Organic radical-ion salts as selective electrochemical sensors

A series of semiconducting organic radical-ion salts has been studied with regard to the potential use of such compounds in solid-state ion-selective electrodes. Improvements in working activity ranges and selectivities were obtained in comparison with previously investigated salts of TCNQ; excellent calibration graphs were obtained for lead(II), copper([I) and tctraphenylarsonium ions.     

Different approaches for fabrication of low-cost electrochemical sensors

Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques, such as photolithography and sputtering, are excellent alternatives for producing these platforms. However, owing to the requirement of expensive and sophisticated instrumentation, as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, using consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages.     

Novel electrochemical sensor for the selective recognition of chlorogenic acid

In this article, we demonstrate the fabrication and simultaneous fluorescent detection of two biomarkers related to lung cancer. Polystyrene microspheres (PSM) were introduced as biomolecular immobilizing carriers and a 96-well filter plate was used as the separation platform. The whole experiment could be effectively carried out in a homogeneous system, as exemplified by the detection of carcinoembryonic antigen (CEA) and neuron specific enolase (NSE). First, two capture antibodies for CEA and NSE were immobilized on the PSM surface. Next, they reacted successively with two antigens and two modified detection antibodies. Finally, these two biomarkers could be recognized by streptavidin-conjugated quantum dots (QD) and goat-anti-FITC conjugated QD with a detection limit of 0.625 ng mL(-1), which was lower than the clinical cut-off level. The protocol showed good precision within 6.36% and good recovery in the range of 90.86-105.02%. Compared with several other assay formats reported previously, our new technique is competitive or even better. Furthermore, the immunosensor was successfully illustrated in 20 serum samples. Overall, this new immunoassay offers a promising alternative for the detection of biomarkers related to cancer diseases, taking advantage of simplicity, specificity, sensitivity and cost-efficiency.     

Performance of selective and partially selective sensors in the recognition of beverages

A sensor array composed of selective and partially selective electrodes is applied to the recognition of beverages: milk, orange juice, and beer. The role of selective and partially selective sensors in classification results is discussed. For this reason two experiments are realized: distinguishing among various types of foodstuffs and the recognition of their origin (manufacturer). In both cases, the measurements were performed in stationary and flow mode. Classical ion-selective electrodes and miniaturized solid-state electrodes were considered.The best results are obtained when the two types of sensor are incorporated in the array, which leads to the highest correctness of the system response. It is however worth to notice, that in the case of some samples (for example, milk) satisfactory results were obtained when only selective or when only partially selective electrodes were applied.     

选择性识别儿茶酚胺的长波长二硼酸荧光探针

儿茶酚胺是人体中重要的神经递质.选择性识别儿茶酚胺对帕金森氏综合症、嗜铬细胞瘤、神经母细胞瘤等疾病临床诊断及病理学研究具有重要意义.2-(4-二羟基硼烷)苯基喹啉-4-羧酸(PBAQA)与糖结合后荧光强度增强,与儿茶酚胺结合后荧光强度下降,可以作为选择性识别儿茶酚胺的荧光探针.但由于发射波长较短,PBAQA及其衍生物在荧光成像方面存在诸多限制.本文作者采用廉价易得的原料制备中间体PBAQA,然后经酰胺缩合、脱保护,制备氨基中间体,再与3-羧基硼酸缩合合成二硼酸.目标化合物的发射波长明显红移至500 nm左右,斯托克位移超过100 nm.初步活性测试发现,目标化合物与儿茶酚胺结合后荧光强度明显降低,且荧光强度改变与儿茶酚胺浓度存在线性关系,可作为选择性识别儿茶酚胺的长波长荧光探针.     

