Determination of lead in blood by square wave anodic stripping voltammetry at a carbon disk ultramicroelectrode

Picomolar Detection of Lead Ions (Pb2+) by Functionally Modified Fluorescent Carbon Quantum Dots from Watermelon Juice and Their Imaging in Cancer Cells

Water contamination due to the presence of lead is one of the leading causes of environmental and health hazards because of poor soil and groundwater waste management. Herein we report the synthesis of functionally modified luminescent carbon quantum dots (CQDs) obtained from watermelon juice as potential nanomaterials for the detection of toxic Pb²⁺ ions in polluted water and cancer cells. By introducing surface passivating ligands such as ethanolamine (EA) and ethylenediamine (ED) in watermelon juice, watermelon-ethanolamine (WMEA)-CQDs and watermelon-ethylenediamine (WMED)-CQDs exhibited a remarkable ~10-fold and ~6-fold increase in fluorescence intensity with respect to non-doped WM-CQDs. The relative fluorescence quantum yields of WMEA-CQDs and WMED-CQDs were found to be 8% and 7%, respectively, in an aqueous medium. Among various functionally-modified CQDs, only WMED-CQDs showed high selectivity towards Pb²⁺ ions with a remarkably good limit of detection (LoD) of 190 pM, which is less than that of the permissible limit (72 nM) in drinking water. The functionally altered WMED-CQDs detected Pb²⁺ metal ions in polluted water and in a human cervical cancer cell line (HeLa), thus advocating new vistas for eco-friendly nanomaterials for their use as diagnostic tools in the environment and biomedical research areas.

An "OR-AND" logic gate based multifunctional colorimetric sensor for the discrimination of Pb2+ and Cd2

Pb²⁺ and Cd²⁺ are the most ubiquitous heavy metal ion pollutants, and they have aroused much attention due to their irreversible and significant damage to human organ. In this work, a new fluorescein-based "OR-AND" logic gate colorimetric probe 3',6'-bis((tert-butyldiphenylsilyl)oxy)-2-(2-((2-hydroxyphenyl)imino)ethylidene)aminspiro[isoindoline-1,9'-xanthen]-3-one (FP) was designed and synthesized via attaching 2-(2-((2-hydroxyphenyl)imino)ethylidene)amino and tert-butyldiphenylsilyl to fluorescein as the specific identification groups. This sensor can rapidly and sensitively discriminate Pb²⁺ and Cd²⁺ by utilizing F^- as an auxiliary reagent. When Pb²⁺ or Cd²⁺ was added into the FP solution, the absorption band at 533 nm increased and the peak at 374 nm decreased, the color changed from colorless to pale-purple, resulting in a ratiometric spectral change. However, adding fluoride ion to the FP solution containing Pb²⁺ or Cd²⁺ resulted in a distinct phenomenon in which the pale purple color fades out to colorless for a Pb²⁺-containing solution and deepen to dark purple for a Cd²⁺-containing solution, which is attributable to the different coordination mechanisms. In aqueous solution, the detection limits of FP can reach 0.42 μM for Pb²⁺ and 0.53 μM for Cd²⁺. The probe exhibited rapid responses for these analytes. Moreover, FP was successfully used to rapidly detect trace amounts of hazardous Pb²⁺ and Cd²⁺ in tap water with good relative recovery and the relative standard deviations (RSD) were 1.8% for Pb²⁺ and 0.3% for Cd²⁺, providing a novel approach for detecting Pb²⁺ and Cd²⁺ in practical application.

Open Source Software for the Real-Time Control, Processing, and Visualization of High-Volume Electrochemical Data

Electrochemical sensors are major players in the race for improved molecular diagnostics due to their convenience, temporal resolution, manufacturing scalability, and their ability to support real-time measurements. This is evident in the ever-increasing number of health-related electrochemical sensing platforms, ranging from single-measurement point-of-care devices to wearable devices supporting immediate and continuous monitoring. In support of the need for such systems to rapidly process large data volumes, we describe here an open-source, easily customizable, multiplatform compatible program for the real-time control, processing, and visualization of electrochemical data. The software’s architecture is modular and fully documented, allowing the easy customization of the code to support the processing of voltammetric (e.g., square-wave and cyclic) and chronoamperometric data. The program, which we have called Software for the Analysis and Continuous Monitoring of Electrochemical Systems (SACMES), also includes a graphical interface allowing the user to easily change analysis parameters (e.g., signal/noise processing, baseline correction) in real-time. To demonstrate the versatility of SACMES we use it here to analyze the real-time data output by (1) the electrochemical, aptamer-based measurement of a specific small-molecule target, (2) a monoclonal antibody-detecting DNA-scaffold sensor, and (3) the determination of the folding thermodynamics of an electrode-attached, redox-reporter-modified protein.

