Dandelion-like CuO microspheres decorated with Au nanoparticle modified biosensor for Hg2+ detection using a T-Hg2+-T triggered hybridization chain reaction amplification strategy

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au-S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

Critical review on toxic contaminants in surface water ecosystem: sources, monitoring, and its impact on human health

Surface water pollution is a critical and urgent global issue that demands immediate attention. Surface water plays a crucial role in supporting and sustaining life on the earth, but unfortunately, till now, we have less understanding of its spatial and temporal dynamics of discharge and storage variations at a global level. The contamination of surface water arises from various sources, classified into point and non-point sources. Point sources are specific, identifiable origins of pollution that release pollutants directly into water bodies through pipes or channels, allowing for easier identification and management, e.g., industrial discharges, sewage treatment plants, and landfills. However, non-point sources originate from widespread activities across expansive areas and present challenges due to its diffuse nature and multiple pathways of contamination, e.g., agricultural runoff, urban storm water runoff, and atmospheric deposition. Excessive accumulation of heavy metals, persistent organic pollutants, pesticides, chlorination by-products, pharmaceutical products in surface water through different pathways threatens food quality and safety. As a result, there is an urgent need for developing and designing new tools for identifying and quantifying various environmental contaminants. In this context, chemical and biological sensors emerge as fascinating devices well-suited for various environmental applications. Numerous chemical and biological sensors, encompassing electrochemical, magnetic, microfluidic, and biosensors, have recently been invented by hydrological scientists for the detection of water pollutants. Furthermore, surface water contaminants are monitored through different sensors, proving their harmful effects on human health.

Unique three-dimensional ordered macroporous dealloyed gold-silver electrochemical sensing platforms for ultrasensitive mercury(II) monitoring

To address the requirement of ultra-sensitive detection of trace mercury(II) (Hg2+) ions in the environment and food, we developed an electrochemical biosensor with super-sensitivity, extremely high selectivity, and reusability. This biosensor comprised two signal amplification components: a three-dimensional macroporous dealloyed (3DOMD) Au-Ag thin-film electrode and a multifunctional encoded Au@Pt nanocage (APNC). As a platform for immobilized capture DNA (cDNA), a 3DOMD Au-Ag thin film prepared by a dealloying method with an active surface area 4.8 times higher than that of 3D macroporous gold films generated by cyclic voltammetry (CV) with sulfuric acid was capable of increasing the sensing surface area while also strengthening the electron transport capacity of the sensing substrate due to its multilayered multi-porous framework. In the presence of Hg2+, probe DNA (pDNA) could be hybridized with the mismatched capture DNA (cDNA) through stable thymine-Hg2+-thymine (T-Hg2+-T) linkages, connecting thionine-APNC to the electrode surface and utilizing the large specific surface area to accomplish highly sensitive detection of Hg2+. With an extremely low Hg2+ detection limit of 2 pM and a detection range from 0.01 to 1000 nM, this technique opened up a new avenue for the ultrasensitive detection of a wider range of heavy metal ions or biomolecules.

Highly sensitive surface acoustic wave biosensor for the detection of Hg2+ based on the thymine-Hg2+-thymine structure

The detection of mercury ions (Hg2+) with an ultralow concentration is of great significance for the treatment of heavy metal pollution in industrial waste water and the monitoring of drinking water quality. In this study, a simple, sensitive, and portable surface acoustic wave (SAW) biosensor for the determination of Hg2+ concentration was developed. First, a DNA fragment with a specific binding capacity for Hg2+ was chemically adsorbed on to the sensitive region through forming Au-S bonds with the SAW biosensor. The DNA probe could then form a thymine-Hg2+-thymine (T-Hg2+-T) complex with strong affinity for Hg2+ after immersion in a test solution containing Hg2+, resulting in a significant change in the response frequency of the device. The linear detection range of the device was 10 pM to 1 nM, while the limit of detection (LOD) was as low as 6.3 pM. Furthermore, the SAW biosensor exhibited excellent selectivity to Hg2+ compared with that of interfering ions, e.g., Ag+, Ba2+, Cu2+, Zn2+, Mn2+, Fe3+, Ca2+, and Na+. The results provide a new strategy for the preparation of portable devices that can monitor toxic heavy metal ions with high sensitivity and selectivity.

