Noncovalent sidewall functionalization of single-walled carbon nanotubes for protein immobilization

Precipitation of PEG/Carboxyl-Modified Gold Nanoparticles with Magnesium Pyrophosphate: A New Platform for Real-Time Monitoring of Loop-Mediated Isothermal Amplification

Gold nanoparticles have proven to be promising for decentralized nucleic acid testing by virtue of their simple visual readout and absorbance-based quantification. A major challenge toward their practical application is to achieve ultrasensitive detection without compromising simplicity. The conventional strategy of thermocycling amplification is unfavorable (because of both instrumentation and preparation of thermostable oligonucleotide-modified gold nanoparticle probes). Herein, on the basis of a previously unreported co-precipitation phenomenon between thiolated poly(ethylene glycol)/11-mercaptoundecanoic acid co-modified gold nanoparticles and magnesium pyrophosphate crystals (an isothermal DNA amplification reaction byproduct), a new ultrasensitive and simple DNA assay platform is developed. The binding mechanism underlying the co-precipitation phenomenon is found to be caused by the complexation of carboxyl and pyrophosphate with free magnesium ions. Remarkably, poly(ethylene glycol) does not hinder the binding and effectively stabilizes gold nanoparticles against magnesium ion-induced aggregation (without pyrophosphate). In fact, a similar phenomenon is observed in other poly(ethylene glycol)- and carboxyl-containing nanomaterials. When the gold nanoparticle probe is incorporated into a loop-mediated isothermal amplification reaction, it remains as a red dispersion for a negative sample (in the absence of a target DNA sequence) but appears as a red precipitate for a positive sample (in the presence of a target). This results in a first-of-its-kind gold nanoparticle-based DNA assay platform with isothermal amplification and real-time monitoring capabilities.

Functionalized single-walled carbon nanotubes: cellular uptake, biodistribution and applications in drug delivery

The unique properties of single-walled carbon nanotubes (SWNTs) enable them to play important roles in many fields. One of their functional roles is to transport cargo into cell. SWNTs are able to traverse amphipathic cell membranes due to their large surface area, flexible interactions with cargo, customizable dimensions, and surface chemistry. The cargoes delivered by SWNTs include peptides, proteins, nucleic acids, as well as drug molecules for therapeutic purpose. The drug delivery functions of SWNTs have been explored over the past decade. Many breakthrough studies have shown the high specificity and potency of functionalized SWNT-based drug delivery systems for the treatment of cancers and other diseases. In this review, we discuss different aspects of drug delivery by functionalized SWNT carriers, diving into the cellular uptake mechanisms, biodistribution of the delivery system, and safety concerns on degradation of the carriers. We emphasize the delivery of several common drugs to highlight the recent achievements of SWNT-based drug delivery.

Nanoscale hybrid systems based on carbon nanotubes for biological sensing and control

This paper provides a concise review on the recent development of nanoscale hybrid systems based on carbon nanotubes (CNTs) for biological sensing and control. CNT-based hybrid systems have been intensively studied for versatile applications of biological interfaces such as sensing, cell therapy and tissue regeneration. Recent advances in nanobiotechnology not only enable the fabrication of highly sensitive biosensors at nanoscale but also allow the applications in the controls of cell growth and differentiation. This review describes the fabrication methods of such CNT-based hybrid systems and their applications in biosensing and cell controls.

Thermal and aqueous stability improvement of graphene oxide enhanced diphenylalanine nanocomposites

Nanocomposites of diphenylalanine (FF) and carbon based materials provide an opportunity to overcome drawbacks associated with using FF micro- and nanostructures in nanobiotechnology applications, in particular their poor structural stability in liquid solutions. In this study, FF/graphene oxide (GO) composites were found to self-assemble into layered micro- and nanostructures, which exhibited improved thermal and aqueous stability. Dependent on the FF/GO ratio, the solubility of these structures was reduced to 35.65% after 30 min as compared to 92.4% for pure FF samples. Such functional nanocomposites may extend the use of FF structures to e.g. biosensing, electrochemical, electromechanical or electronic applications.

