Practical and regenerable electrochemical aptasensor based on nanoporous gold and thymine-Hg 2+ -thymine base pairs for Hg 2+ detection

Preparation of CoFe@C composite modified electrode for neohesperidin dihydrochalcone sensing and its application in Chinese medicine

CoFe@C was first prepared by calcining the precursor of CoFe-metal-organic framework-74 (CoFe-MOF-74), then an electrochemical sensor for the determination of neohesperidin dihydrochalcone (NHDC) was constructed, which was stemmed from the novel CoFe@C/Nafion composite film modified glassy carbon electrode (GCE). The CoFe@C/Nafion composite was verified by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) was used to evaluate its electrical properties as a modified material for an electrochemical sensor. Compared with CoFe-MOF-74 precursor modified electrode, CoFe@C/Nafion electrode exhibited a great synergic catalytic effect and extremely increased the oxidation peak signal of NHDC. The effects of various experimental conditions on the oxidation of NHDC were investigated and the calibration plot was tested. The results bespoken that CoFe@C/Nafion GCE has good reproducibility and anti-interference under the optimal experimental conditions. In addition, the differential pulse current response of NHDC was linear with its concentration within the range 0.08 ~ 20 µmol/L, and the linear regression coefficient was 0.9957. The detection limit was as low as 14.2 nmol/L (S/N = 3). In order to further verify the feasibility of the method, it was successfully used to determine the content of NHDC in Chinese medicine, with a satisfactory result, good in accordance with that of high performance liquid chromatography (HPLC).

Efficient 2D MOFs nanozyme combining with magnetic SERS substrate for ultrasensitive detection of Hg2

Biomimetic inorganic nanoenzyme is a kind of nanomaterial with long-term stability, easy preparation and low cost, which could instead of natural biological enzyme. Metal-organic framework (MOFs) as effectively nanoenzyme was attracted more attention for the adjustability and large specific surface area. This design is based on the catalase-like catalytic activity of 2D metal-organic frameworks (MOFs) and the high sensitivity of surface enhanced Raman spectroscopy (SERS) biosensors to construct a novel SERS biosensor capable of efficiently detecting mercury (Hg2+). In this study, 2D MOFs nanozyme was instead of 3D structure with more effecient catalytic site, which can catalyze o-Phenylenediamine (OPD) to OPDox with the assistance of H2O2. Besides, a magnetic composite nanomaterial Fe3O4@Ag@OPD was prepared as a signal carrier. In the presence of Hg2+, T-Hg2+-T base pairs were used to connect the two materials to realize Raman signal change. Based on this principle, the SERS sensor can realize the sensitive detection of Hg2+, the detection range is 1.0 × 10-12 ∼ 1.0 × 10-2 mol‧L-1, and the detection limit is 1.36 × 10-13 mol‧L-1. This method greatly improves the reliability of SERS sensor for detecting the target, and provides a new idea for detecting metal ions in the environment.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Rapid electrochemical quantification of trace Hg2+ using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg²⁺) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn–Ag–In–S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg²⁺ detection. Based on the “turn-off” reaction of a hairpin DNA probe binding with a mismatched target and Hg²⁺ through the formation of T–Hg²⁺–T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg²⁺ with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg²⁺. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg²⁺ was studied in vitro, with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg²⁺ ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg²⁺ in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.

A ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quantum dot on screen-printed gold electrodes, was developed for Hg²⁺ detection.

In situ fabrication of urchin-like Cu@carbon nanoneedles based aptasensor for ultrasensitive recognition of trace mercury ion

Mercury ion (Hg²⁺) is a strong toxic heavy ion that causes severe damages to the environment and readily accumulates in the food chain. However, it remains a major challenge to realize a sensitive and precise recognition of Hg²⁺ with a trace concentration for early identifying the pollution source. In this work, a novel electrochemical aptasensor was designed to achieve an ultrasensitive and quantitative detection of trace Hg²⁺, relying on an urchin-like architecture of Cu@carbon nanoneedles (Cu@CNNs) as the electroactive probe. This specific nanostructure was in-situ constructed through a controllable pyrolysis process, serving as a signal magnifier and DNA loading platform owing to its outstanding electrocatalysis and large specific surface areas. Meanwhile, an exonuclease III-assisted cycling amplification strategy was designed to efficiently amplify the signal strength of trace Hg²⁺via the consecutive release of report probes in nicking reaction. This as-prepared Hg²⁺ aptasensor exhibited an ultralow detection limit of 3.7 fM (7 × 10^-6 ppm) and a wide linear range from 10 fM to 10 μM, together with the satisfactory stability and reusability for assay in real water samples. It is highly expected that this Cu@CNNs based aptasensor will have tremendous potentials in the early warning and efficient pollution monitoring of heavy metal ions.

