Bacterial infectious disease is a serious public health concern throughout the world. Pathogen drug resistance, arising from both rational use and abuse/misuse of germicides, complicates the situation. Aside from developing novel antibiotics and antimicrobial agents, molecular approaches have become another significant method to overcome the problem of pathogen drug resistance. Established supramolecular systems, the antibiotic properties of which can be switched “on” and “off” through host–guest interactions, show great potential in combating issues regarding antibiotic resistance in the long term, as indicated by several recent studies. In this Concept, recently developed strategies for antibacterial regulation are summarized and further directions for research into antibiotic switches are proposed.

The conformation of calmodulin (CaM) changes from closed configuration to open one, converting to a claviform dumbbell-shaped biomolecule upon Ca²⁺-binding. A hybrid probe of graphene oxide (GO) cationic conjugated polymer for detection of the conformation transition of CaM by using FRET technique is demonstrated. The stronger hydrophobic interaction and weaker electrostatic repulsion leads to more CaM adsorption to the surface of GO upon binding with Ca²⁺ than that of CaM in the absence of Ca²⁺ (apoCaM), resulting in much farther proximity between poly[(9,9-bis(6′-N,N,N-trimethy­lammonium)hexyl)-fluorenylene phenylene dibromide] (PFP) and green fluorescent protein labeled at the N-terminus of CaM and therefore much weaker FRET efficiency for PFP/Ca²⁺/CaM in comparison with that of PFP/apoCaM in the presence of GO. Notably, the assembly of CaM with GO is quantitatively and reversibly controlled by Ca²⁺ ions.

Conjugated polymers (CPs) attract a lot of attention in sensing, imaging, and biomedical applications because of recent achievements that are highlighted in this Research News article. A brief review of recent progress in the application of CP-based energy-transfer systems in antimicrobial and anticancer treatments is provided. The transfer of excitation energy from CPs to photosensitizers leads to the generation of reactive oxygen species (ROS) that are able to efficiently kill pathogenic microorganisms and cancer cells in the surroundings. Both fluorescence resonance energy transfer (FRET) and bioluminescence energy transfer (BRET) modes are discussed.

Four new fluorescent dyes containing tetrahydro[5]helicene moiety characterized by three-primary emission colors (blue-green-red) are designed and synthesized, and their structures are characterized by NMR, MS, and single crystal X-ray crystallography. Organic nanoparticles based on the fluorescent dyes are then prepared by re-precipitation method, and their photophysical properties are investigated. These nanoparticles retain the strong emissions of the organic dyes, and multicolor nanoparticles were also prepared by simply tuning the ratios of the three-primary colors dyes. These organic nanoparticles exhibit low cytotoxicity, good photostability, and high quantum yields. Moreover, the nanoparticles can also be applied in the cell fluorescence imaging. Especially, it is interestingly found that the stained regions of these nanoparticles from membrane to cytoplasm for HeLa cells show obvious structure-dependent properties. This strategy provides a new perspective to fluorescence probe by molecular design for specific location imaging of living cells.

The development of biomolecular fiber materials with imaging ability has become more and more useful for biological applications. In this work, cationic conjugated polymers (CCPs) were used to construct inherent fluorescent microfibers with natural biological macromolecules (DNA and histone proteins) through the interfacial polyelectrolyte complexation (IPC) procedure. Isothermal titration microcalorimetry results show that the driving forces for fiber formation are electrostatic and hydrophobic interactions, as well as the release of counterions and bound water molecules. Color-encoded IPC fibers were also obtained based on the co-assembly of DNA, histone proteins, and blue-, green-, or red- (RGB-) emissive CCPs by tuning the fluorescence resonance energy-transfer among the CCPs at a single excitation wavelength. The fibers could encapsulate GFP-coded Escherichia coli BL21, and the expression of GFP proteins was successfully regulated by the external environment of the fibers. These multi-colored fibers show a great potential in biomedical applications, such as biosensor, delivery, and release of biological molecules and tissue engineering.

The outstanding optical properties and biocompatibility of fluorescent conjugated polymer nanoparticles (CPNs) make them favorable for bioimaging application. However, few CPNs could achieve stable cell membrane labeling due to cell endocytosis. In this work, conjugated polymer nanoparticles (PFPNP-PLE) encapsulated with PFP and PLGA-PEG-N₃ in the matrix and functionalized with the small-molecule drug plerixafor (PLE) on the surface were prepared by a mini-emulsion method. PFPNP-PLE exhibits excellent photophysical properties, low cytotoxicity, and specific cytomembrane location, which makes it a potential cell membrane labeling reagent with blue fluorescence emission, an important component for multilabel/multicolor bioimaging.

