Review: Carbon nanotube based electrochemical sensors for biomolecules

Carbon nanotubes (CNTs) have been incorporated in electrochemical sensors to decrease overpotential and improve sensitivity. In this review, we focus on recent literature that describes how CNT-based electrochemical sensors are being developed to detect neurotransmitters, proteins, small molecules such as glucose, and DNA. Different types of electrochemical methods are used in these sensors including direct electrochemical detection with amperometry or voltammetry, indirect detection of an oxidation product using enzyme sensors, and detection of conductivity changes using CNT-field effect transistors (FETs). Future challenges for the field include miniaturizing sensors, developing methods to use only a specific nanotube allotrope, and simplifying manufacturing.     

Recent advances in photoelectrochemical sensors for detection of ions in water

Over the last 50 years, the explosive adoption of modern agricultural practices has led to an enormous increase in the emission of non-biodegradable and highly biotoxic ions into the hydrosphere. Excess intake of such ions, even essential trace elements such as Cu²⁺ and F⁻, can have serious consequences on human health. Therefore, to ensure safe drinking water and regulate wastewater discharge, photoelectrochemical (PEC) online sensors were developed, with advantages such as low energy consumption, inherent miniaturization, simple instrumentation, and fast response. However, there is no publicly available systematic review of the recent advances in PEC ion sensors available in the literature since January 2017. Thus, this review covers the various strategies that have been used to enhance the sensitivity, selectivity, and limit of detection for PEC ion sensors. The photoelectrochemically active materials, conductive substrates, electronic transfer, and performance of various PEC sensors are discussed in detail and divided into sections based on the measurement principle and detected ion species. We conclude this review by highlighting the challenges and potential future avenues of research associated with the development of novel high-performance PEC sensors.     

Polymethacrylate polymers with appended aluminum(III)-tetraphenylporphyrins: Synthesis, characterization and evaluation as macromolecular ionophores for electrochemical and optical fluoride sensors

The synthesis and characterization of a novel polymethacylate polymer with covalently linked Al(III)-tetraphenylporphyrin (Al(III)-TPP) groups is reported. The new polymer is examined as a potential macromolecular ionophore for the preparation of polymeric membrane-based potentiometric and optical fluoride selective sensors. To prepare the polymer, an Al(III) porphyrin monomer modified with a methacrylate functionality is synthesized, allowing insertion into a polymethacrylate block copolymer (methyl methacrylate and decyl methacrylate) backbone. The resulting polymer can then be incorporated, along with appropriate additives, into conventional plasticized poly(vinyl chloride) films for testing electrochemical and optical fluoride response properties. The covalent attachment of the Al(III)-TPP ionophore to the copolymer matrix provides potentiometric sensors that exhibit significant selectivity for fluoride ion with extended lifetimes (compared to ion-selective membrane electrodes formulated with conventional free Al(III)-TPP structure). However, quite surprisingly, the attachment of the ionophore to the polymer does not eliminate the interaction of Al(III)-TPP structures to form dimeric species within the membrane phase in the presence of fluoride ion. Such interactions are confirmed by UV/visible spectroscopy of the blended polymeric films. Use of the new polymer-Al(III)-TPP conjugates to prepare optical fluoride sensors by co-incorporating a lipophilic pH indicator (4′,5′-dibromofluorescein octadecyl ester; ETH7075) is also examined and the resulting optical sensing films are shown to exhibit excellent selectivity for fluoride, with the potential for prolonged operational lifetime.     

