Scalable and Effective Enrichment of Semiconducting Single-Walled Carbon Nanotubes by a Dual Selective Naphthalene-Based Azo Dispersant

Reproducible, Accurate, and Sensitive Food Toxin On-Site Detection with Carbon Nanotube Transistor Biosensors

Field-effect transistor (FET) biosensors based on nanomaterials are promising in the areas of food safety and early disease diagnosis due to their ultrahigh sensitivity and rapid response. However, most academically developed FET biosensors lack real-world reproducibility and comprehensive methodological validation to meet the standards of regulatory bodies. Here, highly uniform and well-packaged semiconducting carbon nanotube (CNT) FET biosensor chips were developed and assessed for the plug-and-play sensing for the rapid and highly sensitive detection of aflatoxin B1 (AFB1) in real food samples to meet international standards. In order to meet the requirements for reproducibility and stability, a scalable residual-free passivation and packaging process was developed for CNT FET biosensors. Portable detection systems were then constructed for on-site detection. The resulting packaged chips were functionalized with nucleic aptamers to enable highly selective detection of AFB1 in food samples with a detection limit (LOD) of 0.55 fg/mL (standard) for AFB1 and cross-reactivity coefficients to interferences as low as 1.8 × 10-7 in simulated solutions. Utilizing the portable detection system, on-site real food detection was achieved with a rapid response time less than 60 s, and LOD of 0.25 pg/kg (standard) in complex corn sample matrices. Single-blind tests demonstrated the ability of the chips to detect AFB1-positive food with 100% accuracy, using a set of 30 peanut samples. Validation experiments confirmed that the detection range, stability, and repeatability met international standards. This study showcased the accuracy, reliability, and potential practical applications of CNT FET biosensor chips in areas such as food safety and rapid biomedical testing.

A review on green synthesis, biological applications of carbon dots in the field of drug delivery, biosensors, and bioimaging

Since the beginning of nanoscience and nanotechnology, carbon dots (CDs) have been the foundational idea and have dominated the growth of the nano-field. CDs are an intriguing platform for utilization in biology, technology, catalysis, and other fields thanks to their numerous distinctive structural, physicochemical, and photochemical characteristics. Since several carbon dots have already been created, they have been assessed based on their synthesis process, and luminescence characteristics. Due to their biocompatibility, less toxic effects, and most significantly their fluorescent features in contrast to other carbon nanostructures, CDs have several benefits. This review focuses on the most recent advancements in the characterization, applications, and synthesis techniques used for CDs made from natural sources. It will also direct scientists in the creation of a synthesis technique for adjustable carbon dots that is more practical, effective, and environmentally benign. With low toxicity and low cost, CDs are meeting the new era's requirements for more selectivity and sensitivity in the detection and sensing of various things, such as biomaterial sensing, enzymes, chemical contamination, and temperature sensing. Its variety of properties, such as optical properties, chemiluminescence, and morphological analysis, make it a good option to use in bioimaging, drug delivery, biosensors, and cancer diagnosis.

Cobalt ferrite/semiconducting single-walled carbon nanotubes based field-effect transistor for determination of carbamate pesticides

Carbaryl and carbofuran are the carbamate pesticides which have been widely used worldwide to control insects in crops and house. If the pesticides entered in to the food products and drinking water, they could cause serious health effects in humans. Therefore, the development of a rapid, simple, sensitive and selective analytical device for on-site detection of carbamates is crucial to evaluate food and environmental samples. Recently, semiconducting single-walled carbon nanotube-based field effect transistors (s-SWCNT/FETs) have shown several advantages such as high carrier mobility, good on/off ratio, quasi ballistic electron transport, label-free detection and real-time response. Herein, cobalt ferrite (CFO) nanoparticles decorated s-SWCNTs have been prepared and used to bridge the source and drain electrodes. As-prepared CFO/s-SWCNT/FET had been used for the non-enzymatic detection of carbaryl and carbofuran. When used as a sensing platform, the CFO/s-SWCNT hybrid film exhibited high sensitivity, and selectivity with a wide linear range of detection from 10 to 100 fMand the lowest limit of detections for carbaryl (0.11 fM) and carbofuran (0.07 fM) were estimated. This sensor was also used to detect carbaryl in tomato and cabbage samples, which confirmed its practical acceptance. Such performance may be attributed to the oxidation of carbamates by potent catalytic activity of CFO, which led to the changes in the charge transfer reaction on the s-SWCNTs/FET conduction channel. This work presents a novel CFO/s-SWCNT based sensing system which could be used to quantify pesticide residues in food samples.

