Highly sensitive impedimetric biosensor for Hg2+ detection based on manganese porphyrin-decorated DNA network for precipitation polymerization

Hybrid Nanoparticle/DNAzyme Electrochemical Biosensor for the Detection of Divalent Heavy Metal Ions and Cr3

A hybrid noble nanoparticle/DNAzyme electrochemical biosensor is proposed for the detection of Pb2+, Cd2+, and Cr3+. The sensor takes advantage of a well-studied material that is known for its selective interaction with heavy metal ions (i.e., DNAzymes), which is combined with metallic nanoparticles. The double-helix structure of DNAzymes is known to dissociate into smaller fragments in the presence of specific heavy metal ions; this results in a measurable change in device resistance due to the collapse of conductive inter-nanoparticle DNAzyme bridging. The paper discusses the effect of DNAzyme anchoring groups (i.e., thiol and amino functionalization groups) on device performance and reports on the successful detection of all three target ions in concentrations that are well below their maximum permitted levels in tap water. While the use of DNAzymes for the detection of lead in particular and, to some extent, cadmium has been studied extensively, this is one of the few reports on the successful detection of chromium (III) via a sensor incorporating DNAzymes. The sensor showed great potential for its future integration in autonomous and remote sensing systems due to its low power characteristics, simple and cost-effective fabrication, and easy automation and measurement.

Water-soluble anionic N-confused porphyrin for sensitive and selective detection of heavy metal pollutants in aqueous environment

Efficient detection and quantification of metal ions in real time and in a cost-effective manner is a critical step in combating the increasing danger of heavy metal contamination of our biosphere. The potential of water-soluble anionic derivative of N-confused tetraphenylporphyrin (WS-NCTPP) has been investigated for quantitative detection of heavy metal ions. The results show that the photophysical properties of WS-NCTPP differ significantly in the presence of four metal ions, namely Hg(II), Zn(II), Co(II) and Cu(II). The variation in the spectral behaviour is driven by the formation of 1:1 complexes with all the four cations with varied degree of complexation. The selectivity of the sensing is studied through interference studies, indicating maximum selectivity for Hg(II) cations. Computational studies of the structural features of the metal complexes with WS-NCTPP help in establishing the geometry and binding interactions between the metal ions and the porphyrin nucleus. The results demonstrate the promising potential of the NCTPP probe which should be utilized for detection of heavy metal ions, especially mercury, in the near future.

DNAzyme-based biosensors for mercury (Ⅱ) detection: Rational construction, advances and perspectives

Mercury contamination is one of the most severe issues in society due to its threats to public health and the ecological system. However, traditional methods for mercury ion detection are still limited by their time-consuming procedures, requirement of expensive instruments, and low selectivity. In recent decades, tremendous progress has been made in the development of functional nucleic acid-based, especially DNAzyme sensors for mercury (Ⅱ) (Hg²⁺) determination, including RNA-cleaving DNAzymes and G-quadruplex-based DNAzymes in particular. Researchers have heavily studied the construction of Hg²⁺ sensors, mainly originating from in vitro selection-derived DNAzymes, by incorporating T-Hg²⁺-T recognition moieties in existing DNAzyme scaffolds, and interfacing Hg²⁺-sensitive sequences with nanomaterials. In the last case, the employment of materials (as quenchers, signal transducers and DNA immobilizers) enriches the application scenarios of current Hg²⁺-DNAzymes, due to a combination of their functions. We summarize a broad range of sensing approaches, including optical, electrochemical, and other sensing methods, and compare their features. This review elaborates on the rational design strategies for engineering DNAzymes to selectively sense Hg²⁺, critically discusses their properties in different application scenarios, and summarizes recent advances in this field. Additionally, current progress, challenges and future perspectives are also discussed. This minireview provides deeper insights into the chemistry of these functional nucleic acids when working with Hg²⁺, explains the design ideas of DNAzyme-sensors in each platform, and reveals potential opportunities in developing more advanced DNAzyme sensors for the highly selective and sensitive recognition of Hg²⁺. ENVIRONMENTAL IMPLICATION: Mercury is one of the most toxic metallic contaminants due to its high toxicity, non-biodegradability, and serious human health risks when accumulated in the body. In the recent decade, intensive studies have focused on exploring mercury sensors by combining DNAzymes with various sensing methods, paving a promising avenue to gain ultra-high sensitivity and selectivity. However, so far, no review has introduced the recent advances on DNAzyme-based sensors for mercury detection in a critical way. In this review, we comprehensively summarized the studies on DNAzyme-based sensors for mercury detection using various sensing techniques including optical, electrochemical and other sensing methods.

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.