An ultrasensitive surface-enhanced Raman scattering sensor for the detection of hydrazine via the Schiff base reaction

The development of convenient assays for the determination of hydrazine (N₂H₄) has drawn significant attention due to the high toxicity of this substance. Herein, we developed a concise, rapid and ultrasensitive surface-enhanced Raman scattering (SERS) sensor for N₂H₄ detection based on alpha-cyclodextrin-silver nanoparticles (α-CD-AgNPs) modified by 4-mercaptobenzaldehyde (4-MBA). The 4-MBA molecules can specifically capture the N₂H₄ molecules and undergo a Schiff base reaction. As a result, this induces the aggregation of nanoparticles and generates a new characteristic peak at 1529 cm^-1 that is attributed to CN and CC vibrations. Compared with noble metal nanoparticles, 4-MBA not only formed AgS bonds but could also be fixed in the cavity of cyclodextrin to produce a more stable and stronger SERS signal. The SERS intensity at 1529 cm^-1 and the logarithm of the concentration of N₂H₄ presented a good linear relationship from 10^-9 to 10^-7 M with an unprecedented limit of detection (LOD) of 38 pM. The proposed SERS sensor exhibited satisfactory selectivity and reproducibility and was applied to detect N₂H₄ in real and complex water samples. We expect this assay to be a promising alternative tool for the on-site detection of N₂H₄.

Recognition elements based on the molecular biological techniques for detecting pesticides in food: A review

Excessive use of pesticides can cause contamination of the environment and agricultural products that are directly threatening human life and health. Therefore, in the process of food safety supervision, it is crucial to conduct sensitive and rapid detection of pesticide residues. The recognition element is the vital component of sensors and methods for fast testing pesticide residues in food. Improper recognition elements may lead to defects of testing methods, such as poor stability, low sensitivity, high economic costs, and waste of time. We can use the molecular biological technique to address these challenges as a good strategy for recognition element production and modification. Herein, we review the molecular biological methods of five specific recognition elements, including aptamers, genetic engineering antibodies, DNAzymes, genetically engineered enzymes, and whole-cell-based biosensors. In addition, the application of these identification elements combined with biosensor and immunoassay methods in actual detection was also discussed. The purpose of this review was to provide a valuable reference for further development of rapid detection methods for pesticide residues.

A novel electrochemical biosensor for ultrasensitive Hg2+ detection via a triple signal amplification strategy

We developed a novel electrochemical biosensor for ultrasensitive Hg2+ detection via a triple signal amplification strategy of a DNA dual cycle, organic-inorganic hybrid nanoflowers (Cu3(PO4)2 HNFs) and gold nanoparticle (AuNP) probe. The DNA dual cycle was triggered by exonuclease III (Exo III) in the presence of Hg2+, and Cu3(PO4)2 HNFs were synthesized as an AuNP probe carrier. The electrochemical biosensor displayed high stability, high sensitivity and excellent specificity, which was improved by up to seven orders of magnitude compared to the World Health Organization (WHO) allowed Hg2+ levels in drinking water. This signal amplification strategy could be easily modified and extended to detect other hazardous heavy metals and nucleic acids.

Potential applications of aptamers in veterinary science

Aptamers are small nucleic acids that fold in a three-dimensional conformation allowing them to bind specifically to a target. This target can be an organic molecule, free or carried in cells or tissues, or inorganic components, such as metal ions. Analogous to monoclonal antibodies, aptamers however have certain advantages over the latter: e.g., high specificity for their target, no to low immunogenicity and easy in vitro selection. Since their discovery more than 30 years ago, aptamers have led to various applications, although mainly restricted to basic research. This work reviews the applications of aptamers in veterinary science to date. First, we present aptamers, how they are selected and their properties, then we give examples of applications in food and environmental safety, as well as in diagnosis and medical treatment in the field of veterinary medicine. Because examples of applications in veterinary medicine are scarce, we explore the potential avenues for future applications based on discoveries made in human medicine. Aptamers may offer new possibilities for veterinarians to diagnose certain diseases—particularly infectious diseases—more rapidly or “at the patient’s bedside”. All the examples highlight the growing interest in aptamers and the premises of a potential market. Aptamers may benefit animals as well as their owners, breeders and even public health in a “One Health” approach.

