Functionalization of carbon nanotubes with water-insoluble porphyrin in ionic liquid: direct electrochemistry and highly sensitive amperometric biosensing for trichloroacetic acid

Ionogels for flexible conductive substrates and their application in biosensing

Ionogels are highly conductive gels made from ionic liquids dispersed in a matrix made of organic or inorganic materials. Ionogels are known for high ionic conductivity, flexibility, high thermal and electrochemical stability. These characteristics make them suitable for sensing and biosensing applications. This review discusses about the two main constituents, ionic liquids and matrix, used to make ionogels and effect of these materials on the characteristics of ionogels. Here, the material properties like mechanical, electrochemical and stability are discussed for both polymer matrix and ionic liquid. We have briefly described about the fabrication methods like 3D printing, sol-gel, blade coating, spin coating, aerosol jet printing etc., used to make films or coating of these ionogels. The advantages and disadvantages of each method are also briefly summarized. Finally, the last section provides a few examples of application of flexible ionogels in areas like wearables, human-machine interface, electronic skin and detection of biological molecules.

Hemin-Functionalized Microfluidic Chip with Dual-Electric Signal Outputs for Accurate Determination of Uric Acid

Herein, we develop a hemin-functionalized microfluidic chip with dual-electric signal outputs for accurate determination of uric acid (UA). Hemin is designed as the catalyst, which could trigger a built-in reference signal. Carbon nanotube (CNT) and alkalinized titanium carbide (alk-Ti₃C₂T_x) are used as attachment substrates to strengthen the signal. Benefiting from the synergistic action of hemin, CNT, and alk-Ti₃C₂T_x, the hybrid functionalized sensor shows prominent electrochemical capacity, desirable catalytic activity, and unique built-in signal ability. Through density functional theory calculations, the structure-reactivity relationship and possible signal output mechanism are deeply investigated. The functionalized sensor is further integrated into a microfluidic chip to prepare a portable electrochemical sensing platform, in which multiple sample processing steps including primary filtration, target enrichment, and reliable analysis can be conducted step-by-step. Based on the abovementioned designs, the developed functionalized microfluidic platform presents desirable performance in UA determination with a detection limit of 0.41 μM. Furthermore, it is capable of accurately detecting UA in urine samples, providing a promising idea for biomolecule monitoring.

Graphene and carbon nanotubes interfaced electrochemical nanobiosensors for the detection of SARS-CoV-2 (COVID-19) and other respiratory viral infections: A review

Recent COVID-19 pandemic has claimed millions of lives due to lack of a rapid diagnostic tool. Global scientific community is now making joint efforts on developing rapid and accurate diagnostic tools for early detection of viral infections to preventing future outbreaks. Conventional diagnostic methods for virus detection are expensive and time consuming. There is an immediate requirement for a sensitive, reliable, rapid and easy-to-use Point-of-Care (PoC) diagnostic technology. Electrochemical biosensors have the potential to fulfill these requirements, but they are less sensitive for sensing viruses/viral infections. However, sensitivity and performance of these electrochemical platforms can be improved by integrating carbon nanostructure, such as graphene and carbon nanotubes (CNTs). These nanostructures offer excellent electrical property, biocompatibility, chemical stability, mechanical strength and, large surface area that are most desired in developing PoC diagnostic tools for detecting viral infections with speed, sensitivity, and cost-effectiveness. This review summarizes recent advancements made toward integrating graphene/CNTs nanostructures and their surface modifications useful for developing new generation of electrochemical nanobiosensors for detecting viral infections. The review also provides prospects and considerations for extending the graphene/CNTs based electrochemical transducers into portable and wearable PoC tools that can be useful in preventing future outbreaks and pandemics.

