A New Electrochemical System Based on a Flow-Field Shaped Solid Electrode and 3D-Printed Thin-Layer Flow Cell: Detection of Pb2+ Ions by Continuous Flow Accumulation Square-Wave Anodic Stripping Voltammetry

A new benzothiazole azo dye colorimetric chemosensor for detecting Pb2+ ion

In this work, a new benzothiazole azo dye sensor (BTS) was synthesized, and its cation binding affinity was studied using the colorimetric method, UV-vis, and ¹H NMR spectral data. The results revealed that the sensor BTS exhibits a remarkable tendency for Pb²⁺ ion to perform spontaneous visual color change from blue (BTS) to pink (BTS + Pb²⁺), without any color change in the aqueous solutions of other cations such as Hg²⁺, Cu²⁺, Al³⁺, Ni²⁺, Cd²⁺, Ag⁺_, Ba²⁺, K⁺, Co²⁺, Mg²⁺, Na⁺, Ca²⁺, Fe²⁺, and Fe³⁺ ions. The observed selectivity could be due to the formation of the complex (BTS + Pb²⁺⁾, which led to a blue shift from 586 nm (BTS) to 514 nm (BTS + Pb²⁺) in the UV spectrum. The job's plot provided the stoichiometry ratio of the complex (BTS + Pb²⁺) to be 1:1. The limit of detection (LOD) of BTS for Pb²⁺ ion sensing was obtained at 0.67 µM. Additionally, the binding constant for BTS toward Pb ²⁺ ion was studied using the Benesi-Hildebrand equation. As a result of the BTS test paper strips investigations, it was found that the synthesized sensor BTS could be used as a rapid colorimetric chemosensor for the detection of the Pb²⁺ ions in the distilled, tap, and sea waters.

Microfluidic Devices for Heavy Metal Ions Detection: A Review

The contamination of air, water and soil by heavy metal ions is one of the most serious problems plaguing the environment. These metal ions are characterized by a low biodegradability and high chemical stability and can affect humans and animals, causing severe diseases. In addition to the typical analysis methods, i.e., liquid chromatography (LC) or spectrometric methods (i.e., atomic absorption spectroscopy, AAS), there is a need for the development of inexpensive, easy-to-use, sensitive and portable devices for the detection of heavy metal ions at the point of interest. To this direction, microfluidic and lab-on-chip (LOC) devices fabricated with novel materials and scalable microfabrication methods have been proposed as a promising approach to realize such systems. This review focuses on the recent advances of such devices used for the detection of the most important toxic metal ions, namely, lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd) and chromium (Cr) ions. Particular emphasis is given to the materials, the fabrication methods and the detection methods proposed for the realization of such devices in order to provide a complete overview of the existing technology advances as well as the limitations and the challenges that should be addressed in order to improve the commercial uptake of microfluidic and LOC devices in environmental monitoring applications.

Homogeneous voltammetric sensing strategy for lead ions based on aptamer gated methylthionine chloride@UiO-66-NH2 framework as smart target-stimulated responsive nanomaterial

Herein an innovative electrochemical method is proposed for the determination of lead ions (Pb²⁺) based on a homogeneous voltammetric (HVC) sensing strategy using an aptamer gated methylthionine chloride@UiO-66-NH₂ framework as a smart target-stimulated responsive material. The proposed HVC sensor exhibits excellent sensing performance: ultralow detection limit (0.166 pM) and wide linearity (5.0 pM-500.0 nM), simultaneously, it avoids electrodeposition processes and it is simple to modify the electrode compared to previous electrochemical methods for Pb²⁺ detection. Thus our method shows great potential in the highly efficient detection of Pb²⁺ and other heavy metal ions by simply altering the related specific aptamer.

A 3D-printed analytical device seamlessly integrating sample treatment for electrochemical detection of IAA in Marchantia polymorpha

