Au@gap@AuAg Nanorod Side-by-Side Assemblies for Ultrasensitive SERS Detection of Mercury and its Transformation

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Preparation of arsenic(III) monoclonal antibodies and preliminary evaluation of a novel silver-coated gold nanorod SERS immunoassay strip construction

Heavy metal pollution has become a growing concern in industrial, agricultural, and manufacturing processes, posing a significant threat to human health. Among these heavy metals, arsenic (As) is highly toxic and shares similar chemical properties and environmental behavior with other heavy metals. As(III) is particularly toxic compared to other forms of arsenic. Therefore, it is essential to develop a real-time, rapid, and sensitive method for the determination of As(III). In this study, we employed a unique bifunctional chelator, 1-(4-isothiocyanobenzyl)-ethylenediamine N,N,N',N'-tetraacetic acid (ITCBE), to prepare a complete antigen. Through a series of tests including balb/c mouse immunization, cell fusion (mouse L2041 spleen cells with mouse myeloma cells SP2/0), and subcloning, we generated four monoclonal cell lines (1C1, 2C2, 3A9, and 4A11). These cell lines demonstrated high purity, high affinity, and IC50 values of less than 50 μg mL-1. Monoclonal antibody 4A11, which exhibited a strong Raman signal, was selected as the probe, and Au@Ag 200 was utilized as the surface-enhanced Raman scattering (SERS) substrate for the preliminary establishment of SERS immunochromatographic test strips. The sensitivity of the SERS immunochromatographic test strips, measured through Raman signal detection, showed a significant improvement compared to the SERS immunochromatographic test strips analyzed by colorimetry (LOD = 49.43 μg mL-1 and LDR = 5.32-81.31 μg mL-1). The SERS immunochromatographic test strips achieved a LOD of 7.62 μg mL-1 and an LDR of 12.66-71.84 μg mL-1. This study presents innovative methodologies for the rapid detection of As(III) using SERS immunochromatographic test strips.

Fluorogenic response from DNA templated micrometer range self-assembled gold nanorod

Plasmonic gold nanorod (AuNR) on a macromolecular matrix exhibits an end-to-end (ETE) long-range self-assembly (AuNR)n with n > 100. In the case of small molecules as a template, the pre-synthesized macromolecular matrix is missing and this brings a synthetic challenge in directed long-range assembly of AuNR. Self-assembly with thiol-modified small DNA and AuNR shows a much short-range ETE assembly with n < 25 via a simple evaporation technique on a solid surface. In this study, the introduction of two short amine modified probe DNAs (∼2.5 nm) and one 22-mer complementary single strand (ss)-DNA template (∼7 nm) show the long-range ETE self-assembly of (AuNR)n with n > 130. In the solution state, the zigzag arrangement within the assembled structure controls the typical change in the absorption behavior for (AuNR)n ETE assembly. The formation of this long-range ETE self-assembly in a solution state was verified from the combined effect of fluorescence resonance energy transfer (FRET) and hotspot-induced fluorescence enhancement. The probe DNAs and templated DNA concentration on fluorescence enhancement have been varied to monitor the effect of (AuNR)n with n = ∼5-130 in ETE self-assembly. Primarily quenched FRET acceptor in the presence of AuNR decisively exhibits remarkable fluorogenic response in ETE self-assembly with maximum n value. Although the FRET efficiencies among the fluorophores are comparable, the fluorogenic boost in ETE AuNR is due to the increased number of intrinsic navigated hotspots in these assemblies.

