Development of a two-in-one integrated bioassay for simultaneous and rapid on-site detection of Pb2+ and Hg2+ in water

Recent developments of (bio)-sensors for detection of main microbiological and non-biological pollutants in plastic bottled water samples: A critical review

The importance of water in all biological processes is undeniable. Ensuring access to clean and safe drinking water is crucial for maintaining sustainable water resources. To elaborate, the consumption of water of inadequate quality can have a repercussion on human health. Furthermore, according to the instability of tap water quality, the consumption rate of bottled water is increasing every day at the global level. Although most people believe bottled water is safe, it can also be contaminated by microbiological or chemical pollution, which can increase the risk of disease. Over the last decades, several conventional analytical tools applied to analyze the contamination of bottled water. On the other hand, some limitations restrict their application in this field. Therefore, biosensors, as emerging analytical method, attract tremendous attention for detection both microbial and chemical contamination of bottled water. Biosensors enjoy several facilities including selectivity, affordability, and sensitivity. In this review, the developed biosensors for analyzing contamination of bottled water were highlighted, as along with working strategies, pros and cons of studies. Challenges and prospects were also examined.

A near-infrared fluorescent ratiometric probe with large Stokes shift for multi-mode sensing of Pb2+ and bioimaging

Pb2+ is a heavy metal ion pollutant that poses a serious threat to human health and ecosystems. The conventional methods for detecting Pb2+ have several limitations. In this study, we introduce a novel fluorescent probe that enables the detection of Pb2+ in the near-infrared region, free from interference from other common ions. A unique characteristic of this probe is its ability to rapidly and accurately identify Pb2+ through ratiometric measurements accompanied by a large Stokes shift of 201 nm. The limit of detection achieved by probe was remarkably low, surpassing the standards set by the World Health Organization, and outperforming previously reported probes. To the best of our knowledge, this is the first organic small-molecule fluorescent probe with both near-infrared emission and ratiometric properties for the detection of Pb2+. We present a triple-mode sensing platform constructed using a probe that allows for the sensitive and selective recognition of Pb2+ in common food items. Furthermore, we successfully conducted high-quality fluorescence imaging of Pb2+ in various samples from common edible plants, HeLa cells, Caenorhabditis elegans, and mice. Importantly, the probe-Pb2+ complex exhibited tumour-targeting capabilities. Overall, this study presents a novel approach for the development of fluorescent probes for Pb2+ detection.

A novel ratiometric electrochemical aptasensor based on M-shaped functional DNA complexes for simultaneous detection of trace lead and mercury ions in series aquatic edible vegetables

Simultaneous quantification of multiple heavy metal ions (HMIs) is essential due to enhanced toxicity induced by synergistic effects. The currently available detection methods suffer from drawbacks such as costly devices, poor anti-interference, and specificity. In this work, a ratiometric electrochemical aptasensor for simultaneous detection of trace lead (Pb2+) and mercury ions (Hg2+) was developed. Here, a metal-organic framework, UiO-66-CNTs, with inherent and stable electrochemical signal was used for loading complementary strands (CSs) and internal reference. Guanine-rich and thymine-rich oligonucleotides, labelled with carbon dots (CDs), acted as aptamers (Apts) and hybridized with CSs to form M-shaped DNA complexes. Pb2+ and Hg2+ could be recognized and captured by Apts to form Pb2+-G-quadruplex and T-Hg2+-T complexes, leading to the destruction of M-shaped DNA complexes and changes in CDs' signal. The current ratios, ICDs/IUiO-66-CNTs, were applied to quantify Pb2+ and Hg2+. Benefiting from the anti-interference ability of the ratiometric strategy and the specificity of Apts, the proposed method enabled detection Pb2+ and Hg2+ through simple instrumentation, with detection limits of 2.0 ng mL-1 and 0.5 ng mL-1. Moreover, it was applied to assess Pb2+ and Hg2+ contamination in series of aquatic edible vegetables. The experimental results were consistent with inductively coupled plasma-mass spectrometry (ICP-MS), demonstrating its potential in practical applications.

Label-free fluorescence detection of mercury ions based on thymine-mercury-thymine structure and CRISPR-Cas12a

In this work, we developed a novel label-free fluorescent sensor for the highly sensitive detection of mercury ions (Hg2+) based on the coordination chemistry of thymine-Hg2+-thymine (T-Hg2+-T) structures and the properties of CRISPR-Cas12a systems. Most notably, two T-rich sequences (a blocker and an activator) were designed to form stable double-stranded structures in the presence of Hg2+ via the T-Hg2+-T base pairing. The formation of T-T mismatched double-stranded DNA between the blocker and the activator prevented the cleavage of G-rich sequences by Cas12a, allowing them to fold into G-quadruplex-thioflavin T complexes, resulting in significantly enhanced fluorescence. Under the optimized conditions, the developed sensor showed an excellent response for Hg2+ detection in the linear range of 0.05 to 200 nM with a detection limit of 23 pM. Moreover, this fluorescent sensor exhibited excellent selectivity and was successfully used for the detection of Hg2+ in real samples of Zhujiang river water and tangerine peel, demonstrating its potential in environmental monitoring and food safety applications.

