Oligonucleotides such as siRNA and plasmid DNA (pDNA) have great potential for gene therapies. Multifunctional, environment-resistant carriers with imaging capabilities are required to track the assembly and disassembly of oligonucleotides, monitor the delivery processes, and develop new delivery systems. Conjugated polymers and oligomers can potentially be used as novel materials for functional nanocarriers with both delivery and imaging abilities. In this work, a novel π-conjugated oligomer 4,7-(9,9′-bis(6-adenine hexyl)fluorenyl)-2,1,3-benzothiadiazole (OFBT-A) modified with nucleotide adenine (A) groups in its side chains is synthesized and characterized. Fluorescent nanoparticles based on the π-conjugated oligomers OFBT-A are developed as novel functional nanocarriers for oligonucleotides. Single-stranded DNA (ssDNA) TR-T5 labeled with Texas Red (TR) fluorescent dye is selected as a model payload oligonucleotide. The capture abilities and stability of OFBT-A are investigated by monitoring the fluorescence resonance energy transfer (FRET) efficiency between the OFBT-A nanoparticles and TR labels in solution. The OFBT-A/TR-T5 composites are stable in solution at high ionic strengths (0–500 mM) and have a wide working pH range, from 3.0 to 9.5. The in vitro profile demonstrates that the release of the TR-DNA is induced by the ssDNA A43, which has a high charge density. The release process is monitored by measuring the changes in FRET efficiency and fluorescence color for the OFBT-A/TR-T5 composites. Using this carrier, the uptake of TR-DNA by A549 lung cancer cells is observed. Both the OFBT-A nanoparticles and the OFBT-A/TR-T5 composites show high cytocompatibility. We anticipate that these novel functional nanocarriers will provide a safe strategy for monitoring the gene delivery process.Keywords: conjugated oligomers; delivery; fluorescence; fluorescence resonance energy transfer; nanocarrier; nanoparticles;

In the present work, a facile one-pot method is designed to fabricate a core–shell fluorescent nanoparticle (NP) for cellular imaging based on a new cationic conjugated polymer, poly[9,9′-bis(6,6′-(N,N,N-trimethylaminium)fluorene-2,7-ylenevinylene-co-alt-2,5-dicyano-1,4-phenylene] (PFVCN). Gold nanoflowers (AuNFs) are prepared by a seedless method, in which a gelatin layer formed through a sol–gel phase transition is deposited on the surface of each AuNF. The cationic PFVCN self-assembles onto the negative surface of the resultant (AuNF@Gelatin NPs) driven by electrostatic attraction. An obvious enhancement of fluorescence intensity is observed. The AuNF@Gelatin/PFVCN NPs exhibit excellent cytocompatibility, and their cellular imaging ability is demonstrated when cocultured with HeLa cells. AuNF@Gelatin/PFVCN hybrid NPs are expected to be a desirable material in the field of cellular imaging and biosensing.Keywords: cellular imaging; conjugated polymers; core−shell nanoparticles; fluorescence; gold nanoflowers; self-assembly;

This work shows the sodium citrate induced efficient interpolymer π-stacking aggregation of the planar cationic conjugated polyelectrolyte poly[{9,9-bis[6′-(N,N-trimethylamino)hexyl]-2,7-fluorenyleneethynylene}-alt-co-(1,4-phenylene)] dibromide (PFE) in aqueous solution, which results in the self-quenching of fluorescence. Using the citrate-induced aggregation properties of PFE and the strong chelation ability of citrate with aluminum ions (Al3+), a sensitive and selective Al3+-ion detection assay in aqueous solution was developed through monitoring of the fluorescence recovery of PFE. The fluorescence intensity recovery of PFE depends on the concentration of Al3+ ions, and linear fluorescence recovery was observed in the range of 0.5–9 μM. The limit of detection of this assay is 0.37 μM. Its simplicity and rapidity mean this assay shows promise for the real-time detection of Al3+.Keywords: aggregation; chelation; citrate; conjugated polymer; fluorescence; ion detection;

A new label-free heterogeneous DNA detection method was developed using the fluorescent conjugated polyelectrolyte poly[9,9′-bis(6′′-(N,N,N-trimethylammonium)-hexyl)fluorene-2,7-ylenevinylene-co-alt-1,4-phenylene dibromide] (PFV). In this assay, Layer-by-Layer (LbL) assembly was used to form a polyelectrolyte multilayer thin film on a substrate, and enhance the adsorption ability and stability of PFV. A cationic poly-(allylamine hydrochloride) (PAH) buffer layer was deposited to increase deposition of DNA. DNA detection was studied using a platform with the double-stranded DNA (dsDNA) intercalator ethidium bromide (EB). The thickness of the PAH layer was controlled by pH to obtain an optimum distance between PFV and EB for efficient fluorescence resonance energy transfer (FRET). Because of the different interactions of dsDNA and single-stranded DNA (ssDNA) with EB, DNA hybridization was selectively detected by monitoring the FRET efficiency.

