Chemosensors, Volume 10, Issue 12 (December 2022) – 50 articles

Two different, commercial colourimetric CO₂ indicators are made in the lab, namely one based on an indicator in solution for monitoring the level of dissolved CO₂ in an aquarium, i.e., a drop check indicator, and another based on an ink, for monitoring the level of CO₂ in breath (capnography), i.e., a correct tracheal placement indicator. The selected commercial indicators are limited currently in terms of the analytical information they provide (qualitative) as they are normally assessed by eye. Thus, in each case, for both the lab-made and commercial indicators, colour photography coupled with digital image analysis, i.e., digital colour analysis (DCA), is used to convert the colour data from the indicator into a quantitative measure of CO₂ and so markedly improve the quality of the analytical information provided by original indicator. This is the first time either indicator has been studied as a quantitative analytical system. The CO₂ sensitivity of each of the lab-made indicators is found to match well that of its commercial counterpart. A simple program is provided to help non-experts and experts alike to apply DCA in this way. The potential of DCA to enhance the performance of other commercial indicators is discussed briefly. Full article

Ascorbic acid (AA) has been widely used to improve human health since it was first found, such as resisting scurvy, enhancing immunity, and preventing arteriosclerosis. Moreover, it plays a very important role in the anti-oxidation process in the human body. Therefore, it is of great significance to develop sensitive and accurate detection methods. In this work, silver-coated gold nanorods (Au@Ag NRs) acted as the optical probe, which could be etched with hydroxyl radicals (·OH) from the Fenton reaction between H₂O₂ and Fe²⁺, leading to the blue shift of longitudinal localized surface plasmon resonance absorption. However, as a free radical scavenger, AA was able to inhibit the Fenton reaction, resulting in a red shift of plasmon resonance absorption. Based on the change in longitudinal plasma resonance absorption of silver-coated gold nanorods, a linear relationship between the maximum longitudinal absorption wavelength and the concentration of AA was established in the range of 2.5–17.5 μM with a limit of detection (LOD) of 0.48 μM and a limit of quantitation (LOQ) of 1.61 μM, which was feasible to detect AA in tablets. Full article

Here, we present a direct comparison of different dyes and assays for the determination of protein concentrations. We compared the classical Bradford assay with two modern assays based on the fluorogenic dyes QuDye and ProteOrange and showed that the Bradford reagent achieved excellent results in the determination of protein concentrations as compared with more modern rivals. We also showed that standard approaches for determining the limit of detection (LoD) and limit of quantification (LoQ) may not work correctly with the tested dyes. We proposed a new approach that extends the standard algorithm for LoD and LoQ determination. This approach works well with both classical colorimetric and fluorogenic dyes, as well as with nontrivial fluorescent probes. Full article

A guided-mode resonance (GMR) sensor with multiple resonant modes is used to measure the collection of biomolecules on the sensor surface and the index of refraction of the sensor environment (bulk). The number of sensor variables that can be monitored (biolayer index of refraction, biolayer thickness, and bulk, or background, index of refraction) is determined by the number of supported resonant modes that are sensitive to changes in these variable values. The sensor we use has a grating and homogeneous layer, both of which are made of silicon nitride (Si₃N₄), on a quartz substrate. In this work, we simulate the sensor reflection response as a biolayer grows on the sensor surface at thicknesses from 0 to 20 nm and biolayer indices of refraction from 1.334 to 1.43 RIU; simultaneously, we vary the bulk index of refraction from 1.334 to 1.43 RIU. In the specified span of sensor variable values, the resonance wavelength shifts for 2023 permutations of the biolayer index of refraction, biolayer thickness, and bulk index of refraction are calculated and accurately inverted. Inversion is the process of taking resonant wavelength shifts, for resonant modes of a sensor, as input, and finding a quantitative variation of sensor variables as output. Analysis of the spectral data is performed programmatically with MATLAB. Using experimentally measured resonant wavelength shifts, changes in the values of biolayer index of refraction, biolayer thickness, and bulk index of refraction are determined. In a model experiment, we deposit Concanavalin A (Con A) on our sensor and subsequently deposit yeast, which preferentially bonds to Con A. A unique contribution of our work is that biolayer index and biolayer thickness are simultaneously determined. Full article