A dicyanoisophorone-based ICT fluorescent probe for the detection of Hg2+ in water/food sample analysis and live cell imaging

Mercury ions are notoriously difficult to biodegradable, and its abnormal bioaccumulation in the human body through the food chain can cause various diseases. Therefore, the quantitative and real-time detection of Hg²⁺ is very extremely important. Herein, we have brilliant designed and synthesized (E)-O-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenyl) O-phenyl carbonothioate (ICM-Hg) as a selective fluorescent probe for Hg²⁺ detection in real samples and intracellular staining. ICM-Hg displayed high specificity toward Hg²⁺ by activating the intramolecular charge transfer (ICT) process, resulting in distinguished color change from colorless to bright yellow along with noticeable switch on yellow fluorescence emission. The fluorescent intensity of ICM-Hg at 585 nm shows a well linear relationship in the range of Hg²⁺ concentration (0-45 μM), and the detection of limit for Hg²⁺ is calculated to be 231 nM. Promisingly, ICM-Hg can efficiently detect Hg²⁺ in real samples including tap water, tea, shrimp, and crab with quantitative recovery as well as the intracellular fluorescence imaging.

Design, Fabrication, and Applications of SERS Substrates for Food Safety Detection: Review

Sustainable and safe food is an important issue worldwide, and it depends on cost-effective analysis tools with good sensitivity and reality. However, traditional standard chemical methods of food safety detection, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and tandem mass spectrometry (MS), have the disadvantages of high cost and long testing time. Those disadvantages have prevented people from obtaining sufficient risk information to confirm the safety of their products. In addition, food safety testing, such as the bioassay method, often results in false positives or false negatives due to little rigor preprocessing of samples. So far, food safety analysis currently relies on the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), HPLC, GC, UV-visible spectrophotometry, and MS, all of which require significant time to train qualified food safety testing laboratory operators. These factors have hindered the development of rapid food safety monitoring systems, especially in remote areas or areas with a relative lack of testing resources. Surface-enhanced Raman spectroscopy (SERS) has emerged as one of the tools of choice for food safety testing that can overcome these dilemmas over the past decades. SERS offers advantages over chromatographic mass spectrometry analysis due to its portability, non-destructive nature, and lower cost implications. However, as it currently stands, Raman spectroscopy is a supplemental tool in chemical analysis, reinforcing and enhancing the completeness and coverage of the food safety analysis system. SERS combines portability with non-destructive and cheaper detection costs to gain an advantage over chromatographic mass spectrometry analysis. SERS has encountered many challenges in moving toward regulatory applications in food safety, such as quantitative accuracy, poor reproducibility, and instability of large molecule detection. As a result, the reality of SERS, as a screening tool for regulatory announcements worldwide, is still uncommon. In this review article, we have compiled the current designs and fabrications of SERS substrates for food safety detection to unify all the requirements and the opportunities to overcome these challenges. This review is expected to improve the interest in the sensing field of SERS and facilitate the SERS applications in food safety detection in the future.

Recent advances of Au@Ag core-shell SERS-based biosensors

The methodological advancements in surface-enhanced Raman scattering (SERS) technique with nanoscale materials based on noble metals, Au, Ag, and their bimetallic alloy Au-Ag, has enabled the highly efficient sensing of chemical and biological molecules at very low concentration values. By employing the innovative various type of Au, Ag nanoparticles and especially, high efficiency Au@Ag alloy nanomaterials as substrate in SERS based biosensors have revolutionized the detection of biological components including; proteins, antigens antibodies complex, circulating tumor cells, DNA, and RNA (miRNA), etc. This review is about SERS-based Au/Ag bimetallic biosensors and their Raman enhanced activity by focusing on different factors related to them. The emphasis of this research is to describe the recent developments in this field and conceptual advancements behind them. Furthermore, in this article we apex the understanding of impact by variation in basic features like effects of size, shape varying lengths, thickness of core-shell and their influence of large-scale magnitude and morphology. Moreover, the detailed information about recent biological applications based on these core-shell noble metals, importantly detection of receptor binding domain (RBD) protein of COVID-19 is provided.

