Covalently modified graphene quantum dot using a thiourea based imprinted polymer for the selective electrochemical sensing of Hg(II) ions

Preparation and application of a new ion-imprinted polymer for nanomolar detection of mercury(II) in environmental waters

This study introduces a novel ion-imprinted polymer for the ultrasensitive detection of mercury(II) in water. The ion-imprinted polymer was synthesized via a simple bulk polymerization process using methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, morpholine-4-carbodithioic acid phenyl ester as the chelating agent, and ammonium persulfate as the initiator. The electrochemical mercury(II) sensing capability of the ion-imprinted polymer was studied via the modification of a cost-effective carbon paste electrode. A stripping voltammetric technique was utilized to quantify the analyte ions following open-circuit enrichment. Critical experimental parameters, including the nature and concentration of the eluent, solution pH, preconcentration duration, ion-imprinted polymer dosage, sample solution volume and reduction potential, were systematically studied and optimized. Under optimal conditions, the sensor exhibited a linear response in the range of 1.0 to 240.0 nM, with a low detection limit of 0.2 nM. The sensor demonstrated remarkable selectivity against potential interfering ions, including lead(II), cadmium(II), copper(II), zinc(II), manganese(II), iron(II), magnesium(II), calcium(II), sodium(I) and cobalt(II). The practical applicability of the developed method was successfully validated through the analysis of real water samples, suggesting its potential for environmental monitoring applications.

Signal amplification in molecular sensing by imprinted polymers

In the field of sensing, the development of sensors with high sensitivity, accuracy, selectivity, sustainability, simplicity, and low cost remains a key focus. Over the past decades, optical and electrochemical sensors based on molecular imprinting techniques have garnered significant attention due to the above advantages. Molecular imprinting technology utilizes molecularly imprinted polymers (MIPs) to mimic the specific recognition capabilities of enzymes or antibodies for target molecules. Recently, MIP-based sensors rooting in signal amplification techniques have been employed to enhance molecular detection level and the quantitative ability for environmental pollutants, biomolecules, therapeutic compounds, bacteria, and viruses. The signal amplification techniques involved in MIP-based sensors mainly cover nucleic acid chain amplification, enzyme-catalyzed cascade, introduction of high-performance nanomaterials, and rapid chemical reactions. The amplified analytical signals are centered around electrochemical, fluorescence, colorimetric, and surface-enhanced Raman techniques, which can effectively realize the determination of some low-abundance targets in biological samples. This review highlights the recent advancements of electrochemical/optical sensors based on molecular imprinting integrated with various signal amplification strategies and their dedication to the study of trace biomolecules. Finally, future research directions on developing multidimensional output signals of MIP-based sensors and introducing multiple signal amplification strategies are proposed.

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Chitosan-assisted self-assembly of flower-shaped ε-Fe2O3 nanoparticles on screen-printed carbon electrode for Impedimetric detection of Cd2+, Pb2+, and Hg2+ heavy metal ions in various water samples

This study focuses on the fabrication of a novel sensing platform on a screen-printed carbon electrode, modified by a combination of hydrothermally synthesized iron dioxide (ε-Fe2O3) nanoparticles and Chitosan (CS) biopolymer. This unique organic-inorganic hybrid material was developed for Electrochemical Impedance Spectroscopy (EIS) sensing, specifically targeting heavy metal ions that include Hg2+, Cd2+, as well as Pb2+. The investigation encompassed a comprehensive analysis of various aspects of the prepared Fe2O3 and CS/ε-Fe2O3 nanocomposites, including phase identification, determination of crystallite size, assessment of surface morphology, etc. CS/ε-Fe2O3 was drop-casted and deposited on the Screen-Printed Electrode (SPE). The resulting sensor exhibited excellent performance in the precise and selective quantification of Hg2+, Cd2+, and Pb2+ ions, with minimal interference from other substances. The fabricated sensor exhibits excellent performance as the detection range for Hg2+, Cd2+, and Pb2+ ions linearity is 2-20 μM, sensitivity, and LOD are 243 Ω/ μM cm2 and 0.191 μM, 191 Ω/μM cm2, and 0.167 μM, 879 Ω/ μM cm2, and 0.177 μM respectively. The stability of the CS/ε-Fe2O3/SPE electrode is demonstrated by checking its conductivity for up to 60 days for Hg2+, Cd2+, and Pb2+ ions. The reusability of the fabricated electrode is 14 scans, 13 scans, and 12 scans for Hg2+, Cd2+, and Pb2+ ions respectively. The findings indicate the successful development of an innovative CS/ε-Fe2O3 electrode for the EIS sensing platform. This platform demonstrates notable potential for addressing the critical need for efficient and sensitive EIS sensors capable of detecting a range of hazardous heavy metal ions, including Hg2+, Cd2+, and Pb2+.