Adsorption of DNA binding proteins to functionalized carbon nanotube surfaces with and without DNA wrapping

We examined the adsorption of DNA binding proteins on functionalized, single-walled carbon nanotubes (SWNTs). When SWNTs were functionalized with polyethylene glycol (PEG-SWNT), moderate adsorption of protein molecules was observed. In contrast, nanotubes functionalized with CONH₂ groups (CONH₂-SWNT) exhibited very strong interactions between the CONH₂-SWNT and DNA binding proteins. Instead, when these SWNT surfaces were wrapped with DNA molecules (thymine 30-mers), protein binding was a little decreased. Our results revealed that DNA wrapped PEG-SWNT was one of the most promising candidates to realize DNA nanodevices involving protein reactions on DNA-SWNT surfaces. In addition, the DNA binding protein RecA was more adhesive than single-stranded DNA binding proteins to the functionalized SWNT surfaces.

Amino Acid Analogue-Conjugated BN Nanomaterials in a Solvated Phase: First Principles Study of Topology-Dependent Interactions with a Monolayer and a (5,0) Nanotube

Using density functional theory and an implicit solvation model, the relationship between the topology of boron nitride (BN) nanomaterials and the protonated/deprotonated states of amino acid analogues is investigated. In the solvated phase, the calculated results show distinct "physisorbed versus chemisorbed" conditions for the analogues of arginine (Arg)- and aspartic acid (Asp)-conjugated BN nanomaterials, including a monolayer (ML) and a small-diameter zigzag nanotube (NT). Such a distinction does not depend on the functional groups of amino acids but rather depends on the curvature-induced interactions associated with the tubular configuration. Arg and Asp interact with the BNML to form physisorbed complexes irrespective of the state of the amino acids in the solvated phase. For the NT, Arg and Asp form chemisorbed complexes, and the distinct nature of bonds between the donor electron moieties of N_(Arg) and O_(Asp) and the boron of the tubular surface is revealed by the natural bond orbital analysis; stronger s-type bonds for the deprotonated conjugated complexes and slightly weaker p-type dominated bonds for the protonated conjugated complexes. The interaction of neutral Trp with BN nanomaterials results in physisorbed configurations through π-stacking interactions with the indole ring of the Trp and BN nanomaterials. The calculated results form the basis for a theoretical study of more complex protein macromolecules interacting with nanomaterials under physiological conditions.

An Overview of Carbon Nanotubes and Graphene for Biosensing Applications

With the development of carbon nanomaterials in recent years, there has been an explosion of interests in using carbon nanotubes (CNTs) and graphene for developing new biosensors. It is believed that employing CNTs and graphene as sensor components can make sensors more reliable, accurate, and fast due to their remarkable properties. Depending on the types of target molecular, different strategies can be applied to design sensor device. This review article summarized the important progress in developing CNT- and graphene-based electrochemical biosensors, field-effect transistor biosensors, and optical biosensors. Although CNTs and graphene have led to some groundbreaking discoveries, challenges are still remained and the state-of-the-art sensors are far from a practical application. As a conclusion, future effort has to be made through an interdisciplinary platform, including materials science, biology, and electric engineering.

Recent advances in controlling the internal and external properties of self-assembling cyclic peptide nanotubes and dimers

Tuning the internal and external properties of self-assembling cyclic peptide nanotubes.

New insights into the spectral, thermal and morphological analysis of time dependent structural changes during open end functionalization of single walled carbon nanotubes

Acid functionalization inserts different types of functionalities on SWCNTs at different time intervals.

Computational studies on the interactions of glycine amino acid with graphene, h-BN and h-SiC monolayers

In the present work, the adsorption of glycine amino acid and its zwitterionic form onto three different hexagonal sheets, namely graphene, boron-nitride (h-BN) and silicon carbide (h-SiC), has been investigated within the framework of density functional theory (DFT) calculations.

Single-walled carbon nanotubes as optical probes for bio-sensing and imaging

A review on the applications of single-walled carbon nanotube photoluminescence in biomolecular sensing and biomedical imaging.

