Polythymine Oligonucleotide-Modified Gold Electrode for Voltammetric Determination of Mercury(II) in Aqueous Solution

Identification of medium- and mechanism-related pitfalls towards improved performance and applicability of electrochemical mercury(II) aptasensors

The importance of understanding the mercury (II) ion interactions with thymine-rich DNA sequences is the reason for multiple comparative investigations carried out with the use of optical detection techniques directly in the depth of solution. However, the results of such investigations have limited applicability in the interpretation of the Hg2+ binding phenomenon by DNA sequences in thin, interfacial (electrode/solution), self-organized monolayers immobilized on polarizable surfaces, often used for sensing purposes in electrochemical biosensors. Overlooking the careful optimization of the measurement conditions is the source of discrepancies in the interpretation of the registered electrochemical signal. In this study, the chosen effects accompanying the efficiency of surface related recognition of Hg2+ by polyThymine DNA sequences labelled with methylene blue were investigated by voltammetry, QCM and spectro-electrochemical techniques. As was shown, the composition of the biosensing layer and buffers or the analytical procedures have a significant impact on the registered electrochemical readout which translates into signal stability, the biosensor's working parameters or even the mechanism of detection. After elucidation of the above factors, the complete and ready-to-use biosensor-based analytical solution was proposed offering subpicomolar mercury ion determination with high selectivity (also in aqueous real samples), reusability, and high signal stability even after long-term storage. The developed procedures were successfully used during the miniaturization process with self-prepared (PVD) elastic transducers. The obtained sensor, together with the simplicity of its use, low manufacturing cost, and attractive analytical parameters (i.e., LOD < < Hg2+ WHO limit) can present an interesting alternative for on-site mercury ion detection in environmental samples.

Electric Field-Induced Specific Preconcentration to Enhance DNA-Based Electrochemical Sensing of Hg2+ via the Synergy of Enrichment and Self-Cleaning

Efficient preconcentration is critical for sensitive and selective electrochemical detection of metal ions, but rapid specific enrichment with depressed absorption of interfering ions at the electrode is challenging. Here, we proposed an electric field-induced specific preconcentration to boost the analytical performance of DNA-based electrochemical sensors for Hg²⁺ detection. As for such preconcentration, a positive external electric field was first used to enrich Hg²⁺ at an electrode assembled with T-rich DNA, thus boosting T-Hg²⁺-T recognitions. The following applied inverse electric field strips the nonspecifically absorbed Hg²⁺ and other interfering ions, thus depressing matrix interferences via self-cleaning. Based on this principle, we designed a portable device to realize programmable control of electric fields; a T-Hg²⁺-T recognition-based electrochemical sensor was thus fabricated as a model platform to assess the feasibility of electric field-induced preconcentration. The experimental results revealed that such a strategy decreased the time of T-Hg²⁺-T-based recognition from 60 to 20 min and led to detection with better reproducibility by depressing the influence of free Hg²⁺ as well as interfering ions. This strategy offered Hg²⁺ detection limits of 0.01 pM─three-fold better than that without preconcentration─within 22 min. The proposed preconcentration strategy offers a new way to enhance the analytical performance of sensing at the solid-liquid interface.

Ultrasensitive Au Nanooctahedron Micropinball Sensor for Mercury Ions

Mercury ion (Hg²⁺) is one of the most toxic heavy metals that has severe adverse effects on the environment and human organs even at very low concentrations. Therefore, highly sensitive and selective detection of Hg²⁺ is desirable. Here, we introduce plasmonic micropinball constructed from Au nanooctahedron as a three-dimensional surface-enhanced Raman spectroscopy (SERS) platform, enabling ultrasensitive detection of trace Hg²⁺ ions. Typically, strong SERS signals could be obtained when the single-stranded DNA structure converts to the hairpin structure in the presence of Hg²⁺ ions, due to the formation of thymine (T)-Hg²⁺-T. As a result, the detection limit of Hg²⁺ ions is as low as 1 × 10^-16 M, which is far below compared to that reported for conventional analytical strategies. Moreover, to achieve rapid multiple detection, we combine the micropinball sensors with microflow tube online detection. Our platform prevents cross-talk and tube contamination, allowing multiassay analysis, rapid identification, and quantification of different analytes and concentrations across separate phases.

