Carbazole-Based Colorimetric Anion Sensors

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.     

Advances in nucleic acid architectures for electrochemical sensing

Nucleic acid–based electrochemical sensors are ideally suited to the detection of molecular targets for which enzymatic detection or direct electrochemical oxidation – reduction reactions are not possible. Moreover, the versatility of nucleic acids in their ability to bind a great variety of target types, from small molecules to single-entity mesoscopic targets, makes them attractive receptors for the development of electrochemical biosensors. In this brief opinion piece, we discuss field advances from the past two years. We hope the works highlighted here will inspire the community to pursue creative designs enabling the detection of larger and more complex targets with a specific focus on analytical validation and translation into preclinical or clinical applications.     

Molecularly imprinted polymer-carbon paste electrode (MIP-CPE)-based sensors for the sensitive detection of organic and inorganic environmental pollutants: A review

The rapidly growing existence of a number of contaminants (i.e. heavy metals, dye compounds, explosives and pesticides etc.) in environment is an alarming concern not only due to their harmful impacts for the environment bur also due to their potential high risk for human health. Thus, the careful and sensitive detection of these environmental contaminants is ver crucial. Electrochemical sensors combined with molecularly imprinted polymers (MIPs) become an attractive area for environmental monitoring. Benefiting from their great features such as high chemical and physical stability, cheap preparation process, excellent selectivity, sensitivity and fast response towards the target compound/s.This review paper aims to present and highlight the latest progresses in the design and development of novel electrochemical sensor systems composed of MIPs and carbon paste electrodes (CPEs) for the sensitive detection of pollutants in environmental samples.     

Challenges for impedimetric affinity sensors targeting protein detection

The review provides articles discussing big challenges behind successful design of impedimetric biosensors and the way such challenges were/could be addressed for highly sensitive affinity detection of proteins. In particular, the effect of gold etching by chloride ions or by CN^? ions (released from the redox probe [Fe(CN)₆]^3-/4-), the effect of ionic strength of the assay buffer; the effect of initial interfacial properties (capacitance) and the effect of the high analyte:bioreceptor ratio on electrochemical impedance spectroscopy–based biosensing are discussed. The review provides also short discussion related to other factors, which can significantly affect operational performance of electrochemical impedance spectroscopy–based biosensing including novel conductive interfaces, small bioreceptors, strategies for improved selectivity (nonbiofouling interfaces) and sensitivity (use of nanoparticles).     

Layer-by-layer sensor architecture of polymers and nanoparticles for electrochemical detection of uric acid in human urine samples

Excessive uric acid levels in the human body (hyperuricemia) are the main causes of kidney stones and diabetes. In this study, a layer-by-layer arrangement of polymers and nanocomposites is used as a new electrode sensing material for rapid and direct electrochemical determination of uric acid (UA). The electrode surface architecture was constructed by the incorporation of poly (amidoamine) dendrimer with 0.5 generation (poly (amidoamine) [PAMAM] [D-G0.5]) of multiwalled carbon nanotube-silver nanoparticles (MWCNT-AgNP) and a poly (neutral-red) (poly [NR]) polymer. The PAMAM (D-G0.5)/MWCNT-AgNP/poly (NR)-coated electrode has a good electrocatalytic activity for the determination of UA using cyclic voltammetry and showed remarkable enhancement in current response at a low-oxidation potential (0.3 V). Under optimal conditions, the developed electrochemical sensor showed an excellent and wide linear range for the determination of UA (i.e. 0.016 μM–2500 μM), and the limit of detection was found to be 0.005 μM. The modified sensor system demonstrated excellent sensitivity and selectivity toward the detection of UA in the presence of interfering substances, which are commonly found in urine and human fluid samples. Furthermore, the developed sensor has represented both reproducibility and excellent stability for the UA determination in real samples (human urine).     

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: A review

The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.     

A circular dichroism sensor for Ni and Co based on l-cysteine capped cadmium sulfide quantum dots

A new circular dichroism sensor for detecting Ni²⁺ and Co²⁺ was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni²⁺ or Co²⁺. l-Cysteine capped cadmium sulfide quantum dots (l-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of l-Cyst-CdS QDs was significantly changed in the presence of Ni²⁺ and Co²⁺. On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni²⁺ or Co²⁺, the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10–60 μM and 4–80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni²⁺ and Co²⁺, respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni²⁺ and Co²⁺ in real water samples, and the results agreed well with the analysis using the standard ICP-OES.     

Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine

A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, d-penicillamine (DPA) and l-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 μM. Detection limits of this sensor were 0.49 and 0.74 μM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications.     

Solar‐Energy‐Driven Photoelectrochemical Biosensing Using TiO2 Nanowires

Photoelectrochemical sensing represents a unique means for chemical and biological detection, with foci of optimizing semiconductor composition and electronic structures, surface functionalization layers, and chemical detection methods. Here, we have briefly discussed our recent developments of TiO₂ nanowire‐based photoelectrochemical sensing, with particular emphasis on three main detection mechanisms and corresponding examples. We have also demonstrated the use of the photoelectrochemical sensing of real‐time molecular reaction kinetic measurements, as well as direct interfacing of living cells and probing of cellular functions.     

Cysteine‐Mediated Intracellular Building of Luciferin to Enhance Probe Retention and Fluorescence Turn‐On

The development of sensitive and selective small molecular probes that enable real‐time detection of endogenous cysteine (Cys) has become an attractive topic because of the essential roles played by Cys in controlling the cellular nitrogen balance and in maintaining biological redox homeostasis. Herein, we report a Cys‐specific probe, 2‐cyanobenzothiazol‐6‐yl acrylate (CBTOA), that shows not only fluorescence turn‐on for sensitive detection of endogenous Cys but also enhanced probe retention inside cells for real‐time monitoring of Cys levels upon external stimulation. Cys‐mediated intracellular formation of luciferin from CBTOA was the key strategy leading to this new type of fluorogenic probe. CBTOA showed fast response to Cys in living cells and liver tissue slices with high sensitivity and selectivity. By using CBTOA as a real‐time probe, we were able to monitor the change in Cys levels in living HeLa cells under ROS‐induced oxidative stress as well as in human mesenchymal stem cells during adipogenic differentiation.