Analytical use of the selective extraction of copper as its phenylacetate

Chloroform solution of phenylacetic add has been found very suitable for extraction and colorimetric determination of copper. Iron and uranium are the main interferences, which can be overcome by masking with ammonium fluoridc. Under these conditions, only gold(III), platinum(IV) and palladium(II) are co-extracted, but their colour does not interfere with measurement of the green copper extract at 700 nm. The method has been applied to the determination of copper in iron, steels, uranium, lead concentrates and alloys containing nickel, cobalt, etc. The extraction procedure can also be used to remove interference of iron, copper and uranium in the determination of manganese with formaldoxime.     

A selective artemisinin-sensor using metalloporphyrin as a recognition element entrapped in the Au-nanoparticles-chitosan modified electrodes

An amperometric artemisinin (ARN) sensor based on the supramolecular recognition of glycosylated metalloporphyrin, which is included in the Au-nanoparticles-chitosan film coated on the glass carbon electrodes, was developed. For the improvement of the selectivity of artemisinin detection, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-d-glucopyranosyl)-1-O-phenyl]porphyrin (T(o-glu)PPH) metal complex [FeT(o-glu)PPCl] was synthesized and employed as a ARN-sensitive and -selective material in the amperometric sensors. The proposed [FeT(o-glu)PPCl]/Au-nanoparticles modified electrodes showed excellent selectivity and sensitivity toward ARN with respect to a number of interferents and exhibited stable current response, which can be attributed to the coordination of ARN with the [FeT(o-glu)PPCl] in the electrodes. The calibration graph obtained with the proposed sensor was linear over the range of 1.8 × 10⁻⁷-1.7 × 10⁻⁹ mol l⁻¹, with a detection limit of 1.7 × 10⁻⁹ mol l⁻¹ for ARN. Significant advantages of the proposed procedure over the conventional reductive electrochemical methods are the selective detection and the relatively low applied potential requirement of the ARN-sensor. The prepared sensor is applied for the determination of ARN in plant samples and the results agreed with the values obtained by the pharmacopoeia method.     

Facile electrochemical fabrication of polymeric templates for spatially selective deposition of metals

Here, we report on a simple and general approach to fabricate polymeric (poly(2-methoxyaniline)) templates for deposition of silver in the form of micro islands on the electrode surface. The method is based on the application of electrochemically generated hydrogen microbubbles to locally block polymerization of monomers on the surface. This yields micrometer-sized holes within the forming polymeric film, which act as gate sites enabling further selective deposition of the metal on the surface.     

Unusual metals as electrode materials for electrochemical sensors

Although noble metals are still widely used in electroanalysis, a plethora of different nonconventional metals is now enriching the panorama of materials acting as the electrochemical transducer in sensing systems. In particular, Ti, Cu, Co, Fe, Mo, Ta, W, Rh, Bi, Sb, Te and Pb are discussed here in view of their peculiar physicochemical properties and of the interesting electrocatalytic activities ascribable to these elements and to the relevant metal oxide ultrathin films that spontaneously form at the electrode–solution interface. This behaviour, exploitable in electroanalysis for the detection of a number on analytes, is often accompanied by low price and high resistance to corrosion and to abrasion characterising these materials. These peculiarities encourage the possible use of the cited metals in a wide number of analytical frames, ranging from process control to bioimplantable sensing systems.     

Gold chloride electrodes as electrochemical sensors for liquid chromatography

A fast, simple, inexpensive and reproducible method for the fabrication of a gold chloride electrode is presented. The response of this electrode is highly stable and it leads to improved detection for various redox species. Experiments demonstrating the utility of the gold chloride electrode as a sensitive sensor for liquid chromatography are described.     

Triphenylamine-based novel PET sensors in selective recognition of dicarboxylic acids

The triphenylamine-based chemosensors 1 and 2 have been designed and synthesized, for the first time, for the selective recognition of dicarboxylic acids. Carboxylic acid binding takes place through charge neutral pyridyl amide receptor sites with concomitant quenching of fluorescence of the triphenylamine moiety. The bindings were examined using ¹H NMR, fluorescence and UV-vis spectroscopic methods. The receptor 1 was found to be selective for glutaric and adipic acids and the macrocycle 2 was specific for 2,2-dimethylmalonic acid.     