Electrochemical plasmonic sensors

The enormous progress of nanotechnology during the last decade has made it possible to fabricate a great variety of nanostructures. On the nanoscale, metals exhibit special electrical and optical properties, which can be utilized for novel applications. In particular, plasmonic sensors including both the established technique of surface plasmon resonance and more recent nanoplasmonic sensors, have recently attracted much attention. However, some of the simplest and most successful sensors, such as the glucose biosensor, are based on electrical readout. In this review we describe the implementation of electrochemistry with plasmonic nanostructures for combined electrical and optical signal transduction. We highlight results from different types of metallic nanostructures such as nanoparticles, nanowires, nanoholes or simply films of nanoscale thickness. We briefly give an overview of their optical properties and discuss implementation of electrochemical methods. In particular, we review studies on how electrochemical potentials influence the plasmon resonances in different nanostructures, as this type of fundamental understanding is necessary for successful combination of the methods. Although several combined platforms exist, many are not yet in use as sensors partly because of the complicated effects from electrochemical potentials on plasmon resonances. Yet, there are clearly promising aspects of these sensor combinations and we conclude this review by discussing the advantages of synchronized electrical and optical readout, illustrating the versatility of these technologies.     

Recent advances in electrochemical sensors for antibiotics and their applications

The abuse of antibiotics will cause an increase of drug-resistant strains and environmental pollution,which in turn will affect human health.Therefore,it is important to develop effective detection techniques to determine the level of antibiotics contamination in various fields.Compared with traditional detection methods,electrochemical sensors have received extensive attention due to their advantages such as high sensitivity,low detection limit,and good selectivity.In this mini review,we summarized the latest developments and new trends in electrochemical sensors for antibiotics.Here,modification methods and materials of electrode are discussed.We also pay more attention to the practical applications of antibiotics electrochemical sensors in different fields.In addition,the existing problems and the future challenges ahead have been proposed.We hope that this review can provide new ideas for the development of electrochemical sensors for antibiotics in the future.     

Analysis and identification of several apple varieties using ISFETs sensors

There are a number of variables that are useful to determine the optimal moment for the fruit collection such as starch content, sugar content, acidity and firmness. Other variables, including calcium and potassium concentrations, may establish better the state of ripeness of fruit and can help to optimise the collection process as well as augmenting the nutritional value of fruits. At present, these novel parameters cannot be used for the control of fruit collection due to the slow standard methods required. The need for in situ and in real-time ion measurements calls for fast response sensors and simpler and portable instrumentation. Solid-state sensors respond to these requirements. This work describes the application of ISFET sensors to analyse calcium, potassium and nitrates in several apple varieties, both in juice and in situ fruit. Results show that the analysis of potassium, calcium and nitrate permits to distinguish among apple varieties and can also be used to determine correctly the concentrations of these ions.     

Toward decentralized analysis of mercury (II) in real samples. A critical review on nanotechnology-based methodologies

In recent years, it has increased the number of works focused on the development of novel nanoparticle-based sensors for mercury detection, mainly motivated by the need of low cost portable devices capable of giving fast and reliable analytical response, thus contributing to the analytical decentralization. Methodologies employing colorimetric, fluorometric, magnetic, and electrochemical output signals allowed reaching detection limits within the pM and nM ranges. Most of these developments proved their suitability in detecting and quantifying mercury (II) ions in synthetic solutions or spiked water samples. However, the state of art in these technologies is still behind the standard methods of mercury quantification, such as cold vapor atomic absorption spectrometry and inductively coupled plasma techniques, in terms of reliability and sensitivity. This is mainly because the response of nanoparticle-based sensors is highly affected by the sample matrix. The developed analytical nanosystems may fail in real samples because of the negative incidence of the ionic strength and the presence of exchangeable ligands. The aim of this review is to critically consider the recently published innovations in this area, and highlight the needs to include more realistic assays in future research in order to make these advances suitable for on-site analysis.     

Preparation and characterization of implantable sensors with nitric oxide release coatings

