pH-Sensing Properties of Poly(aniline) Ultrathin Films Self-Assembled on Indium−Tin Oxide

Ingestible pH sensing device for gastrointestinal health monitoring based on thread-based electrochemical sensors

There exists a strong correlation between the pH levels of the gastrointestinal (GI) tract and GI diseases such as inflammatory bowel disease (IBS), ulcerative colitis, and pancreatis. Existing methods for diagnosing many GI diseases predominantly rely on invasive, expensive, and time-consuming techniques such as colonoscopy and endoscopy. In this study, an autonomous ingestible smart biosensing system in a pill format with integrated pH sensors is reported. The smart sensing pills will measure the pH profile as they transit through the GI tract. The data is then downloaded from the pills after they are collected from the feces. The sensor is based on electrodeposited PANI on carbon-coated conductive threads providing high pH sensitivity. Engineering innovations allowed integration of thread-based sensors on 3D-printed pill surfaces with front-end readout electronics, memory, and microcontroller assembled on mm-size circular printed circuit boards. The entire smart sensing pill possesses an overall length of 22.1 mm and an outer diameter of 9 mm. The modular biosensing system allows integration of thread-based biosensors to monitor other biomarkers in GI tract that mitigates the complex sensor fabrication process as well as overall pill assembly.

Single-Nanoparticle-Level Understanding of Oxidase-like Activity of Au Nanoparticles on Polymer Nanobrush-Based Proton Reservoirs

Enzyme-mimicking nanoparticles play a key role in important catalytic processes, from biosensing to energy conversion. Therefore, understanding and tuning their performance is crucial for making further progress in biological applications. We developed an efficient and sensitive electrochemical method for the real-time monitoring of the glucose oxidase (GOD)-like activity of single nanoparticle through collision events. Using brush-like sulfonate (-SO3-)-doped polyaniline (PANI) decorated on TiO2 nanotube arrays (TiNTs-SPANI) as the electrode, we fabricated a proton reservoir with excellent response and high proton-storage capacity for evaluating the oxidase-like activity of individual Au nanoparticles (AuNPs) via instantaneous collision processes. Using glucose electrocatalysis as a model reaction system, the GOD-like activity of individual AuNPs could be directly monitored via electrochemical tests through the nanoparticle collision-induced proton generation. Furthermore, based on the perturbation of the electrical double layer of SPANI induced by proton injection, we investigated the relationship between the measured GOD-like activities of the plasmonic nanoparticles (NPs) and the localized surface plasmon resonance (LSPR) as well as the environment temperature. This work introduces an efficient platform for understanding and characterizing the catalytic activities of nanozymes at the single-nanoparticle level.

Rapid-Response and Wide-Range pH Sensors Enabled by Self-Assembled Functional PAni/PAA Layer on No-Core Fiber

The measurement of pH has received great attention in diverse fields, such as clinical diagnostics, environmental protection, and food safety. Optical fiber sensors are widely used for pH sensing because of their great advantages. In this work, an optical fiber pH sensor is fabricated, by combining the merits of the multimode interference configuration and pH-sensitive polyaniline/polyacrylic acid (PAni/PAA) coatings, which was successfully in situ deposited on the no-core fiber (NCF) by the layer-by-layer (LBL) self-assembly method. The sensors' performance was experimentally characterized when used for pH detection. It has a high sensitivity of 0.985 nm/pH and a great linear response in a universal pH range of 2-12. The response time and recovery time is measured to be less than 10 s. In addition, its temperature sensitivity is tested to be about 0.01 nm/°C with a low temperature crosstalk effect, which makes it promising for detecting pH in the liquid phase with temperature variation. The sensors also demonstrated easy fabrication, good stability, and repeatability, which are adapted to pH detection in most practical applications.

