Covalent Photochemical Functionalization of Amorphous Carbon Thin Films for Integrated Real-Time Biosensing

Abstract

Recent studies have demonstrated that carbon, in the form of diamond, can be functionalized with molecular and/or biomolecular species to yield interfaces exhibiting extremely high stability and selectivity in binding to target biomolecules in solution. However, diamond and most other crystalline forms of carbon involve high-temperature deposition or processing steps that restrict their ability to be integrated with other materials. Here, we demonstrate that photochemical functionalization of amorphous carbon films followed by covalent immobilization of DNA yields highly stable surfaces with excellent biomolecular recognition properties that can be used for real-time biological detection. Carbon films deposited onto substrates at 300 K were functionalized with organic alkenes bearing protected amine groups and characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The functionalized carbon surfaces were covalently linked to DNA oligonucleotides. Measurements show very high selectivity for binding to the complementary sequence, and a high density of hybridizing DNA molecules. Samples repeatedly hybridized and denatured 25 times showed no significant degradation. The ability to use amorphous carbon films as a basis for real-time biosensing is demonstrated by coating quartz crystal microbalance (QCM) crystals with a thin carbon film and using this for covalent modification with DNA. Measurements of the resonance frequency show the ability to detect DNA hybridization in real time with a detection limit of <3% of a monolayer, with a high degree of reversibility. These results demonstrate that functionalized films of amorphous carbon can be used as a chemically stable platform for integrated biosensing using only room-temperature processing steps.

Covalent modification of graphitic carbon substrates by non-electrochemical methods

“…More recently, Hamers has reported a detailed study of the photografting of an alkene to H-terminated amorphous carbon thin films [74]. Films were prepared by DC magnetron sputtering and electron-beam evaporation giving amorphous materials with a high sp 2 carbon content.…”

“…Alkenes do not absorb at the wavelength employed for photografting and no grafting occurred in the absence of UV irradiation [75], hence the UV activation of the carbon surface appears to be involved in the initiation of grafting. Hamers suggests that the mechanism of grafting on H-terminated amorphous carbon is likely to be analogous to that operative at H-terminated diamond surfaces [74]. The surface of hydrogen-plasma treated GC has been shown to have sp 3 diamond-like character [76,77] and so reaction at these sites is expected.…”

Determination of surface amine groups on amorphous carbon nitride thin films using a one step covalent grafting of a redox probe

“…One can simply remind here that, whereas poor nitrogen contents are expected to produce higher amounts of sp 3 and sp 2 type hybridizations leading to more compact films at the atomic level, rich contents of nitrogen are likely to lead to bulkier and more amorphous structures resulting from sp 1 type hybridizations (e.g. nitriles) [38][39]65].…”

“…A major contribution to this latter is aimed at exploiting their surface as a starting platform for various molecular architectures in view of various applications such as electrochemical or bio-sensors, molecular electronics or coatings with special physical or chemical properties [1][2][3]. As an example and besides glassy carbon or raw carbon materials (such as graphite), thin films of boron doped diamond (BDD) have been widely investigated in this research field due to their remarkable physical properties: mechanical resistance, chemical stability, biocompatibility and electronic conductivity [4].…”

“…There is an abundant literature dealing with the characterization of chemical composition and C/N bond structures in a-CN x or a-CN x H y materials depending upon the nature of precursors, N 2 partial pressure in the sputtering gas, or power imposed during the deposition process. Either vibrational (IR or Raman) spectroscopies or XPS technique allowed to prove the existence of sp 3 to sp 1 (C-N, C=N or C N) hybridizations [6,13,16,[36][37][38][39][40][41][42]. In particular, infrared absorption spectra of a-CN x thin films showed bands at 1220 cm -1 and 1650 cm -1 that can be reasonably assigned to sp 3 C-N and sp 2 C=N bonds respectively [6,13,43].…”