Selective Chemistry-Based Separation of Semiconducting Single-Walled Carbon Nanotubes and Alignment of the Nanotube Array Network under Electric Field for Field-Effect Transistor Applications

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are considered as a replacement for silicon in field-effect transistors (FETs), solar cells, logic circuits, and so forth, because of their outstanding electronic, optical, and mechanical properties. Herein, we have studied the reaction of pristine SWCNTs dispersed in a pluronic F-68 (PF-68) polymer solution with para-amino diphenylamine diazonium sulfate (PADDS) to separate nanotubes based on their metallicity. The preferential selectivity of the reactions was monitored by changes in the semiconducting (S22 and S33) and metallic (M11) bands by ultraviolet-visible-near infrared spectroscopy. Metallic selectivity depended on the concentrations of PADDS, reaction time, and the solution pH. Furthermore, separation of pure s-SWCNTs was confirmed by Raman spectroscopy and Fourier-transform infrared spectroscopy. After the removal of metallic SWCNTs, direct current electric field was applied to the pure s-SWCNT solution, which effectively directed the nanotubes to align in one direction as nanotube arrays with a longer length and high density. After that, electrically aligned s-SWCNT solution was cast on a silicon substrate, and the length of the nanotube arrays was measured as ∼2 to ∼14 μm with an areal density of ∼2 to ∼20 tubes/μm of s-SWCNTs. Next, electrically aligned s-SWCNT arrays were deposited on the channel of the FET device by drop-casting. Field-emission scanning electron microscopy and electrical measurements have been carried out to test the performance of the aligned s-SWCNTs/FETs. The fabricated FETs with a channel length of 10 μm showed stable electrical properties with a field-effect mobility of 30.4 cm2/Vs and a log10 (I on/I off) current ratio of 3.96. We envisage that this new chemical-based separation method and electric field-assisted alignment could be useful to obtain a high-purity and aligned s-SWCNT array network for the fabrication of high-performance FETs to use in digital and analog electronics.

Electrochemical biosensor for methyl parathion based on single-walled carbon nanotube/glutaraldehyde crosslinked acetylcholinesterase-wrapped bovine serum albumin nanocomposites

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been demonstrated as an excellent material for transistors, miniaturized devices and sensors due to their high carrier mobility, stability, scattering-free ballistic transport of carriers etc. Herein, we have designed a biosensor to selectively detect methyl parathion (MP, organophosphorus pesticide) using glutaraldehyde (Glu) cross-linked with acetylcholinesterase (AChE) immobilized on s-SWCNTs wrapped with bovine serum albumin (BSA). The fabricated biosensor was characterized and confirmed by Fourier-transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV). In the presence of MP, the effective interaction between AChE and MP favours the accumulation of MP-AChE complex on the glassy carbon electrode (GCE) surface which reduces the electron transfer property. Based on this interaction, detection of various concentration of MP was demonstrated by SWV using BSA/AChE-Glu-s-SWCNTs composite modified electrode. The proposed biosensor exhibited a wide linear range (WLR) for MP target in 100 mM phosphate buffered saline solution (PBS) (pH 7.4) from 1 × 10^-10 M to 5 × 10^-6 M with a limit of detection (LOD) of 3.75 × 10^-11 M. In addition, the BSA/AChE-Glu-s-SWCNTs/GCE biosensor showed good repeatability and reproducibility for MP detection. Moreover, the proposed biosensor showed better electrode stability when stored at 4 °C. This new electrochemical biosensor is also exhibited high selectivity and sensitivity for MP, which made it possible to test MP in real strawberry and apple juices. Furthermore, the BSA/AChE-Glu-s-SWCNTs/GCE offered a favourable electron transfer between the acetylthiocholine chloride (ATCl) and electrode interface than BSA/AChE-s-SWCNTs/GCE, s-SWCNTs/GCE and bare GCE.

Solution-Processing of High-Purity Semiconducting Single-Walled Carbon Nanotubes for Electronics Devices

High-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) are of paramount significance for the construction of next-generation electronics. Until now, a number of elaborate sorting and purification techniques for s-SWCNTs have been developed, among which solution-based sorting methods show unique merits in the scale production, high purity, and large-area film formation. Here, the recent progress in the solution processing of s-SWCNTs and their application in electronic devices is systematically reviewed. First, the solution-based sorting and purification of s-SWCNTs are described, and particular attention is paid to the recent advance in the conjugated polymer-based sorting strategy. Subsequently, the solution-based deposition and morphology control of a s-SWCNT thin film on a surface are introduced, which focus on the strategies for network formation and alignment of SWCNTs. Then, the recent advances in electronic devices based on s-SWCNTs are reviewed with emphasis on nanoscale s-SWCNTs' high-performance integrated circuits and s-SWCNT-based thin-film transistors (TFT) array and circuits. Lastly, the existing challenges and development trends for the s-SWCNTs and electronic devices are briefly discussed. The aim is to provide some useful information and inspiration for the sorting and purification of s-SWCNTs, as well as the construction of electronic devices with s-SWCNTs.