In biomedical diagnosis, the efficient separation and purification of specific targets from clinical samples is the desired first step. Herein, the concept of virtual filter membranes based on optically-induced dielectrophoresis (ODEP) manipulation in a microfluidic channel is proposed as a light screening membrane for the separation of polystyrene (PS) microparticles with three different diameters of 15.8, 10.8 and 5.8 µm. The ODEP manipulation velocity of three types of PS microparticles reacted with the color brightness setting was investigated to determine the light intensity to induce an ODEP force higher than the drag force of fluid speed. The color brightness of the light bar in three areas of the light screening membrane was selected as 60%, 70% and 100% to isolate PS microparticles with diameters of 15.8, 10.8 and 5.8 µm, respectively. With a double light bar and a flow rate of 3 µL/min, the recovery rate and isolation purity was improved by 95.1~100% and 94.4~98.6% from the mixture of three types of PS microparticles within 2 min, respectively. This proposed light screening membrane could be a candidate for the separation of small-volume and rare biomedical samples, including circulating tumor cells (CTCs) and bacteria in the blood. Full article

Porous noble metal nanomaterials can be employed to construct sensitive surface-enhanced Raman scattering (SERS) substrates, because the plasmonic nanopores and nanogaps of the porous materials can provide a larger number of hotspots, and can also serve as containers of analyte molecules. However, the fabrication processes of nanoporous noble metal are generally complicated. Here, a facile method is presented to prepare nanoporous Ag nanoparticles-decorated Ag₇O₈NO₃ micro-pyramids, which are fabricated through the chemical reduction of the electrodeposited Ag₇O₈NO₃ micro-pyramids using NaBH₄. The Ag₇O₈NO₃ micro-pyramids are fabricated by electrodeposition by using a simple aqueous solution of AgNO₃ as electrolyte. Then, porous Ag-decorated Ag₇O₈NO₃ micro-pyramids are achieved by the chemical reduction of the surface of the electrodeposited Ag₇O₈NO₃ micro-pyramids with NaBH₄. The high-density nanopores and nanogaps of the fabricated nanoporous Ag can provide plenty of hot spots for Raman enhancement. Additionally, the nanopores have an effective capacity to trap and enrich analytes. Using rhodamine 6G (R6G) as a probe molecule, the SERS performance of the fabricated SERS substrate has been investigated. It is found that a limit of detection (LOD) ~1.0 × 10⁻¹⁵ M can be achieved for R6G. Then, the SERS substrates are employed to detect dye molecule (crystal violet) and pesticide (thiram), and their LODs are calculated down to 9.6 × 10⁻¹³ M and 1.3 × 10⁻¹⁵ M, respectively. The enhancement factor of the fabricated SERS substrate is estimated to be as high as 5.6 × 10⁸. Therefore, the nanoporous Ag-decorated Ag₇O₈NO₃ micro-pyramids have shown promising application in the sensitive SERS detection of organic molecules. Full article

Gold- and silver nanoparticles (Au NPs and Ag NPs)-based colorimetric detection of specific analytes has attracted intense research interest and is still in great demand. The majority of Au NPs- and Ag NPs-based sensory reports have revealed that, during the analyte recognition, dispersed NPs typically aggregated and displayed color changes from wine-red to blue/purple and yellow to orange/brown, respectively. On the other hand, only a few reports demonstrated that the aggregated Au NPs and Ag NPs underwent anti-aggregation in the presence of certain analytes, which displayed reversed color changes from blue/purple to wine-red and orange/brown to yellow, correspondingly. There are some examples of anti-aggregation phenomena mentioned in a vast number of studies on Au NPs- and Ag NPs-based colorimetric sensors via NP aggregation. However, a review targeting the anti-aggregation-enabled Au NPs- and Ag NPs-based colorimetric sensing of diverse analytes is not yet available. In this review, anti-aggregation-facilitated Au NPs- and Ag NPs-based colorimetric detection of metal ions, anions, bio-analytes, pesticides, and herbicides is delivered with detailed underlying mechanisms. Moreover, the probe design, sensory requirement, merits, limitations, and future scope of anti-aggregation-enabled Au NPs- and Ag NPs-based colorimetric sensors are discussed. Full article

