Sidewalls Of Single-walled Carbon Nanotubes Research Articles

DFT modeling of new composite based on PANI/PVK functionalized With single-walled carbon nanotubes for optoelectronic applications

We present a comparative experimental and theoretical study of the vibrational, optical, and electronic properties of polyaniline at both emeraladine leuco-emeraldine forms and PVK. Our objective is first to select the appropriate form of PANI to be linked with PVK to form a hybrid polymer matrix. Then, on the basis of quantum chemical calculations, we present a theoretical study of a hybrid composite PANI/PVK functionalized with lower radius (5, 5) chiral single-walled carbon nanotubes (SWCNTs). The relationship structure-properties of the resulting nano-composite are proved based on the conformational and optical study made from Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) using B3LYP method with 6-31-G(d) basis set. First, it has been demonstrated that the resulting interaction between PANI and PVK leads to more advantageous properties, such as good optical absorption compatibility with the solar emission spectrum. It has also been found that after the incorporation of SWCNTs into the matrix of PANI/PVK hybrid polymer, a good organization of SWCNTs via π-staking interaction is imposed by polyaniline sequences. However, PVK moieties are grafted on the sidewalls of SWCNTs. Finally, the electronic structure of the resulting hybrid nano-composite PANI/PVK/SWCNTs was carried out with the use of different electrodes on both sides.

Broadband Full-Spectrum Raman Excitation Mapping Reveals Intricate Optoelectronic-Vibrational Resonance Structure of Chirality-Pure Single-Walled Carbon Nanotubes.

The Raman excitation spectra of chirality-pure (6,5), (7,5), and (8,3) single-walled carbon nanotubes (SWCNTs) are explored for homogeneous solid film samples over broad excitation energy and scattering energy ranges using a rapid and relatively simple full spectrum Raman excitation mapping technique. Identification of variation in scattering intensity with sample type and phonon energy related to different vibrational bands is clearly realized. Excitation profiles are found to vary strongly for different phonon modes. Some modes' Raman excitation profiles are extracted, with the G band profile compared to earlier work. Other modes, such as the M and iTOLA modes, have quite sharp resonance profiles and strong resonances. Conventional fixed wavelength Raman spectroscopy can miss these effects on the scattering intensities entirely due to the significant intensity changes observed for small variations in excitation wavelength. Peak intensities for phonon modes traceable to a pristine carbon lattice forming a SWCNT sidewall were greater for high-crystallinity materials. In the case of highly defective SWCNTs, the scattering intensities of the G band and the defect-related D band are demonstrated to be affected both in absolute intensities and in relative ratio, with the ratio that would be measured by single wavelength Raman scattering dependent on the excitation wavelength due to differences in the resonance energy profiles of the two bands. Lastly it is shown that the approach of this contribution yields a clear path toward increasing the rigor and quantification of resonance Raman scattering intensity measurements through tractable corrections of excitation and emission side variations in efficiency with excitation wavelength.

Voltammetric Evidence of Proton Transport through the Sidewalls of Single-Walled Carbon Nanotubes.

Understanding ion transport in solid materials is crucial in the design of electrochemical devices. Of particular interest in recent years is the study of ion transport across 2-dimensional, atomically thin crystals. In this contribution, we describe the use of a host-guest hybrid redox material based on polyoxometalates (POMs) encapsulated within the internal cavities of single-walled carbon nanotubes (SWNTs) as a model system for exploring ion transport across atomically thin structures. The nanotube sidewall creates a barrier between the redox-active molecules and bulk electrolytes, which can be probed by addressing the redox states of the POMs electrochemically. The electrochemical properties of the {POM}@SWNT system are strongly linked to the nature of the cation in the supporting electrolyte. While acidic electrolytes facilitate rapid, exhaustive, reversible electron transfer and stability during redox cycling, alkaline-salt electrolytes significantly limit redox switching of the encapsulated species. By "plugging" the {POM}@SWNT material with C60-fullerenes, we demonstrate that the primary mode of charge balancing is proton transport through the graphenic lattice of the SWNT sidewalls. Kinetic analysis reveals little kinetic isotope effect on the standard heterogeneous electron transfer rate constant, suggesting that ion transport through the sidewalls is not rate-limiting in our system. The unique capacity of protons and deuterons to travel through graphenic layers unlocks the redox chemistry of nanoconfined redox materials, with significant implications for the use of carbon-coated materials in applications ranging from electrocatalysis to energy storage and beyond.