An electrochemically reduced graphene oxide chemiresistive sensor for sensitive detection of Hg2+ ion in water samples

Divalent mercuric (Hg²⁺) ion is one of the most prevalent forms of mercury species in waters with high toxicity and bioaccumulation in the human body, for which sensitive and selective detection methods are highly necessary to carry out its recognition and quantification. Here an electrochemically reduced graphene oxide (RGO) based chemiresistive sensor was constructed and used for the detection of Hg²⁺ ion in various water samples. Monolayer GO sheets were assembled onto interdigitated electrodes, followed by reduction through linear sweep voltammetry and then modification with a single-stranded DNA aptamer. The electrochemically derived RGO based sensor showed selective response to as low as 0.5nMHg²⁺ ion in presence of other metal ions and matrices. A comparison between chemiresistive sensors prepared with electrochemically and chemically derived RGO showed that the former had better response performance for sensing Hg²⁺ ion. The proposed method provides a simple tool for rapid, selective and sensitive monitoring of Hg²⁺ ion in environmental samples.

Specific detection of biomolecules in physiological solutions using graphene transistor biosensors

Nanomaterial-based field-effect transistor (FET) sensors are capable of label-free real-time chemical and biological detection with high sensitivity and spatial resolution, although direct measurements in high-ionic-strength physiological solutions remain challenging due to the Debye screening effect. Recently, we demonstrated a general strategy to overcome this challenge by incorporating a biomolecule-permeable polymer layer on the surface of silicon nanowire FET sensors. The permeable polymer layer can increase the effective screening length immediately adjacent to the device surface and thereby enable real-time detection of biomolecules in high-ionic-strength solutions. Here, we describe studies demonstrating both the generality of this concept and application to specific protein detection using graphene FET sensors. Concentration-dependent measurements made with polyethylene glycol (PEG)-modified graphene devices exhibited real-time reversible detection of prostate specific antigen (PSA) from 1 to 1,000 nM in 100 mM phosphate buffer. In addition, comodification of graphene devices with PEG and DNA aptamers yielded specific irreversible binding and detection of PSA in pH 7.4 1x PBS solutions, whereas control experiments with proteins that do not bind to the aptamer showed smaller reversible signals. In addition, the active aptamer receptor of the modified graphene devices could be regenerated to yield multiuse selective PSA sensing under physiological conditions. The current work presents an important concept toward the application of nanomaterial-based FET sensors for biochemical sensing in physiological environments and thus could lead to powerful tools for basic research and healthcare.

Reliable Diameter Control of Carbon Nanotube Nanobundles Using Withdrawal Velocity

Carbon nanotube (CNT) nanobundles are widely used in nanoscale imaging, fabrication, and electrochemical and biological sensing. The diameter of CNT nanobundles should be controlled precisely, because it is an important factor in determining electrode performance. Here, we fabricated CNT nanobundles on tungsten tips using dielectrophoresis (DEP) force and controlled their diameters by varying the withdrawal velocity of the tungsten tips. Withdrawal velocity pulling away from the liquid-air interface could be an important, reliable parameter to control the diameter of CNT nanobundles. The withdrawal velocity was controlled automatically and precisely with a one-dimensional motorized stage. The effect of the withdrawal velocity on the diameter of CNT nanobundles was analyzed theoretically and compared with the experimental results. Based on the attachment efficiency, the withdrawal velocity is inversely proportional to the diameter of the CNT nanobundles; this has been demonstrated experimentally. Control of the withdrawal velocity will play an important role in fabricating CNT nanobundles using DEP phenomena.

