Facile Electrochemical Hydrogenation and Chlorination of Glassy Carbon to Produce Highly Reactive and Uniform Surfaces for Stable Anchoring of Thiolated Molecules

Abstract

Carbon is a highly adaptable family of materials and is one of the most chemically stable materials known, providing a remarkable platform for the development of tunable molecular interfaces. Herein, we report a two-step process for the electrochemical hydrogenation of glassy carbon followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The carbon surface at each stage of the process is characterized by AFM, SEM, Raman, attenuated total reflectance (ATR) FTIR, X-ray photoelectron spectroscopy (XPS), and electroanalytical techniques. Electrochemical chlorination of hydrogen-terminated surfaces is achieved in just 5 min at room temperature with hydrochloric acid, and chemical chlorination is performed with phosphorus pentachloride at 50 °C over a three-hour period. A more controlled and uniform surface is obtained using the electrochemical approach, as chemical chlorination is observed to damage the glassy carbon surface. A ferrocene-labeled alkylthiol is used as a model system to demonstrate the genericity and potential application of the highly reactive chlorinated surface formed, and the methodology is optimized. This process is then applied to thiolated DNA, and the functionality of the immobilized DNA probe is demonstrated. XPS reveals the covalent bond formed to be a C-S bond. The thermal stability of the thiolated molecules anchored on the glassy carbon is evaluated, and is found to be far superior to that on gold surfaces. This is the first report on the electrochemical hydrogenation and electrochemical chlorination of a glassy carbon surface, and this facile process can be applied to the highly stable functionalization of carbon surfaces with a plethora of diverse molecules, finding widespread applications.

Quantum and electrochemical interplays in hydrogenated graphene

“…We would like to note here that the decrease in k 0 (Fig. 4d ) is unlikely due to H- sp 3 termination, as the formed C–H dipole is more susceptible towards nucleophilic attack 49 , which could increase the electrochemical activity. Nor is it likely that the kinetics were affected by surface oxidation during exposure to air: XPS spectra demonstrate the negligible oxidation of H-graphene after its exposure to the ambient conditions even for 1 week (Supplementary Figure 8 and Supplementary Table 1 ).…”

Carbon Substrates: A Stable Foundation for Biomolecular Arrays

“…It is difficult to introduce functional groups for attaching biomolecules with this chemistry because these organometallic reagents are highly reactive. A similar two-step approach formed monolayers of alkanethiols on chlorine-terminated amorphous carbon or glassy carbon substrates (70, 71). Although the alkanethiols do not result in a carbon-carbon bond with the surface, they do provide a means of modifying both the wettability and chemical reactivity of the surface.…”

Modification of Carbon Electrode Surfaces

“…Hydrogenation results in the formation of C-H dipoles with electropositive hydrogen slightly susceptible to nucleophilic attack [117]. H-terminated surfaces have been exploited to form stable layer of alkenes, azides, and alkylthiols [118][119][120]. The hydrogen-carbon bond is quite stable, such that a high energy source such as UV light is required to break the bond for further modifications.…”

“…This surface modification strategy has potential for various sensing applications, such as formation of molecular wires, DNA patterning, and cell adhesion. In another study [120], a two-step process has been described for the electrochemical hydrogenation of a GC electrode followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The GC surface was hydrogenated by applying a potential of −5 V versus Ag/AgCl and 20 mA current in a solution of 2 M HCl for 15 min, whereas for chlorination 2 V and 20 mA current was applied at the hydrogenated surface for 5 min in a solution of 2 M HCl/2 M HNO 3 (3 : 1 ratio).…”