Ultrasensitive sliver nanorods array SERS sensor for mercury ions

With years of outrageous mercury emissions, there is an urgent need to develop convenient and sensitive methods for detecting mercury ions in response to increasingly serious mercury pollution in water. In the present work, a portable, ultrasensitive SERS sensor is proposed and utilized for detecting trace mercury ions in water. The SERS sensor is prepared on an excellent sliver nanorods array SERS substrate by immobilizing T-component oligonucleotide probes labeled with dye on the 3'-end and -SH on the 5'-end. The SERS sensor responses to the specific chemical bonding between thymine and mercury ions, which causes the previous flexible single strand of oligonucleotide probe changing into rigid and upright double chain structure. Such change in the structure drives the dyes far away from the excellent SERS substrate and results in a SERS signal attenuation of the dye. Therefore, by monitoring the decay of SERS signal of the dye, mercury ions in water can be detected qualitatively and quantitatively. The experimental results indicate that the proposed optimal SERS sensor owns a linear response with wide detecting range from 1pM to 1μM, and a detection limit of 0.16pM is obtained. In addition, the SERS sensor demonstrates good specificity for Hg²⁺, which can accurately identify trace mercury ions from a mixture of ten kinds of other ions. The SERS sensor has been further executed to analyze the trace mercury ions in tap water and lake water respectively, and good recovery rates are obtained for sensing both kinds of water. With its high selectivity and good portability, the ultrasensitive SERS sensor is expected to be a promising candidate for discriminating mercury ions in the fields of environmental monitoring and food safety.

Development of mercury (II) ion biosensors based on mercury-specific oligonucleotide probes

Mercury (II) ion (Hg(2+)) contamination can be accumulated along the food chain and cause serious threat to the public health. Plenty of research effort thus has been devoted to the development of fast, sensitive and selective biosensors for monitoring Hg(2+). Thymine was demonstrated to specifically combine with Hg(2+) and form a thymine-Hg(2+)-thymine (T-Hg(2+)-T) structure, with binding constant even higher than T-A Watson-Crick pair in DNA duplex. Recently, various novel Hg(2+) biosensors have been developed based on T-rich Mercury-Specific Oligonucleotide (MSO) probes, and exhibited advanced selectivity and excellent sensitivity for Hg(2+) detection. In this review, we explained recent development of MSO-based Hg(2+) biosensors mainly in 3 groups: fluorescent biosensors, colorimetric biosensors and electrochemical biosensors.

Sensitive naked-eye detection of Hg2+based on the aggregation and filtration of thymine functionalized vesicles caused by selective interaction between thymine and Hg2+

A sensitive and low-cost method based on rapid interaction between functionalized PDA vesicles and Hg²⁺for the naked-eye detection of Hg²⁺.

Electrogenerated chemiluminescence detection of mercury(II) ions based on DNA probe labeled with ruthenium complex

A novel mercury(II) ion (Hg(2+)) biosensor with electrogenerated chemiluminescence (ECL) detection using tris(2,2'-bipyridyl) ruthenium derivatives (ruthenium complex) as labeling was developed in the prescent work. One thymine (T)-rich single-strand DNA (ssDNA) labeled with a ruthenium complex was taken as an ECL probe. When the other T-rich capture ssDNA was self-assembled onto the surface of a gold electrode with a thiol group, and then hybridized with the ECL probe to form double-strand DNA (dsDNA) structures in the presence of Hg(2+), a strong ECL response was electrochemically generated. The ECL intensity was linearly related to the concentration of Hg(2+) in the range from 1.0 × 10(-6) to 1 × 10(-9) M with a detection limit of 3.0 × 10(-10) M. The relative standard deviation was 4.1% at 1.0 × 10(-7) M Hg(2+) (n = 5). This work demonstrates that the combination of the strongly binding T-rich DNA to Hg(2+) with the highly sensitive ECL technique to design an ECL Hg(2+) biosensor is a great promising approach for the determination of metal ions.