Chemosensors

The α-glucosidase inhibitor is regarded as one of the most important drugs for the treatment of diabetes, which can control postprandial blood glucose levels via prolonging the carbohydrate digestion time and retarding the carbohydrates’ absorption. The present work aims to establish a facile bioanalytical method, based on α-glucosidase catalyzing the hydrolysis of 2-O-alpha-D-Glucopyranosyl-L-ascorbic acid (AA-2G), for the quantification of acarbose and migliol using a personal glucose meter (PGM). The hydrolysis products (ascorbic acid and glucose) can trigger the reduction of K₃[Fe(CN)₆] to K₄[Fe(CN)₆] in the glucose test strips, which results in the formation of the electron, which can be measured by PGM. Thus, ascorbic acid and glucose can be simultaneously measured by a simplified and miniaturized PGM method. However, the products produced by the hydrolysis of AA-2G will be decreased after the addition of acarbose or migliol to inhibit the activity of α-glucosidase, thereby resulting in a decreased PGM readout. After being incubated with α-glucosidase for 3.0 min and enzymatic reaction for 5.0 min, the quantitative detection of acarbose and migliol can be achieved within the ranges of 1.0–30.0 μM with the limit of detection of 0.33 μM and 3.0–33.3 μM with the limit of detection of 1.0 μM, respectively. IC₅₀ values for acarbose and migliol are calculated to be 10.0 μM and 16.0 μM, respectively. The recoveries of the acarbose and migliol spiked with three different concentrations (final concentrations of 10.0, 20.0, and 30.0 μM) in human serum sample are in the ranges of 89.6–114.5% and 93.9–106.5%, respectively. These results demonstrate that the developed PGM method may be useful in future studies on therapeutic monitoring of acarbose and migliol. Full article

We present a combination of micromachined optofluidic platforms equipped with a fiber-optic sensing configuration based on a three-path Mach–Zehnder interferometer (MZI) for simultaneous measurement of the refractive index of liquids and the autocalibration in dynamic regime. The sensing principle is based on the low-coherence interferometry, characterized by a generation of Gaussian enveloped interferograms, for which the position of its maximum depends on the optical path difference (OPD) between the sensing and reference arm of the MZI. When liquid flows through the central microchannel of the optofluidic platform it crosses the light beam between the two optical fibers in the sensing arm causing the OPD change. An algorithm has been applied for the calculation of the refractive index of liquids out of the raw interference signals. We obtained a very good agreement between the experimental results and literature data of refractive indices of subjected fluids. The accuracy of refractive index measurement is approximately 1%, predominantly determined by the accuracy of reading the position of the mechanical scanner. The proposed sensor is attractive for the label-free biological, biochemical, and chemical sensing owing autocalibration and high sensitivity yet consuming a very small sample volume of 1 µL. It is capable to measure the refractive index of various liquids and/or gases simultaneously in the process. Full article

The sorption affinity of iodide on organo-bentonite, modified with hexadecyl pyridinium (HDPy), was investigated with the iodine–starch method coupled with UV/Vis absorption spectroscopy. The iodine–starch complex method was optimized in terms of the reaction time and sample compositions, based on the UV/Vis absorbance. The batch sorption experiment for iodide on organo-bentonites, modified using two different loading amounts of HDPy, was conducted to analyze the influence of equilibrium time, liquid-to-solid ratio, and temperature, on the iodide sorption affinity. The experimental results regarding the removal capacity were further employed to derive the distribution coefficients of iodide on the organo-bentonites. The novelty of this work lies in the first application of the iodine–starch method coupled with UV/Vis absorption spectroscopy for analyzing the sorption behavior of iodide on modified bentonites. It is expected that the iodide-starch method can be complementarily employed for future research, with respect to the quantification of iodide. Full article