Synthesis and characterization of macroporous europium-doped Ca12Al14O33 (C12A7:Eu3+) and its application in metal ion detection

Macroporous europium-doped Ca₁₂Al₁₄O₃₃ (C12A7:Eu³⁺) was prepared via a sol–gel method followed by heat-treatment, and the resultant macroporous C12A7:Eu³⁺ shows potential for practical application in metal ion detection and has a good response to Pb²⁺ ions.

One-step synthesis of a dual-emitting carbon dot-based ratiometric fluorescent probe for the visual assay of Pb2+ and PPi and development of a paper sensor

Herein, an easy and effective ratiometric fluorescent nanoprobe for the selective detection of Pb²⁺ and pyrophosphate (PPi) was developed based on label-free carbon dots (CDs).

Highly selective and sensitive coumarin-triazole-based fluorometric 'turn-off' sensor for detection of Pb2+ ions

Exposure to even very low concentrations of Pb²⁺ is known to cause cardiovascular, neurological, developmental, and reproductive disorders, and affects children in particular more severely. Consequently, much effort has been dedicated to the development of colorimetric and fluorescent sensors that can selectively detect Pb²⁺ ions. Here, we describe the development of a triazole-based fluorescent sensor L5 for Pb²⁺ ion detection. The fluorescence intensity of chemosensor L5 was selectively quenched by Pb²⁺ ions and a clear color change from colorless to yellow could be observed by the naked eye. Chemosensor L5 exhibited high sensitivity and selectivity towards Pb²⁺ ions in phosphate-buffered solution [20 mM, 1:9 DMSO/H₂ O (v/v), pH 8.0] with a 1:1 binding stoichiometry, a detection limit of 1.9 nM and a 6.76 × 10⁶  M^-1 binding constant. Additionally, low-cost and easy-to-prepare test strips impregnated with chemosensor L5 were also produced for efficient of Pb²⁺ detection and proved the practical use of this test.

Colorimetric Determination of Pb2+ in Perfect Aqueous Solution Using Carminic Acid as a Selective Chemosensor

The commercially available natural organic dye, carminic acid (CA), an anthraquinone derivative bearing hydroxyl and carboxyl groups as recognition sites was found to be a colorimetric probe for Pb²⁺ in perfect aqueous solution under neutral conditions with specific selectivity and high sensitivity. Upon addition of Pb²⁺, the absorption maximum of CA showed a large red shift, and the resulted color change from red to purple could be easily identified even by the naked eye. The chemical stoichiometric ratio between CA and Pb²⁺ was determined to be 1:2 through Job plot, Pb²⁺ titration, and kinetic experiments. Moreover, other environmental relevant metal ions induced no or minimal spectral and color changes. The reversibility of Pb²⁺ to CA with EDTA even through several cycles was established for practical applications. The results indicated that CA can be a good candidate for simple, convenient and reversible colorimetric detection of Pb²⁺ in aqueous solution even though it was hard to be applied to determine Pb²⁺ on the water testing by US EPA.

The Importance of Magnesium in the Human Body: A Systematic Literature Review

Magnesium, the second and fourth most abundant cation in the intracellular compartment and whole body, respectively, is of great physiologic importance. Magnesium exists as bound and free ionized forms depending on temperature, pH, ionic strength, and competing ions. Free magnesium participates in many biochemical processes and is most commonly measured by ion-selective electrode. This analytical approach is problematic because complete selectivity is not possible due to competition with other ions, i.e., calcium, and pH interference. Unfortunately, many studies have focused on measurement of total magnesium rather than its free bioactive form making it difficult to correlate to disease states. This systematic literature review presents current analytical challenges in obtaining accurate and reproducible test results for magnesium.

Development of fluorescent lead II sensor based on an anthracene derived chalcone

A simple anthracene based chalcone as a fluorescent chemosensor 1, capable of detecting Pb(2+) in aqueous media, has been synthesized by the reaction between pyridine 2-carboxaldehyde and 9-acetyl anthracene. The Pb(2+) recognition processes follows a photo induced electron transfer (PET) mechanism and are scarcely influenced by other coexisting metal ions. In addition, determination of lead in a variety of samples was also determined.