DNA Nanosieve-Based Regenerative Electrochemical Biosensor Utilizing Nucleic Acid Flexibility for Accurate Allele Typing in Clinical Samples

Herein, an interface-based DNA nanosieve that has the ability to differentiate ssDNA from dsDNA has been demonstrated for the first time. The DNA nanosieve could be readily built through thiol-DNA's self-assembly on the gold electrode surface, and its cavity size was tunable by varying the concentration of thiol-DNAs. Electrochemical chronocoulometry using [Ru(NH₃)₆]³⁺ as redox revealed that the average probe-to-probe separation in the 1 μM thiol-DNA-modified gold electrode was 10.6 ± 0.3 nm so that the rigid dsDNA with a length of ∼17 nm could not permeate the nanosieve, whereas the randomly coiled ssDNA could enter it due to its high flexibility, which has been demonstrated by square wave voltammetry and methylene blue labels through an upside-down hybridization format. After combining the transiently binding characteristic of a short DNA duplex and introducing a regenerative probe (the counterpart of ssDNA), a highly reproducible nanosieve-based E-DNA model was obtained with a relative standard deviation (RSD) as low as 2.7% over seven cycles. Finally, we built a regenerative nanosieve-based E-DNA sensor using a ligation cycle reaction as an ssDNA amplification strategy and realized one-sensor-based continuous measurement to multiple clinical samples with excellent allele-typing performance. This work holds great potential in low-cost and high-throughput analysis between biosensors and biochips and also opens up a new avenue in nucleic acid flexibility-based DNA materials for future applications in DNA origami and molecular logic gates.

Capture-SELEX for aptamer selection: A short review

The emerging aptamer, developed through the systematic evolution of ligands by exponential enrichment (SELEX) process, has revolutionized and facilitated the discoveries in basic research. Among all SELEX technology, Capture-SELEX is a variant of the in vitro selection process, which is suitable for isolating aptamers against small molecules. Capture-SELEX library was developed to enable the immobilization of the oligonucleotides instead of the target molecules during the aptamer selection process. The review provides an update on the recent-advances in this new screening method with particular emphasis on key points of capture protocol and its applications. The limitations and the prospects of the Capture-SELEX are also discussed. We hope that present review will inspire more researchers to understand the selection problems from the perspective of Capture-SELEX. Moreover, it will open new pave to improve the efficiency and success of screening to meet the growing demand for aptasensor discovery in small molecules.

A double signal amplification-based homogeneous electrochemical sensor built on catalytic hairpin assembly and bisferrocene markers

A facile, sensitive and unmodified Hg²⁺ homogeneous electrochemical sensor based on bisferrocene signal markers and catalytic hairpin self-assembly (CHA) was built on a gold disk electrode. Three hairpin probes were designed, in which thiol was labeled at both ends of the hairpin probe 1(HP1), while bisferrocene, a redox signal marker, was labeled at both ends of the hairpin probe 2(HP2) and hairpin probe 3(HP3). Due to the Hg²⁺ mediated thymine-Hg (II)-thymine (T-Hg²⁺-T) structure, when Hg²⁺ is introduced, the T-Hg²⁺-T that occurred between the probe DNA and helper DNA could open the hairpin structure of probe DNA and form a rigid DNA triangles structure by CHA. Simultaneously, four bisferrocene signal markers also reached the surface of the electrode and built potential-assisted Au-S self-assembly to achieve signal amplification. Under the optimized condition, the sensor can achieve good electrochemical response Hg²⁺detection, and the detection limit is as low as 0.6 pM. furthermore, this sensor has high selectivity for Hg²⁺ detection.