Hepatocellular carcinoma (HCC) is a malignant tumor with high morbidity and mortality on a global scale, and the development of accurate detection and imaging methods for HCC cells is urgently needed. Herein, by connecting peptide L5, which can specifically bind to the overexpressed Glypican-3 (GPC-3) protein of HCC cells with aggregation-induced emission (AIE) moiety ammonium cation-functionalized 9,10-distyrylanthracene (NDSA) via the “click” reaction, we synthesized a fluorescent probe NDSA-L5. In an aqueous solution, the probe shows weak emission, whereas, in the presence of the GPC-3 protein, bright fluorescence can be obtained since NDSA-L5 binds to the GPC-3 protein, leading to the restricted intramolecular movement of AIE-active NDSA-L5. The imaging and flow cytometry experiments demonstrate that the NDSA-L5 probe can rapidly accumulate in the subcutaneous HCC cells and liver tumor tissue and shows a potential application in early detection and surgical navigation for HCC cancer. Full article

Since the first successful transgenic plants obtained in 1983, dozens of plants have been tested. On the one hand, genetically modified plants solve the problems of agricultural production. However, due to exogenous genes of transgenic plants, such as its seeds or pollen drift, diffusion between populations will likely lead to superweeds or affect the original traits. The detection technology of transgenic plants and their products have received considerable attention. Electrochemical sensing technology is a fast, low-cost, and portable analysis technology. This review interprets the application of electrochemical technology in the analysis and detection of transgenic products through bibliometrics. A total of 83 research articles were analyzed, spanning 2001 to 2021. We described the different stages in the development history of the subject and the contributions of countries and institutions to the topic. Although there were more annual publications in some years, there was no explosive growth in any period. The lack of breakthroughs in this technology is a significant factor in the lack of experts from other fields cross-examining the subject. Through keyword co-occurrence analysis, different research directions on this topic were discussed. The use of nanomaterials with excellent electrical conductivity allows for more sensitive detection of GM crops by electrochemical sensors. Furthermore, co-citation analysis was used to interpret the most popular reports on the topic. In the end, we predict the future development of this topic according to the analysis results. Full article

Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling. Full article

In the context of bacteriophage (phage) therapy, there is an urgent need for a method permitting multiplexed, parallel phage susceptibility testing (PST) prior to the formulation of personalized phage cocktails for administration to patients suffering from antimicrobial-resistant bacterial infections. Methods based on surface plasmon resonance imaging (SPRi) and phase imaging were demonstrated as candidates for very rapid (<2 h) PST in the broth phase. Biosensing layers composed of arrays of phages 44AHJD, P68, and gh-1 were covalently immobilized on the surface of an SPRi prism and exposed to liquid culture of either Pseudomonas putida or methicillin-resistant Staphylococcus aureus (i.e., either the phages’ host or non-host bacteria). Monitoring of reflectivity reveals susceptibility of the challenge bacteria to the immobilized phage strains. Investigation of phase imaging of lytic replication of gh-1 demonstrates PST at the single-cell scale, without requiring phage immobilization. SPRi sensorgrams show that on-target regions increase in reflectivity more slowly, stabilizing later and to a lower level compared to off-target regions. Phage susceptibility can be revealed in as little as 30 min in both the SPRi and phase imaging methods. Full article

NiO-sensitive materials have been synthesized via the hydrothermal synthesis route and calcined in air at 400 °C and, alternatively, at 500 °C. Structural, morphological, and spectroscopic investigations were involved. As such, the XRD patterns showed a higher crystallinity degree for the NiO calcined at 500 °C. Such an aspect is in line with the XPS data indicating a lower surface hydroxylation relative to NiO calcined at 400 °C. An HRTEM microstructural investigation revealed that the two samples differ essentially at the morphological level, having different sizes of the crystalline nanoparticles, different density of the surface defects, and preferential faceting according to the main crystallographic planes. In order to identify their specific gas-sensing mechanism towards CO exposure under the in-field atmosphere, the simultaneous evaluation of the electrical resistance and contact potential difference was carried out. The results allowed the decoupling of the water physisorption from the chemisorption of the ambient oxygen species. Thus, the specific CO interaction mechanism induced by the calcination temperature of NiO has been highlighted. Full article

