Valence States Modulation Strategy for Picomole Level Assay of Hg2+ in Drinking and Environmental Water by Directional Self-Assembly of Gold Nanorods

Sensitive and quick electrochemiluminescence biosensor for the detection of reactive oxygen species in seminal plasma based on the valence regulation of gold nanoclusters

BACKGROUND

Gold nanoclusters (AuNCs) obtained by electroreduction have excellent electrochemiluminescence (ECL) properties, and its ECL intensity is regulated by the valence state. In addition, their ECL signals can be rapidly quenched by reactive oxygen species (ROS). Based on this observation, a sensitive ROS biosensor was designed based on valence regulation of AuNCs. Excessive ROS in seminal plasma can lead to male infertility, and the short half-life and instability of ROS pose a challenge for their detection. Since valence regulation can be done quickly and is very sensitive, this ECL biosensor holds promise to address this issue.

RESULTS

The ECL mechanism of AuNCs and the quenching mechanism of AuNCs by ROS were explored, mainly because ROS change the valence state of AuNCs. The ECL signals of the biosensor have a linear relationship with logarithm of the target concentration in the range of 1.0 × 10-8 to 1.0 × 10-3 M and 1.0 × 10-3 to 1.0 × 10-1 M, with a detection limit of 0.75 × 10-10 M (S/N = 3). The biosensor enables rapid one-step detection of ROS and has the advantage of being stable and reusable. More notably, the results of 57 real samples showed that the biosensor can be used to accurately assess the concentration of seminal plasma ROS, guiding the monitoring of sperm quality and the diagnosis of male infertility.

SIGNIFICANCE

Compared with the traditional strategy of applying AuNCs only as a luminescent body, this strategy of regulating the valence state of AuNCs to achieve sensitive and rapid detection broadens the application of AuNCs in the field of analysis. Compared with other ROS detection strategies, the one-step immediate detection method effectively avoids the inaccuracy caused by the short half-life and natural dissipation of ROS, and is expected to improve the accuracy and efficiency of clinical diagnosis.

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.

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.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

How Stabilizers and Reducing Agents Affect the Formation of Nanogold Amalgams

The influence of mercury on the morphology and formation mechanism of gold amalgams in the presence of different reducing agents (ascorbic acid and sodium borohydride) was systematically studied. In the presence of cetyltrimethylammonium bromide (CTAB), chemical reducing agents not only reduced mercury ions in the solution but also replaced the CTAB molecules on the surface of the gold nanorod. The stability of the reducing agents in the colloidal system and the combining capacity of the reducing agent to the gold nanoparticles can affect the alloying process of mercury and gold, thereby forming a rod-shaped or spherical gold amalgam. Once CTAB was removed, a similar transformation process occurs between the gold nanorods and mercury. In addition, without the presence of a stabilizer, mercury that cannot be dispersed undergoes Ostwald ripening growth, which causes the gold amalgam nanoalloys to form a tip-to-tip structure as a result of mercury enrichment because of the weak shielding effects occurring at the tips of the gold nanorods. After the CTAB molecules were substituted with ascorbic acid and alkylthiol molecules, the question of whether the shielding effect weakened or disappeared was also investigated. By investigation, this research found that, in comparison to the blocking effect of CTAB molecules, the binding ability of the reducing agent to gold plays a dominant role in the nanoamalgam formation process.

Analysis of lead forms and transition in agricultural soil by nano-fluorescence method

The physicochemical properties of gold nanorods were used to develop many methods and techniques of detecting heavy metals recently. In this paper, the feasibility of gold nanorods was studied to detect metal lead in agricultural soil. The effects of soil properties on the form change of lead in soil were explored by gold nanorod detection technology. The results showed that the humic acid significantly increased Pb mobility and ion state exchanging. It also increased the lead content of organic bound state and Fe-Mn oxides state. And the detection process by gold nanorods proved to be a more simple and convenient method.

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.

Redox-modulated colorimetric detection of ascorbic acid and alkaline phosphatase activity with gold nanoparticles

Gold nanoparticles (AuNPs) exhibit characteristic absorption peaks in the ultraviolet visible region due to their special surface plasmon resonance effect. This characteristic absorption peak would change with the relative colour varying from wine red to orange-yellow upon sequential addition of ascorbic acid (AA) into the mixture of AuNPs and Ag(I). Similar observations also could be found when the hydrolysis product of sodium l-ascorbyl-2-phosphate with alkaline phosphatase (ALP) was used as an alternative to AA. Results of structure characterization confirmed that the phenomena were due to the reduction of Ag(I) to Ag(0) on the surface of AuNPs and the formation of core-shell AuNPs@Ag. Therefore, a colorimetric assay for rapid visual detection of AA and ALP based on redox-modulated silver deposition on AuNPs has been proposed. Under the optimal experimental conditions, the absorbance variation ΔA_{522 nm} /A_{370 nm} of AuNPs was proportional to the concentration of AA (5-60 μmol/L) and ALP (3-18 U/L) with the corresponding detection limit of 2.44 μmol/L for AA and 0.52 U/L for ALP. The assay showed excellent selectivity towards AA and ALP. Moreover, the assay has been applied to detect AA and ALP activity in real samples with satisfying results.

A gold nanorod-based plasmonic platform for multi-logic operation and detection

A multi-logic gate platform was designed based on morphological changes of gold nanorods (AuNRs) resulted from the iodine-mediated etching. By utilizing the anti-etching effects of mercapto compounds and Au-Hg amalgams as well as the etch-promoting effect of Cu²⁺, we successfully built five logic gates, namely, AND, NOR, XNOR, YES and IMPLY, along with a three-input combinational logic gate XNOR-IMPLY. The platform was versatile and easy to use, did not require complex surface modification or separation/purification steps as the conventional AuNR-based logic gates did. The logic operations, accompanied by distinct color changes, enabled multi-task detection by naked-eye for 'have' or 'none' discrimination or highly sensitive and selective analysis by spectroscopy with wide linear ranges.