Real-time monitoring of isothermal nucleic acid amplification on a smartphone by using a portable electrochemical device for home-testing of SARS-CoV-2

Home-testing of SARS-CoV-2 is an ideal approach for controlling the pandemic of COVID-19 and alleviating the shortage of medical resource caused by this acute infectious disease. Herein, a portable device that enables real-time monitoring of isothermal nucleic acid amplification tests (INAATs) through the electrochemistry method was fabricated for home-testing of SARS-CoV-2. First, a disposable plug-and-play pH-sensitive potentiometric sensor that matches this electrochemical INAATs (E-INAATs) device was designed to allow the label-free pH sensing detection of nucleic acid. By applying Nafion film on the polyaniline-based working electrode, this sensor exhibited an excellent linear potentiometric response to pH value in the range of 6.0–8.5 with a slope of −37.45 ± 1.96 mV/pH unit. A Bluetooth module was integrated into this device to enable the users real-time monitoring INAATs on their smartphones at home. Moreover, by presetting criteria, the detection results could be automatically judged by the device to avoid human errors. Finally, the utility of this E-INAATs device was demonstrated by detecting the presence of SARS-CoV-2 nucleocapsid protein gene in artificial samples with a sensitivity of 2 × 10² copies/test within 25 min, which was comparable with fluorescence and colorimetric assay. This portable, easy-operated, sensitive, and affordable device is particularly desirable for the full integration of household SARS-CoV-2 detection products and will open a new prospect for the control of infectious diseases via electrochemical NAATs.

A flexible polyaniline-based bioelectronic patch

Bioelectronic materials based on conjugated polymers are being developed in the hope to interface with electroresponsive tissues. We have recently demonstrated that a polyaniline chitosan patch can efficiently electro-couple with cardiac tissue modulating its electrophysiology. As a promising bioelectronic material that can be tailored to different types of devices, we investigate here the impact of varying the synthesis conditions and time of the in situ polymerization of aniline (An) on the sheet resistance of the bioelectronic patch. The sheet resistance increases significantly for samples that have either the lowest molar ratio of oxidant to monomer or the highest molar ratio of dopant to monomer, while the polymerization time does not have a significant effect on the electrical properties. Conductive atomic force microscopy reveals that the patch with the lowest sheet resistance has a connected network of the conductive phase. In contrast, patches with higher sheet resistances exhibit conductive areas of lower current signals or isolated conductive islands of high current signals. Having identified the formulation that results in patches with optimal electrical properties, we used it to fabricate patches that were implanted in rats for two weeks. It is shown that the patch retains an electroactive nature, and only mild inflammation is observed with fibrous tissue encapsulating the patch.

Rendering cross-conjugated azophenine derivatives emissive to probe the silent photophysical properties of emeraldine

An azophenine derivative was synthesized by coupling truxene and azophenine via the copper-free Sonagashira reaction using Pd₂(dba)₃ and As(PPh)₃ as catalysts. The crystal structure of this heavy azophenine model (∼4000) was made and the identity of the structure was confirmed. By introducing truxene groups into this cross-conjugated structure, the deactivating rotations around the NH-C₆H₄ bonds were slowed down, which rendered this derivative near-IR emissive at 298 K. This species provided then the appropriate spectral and kinetic signatures for knowing where and what to look for in emeraldine, which was called non-emissive. Besides, two other compounds were also synthesized as models for this azophenine derivative for comparison and interpretation purposes.

Nanostructured surfaces for analysis of anticancer drug and cell diagnosis based on electrochemical and SERS tools

Discovering new anticancer drugs and screening their efficacy requires a huge amount of resources and time-consuming processes. The development of fast, sensitive, and nondestructive methods for the in vitro and in vivo detection of anticancer drugs' effects and action mechanisms have been done to reduce the time and resources required to discover new anticancer drugs. For the in vitro and in vivo detection of the efficiency, distribution, and action mechanism of anticancer drugs, the applications of electrochemical techniques such as electrochemical cell chips and optical techniques such as surface-enhanced Raman spectroscopy (SERS) have been developed based on the nanostructured surface. Research focused on electrochemical cell chips and the SERS technique have been reviewed here; electrochemical cell chips based on nanostructured surfaces have been developed for the in vitro detection of cell viability and the evaluation of the effects of anticancer drugs, which showed the high capability to evaluate the cytotoxic effects of several chemicals at low concentrations. SERS technique based on the nanostructured surface have been used as label-free, simple, and nondestructive techniques for the in vitro and in vivo monitoring of the distribution, mechanism, and metabolism of different anticancer drugs at the cellular level. The use of electrochemical cell chips and the SERS technique based on the nanostructured surface should be good tools to detect the effects and action mechanisms of anticancer drugs.