Nanocalipers as novel molecular scaffolds for carbon nanotubes

Nanocalipers were synthesized by connecting directly the five aromatic moieties including two receptors, two corners and a core, and found to discriminate the diameter, metallicity and handedness of carbon nanotubes through selective complexation.

Selective Dispersion of Highly Pure Large-Diameter Semiconducting Carbon Nanotubes by a Flavin for Thin-Film Transistors

Scalable and simple methods for selective extraction of pure, semiconducting (s) single-walled carbon nanotubes (SWNTs) is of profound importance for electronic and photovoltaic applications. We report a new, one-step procedure to obtain respective large-diameter s- and metallic (m)-SWNT enrichment purity in excess of 99% and 78%, respectively, via interaction between the aromatic dispersing agent and SWNTs. The approach utilizes N-dodecyl isoalloxazine (FC12) as a surfactant in conjunction with sonication and benchtop centrifugation methods. After centrifugation, the supernatant is enriched in s-SWNTs with less carbonaceous impurities, whereas precipitate is enhanced in m-SWNTs. In addition, the use of an increased centrifugal force enhances both the purity and population of larger diameter s-SWNTs. Photoinduced energy transfer from FC12 to SWNTs is facilitated by respective electronic level alignment. Owing to its peculiar photoreduction capability, FC12 can be employed to precipitate SWNTs upon UV irradiation and observe absorption of higher optical transitions of SWNTs. A thin-film transistor prepared from a dispersion of enriched s-SWNTs was fabricated to verify electrical performance of the sorted sample and was observed to display p-type conductance with an average on/off ratio over 10(6) and an average mobility over 10 cm(2)/V·s.

Selective Surface Charge Sign Reversal on Metallic Carbon Nanotubes for Facile Ultrahigh Purity Nanotube Sorting

Semiconducting (semi-) single-walled carbon nanotubes (SWNTs) must be purified of their metallic (met-) counterparts for most applications including nanoelectronics, solar cells, chemical sensors, and artificial skins. Previous bulk sorting techniques are based on subtle contrasts between properties of different nanotube/dispersing agent complexes. We report here a method which directly exploits the nanotube band structure differences. For the heterogeneous redox reaction of SWNTs with oxygen/water couple, the aqueous pH can be tuned so that the redox kinetics is determined by the availability of nanotube electrons only at/near the Fermi level, as predicted quantitatively by the Marcus-Gerischer (MG) theory. Consequently, met-SWNTs oxidize much faster than semi-SWNTs and only met-SWNTs selectively reverse the sign of their measured surface zeta potential from negative to positive at the optimized acidic pH when suspended with nonionic surfactants. By passing the redox-reacted nanotubes through anionic hydrogel beads, we isolate semi-SWNTs to record high electrically verified purity above 99.94% ± 0.04%. This facile charge sign reversal (CSR)-based sorting technique is robust and can sort SWNTs with a broad diameter range.

Printed thin film transistors and CMOS inverters based on semiconducting carbon nanotube ink purified by a nonlinear conjugated copolymer

Two innovative research studies are reported in this paper. One is the sorting of semiconducting carbon nanotubes and ink formulation by a novel semiconductor copolymer and second is the development of CMOS inverters using not the p-type and n-type transistors but a printed p-type transistor and a printed ambipolar transistor. A new semiconducting copolymer (named P-DPPb5T) was designed and synthesized with a special nonlinear structure and more condensed conjugation surfaces, which can separate large diameter semiconducting single-walled carbon nanotubes (sc-SWCNTs) from arc discharge SWCNTs according to their chiralities with high selectivity. With the sorted sc-SWCNTs ink, thin film transistors (TFTs) have been fabricated by aerosol jet printing. The TFTs displayed good uniformity, low operating voltage (±2 V) and subthreshold swing (SS) (122-161 mV dec(-1)), high effective mobility (up to 17.6-37.7 cm(2) V(-1) s(-1)) and high on/off ratio (10(4)-10(7)). With the printed TFTs, a CMOS inverter was constructed, which is based on the p-type TFT and ambipolar TFT instead of the conventional p-type and n-type TFTs. Compared with other recently reported inverters fabricated by printing, the printed CMOS inverters demonstrated a better noise margin (74% 1/2 Vdd) and was hysteresis free. The inverter has a voltage gain of up to 16 at an applied voltage of only 1 V and low static power consumption.

