Reduced Graphene Oxide-Poly(3,4-ethylenedioxythiophene) Polystyrenesulfonate Based Dual-Selective Sensor for Iron in Different Oxidation States

Development of an ultrasensitive sensor for detecting metol in environmental water samples using ruddlesden-popper type layered perovskite (La2NiO4) combined with graphene oxide

Metol (MTO), a commonly used photographic developer, has become an environmental pollutant due to its extensive use and subsequent release into water sources. The accumulation of MTO poses significant risks, including aquatic toxicity and potential bioaccumulation, leading to adverse effects on ecosystems. To address these environmental challenges, we developed a La₂NiO4 combined with graphene oxide (La₂NiO₄@GO) nanocomposite modified glassy carbon electrode (GCE) for the ultrasensitive detection of MTO. The La₂NiO₄ was synthesized via a hydrothermal method and subsequently integrated with graphene oxide through a sonochemical technique, with comprehensive characterization using Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and High-resolution transmission electron microscopy (HR-TEM). Electrochemical analysis revealed that the La₂NiO₄@GO-modified electrode exhibited a low charge transfer resistance of 20 Ω. Using differential pulse voltammetry (DPV), the electrode demonstrated a limit of detection (LOD) of 6.4 nM for MTO, with a high sensitivity of 10.84 µA µM⁻¹cm⁻² and excellent anti-inference property towards MTO tested along with interfering substances. The sensor was successfully applied to real environmental water samples and human urine samples, showing excellent recovery rates of MTO. This work underscores the potential of La₂NiO₄@GO-modified electrodes in monitoring and mitigating the environmental impact of MTO, contributing to a healthy environment.

A small molecule modified UiO series MOFs for simultaneous detection of Fe3+ and Zn2

Iron and zinc are two metal ions with important roles in biology, industry and the environment, however, the excess or deficiency of both Fe3+ and Zn2+ can have negative effects on organisms and environment. Therefore, the development of efficient method for simultaneous detection of Fe3+ and Zn2+ provides timely information on metal content, simplifies operations and improves efficiency. In this work, a small molecule (COOH-BPEA) of recognizing Zn2+ modified the four metal-organic-framework (MOF) (UiO-66-X(66, OH, NH2 and OH/NH2)) was developed for the simultaneous detection of Fe3+ and Zn2+. The fluorescence signal of the small molecule is enhanced by small molecule chelating Zn2+ to block the photoinduced electron transfer (PET) effect. The fluorescence signals of the UiO series MOFs were quenched through Fe3+ with electron transfer and static quenching effect (SQE). It's worth mentioning that the emission wavelengths of the small molecules and MOFs did not interfere with each other. The UiO-66-NH2@BPEA with optimal performance was selected by fluorescence spectra for the detection of Fe3+ and Zn2+ with detection limit of 0.175 μM and 0.021 μM, respectively. The nanoprobe provides a fast response (less than 1 min) for both Fe3+ and Zn2+. Finally, we applied it to the simultaneous detection of Fe3+ and Zn2+ in environmental water, human serum and cell lysates.

l-cysteine capped MoS2 QDs for dual-channel imaging and superior Fe3+ ion sensing in biological systems

MoS2 quantum dots (MQDs) with an average size of 1.9 ± 0.7 nm were synthesized using a microwave-assisted method. Absorbance studies confirmed characteristic transitions of MoS2, with absorption humps at 260-280 nm and 300-330 nm, and a band gap of 3.6 ± 0.1 eV. Fluorescence emission studies showed dominant blue and some green emissions under 315 nm excitation, with an absolute quantum yield of ∼9%. The MQDs exhibited fluorescence stability over time after repeated quenching cycles across various pH and media systems. In vitro toxicity tests indicated cytocompatibility, with around 80% cell survival at 1000 mg L-1. Confocal imaging demonstrated significant uptake and vibrant fluorescence in cancerous and non-cancerous cell lines. The MQDs showed strong selectivity towards Fe3+ ions, with a detection limit of 27.61 ± 0.25 nM. Recovery rates for Fe3+ in phosphate buffer saline (PBS) and simulated body fluid (SBF) systems were >97% and >98%, respectively, with a relative standard deviation (RSD) within 3%, indicating precision. These findings suggest that MQDs have high potential for diagnostic applications involving Fe3+ detection due to their fluorescence stability, robustness, enhanced cell viability, and dual-channel imaging properties.