Dynamic DNA Nanostructures for Cell Manipulation

Dynamic DNA nanostructures are DNA nanostructures with reconfigurable elements that can undergo structural transformations in response to specific stimuli. Thus, anchoring dynamic DNA nanostructures on cell membranes is an attractive and promising strategy for well-controlled cell manipulation. Here, we review the latest progress in dynamic DNA nanostructures for cell manipulation. Commonly used mechanisms for dynamic DNA nanostructures are first introduced. Subsequently, we summarize the anchoring strategies for dynamic DNA nanostructures on cell membranes and list possible applications (including programming cell membrane receptors, controlling ligand activity and drug delivery, capturing and releasing cells, and assembling cells into clusters). Finally, insights into the remaining challenges are presented.

A highly parallel DTT/MB-DNA/Au electrochemical biosensor for trace Hg monitoring by using configuration occupation approach and SECM

Environmental pollution and medicine safety have aroused increasing public concerns due to human health. Amongst various contaminants, mercury is of special attention owing to their environmental persistence and biogeochemical recycling and ecological risks. Herein, a simple and highly parallel electrochemical biosensor for Hg determination was designed and investigated. The proposed biosensor was prepared and compared between (1) DTT/MB-DNA/Au with configuration occupation approach and (2) MCH/MB-DNA/Au with passivation approach. According to the combined results of scanning electrochemical microscope (SECM) and Randles-Sevcik equation, the DTT modified electrode exhibited high uniformity on DNA distribution and superb stability on electron transfer in Hg2+ detection. Evidentially, the response value of proposed DTT/MB-DNA/Au was increased from 57.518% to 97.607%, while RSD% between duplicate runs had dropped from 22.658% to 0.223% (n = 3). Moreover, the increased proportion of effective working area was 467.380% compared with general sensors. Besides, DTT concentration, DNA concentration as well as assembly time were optimized, utilizing electrochemical impedance spectroscopy (EIS), Cyclic Voltammetry (CV) and Square Wave Anode Stripping Voltammetry (SWASV). This optimized biosensor exhibited an excellent selectivity toward Hg2+ over Cu2+, As2+, Cd2+, Pb2+, Cr3+, Ni2+ and Zn2+ etc., and the stability of DTT/MB-DNA/Au were at least two times better even after 3 days under room temperature. Also, a linear relation was observed between the peak current and Hg2+concentrations in a range from 0.25 nM to 2.00 μM with a detection limit of 53.00 pM under optimal conditions. Finally, DTT/MB-DNA/Au was applied for plants and medical products analysis. In all, this optimized DTT/MB-DNA/Au with advantages of high repeatability and sensitivity would provide a new insight into the design and application of biosensor for reliable sensing in safeguarding plant protection and medicinal safety.

Core-shell microparticles: From rational engineering to diverse applications

Core-shell microparticles, composed of solid, liquid, or gas bubbles surrounded by a protective shell, are gaining considerable attention as intelligent and versatile carriers that show great potential in biomedical fields. In this review, an overview is given of recent developments in design and applications of biodegradable core-shell systems. Several emerging methodologies including self-assembly, gas-shearing, and coaxial electrospray are discussed and microfluidics technology is emphasized in detail. Furthermore, the characteristics of core-shell microparticles in artificial cells, drug release and cell culture applications are discussed and the superiority of these advanced multi-core microparticles for the generation of artificial cells is highlighted. Finally, the respective developing orientations and limitations inherent to these systems are addressed. It is hoped that this review can inspire researchers to propel the development of this field with new ideas.

