Surface Functionalization by Poly-Acrylic Acid Plasma-Polymerized films for Microarray DNA Diagnostics

The rapid detection of enteropathogens with high sensitivity and selectivity continues to be a significant challenge, especially in order to transfer laboratory analyses to the Point-Of -Care (POC) by developing simple and reliable diagnostics kits. Bacterial infections are already detected, in analytical labs, by means of high-density Microarray Biochips based both on RNA/DNA fragments and antibodies as probes and antigens receptors, respectively, immobilized on the chip surface. Many efforts to obtain an high efficiency of the surface chemical properties for a stable probes grafting in order to avoid unspecificity or non-selectivity of the bio-recognition are still under way. The aim of this work is to show the advantages of applying a low pressure plasma polymerized Acrylic Acid (exposing -COOH groups) thin coating to a low-density microarray biochip for the efficient grafting of suitable NH2 terminated probes able to match complementary DNA oligonucleotides of Listeria monocytogenes by means of a novel hybridization protocol and a commercial simple and low-cost colorimetric detection method compatible with POC applications. The chemical properties of the obtained PolyAcrylic Acid thin films are characterized by means of ATR FT-IR Spectroscopy, XPS and contact angle (OCA) measurements. The surface density of the carboxylic functionalities is quantified by colorimetric titration with Toluidine Blue O (TBO). The optimized functional thin film is shown to provide good advantages for DNA Microarray diagnostics in terms of chemical stability, density of readily accessible -COOH groups and at the same time low hydrophilicity, crucial for reducing the dilution of spotted probes on the surface and thus resulting in higher and satisfying intensity of the detect signals in the Microarray test.