Ferrocene-mannose conjugates as electrochemical molecular sensors for concanavalin A lectin

The binding affinity of a series of electroactive glycoconjugates, based on a ferrocene core bearing alpha-mannose units on one or both of its cyclopentadienyl rings, to lectin Con A was studied by isothermal titration calorimetry (ITC) and voltammetry. Voltammetric measurements were performed by differential pulse adsorptive stripping voltammetry (DPAdSV). Upon complexation of ferrocene-mannose conjugates with Con A, voltammograms showed a decrease of the peak current. Both the monomannosylated ferrocene and the bis(mannosylated) ferrocene derivatives form more stable complexes with Con A than methyl alpha-D-mannopyranoside. Bis(mannosylated) ferrocene conjugates were found to bind to Con A with enhanced affinity due to the multivalent effect. A comparison of the thermodynamic data obtained by ITC and voltammetry is presented.     

Films of lutetium bisphthalocyanine nanowires as electrochemical sensors

Lutetium bisphthalocyanine (LuPc(2)) nanowires have been successfully obtained by electrophoretic deposition (EPD). The influence of the deposition conditions and annealing in the structure of the films has been studied by AFM, SEM, X-ray diffraction (XRD), UV-vis absorption, and near-infrared (NIR). The electrochemical properties of the EDP films immersed in different electrolytic solutions (KCl, MgCl(2), KClO(4), HCl, and NaOH) indicate that anions diffuse inside the film to maintain the electroneutrality and the kinetics follows the Randles-Sevcik equation. The stability of the response increases strongly upon annealing due to the improvement of the adhesion of the sensitive material to the substrate. The EPD films have been successfully used to detect caffeic acid (an antioxidant of interest in the food industry). The anodic peak associated with the oxidation of caffeic acid appears at 0.54 V and is linearly dependent on the caffeic acid concentration in the 6 × 10(-5) M to 5 × 10(-4) M range with a detection limit of 3.12 × 10(-5) M. The electrochemical behavior of the annealed LuPc(2) EPD films is similar to that observed using Langmuir-Blodgett (LB) nanostructured films. However, the different molecular organization of the molecules inside the film causes differences in the shape and position of the peaks. Although LuPc(2) sensors prepared with both EPD and LB techniques provide stable and reproducible responses, the use of EPD is preferred for real sensing applications because of its lower cost, shorter preparation time, and longer lifetime.     

An electrochemical sensor for 3,4-dihydroxyphenylacetic acid with carbon nanotubes as electronic transducer and synthetic cyclophane as recognition element

A new electrochemical sensor was demonstrated for selective sensing of 3,4-dihydroxyphenylacetic acid (DOPAC) through a non-oxidative mechanism by using single-walled carbon nanotubes (SWNTs) as the electronic transducer and a synthetic cyclophane electron acceptor as the recognition element.     

Cast films of lipid-coated enzymes as selective sensors for disaccharides

A stable enzyme film was prepared on a platinum electrode by casting organic solutions of a lipid-coated enzyme. The glucose oxidase (GOD)-immobilized electrode acted as a glucose sensor with a high sensitivity and a short response time. When the lipid-coated GOD was combined with a lipid-coated glycosidase on the electrode, the film showed a high selectivity for various disaccharides. For example, combining β-galactosidase with GOD, the electrode responded only to lactose (Galβ1→4Glc), having β-galactoside at the non-reducing side of the disaccharide, but not to maltose (Glcα1→4Glc) and cellobiose (Glcβ1→4Glc) in the aqueous solution. Similarly, an enzyme electrode sensitive only for maltose (Glcα1→4Glc), cellobiose (Glcβ1→4Glc), and sucrose (Glcα1→2Fru) could be prepared by using a mixed cast film of two lipid-coated enzymes, GOD and α-glucosidase, GOD and β-glucosidase, and GOD and invertase, respectively. This technique will become a new process not only for preparing sensor membranes but also for assembling water-soluble proteins on biological electrical components.     