Nanoelectronic Heterodyne Sensor: A New Electronic Sensing Paradigm

Nanoelectronic devices based on nanomaterials such as nanowires, carbon nanotubes, graphene, and other 2D nanomaterials offer extremely large surface-to-volume ratios, high carrier mobility, low power consumption, and high compatibility for integration with modern electronic technologies. These distinct advantages promise great potential for nanoelectronic devices as next generation chemical and biological sensors. Currently, majority of existing nanoelectronic sensors are direct current (DC) sensors, which rely ubiquitously on detection of conductance change associated with molecular adsorption. However, despite the simplicity of the conventional DC sensing technology, it also has severe limitations such as the Debye screening effect in ionic solutions, and the speed-sensitivity trade-off for the detection of charge-neutral molecules. Hence, the development of nanoelectronic sensors calls for new sensing platform technologies that can truly showcase the advantages of electronic sensors. In this Account, we will summarize recent efforts from our group on the development of a new electronic sensing paradigm, the nanoelectronic heterodyne sensors. Unlike conventional charge-detection based sensors, the heterodyne sensor explores the frequency mixing response between molecular dipoles and a nanoscale transistor. As an example, we first discuss the capability of heterodyne sensing in gas sensing applications by using graphene devices. Rapid (down to 0.1 s) and sensitive (down to 1 ppb) detection of a wide range of vapor analytes is achieved, representing orders of magnitude improvement over state-of-the-art nanoelectronic sensors. Furthermore, the heterodyne sensing technique enables electrical probing and tuning of the noncovalent physisorption of polar molecules on graphene surface for the first time. These results provide insight into small molecule-nanomaterial interaction dynamics and signify the ability to electrically tailor interactions, which can lead to rational designs of complex chemical processes for catalysis and drug discovery. Finally, we discuss the application of heterodyne sensing in solution for chemical and biological sensors by using carbon nanotube devices. The fundamental ionic screening effect can be mitigated by operating carbon nanotube field effect transistor as a heterodyne biosensor. Electrical detection of streptavidin binding to biotin in 100 mM buffer solution can be achieved at a frequency beyond 1 MHz. The results should promise a new biosensing platform for point-of-care detection, where biosensors functioning directly in physiologically relevant condition are desired.

Bioelectronic Nose Using Odorant Binding Protein-Derived Peptide and Carbon Nanotube Field-Effect Transistor for the Assessment of Salmonella Contamination in Food

Salmonella infection is the one of the major causes of food borne illnesses including fever, abdominal pain, diarrhea, and nausea. Thus, early detection of Salmonella contamination is important for our healthy life. Conventional detection methods for the food contamination have limitations in sensitivity and rapidity; thus, the early detection has been difficult. Herein, we developed a bioelectronic nose using a carbon nanotube (CNT) field-effect transistor (FET) functionalized with Drosophila odorant binding protein (OBP)-derived peptide for easy and rapid detection of Salmonella contamination in ham. 3-Methyl-1-butanol is known as a specific volatile organic compound, generated from the ham contaminated with Salmonella. We designed and synthesized the peptide based on the sequence of the Drosophila OBP, LUSH, which specifically binds to alcohols. The C-terminus of the synthetic peptide was modified with three phenylalanine residues and directly immobilized onto CNT channels using the π-π interaction. The p-type properties of FET were clearly maintained after the functionalization using the peptide. The biosensor detected 1 fM of 3-methyl-1-butanol with high selectivity and successfully assessed Salmonella contamination in ham. These results indicate that the bioelectronic nose can be used for the rapid detection of Salmonella contamination in food.

Static micro-array isolation, dynamic time series classification, capture and enumeration of spiked breast cancer cells in blood: the nanotube-CTC chip

We demonstrate the rapid and label-free capture of breast cancer cells spiked in blood using nanotube-antibody micro-arrays. 76-element single wall carbon nanotube arrays were manufactured using photo-lithography, metal deposition, and etching techniques. Anti-epithelial cell adhesion molecule (anti-EpCAM), Anti-human epithelial growth factor receptor 2 (anti-Her2) and non-specific IgG antibodies were functionalized to the surface of the nanotube devices using 1-pyrene-butanoic acid succinimidyl ester. Following device functionalization, blood spiked with SKBR3, MCF7 and MCF10A cells (100/1000 cells per 5 μl per device, 170 elements totaling 0.85 ml of whole blood) were adsorbed on to the nanotube device arrays. Electrical signatures were recorded from each device to screen the samples for differences in interaction (specific or non-specific) between samples and devices. A zone classification scheme enabled the classification of all 170 elements in a single map. A kernel-based statistical classifier for the 'liquid biopsy' was developed to create a predictive model based on dynamic time warping series to classify device electrical signals that corresponded to plain blood (control) or SKBR3 spiked blood (case) on anti-Her2 functionalized devices with ∼90% sensitivity, and 90% specificity in capture of 1000 SKBR3 breast cancer cells in blood using anti-Her2 functionalized devices. Screened devices that gave positive electrical signatures were confirmed using optical/confocal microscopy to hold spiked cancer cells. Confocal microscopic analysis of devices that were classified to hold spiked blood based on their electrical signatures confirmed the presence of cancer cells through staining for DAPI (nuclei), cytokeratin (cancer cells) and CD45 (hematologic cells) with single cell sensitivity. We report 55%-100% cancer cell capture yield depending on the active device area for blood adsorption with mean of 62% (∼12 500 captured off 20 000 spiked cells in 0.1 ml blood) in this first nanotube-CTC chip study.