Because of the pivotal point of Marchantia polymorpha (M. polymorpha) in plant evolution, its auxin (mainly indole-3-acetic acid, IAA) levels could provide useful evidence for the study of the evolution of IAA. However, M. polymorpha could not be easily pretreated for electrochemical detection because they are at the entry level of land plants. Herein, we designed a three-dimensional (3D)-printed analytical device for seamless integration of sample treatment and electrochemical detection. Specifically, the electrochemical cell could be used as a mortar in which a tiny plant sample could be ground with a 3D-printed pestle, followed by mixing with the buffer solution under vibration for electrochemical detection of IAA with a disposable working electrode at the bottom of the cell. Using our strategy, the limits of quantification could reach 0.05 μmol L^-1 after optimization of parameters. We were able to demonstrate that IAA in different tissues of wild-type and mutant M. polymorpha could be successfully differentiated after they were treated with the 3D-printed analytical device. The obtained results were comparable to the samples blended with zirconium beads while the differences of IAA levels in different tissues of M. polymorpha agreed well with previous reports. This study suggested the potential of sample treatment integrated with electrochemical detection for analysis of IAA using the 3D printing techniques and their possible applications in the research of plants and other fields.

Nanomaterials-Based Electrochemiluminescence Biosensors for Food Analysis: Recent Developments and Future Directions

Developing robust and sensitive food safety detection methods is important for human health. Electrochemiluminescence (ECL) is a powerful analytical technique for complete separation of input source (electricity) and output signal (light), thereby significantly reducing background ECL signal. ECL biosensors have attracted considerable attention owing to their high sensitivity and wide dynamic range in food safety detection. In this review, we introduce the principles of ECL biosensors and common ECL luminophores, as well as the latest applications of ECL biosensors in food analysis. Further, novel nanomaterial assembly strategies have been progressively incorporated into the design of ECL biosensors, and by demonstrating some representative works, we summarize the development status of ECL biosensors in detection of mycotoxins, heavy metal ions, antibiotics, pesticide residues, foodborne pathogens, and other illegal additives. Finally, the current challenges faced by ECL biosensors are outlined and the future directions for advancing ECL research are presented.

Detection of Pb2+ in Tea Using Aptamer Labeled with AIEgen Nanospheres Based on MOFs Sensors

Tea is an important economic crop and health beverage in China. The presence of heavy metal ions in tea poses a significant threat to public health. Here, we prepared an aptamer biosensor labelled with AIEgen nanospheres to detect Pb²⁺ in tea. The dsDNA modified by amino and phosphoric acid was combined with the carboxylated AIEgen NPs to form AIEgen-DNA with a fluorescence group, which was then fixed to the surface of Zr-MOFs to quench the fluorescence of AIEgen NPs. At the same time, PEG was added to remove nonspecific adsorption. Then Pb²⁺ was added to cut the DNA sequences containing the cutting sites, and AIEgen NPs and part of the DNA sequences were separated from the Zr-MOFs surface to recover the fluorescence. By comparing the fluorescence changes before and after adding Pb²⁺, the detection limit of Pb²⁺ can reach 1.70 nM. The fluorescence sensor was applied to detect Pb²⁺ in tea, and the detection results showed that the tea purchased on the market did not contain the concentration of Pb²⁺ within the detection range. This study provides new insights into monitoring food and agriculture-related pollutants based on fluorescent biosensors.

Hybrid 3D printed integrated microdevice for the determination of copper ions in human body fluids

On-site screening of copper ions in body fluid plays a critical role in monitoring human health, especially in heavy pollution areas. In this study, we have developed a hybrid 3D printed integrated microdevice for the determination of copper ions in human body fluids. A fixed and low volume of sample was detected by using the integrated microdevice without any preprocessing. The hybrid channel enables sample uniform mixing and quantitative dilution with buffer solution by inducing the “horseshoe vortex” phenomenon. The electrolytic microcell based on the flow detection system shows a more effective copper ion reaction ratio and, as a result, a better sensitivity. The simulation of the finite element method (FEM) determined the relevant optimum parameters of the hybrid channel and the microcell. The design, fabrication, and detection procedure of the integrated microdevice are here illustrated. The microdevice presented superior detection properties towards copper ions. The calibration curves covered two linear ranges varying from 20 to 100 ppb and 100 to 400 ppb, respectively. The limit of detection was estimated to be 15 ppb (S/N = 3). The relative standard deviation of the peak current measurements was 2.26%. The designed microdevice was further applied to detect copper ions in practical samples (calf serum sample and synthetic human urine sample) using a standard addition method, and the average recovery was found to be 95–104%. The performance of copper ion detection with the integrated microdevice was consistent with that of the inductively coupled plasma mass spectrometry (ICP-MS) in the same practical samples, demonstrating significant practicality in the test of body fluidics. The portable integrated microdevice is an excellent choice for on-site detection and has a promising prospect in the point-of-care testing (POCT) applications.