A dopamine-modified conjugated polymer PFPDA is synthesized and characterized. At low pH, dopamine exists in its hydroquinone form and lacks the ability to quench fluorescence. At high pH, the proportion of the quinone form of dopamine increases due to its autooxidation, and efficient intramolecular electron transfer from the polymer main chain to quinone occurs, resulting in the quenching of the fluorescence of PFPDA. Thus, PFPDA exhibits a fluorescence “turn-on” response at low pH. PFPDA possesses excellent photostability and exhibits no cytotoxicity, which makes it a good fluorescent material for pH sensing and cell imaging. A light-induced hydroxyl anion emitter, MGCB, is also used to change the pH of the solution and thus regulate the fluorescence of PFPDA via remote control under light irradiation. Because the cytoplasm becomes acidic when cell autophagy occurs, PFPDA can also be used for autophagy imaging of HeLa cells with good selectivity.

At present, there is an urgent necessity for the discovery of new chemotherapeutic agents with novel molecular skeleton structures that exhibit wide spectrum antitumor activity. In this work, a cationic pentathiophene (5T) is synthesized and discovered to have both anticancer activity and molecular imaging property. 5T can selectively accumulate in mitochondria to exhibit organellar imaging and efficiently induce cell apoptosis associating with JNK pathway activation. Additionally, complexes are prepared through electrostatic interactions between 5T and sodium chlorambucil (a widely used anticancer drug) with varying molar ratios. The complexes form nanoparticles in water with the size of about 50 nm. The 5T-chlorambucil nanoparticles enhance anticancer activity by 2–9 fold due to the synergistical anticancer activity of 5T and chlorambucil. 5T is therefore a promising multifunctional anticancer agent that incorporates optical monitoring capability and anticancer activity that targets mitochondria.

A new bifunctional cationic conjugated polyfluorene derivative (PFPBOH) containing phenylboronic acid group has been synthesized and characterized. The phenylfluorenyl backbone and positively charged groups in the side chain give the polymer PFPBOH excellent fluorescence property and good water solubility. Phenylboronic acid moieties on the side chain of the polymer form cyclic esters with adjacent diols on cell membrane, which can be employed in cell imaging. Besides that, the fluorescence of PFPBOH can be quenched by p-nitroaniline released via enzyme reaction, thus, the polymer can be used for γ-glutamyltranspeptidase detection through a fluorescence “turn off” mechanism. These findings exhibit great potential for developing multifunctional polymer materials for simultaneous imaging and detection.

A fluorescent film sensor was prepared by chemical modification of a polyfluorene derivative on a glass-plate surface. X-ray photoelectron spectroscopy and ellipsometry measurements demonstrate the covalent attachment of the polyfluorene derivative to the glass-plate surface. The sensor was used to detect Cu²⁺ ions in aqueous solution by a mechanism exploiting fluorescence quenching of conjugated polymers. Among the tested metal ions, the film sensor presents good selectivity towards Cu²⁺ ions. Further experiments show that the sensing process is reversible. Moreover, sensory microarrays based on conjugated polymers targeting Cu²⁺ ions are constructed, which display similar sensing performance to that of the film sensor. The structural motif in which conjugated polymers are covalently confined to a solid substrate surface offers several attractive advantages for sensing applications. First, in comparison with film sensors in which small fluorescent molecules are employed as sensing elements, the sensitivity of our new film sensor is enhanced due to the signal-amplifying effect of the conjugated polymers. Second, the film sensors or microarrays can be used in aqueous environments, which is crucial for their potential use in a wide range of real-world systems. Since the sensing process is reversible, the sensing materials can be reused. Third, unlike physically coated polymer chains, the covalent attachment of the grafted chains onto a material surface precludes desorption and imparts long-term stability of the polymer chains.

Multifunctional materials that simultaneously provide therapeutic action and image the results provide new strategies for the treatment of various diseases. Here, it is shown that water soluble conjugated polymers with a molecular design centered on the polythiophene−porphyrin dyad are effective for killing neighboring cells. Following photoexcitation, energy is efficiently transferred from the polythiophene backbone to the porphyrin units, which readily produce singlet oxygen (¹O₂) that is toxic for the cells. Due to the light-harvesting ability of the electronically delocalized backbone and the efficient energy transfer amongst optical partners, the polythiophene−porphyrin dyad shows a higher ¹O₂ generation efficiency than a small molecule analog. The fluorescent properties of these polymers can also serve to distinguish amongst living and dead cells. Polymers can be designed with folic acid grafted onto the polymer side chain that can specifically kill folate receptor-overexpressed cells, thereby providing an important demonstration of anticancer specificity through molecular design.