Provenance information as a tool for addressing engineered nanoparticle reproducibility challenges

Nanoparticles of various types are of increasing research and technological importance in biological and other applications. Difficulties in the production and delivery of nanoparticles with consistent and well defined properties appear in many forms and have a variety of causes. Among several issues are those associated with incomplete information about the history of particles involved in research studies, including the synthesis method, sample history after synthesis, including time and nature of storage, and the detailed nature of any sample processing or modification. In addition, the tendency of particles to change with time or environmental condition suggests that the time between analysis and application is important and some type of consistency or verification process can be important. The essential history of a set of particles can be identified as provenance information and tells the origin or source of a batch of nano-objects along with information related to handling and any changes that may have taken place since it was originated. A record of sample provenance information for a set of particles can play a useful role in identifying some of the sources and decreasing the extent of particle variability and the lack of reproducibility observed by many researchers.

Horizontally Aligned Carbon Nanotube Based Biosensors for Protein Detection

A novel horizontally aligned single-walled carbon nanotube (CNT) Field Effect Transistor (FET)-based biosensing platform for real-time and sensitive protein detections is proposed. Aligned nanotubes were synthesized on quartz substrate using catalyst contact stamping, surface-guided morphological growth and chemical vapor deposition gas-guided growth methods. Real-time detection of prostate-specific antigen (PSA) using as-prepared FET biosensors was demonstrated. The kinetic measurements of the biosensor revealed that the drain current (I_d) decreased exponentially as the concentration of PSA increased, indicating that the proposed FET sensor is capable of quantitative protein detection within a detection window of up to 1 µM. The limit of detection (LOD) achieved by the proposed platform was demonstrated to be 84 pM, which is lower than the clinically relevant level (133 pM) of PSA in blood. Additionally, the reported aligned CNT biosensor is a uniform sensing platform that could be extended to real-time detections of various biomarkers.

Scalable Production of High-Sensitivity, Label-Free DNA Biosensors Based on Back-Gated Graphene Field Effect Transistors

Scalable production of all-electronic DNA biosensors with high sensitivity and selectivity is a critical enabling step for research and applications associated with detection of DNA hybridization. We have developed a scalable and very reproducible (>90% yield) fabrication process for label-free DNA biosensors based upon graphene field effect transistors (GFETs) functionalized with single-stranded probe DNA. The shift of the GFET sensor Dirac point voltage varied systematically with the concentration of target DNA. The biosensors demonstrated a broad analytical range and limit of detection of 1 fM for 60-mer DNA oligonucleotide. In control experiments with mismatched DNA oligomers, the impact of the mismatch position on the DNA hybridization strength was confirmed. This class of highly sensitive DNA biosensors offers the prospect of detection of DNA hybridization and sequencing in a rapid, inexpensive, and accurate way.

Label-free graphene biosensor targeting cancer molecules based on non-covalent modification

A label-free immunosensor based on antibody-modified graphene field effect transistor (GFET) was presented. Antibodies targeting carcinoembryonic antigen (Anti-CEA) were immobilized to the graphene surface via non-covalent modification. The bifunctional molecule, 1-pyrenebutanoic acid succinimidyl ester, which is composed of a pyrene and a reactive succinimide ester group, interacts with graphene non-covalently via π-stacking. The succinimide ester group reacts with the amine group to initiate antibody surface immobilization, which was confirmed by X-ray Photoelectron Spectroscopy, Atomic Force Microscopy and Electrochemical Impedance Spectroscopy. The resulting anti-CEA modified GFET sufficiently monitored the reaction between CEA protein and anti-CEA in real-time with high specificity, which revealed selective electrical detection of CEA with a limit of detection (LOD) of less than 100pg/ml. The dissociation constant between CEA protein and anti-CEA was estimated to be 6.35×10^-11M, indicating the high affinity and sensitivity of anti-CEA-GFET. Taken together, the graphene biosensors provide an effective tool for clinical application and point-of-care medical diagnostics.

