Rational design of carboxyl groups perpendicularly attached to a graphene sheet

A platform for enhanced biosensing applications

Alessandra Bonanni, Chun Kiang Chua, Martin Pumera

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Graphene oxide (GO)-based materials offer great potential for biofunctionalization with applications ranging from biosensing to drug delivery. Such biofunctionalization utilizes specific functional groups, typically a carboxyl moiety, as anchoring points for biomolecule. However, due to the fact that the exact chemical structure of GO is still largely unknown and poorly defined (it was postulated to consist of various oxygen-containing groups, such as epoxy, hydroxyl, carboxyl, carbonyl, and peroxy in varying ratios), it is challenging to fabricate highly biofunctionalized GO surfaces. The predominant anchoring sites (i.e., carboxyl groups) are mainly present as terminal groups on the edges of GO sheets and thus account for only a fraction of the oxygen-containing groups on GO. Herein, we suggest a direct solution to the long-standing problem of limited abundance of carboxyl groups on GO; GO was first reduced to graphene and consequently modified with only carboxyl groups grafted perpendicularly to its surface by a rational synthesis using free-radical addition of isobutyronitrile with subsequent hydrolysis. Such grafted graphene oxide can contain a high amount of carboxyl groups for consequent biofunctionalization, at which the extent of grafting is limited only by the number of carbon atoms in the graphene plane; in contrast, the abundance of carboxyl groups on "classical" GO is limited by the amount of terminal carbon atoms. Such a graphene platform embedded with perpendicularly grafted carboxyl groups was characterized in detail by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy, and its application was exemplified with single-nucleotide polymorphism detection. It was found that the removal of oxygen functionalities after the chemical reduction enhanced the electron-transfer rate of the graphene. More importantly, the introduction of carboxyl groups promoted a more efficient immobilization of DNA probes on the electrode surface and improved the performance of graphene as a biosensor in comparison to GO. The proposed material can be used as a universal platform for biomolecule immobilization to facilitate rapid and sensitive detection of DNA or proteins for point-of-care investigations. Such reactive carboxyl groups grafted perpendicularly on GO holds promise for a highly efficient tailored biofunctionalization for applications in biosensing or drug delivery. Superior properties: It was demonstrated that it is possible to considerably increase the amount of carboxyl groups on graphene oxide by grafting carboxyl groups perpendicularly to the graphene sheets by free-radical addition. Such reactive carboxyl groups can be used as anchoring points for biomolecule attachment by carbodiimide chemistry (see figure).

Original languageEnglish
Pages (from-to)217-222
Number of pages6
JournalChemistry - A European Journal
Volume20
Issue number1
DOIs
Publication statusPublished - 2014 Jan 3

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Graphite
Graphene
Oxides
Biomolecules
Oxygen
Free radicals
Drug delivery
Free Radicals
DNA
Carbon
Carbodiimides
Atoms
DNA Probes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

Cite this

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title = "Rational design of carboxyl groups perpendicularly attached to a graphene sheet: A platform for enhanced biosensing applications",
abstract = "Graphene oxide (GO)-based materials offer great potential for biofunctionalization with applications ranging from biosensing to drug delivery. Such biofunctionalization utilizes specific functional groups, typically a carboxyl moiety, as anchoring points for biomolecule. However, due to the fact that the exact chemical structure of GO is still largely unknown and poorly defined (it was postulated to consist of various oxygen-containing groups, such as epoxy, hydroxyl, carboxyl, carbonyl, and peroxy in varying ratios), it is challenging to fabricate highly biofunctionalized GO surfaces. The predominant anchoring sites (i.e., carboxyl groups) are mainly present as terminal groups on the edges of GO sheets and thus account for only a fraction of the oxygen-containing groups on GO. Herein, we suggest a direct solution to the long-standing problem of limited abundance of carboxyl groups on GO; GO was first reduced to graphene and consequently modified with only carboxyl groups grafted perpendicularly to its surface by a rational synthesis using free-radical addition of isobutyronitrile with subsequent hydrolysis. Such grafted graphene oxide can contain a high amount of carboxyl groups for consequent biofunctionalization, at which the extent of grafting is limited only by the number of carbon atoms in the graphene plane; in contrast, the abundance of carboxyl groups on {"}classical{"} GO is limited by the amount of terminal carbon atoms. Such a graphene platform embedded with perpendicularly grafted carboxyl groups was characterized in detail by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy, and its application was exemplified with single-nucleotide polymorphism detection. It was found that the removal of oxygen functionalities after the chemical reduction enhanced the electron-transfer rate of the graphene. More importantly, the introduction of carboxyl groups promoted a more efficient immobilization of DNA probes on the electrode surface and improved the performance of graphene as a biosensor in comparison to GO. The proposed material can be used as a universal platform for biomolecule immobilization to facilitate rapid and sensitive detection of DNA or proteins for point-of-care investigations. Such reactive carboxyl groups grafted perpendicularly on GO holds promise for a highly efficient tailored biofunctionalization for applications in biosensing or drug delivery. Superior properties: It was demonstrated that it is possible to considerably increase the amount of carboxyl groups on graphene oxide by grafting carboxyl groups perpendicularly to the graphene sheets by free-radical addition. Such reactive carboxyl groups can be used as anchoring points for biomolecule attachment by carbodiimide chemistry (see figure).",
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Rational design of carboxyl groups perpendicularly attached to a graphene sheet : A platform for enhanced biosensing applications. / Bonanni, Alessandra; Chua, Chun Kiang; Pumera, Martin.

In: Chemistry - A European Journal, Vol. 20, No. 1, 03.01.2014, p. 217-222.

Research output: Contribution to journalArticle

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