Abstract
ABSTRACT Four types of calcined MCM-41 silica nanoparticles, loaded with dyes and capped with different gating ensembles are prepared and characterized. N1 and N2 nanoparticles are loaded with rhodamine 6G and capped with bulky poly(ethylene glycol) derivatives bearing ester groups (1 and 2). N3-N4 nanoparticles are loaded with sulforhodamine B and capped with self-immolative derivatives bearing ester moieties. In the absence of esterase enzyme negligible cargo release from N1, N3 and N4 nanoparticles is observed whereas a remarkable release for N2 is obtained most likely due to the formation of an irregular coating on the outer surface of the nanoparticles. In contrast, a marked delivery is found in N1, N3, and N4 in the presence of esterase enzyme. The delivery rate is related to the hydrophilic/hydrophobic character of the coating shell. The use of hydrophilic poly(ethylene glycol) derivatives as gating ensembles on N1 and N2 enables an easy access of esterase to the ester moieties with subsequent fast cargo release. On the other hand, the presence of a hydrophobic monolayer on N3 and N4 partially hinders esterase enzyme access to the ester groups and the rate of cargo release was decreased.
Highlights
The synthesis of gated nanodevices able to perform smart tasks has boosted in the last years and a number of examples have been published so far [1–4]
We present the synthesis and characterization of four types of calcined MCM-41 silica nanoparticles loaded with dyes and capped with several gating ensembles of different sizes and shapes, containing hydrophilic and hydrophobic moieties and equipped with enzyme-sensible ester bonds
The presence of esterase enzyme induced cargo release from N1-N4 nanoparticles due to the hydrolysis of ester bonds located in the structure of the capping ensemble
Summary
The synthesis of gated nanodevices able to perform smart tasks has boosted in the last years and a number of examples have been published so far [1–4]. In spite of the amount of work devoted to the synthesis of smart-gated nanodevices and its potential applications in several fields there is a clear lack of systematic studies related to the chemical nature of the capping ensemble (size, polarity, hydrophobicity, hydrophilicity, possibility of intermolecular/intramolecular interactions, etc.) and how these features influence capping and the rate and efficiency of cargo release [24] Such studies can be important as the required rate of delivery can be different depending on the application. Whereas for sensing applications a quick cargo release is recommendable, in (bio)medical applications a more sustainable delivery can be necessary [25–29] In this sense, we have previously reported the use of enzymes (esterases and amidases) as external stimuli with specific purposes [30,31] and during the development of these research we have observed that the characteristics of the organic molecules used as molecular gates have strong influence in the capping process and in the release one. Two of the ester-capping units contained one (compound 1) or two (derivative 2) poly(ethylene glycol) chains whereas the others are formed by self-immolative structures containing aromatic rings (3 and 4)
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