Cobalt metal-organic framework modified carbon cloth/paper hybrid electrochemical button-sensor for nonenzymatic glucose diagnostics

In the growing pandemic, family healthcare is widely concerned with the increase of medical self-diagnosis away from the hospital. A cobalt metal-organic framework modified carbon cloth/paper (Co-MOF/CC/Paper) hybrid button-sensor was developed as a portable, robust, and user-friendly electrochemical analytical chip for nonenzymatic quantitative detection of glucose. Highly integrated electrochemical analytical chip was successfully fabricated with a flexible Co-MOF/CC sensing interface, effectively increasing the specific area and catalytic sites than the traditional plane electrode. Based on the button-sensor, rapid quantitative detection of glucose was achieved in multiple complex bio-matrixes, such as serum, urine, and saliva, with desired selectivity, stability, and durability. With the advantages of low cost, high environment tolerance, ease of production, our nanozyme-based electrochemical analytical chip achieved reliable nonenzymatic electrocatalysis, has great potential for the application of rapid on-site analysis in personalized diagnostic and disease prevention.

From Small Molecules Toward Whole Cells Detection: Application of Electrochemical Aptasensors in Modern Medical Diagnostics

This paper focuses on the current state of art as well as on future trends in electrochemical aptasensors application in medical diagnostics. The origin of aptamers is presented along with the description of the process known as SELEX. This is followed by the description of the broad spectrum of aptamer-based sensors for the electrochemical detection of various diagnostically relevant analytes, including metal cations, abused drugs, neurotransmitters, cancer, cardiac and coagulation biomarkers, circulating tumor cells, and viruses. We described also possible future perspectives of aptasensors development. This concerns (i) the approaches to lowering the detection limit and improvement of the electrochemical aptasensors selectivity by application of the hybrid aptamer-antibody receptor layers and/or nanomaterials; and (ii) electrochemical aptasensors integration with more advanced microfluidic devices as user-friendly medical instruments for medical diagnostic of the future.

Reusable, facile, and rapid aptasensor capable of online determination of trace mercury

Herein, we reported a homemade waveguide-based evanescent wave aptasensor for the facile online monitoring of mercury pollution. The aptasensor exploited the high selectivity of hairpin structure-based thymidine-Hg²⁺-thymidine coordination chemistry (T-T mismatch) for Hg²⁺ recognition and the stably regenerable capability of DNA-functionalized waveguide surfaces. The presence of Hg²⁺ caused the T-T mismatch of Cy5.5-labeled T-rich single-stranded DNA sequences. The formed hairpin structures blocked the further hybridization of T-rich single-stranded DNA sequences with the complementary DNA strands that are modified on the waveguide surface; this phenomenon was accompanied by the decrease in the fluorescent signals excited by the evanescent wave. The limit of detection in real water samples was determined to be 0.2 μg/L, which was comparable with that of 0.4 μg/L in an ultrapure water under controlled conditions. And the linear range was observed from 1.4 µg/L to 240.7 µg/L. The negligible environmental matrix effect on the performance ensured the reliability of the proposed aptasensor. Moreover, the cross reactivity of this method toward other investigated metal ions was negligible. Through the delicate surface modification with DNA molecules covalently, the chip was reused at least 31 times with a relative standard deviation (RSD) of less than 19%. A Hg²⁺ pollution accident was successfully detected within 30 min, shedding new light in pollution monitoring, environment restoration, and emergency treatment.

Detection of pollutants in water bodies: electrochemical detection or photo-electrochemical detection?

The massive discharge of pollutants including endocrine-disrupting chemicals (EDCs), heavy metals, pharmaceuticals and personal care products (PPCPs) into water bodies is endangering the ecological environment and human health, and needs to be accurately detected. Both electrochemical and photo-electrochemical detection methods have been widely used for the detection of these pollutants, however, which one is better for the detection of different environmental pollutants? In this feature article, different electrochemical and photo-electrochemical detection methods are summarized, including the principles, classification, common catalysts, and applications. By summarizing the advantages and disadvantages of different detection methods, this review provides a guide for other researchers to detect pollutants in water bodies by using electrochemical and photo-electrochemical analysis.

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.

