Dual sensor for Cd(II) and Ca(II): selective nanoliter-scale sensing of metal ions

Hydrogel binding sodium alginate based optical fiber surface plasmon resonance for calcium ion trace detection

A plasmonic tilted fiber Bragg grating (TFBG)-based sensor for the detection of calcium ion (Ca2+) was proposed and demonstrated experimentally. Hydrogel material was synthesized by utilizing hydrogen bond recombination between cellulose nanocrystals (CNC) and polyvinyl alcohol (PVA). Sodium alginate (SA) was incorporated into this hydrogel material, resulting in a composite membrane with specific binding properties for Ca2+. The membrane was applied as a coating on the surface of a gold-coated TFBG. The CNC/PVA-SA modified gold on the TFBG surface enhanced the localized refractive index changes caused by variations of Ca2+ concentrations. The experimental results demonstrated an impressive limit of detection (LOD) of approximately 0.025 fM, which is five orders of magnitude better than the current LODs of similar Ca2+ sensors. And the proposed Ca2+ sensor exhibited a wide dynamic range of 10-16 M to 10-6 M.

Single-fiber probes for combined sensing and imaging in biological tissue: recent developments and prospects

Single-fiber-based sensing and imaging probes enable the co-located and simultaneous observation and measurement (i.e., 'sense' and 'see') of intricate biological processes within deep anatomical structures. This innovation opens new opportunities for investigating complex physiological phenomena and potentially allows more accurate diagnosis and monitoring of disease. This prospective review starts with presenting recent studies of single-fiber-based probes for concurrent and co-located fluorescence-based sensing and imaging. Notwithstanding the successful initial demonstration of integrated sensing and imaging within single-fiber-based miniaturized devices, the realization of these devices with enhanced sensing sensitivity and imaging resolution poses notable challenges. These challenges, in turn, present opportunities for future research, including the design and fabrication of complex lens systems and fiber architectures, the integration of novel materials and other sensing and imaging techniques.

An "off-on" fluorescent nanosensor for the detection of cadmium ions based on APDC-etched CdTe/CdS/SiO2 quantum dots

In this study, we have developed a novel fluorescent "OFF-ON" quantum dots (QDs) sensor based on CdTe/CdS/SiO2 cores. Ammonium pyrrolidine dithiocarbamate (APDC), ethylenediamine tetraacetic acid (EDTA), and 1,10-phenanthroline (Phen) served as potential chemical etchants. Among these three etchants, APDC exhibited the most pronounced quenching effect (94.06%). The APDC-etched CdTe/CdS/SiO2 QDs demonstrated excellent optical properties: the fluorescence of the APDC-etched CdTe/CdS/SiO2 QDs system (excitation wavelength: 365 nm and emission wavelength: 622 nm) was significantly and selectively restored upon the addition of cadmium ions (Cd2+) (89.22%), compared to 15 other metal ions. The linear response of the APDC-etched CdTe/CdS/SiO2 QDs was observed within the cadmium ion (Cd2+) concentration ranges of 0-20 μmol L-1 and 20-160 μmol L-1 under optimized conditions (APDC: 300 μmol L-1, pH: 7.0, reaction time: 10 min). The detection limit (LOD) of the APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ was 0.3451 μmol L-1 in the range of 0-20 μmol L-1. The LOD achieved by the QDs in this study surpasses that of the majority of previously reported nanomaterials. The feasibility of using APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ detection in seawater, freshwater, and milk samples was verified, with average recoveries of 95.27%-110.68%, 92%-106.47%, and 90.73%-111.60%, respectively, demonstrating satisfactory analytical precision (RSD ≤ 8.26).