Diameter-Selective Sorting of Single-Walled Carbon Nanotubes Using π-Molecular Tweezers for Energy Materials

Single-walled carbon nanotubes (SWCNTs) have remarkable electrical properties, making them excellent candidate energy materials for applications, such as transistors and thermoelectric devices. However, as-prepared SWCNTs are mixtures of various chiral indices associated with different diameters, and this heterogeneity hinders their practical applications. Therefore, the development of a method for sorting SWCNTs according to the diameter is required. Here, we report one-pot diameter sorting of SWCNTs through noncovalent functionalization with π-molecular tweezers, which act as a structure-selective oligomeric dispersant for SWCNTs. The tweezers are capable of isolating (9,4) SWCNTs and (7,6) SWCNTs with diameters of ∼0.9 nm from as-prepared SWCNTs to a sorting ratio of 90%. This high-diameter selectivity originates from molecular wrapping of the π-molecular tweezers around the SWCNT sidewalls based on π–π and hydrophobic interactions. Our findings are promising not only in terms of developing a suitable SWCNT sorting methodology but also for understanding their molecular-level sorting mechanism.

Decoupling Individual Optical Nanosensor Responses Using a Spin-Coated Hydrogel Platform.

Significant advances have been made in fields such as nanotechnology and biomedicine using the unique properties of single-walled carbon nanotubes (SWCNTs). Specifically, SWCNTs are used as near-infrared fluorescence sensors in the solution phase to detect a wide array of biologically relevant analytes. However, solution-based sensing has several limitations, including limited sensitivity and poor spatial resolution. We have therefore devised a new spin-coated poly(ethylene glycol) diacrylate (PEG-DA) hydrogel platform to examine individual DNA-functionalized SWCNTs (DNA-SWCNTs) in their native aqueous state and have subsequently used this platform to investigate the temporal modulations of each SWCNT in response to a model analyte. A strong surfactant, sodium deoxycholate (SDC), was chosen as the model analyte as it rapidly exchanges with DNA oligonucleotides on the SWCNT surface, modulating several optical properties of the SWCNTs and demonstrating multiparameter analyte detection. Upon addition of SDC, we observed time-dependent spectral modulations in the emission center wavelengths and peak intensities of the individual SWCNTs, indicative of a DNA-to-surfactant exchange process. Interestingly, we found that the modulations in the peak intensities, as determined by kinetic data, were significantly delayed when compared to their center wavelength counterparts, suggesting a potential decoupling of the response of these two spectral features. We used a 1-D diffusion model to relate the local SDC concentration to the spectral response of each SWCNT and created dose-response curves. The peak intensity shifts at a higher SDC concentration than the center wavelength, indicating a potential change in the conformation of the surfactant molecules adsorbed to the SWCNT sidewall after the initial exchange process. This platform allows for a unique single-molecule analysis technique that is significantly more sensitive and modifiable than utilizing SWCNTs in the solution phase.

Interactions of amine functional group with Stone-Wales defects on single-walled carbon nanotubes: A theoretical study

Spin-polarized density functional theory has been used to investigate the functionalization of single-walled carbon nanotubes (SWNT) with and without a Stone-Wales (SW) defect by amine (NH2) functional group. The reactivity of SW defects is compared to that of the pristine sidewalls of (5,0), (8,0), and (13,0) SWNT. Our calculations demonstrate that the adsorption of NH2 on SW defect sites is more energetically favorable than that on pristine SWNT sidewalls. All SW defect sites, and particularly the site S1, were considered low-energy adsorption sites for the functionalization process. Furthermore, the binding between the amine group and SW-SWNT is improved for tubes with smaller diameters. The adsorption of NH2 groups on defect sites has a significant influence on the electronic properties of SWNT, changing the electronic states around the Fermi level and converting nonmagnetic semiconductor SWNT to magnetic nanotubes, which is beneficial for the electrical conductivity.

