Search Results (1,724)

In human blood serum, the concentration of magnesium ions typically ranges from 0.7 mM to 1.05 mM. However, exceeding the upper limit of 1.05 mM can lead to the condition known as hypermagnesemia. In this regard, a highly sensitive and selective electrochemical sensor for Mg(II) ion detection was successfully fabricated by immobilizing cerium oxide (CeO₂) microcuboids, synthesized via microwave radiation method, onto the surface of glassy carbon electrode (GCE). Cyclic voltammetry studies revealed the exceptional electrocatalytic effect of CeO₂ microcuboid-modified GC electrode, particularly in relation to the irreversible reduction signal of Mg(II). The microcuboid-like structure of CeO₂ microparticles facilitated enhanced adsorption of Mg(II) ion ($\Gamma =2.17\times {10}^{-7}$mol cm⁻²) and electron transfer ($k_s=8.94$ s⁻¹) between the adsorbed Mg(II) ions and GCE. A comprehensive analysis comparing the performance characteristics of amperometry, differential pulse voltammetry, cyclic voltammetry, and square wave voltammetry was conducted. The square wave voltammetry-based Mg(II) sensor exhibited remarkable sensitivity of 2.856 μA mM⁻¹, encompassing a broad linear detection range of 0–3 mM. The detection and quantification limits were impressively low, with values of 19.84 and 66.06 μM, respectively. Remarkably, the developed electrode showed a rapid response time of less than 140 s. Multiple linear regression and partial least squares regression models were employed to establish a mathematical relationship between magnesium ion levels and electrochemical parameters. Notably, the proposed sensor exhibited excellent anti-interferent ability, repeatability, stability, and reproducibility, enabling the fabricated electrode to be used effectively for Mg(II) ion sensing in real-world samples. Full article

Flexible substrates have known increased popularity over rigid ones due to their use in surface-enhanced Raman scattering (SERS). They provide irregular surfaces, ideal for in situ sensing. In this context, we report the SERS performance of hybrid ZnO@Ag thin films deposited by magnetron sputtering (MS) on flexible, thermoplastic substrates. This physical deposition method is acknowledged for obtaining high-quality and reproducible ZnO films that can be embedded in (bio)sensing devices with various applications. Three types of thermoplastic-based, commercially available substrates with different glass transition temperatures (T_g) were chosen for the variation in flexibility, transparency, and thickness. Zeonor^® (T_g = 136 °C, thickness of 188 μm) and two types of Topas (Topas^®: T_g = 142 °C, thickness of 176 μm; Topas2: T_g = 78 °C, thickness of 140 μm) thermoplastic sheets are nonpolar and amorphous cyclo-olefin polymer (COP) and cyclo-olefin copolymers (COC), respectively. Their thicknesses and different values of T_g can greatly affect the topographical and roughness properties of films with small thicknesses and, thus, can greatly influence the enhancement of the Raman signal. The ZnO films deposited on top of Zeonor^® or Topas^® have identical morphological properties, as shown by the scanning electron microscopy (SEM) characterization. Subsequently, by using the MS technique, we tuned the thickness of the deposited silver (Ag) films in the range of 7–30 nm to assess the growth influence on the morphology and the SERS signal amplification of the substrates with and without the ZnO intermediate layer. The SEM analysis showed that the Ag atoms migrated both into the interstitial areas, filling the voids between the ZnO granular structures, and over the latter, forming, in this case, isolated Ag clusters. SERS analysis performed on the ZnO-Ag hybrid films using crystal violet (CV) molecule revealed a limit of detection (LOD) of 10⁻⁷ M in the case of 15 nm thick Ag/Zeonor^® interlayer films ZnO and relative standard deviation (RSD) below 10%. Full article

Reactive oxygen species (ROS) play an important role in maintaining human health and are recognized as indicators of oxidative stress linked to various conditions such as neurodegenerative and cardiovascular diseases, as well as cancer. Consequently, detecting ROS levels in biological systems is crucial for biomedical and analytical research. Electrochemical approaches offer promising opportunities for ROS determination due to their exceptional sensitivity, speed, and simplicity of equipment. This review covers studies using advanced electrochemical nanozyme sensors for detecting ROS in biological samples that were published over the last ten years, from 2013 to 2023. Emphasis is placed on the sensor materials and different types of modifiers employed for selective ROS detection. Furthermore, a comprehensive analysis of the sensors’ selectivity was performed. Full article