Microfluidic analysis of 3T3 cellular transport in a photonic crystal fiber: part I

This microfluidic-optical fiber sensor is an experimental system designed to transport and monitor 3D cell cultures, facilitating medical research and technology. This system includes a photonic crystal fiber with a hollow core diameter of 22 µm, which functions as a bridge between two microfluidic devices. The purpose of this system was to transport 3T3 cells (of diameters from 15 µm to 23 µm) between the two devices. At low Reynold's and capillary numbers, spectroscopic analysis confirmed the presence of cellular aggregation at the interface of the fiber and microfluidic device. The transcapillary conductance, T C, is a separate analysis that models the behavior of a cellular aggregate through the hollow channel of a photonic crystal fiber. For the experimental system, conventional fluid mechanics theory is limited and requires special treatment of conditions at the microscale, such that transcapillary conductance treatment was employed. The transcapillary conductance, T C, was empirically derived to model cellular transport at the microfluidic scale and is useful for comparing transport events. For example, for a pressure differential of Δ p=1.5⋅103 c m H 2 O, the transcapillary conductance values were determined to be 10-12 Collapse

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Ultrasensitive detection of cadmium ions using a microcantilever-based piezoresistive sensor for groundwater

This paper proposes the selective and ultrasensitive detection of Cd(II) ions using a cysteamine-functionalized microcantilever-based sensor with cross-linked ᴅʟ-glyceraldehyde (DL-GC). The detection time for various laboratory-based techniques is generally 12-24 hours. The experiments were performed to create self-assembled monolayers (SAMs) of cysteamine cross-linked with ᴅʟ-glyceraldehyde on the microcantilever surface to selectively capture the targeted Cd(II). The proposed portable microfluidic platform is able to achieve the detection in 20-23 min with a limit of detection (LOD) of 0.56 ng (2.78 pM), which perfectly describes its excellent performance over other reported techniques. Many researchers used nanoparticle-based sensors for the detection of heavy metal ions, but daily increasing usage and commercialization of nanoparticles are rapidly expanding their deleterious effect on human health and the environment. The proposed technique uses a blend of thin-film and microcantilever (micro-electromechanical systems) technology, which mitigate the disadvantages of the nanoparticle approaches, for the selective detection of Cd(II) with a LOD below the WHO limit of 3 μg/L.

A luminescent terbium coordination complex as multifunctional sensing platform

In this paper, we report the synthesis of a multifunctional fluorescent probe Tb-CP, Tb(HL)(EtOH)₂(NO₃)₂ (HPU-10) (H₂L = 2,6-bis-(5-pyridin-4-yl-1H-[1,2,4]triazol-3-yl)- pyridine), and demonstrate that this novel chemosensor has the property of ratiometric detection of Zn²⁺ and Cd²⁺. The detection limit of HPU-10 sensing Zn²⁺ and Cd²⁺ is 0.319 and 0.965 μM, respectively. The sensing mechanism can be explained by (i) the decomposition of HPU-10 and (ii) the recombination of Zn²⁺ or Cd²⁺ with ligand forming 2HL^--Zn²⁺ or 2HL^--Cd²⁺, respectively. Moreover, the fluorescent sensor HPU-10 can detect the nitroaromatic compound 2, 4-DNP via a fluorescence quenching mechanism. The detection limits obtained from linear regression curve plots of 2, 4-DNP is calculated to be 1.69 μM. In addition, the possible use of the probe coated paper for tracing the target analytes has also been presented.

Sensitive, selective and simultaneous electrochemical detection of multiple heavy metals in environment and food using a lowcost Fe3O4 nanoparticles/fluorinated multi-walled carbon nanotubes sensor

Multiple heavy metals pollution in environment and food has become an ever-increasing concern and poses a serious threat towards humans and animals. To broad the multiple heavy metals detection, Fe₃O₄ nanoparticles, Fe₃O₄/multi-walled carbon nanotubes (Fe₃O₄/MWCNTs) and Fe₃O₄/fluorinated multi-walled carbon nanotubes (Fe₃O₄/F-MWCNTs) nanocomposites were synthesized by hydrothermal method and constructed as a simultaneous electrochemical sensor, respectively. Compared the catalytic performances of the three electrochemical sensors for the simultaneous detection of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, the results showed that the Fe₃O₄/F-MWCNTs sensor demonstrated preponderant performance. It showed the sensitivity of 108.79, 125.91, 160.85, and 312.65 μA mM^-1 cm^-2 toward Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, which was obviously higher than that of Fe₃O₄/MWCNTs and Fe₃O₄. Additionally, the Fe₃O₄/F-MWCNTs sensor exhibited the wider linear detection ranges of 0.5-30.0, 0.5-30.0, 0.5-30.0, and 0.5-20.0 μM for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively. The limit of detections of the Fe₃O₄/F-MWCNTs sensor were 0.05, 0.08, 0.02, and 0.05 nM (signal to noise ratio of 3) for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, fulfilling the governmental requests of the World Health Organization, China and Indian. The excellent agreement was recorded between the lowcost Fe₃O₄/F-MWCNTs sensor and typical methods (inductively coupled plasma mass spectrometry or atomic fluorescence spectrometry) in river water and soybean samples. Additionally, the sensor also exhibited excellent performances in selectivity, recovery, stability, and reproducibility. This proposal sensor provides a promising strategy to monitor multiple targets in the environment and food.