A novel water-soluble conjugated polymer poly{(4,4′-azobenzene)-2,7-[9,9-bis(6′-N,N,N,-trimethylammonium)hexyl fluorene]dibromide} (PFAB) has been designed and synthesized via Suzuki cross-coupling the fluorene units and azobenzene units. Through simple photoreduction, the azo group of the nonfluorescent PFAB to hydrazine group using UV light, polyfluorene PFAB-L with turn-on fluorescence in aqueous solution is obtained. The optical measurements illustrate that the generation of the flexible hydrazine group induces face-to-face arrangement of phenyl–fluorene–phenyl moieties. Therefore, the excimer formation of phenyl–fluorene–phenyl moieties was induced in PFAB-L. And the fluorescence of PFAB-L can be controlled through modulating the protonation of the −NH–NH– group in solution with different pH. The pH-responsive property is reversible. Moreover, the Fe3+ ions can selectively quench the fluorescence of the PFAB-L. This new polymer PFAB-L could be used for selective and sensitive sensing Fe3+ ions in aqueous solution.Keywords: excimer; fluorescence; ion detection; pH-responsive; photoreduction; polyfluorene;

A unique fluorescent–magnetic hybrid bimodal nanocomposite was prepared by the layer-by-layer self-assembly (LbL) technique fabrication of water-soluble conjugated polymers (CPs) onto the CoFe2O4@SiO2 core–shell nanoparticles (NPs). First, magnetic CoFe2O4 nanoparticles were prepared as the magnetic core and coated with a SiO2 shell to obtain a good dispersion in aqueous solution. Then the polyelectrolytes and cationic conjugated polymer PFV was assembled onto the surface of core–shell nanoparticles by the LbL technique. The prepared nanocomposites were magnetically responsive and fluorescent, simultaneously. Finally, the biomacromolecule heparin sodium (HS) was then assembled on the outer layer of the nanocomposite to provide a cytocompatible surface. The nanocomposites show monodispersity, good fluorescence and good biocompatibility that are useful for efficient cellular imaging. Moreover, the colloidal stability and the cellular uptake ability of the nanocomposition with HS layer were efficiently improved.Graphical abstractHighlights► Hybrid fluorescent–magnetic nanocomposite was prepared by self-assembly technique. ► The nanocomposites with a cytocompatible surface show monodispersity, good fluorescence and good biocompatibility. ► The colloidal stability and the cellular uptake ability of the nanocomposition were efficiently improved.

A novel fluorescent nanoparticle was prepared via a simple self-assembly technique based on water-soluble conjugated polymers (CPs) and Ag@SiO2 core−shell nanoparticles. Core−shell nanoparticles with silver NPs core show a unique property referred to as metal-enhanced fluorescence (MEF). In the present work, the cationic conjugated polymer poly[9,9′-bis(6′′-(N,N,N-trimethylammonium)-hexyl) fluorene-2,7-ylenevinylene-co-alt-1,4−phenylene dibromide] (PFV) was hybridized with Ag@SiO2 NPs via simple self-assembly procedure, and given high stability, monodispersity. The fluorescence intensity of PFV after assembling on Ag@SiO2 core−shell NPs is enhanced 1.3-fold compared with the fluorescence intensity of PFV assembled on silica NPs without silver cores for the MEF property of the Ag@SiO2 nanostructure. Nanocomposite with bright fluorescence was obtained. Moreover, the nanocomposition exhibits good monodispersity and low cytotoxicity, which promote their application in cellular imaging. Furthermore, fluorescent nanoparticles with amendable peripheral surfaces can also be potentially obtained because of the easy modification property of CPs and give potential application in selective biological sensing and imaging.

A new label-free heterogeneous DNA detection method was developed using the fluorescent conjugated polyelectrolyte poly[9,9′-bis(6′′-(N,N,N-trimethylammonium)-hexyl)fluorene-2,7-ylenevinylene-co-alt-1,4-phenylene dibromide] (PFV). In this assay, Layer-by-Layer (LbL) assembly was used to form a polyelectrolyte multilayer thin film on a substrate, and enhance the adsorption ability and stability of PFV. A cationic poly-(allylamine hydrochloride) (PAH) buffer layer was deposited to increase deposition of DNA. DNA detection was studied using a platform with the double-stranded DNA (dsDNA) intercalator ethidium bromide (EB). The thickness of the PAH layer was controlled by pH to obtain an optimum distance between PFV and EB for efficient fluorescence resonance energy transfer (FRET). Because of the different interactions of dsDNA and single-stranded DNA (ssDNA) with EB, DNA hybridization was selectively detected by monitoring the FRET efficiency.