Nucleic Acid Tests for Clinical Translation

Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are natural biopolymers composed of nucleotides that store, transmit, and express genetic information. Overexpressed or underexpressed as well as mutated nucleic acids have been implicated in many diseases. Therefore, nucleic acid tests (NATs) are extremely important. Inspired by intracellular DNA replication and RNA transcription, in vitro NATs have been extensively developed to improve the detection specificity, sensitivity, and simplicity. The principles of NATs can be in general classified into three categories: nucleic acid hybridization, thermal-cycle or isothermal amplification, and signal amplification. Driven by pressing needs in clinical diagnosis and prevention of infectious diseases, NATs have evolved to be a rapidly advancing field. During the past ten years, an explosive increase of research interest in both basic research and clinical translation has been witnessed. In this review, we aim to provide comprehensive coverage of the progress to analyze nucleic acids, use nucleic acids as recognition probes, construct detection devices based on nucleic acids, and utilize nucleic acids in clinical diagnosis and other important fields. We also discuss the new frontiers in the field and the challenges to be addressed.

Paper and Other Fibrous Materials-A Complete Platform for Biosensing Applications

Paper-based analytical devices (PADs) and Electrospun Fiber-Based Biosensors (EFBs) have aroused the interest of the academy and industry due to their affordability, sensitivity, ease of use, robustness, being equipment-free, and deliverability to end-users. These features make them suitable to face the need for point-of-care (POC) diagnostics, monitoring, environmental, and quality food control applications. Our work introduces new and experienced researchers in the field to a practical guide for fibrous-based biosensors fabrication with insight into the chemical and physical interaction of fibrous materials with a wide variety of materials for functionalization and biofunctionalization purposes. This research also allows readers to compare classical and novel materials, fabrication techniques, immobilization methods, signal transduction, and readout. Moreover, the examined classical and alternative mathematical models provide a powerful tool for bioanalytical device designing for the multiple steps required in biosensing platforms. Finally, we aimed this research to comprise the current state of PADs and EFBs research and their future direction to offer the reader a full insight on this topic.

DNA rearrangement on the octadecylamine modified graphite surface by heating and ultrasonic treatment

The evolution of single-stranded DNA (ssDNA) assembly on octadecylamine (ODA) modified highly oriented pyrolytic graphite (HOPG) surface by heating and ultrasonic treatment has been studied for the first time. We have observed that DNA on the ODA coated HOPG surface underwent dramatic morphological changes as a function of heating and ultrasonic treatment. Ordered DNA firstly changed to random aggregates by heating and then changed to three-dimensional (3D) networks by ultrasonic treatment. This finding points to previously unknown factors that impact graphite-DNA interaction and opens new opportunities to control the deposition of DNA onto graphitic substrates. In this way, we built a cost-effective method to produce large-scale 3D ssDNA networks. All of these studies pave the way to understand the properties of DNA-solid interface, design novel nanomaterials, and improve the sensitivity of DNA biosensors.

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.

Recent development of advanced biotechnology for wastewater treatment

The importance of highly efficient wastewater treatment is evident from aggravated water crises. With the development of green technology, wastewater treatment is required in an eco-friendly manner. Biotechnology is a promising solution to address this problem, including treatment and monitoring processes. The main directions and differences in biotreatment process are related to the surrounding environmental conditions, biological processes, and the type of microorganisms. It is significant to find suitable biotreatment methods to meet the specific requirements for practical situations. In this review, we first provide a comprehensive overview of optimized biotreatment processes for treating wastewater during different conditions. Both the advantages and disadvantages of these biotechnologies are discussed at length, along with their application scope. Then, we elaborated on recent developments of advanced biosensors (i.e. optical, electrochemical, and other biosensors) for monitoring processes. Finally, we discuss the limitations and perspectives of biological methods and biosensors applied in wastewater treatment. Overall, this review aims to project a rapid developmental path showing a broad vision of recent biotechnologies, applications, challenges, and opportunities for scholars in biotechnological fields for "green" wastewater treatment.

Fluorometric determination of mercury(II) via a graphene oxide-based assay using exonuclease III-assisted signal amplification and thymidine-Hg(II)-thymidine interaction

A highly sensitive and selective fluorometric method is described for determination of mercury(II). It is based on (a) the use of graphene oxide (GO) acting as a quencher of the fluoresence of the carboxy-fluorescein (FAM), and (b) of Hg(II)-triggered cleavage of the newly formed nucleic acid sequences harbored blunt 3'-hydroxyl termini by exonuclease III (Exo III) that leads to signal amplification. Two DNA probes are used, viz. a capture probe (CP) and a help probe; HP) that is partially complementary. In the absence of Hg(II), the FAM-labeled hairpin (signal probe, SP) is adsorbed onto the surface of GO via π-stacking interactions. CP blocks the release of the HP for binding to SP. This results in quenching of the green fluorescence of the label. Upon addition of Hg(II), the linear structure of CP is converted to a hairpin structure due to the formation of thymidine-Hg(II)-thymidine duplexes. HP is released from the CP/HP hybrids, and this causes SP to be released from from GO and fluorescence to be recovered. The signal is strongly amplified by using Exo III-assisted targeting and recycling of HP. Hence, Hg(II) can be detected via the strong increase in fluorescence. The method has a linear response in the 0.1 to 30 nM Hg(II) concentration range and a 10 pM detection limit. It was applied to the determination of Hg(II) in three (spiked) Chinese medicines. Graphical abstract Schematic representation of fluorescence sensing strategy for Hg²⁺ by using graphene oxide as a quencher and exonuclease III-assisted signal amplification.