An electronic nose sensor array can classify and quantify different types of gases; however, the sensor can alter its measurement capability over time. The main problem presented during the measurements of the sensors is related to the variation of the data acquired for long periods due to changes in the chemosensory response, thus affecting the correct functioning of the implemented measuring system. This research presents an approach to improve gas quantification through the implementation of machine learning regression techniques in an array of nose-type electronic sensors. The implemented methodology uses a domain adaptation approach with the Kullback–Leibler importance estimation procedure (KLIEP) to improve the performance of the gas quantification electronic nose array. This approach is validated using a three-year dataset measured by a 16-electronic-nose-sensor array. The R2 regression error obtained for each of the gases fits the resulting dataset’s measured values with good precision. Full article

Herein, a fabric phase sorptive extraction-based scheme was reported for the determination of amphotericin B in human urine. The developed method allowed the direct extraction of the analyte from the biological matrix with improved selectivity, repeatability and recovery. Due to the membrane’s engineered affinity towards the analyte, extraction equilibrium was achieved in 30 min. Moreover, no additional sample pretreatment was required due to the high permeability of the FPSE membrane and the small volume of eluting solvent required for quantitative back-extraction of the analytes. The hydrophobic sol–gel polydimethylphenylsiloxane (sol–gel PDMDPheS) coated membrane provided the optimum extraction performance. Important parameters that affect the extraction efficiency (such as sample volume, extraction time, membrane size, stirring rate, ion strength, elution solvent and time) were thoroughly investigated. The analyte was separated from the internal standard (nimesulide) and endogenous compounds of the human urine using a gradient elution program. The proposed assay was linear within the range of 0.10–10.0 μg mL⁻¹ while the relative standard deviation of the repeatability (s_r) and within-laboratory reproducibility (s_R) were less than 12.7% in all cases. The method exhibited good accuracy which varied between 88.1 to 110.3%. The developed method was successfully applied for the monitoring of amphotericin B concentration in human urine. Full article

Aerosol is a suspension of fine chemical or biological particles in the air, and it is harmful, easily causing air pollution, respiratory diseases, infrastructure corrosion, and poor visibility. Therefore, the development of advanced optical sensors for real-time detection of aerosol deposition is of great significance. In this work, a prism-coupled composite optical waveguide (COWG) sensor for aerosol deposition detection based on surface scattering is proposed and demonstrated theoretically and experimentally. The COWG consists of a single-mode slab glass waveguide locally covered with a tapered thin film of high-index metal oxide. The tapered film can greatly enhance the evanescent field through the adiabatic transition of the fundamental transverse electric (TE₀) mode between the uncovered and film-covered regions, thereby enabling the COWG to serve as a simple yet highly sensitive evanescent-wave scattering sensor for sensitive detection of aerosol deposition. The COWG with a tapered layer of Ta₂O₅ was prepared by masked sputtering, aerosol salt particle deposition on the COWG was successfully detected, and the influence of surface water droplets on the COWG sensor performance was analyzed. The experimental results indicate that the sensitivity of the COWG is 30 times higher than that of the bare glass waveguide. Full article

Large specific surface area nanostructures are desirable in a wide range of sensing applications due to their longer light-trapping path and increased absorption. Engineering of the specific nanotree structure which possesses a high branch density turned out to be challenging from the experimental point of view, and certainly not adequately explored. This paper shows how to design substrates with a silicon nanotree structure for surface-enhanced Raman spectroscopy (SERS) applications. Silicon nanotrees were synthesized by a Ag-Au nanocluster-catalyzed low-pressure chemical vapor deposition method (LPCVD). By the presented approaches, it is possible to manipulate branches’ number, length and thickness. The synthesized nanostructures are flexible after immersion in water which improves SERS performance. The amount of sputtered metal played a key role in preserving the flexibility of the nanotree structure. The obtained substrates with highly fractal nanostructure were tested on 4-mercaptophenylboronic acid (MPBA) to match the optimal SERS parameters. The silicon nanotrees fabrication, and particularly obtained SERS substrates plated with Ag and Au nanoparticles, demonstrated good features and a promising approach for further sensor development. Full article

