Elsevier

Surface and Coatings Technology

Volume 271, 15 June 2015, Pages 242-246
Surface and Coatings Technology

Impact of polyelectrolyte coating in fluorescent response of Eu(III)-containing nanoparticles on small chelating anions including nucleotides

https://doi.org/10.1016/j.surfcoat.2014.11.076Get rights and content

Highlights

  • Polyelectrolyte coating of luminescent nanoparticles based on Eu(III) complex.

  • Luminescence of Eu(III)-based core is quenched by biophosphates.

  • Concentration dependent quenching is affected by the nature of polyelectrolyte.

  • Nature of coating affects penetration of biophosphates to Eu(III)-based core.

  • Permeability of coating can be sensed through quenching measurements.

Abstract

The present work introduces a novel route to sense the permeability of the polyelectrolyte layer deposited onto luminescent core. The use of ternary Eu(III) complexes as the luminescent core enables to detect the permeability of the polyelectrolyte layers through the change of the Eu(III)-centered luminescence. The chelating anions, such as adenosine phosphates, glutamic acid and ethylenediaminetetraacetic acid disodium salt were used as substrates. The origin of the fluorescent response is the complex formation of the substrates with the Eu(III) complexes, which is greatly affected by the equilibrium concentration of the substrates at the surface of the core. The latter in turn is influenced by the permeability of the polyelectrolyte layer. The obtained results highlight the impact of the nature of the exterior layer in the penetration of the substrates through the negatively and positively charged polyelectrolyte layers.

Introduction

The layer-by-layer deposition of oppositely charged polyelectrolytes is widely applied to build up capsules for drug delivery, as well as to protect hazardous magnetic or luminescent templates from the environment [1], [2], [3], [4], [5], [6], [7], [8], [9]. This sort of coating is soft, since it is based on a cooperative effect of rather weak non-covalent interactions [6]. Nevertheless the colloids that resulted from the adsorption and further layer-by-layer deposition of multi-charged polyelectrolytes onto hard templates are both stable enough and stimuli responsive. Thus a permeability of small molecules through a polyelectrolyte multilayer is a key point in the development of both polyelectrolyte capsules and core-shell nanomaterials. Moreover environmentally controlled gating of substrates is of particular importance in drug delivery development [10]. The covalent labeling of substrates by organic luminophores is the known route to reveal the penetration of substrates through polyelectrolyte layers [11], [12]. Radiolabeling should be mentioned as another route to detect the ion exchange between the polyelectrolyte multilayer and the bulk of solution [6]. The encapsulation of the dye nanocrystals into polyelectrolyte capsules and following monitoring of its release exemplify more facile route to study the permeability of the polyelectrolyte multilayers [13], [14]. The specified stability of these colloids in time is explained by the slowed down exchange between polyelectrolytes within the multilayer and those in the solutions [15]. Taking into account that kinetic control is predominant versus thermodynamic one in the deposition of polyelectrolyte layers on templates, the mechanisms of release and/or penetration of substrates should significantly depend on their nature. Thus a development of facile procedure to monitor the penetration of small molecules through polyelectrolyte capsules is still an appealing task.