Advances in the determination of trace amounts of iron cations through electrochemical methods: A comprehensive review of principles and their limits of detection

Quantification of trace amounts of iron is of great importance in various fields. In the industrial sector, it is crucial to monitor the release of iron out of corrosion, pickling treatment, and steel manufacturing to address potential environmental and economic challenges. In biological systems, despite its indispensability, it is essential to maintain iron concentration below a specific threshold. Electrochemical (EC) methods provide significant analytical capabilities due to their simplicity, ease of use, and cost-effectiveness. This review focuses on the fundamental principles of EC methods for iron detection, including potentiometry, amperometry, coulometry, voltammetry, and electrochemical impedance spectroscopy (EIS). It further explains the process of obtaining calibration curves, and subsequently, determining the concentration of unknown ions. Additionally, technical notes are presented on selecting the initial signal value, reducing the duration of tests, excluding non-faradaic signals, and extending the linear region with the lowest detection limit. These notes are supported by key findings from relevant case studies.

PSS functionalized and stabilized carbon nanodots for specific sensing of iron in biological medium

Carbon Quantum Dots (CQDs) are already emerged as an excellent sensing element for its exceptional behavior in fluorescence, biocompatibility, and water dispersibility. However, its poor stability, selectivity and reproducibility in complex medium still be a big problem for its practical application. To overcome this, in the work, we have developed a new type of carbon quantum dot-PSS fluorescent nanocomposites which has been used for specific Fe³⁺ detection. The polystyrene sulfonate (PSS) polymer not only stabilize the QDs but also produces specific sites for Fe³⁺ to make a co-ordinate complex via Fe³⁺-SO3. The detection limit is calculated as low as 1 ppm which is adequate for measuring Fe³⁺ in blood or water samples. The mechanism of the quenching is very specific towards the Fe³⁺ ion due to the presence of PSS which makes the sensor selective among other metal ions and possible interferences. The rapid process of sensing, simple instrumentation, and excellent performances in presence of 1 % BSA and serum samples indicates the possible application for diagnostic usage in near future.

Fabrication of Hybrid Electrodes by Laser-Induced Forward Transfer for the Detection of Cu2+ Ions

Composites based on poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS)-graphene oxide (GO) are increasingly considered for sensing applications. In this work we aim at patterning and prototyping microscale geometries of PEDOT:PSS: GO composites for the modification of commercially available electrochemical sensors. Here, we demonstrate the laser-induced forward transfer of PEDOT:PSS: GO composites, a remarkably simple procedure that allows for the fast and clean transfer of materials with high resolution for a wide range of laser fluences (450-750 mJ/cm²). We show that it is possible to transfer PEDOT:PSS: GO composites at different ratios (i.e., 25:75 %wt and 50:50 %wt) onto flexible screen-printed electrodes. Furthermore, when testing the functionality of the PEDOT:PSS: GO modified electrodes via LIFT, we could see that both the PEDOT:PSS: GO ratio as well as the addition of an intermediate release layer in the LIFT process plays an important role in the electrochemical response. In particular, the ratio of the oxidation peak current to the reduction peak current is almost twice as high for the sensor with a 50:50 %et PEDOT:PSS: GO pixel. This direct transfer methodology provides a path forward for the prototyping and production of polymer: graphene oxide composite based devices.

Green synthesis of CQDs for determination of iron and isoniazid in pharmaceutical formulations

Camphor leaves were used as the precursor for the hydrothermal synthesis of carbon quantum dots. The preparation method is simple and rapid, and the raw material is environmentally friendly and easy to obtain. Without additional modification, the carbon quantum dots were used as fluorescent probes for the sensitive and selective detection of Fe³⁺ and isoniazid at different excitation wavelengths. For Fe³⁺, at the excitation wavelength of 320 nm, the ratio of fluorescence intensity of CQD solution after adding Fe³⁺ to CQD solution without Fe³⁺ addition, F/F₀, and Fe³⁺ concentration showed a good linear relationship in the range of 2.72 × 10^-5 to 1.00 × 10^-4 mol L^-1 (R² = 0.9912), and the limit of detection was 8.16 μmol L^-1. For isoniazid, at the excitation wavelength of 270 nm, the ratio of fluorescence intensity of CQDs solution with isoniazid to CQDs solution without isoniazid, F/F₀, and isoniazid concentration showed good linear relationships in the range of 3.81 × 10^-6 to 1.00 × 10^-5 mol L^-1 (R² = 0.9941) and 1.00 × 10^-5 to 2.10 × 10^-4 mol L^-1 (R² = 0.9910) respectively, and the limit of detection was 1.14 μmol L^-1. A fluorescence method for the determination of Fe and isoniazid content was proposed. The method has been used to detect iron in iron supplement tablets and isoniazid in isoniazid tablets with satisfactory results.