Multiplexed Anodic Stripping Voltammetry Detection of Heavy Metals in Water Using Nanocomposites Modified Screen-Printed Electrodes Integrated With a 3D-Printed Flow Cell

In this study, we present multiplexed anodic stripping voltammetry (ASV) detection of heavy metal ions (HMIs)—As(III), Cd(II), and Pb(II)—using a homemade electrochemical cell consisting of dual working, reference and counter screen-printed electrodes (SPE) on polyimide substrate integrated with a 3D-printed flow cell. Working and counter electrodes were fabricated by the screen-printing of graphite paste while the Ag/AgCl paste was screen-printed as a reference electrode (Ag/AgCl quasi-reference electrode). The working electrodes were modified with (BiO)2CO3-reduced graphene oxide (rGO)-Nafion [(BiO)2CO3-rGO-Nafion] and Fe3O4 magnetic nanoparticles (Fe3O4MNPs) decorated Au nanoparticles (AuNPs)-ionic liquid (IL) (Fe3O4-Au-IL) nanocomposites separately to enhance HMIs sensing. Electrochemical detection was achieved using square wave ASV technique. The desired structure of the flow electrochemical cell was optimized by the computational fluid dynamic (CFD). Different experimental parameters for stripping analysis of HMIs were optimized including deposition time, deposition potential and flow rate. The linear range of calibration curves with the sensing nanocomposites modified SPE for the three metal ions was from 0–50 μg/L. The limits of detection (S/N = 3) were estimated to be 2.4 μg/L for As(III), 1.2 μg/L for Pb(II) and 0.8 μg/L for Cd(II). Furthermore, the homemade flow anodic stripping sensor platform was used to detect HMIs in simulated river water with a 95–101% recovery, indicating high selectivity and accuracy and great potential for applicability even in complex matrices.

A graphene-based electrochemical flow analysis device for simultaneous determination of dopamine, 5-hydroxytryptamine, and melatonin

A graphene-based electrochemical flow analysis device for simultaneous determination of dopamine, 5-hydroxytryptamine, and melatonin.

How 3D printing can boost advances in analytical and bioanalytical chemistry

3D printing fabrication methods have received lately an enormous attention by the scientific community. Laboratories and research groups working on analytical chemistry applications, among others, have advantageously adopted 3D printing to fabricate a wide range of tools, from common laboratory hardware to fluidic systems, sample treatment platforms, sensing structures, and complete fully functional analytical devices. This technology is becoming more affordable over time and therefore preferred over the commonly used fabrication processes like hot embossing, soft lithography, injection molding and micromilling. However, to better exploit 3D printing fabrication methods, it is important to fully understand their benefits and limitations which are also directly associated to the properties of the materials used for printing. Costs, printing resolution, chemical and biological compatibility of the materials, design complexity, robustness of the printed object, and integration with commercially available systems represent important aspects to be weighted in relation to the intended task. In this review, a useful introductory summary of the most commonly used 3D printing systems and mechanisms is provided before the description of the most recent trends of the use of 3D printing for analytical and bioanalytical chemistry. Concluding remarks will be also given together with a brief discussion of possible future directions.

Electrochemical detection of heavy metal ions in water

Heavy metal ions are one of the main sources of water pollution. Most heavy metal ions are carcinogens that pose a threat to both ecological balance and human health. With the increasing demand for heavy metal detection, electrochemical detection is favorable due to its high sensitivity and efficiency. Here, after discussing the pollution sources and toxicities of Hg(ii), Cd(ii), As(iii), Pb(ii), UO₂(ii), Tl(i), Cr(vi), Ag(i), and Cu(ii), we review a variety of recent electrochemical methods for detecting heavy metal ions. Compared with traditional methods, electrochemical methods are portable, fast, and cost-effective, and they can be adapted to various on-site inspection sites. Our review shows that the electrochemical detection of heavy metal ions is a very promising strategy that has attracted widespread attention and can be applied in agriculture, life science, clinical diagnosis, and analysis.