Our previous results highlight the encapsulation of the Eu(III) luminescent complexes as the hard templates or cores into capsules built through layer-by-layer polyelectrolyte deposition [16]. The encapsulation of [Eu(TTA)31] (TTA and 1 are thenoyltrifluoroacetonate and phosphine oxide derivative) in the form of nanosized templates into polyelectrolyte capsules built from the appositively charged poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) represents a convenient route to develop stable in time colloids with efficient Eu(III) centered luminescence [16], [17]. The ligand exchange at the nanoparticle/water interface is the reason of the substrate induced sensitization or quenching of the luminescence, which has been successfully applied in the sensing of fluoroquinolones in aqueous solutions [18]. Thus the ligand environment of Eu(III) ion is of great impact in the substrate induced luminescence response of the Eu(III) containing cores. Moreover our previous work highlights the nature of the exterior layer and the number of layers as the factors affecting the luminescence response arisen from the interfacial complex formation [18]. These results point to the permeability of the analytes through the polyelectrolyte layers as the key point in the improvement of the substrate responsibility of the Eu(III) containing cores coated by polyelectrolyte layers. Thus the deeper insight into the correlation between the substrate induced luminescence response of the Eu(III) cores and the polyelectrolyte layer can be considered as a tool to detect the penetration of the substrate through the polyelectrolyte layer by measuring Eu(III)-centered luminescence. The choice of substrates is inspired by the idea to induce the fluorescent response by complex formation at the nanoparticle/water interface. The literature results highlight the use of lanthanide complexes with β-diketonates as sensors due to their ternary complex formation with chelating substrates [19], [20], [21], [22], [23], [24], [25]. The series of chelating anions, namely ethylenediaminetetraacetic acid disodium salt (Na2EDTA) and some biorelevant chelating anions, such as glutamic acid (Glu), glutamine (Gln), lysine (Lys), adenosine 5′-monophosphate (AMP), adenosine 5′-diphosphate (ADP) and adenosine 5′-triphosphate (ATP) have been chosen as substrates.

The choice of [Eu(TTA)3(H2O)2] and [Eu(TTA)3L], where L represents the phosphine oxide derivatives with various antennae effects on Eu(III) centered luminescence is aimed to reveal the impact of TTA and L in the ligand exchange. The previously reported results highlight the effect of the number and position of methoxy substituents of the aromatic rings neighboring to Pdouble bondO group on the antennae effect of phosphine oxide derivatives on Eu(III) centered luminescence [16], [26]. Thus the phosphine oxide derivatives L presented in Fig. 1 are chosen as a route to modify their antennae effect. The successfully applied PSS and PEI [16], [17], [18] are also used in the present work. The fluorescent response that originated from the interactions of the substrates with the Eu(III)-based luminescent cores is introduced as a tool to reveal a penetration of the substrates through the polyelectrolyte layer deposited onto the core.

Section snippets

Material and methods

Commercial chemicals adenosine 5′-monophosphate (AMP) (99%), adenosine 5′-diphosphate disodium salt (ADP) (98%) and adenosine 5′-triphosphate disodium salt (ATP) (98%) and EuCl3 6H2O were purchased from Acros Organic. Ethylenediaminetetraacetic acid disodium salt dihydrate (Na2EDTA), lysine, glutamine and glutamic acid were purchased from Alfa Aesar.

The phosphine oxide derivatives L (Fig. 1) (2-(5-chlorophenyl-2-hydroxy)-2-phenylethenyl-bis-(2-methoxyphenyl)phosphine oxide) were synthesized as

Synthesis and photophysical properties of the aqueous colloids of [Eu(TTA)3L] (L = 1, 2, 3)

The synthetic procedure applied for the synthesis of the luminescent colloids is based on the reprecipitation of the complex from organic to aqueous solutions of PSS similar with the previously reported technique [16]. The colloidal properties of the obtained colloids were analyzed by dynamic light scattering (DLS) and electrokinetic potentials (ζ) data, which are presented in Suppl. data (Table S1). The sizes revealed from the DLS measurements lie within 180–280 nm and indicate the diameters of

Summary

Summarizing it is worth noting that the fluorescent response of the [Eu(TTA)3L]-based cores coated by polyelectrolyte layer provides the powerful tool to highlight the permeability of the biorelevent substrates such as adenosine-phosphates through the polyelectrolyte layer. The obtained results reveal the great impact of the electrostatic repulsive or attractive interactions in the permeability of the polyelectrolyte layers towards the substrates. The highlighted tendencies introduce the

Acknowledgment

This work was partially funded by the subsidy allocated to Kazan Federal University for the state assignment in the sphere of scientific activities.

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