Exploring the Covalent Doping of Single-Wall Carbon Nanotubes Induced By Photoexcited Hypochlorite

Chemical functionalization of the sidewalls of single-wall carbon nanotubes remains a topic of current interest because it can modify and enhance nanotube optical properties. These modifications can shift SWCNT structure-specific optical transitions further into the near-infrared, which may prove useful for applications in bio-imaging or quantum information processing. Here we present a study on the use of photoexcited hypochlorite ions as a reactant to efficiently produce sparse oxygen-containing defects in SWCNTs. Our studies highlight the formation of new secondary reaction products in the absence of dissolved oxygen. These results in combination with quantum computations provide insight into the structure of the new photoadducts. Additionally, we find that product spectra depend on pH of the reacting system, implying more than one reaction pathway. This finding is supported by measurements of the effects of radical quenchers on product properties. Our results provide improved understanding and control of an important class of nanotube functionalization reactions.

(Digital Presentation) Realistic Molecular Dynamics Modeling of ssDNA/SWCNT Hybrids

Despite the importance of single-wall carbon nanotubes (SWCNTs) coated with short oligos of single-stranded DNA (ssDNA), the structure-specific interactions in these hybrids remain poorly understood. It is known that the interactions can depend on the DNA base sequence and length, and on the nanotube diameter and roll-up angle. To study these phenomena, we are applying a combination of computational and experimental methods. A major goal for guiding and validating molecular dynamics simulations of the hybrid structures is finding the average length of nanotube covered by each ssDNA oligo. We have quantified this by carefully preparing dialyzed aqueous dispersions of SWCNTs in specific oligos and then measuring the absolute mass concentrations of both components using total organic carbon analysis. Corresponding absorption spectra were also measured to deduce ultraviolet SWCNT molar absorptivities (structurally averaged), which in combination with known ssDNA nucleobase absorptivities allow quicker determinations of mass ratios in the hybrids. Our results for a library of hybrids indicate that purine nucleobases on average cover a larger region on the nanotube surface than do pyrimidine nucleobases, as is consistent with the sizes of those aromatic structures. This average coverage is key to developing realistic atomistic molecular dynamics models for the conformations of ssDNA adsorbed on SWCNT sidewalls. Examples of such computed hybrid structures and their significance will be presented.

(Invited) Theoretical Insight into New Strategies of Carbon Nanotube Functionalization

An intentional introduction of quantum defects to the single-walled carbon nanotube (SWCNT) surface leads to unique photoluminescence properties that may be useful for a wide range of optoelectronic, sensing, imaging and quantum communication applications. Quantum-chemical simulations help to rationalize spectroscopic observation and fine tune synthetic strategies. I will overview photosynthetic control of chemical binding configurations of quantum defects through the spin multiplicity of photoexcited intermediates. Here photoexcited aromatics react with SWCNT sidewalls to undergo a singlet-state pathway in the presence of dissolved oxygen, leading to ortho binding configurations of the aryl group on the nanotube. In contrast, the oxygen-free photoreaction activates previously inaccessible para configurations through a triplet-state mechanism. To understand the atomistic mechanism of these photo-activated reactions and their dependence on spin multiplicity, we have modeled the reaction with and without triplet quenching using density functional theory. Computed reaction pathways demonstrate selectivity and dependence of outcomes of the photo-activated reaction on the presence or absence of triplet quenching, corresponding to presence or absence of oxygen, respectively. Such spin-selective photochemistry diversifies SWCNT emission tunability by controlling the morphology of the emitting sites.