Ultrasensitive Electrochemical Detection of cancer-Related Point Mutations Based on Surface-Initiated Three-Dimensionally Self-Assembled DNA Nanostructures from Only Two Palindromic Probes

Sensitive and selective detection of proto-oncogenes, especially recognition of point mutation, is of great importance in cancer diagnosis. Here, a ligation-mediated technique is demonstrated for the construction of an intertwined three-dimensional DNA nanosheet (3D SDN) on an electrode surface from only two palindromic hairpin probes (HP1 and HP2), creating a powerful electrochemical biosensor (E-biosensor) for the detection of the p53 gene. First, a capturing probe (CP) is immobilized on an electrode surface via Au-S chemistry, forming an electrochemical sensing interface. In the presence of the target p53 (T), the triggering probe is covalently linked to CP by a ligase. Moreover, target hybridization/ligation/dehybridization process is repeated, amplifying the target hybridization event and increasing the content of surface-confined triggering fragments. As a result, HP1 is opened and in turn interacts with HP2, forming intertwined 3D SDN where HP1 and HP2 are alternately arranged in parallel. Common hybridization and interaction between palindromic fragments are responsible for the assembly in the horizontal and vertical directions, respectively. An electrochemical indicator, methylene blue (MB), can be inserted into 3D SDN, generating a strong electrochemical signal. Utilizing the 3D SDN-based E-biosensor, the target DNA is detected down to 3 fM with a linear response range from 10 fM to 10 nM. Single point mutations are reliably identified even in fetal bovine serum and cellular homogenate. Because of the several advantages of simple design, good universality, inexpensive instrumentation, high assay specificity, and sensitivity, the 3D SDN-based E-biosensor is expected to provide a potential platform for screening point mutation required by early clinical diagnostics and medical research.

Label-free Hg(II) electrochemiluminescence sensor based on silica nanoparticles doped with a self-enhanced Ru(bpy)32+-carbon nitride quantum dot luminophore

Herein, a label-free, self-enhanced electrochemiluminescence (ECL) sensing strategy for divalent mercury (Hg(II)) detection was presented. First, a novel self-enhanced ECL luminophore was prepared by combining the ECL reagent tris(2, 2'-bipyridyl) dichlororuthenium(II) hexahydrate (Ru(bpy)₃²⁺) and its co-reactant carbon nitride quantum dots (CNQDs) via electrostatic interactions. In contrast to traditional ECL systems where the emitter and its co-reactant underwent an intermolecular reaction, the self-enhanced ECL system exhibited a shortened electron-transfer distance and enhanced luminous efficiency because the electrons transferred from CNQDs to oxidized Ru(bpy)₃²⁺ via an intramolecular pathway. Furthermore, the as-prepared self-enhanced ECL material was encapsulated in silica (SiO₂) nanoparticles to generate a Ru-QDs@SiO₂ luminophore. Based on the different affinity of Ru-QDs@SiO₂ nanoparticles for single-stranded DNA (ssDNA) and Hg(II)-triggered double-stranded DNA (dsDNA), a label-free ECL biosensor for Hg(II) detection was developed as follows: in the absence of Hg(II), ssDNA was adsorbed on Ru-QDs@SiO₂ surface via hydrogen bond, electrostatic, and hydrophobic interaction. Thus, quenched ECL signal was observed. On the contrary, in the presence of Hg(II), stable dsDNA was formed and carried the ssDNA separating from Ru-QDs@SiO₂ surface, resulting in most of Ru-QDs@SiO₂ existing in their free state. Therefore, a recovered ECL intensity was obtained. On this basis, Hg(II) was measured by the proposed method in the range of 0.1 nM-10 μM, with a detection limit of 33 pM. Finally, Hg(II) spiked in water samples was measured to evaluate the practicality of the fabricated biosensor.