The development of a rapid, highly sensitive, and dependable acetone sensor holds significant importance for human health and safety. To enhance the acetone sensing performance of LaFeO₃ nanoparticles for practical applications, commercial n-type WO₃ nanoparticles were incorporated as additives. They were directly mixed with LaFeO₃ nanoparticles produced through a sol-gel method, creating a series of WO₃-LFO nanocomposites with varying mass ratios. These nanocomposites were characterized using XRD, SEM, BET, and XPS techniques. Compared to pure LFO nanoparticles, the prepared nanocomposites exhibited larger specific surface areas with enhanced surface reactivity. The introduction of p-n heterojunctions through the mixing process improved the regulation of acetone molecules on internal carrier conduction within nanocomposites. As a result, the nanocomposites demonstrated superior acetone sensing performance in terms of optimal operating temperature, vapor response value, selectivity, and response/recovery speed. Notably, the nanocomposites with a 5wt% addition of WO₃ showed the lowest optimal operating temperature (132 °C), the fastest response/recovery speed (28/9 s), and the highest selectivity against ethanol, methanol, and EG. On the other hand, the nanocomposites with a 10wt% addition of WO₃ displayed the maximum vapor response value (55.1 to 100 ppm) at an optimal operating temperature of 138 °C, along with relatively good repeatability, stability, and selectivity. Full article

Aptamers are synthetic single-stranded oligonucleotides that exhibit selective binding properties to specific targets, thereby providing a powerful basis for the development of selective and sensitive (bio)chemical assays. Electrochemical biosensors utilizing aptamers as biological recognition elements, namely aptasensors, are at the forefront of current research. They exploit the combination of the unique properties of aptamers with the advantages of electrochemical detection with the view to fabricate inexpensive and portable analytical platforms for rapid detection in point-of-care (POC) applications or for on-site monitoring. The immobilization of aptamers on suitable substrates is of paramount importance in order to preserve their functionality and optimize the sensors’ sensitivity. This work describes different immobilization strategies for aptamers on the surface of semiconductor-based working electrodes, including metal oxides, conductive polymers, and carbon allotropes. These are presented as platforms with tunable band gaps and various surface morphologies for the preparation of low cost, highly versatile aptasensor devices in analytical chemistry. A survey of the current literature is provided, discussing each analytical method. Future trends are outlined which envisage aptamer-based biosensing using semiconductors. Full article

The introduction of solid-phase imprinting has had a significant impact in the molecular imprinting field, mainly due to its advantage of orienting the template immobilisation, affinity separation of nanoMIPs and faster production time. To date, more than 600 documents on Google Scholar involve solid-phase synthesis, mostly relying on silanes mediating template immobilisation on the solid phase. Organosilanes are the most explored functionalisation compounds due to their straightforward use and ability to promote the binding of organic molecules to inorganic substrates. However, they also suffer from well-known issues, such as lack of control in the layer’s deposition and poor stability in water. Since the first introduction of solid-phase imprinting, few efforts have been made to overcome these limitations. The work presented in this research focuses on optimising the silane stability on glass beads (GBs) and iron oxide nanoparticles (IO-NPs), to subsequently function as solid phases for imprinting. The performance of three different aminosilanes were investigated; N-(6-aminohexyl) aminomethyltriethoxy silane (AHAMTES), 3-Aminopropyltriethoxysilane (APTES), and N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), as well as studying the effect of dipodal silane bis(triethoxysilyl)ethane (BTSE). A stable solid phase was consequently achieved with 3% v/v AEAPTES and 2.4% BTSE, providing an upgraded protocol from Canfarotta et al. for the silanisation of the solid phase for molecular imprinting purposes. Full article

Lead and nickel, as heavy metals, are still used in industrial processes, and are classified as “environmental health hazards” due to their toxicity and polluting potential. The detection of heavy metals can prevent environmental pollution at toxic levels that are critical to human health. In this sense, the electrolyte–insulator–semiconductor (EIS) field-effect sensor is an attractive sensing platform concerning the fabrication of reusable and robust sensors to detect such substances. This study is aimed to fabricate a sensing unit on an EIS device based on Sn₃O₄ nanobelts embedded in a polyelectrolyte matrix of polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) using the layer-by-layer (LbL) technique. The EIS-Sn₃O₄ sensor exhibited enhanced electrochemical performance for detecting Pb²⁺ and Ni²⁺ ions, revealing a higher affinity for Pb²⁺ ions, with sensitivities of ca. 25.8 mV/decade and 2.4 mV/decade, respectively. Such results indicate that Sn₃O₄ nanobelts can contemplate a feasible proof-of-concept capacitive field-effect sensor for heavy metal detection, envisaging other future studies focusing on environmental monitoring. Full article