In the last decade, there has been a rapid increase in the number of surface-enhanced Raman scattering (SERS) spectroscopy applications in medical research. In this article we review some recent, and in our opinion, most interesting and promising applications of SERS spectroscopy in medical diagnostics, including those that permit multiplexing within the range important for clinical samples. We focus on the SERS-based detection of markers of various diseases (or those whose presence significantly increases the chance of developing a given disease), and on drug monitoring. We present selected examples of the SERS detection of particular fragments of DNA or RNA, or of bacteria, viruses, and disease-related proteins. We also describe a very promising and elegant ‘lab-on-chip’ approach used to carry out practical SERS measurements via a pad whose action is similar to that of a pregnancy test. The fundamental theoretical background of SERS spectroscopy, which should allow a better understanding of the operation of the sensors described, is also briefly outlined. We hope that this review article will be useful for researchers planning to enter this fascinating field. Full article

Extracellular vesicles are involved in many physiological and pathological activities. They transport miRNAs to recipient cells during their role in intercellular communication, making them emerging biomarkers of many diseases. Interest in exosomal miRNAs has grown after they have shown numerous advantages as biomarkers for diagnosis, prognosis, and evaluation of cancer treatment. This work describes the development of a biosensor for the detection of 21-5p miRNA in human serum using screen-printed carbon electrodes modified with gold nanoparticles fabricated in situ, an innovative approach to avoid the use of more expensive gold substrates that provide better analytical outputs. The several variables involved in the assembly of the biosensor were optimized by univariant mode. Under the best conditions, the biosensor showed a linear response from 0.010 fM to 10 pM, with a limit of detection (LOD) of 4.31 aM. The sensitivity was 0.3718 relative Ω per decade concentration in buffered saline solutions, and the standard deviation of the blank is 2.94 Ω. A linear response was also obtained when human serum samples were tested with miRNA 21-5p. Interference from similar miRNA and miss-match miRNA sequences was evaluated and good selectivity for miRNA 21-5p was observed. Overall, the device proposed is an alternative approach to gold substrates, which typically result in more sensitive systems and lower LODs, which compares favorably to current gold-based biosensors for the targeted miRNA. This design may be further extended to other nucleic acids. Full article

Background: Benzoxazole-containing ligands find many applications both in medicinal chemistry, catalysis and fluorescence chemosensing. Benzoxazole-containing macrocycles could be therefore a good strategy to achieve stable and selective fluorescent complexes with suitable metal ions. In this work, the synthesis, binding, and photochemical properties of a new fluorescent ligand (L) are reported. L is a cyclophane macrocycle containing the 1,3-bis(benzo[d]oxazol-2-yl)phenyl (BBzB) fluorophore and an aliphatic tetra-amine chain to form the macrocyclic skeleton. Methods: Spectrophotometric and spectrofluorimetric measurements, ¹H NMR analysis, and DFT calculations were performed. Results: L behaves as a PET-mediated chemosensor, being emissive at 390 nm at acidic pH and non-emissive at basic pH. The chemosensor is able to detect Zn²⁺ and Cd²⁺ in an aqueous medium (acetonitrile–water, 4:1 v/v) at neutral pH through a CHEF effect upon metal ion coordination. Paramagnetic metal ions (Cu²⁺) and heavy atoms (Pb²⁺, Hg²⁺) resulted in a quenching of fluorescence or very low emission. Conclusions: The new cyclophane macrocycle L was revealed to be a selective PET-regulated chemosensor for Zn²⁺ and Cd²⁺ in an aqueous medium, being able to bind up to two and one metal cations, respectively. The molecule showed a shifted emission towards the visible region compared to similar systems, suggesting a co-planar conformation of the aromatic fragment upon metal coordination. All these data are supported by both experimental measurements and theoretical calculations. Full article