A Reduced Graphene Oxide Based Radio Frequency Glucose Sensing Device Using Multi-Dimensional Parameters

A reduced graphene oxide (RGO) based glucose sensor using a radio frequency (RF) signal is demonstrated. An RGO with outstanding electrical property was employed as the interconnector material between signal electrodes in an RF electric circuit, and it was functionalized with phenylbutyric acid (PBA) as a linker molecule to bind glucoses. By adding glucose solution, the fabricated sensor with RGO and PBA showed detecting characteristics in RF signal transmission and reflection. Frequency dependent electrical parameters such as resistance, inductance, shunt conductance and shunt capacitance were extracted from the RF results under the equivalent circuit model. These parameters also provided sensing characteristics of glucose with different concentrations. Using these multi-dimensional parameters, the RF sensor device detected glucose levels in the range of 1–4 mM, which ordinarily covers the testing range for diabetes or medical examination. The RGO based RF sensor, which fits well to a linear curve with fine stability, holds considerable promise for biomaterials detection, including glucose.

Segmentation and additive approach: A reliable technique to study noncovalent interactions of large molecules at the surface of single-wall carbon nanotubes

This investigation explores a new protocol, named Segmentation and Additive approach (SAA), to study exohedral noncovalent functionalization of single-walled carbon nanotubes with large molecules, such as polymers and biomolecules, by segmenting the entire system into smaller units to reduce computational cost. A key criterion of the segmentation process is the preservation of the molecular structure responsible for stabilization of the entire system in smaller segments. Noncovalent interaction of linoleic acid (LA, C18 H32 O2 ), a fatty acid, at the surface of a (10,0) zigzag nanotube is considered for test purposes. Three smaller segmented models have been created from the full (10,0)-LA system and interaction energies were calculated for these models and compared with the full system at different levels of theory, namely ωB97XD, LDA. The success of this SAA is confirmed as the sum of the interaction energies is in very good agreement with the total interaction energy. Besides reducing computational cost, another merit of SAA is an estimation of the contributions from different sections of the large system to the total interaction energy which can be studied in-depth using a higher level of theory to estimate several properties of each segment. On the negative side, bulk properties, such as HOMO-LUMO (highest occupied molecular orbital - lowest occupied molecular orbital) gap, of the entire system cannot be estimated by adding results from segment models. © 2016 Wiley Periodicals, Inc.

Nanohelices from planar polymer self-assembled in carbon nanotubes

The polymer possessing with planar structure can be activated and guided to encapsulate the inner space of SWNT and form a helix through van der Waals interaction and the π-π stacking effect between the polymer and the inner surface of SWNT. The SWNT size, the nanostructure and flexibility of polymer chain are all determine the final structures. The basic interaction between the polymer and the nanotubes is investigated, and the condition and mechanism of the helix-forming are explained particularly. Hybrid polymers improve the ability of the helix formation. This study provides scientific basis for fabricating helical polymers encapsulated in SWNTs and eventually on their applications in various areas.

Electrostatic gating in carbon nanotube aptasensors

Synthetic DNA aptamer receptors could boost the prospects of carbon nanotube (CNT)-based electronic biosensors if signal transduction can be understood and engineered. Here, we report CNT aptasensors for potassium ions that clearly demonstrate aptamer-induced electrostatic gating of electronic conduction. The CNT network devices were fabricated on flexible substrates via a facile solution processing route and non-covalently functionalised with potassium binding aptamers. Monotonic increases in CNT conduction were observed in response to increasing potassium ion concentration, with a level of detection as low as 10 picomolar. The signal was shown to arise from a specific aptamer-target interaction that stabilises a G-quadruplex structure, bringing high negative charge density near the CNT channel. Electrostatic gating is established via the specificity and the sign of the current response, and by observing its suppression when higher ionic strength decreases the Debye length at the CNT-water interface. Sensitivity towards potassium and selectivity against other ions is demonstrated in both resistive mode and real time transistor mode measurements. The effective device architecture presented, along with the identification of clear response signatures, should inform the development of new electronic biosensors using the growing library of aptamer receptors.

