A graphene-based platform for the assay of duplex-DNA unwinding by helicase

Immobilization-free screening of aptamers assisted by graphene oxide

Graphene oxide (GO) has the ability to separate free short ssDNA in heterogeneous solution. This feature is applied as a label free platform for screening of aptamers that bind to their target with high affinity and specificity. Herein, we report an aptamer selection strategy for Nampt protein based on GO.

Interfacing living yeast cells with graphene oxide nanosheaths

The first example of the encapsulation of living yeast cells with multilayers of GO nanosheets via LbL self-assembly is reported. The GO nanosheets with opposite charges are alternatively coated onto the individual yeast cells while preserving the viability of the yeast cells, thus affording a means of interfacing graphene with living yeast cells. This approach is expanded by integrating other organic polymers or inorganic nanoparticles to the cells by hybridizing the entries with GO nanosheets through LbL self-assembly. It is demonstrated that incorporated iron oxide nanoparticles can deliver magnetic properties to the biological systems, allowing the integration of new physical and chemical functions for living cells with a combination of GO nanosheets.

Sensitive and rapid screening of T4 polynucleotide kinase activity and inhibition based on coupled exonuclease reaction and graphene oxide platform

Phosphorylation of DNA with 5'-hydroxyl termini plays a critical role in a majority of normal cellular events, including DNA recombination, DNA replication, and repair of DNA during strand interruption. Determination of nucleotide kinase activity and inhibition is under intense development due to its importance in regulating nucleic acid metabolism. Here, by using T4 polynucleotide kinase (PNK) as a model, which plays an essential role in cellular nucleic acid metabolism, particularly in the cellular responses to DNA damage, we describe a strategy for simply and accurately determining nucleotide kinase activity and inhibition by means of a coupled λ exonuclease cleavage reaction and graphene oxide (GO) based platform. The dye attached dsDNA preserves most of the fluorescence when mixed with GO. While dsDNA is phosphorylated by PNK and then immediately cleaved by λ exonuclease, fluorescence is greatly quenched. Because of the super quenching ability and the high specific surface area of GO, the as-proposed platform presents an excellent performance with wide linear range and low detection limit in the cell extracts environment. Additionally, inhibition effects of adenosine diphosphate, ammonium sulfate, and sodium hydrogen phosphate have also been investigated. The method not only provides a universal platform for monitoring activity and inhibition of nucleotide kinase but also shows great potential in biological process researches, drug discovery, and clinic diagnostics.

The photoluminescent graphene oxide serves as an acceptor rather than a donor in the fluorescence resonance energy transfer pair of Cy3.5-graphene oxide

We have systematically studied the fluorescence resonance energy transfer (FRET) efficiency between the photoluminescent graphene oxide (GO) and Cy3.5 dye by controlling the donor-acceptor distance with a double stranded DNA and demonstrated that the GO serves as an acceptor rather than a donor in this FRET system.

Aptamer biosensor based on fluorescence resonance energy transfer from upconverting phosphors to carbon nanoparticles for thrombin detection in human plasma

We presented a new aptamer biosensor for thrombin in this work, which was based on fluorescence resonance energy transfer (FRET) from upconverting phosphors (UCPs) to carbon nanoparticles (CNPs). The poly(acrylic acid) (PAA) functionalized UCPs were covalently tagged with a thrombin aptamer (5'-NH(2)- GGTTGGTGTGGTTGG-3'), which bound to the surface of CNPs through π-π stacking interaction. As a result, the energy donor and acceptor were taken into close proximity, leading to the quenching of fluorescence of UCPs. A maximum fluorescence quenching rate of 89% was acquired under optimized conditions. In the presence of thrombin, which induced the aptamer to form quadruplex structure, the π-π interaction was weakened, and thus, the acceptor was separated from the donor blocking the FRET process. The fluorescence of UCPs was therefore restored in a thrombin concentration-dependent manner, which built the foundation of thrombin quantification. The sensor provided a linear range from 0.5 to 20 nM for thrombin with a detection limit of 0.18 nM in an aqueous buffer. The same linear range was obtained in spiked human serum samples with a slightly higher detection limit (0.25 nM), demonstrating high robustness of the sensor in a complex biological sample matrix. As a practical application, the sensor was used to monitor thrombin level in human plasma with satisfactory results obtained. This is the first time that UCPs and CNPs were employed as a donor-acceptor pair to construct FRET-based biosensors, which utilized both the photophysical merits of UCPs and the superquenching ability of CNPs and thus afforded favorable analytical performances. This work also opened the opportunity to develop biosensors for other targets using this UCPs-CNPs system.

A graphene oxide-peptide fluorescence sensor tailor-made for simple and sensitive detection of matrix metalloproteinase 2

A graphene oxide-peptide based fluorescence sensor has been developed for matrix metalloproteinase 2 (MMP2), and its applicability has been demonstrated by monitoring the concentration of MMP2 secreted by HeLa cells, revealing that HeLa cells with a density of 5.48 × 10(5) cells per mL can produce 22 nM in cell culture media in 24 h.