Tungstate and molybdate phosphors have received great attention for their excellent photoluminescent properties and thermal stabilities. In the article, Tb³⁺-activated tungstate and molybdate green phosphors were prepared by a solid-state reaction method at different caline temperatures and were compared and studied. The crystal structures and the morphologies of samples were characterized by X-ray diffraction (XRD) patterns and field emission scanning electron microscopy (FE-SEM) images. The energy-dispersive spectra (EDS) proved the compositions of the prepared samples. The photoluminescence (PL) spectra showed that the PL excitation spectra of Tb³⁺-doped Lu₂W₃O₁₂ and Lu₂Mo₃O₁₂ green phosphors consisted of a broad and strong charge transfer band (CTB) and 4f–5d transitions of Tb³⁺ in the ultraviolet (UV) wavelength range and some narrowed excitation peaks from the 4f–4f transition of Tb³⁺ in the near ultraviolet (NUV) wavelength region. The PL emission spectra of the phosphors exhibited the characteristic green emissions owing to the ⁵D₄→⁷F₅ transition of Tb³⁺ located at about 547 nm. The values of energy gap E_g were calculated based on the diffuse reflection spectra (DRS). The measuring temperature-dependent PL spectra illustrated the thermal stabilities of phosphors. The Tb³⁺-doped Lu₂Mo₃O₁₂ phosphor presented normal thermal quenching phenomena and the values of the thermal activation energy E_a were calculated based on the measuring temperature dependent PL emission spectra. The Tb³⁺-doped Lu₂W₃O₁₂ phosphor exhibited abnormal thermal enhancing CTB excitation intensity at about 170 °C. Furthermore, the PL decay curves suggested that the lifetime corresponding to the ⁵D₄ level of Tb³⁺ in the Lu₂W₃O₁₂ host lattice was longer than that in the Lu₂Mo₃O₁₂ host lattice. Compared the Tb³⁺-doped Lu₂Mo₃O₁₂ phosphor, the Tb³⁺-doped Lu₂W₃O₁₂ phosphor has shown potential as an application in temperature sensors. Full article

Luminescent carbon dots (CDs) synthesized from Pithecellobium dulce (P. Dulce) leaves, in a simple, single-step carbonization procedure, were used as optical nanosensors. TEM revealed the crystalline nature of the CDs with the average dimension of 20 nm with a quantum yield of 24%. In addition to carbon, the X-ray photoelectron spectroscopy shows the presence of oxygen and nitrogen. The FTIR spectra and Zeta potential were used for additional characterization of the nanoprobes. Among the contaminants and heavy metals, the proposed nanoprobes were found to be selective towards 4-nitrophenol (4-NP) and Cr(VI), respectively. The emission response of CDs towards 4-NP solution not only reveals the high sensitivity of the CDs (Limit of detection (LOD) of 14 nM) but also demonstrates a color change (light to dark yellow) that is attributed to spontaneous deprotonation detectable with the naked eye. The selectivity of CDs towards Cr(VI) (LOD 0.9 nM) was also tested in the presence of other metals. The quenching mechanism has been attributed to the inner filter effect for both analytes. The observed low detection limits in river and tap water opens up the possible applicability of the proposed nanoprobes as optical sensors in environmental pollution monitoring. Full article

This study enables the simultaneous monitoring of persistent organics pollutants (POPs) in the relevant marine seagrass Posidonia oceanica (L.) Delile (P. oceanica), without causing damage and preserving their ecological integrity and their key ecosystem services, and in marine sediments. Two classes of POPs that suppose a current threat to the environmental health status are investigated: polychlorinated biphenyls (PCBs) and pesticides. Comparisons between tissues and sediment compartmentation are studied for the first time. For these purposes, the sediments, P. oceanica leaves and, as a novelty, rhizomes, were studied. Samples were analyzed by gas chromatography coupled with high-resolution mass spectrometry (GC-Q-Orbitrap MS) for a comprehensive study. Eco-friendly methods were developed and validated for the determination of 38 POPs, 25 PCBs and 13 priority pesticides. The results showed that, when detected, regulated contaminants were localized mainly in the long-lived rhizomes, and 7 PCBs (the most abundant being PCB 44) and 4 priority pesticides (trifluralin, chlorpyrifos, isodrin and o,p’-DDT) were seen. Additionally, a retrospective analysis (suspect screening) was conducted, exhibiting up to 13 current-use pesticide residues in leaves and rhizomes alike. The results suggest that P. oceanica might be acting as a sink to contaminants in coastal areas and that rhizomes, due to their longer lifespan, reflect past and legacy contamination. Full article

