A new ethylene glycol-silane monolayer for highly-specific DNA detection on Silicon Chips

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o Keywords: AFM Ethylene-glycol materials Silanes Silicon chip Fluorescence Monolayer thin films with ethylene-glycol function onto gold surfaces by using thiols have been extensively investigated. They have been proposed as precursors for applications to bio-detection, where their hydrophilic character improves both specificity and sensitivity. The aim of this letter is to characterize ethylene-glycol monolayer precursors formed onto silicon chips by using silanes. The importance of the ethylene-glycol function is demonstrated by comparing with the well known 3-Aminopropyltriethoxysilane. The different nano-scale structures of the two precursor monolayers are investigated by using atomic force microscopy (AFM). Longer, wider, and deeper grooves were measured in the images acquired on 3-Aminopropyltriethoxysilane. Fluorescence investigation demonstrates that the presence of ethylene-glycol function improves target hybridization onto silicon chips, assuring highly-specific detection of DNA. A pH imager realized with a CMOS chip has been recently realized [1] for measuring two-dimensional distributions and for real-time dynamic imaging of various chemical reactions. This technology was very recently proposed both for enhanced glucose sensing [2] and for DNA detection [3]. However, false positive signals from mismatching DNA were also acquired (Fig. 3(d) in Ref. [3]) clearly showing that the probe surface is not specific enough. Moreover, overlapping ranges in acquired voltages were registered for match and mismatch DNA (Fig. 4(a) and (b) in [3]). This means that the acquired signals do not distinguish among specific hybridization and non-specific adsorption of DNA onto the chip surface. A similar situation has also been observed in fully-electronic capacitance detection of DNA onto gold surfaces (Fig. 12 in [4]). In the latter case, the poor detection quality has been related to the nano-scale properties of DNA probe films [5]. In particular, AFM investigations have shown that DNA probe film presents grooves at the nano-scale. These grooves cross the entire probe film, providing conducting pathways to solution ions. These conductive pathways affect the capacitance detection and cause time instabilities and large detection errors. Capacitance DNA detection onto gold has been highly-improved by using ethylene-glycol thiol monolayers as precursors for probe anchoring [6]. These films do not show …