Arresting Photodegradation in Semiconducting Single-Walled Carbon Nanotube Thin Films

Solid-state dispersions of isolated single-walled carbon nanotubes (SWCNTs) in polymer matrices or networks of electronically coupled SWCNTs are gaining interest for a broad variety of optoelectronic applications. However, little is known about either the stability or degradation mechanisms of these systems. We show dramatic sp2-to-sp3 defect transformations of the SWCNT sidewall when either the S11 or S22 exciton transitions are optically pumped in ambient conditions, leading to the rapid decay of absorption and emission properties in less than 24 h for conditions similar to exposure to solar illumination. Importantly, we demonstrate that either (i) encapsulation to block reactive O2 from SWCNT excited states or (ii) exciton quenching via donor-to-acceptor electron transfer is an effective route for “kinetic stabilization” against photodegradation, with <8% loss in absorbance after 1200 h of illumination. We find that SWCNT:polymer loading does not impact degradation. Our study suggests that the sp3 defects are associated with the formation of oxygenic groups on the SWCNT sidewall. While such defect populations can detrimentally evolve over time in films where SWCNTs are environmentally exposed in the presence of light, we offer multiple pathways to arrest this degradation and enable their robust application as advanced optical materials in optical and electronic devices.

Molecular dynamics studies for enhancing the anticancer drug efficacy: Toward designing a new carbon nanotube-based paclitaxel delivery system

The promising outcomes for biological applications of single-walled carbon nanotubes (SWCNTs) including biomolecules carriers have been reported before. Therefore, the investigation of the interactions of these nano-vectors with drug molecules can provide fundamental knowledge to design appropriate SWCNT-based carriers for drug delivery purposes. The current study addressed the underlying mechanism of a widely-used anticancer drug, paclitaxel (PTX), loading on the pristine SWCNT as well as that functionalized with (-OH), (-COOH), and PW3 peptide (a biologically compatible peptide as a novel candidate for nano-carrier surface modification). The effect of the functional group of nano-carrier on the drug binding was also investigated by all-atom molecular dynamics (MD) simulations. The binding free energy calculations based on the MM-PBSA approach indicated the exothermic and spontaneous adsorption of PTX molecules onto the pristine and modified SWCNTs. The π − π stacking interactions between three separate phenyl rings of PTX and SWCNT sidewall can explain the proper drug adsorption. Moreover, remarkable differences were identified in the arrangements of the aromatic rings toward the surface of nanotubes in the four studied complexes. According to the qualitatively and quantitatively analyses, the PTX drug delivery system exhibited especial effectiveness due to the stronger interactions with the nano-carrier and more water solubility upon coupling with the PW3-functionalized SWCNT at 310 K which could be well explained by microscopic structural evaluations. For the peptide-modified SWCNT system, PTX molecules still prefer to bind the sidewall of the nano-vector rather than the peptides.

Covalent Surface Modification Effects on Single‐Walled Carbon Nanotubes for Targeted Sensing and Optical Imaging

AbstractOptical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single‐walled carbon nanotubes (SWCNTs) can enable real‐time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT's pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence‐based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self‐assemble on passivated microscopy slides, and these dual‐functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.

Photoexcited Aromatic Reactants Give Multicolor Carbon Nanotube Fluorescence from Quantum Defects.

Covalent functionalization of single-wall carbon nanotubes (SWCNTs) can be valuable for modifying their electronic properties and creating fluorescent quantum defects. We report here a previously unreported category of such reactions involving interactions of photoexcited aromatic compounds with SWCNT sidewalls. When aqueous suspensions of SWCNTs are exposed to organic aromatic compounds and then irradiated by UV light, fluorescent defects are formed in the nanotubes at rates that depend on the aromatic ring substituents. In reactions with aniline or iodoaniline, strong spectral sidebands appear within 1 min. Total SWCNT photoluminescence can be enhanced by a factor as large as ∼5. Notably, emission spectra of reacted SWCNTs depend on the presence or absence of dissolved oxygen during the reaction. For (6,5) SWCNTs, treatment when oxygen is present gives an additional emission band red-shifted by 160 meV from the pristine position, whereas treatment without oxygen leads to two additional emission bands red-shifted by 140 and 270 meV. Variance spectroscopy shows the presence of individual "multicolor" nanotubes with three distinct emission bands (pristine plus two shifted). The facile generation of dual fluorescent quantum defects in SWCNTs provides emission closer to standard telecom wavelengths, advancing the prospects for applications as single-photon sources in quantum information processing.