Biochar-mediated Fenton-like reaction for the degradation of sulfamethazine: Role of environmentally persistent free radicals

Swine manure biochar (SBC) pyrolyzed at 300 °C, 600 °C and 900 °C were utilized to degrade sulfamethazine (SMT) in heterogeneous Fenton-like systems which achieved excellent degradation efficiency (over 85% in 30 min). Experiments results demonstrated that SBC possessed the poor SMT adsorption capacity but high catalytic performance. Electron Paramagnetic Resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that there were oxygen-centered environmentally persistent free radicals (EPFRs) and carbon-centered EPFRs with an adjacent oxygen atom in SBC. The oxygen-centered EPFRs played a major role in the catalytic process which tended to convert to carbon-centered EPFRs after the reaction. Besides, the electron transfer pathways were the most likely catalytic mechanism of SBC and the contribution of OH was dominant through Electron capture experiments and Linear sweep voltammetry (LSV) measurements. The acidic or alkaline condition can promote the catalytic ability of SBC. The presence of dissolved salts (NaCl) inhibited the catalytic process but the inhibition was slightly weakened at high concentration of NaCl, which showed the high tolerance of Cl^- in Fenton/Fenton-like systems. Moreover, real wastewater application suggested that SBC600/H₂O₂ system possessed excellent catalytic efficiency and good adaptability. This research provides a novel swine manure reuse process with high practicability and presents a more explicit perspective about the reaction mechanisms of EPFRs in biochar.

An Electrochemical Aptasensor Platform Based on Flower-Like Gold Microstructure-Modified Screen-Printed Carbon Electrode for Detection of Serpin A12 as a Type 2 Diabetes Biomarker

Purpose

In the present study, a highly sensitive and simple electrochemical (EC) aptasensor for the detection of serpin A12 as a novel biomarker of diabetes was developed on a platform where flower-like gold microstructures (FLGMs) are electrodeposited onto a disposable screen-printed carbon electrode. Meanwhile, serpin A12-specific thiolated aptamer was covalently immobilized on the FLGMs.

Methods

The electrochemical activity of a fabricated aptasensor under various conditions were examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Aptamer concentration, deposition time, self-assembly time, and incubation time were optimized for assay of serpin A12. The differential pulse voltammetry (DPV) was implemented for quantitative detection of serpin A12 in K₃ [Fe (CN) ₆]/K₄ [Fe (CN) ₆] solution (redox probe).

Results

The label-free aptasensor revealed a linear range of serpin A12 concentration (0.039–10 ng/mL), detection limit of 0.020 ng/mL (S/N=3), and 0.031 ng/mL in solution buffer and plasma, respectively.

Conclusion

The results indicate that this aptasensor has a high sensitivity, selectivity, stability, and acceptable reproducibility for detection of serpin A12 in diabetic patients.

A low-cost paper-based aptasensor for simultaneous trace-level monitoring of mercury (II) and silver (I) ions

Mercury (Hg²⁺) and silver (Ag⁺) ions possess the harmful effects on public health and environment that makes it essential to develop the sensing techniques with great sensitivity for the ions. Metal ions commonly coexist in the different biological and environmental systems. Hence, it is an urgent demand to design a simple method for the simultaneous detection of metal ions, peculiarly in the case of coexisting Hg²⁺ and Ag⁺. This study introduces a low-cost paper-based aptasensor to monitor Hg²⁺ and Ag⁺, simultaneously. The strategy of the sensing array is according to the conformational changes of Hg²⁺- and Ag⁺-specific aptamers and their release from the GO surface after the injection of the target sample on the sensing platform. Through monitoring the fluorescence recovery changes against the concentrations of the ions, Hg²⁺ and Ag⁺ can be determined as low as 1.33 and 1.01 pM. The paper-based aptasensor can simultaneously detect the ions within about 10 min. The aptasensor is applied prosperously to monitor Hg²⁺ and Ag⁺ in human serum, water, and milk. The designed aptasensor with the main advantages of simplicity and feasibility holds the supreme potential to develop a cost-effective sensing method for environmental monitoring, food control, and human diagnostics.

Remediation of Multiply Contaminated Ground via Permeable Reactive Barrier and Electrokinetic Using Recyclable Food Scrap Ash (FSA)

A study of the application of electrokinetic (EK) remediation and Permeable Reactive Barriers (PRB) using recyclable Foods Scrap Ash (FSA) in multiple contaminated soils was carried out. An FSA was chosen as a PRB fill material due to its highly efficient capacity for contaminant removal. Acetic acid and Brij30 were used as enhancers on copper and phenanthrene, respectively, to improve EK remediation performance in removing the heavy metal and organic contaminants. Copper adsorption in PRB was so substantial that the confirmed removal efficiency was 83.86–90.17% and the remaining amount was 105–212 mg. While a high removal efficiency of acetic acid was observed on copper in multiple contamination soils; the removal of phenanthrene was hardly detected and the recovery rate of the contaminant was low during pretreatment. Therefore; an additional study of pretreatment on the phenanthrene-contaminated kaolinite needs to be performed.