Highly selective chemosensor for the sensitive detection of Hg2+ in aqueous media and its cell imaging application

The deleterious toxicity of Hg²⁺ on ecological and biological system makes it crucial for the precise monitoring of Hg²⁺. Herein, we prepared a novel "turn-on" chemosensor N'-(4-(methylthio)butan-2-ylidene) rhodamine B hydrazide (denoted as MTRH) by a simple two-step reaction. MTRH exhibited an ultra-low detection limit (LOD) in fluorescence measurement of Hg²⁺ in pure aqueous media, which was estimated to be 1.3 × 10^-9 mol·L^-1. Moreover, the proposed chemosensor holds the ability of visualizing Hg²⁺ by the distinct color change of the solution. The corresponding recognition mechanism was investigated by Job's plots, mass spectrometry and DFT calculation analysis. Importantly, the characteristics such as high sensitivity, low cytotoxicity and good biocompatibility of MTRH exhibited in the application of detecting Hg²⁺ in real water sample and bioimaging of intracellular Hg²⁺ prove that MTRH is a promising tool to evaluate the levels of Hg²⁺ in complex biological systems.

Programmable Nanostructures Based on Framework-DNA for Applications in Biosensing

DNA has been actively utilized as bricks to construct exquisite nanostructures due to their unparalleled programmability. Particularly, nanostructures based on framework DNA (F-DNA) with controllable size, tailorable functionality, and precise addressability hold excellent promise for molecular biology studies and versatile tools for biosensor applications. In this review, we provide an overview of the current development of F-DNA-enabled biosensors. Firstly, we summarize the design and working principle of F-DNA-based nanodevices. Then, recent advances in their use in different kinds of target sensing with effectiveness have been exhibited. Finally, we envision potential perspectives on the future opportunities and challenges of biosensing platforms.

A Critical Review on the Development of Optical Sensors for the Determination of Heavy Metals in Water Samples. The Case of Mercury(II) Ion

Recent publications are reviewed concerning the development of sensors for the determination of mercury in drinking water, based on spectroscopic methodologies. A critical analysis is made of the specific details and figures of merit of the developed protocols. Special emphasis is directed to the validation and applicability to real samples in the usual concentration range of mercury, considering the maximum allowed limits in drinking water established by international regulations. It was found that while most publications describe in detail the synthesis, structure, and physicochemical properties of the sensing phases, they do not follow the state of the art in the analytical developments. Recommendations are provided regarding the proper method development and validation, including the setting of the calibration concentration range, the correct estimation of the limits of detection and quantitation, the concentration levels to be set for producing spiked water samples, the number of real samples for adequate validation, the comparison of the developed method with a reference technique, and other analytical features which should be followed.

Detection of Heavy Metal Ions by Ratiometric Photoelectric Sensor

In recent years, heavy metal pollution has become increasingly serious. Heavy metals exist in an environment mainly in the form of ions (heavy metal ions, HMs). They can contaminate food, water, soil, and the atmosphere, leading to serious harm to plants and animals. With high bioavailability and nonbiodegradability, HMs can accumulate through biomagnification. Consequently, heavy metal pollution has become the cause of many fatal diseases threatening human health and ecological environment. Therefore, the accurate detection of HMs is vital and necessary. In this paper, the harm and limit standards of heavy metals were systematically summarized and the common analysis methods were overviewed and compared. Specifically, the latest research progress of ratiometric photoelectric sensor, including optical and electrical sensor, were mainly described. The research status and advantages and disadvantages of a photoelectric sensor were summarized. Furthermore, the future directions were proposed, which provided the reference for the further research and application of the ratiometric photoelectric sensor.

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.

Amplification of the Fluorescence Signal with Clustered Regularly Interspaced Short Palindromic Repeats-Cas12a Based on Au Nanoparticle-DNAzyme Probe and On-Site Detection of Pb2+ Via the Photonic Crystal Chip

Although great headway has been made in DNAzyme-based detection of Pb²⁺, its adaptability, sensitivity, and accessibility in complex media still need to be improved. For this, we introduce new ways to surmount these hurdles. First, a spherical nucleic acid (SNA) fluorescence probe (Au nanoparticles-DNAzyme probe) is utilized to specifically identify Pb²⁺ and its suitability for precise detection of Pb²⁺ in complex samples due to its excellent nuclease resistance. Second, the sensitivity of Pb²⁺ detection is greatly enhanced via the use of a clustered regularly interspaced short palindromic repeats-Cas12a with target recognition accuracy to amplify the fluorescent signal upon the trans cleavage of the SNA (signal probe), and the limit of detection reaches as low as 86 fM. Third, we boost the fluorescence on photonic crystal chips with a bionic periodic arrangement by employing a straightforward detection device (smartphone and portable UV lamp) to achieve on-site detection of Pb²⁺ with the limit of detection as low as 24 pM. Based on the abovementioned efforts, the modified Pb²⁺ fluorescence sensor has the advantages of higher sensitivity, better specificity, accessibility, less sample consumption, and so forth. Moreover, it can be applied to accurately detect Pb²⁺ in complex biological or environmental samples, which is of great promise for widespread applications.