Facile Assembly Enhanced Spontaneous Fluorescent Response of Ag⁺ Ion Containing Polyelectrolyte Multilayer Films

Abstract

Fluorescent organic−inorganic composite materials exhibiting "turn-on" response are often based on conjugated small molecules. Conjugated polymers, however, often exhibit a "turn-off" response in combination with metal ions. Here we present fluorescent turn-on behavior of a branched poly(ethylene imine)-poly(acrylic acid)-Ag + ion complex in a thin film. The material is characterized by UV−vis, spectrofluorometry, XPS, and ICP-MS. The turn-on response is exhibited only with all three components present, implying that the optically active metal coordination complex contains amine and carboxylic acid groups. This behavior is observed in the solid state, meaning this material could be easily integrated into devices. We demonstrate sensing of formaldehyde vapor as well as halide containing solutions based on fluorescence quenching. This fluorescent material is simply made using the layerby-layer technique and commercially available polymers. C oordinative assembly, taking advantage of coordination complex formation, allows organic−inorganic functional assemblies to be formed from combinations of polymers, oligomers, metal ions, and metallopolymers. 1−4 Functionality of these materials includes optical properties such as fluorescence. Many fluorescent organo-metallic complexes are formed from the combination of a conjugated small molecule and a metal ion. 5,6 On the other hand, fluorescence of conjugated polyelectrolytes is often quenched (turn-off response) upon complexation with metal ions. 7−9 This can be explained by selfquenching and intermolecular energy transfer caused by the aggregation of chromophores in aqueous solution, or aggregation-caused quenching. 10 In certain cases when nonluminescent organic gelators aggregate, their gelation actually enhances luminescent emission (turn-on response). 11−13 One example is organogels assembled through metal ion coordination complexes. However, there are only a few reports describing fluorescent Ag + ion complexes, usually with conjugated small molecules, and Ag + ion complexation induced formation of fluorescent supramolecular gels. 14 More commonly, quenching of photoluminesence occurs, even though the unbound ligand may exhibit a strong fluorescence before chelating with Ag + ion. 14 Therefore, creation of this turn-on type of fluorescent probe in combination with Ag + ion still remains a significant challenge. Park et al. 11 presented a turn-on fluorescent supramolecular gel triggered by coordination of silver ion with a conjugated small molecule. The ligand itself is nonfluorescent in solution but it then becomes highly fluorescent when self-assembled with Ag + ion to form supramolecular fibers. Zhang et al. 15,16 reported a turn-on fluorescent gel based on tetraphenylethylene derivatives, which show very weak fluorescence in solution, but when complexed with Ag + ion, a strong emission is exhibited.The layer-by-layer (LbL) method for directing the complexation of polyelectrolytes is a versatile tool for creating thin films called polyelectrolyte multilayers (PEMs...

Paper-Based Assay for Ascorbic Acid Based on the Formation of Ag Nanoparticles in Layer-by-Layer Multilayers

“…6,13,14 Additionally, silver ions in the PAH/PAA multilayers show a redox property with reducing agents and are reported to be reduced to silver nanoparticles in previous studies. 42,44,46 Therefore, because silver ions in the PAH/PAA LbLfilm showed a redox property with a reducing material, the silver ions in (PAH/PAA) 7 multilayers were reduced to silver nanoparticles by AA after immersion of the filter paper with (PAH/PAA) 7 multilayers containing silver ions into the AA solution. After preparation of silver nanoparticles on the surface of the filter paper, the color of the filter paper was changed to yellow or dark brown by the LSPR scattering of the silver nanoparticles.…”

“…The layer-by-layer (LbL) self-assembly technique is a useful method for fabricating uniform and thickness-controllable polyelectrolyte films on various substrates through the adsorption of alternating polyanions and polycations by electrostatic force − and can be widely applied to chemical sensors for the detection of various chamicals. − Recently, a LbL film containing a metal ion by coordination of the metal ion and polyelectrolytes has been reported. − In these films, we reported a novel method to fabricate poly­(allylamine hydrochloride) (PAH) and poly­(acrylic acid) (PAA) LbL multilayers containing metastable metal ions through coordination between the amine groups of PAH and metal ions . These coating films have been applied for various applications, such as slippery film and gas sensors, by using the redox property of the metal ion contained in PAH/PAA LbL multilayers.…”

Functional polyelectrolyte multilayer assemblies for surfaces with controlled wetting behavior

“…Superhydrophobic surfaces also perform well in preventing microbial adhesion. Yin and coworkers incorporated silver nanoparticles into a PEI/PAA LbL matrix to further enhance the antibiofouling property of the superhydrophobic coating. This superhydrophobic fluorinated multilayer can efficiently prevent microbes (such as sulfate‐reducing bacteria Desulfovibrio salexigens , SRB) from adhering over the course of a week.…”

“…Typically, the films are made of two oppositely charged polyelectrolytes or colloidal materials bound together through electrostatic interactions, assembled with a sequential dipping or spraying process . Exploring the functionalities of LbL films is a highly active research area, incorporating a broad range of materials (including polymers, nanoparticles, metal ions, lipids, proteins, dye molecules, dendrimers, and quantum dots) using various substrates. These materials are assembled not only with electrostatic interactions but also with hydrogen bonding, hydrophobic interactions, coordination interactions, covalent bonding, hydrophobic interactions, and complementary based pairing .…”

Dual Electrophoresis Detection System for Rapid and Sensitive Immunoassays with Nanoparticle Signal Amplification

“…PEMs can be used to easily control the properties of arbitrary substrate surfaces; such properties include the hydrophobicity-hydrophilicity, charge properties, and morphology 25 . Hence, PEMs have been widely applied in the environmental, biomedical, and sensor fields 26 27 . Previously, we demonstrated that PEMs could easily control the protein adsorption properties, including the adsorption capacity and adsorption type from a mixed solution, via electrostatic interactions between the protein and the PEM surface 28 29 30 .…”