Revealing the alloying and dealloying behaviours in AuAg nanorods by thermal stimulus

Binary metallic nanocrystals are attractive as they offer an extra degree of freedom for structure and phase modulation to generate synergistic effects and extraordinary properties. However, whether the binary structures and phases at the nanoscale still follow the rules established on the bulk counterparts remains unclear. In this work, AuAg nanorods were used as a sample to probe into this issue. An in situ heating method by combining aberration-corrected transmission electron microscopes with a chip-based heating holder was employed to perform the heating experiments. It was found that the AuAg nanorods, which initially possessed heterostructures, can be designed and engineered to be gradient phase alloys with thermal pulses over 350 °C. Atomic diffusion inside the rod structures did not alter the shape of the rods but provided a route to fine-tune their properties. At higher temperatures, the discrepant sublimation behaviours between Au and Ag lead to dealloying of the nanorods. Durative sublimation of the Ag element can continuously tailor the lengths of the nanorods while concentrating the Au composition simultaneously. Especially, nearly pure Au nanocrystals can be obtained with the depletion of Ag by sublimation. These findings give insights into the nanoscale structure and phase behaviours in binary alloys and provide an alternative way to fine-tune their structure, phase, and properties.

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

Advances from conventional to real time detection of heavy metal(loid)s for water monitoring: An overview of biosensing applications

The rapid growth of the industrial sector has expedited the accumulation of heavy metal(loid)s in the environment at hazardous levels. The elements such as arsenic, lead, mercury, cadmium and chromium are lethal in terms of toxicity with severe health impacts. With issues like water scarcity, limitations in wastewater treatment, and costs pertaining to detection in environmental matrices; their rapid and selective detection for reuse of effluents is of the utmost priority. Biosensors are the futuristic tool for the accurate qualitative and quantitative analysis of a specific analyte and integrate biotechnology, microelectronics and nanotechnology to fabricate a miniaturized device without compromising the sensitivity, specificity and accuracy. The characteristic features of supporting matrix largely affect the biosensing ability of the device and incorporation of highly sensitive and durable metal organic frameworks (MOFs) are reported to enhance the efficiency of advanced biosensors. Electrochemical biosensors are among the most widely developed biosensors for the detection of heavy metal(loids), while direct electron transfer approach from the recognition element to the electrode has been found to decrease the chances of interference. This review provides an insight into the recent progress in biosensor technologies for the detection of prevalent heavy metal(loid)s; using advanced support systems such as functional metal-based nanomaterials, carbon nanotubes, quantum dots, screen printed electrodes, glass beads etc. The review also delves critically in comparison of various techno-economic studies and the latest advances in biosensor technology.

Inducing Ring Complexation for Efficient Capture and Detection of Small Gaseous Molecules Using SERS for Environmental Surveillance

Gas-phase surface-enhanced Raman scattering (SERS) remains challenging due to poor analyte affinity to SERS substrates. The reported use of capturing probes suffers from concurrent inconsistent signals and long response time due to the formation of multiple potential probe-analyte interaction orientations. Here, we demonstrate the use of multiple non-covalent interactions for ring complexation to boost the affinity of small gas molecules, SO₂ and NO₂ , to our SERS platform, achieving rapid capture and multiplex detection down to 100 ppm. Experimental and in-silico studies affirm stable ring complex formation, and kinetic investigations reveal a 4-fold faster response time compared to probes without stable ring complexation capability. By synergizing spectral concatenation and support vector machine regression, we achieve 91.7 % accuracy for multiplex quantification of SO₂ and NO₂ in excess CO₂ , mimicking real-life exhausts. Our platform shows immense potential for on-site exhaust and air quality surveillance.

Recent advances in the application of Raman spectroscopy for fish quality and safety analysis