Gas Biosensor Arrays Based on Single-Stranded DNA-Functionalized Single-Walled Carbon Nanotubes for the Detection of Volatile Organic Compound Biomarkers Released by Huanglongbing Disease-Infected Citrus Trees.

Volatile organic compounds (VOCs) released by plants are closely associated with plant metabolism and can serve as biomarkers for disease diagnosis. Huanglongbing (HLB), also known as citrus greening or yellow shoot disease, is a lethal threat to the multi-billion-dollar citrus industry. Early detection of HLB is vital for removal of susceptible citrus trees and containment of the disease. Gas sensors are applied to monitor the air quality or toxic gases owing to their low-cost fabrication, smooth operation, and possible miniaturization. Here, we report on the development, characterization, and application of electrical biosensor arrays based on single-walled carbon nanotubes (SWNTs) decorated with single-stranded DNA (ssDNA) for the detection of four VOCs—ethylhexanol, linalool, tetradecene, and phenylacetaldehyde—that serve as secondary biomarkers for detection of infected citrus trees during the asymptomatic stage. SWNTs were noncovalently functionalized with ssDNA using π–π interaction between the nucleotide and sidewall of SWNTs. The resulting ssDNA-SWNT hybrid structure and device properties were investigated using Raman spectroscopy, ultraviolet (UV) spectroscopy, and electrical measurements. To monitor changes in the four VOCs, gas biosensor arrays consisting of bare SWNTs before and after being decorated with different ssDNA were employed to determine the different concentrations of the four VOCs. The data was processed using principal component analysis (PCA) and neural net fitting (NNF).

Applying AuNPs/SWCNT to fabricate electrical nanogap device for DNA hybridization detection

AuNPs/SWCNT, a hybrid nanomaterial which is single-walled carbon nanotube (SWCNT) modified with gold nanoparticles (AuNPs), has great application prospects for chemical and biological sensors. For the innate nanogap between tiny AuNPs deposited on sidewall of SWCNT, AuNPs/SWCNT is suitable for the fabrication of simple and effective electrical signal switching devices. Here, we develop a novel strategy of applying AuNPs/SWCNT to fabricate nanogap device for DNA hybridization detection. The detection strategy is based on the target DNA mediating the catalytic activity of the AuNPs by desorbing the probe DNA from AuNPs. The signal transduction depends on the growth of tiny AuNPs which is closely related to the AuNPs catalytic activity. Sensing occurs at the tiny AuNPs growing and connecting into a continuous nanowire along the SWCNT, leading to a conductimetric response. The biosensing device can detect target DNA with the detection limit of 1 pM and the ability to discriminate triple and quintuple base pair mismatches.

Theoretical Insight into Configurational Selectivity of Functionalized Single-Walled Carbon Nanotubes Based on the Clar Sextet Theory

