New self assembly monolayer onto SiGe as a selective biosensor for single-strand DNA

• Self assembly monolayer onto SiGe as a selective biosensor for single-strand DNA
• Fabrication of n-(2-aminoethyl)-11-aminoundecyltrimethoxysilane SAM onto SiGe for DNA sensor
• Coverage values of APTES and NAATS SAMs are 71.3 and 83%, respectively.
• High selectivity and sensitivity was obtained for SiGe DNA sensor by using the NAATS SAM.
• Minimum concentration of ssDNA detected was 1 nM for NAATS immobilized onto SiGe.

An important step of fabrication of selective DNA probe/receptor is the functionalization of semiconducting surfaces with a self-assembled monolayer (SAM) with an appropriate surface termination to interact with DNA. In this work, we studied an immobilization of single-strand DNA (ssDNA) onto self-assembly monolayer of both the heavily exploited aminopropyltriethoxy silane (APTES) and n-(2-aminoethyl)-11-aminoundecyltrimethoxysilane (NAATS), a bi-functional amino silane onto the surface of SiGe substrate. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the silanization of SAMs on SiGe surface. The immobilization process was confirmed using fluorescence intensity measurements. The coverage values of APTES and NAATS SAMs were estimated to be 71.3 and 83 XPS% at 78°, respectively from the C/Ge ratio. Comparing the performance towards both specific and non-specific ssDNA complements for both silanes, it was observed that a higher selectivity and sensitivity was obtained by using NAATS SAM. This work highlighted the importance of SAM chain length by comparing one short alkyl chains, APTES with that long-chain counterpart, NAATS.

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