Electrochemical flow injection analysis of the interaction between pyrroloquinoline quinone (PQQ) and α-synuclein peptides related to Parkinson's disease

α-Synuclein (α-syn) is a hallmark protein of Parkinson's disease (PD). The aggregation process of α-syn has been heavily associated with the pathogenesis of PD. With the exponentially growing number of potential therapeutic compounds that can inhibit the aggregation of α-syn, there is now a significant demand for a high-throughput analysis system. Herein, a novel flow injection analysis system with an electrochemical biosensor as the detector was developed to study the interaction of a well-described antioxidant and amyloid inhibitor, pyrroloquinoline quinone (PQQ) with α-synuclein peptides. Screen-printed gold electrodes (SPEs) were modified using heptapeptides from α-syn wild-type (WT) and mutants such as lysine knock-out (ETEE) and E46K. Affinity binding events between these peptides and PQQ were analyzed by electrochemical impedance spectroscopy (EIS) and further confirmed by high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), and nuclear magnetic resonance (NMR) spectroscopy. HPLC and LC/MS results revealed that PQQ formed a stable complex with α-syn. NMR results confirmed that the α-syn-PQQ complex was formed via a Schiff base formation-like process. In addition, results showed that lysine residues influenced the binding event, in which the presence of an extra lysine stabilized the α-syn-PQQ complex, and the absence of a lysine significantly decreased the interaction of α-syn with PQQ. Therefore, we concluded that EIS is a promising technique for the evaluation of the interaction between PQQ-based amyloid inhibitors and α-syn. The electrochemical flow injection analysis assembly provided a rapid and low-cost drug discovery platform for the evaluation of small molecule-protein interactions.

A responsive pure DNA hydrogel for label-free detection of lead ion

It is of great significance to develop facile and economical strategies for on-site detection and treatment of toxic metal ions. Stimulus-responsive DNA hydrogel materials have been increasingly used for convenient detection of metal ions due to their advantages such as simplicity, portability, and ease of storage. However, these methods still require encapsulation of signal tags by labeling or embedding. In this paper, a one-step preparation of Pb²⁺-responsive pure DNA hydrogel material was designed to realize a new label-free strategy for Pb²⁺ biosensing. The Pb²⁺-dependent DNAzyme strand and substrate strand were introduced to fabricate the DNA hydrogel. The presence of Pb²⁺ in the sample activates the enzyme strand in the hydrogel skeleton and triggers the cleavage of the substrate, thereby destroy the hydrogel structure. DNA fragments released by the collapsed hydrogel were readily measured as signal output for quantifying Pb²⁺ concentrations with a minimum detection limit of 7.7 nM. We successfully eliminated the need for embedding or labeling of signal molecules by using the DNA molecules that construct hydrogels as the signal output. And the newly developed method for label-free detection of Pb²⁺ based on pure DNA hydrogel is simple, easy readout, and cost-effective. By adjusting the DNAzyme and substrate sequences, label-free analysis of other metal ions can also be achieved. We expect that our strategy can be applied to the field detection of toxic metal ions.

Recent Advances in Nanotechnology-Based Biosensors Development for Detection of Arsenic, Lead, Mercury, and Cadmium

Heavy metals cause considerable environmental pollution due to their extent and non-degradability in the environment. Analysis and trace levels of arsenic, lead, mercury, and cadmium as the most toxic heavy metals show that they can cause various hazards in humans' health. To achieve rapid, high-sensitivity methods for analyzing ultra-trace amounts of heavy metals in different environmental and biological samples, novel biosensors have been designed with the participation of strategies applied in nanotechnology. This review attempted to investigate the novel, sensitive, efficient, cost-benefit, point of care, and user-friendly biosensors designed to detect these heavy metals based on functional mechanisms. The study's search strategies included examining the primary databases from 2015 onwards and various keywords focusing on heavy metal biosensors' performance and toxicity mechanisms. The use of aptamers and whole cells as two important bio-functional nanomaterials is remarkable in heavy metal diagnostic biosensors' bioreceptor design. The application of hybridized nanomaterials containing a specific physicochemical function in the presence of a suitable transducer can improve the sensing performance to achieve an integrated detection system. Our study showed that in addition to both labeled and label-free detection strategies, a wide range of nanoparticles and nanocomposites were used to modify the biosensor surface platform in the detection of heavy metals. The detection limit and linear dynamic range as an essential characteristic of superior biosensors for the primary toxic metals are studied. Furthermore, the perspectives and challenges facing the design of heavy metal biosensors are outlined. The development of novel biosensors and the application of nanotechnology, especially in real samples, face challenges such as the capability to simultaneously detect multiple heavy metals, the interference process in complex matrices, the efficiency and stability of nanomaterials implemented in various laboratory conditions.

