNs) have been developed, aiming to improve the in vitro and in vivo performances of water-soluble molecular probes through engineering of their primary chemical structures as well as the physicochemical properties of their resultant assemblies. In this review, we introduce strategies and approaches adopted for the identification of functional peptides in the context of molecular imaging and disease diagnostics, and then focus our discussion on the design and construction of PBNs capable of navigating through physiological barriers for targeted delivery and improved specificity and sensitivity in recognizing target biomolecules. We highlight the biological and structural roles that low-molecular-weight peptides play in PBN design and provide our perspectives on the future development of PBNs for clinical translation.

Molecular Wire Effects in Phenyleneethynylene Oligomers: Surprising Insights

The synthesis and quenching behavior of a series of water-soluble, carboxylate-carrying phenyleneethynylene oligomers-monomer to tetramer-and their polymers are reported; their quenching behavior with different test analytes (paraquat, lead salts, mercury salts, picric acid, methylpyridinium iodide) in water were investigated, and the results were compared to that of the conjugated polymer. Significant but analyte-dependent enhancement effects were found. For monovalent quenchers, only the molecular wire effect applies, but for divalent quenchers multivalency effects are also important.

Practical Considerations Regarding the Choice of the Best High-Throughput Assay

All protein engineering studies include the stage of identifying and characterizing variants within a mutant library by employing a suitable assay or selection method. A large variety of different assay approaches for different enzymes have been developed in the last few decades, and the throughput performance of these assays vary considerably. Thus, the concept of a protein engineering study must be adapted to the available assay methods. This introductory review chapter describes different assay concepts on selected examples, including selection and screening approaches, detection of pH and cosubstrate changes, coupled enzyme assays, methods using surrogate substrates and selective derivatization. The given examples should guide and inspire the reader when choosing and developing own high-throughput screening approaches.

A Conjugated Polyelectrolyte with Pendant High Dense Short-Alkyl-Chain-Bridged Cationic Ions: Analyte-Induced Light-Up and Label-Free Fluorescent Sensing of Tumor Markers

A novel cationic water-soluble conjugated polyelectrolyte (CPE) of polyfluorene that contains 15% fraction of 2,1,3-benzothiadiazole (BT) units (PFC3NBT) has been obtained. PFC3NBT demonstrates intramolecular energy transfer from the fluorene segments to BT sites when negatively charged species (SDS or DNAs) are added, following by a shift in emission color from blue to green, has been developed. The high density of positive charges and pendent short alkyl chains of N-propyltrimethylammoniums endow PFC3NBT with high solubility and high fluorescence quantum efficiency of 33.6% in water. The fluorescence emission properties were investigated in the presence of adverse buffer solutions, different surfactants and DNA strands. Interesting fluorescence emission quenching at short wavelength and fluorescence resonance energy transfer (FRET) induced light-on at BT sites were observed and discussed in detail. Very different from previous reports, the fluorescence emission spectra transition happens with an enhancement of integrated fluorescent intensity. The analytes induced a light-up sensing system was studied with a PFC3NBT/SDS complex mode and confirmed with DNA/DNA-FAM sensing systems. More exciting preliminary results on label-free sensing of tumor markers were also reported by investigating the unique fluorescence response to 11 kinds of proteins. These results provide a new insight view for designing CPEs with light-up and label-free features for biomolecular sensing.

End Functionalized Nonionic Water-Dispersible Conjugated Polymers

2,7-Dibromofluorene monomers carrying two or four oligo(ethylene glycol) (OEG) side chains are synthesized. Heck coupling between the monomers and 1,4-divinylbenzene followed by end capping with [4-(4-bromophenoxy)butyl]carbamic acid tert-butyl ester leads to two nonionic water-dispersible poly(fluorene-alt-1,4-divinylenephenylene)s end-functionalized with amine groups after hydrolysis. In water, the polymer with a lower OEG density (P1) has poor water dispersibility with a quantum yield of 0.24, while the polymer with a higher OEG density (P2) possesses excellent water-dispersibility with a high quantum yield of 0.45. Both polymers show fluorescence enhancement and blue-shifted absorption and emission maxima in the presence of surfactant sodium dodecyl sulfate and dodecyltrimethylammonium bromide. The polymers are also resistant to ionic strength with minimal nonspecific interactions to bovine serum albumin. When biotin is incorporated into the end of the polymer backbones through N-hydroxysuccinimide/amine coupling reaction, the biotinylated polymers interact specifically with streptavidin on solid surface.

