Dip-coated carbon nanotube surface deposits as stable, effective response enhancers in pencil lead electrode voltammetry

Graphitic pencil leads (PLs) are inexpensive writing accessories, readily available in stationery shops. Because the round filaments have high conductivity, they are excellent candidates for sustainable electroanalytical sensor fabrication. Here, we show that dip-coated carbon nanotube (CNT) surface deposits can stably enhance the faradaic redox response of cylindrical pencil lead electrodes (PLEs), with just ten simple sequential immersions of assembled PLEs in an aqueous suspension of CNTs producing significant improvement in their analytical performance. Cyclic (CV) and differential pulse (DPV) voltammetry of ferricyanide with unmodified and CNT-modified PLEs confirmed the reproducibility of the modification procedure and the reliability of the extent of signal amplification, as well as the stability of the response. A series of DPV tests with drugs, an environmental pollutant, an enzyme-substrate redox label and an industrial chemical proved the practical applicability of the proposed CNT-PLEs. Based on their observed properties, PLEs with dip-coated CNT deposits are suggested as cost-effective tools for advanced electroanalysis and as green platforms for enzyme biosensor construction.

Non-Covalent Functionalization of Carbon Nanotubes for Electrochemical Biosensor Development

Carbon nanotubes (CNTs) have been widely studied and used for the construction of electrochemical biosensors owing to their small size, cylindrical shape, large surface-to-volume ratio, high conductivity and good biocompatibility. In electrochemical biosensors, CNTs serve a dual purpose: they act as immobilization support for biomolecules as well as provide the necessary electrical conductivity for electrochemical transduction. The ability of a recognition molecule to detect the analyte is highly dependent on the type of immobilization used for the attachment of the biomolecule to the CNT surface, a process also known as biofunctionalization. A variety of biofunctionalization methods have been studied and reported including physical adsorption, covalent cross-linking, polymer encapsulation etc. Each method carries its own advantages and limitations. In this review we provide a comprehensive review of non-covalent functionalization of carbon nanotubes with a variety of biomolecules for the development of electrochemical biosensors. This method of immobilization is increasingly being used in bioelectrode development using enzymes for biosensor and biofuel cell applications.

Globular Shaped Polypyrrole Doped Well-Dispersed Functionalized Multiwall Carbon Nanotubes/Nafion Composite for Enzymatic Glucose Biosensor Application

Herein, we report preparation of a bio-nanohybrid material of homogenously dispersed functionalized multiwall carbon nanotubes (fMWCNTs) in Nafion (Nf) doped with polypyrrole (PPy) and followed by one-step in situ electrochemical polymerization along with glucose oxidase (GOx) on a platinum (Pt) electrode. The bioengineered Nf-GOx-fMWCNTs-PPy/Pt electrode showed excellent electrocatalytic performance to detect glucose with a high sensitivity (54.2 μAmM⁻¹ cm⁻²) in linear range of up to 4.1 mM as well as a low detection limit of 5 μM (S/N = 3), response time within 4 s, good selectivity, stability, and practical applicability. It is our hope that the comprehensive results will contribute to design an efficient glucose biosensor with practical prospects for biomedical applications.

Influence of carbon nanomaterial defects on the formation of protein corona

In any physiological media, carbon nanomaterials (CNM) strongly interact with biomolecules leading to the formation of biocorona, which subsequently dictate the physiological response and the fate of CNMs. Defects in CNMs play an important role not only in material properties but also in the determination of how materials interact at the nano-bio interface. In this article, we probed the influence of defect-induced hydrophilicity on the biocorona formation using micro-Raman, photoluminescence, infrared spectroscopy, electrochemistry, and molecular dynamics simulations. Our results show that the interaction of proteins (albumin and fibrinogen) with CNMs is strongly influenced by charge-transfer between them, inducing protein unfolding which enhances conformational entropy and higher protein adsorption.

Noncovalent Functionalization of Boron Nitride Nanotubes in Aqueous Media Opens Application Roads in Nanobiomedicine

Boron nitride nanotubes (BNNTs) are of intense scientific interest due to their unique physiochemical properties and prospective applications in various nanotechnologies, particularly nanobiomedicine. A critical problem hampering the application processing of BNNTs is the outer sidewall functionalization, which is primarily acquired to lead BNNTs dispersible in various solvents. Furthermore, the surface of BNNTs should be intelligently designed and precisely controlled to satisfy the specific demands of different applications. For these purposes, covalent and noncovalent approaches have been factually developed to help to extend the full potential of applications. Importantly, wrapping the outermost sidewall of BNNTs with either water-soluble polymers or biomolecules through weak noncovalent interactions has been proved to be efficient for giving BNNTs considerable dispersity in aqueous media, and endowing novel chemical functions to BNNTs with almost no change in their pristine physiochemical properties. This article summarizes recent progress in this field and addresses future perspectives on the noncovalent functionalization of BNNTs for promoting their application processing in various bio-related nanotechnologies.