A new water-soluble zwitterionic oligofluorene bearing carboxylic acid and quaternary ammonium as pendant groups (OF-1) is synthesized and characterized. It forms aggregates by intermolecular electrostatic interactions and exhibits similar light-harvesting ability as that of conjugated polymers. Efficient fluorescence resonance energy transfer (FRET) occurs from OF-1 to double-stranded DNA tagged with fluorescein (dsDNA-F1). A photoresponsive oligofluorene (OF-3) is also synthesized by protecting OF-1 with 1-(2-nitrophenyl)ethanol. Photolysis of OF-3 can produce OF-1 to result in a fluorescence “turn-on” response, thus the FRET from OF-3 to dsDNA-Fl can be turned on by light irradiation. OF-3 offers the potential for remote DNA sensing.

In recent years, conjugated polyelectrolytes (CPEs) have attracted increasing attention for their applications in highly sensitive biosensors by taking advantage of their unique optical amplification properties. In comparison to previous applications tailored for highly sensitive biomacromolecule detection, this Focus Review highlights recent research efforts in the development of water-soluble CPEs as a new class of optical platforms for the screening of potential drugs. Three types of biological targets for the search of small-molecule active drugs are described: nucleic acids, enzymes, and RNA–protein complexes. Future research directions for drug screening based on CPEs are also presented.

Water-soluble conjugated polymers have attracted much attention in the biosensor community because of recent exciting experimental results. The transfer of excitation energy along the whole backbone of the conjugated polymer to the reporter results in an amplified fluorescence signal, which makes them useful as optical platforms in highly sensitive chemical and biological sensors. In this Research News Article, we provide a brief review of recent developments in this field, focusing especially on the application of water-soluble optical conjugated polymers in biomacromolecule (DNA and protein) detection.

A new method has been developed to discriminate between proteins with different isoelectric points by using fluorescent conjugated polyelectrolytes. Charged water-soluble polyfluorenes that contain 2,1,3-benzothiadiazole (BT) units demonstrate intramolecular energy transfer from the fluorene units to the BT sites when oppositely charged proteins are added to the mixture. This results in a shift in emission color from blue to green and a change in the emission intensity of conjugated polyelectrolytes, which makes it possible to assay proteins. The formation of conjugated polyelectrolyte/enzyme complexes by electrostatic interactions can be utilized to manipulate the activity of enzymes by means of local alteration of enzyme charge density. The oppositely charged substrate binds to conjugated polyelectrolyte and reduces the distance between the enzyme and the substrate, leading to an increase in the cleavage reaction rate. The new method has three important features: 1) it offers a convenient “mix-and-detect” continuous approach for protein assays and rapid detection of enzyme activity; 2) the use of water-soluble conjugated polyelectrolytes imparts the sensor with a high sensitivity; 3) this method does not require fluorescent labels on the targets, which should significantly reduce the cost.

Three generation of Boc-protected dendritic-conjugated polyfluorenes (Boc-PFP-G_0-2) were synthesized by Suzuki coupling 1,4-phenyldiboronic ester with dendritic monomers that were synthesized through generation-by-generation approach. The gel permeation chromatography (GPC) analyses showed that the weight-average molecular weight (M_w) of Boc-PFP-G_0-2 was in the range of 11,400–20,400 Da with the polydispersity index (PDI) in the range of 1.32–1.96. Treatment of Boc-protected polymers with 6 M HCl in dioxane yielded cationic dendritic-conjugated polyfluorenes (PFP-G_0-2). They were soluble in common polar solvents such as DMSO, DMF, and water with absorption maxima between 345 and 379 nm. The solutions of PFP-G_0-2 in water were highly fluorescent with emission maxima between 416 and 425 nm. Because higher generation dendrons could prevent the formation of π-stacking aggregates of backbones of conjugated polymer, the fluorescence quantum efficiencies (QEs) of PFP-G_0-2 enhance as the dendritic generation grew. The interactions between 25 mer double-stranded DNA (dsDNA) and PFP-G_0-2 were studied using ethidium bromide (EB) as fluorescent probe. The electrostatic bindings of PFP-G_0-2 with dsDNA/EB complex result in displacement of EB from DNA double helix to the solution accompanying by a quenching of EB fluorescence. The PFP-G₂ with highest generation of dendritic side chains possessed a highest charge density and could form most stable complex with dsDNA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7462–7472, 2008