Automated circuit fabrication and direct characterization of carbon nanotube vibrations

Since their discovery, carbon nanotubes have fascinated many researchers due to their unprecedented properties. However, a major drawback in utilizing carbon nanotubes for practical applications is the difficulty in positioning or growing them at specific locations. Here we present a simple, rapid, non-invasive and scalable technique that enables optical imaging of carbon nanotubes. The carbon nanotube scaffold serves as a seed for nucleation and growth of small size, optically visible nanocrystals. After imaging the molecules can be removed completely, leaving the surface intact, and thus the carbon nanotube electrical and mechanical properties are preserved. The successful and robust optical imaging allowed us to develop a dedicated image processing algorithm through which we are able to demonstrate a fully automated circuit design resulting in field effect transistors and inverters. Moreover, we demonstrate that this imaging method allows not only to locate carbon nanotubes but also, as in the case of suspended ones, to study their dynamic mechanical motion.

Integrating carbon nanotubes into electronic devices requires quick and non-invasive imaging of the nanostructures for precision positioning. Here, the authors use the base of the nanotubes to nucleate the growth of optically visible organic nanocrystals, which thus enables simple microscopy.

Fluorescent ampicillin analogues as multifunctional disguising agents against opsonization

Cancer nanomedicines are opening new paradigms in cancer management and recent research points to how they can vastly improve imaging and therapy through multimodality and multifunctionality. However, challenges to achieving optimal efficacy are manifold starting from processing materials and evaluating their intended effectiveness on biological tissue, to developing new strategies aimed at improving transport of these materials through the biological milieu to the target tissue. Here, we report a fluorescent derivative of a beta-lactam antibiotic, ampicillin (termed iAmp) and its multifunctional physicobiochemical characteristics and potential as a biocompatible shielding agent and an effective dispersant. Carbon nanotubes (CNTs) were chosen to demonstrate the efficacy of iAmp. CNTs are known for their versatility and have been used extensively for cancer theranostics as photothermal and photoacoustic agents, but have limited solubility in water and biocompatibility. Traditional dispersants are associated with imaging artifacts and are not fully biocompatible. The chemical structure of iAmp is consistent with a deamination product of ampicillin. Although the four-membered lactam ring is intact, it does not retain the antibiotic properties. The iAmp is an effective dispersant and simultaneously serves as a fluorescent label for single-walled CNTs (SWNTs) with minimal photobleaching. The iAmp also enables bioconjugation of SWNTs to bio-ligands such as antibodies through functional carboxyl groups. Viability tests show that iAmp-coated SWNTs have minimal toxicity. Bio-stability tests under physiological conditions reveal that iAmp coating not only remains stable in a biologically relevant environment with high protein and salt concentrations, but also renders SWNTs transparent against nonspecific protein adsorption, also known as protein corona. Mammalian tissue culture studies with macrophages and opsonins validate that iAmp coating affords immunological resistance to SWNTs. Furthermore, iAmp coating offers protection to SWNTs against their nonspecific adsorption across disparate cell types, which has precluded a targeted strategy, and enables selective molecular targeting. The iAmp can therefore be used as an efficient dispersant, a photostable fluorescent agent, and a biocompatible disguising agent, alleviating CNTs' drawbacks and rendering them suitable for nanotheranostic and drug delivery applications.