Fish is one of the highly demanded aquatic products, and its quality and safety play a pivotal role in daily diet. However, the possible hazardous substance in perishable fish both in pre- and postharvest periods may decrease their values and pose a threat to public health. Laborious and expensive traditional methods drive the need of developing effective tools for detecting fish quality and safety properties in a rapid, nondestructive, and effective manner. Recent advances in Raman spectroscopy (RS) and surface-enhanced Raman scattering (SERS) have shown enormous potential in various aspects, which largely boost their applications in fish quality and safety evaluation. They have incomparable merits such as providing molecule fingerprint information and allowing for rapid, sensitive, and noninvasive detection with simple sample preparation. This review provides a comprehensive overview focusing on the applications of RS and SERS for fish quality assessment and safety inspection, highlighting the hazardous substance and illegal behavior both in preharvest (veterinary drug residues and environmental pollutants) and postharvest (freshness and illegal behavior) particularly. Moreover, challenges and prospects are also proposed to facilitate the vigorous development of RS and SERS. This review is aimed to emphasize potential opportunities for applying RS and SERS as promising techniques for routine food quality and safety detection. PRACTICAL APPLICATION: With these applications, it can be clearly indicated that RS and SERS are promising and powerful in fish quality and safety surveillance, thereby reducing the occurrence of commercial fraud and food safety issues. More efforts still should be concentrated on exploiting the high-performance Raman instruments, establishing a universal Raman database, developing reproducible SERS substrates and combing RS with other versatile spectral techniques to promote these technologies from laboratory to practice. It is hoped that this review should arouse more research interests in RS and SERS technologies for fish quality and safety surveillance, as well as provide more insights to make a breakthrough.

Toroidal dipole-modulated dipole-dipole double-resonance in colloidal gold rod-cup nanocrystals for improved SERS and second-harmonic generation

Colloidal metal nanocrystals (NCs) show great potential in plasmon-enhanced spectroscopy owing to their attractive and structure-depended plasmonic properties. Herein, unique Au rod-cup NCs, where Au nanocups are embedded on the one or two ends of Au nanorods (NRs), are successfully prepared for the first time via a controllable wet-chemistry strategy. The Au rod-cup NCs possess multiple plasmon modes including transverse and longitudinal electric dipole (TED and LED), magnetic dipole (MD), and toroidal dipole (TD) modulated LED resonances, producing large extinction cross-section and huge near-field enhancements for plasmon-enhanced spectroscopy. Particularly, Au rod-cup NCs with two embedded cups show excellent surface-enhanced Raman spectroscopy (SERS) performance than Au NRs (75.6-fold enhancement excited at 633 nm) on detecting crystal violet owing to the strong electromagnetic hotspots synergistically induced by MD, LED, and TED-based plasmon coupling between Au cup and rod. Moreover, the strong TD-modulated dipole-dipole double-resonance and MD modes in Au rod-cup NCs bring a 37.3-fold enhancement of second-harmonic generation intensity compared with bare Au NRs, because they can efficiently harvest photoenergy at fundamental frequency and generate large near-field enhancements at second-harmonic wavelength. These findings provide a strategy for designing optical nanoantennas for plasmon-enhanced applications based on multiple plasmon modes.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (SEM image of Au rod-one-cup NCs; TEM image of Au/PbS hybrids; SEM image of Au rod-two-cup NCs; low-amplification SEM image of Au rod-two-cup NCs; experimental extinction and calculated electric field distributions of Au NR excited at different wavelengths; calculated absorption and scattering spectra of Au rod-one-cup NCs; schematic illustration of the cut plane and the corresponding magnetic field distribution under L3 excitation; Raman spectra of CV (10^-6 M) adsorbed on Au rod-cup NCs with different cup sizes; calculated magnetic field distribution of Au rodcup NCs excited at 532 and 633 nm; calculated electric field distributions of Au rod-one-cup NC excited at 600 nm along TE and LE; the models of Au rod-cup NCs used in the simulations) is available in the online version of this article at 10.1007/s12274-022-4562-5.

Surface etching-dependent geometry tailoring and multi-spectral information of Au@AuAg yolk-shell nanostructure with asymmetrical pyramidal core: The application in Co2+ determination