Plastic particles smaller than 5 mm accumulate in aqueous, terrestrial, and atmospheric environments and their discovery has been a serious concern when it comes to eco-toxicology and human health risk assessment. In the following review, the potential of mass spectrometry (MS) for the detection of microplastic (MP) pollutants has been elaborately reviewed. The use of various mass spectrometric techniques ranging from gas chromatography–mass spectrometry (GC-MS), liquid chromatographic mass spectrometric (LC-MS) to matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), including their variants, have been reviewed. The lapses in the detection system have been addressed and future recommendations proposed. The challenges facing microplastics and their detection have been discussed and future directions, including mitigation methods, have been presented. Full article

Chrysanthemi Flos ‘Hangbaiju’ (HBJ) is a common Chinese medicinal material with the same origin as the medicinal and edible cognate plant in China, whose quality is seriously affected by the place of origin. In this study, four stable isotope ratios (δ¹⁵N, δ²H, δ¹³C, and δ¹⁸O) and 44 elements were detected and analyzed in 191 HBJ flower samples from six locations in China to trace the origin of HBJ. An ANOVA analysis of δ¹⁵N, δ²H, δ¹³C, and δ¹⁸O values, as well as milti-elements, showed that there were significant differences among the six places of origin. Partial least squares discriminant analysis (PLSDA) and one-class partial least squares discriminant analysis (OPLS-DA) models were established to trace the origin of HBJ from these six locations. The results showed that the classification effect of the PLSDA model is poor; however, the established OPLS-DA model can distinguish between products of national geographic origin (Tongxiang City, Zhejiang Province, China) and samples from other origins, among which Ni, Mo, δ¹³C, Cu, and Ce elements (VIP > 1) contribute the most to this classification. Therefore, this study provides a new method for tracing the origins of HBJ, which is of great significance for the protection of origin labeling of products. Full article

The aim of this work is to develop a device based on thin-layer chromatography coupled with surface-enhanced Raman spectroscopy (TLC-SERS) to analyze sulfamethoxazole (SMX) and trimethoprim (TMP) in commercial milk samples using chemometric tools. Samples were eluted in TLC plates, and a central composite design (CCD) of two factors was performed to optimize the gold nanoparticle dispersion on TLC plates for SERS, aiming at the detection of both drugs at concentrations close to their maximum residual limits (MRLs). Following the optimization, hyperspectral images from the SERS were captured of the TLC plates. Multivariate curve resolution (MCR-ALS) and independent component analysis (ICA) chemometric techniques were used to extract the signals of the analytes. All the samples presented recovery values of 81–128% for TMP. The quantification of SMX was not possible due to SERS suppression by an interferent. However, it was possible to detect SMX at a concentration of two times the MRL (8.0 × 10⁻⁷ mol·L⁻¹). The results demonstrate that the TLC-SERS device is a potential tool for the quantification of TMP and the detection of SMX in milk. Full article

Orthorhombic ZrTiO₄ is an attractive dielectric material; its optical properties are, however, less known. In this paper, we reported on the microstructure and luminescence studies of pristine ZrTiO₄ and Eu³⁺-doped ZrTiO₄ phosphors. The results indicated that two types of TiO₆ octahedra, the isolated/ localized and coupled/delocalized, coexisted in host matrix. Eu³⁺ doping could induce oxygen vacancy defect states located below the bottom of the conduction band. Pristine ZrTiO₄ showed bright yellow luminescence via STEs recombination at defects sites at low temperatures, but significant thermal quenching occurred due to STEs migration to quenching centers at elevated temperatures. Effective host sensitized energy transfer to Eu³⁺ was observed in ZrTiO₄:Eu³⁺ phosphors and yielded the red characteristic emissions of Eu³⁺. Anomalous STEs luminescence enhancement and spectral blue-shift in the excitation spectra with higher Eu^{3 +} concentration appeared and were explained by considering three factors: competitive absorption between electron transitions from the top of the valence band to the defect states and host conduction band, Eu³⁺ doping driving the production of more isolated TiO₆ octahedra, and energy back-transfer from Eu³⁺ activators to other titanate groups. On the basis of the dual-emitting combination strategy involving host STEs and Eu³⁺ luminescence, ZrTiO₄:Eu³⁺ phosphors were demonstrated to be ratiometric self-referencing optical thermometric materials, with a working range of 153–313 K and a maxima of relative sensitivity to ~1.1% K⁻¹ at 243 K. Full article