Accurate monitoring is needed for pulsating flow in many healthcare and bio applications. Specifically, real-time monitoring of pulsating blood flow provides rich information regarding a patient’s health conditions. This paper proposes a flexible strain sensor capable of detecting the pulsating fluid flow by directly measuring the circumferential strain induced by a rapid change in the flow rate. The thin and flexible strain sensor consists of a polydimethylsiloxane (PDMS) with a Triton-X treatment to enhance the adhesive property and multi-walled carbon nanotubes (MWCNT) as the piezoresistive sensing layer. MWCNT integration implements a simple spray-coating method. The adhesive PDMS/CNT strain sensor exhibits a highly adhesive nature and can be attached to a silicone tube’s curved surface. By analyzing the theoretical modeling based on fluid energy equation and solid mechanics, strains induced on the soft tube by the change in flow rate, viscosity, and fluid density can be predicted. We performed the flow rate measurement at varying fluid-flow rates and liquid viscosities, and the results match our prediction. The sensitivity and limit of detection of the presented strain sensor are about 0.55 %min/L and 0.4 L/min, respectively. Both the calculation and experiment confirm that the sensor resistance is most sensitive to the fluid-flow rate, thus, enabling the accurate tracking of pulsating fluids’ flow rate, regardless of the viscosity or density. Full article

There are different methods to extract and brew coffee, therefore, coffee processing is an important factor and should be studied in detail. Herein, coffee was brewed by means of a new espresso professional coffee machine, using coffee powder or portioned coffee (capsule). Four different kinds of coffees (Biologico, Dolce, Deciso, Guatemala) were investigated with and without capsules and the goal was to classify the volatiloma of each one by Small Sensor System (S3). The response of the semiconductor metal oxide sensors (MOX) of S3 where recorded, for all 288 replicates and after normalization ∆R/R0 was extracted as a feature. PCA analysis was used to compare and differentiate the same kind of coffee sample with and without a capsule. It could be concluded that the coffee capsules affect the quality, changing on the flavor profile of espresso coffee when extracted different methods confirming the use of s3 device as a rapid and user-friendly tool in the food quality control chain. Full article

This work provides a novel approach for the instant detection of CN⁻ anions based on chromogenic 6-[(E)-(4-nitrophenyl)diazenyl]-1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole] derivatives. New colorimetric detectors were synthesized and characterized. These compounds exhibited a substantial color change from orange to magenta and blue when treated with cyanide ions in a CH₃CN solution buffered with sodium phosphate and demonstrated high selectivity to CN⁻ anions. Common anions were tested, and they did not interfere with cyanide detection, except for carbonates and hydrosulfites. The simple preparation of a molecular sensor and the easily noticeable color change makes this a practical system for the monitoring of CN⁻ ions. This color change is explained by nucleophilic substitution of the pyrane ring oxygen atom at the indoline C-2 atom by the cyanide anion. This generates the appearance of intensively colored 4-(4-nitrophenylazo)phenolate chromophore and allows for determining very low levels of CN⁻ anion. Full article

Abrin is a cytotoxin with strong lethality, which is a serious threat to human health and public safety, and thus, highly sensitive detection methods are urgently needed. The phage display affibody has two major modules, among which, the affibody fragment, with small molecular weight, high affinity and easy preparation, can be used for the specific recognition of the target, and the phage shell, with numerous protein copies, can be used as a carrier for the massive enrichment of signal molecules, and thus is particularly suitable as a sensitive probe for signal amplification in high-sensitivity biosensors. In this study, with antibody-coated magnetic microspheres as capture probes, Ru(bpy)₃²⁺ and biotin dual-labeled phage display affibodies as the specific signal probes and [email protected](bpy)₃²⁺ (Ru(bpy)₃²⁺-coated gold nanoparticles) as the signal amplification nanomaterials, a new electrochemiluminescence (ECL) biosensor with a four-level sandwich structure of “magnetic capture probe-abrin-phage display [email protected](bpy)₃²⁺” was constructed for abrin detection. In this detection mode, [email protected](bpy)₃²⁺, a gold nanocomposite prepared rapidly via electrical interaction, contained an extremely high density of signal molecules, and the phage display affibodies with powerful loading capacity were not only labeled with Ru(bpy)₃²⁺, but also enriched with [email protected](bpy)₃²⁺ in large amounts. These designs greatly improved the detection capability of the sensor, ultimately achieving the ultra-sensitive detection of abrin. The limit of detection (LOD) was 4.1 fg/mL (3δ/S), and the quantification range was from 5 fg/mL to 5 pg/mL. The sensor had good reproducibility and specificity and performed well in the test of simulated samples. This study expanded the application of affibodies in the field of biosensing and also deeply explored the signal amplification potential of phage display technology, which is of high value for the construction of simple and efficient sensors with high sensitivity. Full article