Single-Atom Enzyme-Functionalized Solution-Gated Graphene Transistor for Real-Time Detection of Mercury Ion

Mercury ion (Hg²⁺), a bioaccumulating and toxic heavy metal, can cause severe damages to the environment and human health. Therefore, development of high-performance Hg²⁺ sensors is highly desirable. Herein, we construct a uniform dodecahedral shaped N-doped carbon decorated by single Fe site enzyme (Fe-N-C SAE), which exhibits good performance for Hg²⁺ detection. The N atom on Fe-N-C SAE can specifically recognize Hg²⁺ through chelation between Hg²⁺ and N atom, while the catalytic site on the single-atom enzyme acts as a signal amplifier. The Fe-N-C SAE-functionalized solution-gated graphene transistor exhibits a dramatic improvement in the selectivity and sensitivity of the devices. The sensor can rapidly detect Hg²⁺ down to 1 nM within 2 s. Besides, a relatively good repeatability and reproducibility for the detection of Hg²⁺ have also been found in our sensor platform. Our findings expand the application of single-atom catalysts in the field of food safety and environmental monitoring.

Application of Electrochemical Aptasensors toward Clinical Diagnostics, Food, and Environmental Monitoring: Review

Aptamers are synthetic bio-receptors of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) origin selected by the systematic evolution of ligands (SELEX) process that bind a broad range of target analytes with high affinity and specificity. So far, electrochemical biosensors have come up as a simple and sensitive method to utilize aptamers as a bio-recognition element. Numerous aptamer based sensors have been developed for clinical diagnostics, food, and environmental monitoring and several other applications are under development. Aptasensors are capable of extending the limits of current analytical techniques in clinical diagnostics, food, and environmental sample analysis. However, the potential applications of aptamer based electrochemical biosensors are unlimited; current applications are observed in the areas of food toxins, clinical biomarkers, and pesticide detection. This review attempts to enumerate the most representative examples of research progress in aptamer based electrochemical biosensing principles that have been developed in recent years. Additionally, this account will discuss various current developments on aptamer-based sensors toward heavy metal detection, for various cardiac biomarkers, antibiotics detection, and also on how the aptamers can be deployed to couple with antibody-based assays as a hybrid sensing platform. Aptamers can be used in various applications, however, this account will focus on the recent advancements made toward food, environmental, and clinical diagnostic application. This review paper compares various electrochemical aptamer based sensor detection strategies that have been applied so far and used as a state of the art. As illustrated in the literature, aptamers have been utilized extensively for environmental, cancer biomarker, biomedical application, and antibiotic detection and thus have been extensively discussed in this article.

Noble Metal Nanoparticles-Based Colorimetric Biosensor for Visual Quantification: A Mini Review

Nobel metal can be used to form a category of nanoparticles, termed noble metal nanoparticles (NMNPs), which are inert (resistant to oxidation/corrosion) and have unique physical and optical properties. NMNPs, particularly gold and silver nanoparticles (AuNPs and AgNPs), are highly accurate and sensitive visual biosensors for the analytical detection of a wide range of inorganic and organic compounds. The interaction between noble metal nanoparticles (NMNPs) and inorganic/organic molecules produces colorimetric shifts that enable the accurate and sensitive detection of toxins, heavy metal ions, nucleic acids, lipids, proteins, antibodies, and other molecules. Hydrogen bonding, electrostatic interactions, and steric effects of inorganic/organic molecules with NMNPs surface can react or displacing capping agents, inducing crosslinking and non-crosslinking, broadening, or shifting local surface plasmon resonance absorption. NMNPs-based biosensors have been widely applied to a series of simple, rapid, and low-cost diagnostic products using colorimetric readout or simple visual assessment. In this mini review, we introduce the concepts and properties of NMNPs with chemical reduction synthesis, tunable optical property, and surface modification technique that benefit the development of NMNPs-based colorimetric biosensors, especially for the visual quantification. The “aggregation strategy” based detection principle of NMNPs colorimetric biosensors with the mechanism of crosslinking and non-crosslinking have been discussed, particularly, the critical coagulation concentration-based salt titration methodology have been exhibited by derived equations to explain non-crosslinking strategy be applied to NMNPs based visual quantification. Among the broad categories of NMNPs based biosensor detection analyses, we typically focused on four types of molecules (melamine, single/double strand DNA, mercury ions, and proteins) with discussion from the standpoint of the interaction between NMNPs surface with molecules, and DNA engineered NMNPs-based biosensor applications. Taken together, NMNPs-based colorimetric biosensors have the potential to serve as a simple yet reliable technique to enable visual quantification.

