Özet

DUAL pH/ LIGHT TRIGGERED MONOLAYER FILMS

FOR DNA RELEASE

 

Gökçen Birlik Demirel*, Cansu Korkusuz, and Tuncer Çaykara

1 Department of Chemistry, Faculty Science, Gazi University, 06500, Beşevler,  Ankara, Turkey

 

Abstract— We illustrated a simple strategy to immobilize Cy5-labeled single strand DNA on Si(001) surface and to trigger its release under the exclusive control of light/pH stimuli. A tailored azobenzene derivative has been self-assembled on Si(001) surface to form cationic-terminated monolayer films. These monolayers encourage the binding of DNA (Cy5-ssDNA)with the functionalized Si(001) surface through effective electrostatic interactions with the negatively charged polynucleotide backbone. In order to understand and control reversible phoswitchable mechanism of this surface, we have measured water contact angles after UV and visible light irradiation. The release of DNA from dual pH/light-sensitive sample was performed using fluorescence microscopy. The results show that irradiation of the film with UV light induces trans to cis isomerization of the photoresponsive azobenzene units leading to significant changes of surface hydrophilicity and decreasing the binding affinity for DNA.

 

 

 

 

Immobilization of DNA on two-dimensional (2D) surfaces and its controlled release without damaging its structure are topics of enormous interest in the development of a variety of systems ranging from gene delivery therapy1, biosensors 2 and biochips 3 to studies of DNA itself. For these applications, the surface properties become increasingly significant4. The immobilization of DNA on 2D surfaces is known in the literature, the cationic terminations is one of the simplest and most tested strategies to successfully anchor the DNA through electrostatic interactions, without impairing its intrinsic high order5-6. The stimuli-sensitive materials are able to control of DNA release due to change certain properties in response to specific external stimuli such as heat, pH and/or light7. Light is a very appealing on/off trigger. Its easy availability and manipulation associated with the instantaneous initiation/stopping of the photochemical reactions make light-regulated systems, in principle, particularly suited to accurately control the DNA release kinetics, which is of key importance for clinical applications.

 

Here we illustrated a simple strategy to immobilize Cy5-labeled single strand DNA on the Si(001) surface for the control of DNA release through light-/pH-stimuli. The substrates were prepared by azobenzene-containing self-assembled monolayers (SAMs) on the Si(001) via chemisorption of 3-aminopropyltrimethoxysilane (APTS) and 4’-carboxy-4-(dimethylamino)azobenzen (CDAA). The azobenzene monolayers were formed on Si(001) surfaces by APTS linkages. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The wetting behaviors and the thicknesses of the surfaces were investigated contact angle and ellipsometry measurements, respectively.   The reversible photoswitching performances of CDAA molecule was investigated by UV Spectroscopy in DMSO solution. In order to understand and control the reversible photoswitching mechanism, contact angle (CA) measurements were performed by using a variety of liquids after UV and visible light irradiation. Moreover, to reveal the pH-sensitive properties of this sample, CA measurements were carried out with different pH buffer solutions.

To prepare dual pH/light-triggered DNA sensor, Cy5 labeled single stranded (Cy5-ssDNA) arrays were then immobilized onto the cationic-terminated SAM film via effective electrostatic interactions with the negatively charged polynucleotide backbone. The Cy5-ssDNA release behaviors of these films were performed through fluorescence microscopy under different conditions. It is shown that the amount of DNA released can be precisely tuned by controlling the illumination/pH conditions.

 

 

 

Scheme 1. Schematic illustration of the immobilization and release of Cy5-ssDNA by photochemically- and pH-controlled SAM.

 

 

Keywords: DNA release, light-triggered, pH-triggered, self-assembled monolayer, azobenzene.

 

 

 

*Corresponding author: gbirlik@gazi.edu.tr

 

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[7] E. J. Moore, M. Curtin, J. Ionita, A. R. Maguire, G. Ceccone and P. Galvin, Anal. Chem., 2007, 79, 2050.

 

 

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