Based on Clar’s theory of the aromatic sextet, finite-length models of single-walled carbon nanotubes (SWNTs) have been utilized to study the configurational selectivity of modified SWNTs via covalent functionalization with organic substitutions by density functional theory calculations. After considering near-armchair, near-zigzag, and zigzag SWNTs with distinct chiralities, it is found that the parameter R of semiconducting SWNTs plays a significant role in determining the stability difference of functionalized SWNTs; that is, SWNTs with R = 2 exhibit better configurational selectivity than those with R = 1 when binding the same substituent to the sidewall of SWNTs. Except for the zigzag (7,0) and (10,0) SWNTs with R = 1, the most favorable addition site in the considered SWNTs corresponds to the double bond in their Clar unit cells. The methyl-SWNT radicals with different R values exhibit distinct localizations of the unpaired spin, which is supposed to make a major contribution to the diversity of adducts. The addition sites with the largest spin density lead to the most stable adducts in modifications with small substituents for (6,4), (6,5), (9,1), (8,0), and (11,0) SWNTs, but the correlation tends to disappear for substituents with the increased alkyl chain or bulkiness. Particularly, the bulkiness of alkyl groups is more influential than the alkyl chain length. The degree of bond length change at addition sites is mainly affected by structures of SWNTs, and bulky substituents prefer addition positions in favor of releasing the steric repulsion between substituents. Bond angle changes around addition sites reveal that the extent of sp2 distortion depends on addition sites, and para adducts exhibit much larger sp2 distortion than ortho adducts, resulting in more ideal sp3 carbons. In addition, the increase in the alkyl chain and bulkiness of substituents can weaken the formed C–C bonds between the substituent and SWNT; especially, bulky substituents make the strength of covalent C–C bonds much weaker.

Creating fluorescent quantum defects in carbon nanotubes using hypochlorite and light

Covalent doping of single-walled carbon nanotubes (SWCNTs) can modify their optical properties, enabling applications as single-photon emitters and bio-imaging agents. We report here a simple, quick, and controllable method for preparing oxygen-doped SWCNTs with desirable emission spectra. Aqueous nanotube dispersions are treated at room temperature with NaClO (bleach) and then UV-irradiated for less than one minute to achieve optimized O-doping. The doping efficiency is controlled by varying surfactant concentration and type, NaClO concentration, and irradiation dose. Photochemical action spectra indicate that doping involves reaction of SWCNT sidewalls with oxygen atoms formed by photolysis of ClO− ions. Variance spectroscopy of products reveals that most individual nanotubes in optimally treated samples show both pristine and doped emission. A continuous flow reactor is described that allows efficient preparation of milligram quantities of O-doped SWCNTs. Finally, we demonstrate a bio-imaging application that gives high contrast short-wavelength infrared fluorescence images of vasculature and lymphatic structures in mice injected with only ~100 ng of the doped nanotubes.

Adsorption of free-base phthalocyanine on Stone-Wales defect-containing carbon nanotubes: A DFT study

The present study addresses the influence of topological defects incorporated into sidewalls of single-walled carbon nanotubes (SWNTs) on the strength of noncovalent bonding and the state of adsorbed complex organic molecules. The interaction of free-base phthalocyanine (H2Pc) with Stone-Wales (SW) defect-containing armchair and zigzag nanotube models (ANT and ZNT, respectively) was studied at the PBE-D/DNP and M06-2X/6-31G(d,p) theoretical levels. The results obtained were analyzed by comparing them with those for DFT calculations on similar defect-free nanotube systems, with a particular emphasis on the data accounting for basis set superposition error (BSSE). As a whole, free-base H2Pc adsorbs on SW defect-containing SWNT models stronger than on the parent defect-free nanotubes. In PBE-D calculations, the increase in binding strength varies between 2.01 and 6.31 kcal/mol (0.087 and 0.274 eV), depending on SWNT chirality and defect orientation. In BSSE-corrected M06-2X calculations, this effect is less evident. C(H2Pc)…C(SWNT) are usually the shortest separations, followed by N(H2Pc)…C(SWNT) and H(H2Pc)…C(SWNT). Frontier orbital-related characteristics obtained exhibit insignificant differences as compared to similar systems based on defect-free ANT and ZNT models. For most systems, for both computational techniques HOMO-LUMO gap energies change by less than 0.06 eV. The pattern of HOMO-LUMO orbital distribution was found to be broadly variable.