Recent Progress in DNA Hybridization Chain Reaction Strategies for Amplified Biosensing

With the continuous development of DNA nanotechnology, various spatial DNA structures and assembly techniques emerge. Hybridization chain reaction (HCR) is a typical example with exciting features and bright prospects in biosensing, which has been intensively investigated in the past decade. In this Spotlight on Applications, we summarize the assembly principles of conventional HCR and some novel forms of linear/nonlinear HCR. With advantages like great assembly kinetics, facile operation, and an enzyme-free and isothermal reaction, these strategies can be integrated with most mainstream reporters (e.g., fluorescence, electrochemistry, and colorimetry) for the ultrasensitive detection of abundant targets. Particularly, we select several representative studies to better illustrate the novel ideas and performances of HCR strategies. Theoretical and practical utilities are confirmed for a range of biosensing applications. In the end, a deep discussion is provided about the challenges and future tasks of this field.

Visual assay of Escherichia coli O157:H7 based on an isothermal strand displacement and hybrid chain reaction amplification strategy

Here, we describe a simple, sensitive, and enzyme-free method for visual point-of-care detection of 16S rRNA of Escherichia coli O157:H7 based on an isothermal strand displacement-hybrid chain reaction (ISD-HCR) and lateral flow strip (LFS). In this study, the secondary structure of 16S rRNA of E. coli O157:H7 was unwound by two helper oligonucleotides to expose the single-strand-specific nucleic acid sequence. The free specific sequence promoted the toehold-mediated strand displacement reaction to output a large number of FITC-labeled single-stranded DNA probes (capture probe [CP]). The 3'-end sequence of the reporter probe propagated a chain reaction of hybridization events between the two hairpin probes modified with biotin to form long nicked DNA polymers with multiple biotins (RP-HCR complexes); the free CP and RP-HCR complexes then form CP/RP-HCR complexes. The biotin-labeled double-stranded DNA CP/RP-HCR polymers then introduced numerous streptavidin (SA)-labeled gold nanoparticles (AuNPs) on the LFS. The accumulation of AuNPs produced a characteristic red band, which enabled visual detection of changes in the signal of 16S rRNA of E. coli O157:H7. The current approach could detect E. coli O157:H7 at concentrations as low as 10² CFU mL^-1 without instrumentation. This approach thus provides a simple, sensitive, and low-cost tool for point-of-care detection of pathogenic bacteria, especially in resource-limited countries.

Bioinspired dandelion-like silica nanoparticles modified with L-glutathione for highly efficient enrichment of N-glycopeptides in biological samples

The pretreatment of complicated biological samples to eliminate the interference of nonglycopeptides and improve the efficiency of glycopeptides detection is crucial in glycoproteomics research. Hydrophilic interaction chromatography (HILIC) has been adopted for enrichment of glycosylated peptides following identification with mass spectrometry, but it is still urgent to develop novel hydrophilic materials to save cost and improve enrichment efficiency. Scientists are pursuing to fabricate freestanding intelligent artificial materials. One promising approach is to use biomimic material. In our case, "one-pot" strategy was developed to prepare bioinspired nano-core-shell silica microspheres (CSSMs), employing tetrapropylorthosilicate as the silicon source and phenolic resin as the soft template. The pore structure of the obtained microspheres diverged from the center to the outside with diameter ranged from 150 to 340 nm, and shell layer ranged from 25 to 83 nm by adjusting the preparation parameters. Some of them showed dandelion-like morphology. After hydrophilic modification, these CSSMs exhibited great hydrophilicity and could be used as sorbents for enriching N-glycopeptides from complicated biological samples in HILIC. Up to 594 unique N-glycopeptides and 367 N-glycosylation sites from 182 N-glycoproteins were unambiguously identified from 2 μL of human serum, which was superior to the enrichment performance of many HILIC materials in reported papers, demonstrating great potential advantages in proteomic application.

