Surface termination, crystal size, and bonding-site density effects on diamond biosensing surfaces

Abstract

Diamond's properties, such as chemical stability and low biofouling rates, make it an ideal material for developing more adequate biosensing technology for single-use bioreactors. We propose a simplistic approach to covalently functionalizing diamond and evaluating the effects of different variables on the sensitivity of the bioactive surface. We hypothesize that by maximizing sensitivity, we can maximize the signal-to-noise ratio of the biosignal. Three different methods of achieving an oxygenated surface on diamond with varying crystal sizes is investigated to see which results in the most active biointerface. Surface termination species were confirmed post‑oxygenation with X-ray Photoelectron Spectroscopy. The diamond was then functionalized with a biotinylated monolayer, which was treated with gold-conjugated streptavidin to quantify the available bonding sites. After complete biofunctionalization, detection sensitivity of IL-8 and antibody density were assessed with ELISA and electrochemical impedance spectroscopy for quantification of sites with functional antibodies. The contradicting correlations between diamond morphology and percentage of CO bonds lead us to conclude that the effectiveness of oxygen-termination method is independent of diamond morphology. Through quantifying bonding sites, it was found that both the number of available sites and active sites increased with increasing crystal size. This result is suspected to be directly correlated to the hybridization of the diamond-carbon material in that functional species prefer sp3 carbon over sp2. Therefore, a diamond film with the largest possible crystals is predicted to have a higher detection sensitivity in biosensing applications.