Graphene and graphene oxide: biofunctionalization and applications in biotechnology

Abstract

Graphene is the basic building block of 0D fullerene, 1D carbon nanotubes, and 3D graphite. Graphene has a unique planar structure, as well as novel electronic properties, which have attracted great interests from scientists. This review selectively analyzes current advances in the field of graphene bioapplications. In particular, the biofunctionalization of graphene for biological applications, fluorescence-resonance-energy-transfer-based biosensor development by using graphene or graphene-based nanomaterials, and the investigation of graphene or graphene-based nanomaterials for living cell studies are summarized in more detail. Future perspectives and possible challenges in this rapidly developing area are also discussed.

Figure 1

(a) The epitome of graphite forms. Graphene is a 2D building material for carbon materials of all other dimensionalities. It can be wrapped up into 0D buckyballs, rolled into 1D nanotubes, or stacked into 3D graphite . (b) Schematic image representing the loading of doxorubicin (DOX) and camptothecin (CPT) onto FA-modified NGO. The NGO is functionalized with sulfonic acid groups to form NGO–SO₃H, which render it stable in physiological solution. NGO–FA was prepared through formation of an amide bond by the reaction between the NH₂ groups of FA and COOH groups of NGO–SO₃H. Finally, two anticancer drugs, DOX and CPT were conjugated onto the FA–NGO via π–π stacking and hydrophobic interactions . (c) Electronic dispersion in graphene. Left: energy spectrum (in units of t) for finite values of t and t′, with t=2.7 eV and t′= –0.2t. Right: magnified image of energy bands close to one of the Dirac points . (d) PEG modification of NGO: photos of (i) GO and (ii) NGO–PEG in different solutions recorded after centrifugation at 10 000 times gravity for 5 min. GO crashed out slightly in PBS and completely in cell medium and serum (top panel). NGO–PEG was stable in all solutions; Atomic force microscopy (AFM) images of (iii) GO and (iv) NGO–PEG . Reproduced with permission from , , , .

Figure 2

Graphene and its derivatives have been reported to be functionalized with avidin–biotin, peptides, NAs, proteins, aptamers, small molecules, bacteria, and cells through physical adsorption or chemical conjugation. The functionalized graphene biosystems with the unique properties have been used to build up biological platforms, biosensors, and biodevices.

Figure 3

Principles of graphene-based FRET biosensors. ssDNA, aptamers and MBs can be adsorbed onto the surfaces of graphene or graphene derivates (which also possess a planar surface and 2D structure). Fluorophore labels on the ends of probes are quenched rapidly when adsorbed onto the graphene surface. When analytes (e.g. cDNA, thrombin and a designed complementary ssDNA or functional NAs like survivin mRNA [64]) are introduced into the systems and bind their probes (ssDNA, aptamer and MB, respectively), the probe fluorescence is recovered, thus allowing detection. Conversely, dsDNA remains fluorescent before an enzyme (e.g. helicase) is introduced; ssDNA is then released, and fluorophore on the ssDNA is quenched by graphene-based nanomaterials.

Figure 4

Design of aptamer-carboxyfluorescein/GO-nS (aptamer-FAM/GO-nS) used for preliminarily investigation of the ability to probe living cells at the molecular level. A FAM-labeled ATP aptamer was first incubated with GO-nS to produce the aptamer-FAM/GO-nS nanocomplex. Then, the nanocomplex was cultured together with JB6 cells and observed with a wide-field microscope. Significant FAM fluorescence could be observed for JB6 cells incubated with aptamer-FAM/GO-nS, which indicated successful intracellular aptamer delivery and ATP probing in living cells. As controls, JB6 cells were also cultured with or without random DNA-FAM/GO-nS as well as with ATP aptamer–FAM or GO alone, and almost no fluorescence signals were observed in the control samples. These results demonstrate that GO-nS is an efficient cargo for DNA transport through cell membranes. Reproduced with permission from .