The widespread use of miniaturized chemical sensors to monitor clinically important analytes such as PO₂, PCO₂, pH, electrolytes, glucose and lactate in a continuous, real-time manner has been seriously hindered by the erratic analytical results often obtained when such devices are implanted in vivo. One major factor that has influenced the analytical performance of indwelling sensors is the biological response they elicit when in contact with blood or tissue (e.g. thrombus formation on the device surface, inflammatory response, encapsulation, etc.). Nitric oxide (NO) has been shown to be a potent inhibitor of platelet adhesion and activation as well as a promoter of wound healing in tissue. Herein, we review recent work aimed at the development of hydrophobic NO-releasing polymers that can be employed to coat catheter-type amperometric oxygen sensors without interfering with the analytical performance of these devices. Such modified sensors are shown to exhibit greatly enhanced hemocompatibility and improved analytical performance when implanted within porcine carotid and femoral arteries for up to 16 h. Further, results from preliminary studies also demonstrate that prototype fluorescent oxygen sensors, catheter-style potentiometric carbon dioxide sensors and subcutaneous needle-type enzyme-based amperometric glucose sensors can also be fabricated with new NO-release outer coatings without compromising the analytical response characteristics of these devices. The NO-release strategy may provide a solution to the lingering biocompatibility problems encountered when miniature chemical sensors are implanted in vivo.     

Multifunctional Features of Organic Charge-Transfer Complexes: Advances and Perspectives

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.     

Application of split aptamers-based sensors for the detection of small moleculesEI北大核心CSCD

The split aptamers (SPAs)-based sensors is a novel kind of biosensors, assembled by two or more oligonucleotides in the presence of specific targets. To be successfully assembled, the sensor has to be induced by a specific target, which can aviod false-positive results and thus has a high degree of specificity and sensitivity. SPAs are suitable for the detection of various targets and show great advantages and potential in the development of aptasensors, especially for the detection of small molecules. However, the development and application of SPA-based sensors still remain challenging. Currently, the major difficulty is how to improve the stability of SPA-target complexes. Herein, this review summarizes the SPAs, strategies of splitting aptamers, and their applications in the detection of small molecules, aiming to provide new ideas for the development of novel, sensitive, and specific aptasensors. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Visible and FTIR Microscopic Observation of Bisthiourea Ionophore Aggregates in Ion‐Selective Electrode Membranes

Since conventional response models for ionophore‐based ISEs are based on the assumption of a homogeneous membrane phase, they cannot accurately predict the response of membranes containing self‐aggregating ionophores. However, meaningful conclusions about the relationship between ionophore structure and potentiometric responses can only be drawn if ionophore aggregation is properly recognized. This study demonstrates that dark field visible microscopy and FTIR microspectroscopy are valuable tools for the observation of such ionophore self‐aggregation and, thereby, the development of new ionophore‐based ISEs. Sulfate selective electrodes with solvent polymeric membranes containing bisthiourea ionophores that differ only by peripheral nonpolar substituents were shown to exhibit very different interferences from the sample pH. On one hand, optimized electrodes based on an ionophore with a phenyl substituent on each thiourea group ( 1 ) do not respond to pH at all and function well as sulfate‐selective electrodes. On the other hand, membranes containing a more lipophilic ionophore with two additional hexyl‐substituted adamantyl groups ( 2 ) exhibit severe pH interference at pH values as low as pH 5. The observation of membranes containing ionophore 2 with dark field visible microscopy and FTIR microspectroscopy shows supramolecular aggregation, and explains the startling difference between the potentiometric responses of the two types of electrodes.     

Ribonucleic acid as a novel ionophore for potentiometric membrane sensors of some transition metal ions

Ribonucleic acid (RNA) is used as a novel ionophore in plasticized poly(vinyl chloride) matrix membrane sensors for some transition metal ions. Membranes incorporating RNA and doped in Cu(2+), Cd(2+) and Fe(2+) display fast near-Nernstian and stable responses for these ions with cationic slopes of 31.1, 31.3 and 35.5 mV per decade, respectively, over the concentration range 10(-6)-10(-2) M and pH range 4-6.5. The cadmium RNA-based sensor shows no interference by Cu(2+), Fe(2+) Hg(2+) and Ag(+), which are known to interfere significantly with the solid-state CdS/Ag(2)S membrane electrode. The copper RNA-based sensor displays general potentiometric characteristics similar to those based on macrocyclic ionophores and organic ion exchangers and has the advantage of a better selectivity for Cu(2+) over some alkaline earth, divalent and transition metal ions. The iron RNA-based membrane sensor exhibits no interference by Hg(2+) and Zn(2+), which are known to interfere with other previously suggested sensors. The nature and composition of the RNA ionophore and its cadmium complex are examined using electrophoresis, Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques.     