Defect-enhanced electrochemical property of h-BN for Pb2+ detection

A new strategy has been developed for the determination of trace lead ions (Pb²⁺) based on hexagonal boron nitride (h-BN) laden with point defect. The defect-laden boron nitride (D-BN) was synthesized by a thermal polymerization route, in which melamine borate was used as a precursor. The defect microstructure was confirmed by photoluminescence (PL) and x-ray diffraction (XRD) techniques. As compared with h-BN, the D-BN-modified glassy carbon electrode (GCE) showed an enhanced electrochemical response towards Pb²⁺ peaking at - 0.551 V (vs. SCE), which was evidenced by linear sweep anodic stripping voltammetry (LSASV) results. The point defect plays a pivotal role in the electrocatalytic reaction process, which can mediate the electronic structure and surface properties of h-BN. Accordingly, the sensor presented a low detection limit of 0.15 μg/L towards Pb²⁺ and a wide linear response concentration range from 0.5 to 400 μg/L (correlation coefficient = 0.995). In view of its superior selectivity, stability, and reproducibility, the proposed method was applied for Pb²⁺ determination in real samples and exhibited satisfactory results. This work provides insight for the construction of electrochemical sensor with high-performance by engineering defects of modifying materials. Defect-loaden h-BN exhibited enhanced electrocatalytic redox reaction towards lead ions and thus a novel Pb²⁺ sensor with high performances was constructed.

A label-free lead(II) ion sensor based on surface plasmon resonance and DNAzyme-gold nanoparticle conjugates

Detection of lead(II) (Pb²⁺) ions in water is important for the protection of human health and environment. The growing demand for onsite detection still faces challenges for sensitive and easy-to-use methods. In this work, a novel surface plasmon resonance (SPR) biosensor based on GR-5 DNAzyme and gold nanoparticles (AuNPs) was developed. Thiolated DNAzyme was immobilized on the gold surface of the sensor chip followed by anchoring the substrate-functionalized AuNPs through the DNAzyme-substrate hybridization. The coupling between the localized surface plasmon (LSP) of AuNPs and the surface plasmon polaritons (SPP) on the gold sensor surface was used to improve the sensitivity. The substrate cleavage in the presence of Pb²⁺ ions was catalyzed by DNAzyme, leading to the removal of AuNPs and the diminished LSP-SPP coupling. The optimal detection limit was 80 pM for the sensor fabricated with 1 μM DNAzyme, corresponding to two or three orders of magnitude lower than the toxicity levels of Pb²⁺ in drinking water defined by WHO and USEPA. By tuning the surface coverage of DNAzyme, the sensitivity and dynamic range could be controlled. This sensor also featured high selectivity to Pb²⁺ ions and simple detection procedure. Successful detection of Pb²⁺ ions in groundwater indicates that this method has the prospect in the onsite detection of Pb²⁺ ions in water. Given the variety of AuNPs and metal-specific DNAzymes, this detection strategy would lead to the development of more sensitive and versatile heavy metal sensors. Graphical abstract.

3D Printed Microfluidics

Traditional microfabrication techniques suffer from several disadvantages, including the inability to create truly three-dimensional (3D) architectures, expensive and time-consuming processes when changing device designs, and difficulty in transitioning from prototyping fabrication to bulk manufacturing. 3D printing is an emerging technique that could overcome these disadvantages. While most 3D printed fluidic devices and features to date have been on the millifluidic size scale, some truly microfluidic devices have been shown. Currently, stereolithography is the most promising approach for routine creation of microfluidic structures, but several approaches under development also have potential. Microfluidic 3D printing is still in an early stage, similar to where polydimethylsiloxane was two decades ago. With additional work to advance printer hardware and software control, expand and improve resin and printing material selections, and realize additional applications for 3D printed devices, we foresee 3D printing becoming the dominant microfluidic fabrication method.