Immobilization of hemoglobin on MnCO3 sphere-loaded Au nanoparticles as highly efficient sensing platform towards hydrogen peroxide

In this paper, we report the synthesis of MnCO₃-Au hybrid microspheres and their application on the electrochemical biosensing of hydrogen peroxide (H₂O₂) based on the immobilization of hemoglobin (Hb). The characterization of MnCO₃-Au microspheres revealed that an abundance of Au nanoparticles (AuNPs) has been absorbed on the surface of the spherical MnCO₃ by the electrostatic assembly. The combined unique properties of MnCO₃-Au microspheres are beneficial for the realization of the direct electron transfer of Hb. Hb immobilized on the microspheres maintained its biological activity, showing a surface-controlled process with the heterogeneous electron transfer rate constant (k _s) of 2.63 s^-1. The fabricated biosensor displayed an excellent performance for the electrocatalytic reduction of H₂O₂. The linear range for the determination of H₂O₂ was from 0.06-40.0 μM with a detection limit of 0.015 µM (S/N = 3). The biosensor also exhibited high selectivity, good repeatability and long-term stability, which offers great potential for H₂O₂ detection in real sample analysis.

Sensing of mercury ions in Porphyra by Copper @ Gold nanoclusters based ratiometric fluorescent aptasensor

A novel aptamer-modified Copper @ Gold nanoclusters (apt-Cu@Au NCs) based ratiometric fluorescent probe was developed for mercury ions (Hg²⁺) determination in Porphyra. The apt-Cu@Au NCs were well dispersed in solution without Hg²⁺ but combined together for the formation of thymidine-Hg-thymidine structure with the addition of Hg²⁺, which further caused the changes in their fluorescence intensities owing to fluorescence resonance energy transfer. Along with that, the changes in fluorescent colors are visible to the naked eye. Accordingly, Hg²⁺ were determined ranging from 0.1 to 9.0 μM by fluorescence analysis with the detection limit of 4.92 nM. Moreover, a homemade device utilizing smartphone and microfluidic chip was designed for colorimetric determination of Hg²⁺ ranging from 0.5 to 7.0 μM with good portability and usefulness. The proposed methods were used for Hg²⁺ detection in Porphyra with the recoveries of 101.83-114.00%, suggesting the considerable potential for evaluating Hg²⁺ levels in aquatic products.

The Recent Development of Hybridization Chain Reaction Strategies in Biosensors

With the continuous development of biosensors, researchers have focused increasing attention on various signal amplification strategies to pursue superior performance for more applications. In comparison with other signal amplification strategies, hybridization chain reaction (HCR) as a powerful signal amplification technique shows its certain charm owing to nonenzymatic and isothermal features. Recently, on the basis of conventional HCR, this technique has been developed and improved rapidly, and a variety of HCR-based biosensors with excellent performance have been reported. Herein, we present a systematic and critical review on the research progress of HCR in biosensors in the last five years, including the newly developed HCR strategies such as multibranched HCR, migration HCR, localized HCR, in situ HCR, netlike HCR, and so on, as well as the combination strategies of HCR with isothermal signal amplification techniques, nanomaterials, and functional DNA molecules. By illustrating some representative works, we also summarize the advantage and challenge of HCR in biosensors, and offer a deep discussion of the latest progress and future development trends of HCR in biosensors.

An electrochemical Hg2+ sensor based on signal amplification strategy of target recycling

In this work, an unmodified homogeneous electrochemical sensor based on electrochemical bonding and catalytic hairpin assembly (CHA) was first constructed for the high sensitivity detection of Hg²⁺. Herein, tetraferrocene, a synthesized compound, was used as a signal marker that modified both ends of the hairpin probe to amplify the electrochemical signal. The interaction of T-Hg²⁺-T could induce the catalytic self-assembly of hairpins by means of auxiliary DNA. The rigid DNA triangle that was formed easily reaches the electrode and induced Au-S self-assembly assisted by potential, allowing tetraferrocene to reach the electrode surface and generate a sensitive electrochemical signal. CHA and tetraferrocene signal markers accomplished dual signal amplification, and the limit of detection was 0.12 pM. Differential pulse voltammetry experiments in the presence of tetraferrocene redox indicator show that the linear response range of electrochemical biosensors to mercury ions is 0.2-2000 pM, This technology offers good selectivity and high recognition efficiency for the detection of mercury ions and has broad application prospects in actual sample detection.