Functionalizing metal nanostructured film with graphene oxide for ultrasensitive detection of aromatic molecules by surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) as a powerful analytical tool has gained extensive attention. Despite of many efforts in the design of SERS substrates, it remains a grand challenge for creating a general substrate that can detect diverse target analytes. Herein, we report our attempt to address this issue by constructing a novel metal-graphene oxide nanostructured film as SERS substrate. Taking advantages of the high affinity of graphene oxide (GO) toward aromatic molecules and the SERS property of nanostructured metal, this structure exhibits great potential for diverse aromatic molecules sensing, which is demonstrated by using crystal violet (CV) with positive charge, amaranth with negative charge, and neutral phosphorus triphenyl (PPh(3)) as model molecules.

Adsorption and desorption of DNA on graphene oxide studied by fluorescently labeled oligonucleotides

Being the newest member of the carbon materials family, graphene possesses many unique physical properties resulting is a wide range of applications. Recently, it was discovered that graphene oxide can effectively adsorb DNA, and at the same time, it can completely quench adsorbed fluorophores. These properties make it possible to prepare DNA-based optical sensors using graphene oxide. While practical analytical applications are being demonstrated, the fundamental understanding of binding between graphene oxide and DNA in solution received relatively less attention. In this work, we report that the adsorption of 12-, 18-, 24-, and 36-mer single-stranded DNA on graphene oxide is affected by several factors. For example, shorter DNAs are adsorbed more rapidly and bind more tightly to the surface of graphene. The adsorption is favored by a lower pH and a higher ionic strength. The presence of organic solvents such as ethanol can either increase or decrease adsorption depending on the ionic strength of the solution. By adding the cDNA, close to 100% desorption of the absorbed DNA on graphene can be achieved. On the other hand, if temperature is increased, only a small percentage of DNA is desorbed. Further, the adsorbed DNA can also be exchanged by free DNA in solution. These findings are important for further understanding of the interactions between DNA and graphene and for the optimization of DNA and graphene-based devices and sensors.

Graphene and graphene oxide: biofunctionalization and applications in biotechnology

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.

Graphene based gene transfection

Graphene as a star in materials research has been attracting tremendous attentions in the past few years in various fields including biomedicine. In this work, for the first time we successfully use graphene as a non-toxic nano-vehicle for efficient gene transfection. Graphene oxide (GO) is bound with cationic polymers, polyethyleneimine (PEI) with two different molecular weights at 1.2 kDa and 10 kDa, forming GO-PEI-1.2k and GO-PEG-10k complexes, respectively, both of which are stable in physiological solutions. Cellular toxicity tests reveal that our GO-PEI-10k complex exhibits significantly reduced toxicity to the treated cells compared to the bare PEI-10k polymer. The positively charged GO-PEI complexes are able to further bind with plasmid DNA (pDNA) for intracellular transfection of the enhanced green fluorescence protein (EGFP) gene in HeLa cells. While EGFP transfection with PEI-1.2k appears to be ineffective, high EGFP expression is observed using the corresponding GO-PEI-1.2k as the transfection agent. On the other hand, GO-PEI-10k shows similar EGFP transfection efficiency but lower toxicity compared with PEI-10k. Our results suggest graphene to be a novel gene delivery nano-vector with low cytotoxicity and high transfection efficiency, promising for future applications in non-viral based gene therapy.

Graphene in biomedicine: opportunities and challenges

Graphene, whose discovery won the 2010 Nobel Prize in physics, has been a shining star in the material science in the past few years. Owing to its interesting electrical, optical, mechanical and chemical properties, graphene has found potential applications in a wide range of areas, including biomedicine. In this article, we will summarize the latest progress of using graphene for various biomedical applications, including drug delivery, cancer therapies and biosensing, and discuss the opportunities and challenges in this emerging field.

Behaviors of NIH-3T3 fibroblasts on graphene/carbon nanotubes: proliferation, focal adhesion, and gene transfection studies

Carbon-based materials, including graphene and carbon nanotubes, have been considered attractive candidates for biomedical applications such as scaffolds in tissue engineering, substrates for stem cell differentiation, and components of implant devices. Despite the potential biomedical applications of these materials, only limited information is available regarding the cellular events, including cell viability, adhesion, and spreading, that occur when mammalian cells interface with carbon-based nanomaterials. Here, we report behaviors of mammalian cells, specifically NIH-3T3 fibroblast cells, grown on supported thin films of graphene and carbon nanotubes to investigate biocompatibility of the artificial surface. Proliferation assay, cell shape analysis, focal adhesion study, and quantitative measurements of cell adhesion-related gene expression levels by RT-PCR reveal that the fibroblast cells grow well, with different numbers and sizes of focal adhesions, on graphene- and carbon nanotube-coated substrates. Interestingly, the gene transfection efficiency of cells grown on the substrates was improved up to 250% that of cells grown on a cover glass. The present study suggests that these nanomaterials hold high potential for bioapplications showing high biocompatibility, especially as surface coating materials for implants, without inducing notable deleterious effects while enhancing some cellular functions (i.e., gene transfection and expression).