In this paper, a novel Au@AuAg yolk-shell heterogeneous nanostructure is designed as plasmonic spectroscopic sensor based on surface etching for ultrasensitive detection of trace cobalt ions (Co²⁺). Due to the surface diffusion of gold atoms, the Ag at one end of the core gold nanobipyramids (Au NBPs) is retained, and Au@AuAg yolk-shell nanostructure with asymmetric core is prepared. The alloy shell is coupled to Au NBPs and the interface of asymmetric Ag respectively, the two local surface plasmon resonance bands will have obvious reverse changes depending on the surface morphology of the shell. By using this distinct plasmon response generated by Co²⁺ induced surface etching, which is driven by discrepancy of double-peaks, a sensing method has been established to realize multi-information spectral detection of Co²⁺. There is a good linear relationship between the intensity ratio and the Co²⁺ concentration in the range of 1-100 nM, in which the limit of detection is 0.2 nM. This method further improves the sensing capability by combining multiple pieces of strongly changing spectral information, and demonstrates great advantages and potential of Au@AuAg yolk-shell heterogeneous nanostructure as a multi-information plasmonic sensor based on etched shell surface for trace detection.

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.

In Situ Microfluidic SERS Chip for Ultrasensitive Hg2+ Sensing Based on I--Functionalized Silver Aggregates

Mercury(II) ions are causing serious environmental pollution and health damage. Developing a simple, rapid, and sensitive sensor for Hg²⁺ detection is of great significance. Herein, we demonstrate an I^--functionalized surface-enhanced Raman scattering (SERS) substrate for rapid and sensitive Hg²⁺ sensing on a highly integrated microfluidic platform. Based on the combination reaction between I^- and Hg²⁺, the Hg²⁺ sensing is achieved via the SERS intensity "turn-off" strategy, where HgI₂ precipitation is formed on an SERS substrate interface, dissociating the Raman reporters that coadsorbed with I^-. Owing to the strong binding constant between I^- and Hg²⁺, our I^--functionalized substrate demonstrates a very fast sensing response (∼150 s). Through reliable in situ SERS detection, a robust calibration curve between the "turn-off" signal and "lgC" is obtained in a broad concentration range of 10^-9 to 10^-13 M. Additionally, the detectable Hg²⁺ concentration can be as low as 1 fM. The good selectivity toward Hg²⁺ is also verified by testing about a dozen common metal ions in water, such as K⁺, Na⁺, Ca²⁺, Mg²⁺, and so forth. Furthermore, we apply the SERS sensor for real tap and lake water sample detection, and good recoveries of 113, 97, and 107% are obtained. With its advantages of high integration, simple preparation, fast response, high sensitivity, and reliability, the proposed I^--functionalized SERS sensor microfluidic chip can be a promising platform for real-time and on-site Hg²⁺ detection in natural water.

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.

A capillary-based SERS sensor for ultrasensitive and selective detection of Hg2+ by amalgamation with Au@4-MBA@Ag core-shell nanoparticles

A capillary-based SERS sensor was fabricated for ultrasensitive and selective detection of Hg²⁺ in water. Au@Ag core-shell NPs embedded with 4-mercaptobenzoic acid (4-MBA) (Au@4-MBA@Ag) were prepared by a seed growth method and fixed on the inner wall of the glass capillary to obtain the sensor. Owing to the amalgamation between Ag and Hg, the capillary-based SERS sensor can specifically recognize the reduced Hg²⁺ without any recognition element, and the resulted Ag/Hg amalgam can weaken the SERS activity of Ag shell; thus, the SERS intensity of the embedded 4-MBA at 1075 cm^-1 gradually decreased with the increase of Hg²⁺ concentration. Under the optimum condition, the fabricated sensor can sensitively determine Hg²⁺ in water with a limit of detection (LOD) as low as 0.03 nM. The capillary-based SERS sensor offers the advantages of simple preparation, superior stability, and high selectivity, which is promising for rapid and on-site detection of Hg²⁺ in water combined with a portable Raman device.