Silver nanoclusters-based fluorescent biosensing strategy for determination of mucin 1: Combination of exonuclease I-assisted target recycling and graphene oxide-assisted hybridization chain reaction

A novel label-free fluorescent biosensing strategy was described for the sensitive detection of mucin 1 (MUC1). It consisted of an M-shaped aptamer probe for exonuclease I (Exo I)-assisted target recycling (EATR) amplification, and two AgNCs-hairpin probes for graphene oxide (GO)-assisted hybridization chain reaction (HCR) amplification. Based on the specificity of aptamer-target recognition, the addition of MUC1 caused a conformational change in the M-shaped aptamer probe, which was split into a MUC1-P3 complex and a P1-P2 duplex. Exo I then catalyzed the cleavage of aptamer sequence P3 from the MUC1-P3 complex and released the target MUC1. The released target MUC1 was free to bind with a new M-shaped probe to perform EATR amplification. Furthermore, the P1-P2 duplex with three single-stranded arms can act as a primer to initiate HCR between hairpin probes AgNCs-H1 and AgNCs-H2. In the process of HCR, two AgNCs-hairpins were autonomously cross-opened, generating long linear double-stranded nanowires containing large numbers of AgNCs. These nanowires cannot be quenched by GO due to the weak affinity between the long double-stranded DNA and GO, thereby retaining a strong fluorescent signal indicative of the concentration of MUC1. With these designs, in addition to an extremely low detection limit of 0.36 fg mL^-1, the method exhibited an acceptable linear response to detect MUC1 from 1 fg mL^-1 to 1 ng mL^-1. Additionally, this method could be exerted with a high degree of success to detect MUC1 in diluted human serum with satisfactory results.

Sequential Ag+/biothiol and synchronous Ag+/Hg2+ biosensing with zwitterionic Cu2+-based metal-organic frameworks

Zwitterionic metal-organic frameworks (MOFs) of {[Cu(Cbdcp)(Dps)(H₂O)₃]·6H₂O}_n (MOF 1) and [Cu₄(Dcbb)₄(Dps)₂(H₂O)₂]_n (MOF 2) (H₃CbdcpBr = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide; H₂DcbbBr = 1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide; Dps = 4,4'-dipyridyl sulfide) quench the fluorescence of cytosine-rich DNA tagged with 5-carboxytetramethylrhodamine (TAMRA, emission at 582 nm, denoted as C-rich P-DNA-1) and yield the corresponding P-DNA-1@MOF hybrids. Exposure of these hybrids to Ag⁺ results in the release of the P-DNA-1 strands from the MOF surfaces as double-stranded, hairpin-like C-Ag^I-C (ds-DNA-1@Ag⁺) with the restoration of TAMRA fluorescence. The ds-DNA-1@Ag⁺ formed on the surface of 1 can subsequently sense biothiols cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) due to the stronger affinity of mercapto groups for Ag⁺ that serves to unfold the ds-DNA-1@Ag⁺ duplex, reforming P-DNA-1, which is re-adsorbed by MOF 1 accompanied by quenching of TAMRA emission. Meanwhile, MOF 2 is also capable of co-loading a thymine-rich probe DNA tagged with 5-carboxyfluorescein (FAM, emission at 518 nm, denoted as T-rich P-DNA-2) to achieve synchronous sensing of Ag⁺ and Hg²⁺, resulting from the simultaneous yet specific ds-DNA-1@Ag⁺ and T-Hg^II-T duplex (ds-DNA-2@Hg²⁺) formation, as well as the distinctive emission wavelengths of TAMRA and FAM. Detection limits are as low as 5.3 nM (Ag⁺), 14.2 nM (Cys), 13.5 nM (GSH), and 9.1 nM (Hcy) for MOF 1, and 7.5 nM (Ag⁺) and 2.6 nM (Hg²⁺) for MOF 2, respectively. The sequential sensing of Ag⁺ and biothiols by MOF 1, and the synchronous sensing of Ag⁺ and Hg²⁺ by MOF 2 are rapid and specific, even in the presence of other mono- and divalent metal cations or other biothiols at much higher concentrations. Molecular simulation studies provide insights regarding the molecular interactions that underpin these sensing processes.