Based on the wide application of sulfur hexafluoride (SF₆) gas in the power industry, the analysis and detection of its decomposition components have become important technical means for state detection and fault evaluation of gas-insulated equipment. The gas-sensitive characteristics and adsorption mechanism of the SnS₂ sensor for SO₂ and SOF₂ gases were investigated using SO₂ and SOF₂, the main SF₆ decomposition components, as the target detection gases. SnS₂ gas-sensitive materials and components were prepared, and the temperature response, concentration response, response recovery and stability of the SnS₂ sensor for the two SF₆ decomposition components were tested based on the gas-sensitive test platform. The results demonstrate that the sensor had the best working performance at 200 °C, with obvious response and ideal recovery for both target gases and good stability in a certain time. Based on the first principle, the SnS₂ surface structure model and the target gas adsorption model were established, and the adsorption mechanism was analyzed in terms of frontier molecular orbital theory to verify the correctness of the gas-sensitive test results. The gas-sensitive test analysis and simulation calculation can provide data basis and theoretical support for the study of SF₆ decomposition components detected by gas sensors. Full article

Room-temperature gas sensors based on granulated carbon nanofiber material were investigated for the detection of NO₂. The granulated material consisting of intertwined carbon nanofibers was synthesized by the decomposition of CH₄ over the Ni/Al₂O₃ catalyst in a vibro-fluidized bed reactor. Carbon material was investigated using transmission electron microscopy, Raman spectroscopy, low-temperature nitrogen adsorption, and X-ray photoelectron spectroscopy. Investigation of the gas sensors towards NO₂ at room temperature (25 ± 2 °C) was carried out in a dynamic flow-through setup in the range from 1 to 500 ppm. A comparison of the sensitivity gas sensor to NH₃ and CH₄ was also given. The sensor based on non-treated carbon nanofiber material showed the response ΔR/R₀ of 5.1 % to 10 ppm of NO₂. It was found that the sensor response to NO₂ decreased when increasing the relative humidity. The effect of the relative humidity was more pronounced for low concentrations of nitrogen dioxide and decreases with a further increase in them. Full article

Malondialdehyde (MDA), one of the most important products of lipid peroxidation, has been widely accepted as a biomarker to indicate food rancidity as well as the progress of some human diseases. However, ready detection of MDA with ultra-high sensitivity remains a challenge. In this work, a microfluidic surface-enhanced Raman scattering (SERS) sensing chip based on phosphoric acid induced nanoparticles aggregation was proposed for ultrasensitive MDA detection. The sensing chip was composed of an ultrafast microfluidic mixer, which efficiently transferred analytes to hot spots via the mixer assisted hot spots occupying (MAHSO) SERS strategy. Phosphoric acid, a reagent used in MDA detection, played the role of aggregator to induce aggregation of silver nanoparticles (Ag NPs); meanwhile, as fast as a few milliseconds mixing time effectively prevented over-aggregation of Ag NPs. Therefore, this process generated a uniform and dense SERS substrate with analyte molecules located in hot spots. As a result, the MDA SERS sensing chip possessed a limit of detection (LOD) lower than 3.3 × 10⁻¹¹ M, high spot-to-spot uniformity with a relative standard deviation (RSD) of 9.0% and an excellent batch-to-batch reproducibility with a RSD of 3.9%. This method also demonstrated excellent specificity and reliability in real sample detection with recoveries of 90.4–109.8% in spiked tests. Full article

As anionic surfactants are used as cleaning agents, they pose an environmental and health threat. A novel potentiometric sensor for anionic surfactants based on the 1,3-dioctadecyl-1H-imidazol-3-ium tetraphenylborate (DODI–TPB) ionophore is presented. The newly developed approach for DODI–TPB synthesis is faster and simpler than the currently used strategies and follows the green chemistry principles. The DODI–TPB ionophore was characterized by computational and instrumental techniques (NMR, LC–MS, FTIR, elemental analysis) and used to produce a PVC-based DODI–TPB sensor. The sensor showed linear response to dodecylbenzenesulfonate and dodecyl sulfate in concentration ranges of 6.3 × 10⁻⁷–3.2 × 10⁻⁴ M and 5.9 × 10⁻⁷–4.1 × 10⁻³ M, for DBS and SDS, respectively. The sensor exhibits a Nernstian slope (59.3 mV/decade and 58.3 mV/decade for DBS and SDS, respectively) and low detection limits (7.1 × 10⁻⁷ M and 6.8 × 10⁻⁷ M for DBS and SDS, respectively). The DODI–TPB sensor was successfully tested on real samples of commercial detergents and the results are in agreement with the referent methods. A computational analysis underlined the importance of long alkyl chains in DODI⁺ and their C–H∙∙∙π interactions with TPB⁻ for the ionophore formation in solution, thereby providing guidelines for the future design of efficient potentiometric sensors. Full article