In this paper, we examined the sensing ability of some fluorinated 1,3,4-oxadiazole-containing assemblies toward various metal ions and their nonlinear optical (NLO) properties. The changes in the spectral characteristics of these compounds in the existence of Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Zn²⁺, Co²⁺, Cu²⁺, Hg²⁺, Sn²⁺, and Ag⁺ metal ions were performed, and they were found to be selective and more sensitive toward the addition of Ag⁺, Co²⁺, and Cu²⁺ ions (new bands appeared). Instead, spectral changes in the presence of Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺, and Sn²⁺ were not significant, so we did not evaluate the corresponding binding parameters. Therefore, all of these compounds were found to be selective and sensitive to Ag⁺, Co²⁺, and Cu²⁺ ions. Furthermore, the first-order polarizability (${\mathsf{\alpha }}_{\mathrm{CT}}$), the first-order hyperpolarizability (${\mathsf{\beta }}_{\mathrm{CT}}$), and the second-order hyperpolarizability (γ_CT) were evaluated using the solvatochromic approach, and the intramolecular charge transfer (ICT) characteristics were investigated using a generalized Mulliken–Hush (GMH) analysis. Full article

A super-hydrophilic pH-sensitive electrode with a porous TiO₂ thin film is proposed in this work and fabricated using the chemical etching method. In total, 30 groups of porous TiO₂ thin film were obtained by immersing a Ti sheet in NaOH, with the solution concentration ranging from 0.5–4 M and the reaction time ranging from 15–240 min. SEM, XRD, XPS, and a contact angle meter were used to investigate the influence of the chemical etching parameters on the morphology, composition, and wettability of the fabricated electrodes. The chemical etching parameters were found to have a significant influence on the specific surface area and the component of the films, which strongly affected the wettability and pH sensing characteristics of the electrodes. The electrode obtained with a solution concentration of 1 M and reaction time of 120 min is the ideal product because of its excellent wettability, with a contact angle of 5.46°, and good pH sensing characteristics in pH buffer solutions. The electrode also showed good stability regarding its wettability and pH sensing properties during storage and utilization. Full article

Acoustic biosensors are widely used in physical, chemical, and biosensing applications. One of the major concerns in acoustic biosensing is the delicacy of the medium through which acoustic waves propagate and reach acoustic sensors. Even a small airgap diminishes acoustic signal strengths due to high acoustic impedance mismatch. Therefore, the presence of a coupling medium to create a pathway for an efficient propagation of acoustic waves is essential. Here, we have reviewed the chemical, physical, and acoustic characteristics of various coupling material (liquid, gel-based, semi-dry, and dry) and present a guide to determine a suitable application-specific coupling medium. Full article

This paper reports the results obtained from the determination of ascorbic acid with platinum-based voltammetric sensors modified with potassium hexacyanoferrate-doped polypyrrole. The preparation of the modified electrodes was carried out by electrochemical polymerization of pyrrole from aqueous solutions, using chronoamperometry. Polypyrrole films were deposited on the surface of the platinum electrode, by applying a constant potential of 0.8 V for 30 s. The thickness of the polymer film was calculated from the chronoamperometric data, and the value was 0.163 μm. Cyclic voltammetry was the method used for the Pt/PPy-FeCN electrode electrochemical characterization in several types of solution, including KCl, potassium ferrocyanide, and ascorbic acid. The thin doped polymer layer showed excellent sensitivity for ascorbic acid detection. From the voltammetric studies carried out in solutions of different concentrations of ascorbic acid, ranging from 1 to 100 × 10⁻⁶ M, a detection limit of 2.5 × 10⁻⁷ M was obtained. Validation of the analyses was performed using pharmaceutical products with different concentrations of ascorbic acid, from different manufacturers and presented in various pharmaceutical forms, i.e., intravascular administration ampoules, chewable tablets, and powder for oral suspension. Full article