Multifunctional Indium Tin Oxide Electrode Generated by Unusual Surface Modification

The indium tin oxide (ITO) material has been widely used in various scientific fields and has been successfully implemented in several devices. Herein, the electrochemical reduction of ITO electrode in an organic electrolytic solution containing alkali metal, NaI, or redox molecule, N-(ferrocenylmethyl) imidazolium iodide, was investigated. The reduced ITO surfaces were investigated by X-ray photoelectron spectroscopy and grazing incident XRD demonstrating the presence of the electrolyte cation inside the material. Reversibility of this process after re-oxidation was evidenced by XPS. Using a redox molecule based ionic liquid as supporting electrolyte leads to fellow electrochemically the intercalation process. As a result, modified ITO containing ferrocenyl imidazolium was easily generated. This reduction process occurs at mild reducing potential around -1.8 V and causes for higher reducing potential a drastic morphological change accompanied with a decrease of the electrode conductivity at the macroscopic scale. Finally, the self-reducing power of the reduced ITO phase was used to initiate the spontaneous reduction of silver ions leading to the growth of Ag nanoparticles. As a result, transparent and multifunctional active ITO surfaces were generated bearing redox active molecules inside the material and Ag nanoparticles onto the surface.

Recent developments in the layer-by-layer assembly of polyaniline and carbon nanomaterials for energy storage and sensing applications. From synthetic aspects to structural and functional characterization

The construction of hybrid polymer-inorganic nanoarchitectures for electrochemical purposes based on the layer-by-layer assembly of conducting polymers and carbon nanomaterials has become increasingly popular over the last decade. This explosion of interest is primarily related to the increasing mastery in the design of supramolecular constructs using simple wet chemical approaches. Concomitantly, this continuous research activity paved the way to the rapid development of nanocomposites or "nanoblends" readily integrable into energy storage and sensing devices. In this sense, the layer-by-layer (LbL) assembly technique has allowed us to access three-dimensional (3D) multicomponent carbon-based network nanoarchitectures displaying addressable electrical, electrochemical and transport properties in which conducting polymers, such as polyaniline, and carbon nanomaterials, such as carbon nanotubes or nanographene, play unique roles without disrupting their inherent functions - complementary entities coexisting in harmony. Over the last few years the level of functional sophistication reached by LbL-assembled carbon-based 3D network nanoarchitectures, and the level of knowledge related to how to design, fabricate and optimize the properties of these 3D nanoconstructs have advanced enormously. This feature article presents and discusses not only the recent advances but also the emerging challenges in complex hybrid nanoarchitectures that result from the layer-by-layer assembly of polyaniline, a quintessential conducting polymer, and diverse carbon nanomaterials. This is a rapidly developing research area, and this work attempts to provide an overview of the diverse 3D network nanoarchitectures prepared up to now. The importance of materials processing and LbL integration is explored within each section and while the overall emphasis is on energy storage and sensing applications, the most widely-used synthetic strategies and characterization methods for "nanoblend" formation and performance evaluation are also presented.

Electrochemical modification of indium tin oxide using di(4-nitrophenyl) iodonium tetrafluoroborate

Optoelectronic applications often rely on indium tin oxide (ITO) as a transparent electrode material. Improvements in the performance of such devices as photovoltaics and light-emitting diodes often requires robust, controllable modification of the ITO surface to enhance interfacial charge transfer properties. In this work, modifier films were deposited onto ITO by the electrochemical reduction of di(4-nitrophenyl) iodonium tetrafluoroborate (DNP), allowing for control over surface functionalization. The surface coverage could be tuned from submonolayer to multilayer coverage by either varying the DNP concentration or the number of cyclic voltammetry (CV) grafting scans. Modification of ITO with 0.8 mM DNP resulted in near-monolayer surface coverage (4.95 × 10(14) molecules/cm(2)). X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of 4-nitrophenyl (NO2Ph) moieties on the ITO surface through the detection of a NO2 nitrogen signal at 405.6 eV after grafting. Further XPS evidence suggests that the NO2Ph radicals do not bond to the surface indium or tin sites, consistent with modification occurring either through bonding to surface hydroxyl groups or through strong physisorption on ITO. CV in the presence of an electroactive probe and electrochemical impedance spectroscopy (EIS) were used to investigate the electronic effects that modification via DNP has on ITO. Even at submonolayer coverage, the insulating organic films can reduce the current response to ferrocene oxidation and reduction by more than 25% and increase the charge transfer resistance by a factor of 10.