Recent advances in M13 bacteriophage-based optical sensing applications

Recently, M13 bacteriophage has started to be widely used as a functional nanomaterial for various electrical, chemical, or optical applications, such as battery components, photovoltaic cells, sensors, and optics. In addition, the use of M13 bacteriophage has expanded into novel research, such as exciton transporting. In these applications, the versatility of M13 phage is a result of its nontoxic, self-assembling, and specific binding properties. For these reasons, M13 phage is the most powerful candidate as a receptor for transducing chemical or optical phenomena of various analytes into electrical or optical signal. In this review, we will overview the recent progress in optical sensing applications of M13 phage. The structural and functional characters of M13 phage will be described and the recent results in optical sensing application using fluorescence, surface plasmon resonance, Förster resonance energy transfer, and surface enhanced Raman scattering will be outlined.

Proteolytic disassembly of peptide-mediated graphene oxide assemblies for turn-on fluorescence sensing of proteases

Molecule-induced assembly of nanomaterials can alter their unique chemical and physical properties, which can be a promising approach for sensing. Herein, we demonstrate an optical 'turn-on' biosensor for the detection of matrix metalloproteinase-2 (MMP-2), fabricated by means of a peptide-induced assembly of fluorescent graphene oxide (GO). Functionalization of GO with a peptide substrate for MMP-2 bearing a thiol group leads to its self-assembly via disulfide bonding, accompanied by self-quenching of GO's strong fluorescence. This peptide-induced GO assembly is then disassembled by proteolytic cleavage in the presence of MMP-2, thereby restoring the level of self-quenched GO fluorescence. With this approach, we are able to detect MMP-2 and to investigate the kinetic parameters of MMP-2 activity. The GO-peptide assembly is successfully applied to the selective and sensitive detection of MMP-2 secreted by living cells, human hepatocytes HepG2, at a concentration of 2 ng mL(-1).

Parallel folding topology-selective label-free detection and monitoring of conformational and topological changes of different G-quadruplex DNAs by emission spectral changes via FRET of mPPE-Ala-Pt(ii) complex ensemble

The formation of supramolecular assemblies between [Pt(bzimpy-Et){C[triple bond, length as m-dash]CC6H4(CH2NMe3-4)}]Cl2 (1) and mPPE-Ala and the FRET properties of the ensemble have been revealed from the UV-vis absorption, steady-state emission and time-resolved emission decay studies. The two-component mPPE-Ala-1 ensemble has been employed in a "proof-of-principle" concept for label-free detection of G-quadruplex DNAs with the intramolecular propeller parallel folding topology, such as c-myc, in aqueous buffer solution. By the modulation of the aggregation/deaggregation of the polymer-metal complex aggregates and hence the FRET from the mPPE-Ala donor to the aggregated 1 as acceptor, the ensemble has been demonstrated for sensitive and selective label-free detection of c-myc via the monitoring of emission spectral changes of the ensemble. Ratiometric emission of the ensemble at 461 and 662 nm has been shown to distinguish the intramolecular propeller parallel G-quadruplex folding topology of c-myc from other G-quadruplex-forming sequences of different folding topologies, owing to the strong and specific interactions between c-myc and 1 as suggested by the UV-vis absorption and UV melting studies. In addition, the formation of high-order intermolecular multimeric G-quadruplexes from c-myc under molecular crowding conditions has been successfully probed by the ratiometric emission of the ensemble. The conformational and topological transition of human telomeric DNA from the mixed-hybrid form to the intramolecular propeller parallel form, as observed from the circular dichroism spectroscopy, has also been monitored by the ratiometric emission of the ensemble. The ability of the ensemble to detect these conformational and topological transitions of G-quadruplex DNAs has been rationalized by the excellent selectivity and sensitivity of the ensemble towards the intramolecular propeller parallel G-quadruplex DNAs and their high-order intermolecular multimers, which are due to the extra stabilization gained from Pt···Pt and π-π interactions in addition to the electrostatic and hydrophobic interactions found in the polymer-metal complex aggregates.