Novel highly selective fluorescence sensing strategy for Mercury(Ⅱ) in water based on nitrogen-doped carbon quantum dots

In this work, a fluorescent signal-closing probe of nitrogen-doped carbon quantum dots (NCQDs) was developed for quantitative detection of mercury ions (Hg²⁺). In this detection system, the NCQDs with high quantum yield (QY, 63.80 %) were synthesized via simple hydrothermal method with Methyl Glycine Diacetic acid Trisodium Salt (MGDA) and m-phenylenediamine (MPD) as carbon and nitrogen sources. The NCQDs have a typical surface structure and exceptional fluorescence stability, and their fluorescence zones are centered on excitation wavelengths of 440 nm and emission wavelengths of 510 nm. Under optimal conditions, the NCQDs have outstanding anti-interference ability to various ions and high selectivity to mercury ions. The fluorescence intensity of the detection system is weakened due to the generation of non-fluorescent groups caused by the static quenching effect. The fluorescence quenching efficiency shows a fascinating linear relationship with Hg²⁺ ions at 0-100 μM (y = 0.0051x-0.015, R² = 0.9943), and the detection limit is 0.9 μM. Acute toxicity test shows that NCQDs have low toxicity and little harm to environment. The detection system can be used for the quantification of mercury ions in environmental water samples, and the recovery rate is between 99.64 % and 103.43 %, indicating that it is a simple and economical fluorescence detection method.

Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review

Heavy metal ions (HMIs) pose a serious threat to the environment and human body because they are toxic and non-biodegradable and widely exist in environmental ecosystems. It is necessary to develop a rapid, sensitive and convenient method for HMIs detection to provide a strong guarantee for ecology and human health. Ion-imprinted electrochemical sensors (IIECSs) based on nanomaterials have been regarded as an excellent technology because of the good selectivity, the advantages of fast detection speed, low cost, and portability. Electrode surfaces modified with nanomaterials can obtain excellent nano-effects, such as size effect, macroscopic quantum tunneling effect and surface effect, which greatly improve its surface area and conductivity, so as to improve the detection sensitivity and reduce the detection limit of the sensor. Hence, the present review focused on the fundamentals and the synthetic strategies of ion-imprinted polymers (IIPs) and IIECSs for HMIs detection, as well as the applications of various nanomaterials as modifiers and sensitizers in the construction of HMIIECSs and the influence on the sensing performance of the fabricated sensors. Finally, the potential challenges and outlook on the future development of the HMIIECSs technology were also highlighted. By means of the points presented in this review, we hope to provide some help in further developing the preparation methods of high-performance HMIIECSs and expanding their potential applications.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Sol-Gel Synthesis and Characterization of Highly Selective Poly(N-methyl pyrrole) Stannous(II)Tungstate Nano Composite for Mercury (Hg(II)) Detection

The sol-gel process was used to create a new type of polypyrrole-Stannous(II)tungstate nanocomposite by poly(N-methyl pyrrole (PNMPy) sol in Stannous(II)tungstate gel, produced separately using sodium silicotungstic acid and Tn(II)chloride. Tin(II)tungstate (SnWO3) was made by changing the mixing volume ratios of SnWO3 and with a constant amount of an organic polymer. The composite was characterized by TGA, XRD, FTIR, and SEM measurements. A commercially available glassy carbon electrode (GCE) was modified with PNMPy/nano-Stannous(II)WO3 nanocomposites to create a chemical sensor for selective detection of Hg2+ ions using an effective electrochemical methodology. In the I-V technique, selectively toxic Hg2+ ion was targeted selectively, which shows a rapid reaction toward PNMPy/nano-Stannous(II)WO3/Nafion/GCE sensor. It also demonstrates long-term stability, an ultra-low detection limit, exceptional sensitivity, and excellent reproducibility and repeatability. For 0.1 mM to 1.0 nM aqueous Hg2+ ion solution, a linear calibration plot (r2: 0.9993) was achieved, with a suitable sensitivity value of 2.8241 AM−1 cm−2 and an extraordinarily low detection limit (LOD) of 3.40.1 pM (S/N = 3). As a result, the cationic sensor modified by PNMPy/nano-Stannous(II)WO3/GCE could be a promising electrode.