Preparation and characterisation of transparent and flexible PEDOT:PSS/PANI electrodes by ink-jet printing and electropolymerisation

A hybrid polymeric electrode PEDOT:PSS/PANI was prepared by ink-jet printing and electropolymerisation, obtaining high capacitance, low resistivity and linear response to pH in a large window.

From the solution processing of hydrophilic molecules to polymer-phthalocyanine hybrid materials for ammonia sensing in high humidity atmospheres

We have prepared different hybrid polymer-phthalocyanine materials by solution processing, starting from two sulfonated phthalocyanines, s-CoPc and CuTsPc, and polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), poly(acrylic acid-co-acrylamide) (PAA-AM), poly(diallyldimethylammonium chloride) (PDDA) and polyaniline (PANI) as polymers. We also studied the response to ammonia (NH₃) of resistors prepared from these sensing materials. The solvent casted films, prepared from s-CoPc and PVP, PEG and PAA-AM, were highly insulating and very sensitive to the relative humidity (RH) variation. The incorporation of s-CoPc in PDDA by means of layer-by-layer (LBL) technique allowed to stabilize the film, but was too insulating to be interesting. We also prepared PANI-CuTsPc hybrid films by LBL technique. It allowed a regular deposition as evidenced by the linear increase of the absorbance at 688 nm as a function of the number of bilayers. The sensitivity to ammonia (NH₃) of PANi-CuTsPc resistors was very high compared to that of individual materials, giving up to 80% of current decrease when exposed to 30 ppm NH₃. Contrarily to what happens with neutral polymers, in PANI, CuTsPc was stabilized by strong electrostatic interactions, leading to a stable response to NH₃, whatever the relative humidity in the range 10%–70%. Thus, the synergy of PANI with ionic macrocycles used as counteranions combined with their simple aqueous solution processing opens the way to the development of new gas sensors capable of operating in real world conditions.

ITO/poly(aniline)/sol-gel glass: An optically transparent, pH-responsive substrate for supported lipid bilayers

Described here is fabrication of a pH-sensitive, optically transparent transducer composed of a planar indium-tin oxide (ITO) electrode overcoated with a a poly(aniline) (PANI) thin film and a porous sol-gel layer. Adsorption of the PANI film renders the ITO electrode sensitive to pH, whereas the sol-gel spin-coated layer makes the upper surface compatible with fusion of phospholipid vesicles to form a planar supported lipid bilayer (PSLB). The response to changes in the pH of the buffer contacting the sol-gel/PANI/ITO electrode is pseudo-Nernstian with a slope of 52 mV/pH over a pH range of 4-9. Vesicle fusion forms a laterally continuous PSLB on the upper sol-gel surface that is fluid with a lateral lipid diffusion coefficient of 2.2 μm2/s measured by fluorescence recovery after photobleaching. Due to its lateral continuity and lack of defects, the PSLB blocks the pH response of the underlying electrode to changes in the pH of the overlying buffer. This architecture is simpler to fabricate than previously reported ITO electrodes derivatized for PSLB formation, and should be useful for optical monitoring of proton transport across supported membranes derivatized with ionophores and ion channels.

Carbon dot-based inorganic-organic nanosystem for two-photon imaging and biosensing of pH variation in living cells and tissues

A carbon dot (C-Dot)-based two-photon fluorescent probe has been developed for the monitoring of pH changes across a broad range with high sensitivity and selectivity. The inorganic-organic probe also shows good biocompatibility and cell permeability, and thus can be successfully applied in bioimaging and biosensing of physiological pH in living cells, as well as living tissues at a depth of 65-185 μm.