A Novel Potentiometric Detection Strategy for the Determination of Amlodipine Besylate Based on Functionalized Particles

A novel potentiometric strategy based on functionalized magnetite nanoparticles and microparticles were compared with the classical potentiometric strategy. This strategy provided nano‐ and microsized particles that were highly dispersed and coated with ionophore and plasticizer to promote an in situ cooperative ion‐pairing interaction between the ionophore and the analyte present in inner solution of sensor membrane, compared to the classical technique. Three amlodipine (AML) sensors were constructed using functionalized nanoparticles in sensor 1; microparticles in sensor 2, as ionophores, and the polymeric membrane ionophoric property in sensor 3.     

Nanothermometry: From Microscopy to Thermal Treatments

Measuring temperature in cells and tissues remotely, with sufficient sensitivity, and in real time presents a new paradigm in engineering, chemistry and biology. Traditional sensors, such as contact thermometers, thermocouples, and electrodes, are too large to measure the temperature with subcellular resolution and are too invasive to measure the temperature in deep tissue. The new challenge requires novel approaches in designing biocompatible temperature sensors—nanothermometers—and innovative techniques for their measurements. In the last two decades, a variety of nanothermometers whose response reflected the thermal environment within a physiological temperature range have been identified as potential sensors. This review covers the principles and aspects of nanothermometer design driven by two emerging areas: single‐cell thermogenesis and image guided thermal treatments. The review highlights the current trends in nanothermometry illustrated with recent representative examples.     

Development of a new gas sensor for binary mixtures based on the permselectivity of polymeric membranes: Application to carbon dioxide/methane and carbon dioxide/helium mixtures

Membrane-based gas sensors were developed and used for determining the composition on bi-component mixtures in the 0-100% range, such as oxygen/nitrogen and carbon dioxide/methane (biogas). These sensors are low cost and are aimed at a low/medium precision market.The paper describes the use of this sensor for two gas mixtures: carbon dioxide/methane and carbon dioxide/helium. The membranes used are poly(dimethylsiloxane) (PDMS) and Teflon-AF hollow fibers. The response curves for both sensors were obtained at three different temperatures. The results clearly indicate that the permeate pressure of the sensors relates to the gas mixture composition at a given temperature. The data is represented by a third order polynomial. The sensors enable quantitative carbon dioxide analysis in binary mixtures with methane or helium. The response of the sensors is fast (less than 50 s), continuous, reproducible and long-term stable over a period of 2.3×10⁷ s (9 months). The absolute sensitivity of the sensors depends on the carbon dioxide feed concentration ranging from 0.03 to 0.13 MPa.     

Highly sensitive and selective solid-contact calcium sensor based on Schiff base of benzil with 3-aminosalycilic acid covalently attached to polyacrylic acid amide for health care

Solid-state potentiometric calcium sensors based on newly synthesized Schiff’s base of 3-aminosalycilic acid with benzil [2-hydroxy-3-(2-oxo-1,2-diphenylethylidene)amino) benzoic acid] ionophore I and with isatin [2-hydroxy-3-(2-oxoindolin-3-ylidene amino)benzoic acid] ionophore II ionophores and their covalently attached to polyacrylamide ionophores III and IV, respectively, were developed. The all-solid-state sensors were constructed by the application of a thin film of polymeric membrane cocktail onto gold electrodes that were pre-coated with the conducting polymer poly (3,4-ethylenedioxy-thiophen) as an ion and electron transducer. More than 40 sensors with membranes containing plasticized PVC or poly(butyl methacrylate-co-dodecyl methacrylate as a plasticizer-free membrane matrix were investigated. The constructed sensors contained various amounts of the different ionophores with and without anionic lipophilic additive. The sensor containing 10% of ionophore III and 3% tetra (p-chlorophenyl) borate in acrylate copolymer exhibited a stable potentiometric response over a wide pH range of 4–9. It possessed a linear concentration range of 6 10^?10 to 1 10^?2 mol L^?1 with a Nernstian slope of 28.5 mV/decade and a limit of detection (LOD) of 2 10^?10 mol L^?1. It exhibited a good selectivity for calcium to other cations. The selectivity coefficients towards different mono-, di- and trivalent cations were determined with the fixed interference method (FIM) and separate solution method (SSM). The sensor’s life time is more than 3 months, without significant deterioration in the slope. The proposed sensors were utilized for the determination of calcium concentration in serum. The results were compared with those obtained from routine clinical laboratory electrolyte analyser. The results reveal that the all-solid-state calcium sensor is promising for the point of care testing.     

