Optical nanosensor architecture for cell-signaling molecules using DNA aptamer-coated carbon nanotubes

Carbon nanotubes as optical biomedical sensors

Biosensors are important tools in biomedical research. Moreover, they are becoming an essential part of modern healthcare. In the future, biosensor development will become even more crucial due to the demand for personalized-medicine, point-of care devices and cheaper diagnostic tools. Substantial advances in sensor technology are often fueled by the advent of new materials. Therefore, nanomaterials have motivated a large body of research and such materials have been implemented into biosensor devices. Among these new materials carbon nanotubes (CNTs) are especially promising building blocks for biosensors due to their unique electronic and optical properties. Carbon nanotubes are rolled-up cylinders of carbon monolayers (graphene). They can be chemically modified in such a way that biologically relevant molecules can be detected with high sensitivity and selectivity. In this review article we will discuss how carbon nanotubes can be used to create biosensors. We review the latest advancements of optical carbon nanotube based biosensors with a special focus on near-infrared (NIR)-fluorescence, Raman-scattering and fluorescence quenching.

Multiplexed optical detection of plasma porphyrins using DNA aptamer-functionalized carbon nanotubes

A novel optical platform based on DNA aptamer-functionalized SWCNTs (a-SWCNTs) is developed for multiplexed detection of plasma porphyrins. We have investigated the interactions of a-SWCNTs with heme (FePP), protoporphyrin (PP), coproporphyrin (CP), and uroporphyrin (UP). Two interaction mechanisms, specific binding, and nonspecific adsorption between porphyrins and a-SWCNTs are proposed based on observed optical signal modulations. The optical transduction signals are used to formulate a multiplexed detection strategy for the four porphyrin species without a laborious separation process. The detection scheme is sensitive, selective, and can readily be used for porphyrin detection in plasma samples when combined with a solvent extraction method. Our optical platform offers novel analytical tools for probing the surface chemistry at the porphyrin/a-SWCNTs interface, showing great promise for both research and clinical applications.

Carbon nanotube-based multicolor fluorescent peptide probes for highly sensitive multiplex detection of cancer-related proteases

In this work, a novel carbon nanotube (CNT)-based multicolor fluorescent peptide nanoprobe is developed for rapid, sensitive, and multiplex detection of cancer-related proteases in homogeneous solution. To prepare the nanoprobe, three peptide substrates, each labeled at the C-terminal with a fluorescent dye (i.e., fluorescein isothiocyanate (FITC), cyanine dye Cy3, cyanine dye Cy5), that respond to one of three different proteases are co-conjugated to the surface of CNTs. This conjugation brings the dyes into the proximity of the CNT surface, which leads to significantly quenched fluorescence due to highly efficient long-range energy transfer from the dyes to CNTs. However, upon incubation with the targeted proteases, specific peptide cleavage occurs and releases the dyes from the CNT surface, which results in the fluorescence recovery that provides the basis for a quantitative measurement of protease activity. With the use of three cancer-related proteases, matrix metalloproteinase-7 (MMP-7), matrix metalloproteinase-2 (MMP-2), and urokinase-type plasminogen activator (uPA), as the proof-of-concept analytes, the nanoprobe could simultaneously detect these proteases with high sensitivity and specificity. The limits of detection for this method are obtained in the range 0.5 pg mL^-1 to 500 pg mL^-1, which are two orders of magnitude lower than many previously reported methods. Moreover, the suitability of this CNT-based sensing platform for complex biological sample analysis has also been demonstrated. This approach holds great promise as a routine tool for the high-throughput screening of proteases in proteomics and clinical diagnostics.

DNA oligonucleotide templated nanohybrids using electronic type sorted carbon nanotubes for light harvesting

Light harvesting nanostructure hybrids have been designed and demonstrated using single-wall carbon nanotubes (SWCNTs) and porphyrin chromophores. DNA oligonucleotides are used to conjugate SWCNTs with light-absorbing chromophores for transparent films which generate photocurrents. High-purity semiconducting SWCNTs demonstrate significant enhancement in the photocurrent compared to metallic or unsorted tubes.

RGD-peptide functionalized graphene biomimetic live-cell sensor for real-time detection of nitric oxide molecules

It is always challenging to construct a smart functional nanostructure with specific physicochemical properties to real time detect biointeresting molecules released from live-cells. We report here a new approach to build a free-standing biomimetic sensor by covalently bonding RGD-peptide on the surface of pyrenebutyric acid functionalized graphene film. The resulted graphene biofilm sensor comprises a well-packed layered nanostructure, in which the RGD-peptide component provides desired biomimetic properties for superior human cell attachment and growth on the film surface to allow real-time detection of nitric oxide, an important signal yet short-life molecule released from the attached human endothelial cells under drug stimulations. The film sensor exhibits good flexibility and stability by retaining its original response after 45 bending/relaxing cycles and high reproducibility from its almost unchanged current responses after 15 repeated measurements, while possessing high sensitivity, good selectivity against interferences often existing in biological systems, and demonstrating real time quantitative detection capability toward nitric oxide molecule released from living cells. This study not only demonstrates a facial approach to fabricate a smart nanostructured graphene-based functional biofilm, but also provides a powerful and reliable platform to the real-time study of biointeresting molecules released from living cells, thus rendering potential broad applications in neuroscience, screening drug therapy effect, and live-cell assays.

Graphene enhanced electron transfer at aptamer modified electrode and its application in biosensing

Graphene (GN), a two-dimensional and one-atom thick carbon sheet, is showing exciting applications because of its unique morphology and properties. In this work, a new electrochemical biosensing platform by taking advantage of the ultrahigh electron transfer ability of GN and its unique GN/ssDNA interaction was reported. Adenosine triphosphate binding aptamer (ABA) immobilized on Au electrode could strongly adsorb GN due to the strong π-π interaction and resulted in a large decrease of the charge transfer resistance (R(ct)) of the electrode. However, the binding reaction between ABA and its target adenosine triphosphate (ATP) inhibited the adsorption of GN, and R(ct) could not be decreased. On the basis of this, we developed a new GN-based biosensing platform for the detection of small molecule ATP. The experimental results confirmed that the electrochemical aptasensor we developed possessed a good sensitivity and high selectivity for ATP. The detection range for ATP was from 15 × 10(-9) to 4 × 10(-3) M. The method here was label-free and sensitive and did not require sophisticated fabrication. Furthermore, we can generalize this strategy to detect Hg(2+) using a thymine (T)-rich, mercury-specific oligonucleotide. Therefore, we expected that this method may offer a promising approach for designing high-performance electrochemical aptasensors for the sensitive and selective detection of a spectrum of targets.

An aptamer based on-plate microarray for high-throughput insulin detection by MALDI-TOF MS

An aptamer microarray was directly fabricated on a MALDI target plate for high-throughput insulin detection. High sensitivities were observed both in standard solutions (5 ng mL(-1), 0.86 nM) and serum sample (20 ng mL(-1), 3.4 nM). This method shows great promise in the field of biomarker detection.