Logarithmic Data Processing Can Be Used Justifiably in the Plotting of a Calibration Curve

The article is a response to a recent opinion piece that log concentration values should not be applied in analytical chemistry. An essential aim in the development of analytical chemistry methods is to obtain more sensitive and accurate detection values. For the application of chemical analysis methods, the obtained experiment data need to fit with the mathematical functions in the first place. As influenced by different detection principles and analytical methods, data can be displayed in a coordinate system with two linear axes for linear function fitting, or the data can first be taken through a logarithmic transformation and then for function fitting. Using raw data or data after logarithmic transformation primarily depends on analytical principles, without special rules of data formats. For example, ultraviolet-visible spectrophotometric data are more suitable for direct linear fitting. However, enzyme-catalyzed reaction or electrochemical data in logarithmic form are more appropriate for function fitting. This transformation of data form will not affect the soundness of fit statistics; rather, it simplifies the complexity of function analysis and calculation, which are the essence of analytical chemistry. In this brief article, we provide justification and legitimacy of the application of logarithmic processing in various fields of quantitative analytical chemistry.

Poly(L-DOPA)-mediated bimetallic core-shell nanostructures of gold and silver and their employment in SERS, catalytic activity, and cell viability

Core-shell gold nanorod (AuNR)@silver (Ag) nanostructures with their unique properties have gained enormous interest and are widely utilized in various applications including sensor systems, catalytic reactions, diagnosis, and therapy. Despite the recent progress, simple, effective, low-cost, and easy-to-tune strategies are heavily required to fabricate these nanoparticles (NP) systems. For this, we propose the employment of the polymer of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) as a ligand molecule. A conformal thin layer of polymer of L-DOPA (PLDOPA) with its various functional groups enabled the reduction of silver ions onto the AuNRs and stabilization of the resultant NPs without using any surfactant, reducing agent, and seed material. The shape and growth model of the AuNR@Ag nanostructures was manipulated by simply tuning the amount of silver ions. This procedure created different NP morphologies ranging from concentric to acentric/island shape core-shell nanostructures. Also, even at the highest Ag deposition, the PLDOPA layer is still conformally present onto the Au@Ag core-shell NRs. The unique properties of NP systems provided remarkable characteristics in surface-enhanced Raman spectroscopy, catalytic activity, and cell viability tests.

One-Step Synthesis of Water-Soluble CdS Quantum Dots for Silver-Ion Detection

To realize fast synthesis of cadmium sulfide (CdS) quantum dots with a low-toxic material, a one-step synthesis method is investigated and conducted. Potato extract is used as a stabilizer and modifier, by which aqueous CdS quantum dots can be prepared at a lower temperature with a shorter time. Through systematic characterization and analysis, a green and fast synthesis mechanism is demonstrated in detail. And the nanoscale CdS quantum dots are uniform in size and dispersity. With low cost and high sensitivity, the prepared CdS quantum dots show promising application in silver-ion detection. This method shows great significance for an environmentally friendly and facile synthesis of CdS quantum dots.

A nanozyme-based enhanced system for total removal of organic mercury and SERS sensing

Total removal of organic mercury in industrial wastewater is a crucially important task facing environmental pollution in the current world. Herein, we demonstrate the fabrication of Au-NiFe layered double hydroxide (LDH)/rGO nanocomposite as not only an efficient nanozyme with oxidase-like activity but also an efficient surface-enhanced Raman spectroscopy (SERS) substrate to determine organic mercury, with the minimum detection concentration as low as 1 × 10^-8 M. According to the binding energy of X-Ray photoelectron spectrometer (XPS) and the free radicals of electron paramagnetic resonance (EPR) spectra, the mechanism of catalytic enhanced degradation is the production of Au-amalgam on Au surface, accelerating the electron transfer and the generation of O₂^•- radicals from oxygen molecules and •CH₃ radicals from the methyl group in MeHg to participate the oxidase-like reaction. Furthermore, the Au-NiFe LDH/rGO nanocomposite is able to degrade and remove 99.9% of organic mercury in two hours without the secondary pollution by Hg²⁺. In addition, the material can be used for the multiple degradation-regeneration cycles in actual applications, which is significant in terms of the environmental and economic point of view. This work may open a new horizon for both highly sensitive detection and thorough degradation of organic mercury in environmental science and technology.