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered.     

Novel ibuprofen potentiometric membrane sensors based on tetraphenylporphyrinato indium(III).

Two novel potentiometric membrane sensors responsive to the ibuprofen drug have been developed. These incorporate poly(vinyl chloride) and polyurethane matrix membranes containing 5,10,15,20-tetraphenylporphrinato (TPP) indium(II) ionophore plasticized with dibutylsebacate. The sensors show a near-Nernstian response with anionic slopes of -53 and -55 mV decade(-1), over the concentration range of 4.2 x 10(-6)-1.0 x 10(-2) and 3.3 x 10(-6)-1.0 x 10(-2) M ibuprofen within pH ranges of 4-9 and 5-9 for PVC and PU matrix membranes, respectively. A sensor based on a polyurethane membrane displays a lower detection limit and a wider linear working range, and a sensor based on a PVC membrane exhibits a better overall selectivity, especially in the presence of lipophilic organic anions. Both sensors are used for the quantification and quality-control assessment of ibuprofen in pharmaceutical preparations. The average recoveries are 99.1+/-0.3% and 99.3+/-0.3% for TPP In(III)-PVC and TPP In(III)-PU based membrane sensors, respectively. High selectivities towards ibuprofen in the presence of many anions, drug excipients and diluents are offered by both sensors, which exhibit a non-Hofmeister selectivity pattern.     

碳点在抗生素分析检测中的应用

抗生素的过度使用对环境造成了极大破坏,对其进行监测控制刻不容缓.常用的分析检测技术,如高效液相色谱(HPLC)、气相色谱(GC)、高效液相色谱-串联质谱(HPLC-MS/MS)等具有高效快速、重现性好、可自动化操作等优点.但对环境样品中抗生素的检测存在样品前处理过程繁琐、检测灵敏度低、实验成本高等问题.结合现有的检测技...     

Phosphate-selective fluorescent sensing microspheres based on uranyl salophene ionophores

Optical dihydrogen phosphate-selective sensors that function on the basis of bulk optode principles and are based on two different uranyl salophene ionophores are reported here for the first time. The influence of the optode composition and measuring conditions such as sample pH on the optode response are characterized, along with sensor selectivity and long-term stability. Three plasticizers of different polarity are considered for optode fabrication: bis(2-ethylhexyl)sebacate (DOS), dodecyl 2-nitrophenyl ether (o-NPDDE), o-nitrophenyloctylether (o-NPOE). The compounds 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo[a]phenoxazine (ETH 5294, chromoionophore I) and 9-(diethylamino)-5-[(2-octyldecyl)imino]benzo[a]phenoxazine (ETH 5350, chromoionophore III) are used as H⁺-selective fluoroionophores that also act as reference ionophores. The resulting optode-based sensors are compared with their ion-selective electrode (ISE) counterparts, and it is revealed that optodes are better suited for operation at physiological pH. The best optode performance was found for the two component optode sensors doped with ETH 5350 and phosphate ionophore(I). The linear range of these sensor was log a = −6.0 to −2.6. Dihydrogen phosphate-selective optode sensors of optimized composition are fabricated in microsphere format and preliminary measurements in diluted sheep blood samples are presented.