Polydopamine (PDA) films were successfully prepared on quartz crystal microbalance (QCM) by in-situ growth method, and the obtained QCM sensor was used for humidity detection. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to study the chemical composition and microstructure of the in-situ grown PDA sensitive films. The experimental results showed that the PDA-QCM humidity sensor with 2 h polymerization growth times (2-PDA-QCM) owned high sensitivity (20.77 Hz/% RH), good selectivity, short response/recovery time (5 s/11 s) and acceptable long-term stability. In addition, the energy loss of the sensors fabricated under different conditions was investigated by impedance analysis. Based on all the test results, it is concluded that the combination of in-situ growth method and QCM can produce a room temperature humidity sensor with excellent performance. Full article

A small indentation embedded in a microchannel creates a surface energy well (SEW) for a confined droplet due to surface energy release. Inspired by this, we developed a SEW-based microfluidic platform to realize high spatiotemporal-resolved signal profiling at the single-cell level applying droplet stimulus on a single chip. The method allows for controlled droplet replacement within only 3 s with almost 100% exchange efficiency, reliable single-cell patterning of adherent cells and successive treatment of adherent cells with reagent droplets. Furthermore, the PDGFR/Akt pathway served as a model system for evaluating the performance of the SEW-based method in determining the effects of ligand stimulation duration (3 s to 3 min) on receptor phosphorylation. The novel strategy offers a general platform for probing the temporal dynamics of single cells, as well for monitoring rapid chemical reactions in various applications. Full article

In this study, a non-labeled sensor system for direct determining human glycated albumin levels for medical application is proposed. Using machine learning methods applied to surface-enhanced Raman scattering (SERS) spectra of human glycated albumin and serum human albumin enabled the avoidance of complex sample preparation. By implementing linear discriminant analysis and regularized linear regression, classification and regression problems were solved based on the spectra obtained as a result of the experiment. The results show that, coupled with data augmentation and a special cross-validation procedure, the methods we employed yield better results in the corresponding tasks in comparison with popular random forest methods and the support vector method. The results show that SERS, in combination with machine learning methods, can be a powerful and effective tool for the simple and direct assay of protein mixtures. Full article

Science the biological activities of chiral enantiomers are often different or even opposite, their chiral recognition is of great significance. A new assembly structure named TCPP-Zn-(S)-BINOL was obtained based on the interaction between chiral binaphthol (BINOL) and the porphyrin-based MOF structure formed by Meso-Tetra(4-carboxyphenyl)porphine (TCPP) and Zn²⁺, and a new chiral sensor was designed relying on TCPP-Zn-(S)-BINOL. The chiral platform was designed by using binaphthol as a chiral recognizer and the porphyrin MOF as an emitter, which can recognize tyrosine (Tyr) enantiomers via the electrochemiluminescence (ECL) method. According to density functional theory (DFT), TCPP-Zn-(S)-BINOL has a different affinity with L/D-Tyr due to the different strength of the hydrogen bond between chiral ligand BINOL and the tyrosine (Tyr) enantiomer. It will be more suitable for combination with L-Tyr, and the presence of L-Tyr will increase the ECL intensity of the modified electrode via the catalytic reduction of co-reactant reagents, achieving the purpose of the chiral recognition of Tyr enantiomers. These findings show that TCPP-Zn-(S)-BINOL can be used as an advanced ECL chiral recognition platform for biomedical applications. Full article