Recent Advances in Nanotechnology-Based Biosensors Development for Detection of Arsenic, Lead, Mercury, and Cadmium

Heavy metals cause considerable environmental pollution due to their extent and non-degradability in the environment. Analysis and trace levels of arsenic, lead, mercury, and cadmium as the most toxic heavy metals show that they can cause various hazards in humans' health. To achieve rapid, high-sensitivity methods for analyzing ultra-trace amounts of heavy metals in different environmental and biological samples, novel biosensors have been designed with the participation of strategies applied in nanotechnology. This review attempted to investigate the novel, sensitive, efficient, cost-benefit, point of care, and user-friendly biosensors designed to detect these heavy metals based on functional mechanisms. The study's search strategies included examining the primary databases from 2015 onwards and various keywords focusing on heavy metal biosensors' performance and toxicity mechanisms. The use of aptamers and whole cells as two important bio-functional nanomaterials is remarkable in heavy metal diagnostic biosensors' bioreceptor design. The application of hybridized nanomaterials containing a specific physicochemical function in the presence of a suitable transducer can improve the sensing performance to achieve an integrated detection system. Our study showed that in addition to both labeled and label-free detection strategies, a wide range of nanoparticles and nanocomposites were used to modify the biosensor surface platform in the detection of heavy metals. The detection limit and linear dynamic range as an essential characteristic of superior biosensors for the primary toxic metals are studied. Furthermore, the perspectives and challenges facing the design of heavy metal biosensors are outlined. The development of novel biosensors and the application of nanotechnology, especially in real samples, face challenges such as the capability to simultaneously detect multiple heavy metals, the interference process in complex matrices, the efficiency and stability of nanomaterials implemented in various laboratory conditions.

Discussions of Fluorescence in Selenium Chemistry: Recently Reported Probes, Particles, and a Clearer Biological Knowledge

In this review from literature appearing over about the past 5 years, we focus on selected selenide reports and related chemistry; we aimed for a digestible, relevant, review intended to be usefully interconnected within the realm of fluorescence and selenium chemistry. Tellurium is mentioned where relevant. Topics include selenium in physics and surfaces, nanoscience, sensing and fluorescence, quantum dots and nanoparticles, Au and oxide nanoparticles quantum dot based, coatings and catalyst poisons, thin film, and aspects of solar energy conversion. Chemosensing is covered, whether small molecule or nanoparticle based, relating to metal ion analytes, H2S, as well as analyte sulfane (biothiols-including glutathione). We cover recent reports of probing and fluorescence when they deal with redox biology aspects. Selenium in therapeutics, medicinal chemistry and skeleton cores is covered. Selenium serves as a constituent for some small molecule sensors and probes. Typically, the selenium is part of the reactive, or active site of the probe; in other cases, it is featured as the analyte, either as a reduced or oxidized form of selenium. Free radicals and ROS are also mentioned; aggregation strategies are treated in some places. Also, the relationship between reduced selenium and oxidized selenium is developed.

Surface-Enhanced Raman Scattering Sensing of Transition Metal Ions in Waters

In this mini-review, we provide a coherent discussion on the sensing schemes exploited in the surface-enhanced Raman scattering (SERS) analysis of transition metal ions in waters. A critical approach was used where illustrative examples are selected to discuss key drawbacks and challenges associated with various experimental configurations and the employed enhancing substrates.

π-π stacking-directed self-assembly of nanoplatelets into diversified three-dimensional superparticles for high surface-enhanced Raman scattering

Ordered, hierarchical structures formed from nanoparticle (NP) self-assembly are of interest as they display the synergistic properties of the individual NP. Herein we report a one-pot approach to form and self-assemble gold (Au) nanoplatelets into brick-wall like (BWL) Au superparticles (AuSPs). We employ an aniline (ANI) derivative, N-(3-amidino)-aniline (NAAN) to reduce the Au precursor into Au nanoplatelets in the presence of Br^-1. The corresponding oxidation product, poly (N-(3-amidino)-aniline) (PNAAN) functions as the capping agent and enables the face-to-face self-assembly of Au nanoplatelets into BWL AuSPs via the π-π stacking interaction. Systematically tuning the reaction conditions leads to spherical, mushroom- or cauliflower-like AuSPs. The significant electromagnetic enhancement of AuSPs via the formation of the nanogaps produces high-density hotspots for excellent surface-enhanced Raman scattering (SERS) enhancement, enabling the ultrasensitive SERS assay with detection limit of pM. Moreover, the as-prepared AuSPs exhibited the intense SERS signals under laser excitation with different wavelength and the excellent reproducibility after long-duration exposure in different media. The developed SERS sensor has a great potential for a wide application of bioanalysis, clinic assays and environmental monitoring.