Development of Novel and Highly Specific ssDNA-Aptamer-Based Electrochemical Biosensor for Rapid Detection of Mercury (II) and Lead (II) Ions in Water

In this work, we report on the development of an electrochemical biosensor for high selectivity and rapid detection of Hg2+ and Pb2+ ions using DNA-based specific aptamer probes labeled with ferrocene (or methylene blue) and thiol groups at their 5′ and 3′ termini, respectively. Aptamers were immobilized onto the surface of screen-printed gold electrodes via the SH (thiol) groups, and then cyclic voltammetry and impedance spectra measurements were performed in buffer solutions with the addition of HgCl2 and PbCl2 salts at different concentrations. Changes in 3D conformation of aptamers, caused by binding their respective targets, e.g., Hg2+ and Pb2+ ions, were accompanied by an increase in the electron transfer between the redox label and the electrode. Accordingly, the presence of the above ions can be detected electrochemically. The detection of Hg2+ and Pb2+ ions in a wide range of concentrations as low as 0.1 ng/mL (or 0.1 ppb) was achieved. The study of the kinetics of aptamer/heavy metal ions binding gave the values of the affinity constants of approximately 9.10−7 mol, which proved the high specificity of the aptamers used.

Nicking enzyme-assisted signal-amplifiable Hg2+ detection using upconversion nanoparticles

A highly specific and sensitive isothermal method for mercury detection using DNA-conjugated upconversion nanoparticles is reported. A single-stranded DNA containing thymine bases, used as the Hg²⁺-capturing element through the formation of thymine-Hg²⁺-thymine complex, is covalently attached to the NaYF₄: Yb^3+, Tm³⁺ nanoparticles. Luminescence resonance energy transfer takes place between the NaYF₄: Yb^3+, Tm³⁺ nanoparticles as donor and DNA-intercalating SYBR Green I as the acceptor upon excitation of 980 nm. The sensitivity and selectivity toward Hg²⁺ are enhanced using the nicking enzyme, Nt. Alwl, which leads to signal amplification. By monitoring the ratio of acceptor emission to a reference peak, the presence of Hg²⁺ ions are quantitatively determined with a lower detection limit of 0.14 nM, which is much lower than the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water.

Adsorption behavior of engineered carbons and carbon nanomaterials for metal endocrine disruptors: Experiments and theoretical calculation

Adsorption behaviors and mechanisms of metal endocrine disruptors (Pb²⁺, Cd²⁺, and Hg²⁺) by pyrogenic carbonaceous materials including engineered carbons (biochar and activated carbon) and carbon nanomaterials (multi-walled carbon nanotubes and graphene oxide) have been investigated by experimental and density functional theory (DFT) studies. The adsorption isotherms of metal endocrine disruptors on carbonaceous materials were better fitted by Langmuir models. The adsorption capacities were in the order as follows: GO > BC600 > BC300 > CNT > AC for Pb²⁺, GO > BC300 > AC > BC600 > CNT for Cd²⁺, and GO > BC300 ≥ AC > CNT > BC600 for Hg²⁺, respectively. The DFT-computed binding energy (kcal/mol) of different oxygen-containing functional groups with metal endocrine disruptors followed the orders: (ⅰ) CMCOCPb (-136.70) > CM-COO^--Pb (-91.58) > CMCOPb (-33.57) > CMOHPb (-4.69), (ⅱ) CM-COO^--Cd (-45.91) > CMCOCCd (-4.49) > CMOHCd (-3.68) > CMCOCd (1.08), (ⅲ) CM-COO^--Hg (-25.51) > CMCOCHg (-3.58) > CMOHHg (-0.63) > CMCOHg (0.23). And COC has the highest binding energy for Pb²⁺, whereas COC has much lower binding energy for Cd²⁺ and Hg²⁺. Comprehensively considering DFT calculations, competitive adsorption results and the cost analysis, this work may provide insights into the design of selective adsorbent for specific contaminant.