Cancer antigen 15-3 (CA 15-3) is a biomarker for breast cancer used to monitor response to treatments and disease recurrence. The present work demonstrates the preparation and application of a fluorescent biosensor for ultrasensitive detection of the cancer antigen CA 15-3 protein tumor marker using mercaptopropionic-acid-functionalized cadmium telluride (CdTe@MPA) quantum dots (QDs) conjugated with CA 15-3 antibodies. First, the QDs were synthesized by the hydrothermal route, resulting in spherical nanoparticles up to 3.50 nm in diameter. Subsequently, the QD conjugates were characterized by Fourier transform infrared spectroscopy (FTIR), UV absorption, and fluorescence. The interaction between the conjugates and the protein was studied by fluorescence spectroscopy in buffer and in 10-fold diluted commercial human serum. Calibration in spiked serum samples gave a detection limit of 0.027 U/mL, 1000-fold lower than the clinical limit for CA 15-3 (25 U/mL to 30 U/mL), indicating that this is an ultrasensitive technique. In addition, a rapid response was obtained within 10 min. The biosensor was selective in the presence of the interfering serum proteins BSA, CEA, and CA-125, with a maximum interference of 2% for BSA. The percent recovery was close to 100% with maximum relative standard deviation (RSD%) values of 1.56. Overall, the developed CA 15-3 biosensor provides a simple and sensitive method for ultrasensitive monitoring of breast cancer, as well as the ability to detect other molecules of interest in human serum matrices. Full article

Irbesartan is a drug used to treat hypertension and high blood pressure. Recent studies associated sartans with several forms of cancer, making removing this class of substances from the environment a high priority. The EU has categorized drugs as emerging pollutants, and they can be more potent than other substances because they were designed to operate at low concentrations. Thus, effective and sensitive methods of determining Irbesartan selectively and accurately in environmental samples are necessary. MIPs have already been used to remove pollutants from complex matrixes, so they were also chosen for this work. In particular, a polyacrylate-based MIP was used to functionalize the graphite working electrode of screen-printed cells (SPCs), aiming to develop a voltammetric method for Irbesartan sensing. The MIP composition and the experimental conditions for the electrochemical determination were optimized through a Design of Experiments (DoE) approach. The whole analysis was replicated with different SPCs obtaining similar results, which highlight the good reproducibility potential. MIP-based electrodes were also applied to determine Irbesartan in fortified tap water samples, obtaining high recovery percentages. Given the good results, the electrochemical method based on MIP-modified screen-printed electrodes is promising for quantifying Irbesartan at a trace level. Full article

Supercapacitors have emerged as one of the promising energy storage systems owing to their rapid charge/discharge capability, long-term cycling stability, and high power density. The application of core-shell nanostructures for supercapacitors is one of the effective strategies to achieve a high specific surface area for abundant reaction sites and good electrical conductivity for fast charge transfer, hence improving the performance of supercapacitors. Particularly, the use of NiMoO₄ for the core-shell structure has drawn great attention due to its outstanding advantages, such as its natural abundance, low material cost, superior electrochemical performance, and wide electrochemical potential window in cyclic voltammetry. In this context, this review comprehensively covers the recent progress of the core-shell nanostructures based on the NiMoO₄-composite materials, which find applications in supercapacitors. The composite materials that incorporate metal oxides such as NiMoO₄, metal hydroxides, metal chalcogenides, carbon materials, and conductive polymers are discussed in detail for such core-shell nanostructures with the aim of understanding how the adopted materials and the relevant morphology govern the electrochemical features for supercapacitors. Finally, the existing challenges in current technologies for supercapacitors are discussed, while possible future directions in developing the NiMoO₄-composite-based core-shell nanostructures are proposed for high-performance supercapacitors. Full article

A comparative analysis of the chemiresistive sensor response of thin films of a series of tetrasubstituted phthalocyanines of various metals with F-substituent in peripheral (MPcF₄-p, M = Cu, Co, Zn, Pb, VO) and non-peripheral (MPcF₄-np) positions in macroring to low concentrations of ammonia (1–50 ppm) was carried out. It was found that MPcF₄-p films exhibit a higher sensor response than MPcF₄-np ones. A CoPcF₄-p film demonstrated a calculated LOD of 0.01 ppm with a recovery time of 215 s, while a VOPcF₄-p film had LOD of 0.04 ppm and the recovery time of 270 s. The selectivity test showed that CO₂, ethanol, acetone, benzene, and formaldehyde did not interfere with the determination of ammonia, while H₂S at a concentration of more than 10 ppm could act as an interfering gas. It was shown that, as a result of quantum-chemical calculations, the observed regularities are best described by the interaction of NH₃ with phthalocyanines through the formation of hydrogen bonds between NH₃ and side atoms of the macroring. In the case of MPcF₄-p, the NH₃ molecule approaches the macrocycle more closely and binds more strongly than in the case of MPcF₄-np. The stronger binding leads to a stronger effect of the ammonia molecule on the electronic structure of phthalocyanine and, as a consequence, on the chemiresistive sensor response of the films to ammonia. Full article