A novel fluorescence probe based on p-acid-Br and its application in thiourea detection

A novel organic fluorescence system was developed to detect thiourea based on p-acid-Br, which in the range of 0.5–1000 nM and with a detection limit of 0.26 nM. And this method provides a new promising platform for clinical analysis.

An emission-tunable fluorescent organic molecule for specific cellular imaging

A color-tunable fluorescent molecule was synthesized and applied in specific lysosomal imaging.

Facile Synthesis of Biocompatible Fluorescent Nanoparticles for Cellular Imaging and Targeted Detection of Cancer Cells

In this work, we report the facile synthesis of functional core-shell structured nanoparticles with fluorescence enhancement, which show specific targeting of cancer cells. Biopolymer poly-l-lysine was used to coat the silver core with various shell thicknesses. Then, the nanoparticles were functionalized with folic acid as a targeting agent for folic acid receptor. The metal-enhanced fluorescence effect was observed when the fluorophore (5-(and-6)-carboxyfluorescein-succinimidyl ester) was conjugated to the modified nanoparticle surface. Cellular imaging assay of the nanoparticles in folic acid receptor-positive cancer cells showed their excellent biocompatibility and selectivity. The as-prepared functional nanoparticles demonstrate the efficiency of the metal-enhanced fluorescence effect and provide an alternative approach for the cellular imaging and targeting of cancer cells.

Nanohybrid conjugated polyelectrolytes: highly photostable and ultrabright nanoparticles

We present a general and straightforward one-step approach to enhance the photophysical properties of conjugated polyelectrolytes. Upon complexation with an amphiphilic polymer (polyvinylpyrrolidone), an anionic conjugated polyelectrolyte (poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene]) was prepared into small nanoparticles with exceptional photostability and brightness. The polymer fluorescence intensity was enhanced by 23 -fold and could be easily tuned by changing the order of addition. Single molecule experiments revealed a complete suppression of blinking. In addition, after only losing 18% of the original intensity, a remarkable amount of photons were emitted per particle (∼10(9), on average). This number is many folds greater than popular organic fluorescent dyes. We believe that an intimate contact between the two polymers is shielding the conjugated polyelectrolyte from the destructive photooxidation. The prepared nanohybrid particles will prove instrumental in single particle based fluorescent assays and can serve as a probe for the current state-of-the-art bioimaging fluorescence techniques.

Oligo(p-phenylene ethynylene) Electrolytes: A Novel Molecular Scaffold for Optical Tracking of Amyloids

Finding new optical probes to detect and track amyloid protein aggregates is key to understanding and defeating the myriad of neurodegenerative and other diseases associated with these misfolded proteins. Herein we report that a series of fluorescent, soluble oligo(p-phenylene ethynylene)s (OPEs) are able to detect amyloids in vitro by massive binding-activated superluminescence, with low micromolar affinity and high selectivity for the amyloid conformer. The OPEs track the kinetics of amyloid fibril formation from native hen egg white lysozyme (HEWL) similarly to thioflavin T (ThT), and the dependence of binding affinity on OPE length supports the theory of a linear binding groove. We hypothesize, based on spectral properties, induced circular dichroism, and previous work in analogous systems, that the fluorescence turn-on mechanism is a combination of the reduction of static solvent-mediated quenching at the ethyl ester end groups of the phenylene ethynylene fluorophore and the formation of chiral J-type aggregates templated on the amyloid fibril surface.

Conjugated Polymer Nanoparticles for Fluorescence Imaging and Sensing of Neurotransmitter Dopamine in Living Cells and the Brains of Zebrafish Larvae

Nanoscale materials are now attracting a great deal of attention for biomedical applications. Conjugated polymer nanoparticles have remarkable photophysical properties that make them highly advantageous for biological fluorescence imaging. We report on conjugated polymer nanoparticles with phenylboronic acid tags on the surface for fluorescence detection of neurotransmitter dopamine in both living PC12 cells and brain of zebrafish larvae. The selective enrichment of dopamine and fluorescence signal amplification characteristics of the nanoparticles show rapid and high-sensitive probing such neurotransmitter with the detection limit of 38.8 nM, and minimum interference from other endogenous molecules. It demonstrates the potential of nanomaterials as a multifunctional nanoplatform for targeting, diagnosis, and therapy of dopamine-relative disease.