Synthetic strategies in construction of organic macromolecular carrier-drug conjugates

Many metabolic inhibitors, considered potential antimicrobial or anticancer drug candidates, exhibit very limited ability to cross the biological membranes of target cells. The restricted cellular penetration of those molecules is often due to their highhydrophilicity. One of the possible solutions to this problem is a conjugation of an inhibitor with a molecular organic nanocarrier. The conjugate thus formed should be able to penetrate the membrane(s) by direct translocation, endocytosis or active transport mechanisms and once internalized, the active component could reach its intracellular target, either after release from the conjugate or in an intact form. Several such nanocarriers have been proposed so far, including macromolecular systems, carbon nanotubes and dendrimers. Herein, we present a comprehensive review of the current status of rational design and synthesis of macromolecular organic nanocarrier-drug conjugates, with special attention focused on the mode of coupling of a nanocarrier moiety with a "cargo" molecule through linking fragments of non-cleavable or cleavable type.

Recent Advances on Electrochemical Sensors for the Detection of Organic Disinfection Byproducts in Water

Irreversible organ damage or even death frequently occurs when humans or animals unknowingly drink contaminated water. Therefore, in many countries drinking water is disinfected to ensure removal of harmful pathogens from drinking water. If upstream water treatment prior to disinfection is not adequate, disinfection byproducts (DBPs) can be formed. DBPs can exist as wide variety of compounds, but up until now, only several typical compounds have drinking water standards attributed to them. However, it is apparent that the range of DBPs present in water can comprise hundreds of compounds, some of which are at high enough concentrations to be toxic or potentially carcinogenic. Hence, it becomes increasingly significant and urgent to develop an accessible, affordable, and durable sensing platform for a broader range and more sensitive detection of DBPs. Compared with well-established laboratory detection techniques, electrochemical sensing has been identified as a promising alternative that will provide rapid, affordable, and sensitive DBP monitoring in remote water sources. Therefore, this Review covers current state-of-the-art development (within the past decade) in electrochemical sensing to detect organic DBPs in water, which covered three major aspects: (1) recognition mechanism, (2) electrodes with signal amplification, and (3) signal read-out techniques. Moreover, comprehensive quality assessments on electrochemical biosensors, including linear detection range, limit of detection (LoD) and recovery, have also been summarized.

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.

A highly conductive thin film composite based on silver nanoparticles and malic acid for selective electrochemical sensing of trichloroacetic acid

A highly conductive thin film composite based on silver nanoparticles (AgNPs) and malic acid (MA) was deposited on glassy carbon electrode (GCE) for the selective and sensitive electrochemical sensing of trichloroacetic acid (TCA). The casting solution containing MA functionalized AgNPs was employed as a precursor for the thermal deposition of the AgNPs integrated MA thin film composite onto the GCE surface. The uniform coverage of AgNPs within the thin film composite at GCE was obtained by field emission scanning electron microscopy (FESEM). A significantly high charge transfer resistance of the modified electrode (85.7 Ω for AgNPs-MA/GCE in 2 mM [Fe(CN)₆]^3-/4- at a bias of +0.235 V as compared to bare GCE (38.01 Ω) verified the optimum coating of AgNPs-MA composite at the surface of the electrode. The AgNPs-MA composite deposited GCE revealed substantial electrocatalytic activity toward TCA reduction with significantly enhanced reduction current. The novel electrode manifested a linear square wave voltammetric (SWV) response over the concentration ranges of 0.1-2 (R² = 0.9953) and 4-100 μM (R² = 0.9969) with a limit of detection (LOD) and limit of quantification (LOQ) of 30 nM and 92.5 nM, respectively. The modified electrode exhibited an excellent long-term stability (30 days) with the retention of >95% of initial current. The selectivity of the proposed electrode for the determination of TCA was examined in the presence of dichloroacetic acid (DCA) and monochloroacetic acid (MCA) with the retention of high recovery percentages.