Somatostatin Receptor-Mediated Tumor-Targeting Nanocarriers Based on Octreotide-PEG Conjugated Nanographene Oxide for Combined Chemo and Photothermal Therapy

Nano-sized in vivo active targeting drug delivery systems have been developed to a high anti-tumor efficacy strategy against certain cancer-cells-specific. Graphene based nanocarriers with unique physical and chemical properties have shown significant potentials in this aspect. Here, octreotide (OCT), an efficient biotarget molecule, is conjugated to PEGylated nanographene oxide (NGO) drug carriers for the first time. The obtained NGO-PEG-OCT complex shows low toxicity and excellent stability in vivo and is able to achieve somatostatin receptor-mediated tumor-specific targeting delivery. Owing to the high loading efficiency and accurate targeting delivery of anti-cancer drug doxorubicin (DOX), our DOX loaded NGO-PEG-OCT complex offers a remarkably improved cancer-cell-specific cellular uptake, chemo-cytotoxicity, and decreased systemic toxicity compared to free DOX or NGO-PEG. More importantly, due to its strong near-infrared absorption, the NGO-PEG-OCT complex further enhances efficient photothermal ablation of tumors, delivering combined chemo and photothermal therapeutic effect against cancer cells.

Single Molecule Bioelectronics and Their Application to Amplification-Free Measurement of DNA Lengths

As biosensing devices shrink smaller and smaller, they approach a scale in which single molecule electronic sensing becomes possible. Here, we review the operation of single-enzyme transistors made using single-walled carbon nanotubes. These novel hybrid devices transduce the motions and catalytic activity of a single protein into an electronic signal for real-time monitoring of the protein’s activity. Analysis of these electronic signals reveals new insights into enzyme function and proves the electronic technique to be complementary to other single-molecule methods based on fluorescence. As one example of the nanocircuit technique, we have studied the Klenow Fragment (KF) of DNA polymerase I as it catalytically processes single-stranded DNA templates. The fidelity of DNA polymerases makes them a key component in many DNA sequencing techniques, and here we demonstrate that KF nanocircuits readily resolve DNA polymerization with single-base sensitivity. Consequently, template lengths can be directly counted from electronic recordings of KF’s base-by-base activity. After measuring as few as 20 copies, the template length can be determined with <1 base pair resolution, and different template lengths can be identified and enumerated in solutions containing template mixtures.

On-chip FRET Graphene Oxide Aptasensor: Quantitative Evaluation of Enhanced Sensitivity by Aptamer with a Double-stranded DNA Spacer

We propose a molecular design for a biomolecular probe to realize an on-chip graphene oxide (GO) aptasensor with enhanced sensitivity. Here, GO works as an excellent acceptor for fluorescence resonance energy transfer. We inserted a rigid double-stranded DNA as a spacer between the GO surface and the aptamer sequence to extend the distance between a fluorescence dye and the GO surface during molecular recognition. We examined the dependence of the sensitivity on the length of the spacer quantitatively by using a 2×2 linear-array aptasensor. We used the modified aptamer with 10 and 30 base pair (bp) double-stranded DNA spacers. The signal with a 30bp-spacer was about twice as strong that with a 10bp-spacer as regards both thrombin and prostate specific antigen detections. The improvement in the sensitivity was supported by a model calculation that estimated the effect of spacer length on fluorescence recovery efficiency.

Thermoresponsive Ultrathin Membranes with Precisely Tuned Nanopores for High-Flux Separation

With the growing demand for small- and large-scale bioprocesses, advanced membranes with high energy efficiency are highly required. However, conventional polymer-based membranes often have to sacrifice selectivity for permeability. In this work, we report the fabrication of a thermoresponsive composite ultrathin membrane with precisely controlled nanopores for high-throughput separation. The composite membrane is made by grafting a PEG analogue thermoresponsive copolymer onto an ultrathin single-wall carbon nanotubes (SWCNTs) membrane via π-π interaction with no use of the common "grafting from" synthesis approach. The composite membrane exhibits ultrahigh water permeation flux as high as 6430 L m(-2) h(-1) at 40 °C, and more importantly, the pore size of the membrane could be finely adjusted by utilizing the thermoresponsive property of the grafted copolymer. With the temperature changing below and above the lower critical solution temperature (LCST) of the copolymer, the effective pore size of the membrane can be tuned precisely between approximately 12 and 14 nm, which could be applied to effectively separate materials with very small size differences through size sieving.