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 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.

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.

An intrinsically fluorescent cationic polyfluorene (CCP) has been designed, synthesized, characterized, and examined as a plasmid DNA (pDNA) delivery vector. This material facilitates nucleic acid binding, encapsulation and efficient cellular uptake. CCP can effectively protect pDNA against nuclease degradation, which is necessary for gene carriers. Green fluorescent protein (GFP) expression experiments reveal that CCP can achieve efficient delivery and transfection of pDNA encoding GFP gene with 92% efficiency, which surpasses that of commercial transfection agents, lipofectamine 2000 (Lipo) and polyethylenimine (PEI). CCP is also highly fluorescent, with 43% quantum yield in water, and exhibits excellent photostability, which allows for real-time tracking the location of gene delivery and transfection. These features and capabilities represent a major step toward designing and applying conjugated polymers that function in both imaging and therapeutic applications.

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.

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.

Rapid and sensitive methods to detect proteins and protein denaturation have become increasingly needful in the field of proteomics, medical diagnostics, and biology. In this paper, we have reported the synthesis of a new cationic water-soluble conjugated polymer that contains fluorene and diene moieties in the backbone (PFDE) for protein identification by sensing an array of PFDE solutions in different ionic strengths using the linear discriminant analysis technique (LDA). The PFDE can form complexes with proteins by electrostatic and/or hydrophobic interactions and exhibits different fluorescence response. Three main factors contribute to the fluorescence response of PFDE, namely, the net charge density on the protein surface, the hydrophobic nature of the protein, and the metalloprotein characteristics. The denaturation of proteins can also be detected using PFDE as a fluorescent probe. The interactions between PFDE and proteins were also studied by dynamic light scattering (DLS) and isothermal titration microcalorimetry (ITC) techniques. In contrast to other methods based on conjugated polymers, the synthesis of a series of quencher or dye-labeled acceptors or protein substrates has been avoided in our method, which significantly reduces the cost and the synthetic complexity. Our method provides promising applications on protein identification and denaturation detection in a simple, fast, and label-free manner based on non-specific interaction-induced perturbation of PFDE fluorescence response.