Vacuum-Deposited Porphyrin Protective Films on Graphite: Electrochemical Atomic Force Microscopy Investigation during Anion Intercalation

The development of graphene products promotes a renewed interest toward the use of graphite in addition to the historical one for its proven viability as battery electrode. However, when exposed to harsh conditions, the graphite surface ages in ways that still need to be fully characterized. In applications to batteries, to optimize the electrode performances in acid solutions, different surface functionalizations have been studied. Among them, aromatic molecules have been recently proposed. In this communication, we report on the protective effect exerted by a physical-vapor-deposited porphyrin layer. Metal-free tetra-phenyl-porphyrins were deposited on a highly oriented pyrolytic graphite crystal to study the modifications that occur during anion intercalation in graphite. The graphite electrode was plunged in an electrolyte solution of 1 M sulfuric acid and subjected to cyclic voltammetry. The results indicate that blister formation, the characteristic swelling of graphite surface induced by anion intercalation, is significantly perturbed by the porphyrin overlayer; the process is inhibited in those areas where the protective porphyrin film is present. We ascribe the inhibition of the anion intercalation to the protective porphyrin wetting layer.

Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads

A potentiometric aptasensing assay that couples the DNA nanostructure-modified magnetic beads with a solid-contact polycation-sensitive membrane electrode for the detection of Vibrio alginolyticus is herein described. The DNA nanostructure-modified magnetic beads are used for amplification of the potential response and elimination of the interfering effect from a complex sample matrix. The solid-contact polycation-sensitive membrane electrode using protamine as an indicator is employed to chronopotentiometrically detect the change in the charge or DNA concentration on the magnetic beads, which is induced by the interaction between Vibrio alginolyticus and the aptamer on the DNA nanostructures. The present potentiometric aptasensing method shows a linear range of 10-100 CFU mL-1 with a detection limit of 10 CFU mL-1, and a good specificity for the detection of Vibrio alginolyticus. This proposed strategy can be used for the detection of other microorganisms by changing the aptamers in the DNA nanostructures.

Extraction of an active enzyme by self-buffering ionic liquids: a green medium for enzymatic research

The extraction of a model enzyme α-chymotrypsin in its active conformation from an aqueous solution by using new biocompatible and self-buffering Good's buffer ionic liquids-based aqueous biphasic systemsis demonstrated.

Mirrorless dye doped ionic liquid lasers

The study of electromagnetic waves propagation in periodically structured dielectrics and the linear and nonlinear optical phenomena in disordered systems doped with gain media represent one of the most challenging and exciting scientific areas of the past decade. Lasing and Random Lasers (RL) are fascinating examples of topics that synergize multiple scattering of light and optical amplification and lately have been the subject of intense theoretical and experimental studies. In this manuscript we demonstrate laser action in a new category of materials, namely dye doped ionic liquids. Ionic liquids prove to be perfect candidates for building, as shown, a series of exotic boundaryless or confined compact laser systems. Lasing is presented in standard wedge cells, freely suspended ionic liquid films and droplets. The optical emission properties are investigated in terms of spectral analysis, below and above lasing energy threshold behavior, emission efficiency, far field spatial laser modes intensity profiling, temporal emission behavior etc. As demonstrated, these materials can be employed as optimal near future replacements of conventional flammable solvents in already available dye laser instruments.

Self-buffering and biocompatible ionic liquid based biological media for enzymatic research

New self-buffering Good's buffer ionic liquids (GBILs) were synthesized for biological research.

Porphyrin functionalized porous carbon derived from metal–organic framework as a biomimetic catalyst for electrochemical biosensing

A novel biomimetic catalyst was designed by the assembly of porphyrin on porous carbon derived from metal–organic frameworks for electrochemical biosensing.

Enrichment of Large-Diameter Single-Walled Carbon Nanotubes (SWNTs) with Metallo-Octaethylporphyrins

We report here a detailed experimental investigation on noncovalent functionalization of single-walled carbon nanotubes (SWNTs) with four different metallo-octaethylporphyrins (MOEPs). It has been found that the identity of the center metal of MOEP strongly influences the solubilization of SWNTs. MnOEPs and ZnOEPs successfully extracted SWNTs in methanol, as confirmed by absorption spectroscopy, while CoOEPs and CuOEPs were not able to extract SWNTs at all. Atomic force microscopy (AFM) studies revealed that large SWNTs bundles could be exfoliated into either individual SWNTs or very small bundles by complexation with ZnOEP molecules. As for enrichment of SWNTs, ZnOEPs and MnOEPs show similar diameter discrimination ability toward 76-CoMoCAT, providing the extracted SWNTs with relatively large diameters.