The content of magnesium ions (Mg²⁺) in drinking water is relatively high and the excessive Mg²⁺ ingestion may lead to pathological lesions in the human body system. At present, the detection of Mg²⁺ still relies on costly devices or/and complex organic fluorescence probes. To solve this problem, this work proposed a NaBH₄-mediated co-reduction strategy for the synthesis of glutathione-stabilized bimetallic AuAg nanoclusters (GSH@AuAg NCs) with performance recognition to Mg²⁺. The preparation of GSH@AuAg NCs was simple and rapid and could be performed at mild conditions. The reaction parameters and sampling orders were optimized to understand the formation mechanism of GSH@AuAg NCs. The GSH@AuAg NCs exhibited a sensitive “light on” fluorescence response to Mg²⁺ due to the re-molding of the interfacial physicochemical environment following the Mg²⁺ coordination, which affected the surface charge transfer process, and thus led to a novel method for fluorescence detection of Mg²⁺ with admirable selectivity for Mg²⁺. The proposed method showed a detection limit of 0.2 μM, and its practical utility for the detection of Mg²⁺ in a real sample of purified drinking water was also demonstrated, confirming its practicability in monitoring the Mg²⁺ concentration in drinking water. Full article

Bisphenol A (BPA), an alkylphenolic compound, is one of the most polluting and hazardous organic chemicals. Its routine detection is, however, still rather expensive due to high-cost equipment. In this context, we applied the effect caused by BPA to the optical properties of surfactant-stabilized silver nanoparticles further modified with the use of ammonia (AgNP-NH₃) to develop a simple and quantitative approach for BPA determination. The experimental conditions of the AgNP-NH₃ probe were adjusted to establish a stable and sensitive response toward BPA in aqueous media. The use of probe dispersion measured at a wavelength of 403 nm enabled a limit of detection of 2.0 nmol L⁻¹ (0.5 ng mL⁻¹), with a linear response as a function of a concentration of BPA ranging from 10 to 120 nmol L⁻¹ (from 2.2 to 27 ng mL⁻¹). The use of vortex-assisted liquid–liquid microextraction ensured the application of selective determination to real tap and stream water samples, with recoveries ranging from 85.0 to 111%. The protocol developed herein is simple, sensitive, and selective, does not require the use of toxic labeling agents, and can be easily adapted for the routine analysis of BPA in different real samples. Full article

The pathological process involves a range of intrinsic biochemical markers. The detection of multiple biological parameters is imperative for providing precise diagnostic information on diseases. In vivo multichannel fluorescence biosensing facilitates the acquisition of biochemical information at different levels, such as tissue, cellular, and molecular, with rapid feedback, high sensitivity, and high spatiotemporal resolution. Notably, fluorescence imaging in the near-infrared-II (NIR-II) window (950–1700 nm) promises deeper optical penetration depth and diminished interferential autofluorescence compared with imaging in the visible (400–700 nm) and near-infrared-I (NIR-I, 700–950 nm) regions, making it a promising option for in vivo multichannel biosensing toward clinical practice. Furthermore, the use of advanced NIR-II fluorophores supports the development of biosensing with spectra-domain, lifetime-domain, and fluorescence-lifetime modes. This review summarizes the versatile designs and functions of NIR-II fluorophores for in vivo multichannel biosensing in various scenarios, including biological process monitoring, cellular tracking, and pathological analysis. Additionally, the review briefly discusses desirable traits required for the clinical translation of NIR-II fluorophores such as safety, long-wavelength emission, and clear components. Full article

Electrochemiluminescence (ECL) is a light-emitting process triggered by the high energy redox between electrochemically oxidized and reduced luminophores or some coreactive intermediate radicals, representing a blooming hot topic over decades with a wide variety of bioanalytical applications. Due to the superb sensitivity, ultralow background noise, specificity, ease of integration, and real-time and in situ analysis, ECL has been developed as a convenient and versatile technique for immunodiagnostics, nucleic acid analysis, and bioimaging. Discovering highly-efficient ECL emitters has been a promising subject that will benefit the development of sensitive bioanalytical methods with prominent potential prospects. To date, the interdisciplinary integrations of electrochemistry, spectroscopy, and nanoscience have brought up the continuous emergences of novel nanomaterials which can be flexibly conjugated with specific bio-recognition elements as functional ECL emitters for bioassays. Therefore, a critical overview of recent advances in developing highly-efficient ECL emitters for ultrasensitive detection of protein biomarkers is presented in this review, where six kinds of the most promising ECL nanomaterials for biosensing and imaging of various disease-related protein biomarkers are separately introduced with references to representative works. Finally, this review discusses the ongoing opportunities and challenges of ECL emitters in developing advanced bioassays for single-molecule analysis and spatiotemporally resolved imaging of protein biomarkers with future perspectives. Full article