Electrochemical lead(II) biosensor by using an ion-dependent split DNAzyme and a template-free DNA extension reaction for signal amplification

A voltammetric biosensor for lead(II) (Pb²⁺) is described that is based on signal amplification by using an ion-dependent split DNAzyme and template-free DNA extension reaction. The Pb²⁺-dependent split DNAzyme was assembled on gold nanoparticles (Au@Fe₃O₄), and this nanoprobe then was exposed to Pb²⁺ which causes the split-off of DNAzymes to release primers containing 3'-OH groups (S₁ and S₂). The template-free DNA extension reaction triggers the generation of long ssDNA nanotails, which then can bind the free redox probe N,N'-bis(2-(trimethylammonium iodide)propylene)perylene-3,4,9,10-tetracarboxyldiimide (PDA⁺) via electrostatic adsorption. Hence, the concentration of PDA⁺ in solution is reduced. Therefore, less free PDA⁺ can be immobilized on a glassy carbon electrode modified with electrodeposited gold nanoparticles (depAu) to produce an electrochemical signal, typically measured at ∼0.38 V (vs. SCE) for quantitation of Pb²⁺. The use of a Pb²⁺-dependent split DNAzyme avoids the usage of a proteinic enzyme. It also increases the sensitivity of the sensor which has a lower detection limit of 30 pM of Pb²⁺. Graphical abstract Novel electrochemical biosensor based on the amplification of ion-dependent split DNAzyme and template-free DNA extension reaction for trace detection of Pb²⁺.

Fluorescence covalent interaction enhanced sensor for lead ion based on novel graphitic carbon nitride nanocones

Novel graphitic carbon nitride nanocones (g-CNNCs) were synthesized for the first time in this study. The SEM, TEM, XPS and FT-IR were used to research the structure of the g-CNNCs. We found that the g-CNNCs showed high selective and sensitive for fluorescence enhancement detection of Pb²⁺ ion via covalent interaction. In addition, the g-CNNCs exhibit stable and specific concentration-dependent fluorescence intensity in the presence of Pb²⁺ ion in the range of 1-200 μmol·dm^-3, and the limit of detection was estimated to be 0.0438 μmol·dm^-3 (3S/k). More importantly, the g-CNNCs were used to detect practical samples with satisfactory results.

Epitaxial Graphene Sensors Combined with 3D-Printed Microfluidic Chip for Heavy Metals Detection

In this work, we investigated the sensing performance of epitaxial graphene on Si-face 4H-SiC (EG/SiC) for liquid-phase detection of heavy metals (e.g., Pb and Cd), showing fast and stable response and low detection limit. The sensing platform proposed includes 3D-printed microfluidic devices, which incorporate all features required to connect and execute lab-on-chip (LOC) functions. The obtained results indicate that EG exhibits excellent sensing activity towards Pb and Cd ions. Several concentrations of Pb²⁺ solutions, ranging from 125 nM to 500 µM, were analyzed showing Langmuir correlation between signal and Pb²⁺ concentrations, good stability, and reproducibility over time. Upon the simultaneous presence of both metals, sensor response is dominated by Pb²⁺ rather than Cd²⁺ ions. To explain the sensing mechanisms and difference in adsorption behavior of Pb²⁺ and Cd²⁺ ions on EG in water-based solutions, we performed van-der-Waals (vdW)-corrected density functional theory (DFT) calculations and non-covalent interaction (NCI) analysis, extended charge decomposition analysis (ECDA), and topological analysis. We demonstrated that Pb²⁺ and Cd²⁺ ions act as electron-acceptors, enhancing hole conductivity of EG, due to charge transfer from graphene to metal ions, and Pb²⁺ ions have preferential ability to binding with graphene over cadmium. Electrochemical measurements confirmed the conductometric results, which additionally indicate that EG is more sensitive to lead than to cadmium.

Addressing the practicalities of anodic stripping voltammetry for heavy metal detection: a tutorial review

We highlight the fundamentals and challenges involved with anodic stripping voltammetry (ASV) using solid electrodes providing a practical guide to anyone wishing to undertake analytical ASV.

Label-free and highly sensitive fluorescence detection of lead(ii) based on DNAzyme and exonuclease III-assisted cascade signal amplification

A Pb²⁺ biosensor has been constructed based on Exo III-assisted cascade signal amplification using 2-amino-5,6,7-trimethyl-1,8-naphthyridine as the signal indicator.