Enzyme-specific sensors via aggregation of charged p-phenylene ethynylenes

Chemical and biological sensors are sought for their ability to detect enzymes as biomarkers for symptoms of various disorders, or the presence of chemical pollutants or poisons. p-Phenylene ethynylene oligomers with pendant charged groups have been recently shown to have ideal photophysical properties for sensing. In this study, one anionic and one cationic oligomer are combined with substrates that are susceptible to enzymatic degradation by phospholipases or acetylcholinesterases. The photophysical properties of the J-aggregated oligomers with the substrate are ideal for sensing, with fluorescence quantum yields of the sensors enhanced between 30 and 66 times compared to the oligomers without substrate. The phospholipase sensor was used to monitor the activity of phospholipase A1 and A2 and obtain kinetic information, though phospholipase C did not degrade the sensor. The acetylcholinesterase sensor was used to monitor enzyme activity and was also used to detect the inhibition of acetylcholinesterase by three different inhibitors. Phospholipase A2 is a biomarker for heart and circulatory disease, and acetylcholinesterase is a biomarker for Alzheimer's, and indicative of exposure to certain pesticides and nerve agents. This work shows that phenylene ethynylene oligomers can be tailored to enzyme-specific sensors by careful selection of substrates that induce formation of a molecular aggregate, and that the sensing of enzymes can be extended to enzyme kinetics and detection of inhibition. Furthermore, the aggregates were studied through all-atom molecular dynamics, providing a molecular-level view of the formation of the molecular aggregates and their structure.

Differential interactions of conjugated polymer nanoparticles with glycosaminoglycans in synthetic urine

Four different conjugated polymer nanoparticles (CPNs) were used to differentiate structurally similar glycosaminoglycans (GAGs) in a urine simulant. Unique emission response patterns of CPNs were analyzed by linear discriminant analysis (LDA), confirming that structurally diverse CPNs are sensitive and effective at differentiating GAGs in a complex biological medium.

Synthesis of triphenylamine-containing conjugated polyelectrolyte and fabrication of fluorescence color-changeable, paper-based sensor strips for biothiol detection

A new emission color-changeable (green-to-blue) conjugated polyelectrolyte was synthesized to use in biothiol sensing with its paper-based strip.

Diphenylether based derivatives as Fe(iii) chemosensors: spectrofluorimetry, electrochemical and theoretical studies

Differential pulse voltammetric studies on DPE-I and DPE-II indicating selective response to Fe³⁺, supported by DFT studies using Gaussian software.

Adenosine deaminase biosensor combining cationic conjugated polymer-based FRET with deoxyguanosine-based photoinduced electron transfer

We demonstrated a sensitive and selective adenosine deaminase (ADA) detection by modulating the fluorescence resonance energy transfer (FRET) between cationic conjugated poly(9,9-bis(6'-N,N,N-trimethylammonium) hexyl)fluorine phenylene) (PFP) and the deoxyguanosine-tailored hairpin aptamer. The hairpin aptamer was labeled with a fluorophore FAM at one end and three deoxyguanosines (Gs) at the other end as a quencher. In the absence of ADA, aptamer forms hairpin-like conformation with adenosines making close affinity of Gs and FAM, which results in the weak FRET from PFP to FAM because of FAM fluorescence being quenched by Gs via photoinduced electron transfer (PET). After addition of ADA, adenosine was hydrolyzed by ADA, followed by the release of free aptamer. In this case, FAM being far away from Gs, the strong FRET thus was obtained due to the quenching process being blocked. Therefore, the new strategy based on the FRET ratio enhancement is reasonably used to detect the ADA sensitively, combining the fluorescence signal amplification of conjugated polymers with the initiative signal decreasing by Gs. The detection limit of the ADA assay is 0.3 U/L in both buffer solution and human serum, which is more sensitive than most of those previously documented methods. Importantly, the assay is rapid, homogeneous, and simple without a complicated treating process. The ADA inhibitor, erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (EHNA), was also studied based on this assay, and the detection limit of EHNA is 10 pM. This strategy provides a new platform for the detection of other biomolecules and enzymes.