A novel peptide-based fluorescent chemosensor for Cd(II) ions and its applications in bioimaging

Nowadays, it is of great significance to develop a novel fluorescent chemosensor for Cd(II) ions detection with cost-effective, rapid, facile and applicable to environment and biological milieus. Herein, we report a new peptide-based fluorescent chemosensor DSC (Dan-Ser-Cys-NH₂) based on dipeptide (Ser-Cys-NH₂) conjugated with dansyl group, which was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, DSC exhibited fluorescent "turn-on" response for Cd²⁺ in 100% aqueous solution over a wide range of pH values based on photoinduced electron transfer (PET). The stoichiometry binding of DSC and Cd²⁺ was determined to be 2:1 by Job's plot and ESI-MS analysis. Furthermore, DSC showed highly sensitive for Cd²⁺ and a low detection limit of 13.8 nM. What's more, DSC has cell permeability and low cytotoxicity, and fluorescence imaging experiments demonstrated that DSC was capable of monitoring Cd²⁺ in living HK2 cells by confocal microscopy.

A novel polymer probe for Zn(II) detection with ratiometric fluorescence signal

A conjugated polymer probe comprised of fluorene, quinolone and benzothiazole units was designed and synthesized by the Suzuki coupling reaction. Through the studies of photophysical and thermal properties, the polymer displays blue-emitting feature and good thermal stability. A ratiometric fluorescence signal of the probe for Zn(II) was observed in ethanol with a new emission peak at 555 nm. The probe possesses a high selectivity and sensitivity for Zn(II) during familiar metal ions in ethanol. The detection limit of the probe for Zn (II) is up to 10^-8 mol/L. The electron distributions of the polymer before and after bonding with Zn (II) were investigated by the Gaussian 09 software, which agreed with the experimental results. Noticeably, based on the color property of the probe with Zn(II), a series of color test paper were developed for visual detecting Zn(II) ions. This work helps to provide a platform or pattern for the development of polymer fluorescence probe in the chemosensor field.

Rationally Designed Probe for Reversible Sensing of Zinc and Application in Cells

Biologically compatible fluorescent ion sensors, particularly those that are reversible, represent a key tool for answering a range of fundamental biological questions. We report a rationally designed probe with a 6'-fluoro spiropyran scaffold (5) for the reversible sensing of zinc (Zn²⁺) in cells. The 6'-fluoro substituent overcomes several limitations normally associated with spiropyran-based sensors to provide an improved signal-to-background ratio and faster photoswitching times in aqueous solution. In vitro studies were performed with 5 and the 6'-nitro analogues (6) in HEK 293 and endothelial cells. The new spiropyran (5) can detect exogenous Zn²⁺ inside both cell types and without affecting the proliferation of endothelial cells. Studies were also performed on dying HEK 293 cells, with results demonstrating the ability of the key compound to detect endogenous Zn²⁺ efflux from cells undergoing apoptosis. Biocompatibility and photoswitching of 5 were demonstrated within endothelial cells but not with 6, suggesting the future applicability of sensor 5 to study intracellular Zn²⁺ efflux in these systems.