Poly(aniline) nanowires in sol-gel coated ITO: a pH-responsive substrate for planar supported lipid bilayers

Facilitated ion transport across an artificial lipid bilayer coupled to a solid substrate is a function common to several types of bioelectronic devices based on supported membranes, including biomimetic fuel cells and ion channel biosensors. Described here is fabrication of a pH-sensitive transducer composed of a porous sol-gel layer derivatized with poly(aniline) (PANI) nanowires grown from an underlying planar indium-tin oxide (ITO) electrode. The upper sol-gel surface is hydrophilic, smooth, and compatible with deposition of a planar supported lipid bilayer (PSLB) formed via vesicle fusion. Conducting tip AFM was used to show that the PANI wires are connected to the ITO, which convert this electrode into a potentiometric pH sensor. The response to changes in the pH of the buffer contacting the PANI nanowire/sol-gel/ITO electrode is blocked by the very low ion permeability of the overlying fluid PSLB. The feasibility of using this assembly to monitor facilitated proton transport across the PSLB was demonstrated by doping the membrane with lipophilic ionophores that respond to a transmembrane pH gradient, which produced an apparent proton permeability several orders of magnitude greater than values measured for undoped lipid bilayers.

Reversible quantum confinement of polarons by reaction of protonated emeraldine with nitric oxide

Nitric oxide (NO), a free radical, adds to green emeraldine acid, a polyradical and a one-dimensional polaronic conductor. As more NO is added, the segments through which protons and their associated unpaired electrons move, i.e., the polarons, are progressively shortened. This confinement of polarons is observed as a spectral progression from the parent green emeraldine acid, with an absorption maximum at 875 nm, to a series of blue polymers, their absorption maxima shifting progressively while decreasing in intensity with NO uptake to 670 nm, then turning colorless, with only a faint residual absorption at lambda (max) = 625 nm for the end member of the series which is insulating and no longer shows a voltammetric wave. The sequence is reversed in dilute HCl where the colorless and insulating polymer releases nitric oxide, the polaron is deconfined and the voltammetric wave reappears.

Multifunctional 3D nanoarchitectures for energy storage and conversion

The design and fabrication of three-dimensional multifunctional architectures from the appropriate nanoscale building blocks, including the strategic use of void space and deliberate disorder as design components, permits a re-examination of devices that produce or store energy as discussed in this critical review. The appropriate electronic, ionic, and electrochemical requirements for such devices may now be assembled into nanoarchitectures on the bench-top through the synthesis of low density, ultraporous nanoarchitectures that meld high surface area for heterogeneous reactions with a continuous, porous network for rapid molecular flux. Such nanoarchitectures amplify the nature of electrified interfaces and challenge the standard ways in which electrochemically active materials are both understood and used for energy storage. An architectural viewpoint provides a powerful metaphor to guide chemists and materials scientists in the design of energy-storing nanoarchitectures that depart from the hegemony of periodicity and order with the promise--and demonstration--of even higher performance (265 references).

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade

Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, polynapthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylenedioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, polycarbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article, we try to give an overview of Solid-Contact ISE (SCISE), Single-Piece ISE (SPISE), Conducting Polymer (CP)-Based, and also non-conducting polymer PVC-based ISEs for various ions which their difference is in the way of the polymer used with selective membrane. In SCISEs and SPISEs, the plasticized PVC containing the ionophore and ionic additives govern the selectivity behavior of the electrode and the conducting polymer is responsible of ion-to-electron transducer. However, in CPISEs, the conducting polymer layer is doped with a suitable ionophore which enhances the ion selectivity of the CP while its redox response has to be suppressed.

Conducting polymers in chemical sensors and arrays

The review covers main applications of conducting polymers in chemical sensors and biosensors. The first part is focused on intrinsic and induced receptor properties of conducting polymers, such as pH sensitivity, sensitivity to inorganic ions and organic molecules as well as sensitivity to gases. Induced receptor properties can be also formed by molecularly imprinted polymerization or by immobilization of biological receptors. Immobilization strategies are reviewed in the second part. The third part is focused on applications of conducting polymers as transducers and includes usual optical (fluorescence, SPR, etc.) and electrical (conductometric, amperometric, potentiometric, etc.) transducing techniques as well as organic chemosensitive semiconductor devices. An assembly of stable sensing structures requires strong binding of conducting polymers to solid supports. These aspects are discussed in the next part. Finally, an application of combinatorial synthesis and high-throughput analysis to the development and optimization of sensing materials is described.