Recent Advances in Nanomaterials for Analysis of Trace Heavy Metals

In an effort to achieve high sensitivity analysis methods for ultra-trace levels of heavy metals, numerous new nanomaterials are explored for the application in preconcentration processes and sensing systems. Nanomaterial-based methods have proven to be effective for selective analysis and speciation of heavy metals in combination with spectrometric techniques. This review outlined the different types of nanomaterials applied in the field of heavy metal analysis, and concentrated on the latest developments in various new materials. In particular, the functionalization of traditional materials and the exploitation of bio-functional materials could increase the specificity to target metals. The hybridization of multiple materials could improve material properties, to build novel sensor system or achieve detection-removal integration. Finally, we discussed the future perspectives of nanomaterials in the heavy metal preconcentration and sensor design, as well as their respective advantages and challenges. Despite impressive progress and widespread attention, the development of new nanomaterials and nanotechnology is still hampered by numerous challenges, particularly in the specificity to the target and the anti-interference performance in complex matrices.

Thymine-Hg2+-thymine coordination chemistry induced entropy driven catalytic reaction to form Hemin/G-quadruplex-HRP-mimicking DNAzyme for colorimetric and visual determination of Hg2

A sensitive and visible colorimetric strategy was proposed for Hg²⁺ detection by thymine-Hg²⁺-thymine (T-Hg²⁺-T) coordination chemistry and entropy driven catalytic reaction. The entropy driven catalytic reaction is induced by T-Hg²⁺-T coordination chemistry, resulting the releasing of G-riched sequence. Hemin/G-quadruplex-HRP-mimicking DNAzyme can be formed with the help of hemin, catalyzing TMB to TMB⁺ with a color change from colorless to blue. The sensitivity of this strategy can be reached to 2 pM, which is significantly improved by entropy driven catalytic reaction. In addition, entropy driven catalytic reaction provides a more reliable and accurate results. This method shows great promise for on-site analysis and in-house diagnosis of Hg²⁺ in water.

An exonuclease-assisted triple-amplified electrochemical aptasensor for mucin 1 detection based on strand displacement reaction and enzyme catalytic strategy

The development of some sensitive methods for MUC1 is critical for preclinical diagnosis of tumors. In this experiment, we built a triple-amplified electrochemical aptasensor to achieve sensitive detection of MUC1, which was based on exonuclease III (Exo III)-assisted with strand displacement reaction and enzyme catalytic strategy. Firstly, with the help of Exo III, MUC1 and aptamer could be recycled during the cycle I, the single stranded DNA-1 (S-1) was produced during the process and was introduced to the hybride reaction on the electrode. Secondly, during the cycle II, strand displacement reaction was triggered on the electrode with the adding of hairpin DNA-2 (H-2). Thirdly, after the gold nanoparticles (AuNPs)-DNA-enzyme conjugates hybrided with the H-2 on the electrode, the AuNPs-DNA-enzyme conjugates could act as signal probe to produce electrochemical catalytic signal. We used the fabricated triple-amplified electrochemical aptasensor that could detect MUC1 from 0.1 pg mL^-1 to 10 ng mL^-1 with the detection limit of 0.04 pg mL^-1 under the optimized experimental conditions. The constructed triple-amplified electrochemical aptasensor could be applied in real samples determination. Besides, the strategy can be applied to detect other proteins for health monitoring.