Effect of surfactant in mitigating cadmium oxide nanoparticle toxicity: Implications for mitigating cadmium toxicity in environment

Cadmium (Cd), classified as human carcinogen, is an extremely toxic heavy metal pollutant, and there is an increasing environmental concern for cadmium exposure through anthropogenic sources including cigarette smoke. Though Cd based nanoparticles such as cadmium oxide (CdO) are being widely used in a variety of clinical and industrial applications, the toxicity of CdO nanoparticles has not been well characterized. Herein we report the toxicity of CdO nanoparticles employing zebrafish as a model. Two different CdO nanoparticles were prepared, calcination of Cd(OH)₂ without any organic molecule (CdO-1) and calcination of Cd-citrate coordination polymer (CdO-2), to evaluate and compare the toxicity of these two different CdO nanoparticles. Results show that zebrafish exposed to CdO-2 nanoparticles expressed reduced toxicity as judged by lower oxidative stress levels, rescue of liver carboxylesterases and reduction in metallothionein activity compared to CdO-1 nanoparticles. Histopathological observations also support our contention that CdO-1 nanoparticles showed higher toxicity relative to CdO-2 nanoparticles. The organic unit of Cd-citrate coordination polymer might have converted into carbon during calcination that might have covered the surface of CdO nanoparticles. This carbon surface coverage can control the release of Cd²⁺ ions in CdO-2 compared to non-covered CdO-1 nanoparticles and hence mitigate the toxicity in the case of CdO-2. This was supported by atomic absorption spectrophotometer analyses of Cd²⁺ ions release from CdO-1 and CdO-2 nanoparticles. Thus the present study clearly demonstrates the toxicity of CdO nanoparticles in an aquatic animal and also indicates that the toxicity could be substantially reduced by carbon coverage. This could have important implications in terms of anthropogenic release and environmental pollution caused by Cd and human exposure to Cd²⁺ from sources such as cigarette smoke.

Microstructured Optical Fiber-based Biosensors: Reversible and Nanoliter-Scale Measurement of Zinc Ions

Sensing platforms that allow rapid and efficient detection of metal ions would have applications in disease diagnosis and study, as well as environmental sensing. Here, we report the first microstructured optical fiber-based biosensor for the reversible and nanoliter-scale measurement of metal ions. Specifically, a photoswitchable spiropyran Zn(2+) sensor is incorporated within the microenvironment of a liposome attached to microstructured optical fibers (exposed-core and suspended-core microstructured optical fibers). Both fiber-based platforms retains high selectivity of ion binding associated with a small molecule sensor, while also allowing nanoliter volume sampling and on/off switching. We have demonstrated that multiple measurements can be made on a single sample without the need to change the sensor. The ability of the new sensing platform to sense Zn(2+) in pleural lavage and nasopharynx of mice was compared to that of established ion sensing methodologies such as inductively coupled plasma mass spectrometry (ICP-MS) and a commercially available fluorophore (Fluozin-3), where the optical-fiber-based sensor provides a significant advantage in that it allows the use of nanoliter (nL) sampling when compared to ICP-MS (mL) and FluoZin-3 (μL). This work paves the way to a generic approach for developing surface-based ion sensors using a range of sensor molecules, which can be attached to a surface without the need for its chemical modification and presents an opportunity for the development of new and highly specific ion sensors for real time sensing applications.

Direct core structuring of microstructured optical fibers using focused ion beam milling

We demonstrate the use of focused ion beam milling to machine optical structures directly into the core of microstructured optical fibers. The particular fiber used was exposed-core microstructured optical fiber, which allowed direct access to the optically guiding core. Two different designs of Fabry-Perot cavity were fabricated and optically characterized. The first cavity was formed by completely removing a section of the fiber core, while the second cavity consisted of a shallow slot milled into the core, leaving the majority of the core intact. This work highlights the possibility of machining complex optical devices directly onto the core of microstructured optical fibers using focused ion beam milling for applications including environmental, chemical, and biological sensing.

Synthesis of an optically switchable salicylaldimine substituted naphthopyran for selective and reversible Cu2+ recognition in aqueous solution

A light controlled reversible switch for copper ion was synthesized by substituting photochromic naphthopyran with a salicylaldimine moiety.