The preparation of a flexible AuNP modified carbon cloth electrode and its application in electrochemical detection of Hg(ii) by continuous flow in environmental water

In this article, a carbon cloth composite electrode modified with gold nanoparticles (AuNPs) was prepared by a facile in situ electrodeposition method and applied to the detection of mercury ions in water. With the optimized electrochemical detection conditions and methods, the limit of detection (LOD) was 0.6 μg L^-1 with the linearity ranging from 2 to 200 μg L^-1 by the SWSV detection method, and the electrode showed good repeatability after many cycles. Based on this detection method, a continuous flow electrochemical detection system was constructed and applied to the detection of Hg ions in environmental water samples. The standard addition experimental results of two real water samples with an addition level of 10 and 50 μg L^-1 showed that the recoveries were between 92.4% and 108.9% with RSDs from 2.01% to 3.22%. These results showed the same performance as that of the ZAAS mercury detection method (recovery: 94-102.4%, RSD 2.09-5.4%). Compared with other electrode materials, a shorter detection time, a wider linear range and high stability with a similar LOD can be achieved by a continuous flow detection method by using the composite electrode. The established continuous flow electrochemical detection system would have promising application in online and real-time detection of heavy metals in environmental water.

3D-printed miniaturized fluidic tools in chemistry and biology

3D printing (3DP), an additive manufacturing (AM) approach allowing for rapid prototyping and decentralized fabrication on-demand, has become a common method for creating parts or whole devices. The wide scope of the AM extends from organized sectors of construction, ornament, medical, and R&D industries to individual explorers attributed to the low cost, high quality printers along with revolutionary tools and polymers. While progress is being made but big manufacturing challenges are still there. Considering the quickly shifting narrative towards miniaturized analytical systems (MAS) we focus on the development/rapid prototyping and manufacturing of MAS with 3DP, and application dependent challenges in engineering designs and choice of the polymeric materials and provide an exhaustive background to the applications of 3DP in biology and chemistry. This will allow readers to perceive the most important features of AM in creating (i) various individual and modular components, and (ii) complete integrated tools.

A nickel nanoparticle/nafion-graphene oxide modified screen-printed electrode for amperometric determination of chemical oxygen demand

A nickel nanoparticle/nafion-graphene oxide (NiNP/Nf-GO) modified screen-printed electrode (SPE) was developed for rapid and environmentally friendly electrochemical determination of chemical oxygen demand (COD). The morphology and the electrochemical performance of the SPEs with different surface modifications were investigated by scanning electron microscopy, electrochemical impedance spectroscopy, amperometry, and cyclic voltammetry, respectively. Interestingly, incorporation of graphene oxide as supporting materials to the NiNP/Nf-GO modified SPE enables high catalyst loading and electrode contact, leading to excellent electrocatalytic oxidation ability. A flow detection system was constructed based the newly designed NiNP/Nf-GO modified SPE with USB connection, a 3D-printed thin-layer flow cell (TLFC), and a peristaltic pump. The flow detection system showed an excellent performance for COD analysis with a linear detection range of 0.1~400 mg L^-1 and a lower detection limit of 0.05 mg L^-1 with an oxidation potential of 0.45 V. The system was further applied to determine the COD in surface water samples. The results were consistent with those obtained by using the standard method (ISO 6060). Graphical abstract A novel nickel nanoparticle/nafion-graphene oxide (NiNP/Nf-GO) modified screen-printed electrode (SPE) with excellent electrocatalytic oxidation ability was designed and fabricated. This electrode with USB connection was applied in a flow detection system equipped with a 3D-printed thin-layer flow cell and a peristaltic pump for environmentally friendly electrochemical determination of chemical oxygen demand.

A novel 4-phenyl amino thiourea derivative designed for real-time ratiometric-colorimetric detection of toxic Pb2

The objective of this study was to develop a ratiometric and colorimetric organic sensor for Pb²⁺ detection in environmental samples. A new probe 4-phenyl amino thiourea (PAT) was designed and synthesized using hydrazine hydrate and phenyl isothiocyanate as raw materials. After its structure was characterized and confirmed, its UV-vis spectral property was investigated in detail. PAT possesses a specifically real-time, ratiometric and colorimetric response to Pb²⁺ in dimethyl formamide (DMF)/H₂O (v/v = 9:1, pH = 7.0) within 18.0 s. There was little interference in the presence of some other common metal ions, such as Fe³⁺, Cd²⁺, Zn²⁺, Mg²⁺, Cr³⁺, Ca²⁺, Ba²⁺, Sn²⁺, Na⁺, Mn²⁺, Hg²⁺, and Pb²⁺. Under the optimized conditions (DMF/H₂O with v/v of 9:1, c_PAT = 1.0 × 10^-3 mol·L^-1, pH = 7.0), the present sensor PAT was successfully applied for Pb²⁺ determination in environmental water samples with satisfied recoveries (83.0%-106.0%) and analytical precision (≤7.2%). The recognition mechanism was confirmed to form a stable 1:1 six-member ring complex between the target dye and Pb²⁺ with a coordination constant of 4.96 × 10⁴.