Ag-doping behavior on (8, 0) single-walled carbon nanotube with single C-vacancy or pyridine-like N3 defect: a DFT study

Single C-vacancy and pyridine-like N3 defect are usually formed on the single-walled carbon nanotube (SWCNT) and they have unique properties for potential applications. In this paper, we use density functional theory to investigate the discrepancies of such two structures from the geometric and electronic aspects. Our results indicate that the existed single vacancy in the SWCNT can lead to somewhat electron localization because of the lone pair electrons; while the N3 embedded SWCNT ( N3-SWCNT) has stronger chemical reactivity and electron localization than the single vacancy SWCNT (SV-SWCNT) due to the great charge transfer between N3 group and C atom on the tube sidewall. Through the investigation of Ag-doping on the above two nano-structures, we found that the single Ag atom is much more stably adsorbed on the N3- SWCNT sidewall compared with SV-SWCNT, forming higher binding energy and higher electron transfer. Our calculation would shed light on the physicochemical property of SWCNT-based material and thus extend their potential applications in many fields.

Carbon Nanotube Biohybrids: From Protein Site-Specific Coupling to the Fabrication of Reconfigurable (multi)Sensing Systems and Devices

We controlled the assembly of different biomolecules, from proteins to DNA and aptamer sequences, on carbon nanotubes (CNTs), so as to couple CNTs electronic output to biomolecular function. First we will present a facile strategy for the site-specific coupling of proteins to single walled carbon nanotubes (SWCNTs): i) in solution and with single-molecule control, with a focus on light harvesting and charge transfer investigations, as well as ii) in device configurations to investigate biomolecular (protein-protein) recognition in the context of antimicrobial resistance enzyme detection. Using an orthogonal Click reaction, Green Fluorescent Protein (GFP) was engineered to contain a genetically encoded azide group and then bound selectively to SWCNT ends in 1:1 nanohybrids with different protein orientations: in close proximity or at longer distances from the GFP’s functional center. Atomic force microscopy and fluorescence analysis in solution and on surfaces at the single-protein level confirmed the importance of bioengineering optimal protein attachment sites to achieve direct protein−nanotube communication and bridging.[1] We will then discuss the extension of this rationale into bioelectornic devices for the development of real-time biosensors with engineered protein interfacing. We assembled different variants of a b-lactamase (BL) inhibitory protein (BLIP) onto SWCNT sidewalls in electronic device configurations. We recorded the current responses in real-time for the detection of different concentrations of a class BL enzymes,[2] that degrade antibiotics, in the context of investigating antimicrobial resistance. (Resistance against the most useful antibiotics, the b-lactams, including the penicillins, is arguably the most pressing issue due to the prevalence of many different BL enzymes that degrade the antibiotic; BLIP acts as the ideal detection element in terms of its specificity to BLs and ability to bind a wide variety of different BLs). Employing a similar strategy, we will report on the fabrication of reconfigurable and solution processable nanoscale biosensing devices with multisensing capability based on SWCNTs functionalized with specific, and different, aptamer sequences employed as selective recognition elements. Distinct, hence water-soluble, SWCNT-aptamer hybrids were immobilized from solution onto different pre-patterned electrodes on the same chip, via a low-cost dielectrophoresis methodology. Multiplexed detection of three different biomarkers indicative of stress and neuro-trauma conditions was successfully performed, and real-time detection was achieved in serum down to physiologically relevant concentrations.[3] Finally, we present a strategy for the controlled assembly of stimuli-responsive end-to-end SWCNT junctions in aqueous solution, employing DNA as a molecular linker. The assembly/disassembly of the nanotubes was controlled via the intrinsic responsiveness to different stimuli of sequence-specific DNA linkers forming the junctions.[4] By and large, we demonstrate novel approaches for the designed assembly of solution-processable bioelectronic systems where single biomolecules modulate the properties of carbon nanotubes.This can yield new insights into biomolecular events down to single-molecule resolution and facilitate biomolecules’ use as integrated nanocomponents in molecular electronics and biosensing devices. [1] Journal of the American Chemical Society, 2017, 139, 17834-17840 [2] Submitted [3] Nano Letters, 2018, 18, 4130-4135 [4] Under 2nd review in Chemistry of Materials