A Dual Sensor for pH and Hydrogen Peroxide Using Polymer-Coated Optical Fibre Tips

This paper demonstrates the first single optical fibre tip probe for concurrent detection of both hydrogen peroxide (H₂O₂) concentration and pH of a solution. The sensor is constructed by embedding two fluorophores: carboxyperoxyfluor-1 (CPF1) and seminaphtharhodafluor-2 (SNARF2) within a polymer matrix located on the tip of the optical fibre. The functionalised fibre probe reproducibly measures pH, and is able to accurately detect H₂O₂ over a biologically relevant concentration range. This sensor offers potential for non-invasive detection of pH and H₂O₂ in biological environments using a single optical fibre.

A peptide-based fluorescent chemosensor for measuring cadmium ions in aqueous solutions and live cells

A novel peptide fluorescent chemosensor (H2L) with a lysine backbone and both -NH2 sites conjugated with cysteine and dansyl groups has been designed and synthesized by solid phase peptide synthesis with Fmoc chemistry. This chemosensor is a promising analytical tool for detecting Cd(2+) based on the photo-induced electron transfer (PET) effect by turn-on response in 100% aqueous solutions. As designed, H2L exhibits excellent cell permeation and low biotoxicity as well as displaying relatively high selectivity and sensitivity. The chemosensor penetrated live HeLa cells and detected intracellular Cd(2+) by turn-on response. The binding stoichiometry and affinity, interference test, pH sensitivity, fluorescence quantum yield, quantum mechanical calculations, lifetimes, and cytotoxicity of the chemosensor H2L to Cd(2+) were also investigated. Moreover, H2L exhibits low biotoxicity with a limit of detection (LOD) for Cd(2+) of about 52 nM, implying that H2L can be used as a highly selective and sensitive peptide fluorescent chemosensor in biological systems.

Two dinuclear Ru(II) polypyridyl complexes with different photophysical and cation recognition properties

Two dinuclear Ru(II) polypyridyl complexes functionalized with vacant coordination sites have been designed and synthesized. Their photophysical properties and interactions with various metal ions have been investigated at room temperature. The two complexes exhibit different UV/Vis absorption and emission intensities. When titrated with various metal ions, complex [{Ru(bpy)2}2(μ2-L(1))](4+) exhibits a notable fluorescence quenching in the presence of Cu(2+) in H2O-CH3CN media (1:1, v/v); its analogous complex [{Ru(bpy)2}2(μ2-L(2))](4+) exhibits no cation selectivity, the fluorescence intensity of complex [{Ru(bpy)2}2(μ2-L(2))](4+) has been enhanced by several transition metal ions due to prevention of the photo-induced electron transfer process. The fluorescence titration spectra and Benesi-Hildebrand expression reveal the formation of a 1:1 bonding mode between [{Ru(bpy)2}2(μ2-L(1))](4+) and Cu(2+) ion with the association constant of 5.50×10(4) M(-1).

A stable 3D porous coordination polymer as multi-chemosensor to Cr(iv) anion and Fe(iii) cation and its selective adsorption of malachite green oxalate dye

A 3D porous coordination polymer was synthesized by three solvent-thermal methods. The sensing and titration experiments show that it can detect Fe(iii) cation and Cr(vi) anions (Cr₂O₇²⁻ or CrO₄²⁻). Besides, it can selectively adsorb the malachite green oxalate dye.

Fabrication, splicing, Bragg grating writing, and polyelectrolyte functionalization of exposed-core microstructured optical fibers

Femtosecond laser written Bragg gratings have been written in exposed-core microstructured optical fibers with core diameters ranging from 2.7 µm to 12.5 µm and can be spliced to conventional single mode fiber. Writing a Bragg grating on an open core fiber allows for real-time refractive index based sensing, with a view to multiplexed biosensing. Smaller core fibers are shown both experimentally and theoretically to provide a higher sensitivity. A 7.5 µm core diameter fiber is shown to provide a good compromise between sensitivity and practicality and was used for monitoring the deposition of polyelectrolyte layers, an important first step in developing a biosensor.