Applications of Ionic Liquids in Electrochemical Sensors and Biosensors

Ionic liquids (ILs) are salt that exist in the liquid phase at and around 298 K and are comprised of a bulky, asymmetric organic cation and the anion usually inorganic ion but some ILs also with organic anion. ILs have attracted much attention as a replacement for traditional organic solvents as they possess many attractive properties. Among these properties, intrinsic ion conductivity, low volatility, high chemical and thermal stability, low combustibility, and wide electrochemical windows are few. Due to negligible or nonzero volatility of these solvents, they are considered “greener” for the environment as they do not evaporate like volatile organic compounds (VOCs). ILs have been widely used in electrodeposition, electrosynthesis, electrocatalysis, electrochemical capacitor, lubricants, plasticizers, solvent, lithium batteries, solvents to manufacture nanomaterials, extraction, gas absorption agents, and so forth. Besides a brief discussion of the introduction, history, and properties of ILs the major purpose of this review paper is to provide an overview on the advantages of ILs for the synthesis of conducting polymer and nanoparticle when compared to conventional media and also to focus on the electrochemical sensors and biosensors based on IL/composite modified macrodisk electrodes. Subsequently, recent developments and major strategies for enhancing sensing performance are discussed.

"Bucky gels" for tailoring electroactive materials and devices: the composites of carbon materials with ionic liquids

Bucky gels are gelatinous composite materials consisting of carbon nanotubes and ionic liquids. This article gives an overview of some promising applications of bucky gels reported mostly in the last few years and a possible extension to the dispersion of graphene sheets.

Thermochemistry of alkyl pyridinium bromide ionic liquids: calorimetric measurements and calculations

Two ionic liquids, 1-ethylpyridinium bromide (EPBr) and 1-propylpyridinium bromide (PPBr), were prepared and the structures were characterized by 1H NMR. The thermodynamic properties of EPBr and PPBr were studied with adiabatic calorimetry (AC) and thermogravimatric analysis (TG-DTG). The heat capacity was precisely measured in the temperature range from 78 to 410 K by means of a fully automated adiabatic calorimeter. For EPBr, the melting temperature, enthalpy, and entropy of solid-liquid phase transition were determined to be 391.31 +/- 0.28 K, 12.77 +/- 0.09 kJ x mol(-1), and 32.63 +/- 0.22 J x K(-1) x mol(-1), respectively, and for PPBr they were 342.83 +/- 0.69 K, 10.97 +/- 0.05 kJ x mol(-1), and 32.00 +/- 0.10 J x K(-1) x mol(-1), respectively. The thermodynamic functions (H(T)(0) - H(298.15)(0)) and (S(T)(0) - S(298.15)(0)) were derived from the heat capacity data in the experimental temperature range with an interval of 5 K. The thermostablility of the compounds was further studied by TGA measurements. The phase change behavior and thermodynamic properties were compared and estimated in a series of alkyl pyridinium bromide ionic liquids. Results indicate that EPBr has higher melting and decomposition temperature, as well as phase transition enthalpy and entropy but lower heat capacity than PPBr due to their different molecular structures.

Low-melting ionic solids: versatile materials for ion-sensing devices

Ionic liquids that melt slightly above room temperature (and may be called low-melting ionic solids, LMISs) were used as sensing materials for the detection of ions in aqueous solutions. A simple procedure based on the consecutive melting and further solidification of the LMISs was applied to prepare solid-contact ion-sensitive electrodes. A potentiometric response toward a number of anions was observed, and the possibility of altering the selectivity by incorporating additional ionophores into the LMIS matrix was demonstrated.