Screen-Printed Electrodes Modified with "Green" Metals for Electrochemical Stripping Analysis of Toxic Elements

This work reviews the field of screen-printed electrodes (SPEs) modified with “green” metals for electrochemical stripping analysis of toxic elements. Electrochemical stripping analysis has been established as a useful trace analysis technique offering many advantages compared to competing optical techniques. Although mercury has been the preferred electrode material for stripping analysis, the toxicity of mercury and the associated legal requirements in its use and disposal have prompted research towards the development of “green” metals as alternative electrode materials. When combined with the screen-printing technology, such environment-friendly metals can lead to disposable sensors for trace metal analysis with excellent operational characteristics. This review focuses on SPEs modified with Au, Bi, Sb, and Sn for stripping analysis of toxic elements. Different modification approaches (electroplating, bulk modification, use of metal precursors, microengineering techniques) are considered and representative applications are described. A developing related field, namely biosensing based on stripping analysis of metallic nanoprobe labels, is also briefly mentioned.

A single-electrode electrochemical system for multiplex electrochemiluminescence analysis based on a resistance induced potential difference

A single-electrode electrochemical system uses only one electrode for multiplex experiments, and is a highly cheap platform for high throughput analysis.

Developing low-cost and simple electrochemical systems is becoming increasingly important but still challenged for multiplex experiments. Here we report a single-electrode electrochemical system (SEES) using only one electrode not only for a single experiment but also for multiplex experiments based on a resistance induced potential difference. SEESs for a single experiment and multiplex experiments are fabricated by attaching a self-adhesive label with a hole and multiple holes onto an ITO electrode, respectively. This enables multiplex electrochemiluminescence analysis with high sensitivity at a very low safe voltage using a smartphone as a detector. For the multiplex analysis, the SEES using a single electrode is much simpler, cheaper and more user-friendly than conventional electrochemical systems and bipolar electrochemical systems using electrode arrays. Moreover, SEESs are free from the electrochemiluminescent background problem from driving electrodes in bipolar electrochemical systems. Since numerous electrodes and cover materials can be used to fabricate SEESs readily and electrochemistry is being extensively used, SEESs are very promising for broad applications, such as drug screening and high throughput analysis.

Colorimetric and Electrochemiluminescence Dual-Mode Sensing of Lead Ion Based on Integrated Lab-on-Paper Device

A highly selective two-point separation strategy was designed based on a cross-like all-in-one lab-on-paper analytical device. The stable and cleavable enzyme-coated reduced graphene oxide (rGO)-PdAu probe was fabricated as the signal reporter to enable the visualization and electrochemiluminescence (ECL) dual-mode sensing of Pb²⁺. Concretely, the experimental workflow consists of the following process: (i) fabrication of the lab-on-paper device and growth of Au nanoparticles on ECL detection zone, (ii) immobilization of Pb²⁺-specific DNAzyme, and (iii) hybridization between DNAzyme and rGO-PdAu-glucose oxidase (GOx) labeled oligonucleotide to form the double-stranded DNA. Upon addition of Pb²⁺ into the prepared system, the double-helix structure of the DNA was destroyed, resulting in the release of cleaved rGO-PdAu-GOx probe to visualization bar to promote the effective oxidation and color change of 3,3',5,5'-tetramethylbenzidine. As a consequence, the color change can be recognized by naked eye, meanwhile GOx on an uncleaved signal probe can oxidize glucose along with the H₂O₂ production. As a co-reaction reagent for luminol ECL system, the concentration of H₂O₂ is proportional to the ECL intensity, which constitutes a new mechanism for colorimetric and ECL dual mode to detect Pb²⁺. With the method developed here, the concentration of Pb²⁺ could be easily determined by the naked eye within a linear range from 5 to 2000 nM, as well as by monitoring the decreased ECL intensity of luminol in a linear range of 0.5-2000 nM. This work not only constructs a simple and versatile platform for on-site visible monitoring of Pb²⁺ in tap water and river water but also furnishes a strategy for designing a dual-mode sensing toward different heavy metal ions based on specific DNAzyme in the fields of environmental monitoring-related technologies.