Fluorometric sensing of Pb2+and CrO42−ions through host–guest inclusion for human lung cancer live cell imaging

The formation of an inclusion complex between 1,5-dihydroxyanthraquinone (1,5-DHAQ;1) and β-cyclodextrin (β-CD) in aqueous media has been studied by UV-visible and fluorescence spectroscopy.

Fluorescent nanohybrid of gold nanoclusters and quantum dots for visual determination of lead ions

Highly green emissive gold nanoclusters (Au NCs) are synthesized using glutathione as a stabilizing agent and mercaptopropionic acid as a ligand, and the intensity of fluorescence is specifically sensitive to lead ions. We then fabricated a ratiometric fluorescence nanohybrid by covalently linking the green Au NCs to the surface of silica nanoparticles embedded with red quantum dots (QDs) for on-site visual determination of lead ions. The green fluorescence can be selectively quenched by lead ions, whereas the red fluorescence is inert to lead ions as internal reference. The different response of the two emissions results in a continuous fluorescence color change from green to yellow that can be clearly observed by the naked eyes. The nanohybrid sensor exhibits high sensitivity to lead ions with a detection limit of 3.5 nM and has been demonstrated for determination of lead ions in real water samples including tap water, mineral water, groundwater, and seawater. For practical application, we dope the Au NCs in poly(vinyl alcohol) (PVA) film and fabricate fluorescence test strips to directly detect lead ions in water. The PVA-film method has a visual detection limit of 0.1 μM, showing its promising application for on-site identification of lead ions without the need for elaborate equipment.

A dual colorimetric and fluorescent sensor for lead ion based on naphthalene hydrazone derivative

A new compound, 2-boronobenzaldehyde-(2'-hydroxyl-4'-sulfonic acid) naphthalene hydrazone (1), was synthesized and its structure was characterized by proton nuclear magnetic resonance, mass and element analyses. The presence of Pb(2+) led 1 to undergo colorimetric and fluorescent changes, which were detectable with the naked eye. Thus, a dual spectral response for Pb(2+) detection was introduced. In KH2PO4-NaOH buffer aqueous solution (pH 6.0), 1 exhibited fluorescence enhancement at 568 nm and hyperchromicity at 595 nm upon the addition of Pb(2+). The fluorescent intensity change was proportionate to the concentration of Pb(2+) with a dynamic working range of 5.0×10(-7) mol L(-1) to 1.0×10(-4) mol L(-1) and a detection limit of 3.7×10(-8) mol L(-1). The fluorometric method was successfully applied for the detection of Pb(2+) water of Qianhu Lake and soil in Nanchang university campus. The recoveries were 111-116% for water and 97.6% for soil respectively, determined via the standard addition method.

A highly sensitive and selective fluorescent chemosensor for Pb2+ ions in an aqueous solution

A new fluorescent sensor based on the BODIPY fluorophore and the polyamide receptor for Pb(2+) was designed and synthesized. The sensor is highly selective for Pb(2+) over relevant competing metal ions, and sensitive to ppb levels of Pb(2+). It features the most sensitive probe to date for Pb(2+) ions in water.

A dual sensor of fluorescent and colorimetric for the rapid detection of lead

This study demonstrated a simple and reliable method to rapidly detect Pb(2+) in aqueous solution, exploiting gold nanoparticles as a lead ion probe; the results indicated that the dual channels sensor showed high selectivity and sensitivity for Pb(2+) as low as ppm levels in aqueous environment.

Development of a fluorescent Pb2+ sensor

A real turn-on: The emission intensity of heterocycle 1 increases upon binding to Pb(2+). Thus, 1 acts as a small-molecule "turn-on" fluorescent sensor for lead. The sensor is highly selective and is functional over a wide range of pH values.