Recent Progress in Obtaining Semiconducting Single-Walled Carbon Nanotubes for Transistor Applications

High purity semiconducting single-walled carbon nanotubes (s-SWCNTs) with a narrow diameter distribution are required for high-performance transistors. Achieving this goal is extremely challenging because the as-grown material contains mixtures of s-SWCNTs and metallic- (m-) SWCNTs with wide diameter distributions, typically inadequate for integrated circuits. Since 2000, numerous ex situ methods have been proposed to improve the purity of the s-SWCNTs. The majority of these techniques fail to maintain the quality and integrity of the s-SWCNTs with a few notable exceptions. Here, the progress in realizing high purity s-SWCNTs in as-grown and post-processed materials is highlighted. A comparison of transistor parameters (such as on/off ratio and field-effect mobility) obtained from test structures establishes the effectiveness of various methods and suggests opportunities for future improvements.

Azo dye functionalized graphene nanoplatelets for selective detection of bisphenol A and hydrogen peroxide

A new electrochemical sensor is developed based on graphene nanoplatelets functionalized with tri-azo dye (direct blue 71) for selective and highly sensitive detection of bisphenol A and hydrogen peroxide in pH 7 phosphate buffered saline solution.

Effect of side-chain halogenation on the interactions of conjugated polymers with SWNTs

Halogenation of polyfluorene side-chain ends with bromine or iodine causes significant differences in the nanotube species that are dispersed in solvent, indicating that subtle changes in polymer structure can affect polymer-nanotube interactions.

Effect of surface wettability properties on the electrical properties of printed carbon nanotube thin-film transistors on SiO2/Si substrates

The precise placement and efficient deposition of semiconducting single-walled carbon nanotubes (sc-SWCNTs) on substrates are challenges for achieving printed high-performance SWCNT thin-film transistors (TFTs) with independent gates. It was found that the wettability of the substrate played a key role in the electrical properties of TFTs for sc-SWCNTs sorted by poly[(9,9-dioctylfluorene-2,7-diyl)-co-(1,4-benzo-2,1,3-thiadiazole)] (PFO-BT). In the present work we report a simple and scalable method which can rapidly and selectively deposit a high concentration of sc-SWCNTs in TFT channels by aerosol-jet-printing. The method is based on oxygen plasma treatment of substrates, which tunes the surface wettability. TFTs printed on the treated substrates demonstrated a low operation voltage, small hysteresis, high mobility up to 32.3 cm(2) V(-1) s(-1), and high on/off ratio up to 10(6) after only two printings. Their mobilities were 10 and 30 times higher than those of TFTs fabricated on untreated and low-wettability substrates. The uniformity of printed TFTs was also greatly improved. Inverters were constructed by printed top-gate TFTs, and a maximum voltage gain of 17 at Vdd = 5 V was achieved. The mechanism of such improvements is that the PFO-BT-functionalized sc-SWCNTs are preferably immobilized on the oxygen plasma treated substrates due to the strong hydrogen bonds between sc-SWCNTs and hydroxyl groups on the substrates.

Effects of the chemical structure of polyfluorene on selective extraction of semiconducting single-walled carbon nanotubes

The selective recognition/extraction of semiconducting (sem)- and metallic (met)-single-walled carbon nanotubes (SWNTs) is still a great challenge in the science and technology of carbon nanotubes because their selective synthesis is still difficult. Poly(9,9-dioctyl-fluorene-2,7-diyl) (2C8-PF) and its derivatives are widely used polymers in carbon nanotube science and technology since they only extract sem-SWNTs from the mixture of sem-/met-SWNTs, while the separation mechanism is still unclear. In this study, we focus on the alkyl chain number on the polyfluorenes (PFs) to understand the mechanism for selective recognition. Here we describe the synthesis of mono-octyl moiety-carrying polyfluorene (poly(9-octyl-9H-fluorene-2,7-diyl), C8H-PF), and characterized its selective SWNT recognition/extraction ability, and found that the C8H-PF solubilized sem-SWNTs with a diameter of 0.9-1.1 nm, whose behavior is similar to that of 2C8-PF. In addition, C8H-PF selectively extracted sem-SWNTs with larger diameters (average diameter = 1.4 nm), whose behavior is different from that of 2C8-PF. Molecular mechanics simulations were carried out to understand such specific solubilization behavior. This study provides an insight into the design and synthesis of PF-based polymers and copolymers that exhibit efficient selective sem-SWNT recognition/extraction ability and their applications.