Carbon based electrodes modified with horseradish peroxidase immobilized in conducting polymers for acetaminophen analysis

The development and optimization of new biosensors with horseradish peroxidase immobilized in carbon nanotubes-polyethyleneimine or polypyrrole nanocomposite film at the surface of two types of transducer is described. The amperometric detection of acetaminophen was carried out at -0.2 V versus Ag/AgCl using carbon based-screen printed electrodes (SPEs) and glassy carbon electrodes (GCEs) as transducers. The electroanalytical parameters of the biosensors are highly dependent on their configuration and on the dimensions of the carbon nanotubes. The best limit of detection obtained for acetaminophen was 1.36 ± 0.013 μM and the linear range 9.99-79.01 μM for the HRP-SWCNT/PEI in GCE configuration. The biosensors were successfully applied for the detection of acetaminophen in several drug formulations.

Nanoengineered glycan sensors enabling native glycoprofiling for medicinal applications: towards profiling glycoproteins without labeling or liberation steps

Nanoengineered glycan sensors may help realize the long-held goal of accurate and rapid glycoprotein profiling without labeling or glycan liberation steps. Current methods of profiling oligosaccharides displayed on protein surfaces, such as liquid chromatography, mass spectrometry, capillary electrophoresis, and microarray methods, are limited by sample pretreatment and quantitative accuracy. Microarrayed platforms can be improved with methods that better estimate kinetic parameters rather than simply reporting relative binding information. These quantitative glycan sensors are enabled by an emerging class of nanoengineered materials that differ in their mode of signal transduction from traditional methods. Platforms that respond to mass changes include a quartz crystal microbalance and cantilever sensors. Electronic response can be detected from electrochemical, field effect transistor, and pore impedance sensors. Optical methods include fluorescent frontal affinity chromatography, surface plasmon resonance methods, and fluorescent carbon nanotubes. After a very brief primer on glycobiology and its connection to medicine, these emerging systems are critically reviewed for their potential use as core sensors in future glycoprofiling tools.

Prospects of Organic Conducting Polymer Modified Electrodes: Enzymosensors

Organic conducting polymer modified electrodes (OCPMEs) have emerged as potential candidates for electrochemical biosensors due to their easy preparation methods along with unique properties, like stability in air and being compatible with biological molecules in a neutral aqueous solution. OCPMEs are playing an important role in the improvement of public health and environment for the detection of desired analytes with high sensitivity and specificity. In this paper, we highlight the prospects of OCMEs-based electrochemical enzymosensors.

Enzymatic biosensors based on SWCNT-conducting polymer electrodes

This short review is focused on recent advances in the combination of conducting polymers and SWCNTs for the fabrication of electrochemical biosensors. The different properties of conducting polymers and SWCNTs are discussed in respect of their use in immobilizing and wiring biomolecules on electrode surfaces. We further describe the functionalization techniques used in the fabrication of these devices and their associated biosensing performances.

Nanoelectronic detection of lectin-carbohydrate interactions using carbon nanotubes

We have used single-walled carbon nanotube field-effect transistor (NTFET) devices to probe the interactions between carbohydrates and their recognition proteins called lectins. These interactions are involved in a wide range of biological processes, such as cell-cell recognition, cell-matrix interaction as well as viral and bacterial infections. In our experiments, NTFETs were functionalized noncovalently with porphyrin-based glycoconjugates synthesized using "click" azide-alkyne chemistry, and change in electrical conductance was measured upon specific binding of two bacterial lectins that present different carbohydrate preference, namely PA-IL, PA-IIL from Pseudomonas aeruginosa and a plant lectin Concanavalin A. However, no significant change in the device characteristics was observed when the devices were exposed to other lectins with different specificity. Detection of PA-IL binding to galactosylated NTFETs was highly sensitive (2 nM) with a measured dissociation constant (K(d) = 6.8 μM) corresponding to literature data. Fluorescence microscopy, atomic force microscopy, UV-vis-NIR spectroscopy, and several control measurements confirmed the NTFET response to selective interactions between carbohydrates and lectins.