As the most abundant catecholamine neurotransmitter in the brain, dopamine plays an important role in the normal physiological process, and its level in urine also changes during human pathological processes. In clinic, the detection of dopamine in urine is a potential marker for the diagnosis and the treatment of endocrine-related diseases. In this work, a copper metal organic framework with catecholase-like activity was prepared via the precipitation of Cu²⁺ and imidazole, simulating the N-Cu coordination environment in the active site of catecholase. Cu-MOF (the copper–metal organic framework) can catalyze the oxidation of DA (dopamine) to dopaquinone using O₂ in the air. The oxidation product can further react with 1,3-dihydroxynaphthalene to produce a fluorophore product. Based on the above reaction, a multimodal sensing platform with three signal outputs, including ratio-metric fluorescence, absorbance and digital information extracted from smartphone images for simple and sensitive determination of DA, was proposed, with detection limits of 0.0679, 0.3206, and 0.3718 μM, respectively. This multimodal sensing platform was able to detect DA in body fluid in a self-correcting way, as demonstrated by the successful determination of DA in normal human urine samples, and samples with a high level of interference. Full article

Optical immunosensors are one of the most popular categories of immunosensors with applications in many fields including diagnostics and environmental and food analysis. The latter field is of particular interest not only for scientists but also for regulatory authorities and the public since food is essential for life but can also be the source of many health problems. In this context, the current review aims to provide an overview of the different types of optical immunosensors focusing on their application for the determination of pathogenic bacteria in food samples. The optical immunosensors discussed include sensors based on evanescent wave transduction principles including surface plasmon resonance (SPR), fiber-optic-, interferometric-, grating-coupler-, and ring-resonator-based sensors, as well as reflectometric, photoluminescence, and immunosensors based on surface-enhanced Raman scattering (SERS). Thus, after a short description of each transduction technique, its implementation for the immunochemical determination of bacteria is discussed. Finally, a short commentary about the future trends in optical immunosensors for food safety applications is provided. Full article

Metal–organic frameworks (MOFs), constructed by coordination between metal-containing nodes and organic linkers, are widely used in various fields due to the advantages of tunable pores, diverse functional sites, stable structure, and multi-functionality. It should be noted that MOF-based materials play a major role in glucose detection, serving as a signal transducer or functional substrate for embedding nanoparticles/enzymes. Diabetes is one of the most common and fast-growing diseases worldwide, whose main clinical manifestation is high blood sugar levels. Therefore, accurate, sensitive, and point-of-care glucose detection is necessary. This review orderly introduces general synthetic strategies of MOF-based materials (pristine MOF, nanoparticles, or enzymes-modified MOF and MOF-derived materials) and detection methods (electrochemical and optical methods) for glucose detection. Then, the review refers to the novel MOF-based glucose detection devices (flexible wearable devices and microfluidic chips), which enable non-invasive continuous glucose monitoring or low-cost microscale detection. On the basis of describing the development of glucose sensors based on MOF materials in the past five years, the review presents merits, demerits, and possible improvements of various detection methods. Full article

Hydrogen sulfide (H₂S), as one of the critical gaseous signaling molecules, has important physiological functions in the human body, and abnormal levels of hydrogen sulfide are closely related to tumors, Parkinson’s disease, Alzheimer’s disease, and other diseases. In order to enable the detection of H₂S in the physiological environment, herein, a new H₂S fluorescence probe, named C-HS, based on a coumarin–chalcone fluorescence platform was developed. The fluorescence probe provides specific recognition of H₂S within a wide pH detection range (5.5–8.5), a rapid recognition response (within 10 min) for H₂S molecules, and a high selectivity for competing species. The probe C-HS possesses low cytotoxicity and is used to achieve the detection of exogenous/ endogenous H₂S in living cells, indicating that the constructed probe C-HS has the ability to track changes in intracellular H₂S levels. Therefore, probe C-HS could be a potential tool for the early diagnosis of H₂S-related diseases. Full article