Nucleic acid aptamers for biosensors and bio-analytical applications

Oligonucleotides were once considered only functional as molecules for the storage of genetic information. However, the discovery of RNAzymes, and later, DNAzymes, unravelled the innate potential of oligonucleotides in many other biological applications. In the last two decades, these applications have been further expanded through the introduction of Systematic Evolution of Ligands by EXponential enrichment (SELEX) which has generated, by repeated rounds of in vitro selection, a type of molecular probe termed aptamers. Aptamers are oligonucleic acid (or peptide) molecules that can bind to various molecular targets and are viewed as complements to antibodies. Aptamers have found applications in many areas, such as bio-technology, medicine, pharmacology, microbiology, and analytical chemistry, including chromatographic separation and biosensors. In this review, we focus on the use of aptamers in the development of biosensors. Coupled with their ability to bind a variety of targets, the robust nature of oligonucleotides, in terms of synthesis, storage, and wide range of temperature stability and chemical manipulation, makes them highly suitable for biosensor design and engineering. Among the many design strategies, we discuss three general paradigms that have appeared most frequently in the literature: structure-switching, enzyme-based, and aptazyme-based designs.

Immobilization of metallothionein as a sensitive biosensor chip for the detection of metal ions by surface plasmon resonance

A biosensor based on mammalian metallothionein (MT) for the detection of metal ions was developed and characterized. MT was immobilized onto a carboxymethylated dextran matrix as a biosensor for the detection of metal ions by surface plasmon resonance (SPR). The optimal pH for the immobilization step was determined to be 4. The temperature for the analysis was also defined, and the highest interaction was observed at 30 degrees C. The MT sensor chip binds cadmium (Cd), zinc (Zn) or nickel (Ni), but not magnesium (Mg), manganese (Mn) and calcium (Ca). Calibration curves for the quantification of metal ions showed excellent linearity. The sensitivity for metal detection is at the micromolar level. The interaction between the metal ions and the sensor chip is influenced significantly by the presence of NaCl, Tween 20 and the pH of the reaction buffer. By decreasing the NaCl in the reaction buffer to 1 mM, the MT chip effectively differentiates cadmium from zinc and nickel. Kinetic parameters of the metal-MT interactions were also determined by using this chip. The binding affinity between the metal ions and the immobilized MT follows the order of cadmium > zinc > nickel, which is the same as that determined for MT in solution. Thus, the MT chip can be an effective biosensor for the detection and measurement of several metal ions.

New highly sensitive and selective catalytic DNA biosensors for metal ions

While remarkable progress has been made in developing sensors for metal ions such as Ca(II) and Zn(II), designing and synthesizing sensitive and selective metal ion sensors remains a significant challenge. Perhaps the biggest challenge is the design and synthesis of a sensor capable of specific and strong metal binding. Since our knowledge about the construction of metal-binding sites in general is limited, searching for sensors in a combinatorial way is of significant value. Therefore, we have been able to use a combinatorial method called in vitro selection to obtain catalytic DNA that can bind a metal ion of choice strongly and specifically. The metal ion selectivity of the catalytic DNA was further improved using a 'negative selection' strategy where catalytic DNA that are selective for competing metal ions are discarded in the in vitro selection processes. By labeling the resulting catalytic DNA with a fluorophore/quencher pair, we have made a new class of metal ion fluorescent sensors that are the first examples of catalytic DNA biosensors for metal ions. The sensors combine the high selectivity of catalytic DNA with the high sensitivity of fluorescent detection, and can be applied to the quantitative detection of metal ions over a wide concentration range and with high selectivity. The use of DNA sensors in detection and quantification of lead ions in environmental samples such as water from Lake Michigan has been demonstrated. DNA is stable, cost-effective, environmentally benign, and easily adaptable to optical fiber and microarray technology for device manufacture. Thus, the DNA sensors explained here hold great promise for on-site and real-time monitoring of metal ions in the fields of environmental monitoring, developmental biology, clinical toxicology, wastewater treatment, and industrial process monitoring.

Indium as internal standard in square wave anodic stripping analysis of lead in blood with microelectrode arrays

The toxic effects of lead on humans, especially children have been well documented. ASV has been an important technique in the analysis of lead in blood of humans. This research has demonstrated that indium(III) can be used as an internal standard in the analysis of lead in blood samples with mercury film microelectrode arrays. Indium is a good choice because of a low endogenous blood concentration and because baseline separation of anodic stripping peaks among Cd, In, and Pb can be achieved under appropriate conditions. The concentration of sodium bromide strongly influences the resolution of these metals and the sensitivity of ASV to In(III) in solution. Square wave anodic stripping voltammetry together with screen-printed microelectrode arrays showed that the ratio of the anodic stripping peak currents of Pb and In varies linearly with the concentration of Pb in blood samples ranging from 1.2 to 30.0 micrograms/dL. The average intraassay precision (rsd) was 6.7%.