Highly sensitive detection of Pb2+ and Cu2+ based on ZIF-67/MWCNT/Nafion-modified glassy carbon electrode

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb²⁺ and Cu²⁺. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb²⁺ and Cu²⁺. In addition, it displayed a wide linear detection range of 1.38 nM-5 μM for Pb²⁺ and 1.26 nM-5 μM for Cu²⁺, a detection accuracy of about 1 nM for both Pb²⁺ and Cu²⁺, and an excellent stability for both Pb²⁺ and Cu²⁺. We also analyzed the real water sample taken from Changchun's Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

DNA-Driven Nanoparticle Assemblies for Biosensing and Bioimaging

DNA molecules with superior flexibility, affinity and programmability have garnered considerable attention for the controllable assembly of nanoparticles (NPs). By controlling the density, length and sequences of DNA on NPs, the configuration of NP assemblies can be rationally designed. The specific recognition of DNA enables changes to be made to the spatial structures of NP assemblies, resulting in differences in tailorable optical signals. Comprehensive information on the fabrication of DNA-driven NP assemblies would be beneficial for their application in biosensing and bioimaging. This review analyzes the progress of DNA-driven NP assemblies, and discusses the tunable configurations determined by the structural parameters of DNA skeletons. The collective optical properties, such as chirality, fluorescence and surface enhanced Raman resonance (SERS), etc., of DNA-driven NP assemblies are explored, and engineered tailorable optical properties of these spatial structures are achieved. We discuss the development of DNA-directed NP assemblies for the quantification of DNA, toxins, and heavy metal ions, and demonstrate their potential application in the biosensing and bioimaging of tumor markers, RNA, living metal ions and phototherapeutics. We hihghlight possible challenges in the development of DNA-driven NP assemblies, and further direct potential prospects in the practical applications of macroscopical materials and photonic devices.

Asymmetrical Molecular Decoration of Gold Nanorods for Engineering of Shape-Controlled AuNR@Ag Core-Shell Nanostructures

Gold-silver (Au@Ag) core-shell nanostructures have a stronger surface plasma response, wider absorption and scattering in the UV-vis-NIR region, and distinctive optical properties, which are widely explored in biosensors, information processing, photothermal therapy, and catalysis. Core-shell nanostructures are usually formed by the deposition of the second metal atoms onto the first core metal particles via the chemical wet method. The conventional approaches for the manipulation of the shape usually were done by homogeneous growth or etching of isotropic nanoparticles. Through in situ modification of the first metal core at the different locations, the different growth model of the second metal can be regulated to control the shapes of core-shell structures. Herein, we modified the gold nanorods (AuNRs) asymmetrically at the end and side parts using thiolated molecules to regulate the morphology of gold nanorod@silver (AuNR@Ag) core-shell nanoparticles. Interestingly, the obvious eccentric nanostructures of AuNR@Ag core-shell nanoparticles were obtained with the increase of the molecular weight of macromolecules modified at the end of AuNRs. Therefore the growth mode was adjusted from Frank-van der Merwe mode to Stranski-Krastanow mode. By changing the length of the hydrocarbon chain and functional groups of the small mercaptan molecules at the side of AuNRs, the silver shell exhibits selective growth at the side of the AuNRs, resulting in heterogeneous core-shell nanoparticles and various shapes of the AuNR@Ag core-shell. Our method opens up a new avenue toward preparing core-shell nanostructures with controlled shapes, and the obtained structures are promising in various applications.