A strategy for improving the sensitivity of molecularly imprinted electrochemical sensors based on catalytic copper deposition

A novel method to improve the sensitivity of molecularly imprinted polymer sensors was developed. Oxytetracycline (OTC), which was selected as the template molecule, was first rebound to the imprinted cavities. Gold nanoparticles were then labeled with the amino groups of OTC molecules via electrostatic adsorption and non-covalent interactions. Copper ions were catalytically reduced by the gold nanoparticles, and copper was deposited onto the electrode. The deposited copper was electrochemically dissolved, and its oxidative currents were recorded by differential pulse voltammetry (DPV). OTC could be determined indirectly within the concentration range of 3.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹ with a detection limit of 6.8 × 10⁻¹¹ mol L⁻¹.     

Bioresponsive DNA-co-polymer hydrogels for fabrication of sensors

Bioresponsive hydrogels that include DNA within a non-DNA network (DNA-co-polymer hydrogels) constitute a group of soft materials possessing selective recognition ability hosted by the included DNA structure. They are furthermore characterized by the changes to the hydrogel properties which follow the recognition of the biological analyte. Such hydrogels can be synthesized with desired recognition ability through the selection of particular nucleotide sequence that is recognizing or binding ions, small molecules, biomolecules or parts of larger entities. The binding of the label-free analyte triggers a response of the hydrogel, such as changes in its swelling volume, mass, optical or mechanical properties. The hydrogel response is mediated by changes in network parameters such as charge density, crosslinking density or a combination of these associated with the interaction with the analyte. Bioresponsive DNA polymer hydrogels have found wide application in biosensors due to their versatile nature.     

Rapid and inexpensive method for the simple fabrication of PDMS‐based electrochemical sensors for detection in microfluidic devices

The fabrication of PDMS microfluidic structures through soft lithography is widely reported. While this well‐established method gives high precision microstructures and has been successfully used for many researchers, it often requires sophisticated instrumentation and expensive materials such as clean room facilities and photoresists. Thus, we present here a simple protocol that allows the rapid molding of simple linear microchannels in PDMS substrates aiming microfluidics‐based applications. It might serve as an alternative to researchers that do not have access to sophisticated facilities such as clean rooms. The method developed here consists on the use of pencil graphite leads as template for the molding of PDMS channels. It yields structures that can be used for several applications, such as housing support for electrochemical sensors or channels for flow devices. Here, the microdevices produced through this protocol were employed for the accommodation of carbon black paste, which was utilized for the first time as amperometric sensor in microchip electrophoresis. This platform was successfully used for the separation and detection of model analytes. Ascorbic acid and iodide were separated within 45 s with peak resolution of 1.2 and sensitivities of 198 and 492 pA/μM, respectively. The background noise was ca. 84 pA. The analytical usefulness of the system developed was successfully tested through the quantification of iodide in commercial pharmaceutical formulations. It demonstrates good efficiency of the microfabrication protocol developed and enables its use for the easy and rapid prototyping of PDMS structures over a low fabrication cost.     

选择性识别果糖的二硼酸荧光探针的合成及初步活性研究

通过以2-(4-二羟基硼烷)苯基喹啉-4-羧酸(PBAQA)和羧酸苯硼酸作为功能单体,哌嗪作为连接片,在甲醇溶液中经过进行两次酰胺缩合,得到具有双结合位点的新型水溶性二硼酸化合物.初步的荧光活性实验证明,果糖能够显著性地增强化合物11,12的荧光强度,结合常数显著高于其他糖类.加入75 mmol·L~(-1)果糖后,荧光强度增加12倍.因此,化合物11,12适合用作果糖选择性识别和检测的荧光探针.本文合成具有双结合位点的新型二硼酸化合物水溶性好,这对寻找新型水溶性硼酸荧光探针,提高探针分子在食品和医药中对果糖识别能力具有重要意义.