Recent Advances in Aptamer Discovery and Applications

Aptamers are short, single-stranded DNA, RNA, or synthetic XNA molecules that can be developed with high affinity and specificity to interact with any desired targets. They have been widely used in facilitating discoveries in basic research, ensuring food safety and monitoring the environment. Furthermore, aptamers play promising roles as clinical diagnostics and therapeutic agents. This review provides update on the recent advances in this rapidly progressing field of research with particular emphasis on generation of aptamers and their applications in biosensing, biotechnology and medicine. The limitations and future directions of aptamers in target specific delivery and real-time detection are also discussed.

A visual and sensitive Hg2+ detection strategy based on split DNAzyme amplification and peroxidase-like activity of hemin-graphene composites

A visual and sensitive Hg²⁺ detection strategy was developed based on split DNAzyme amplification and hemin-graphene oxide composites (H-GNs). Two split DNAzyme sequences can form two entire enzyme-strands DNA (E-DNA) by T-Hg²⁺-T interaction. The E-DNA can bind with the loop of molecular beacon (MB) to form Mg²⁺-dependent DNAzyme structure. The formed DNAzyme can circularly cleave the loop of MB, resulting large amount of DNA fragments. The resultant DNA fragments can prevent H-GNs from aggregation by adsorbing on its surface. Consequently, the supernate with large amount of H-GNs shows dark blue color after chromogenic reaction. This strategy shows a linear range from 50 pM to 1200 pM. The limit detection can be low to 33 pM. This strategy provides a visual and enzyme-free amplification mode for quick and sensitive screen of Hg²⁺.

Synthetic strategies and application of gold-based nanocatalysts for nitroaromatics reduction

With the increasing requirement of efficient organic transformations on the basic concept of Green Sustainable Chemistry, the development of highly efficient catalytic reaction system is greatly desired. In this case, gold (Au)-based nanocatalysts are promising candidates for catalytic reaction, especially for the reduction of nitroaromatics. They have attracted wide attention and well developed in the application of nitroaromatics reduction because of the unique properties compared with that of other conventional metal-based catalysts. With this respect, this review proposes recent trends in the application of Au nanocatalysts for efficient reduction process of nitroaromatics. Some typical approaches are compared and discussed to guide the synthesis of highly efficient Au nanocatalysts. The mechanism on the use of H₂ and NaBH₄ solution as the source of hydrogen is compared, and that proposed under light irradiation is discussed. The high and unique catalytic activity of some carriers, such as oxides and carbons-based materials, based on different sizes, structures, and shapes of supported Au nanocatalysts for nitroaromatics reduction are described. The catalytic performance of Au combining with other metal nanoparticles by alloy or doping, like multi-metal nanoparticles system, is further discussed. Finally, a short discussion is introduced to compare the catalysis with other metallic nanocatalysts.

Electrochemical mercury biosensors based on advanced nanomaterials

This review presents an overview of the synthesis strategies and electrochemical performance of recently developed nanomaterials for the Hg²⁺ assay.

Electrochemical Aptasensor Based on Sulfur-Nitrogen Codoped Ordered Mesoporous Carbon and Thymine-Hg2+-Thymine Mismatch Structure for Hg2+ Detection

A renewable electrochemical aptasensor was proposed for super-sensitive determination of Hg²⁺. The novel aptasensor, based on sulfur-nitrogen codoped ordered mesoporous carbon (SN-OMC) and thymine-Hg²⁺-thymine (T-Hg²⁺-T) mismatch structure, used ferrocene as signal molecules to achieve the conversion of current signals. In the absence of Hg²⁺, the thiol-modified T-rich probe 1 spontaneously formed a hairpin structure by base pairing. After being hybridized with the ferrocene-labeled probe 2 in the presence of Hg²⁺, the hairpin structure of probe 1 was opened due to the preferential formation of the T-Hg²⁺-T mismatch structure, and the ferrocene signal molecules approached the modified electrode surface. SN-OMC with high specific surface area and ample active sites acted as a signal amplification element in electrochemical sensing. The sensitive determination of Hg²⁺ can be actualized by analyzing the relationship between the change of oxidation current caused by ferrocene signal molecules and the Hg²⁺ concentrations. The aptasensor had a fine linear correlation in the range of 0.001-1000 nM with a detection limit of 0.45 pM. The aptasensor also displayed a good response in real sample detection and provided a promising possibility for in situ detection.