Why PEDOT:PSS Should Not Be Used for Raman Sensing of Redox States (and How It Could Be)

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been recently proposed for Raman sensing of redox-active species in solution. Here, we investigated the rationale of this approach through systematic experiments, in which the Raman spectrum of PEDOT:PSS was analyzed in the presence of either nonoxidizing or oxidizing electrolytes. The results demonstrated that Raman spectra precisely reflect the conformation of PEDOT units and their interactions with PSS. Two different responses were observed. In the case of oxidizing electrolytes, the effect of charge transfer is accurately transduced in Raman spectrum changes. On the other hand, reduction induces a progressive separation between the PEDOT and PSS chains, which decreases their mutual interaction. This stimulus determines characteristic variations in the intensity, shape, and position of the Raman spectra. However, we demonstrated that the same effects can be obtained either by increasing the concentration of nonoxidizing electrolytes or by deprotonating PSS chains. This poses severe limitations to the use of PEDOT:PSS for this type of Raman sensing. This study allows us to revise most of the Raman results reported in the literature with a clear model, setting a new basis for investigating the dynamics of mixed electronic/ionic charge transfer in conductive polymers.

Selective non-enzymatic uric acid sensing in the presence of dopamine: electropolymerized poly-pyrrole modified with a reduced graphene oxide/PEDOT:PSS composite

A molecularly imprinted polymer (MIP) with uric acid cavities increases the selectivity of uric acid measurement in the presence of dopamine as an interferent.

Recent progress on carbon nanomaterials for the electrochemical detection and removal of environmental pollutants

Rapid global industrialization and explosive population growth have resulted in an increase in the discharge of harmful and toxic compounds. These toxic inorganic gases, volatile organic compounds, heavy metals, personal care products, endocrine-disrupting chemicals, dyes, and pharmaceuticals are destroying the balance in the Earth and increasing environmental toxicity at an alarming rate. Thus, their detection, adsorption and removal are of great significance. Various carbon nanomaterials including carbon nanotubes, graphene, mesoporous carbon, carbon dots, and boron-doped diamond have been extensively utilized and further proven to be ideal candidates for resolving environmental problems, emerging as adsorbents, electrochemical sensors and electrodes. Herein, we review the recent advances, progress and achievements in the design and properties of carbon nanomaterials and their applications for the electrochemical detection and removal of environmental pollutants.

Electrochemical Sensor of Double-Thiol Linked PProDOT@Si Composite for Simultaneous Detection of Cd(II), Pb(II), and Hg(II)

Heavy metal ions in water, cosmetics, and arable land have become a world-wide issue as they cause a variety of diseases and even death to humans and animals when a certain level is exceeded. Therefore, it is necessary to development a new kind of sensor material for the determination of heavy metal ions. In this paper, we present an electrochemical sensor based on composite material (thiol(-SH) grafted poly(3,4-proplenedioxythiophene) (PProDOT(MeSH)₂)/ porous silicon spheres (Si) composite, denoted as PProDOT(MeSH)₂@Si) from the incorporation of thiol(-SH) grafted poly(3,4-proplenedioxythiophene) (PProDOT(MeSH)₂) with porous silicon spheres (Si) for the electrochemical detection of heavy metal ions (Cd(II), Pb(II), and Hg(II)). The PProDOT(MeSH)₂@Si composite was synthesized via a chemical oxidative polymerization method. The structure and morphology of PProDOT(MeSH)₂@Si composite were characterized by Fourier transform infrared (FT-IR), Ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscope (SEM), Transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET). Furthermore, the electrochemical performance of PProDOT(MeSH)₂@Si was evaluated by detecting of Cd(II), Pb(II), and Hg(II) ions using the differential pulse voltammetry (DPV) method. The relationship between structural properties and the electrochemical performance was systematically studied. The results showed that the entry of two thiol-based chains to the monomer unit resulted in an increase in electrochemical sensitivity in PProDOT(MeSH)_2, which was related to the interaction between thiol group(-SH) and heavy metal ions. And, the combination of PProDOT(MeSH)₂ with Si could improve the electrocatalytic efficiency of the electrode material. The PProDOT(MeSH)₂@Si/GCE exhibited high selectivity and sensitivity in the rage of 0.04 to 2.8, 0.024 to 2.8, and 0.16 to 3.2 μM with the detection limit of 0.00575, 0.0027, and 0.0017 µM toward Cd(II), Pb(II), and Hg(II), respectively. The interference studies demonstrated that the PProDOT(MeSH)₂@Si/GCE possessed a low mutual interference and high selectivity for simultaneous detection of Cd(II), Pb(II), and Hg(II) ions.

Green synthesis of fluorescent carbon dots from Borassus flabellifer flowers for label-free highly selective and sensitive detection of Fe3+ ions

Fluorescent carbon dots were derived from Borassus flabellifer flowers by thermal pyrolysis method and used for label-free highly selective and sensitive detection of Fe³⁺ ions.