Self-assembly of core-satellite gold nanoparticles for colorimetric detection of copper ions

A portable solid sampling visualization nano-sensor for soil Cd based on "three-phase transforming" technique

Direct analysis of solid samples is always challenging for ionic sensors due to solidified elemental presence and matrix interference. In this work, a "three-phase transforming" technique was first established to make solid sampling elemental sensors and visual detection possible in the future. For Cd transforming from soil samples, a metal ceramic heater (MCH) electrothermal vaporizer (ETV) coupled with a dielectric barrier discharge quartz trap (DBD-QT) was first utilized to fulfill the solid sampling and preconcentration of Cd in soil; for on-site analysis, a colorimetric sensor based on the trithiocyanuric acid (TMT) functionalized gold nanoparticles (AuNPs) was chosen as a chromogenic analysis model. The portable and miniature ETV-DBD apparatus directly introduced Cd from soil and then captured Cd, consuming only <130 W and 4.5 kg weight; finally, only 200 μL water was injected as eluent to dissolve Cd for the following colorimetric detection. Herein, the Cd analyte underwent a "three-phase transforming" from solid (Cd compounds in soil), to aerosol (vaporization and transportation), to solid (Cd oxides trapped on quartz surface) and to liquid (Cd2+ in eluate). Under optimized conditions, the method limit of detection (LOD) reached 0.04 mg/kg Cd (50 mg sample), fulfilling fast monitoring of Cd contamination in soil, with <20 % relative standard deviations (RSDs). The analysis time was <10 min excluding sample digestion and acid application, as well as the interference of Pb2+ on the AuNPs sensor can be eliminated via the "three-phase transforming" process, proving an excellent anti-interference for solid analysis. This "three-phase transforming" processing technique coupled with colorimetric sensor holds a great potential for direct and on-site analysis in solid samples without complicated handling, providing a fantastic methodology for the application of ionic sensors and making solid sampling elemental sensor and visual detection possible.

Breaking boundaries: Artificial intelligence for pesticide detection and eco-friendly degradation

Pesticides are extensively used agrochemicals across the world to control pest populations. However, irrational application of pesticides leads to contamination of various components of the environment, like air, soil, water, and vegetation, all of which build up significant levels of pesticide residues. Further, these environmental contaminants fuel objectionable human toxicity and impose a greater risk to the ecosystem. Therefore, search of methodologies having potential to detect and degrade pesticides in different environmental media is currently receiving profound global attention. Beyond the conventional approaches, Artificial Intelligence (AI) coupled with machine learning and artificial neural networks are rapidly growing branches of science that enable quick data analysis and precise detection of pesticides in various environmental components. Interestingly, nanoparticle (NP)-mediated detection and degradation of pesticides could be linked to AI algorithms to achieve superior performance. NP-based sensors stand out for their operational simplicity as well as their high sensitivity and low detection limits when compared to conventional, time-consuming spectrophotometric assays. NPs coated with fluorophores or conjugated with antibody or enzyme-anchored sensors can be used through Surface-Enhanced Raman Spectrometry, fluorescence, or chemiluminescence methodologies for selective and more precise detection of pesticides. Moreover, NPs assist in the photocatalytic breakdown of various organic and inorganic pesticides. Here, AI models are ideal means to identify, classify, characterize, and even predict the data of pesticides obtained through NP sensors. The present study aims to discuss the environmental contamination and negative impacts of pesticides on the ecosystem. The article also elaborates the AI and NP-assisted approaches for detecting and degrading a wide range of pesticide residues in various environmental and agrecultural sources including fruits and vegetables. Finally, the prevailing limitations and future goals of AI-NP-assisted techniques have also been dissected.

A novel fluorescent "OFF-ON" sensing strategy for Hg (II) in water based on functionalized gold nanoparticles

Mercury ion (Hg²⁺) is a heavy metal pollutant that can affect the safety of water environment and endanger human health. A novel detection strategy (GNPs-_L-Cys-Rh6G2) for Hg²⁺ based on a fluorescence "OFF-ON" was proposed. Gold nanoparticles (GNPs) were assembled with _l-cysteine (_L-Cys), which was used as a "bridge" to link with rhodamine 6G derivatives (Rh6G2). The fluorescence state transition of GNPs-_L-Cys-Rh6G2 switching from "OFF"-"ON" was observed because Hg²⁺ opened the spirolactam ring through a catalytic hydrolysis mechanism. The fluorescence signal of the GNPs-_L-Cys-Rh6G2 system mixed with Hg²⁺ in the concentration range of 10-100 μM was analyzed and determined with a limit of detection (LOD) of 2 μM (S/N = 3). Moreover, the spiked Hg²⁺ concentration in real water samples were successfully quantified by GNPs-_L-Cys-Rh6G2, which was in line with the ideal average recovery rate and relative standard deviation. The proposed strategy exhibited high specificity, sensitivity and stability, providing a novel sensing platform for heavy metal ions detection in water environment.

Detection and imaging of Hg(II) in vivo using glutathione-functionalized gold nanoparticles

The optical and biological properties of functionalized gold nanoparticles (GNPs) have been widely used in sensing applications. GNPs have a strong binding ability to thiol groups. Furthermore, thiols are used to bind functional molecules, which can then be used, for example, to detect metal ions in solution. Herein, we describe 13 nm GNPs functionalized by glutathione (GSH) and conjugated with a rhodamine 6G derivative (Rh6G2), which can be used to detect Hg(II) in cells. The detection of Hg²⁺ ions is based on an ion-catalyzed hydrolysis of the spirolactam ring of Rh6G2, leading to a significant change in the fluorescence of GNPs-GSH-Rh6G2 from an "OFF" to an "ON" state. This strategy is an effective tool to detect Hg²⁺ ions. In cytotoxicity experiments, GNPs-GSH-Rh6G2 could penetrate living cells and detect mercury ions through the fluorescent "ON" form.

A Simple Colorimetric Assay for Sensitive Cu2+ Detection Based on the Glutathione-Mediated Etching of MnO2 Nanosheets

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu²⁺) quantification via the redox response of MnO₂ nanosheets with glutathione (GSH). This reaction consumed MnO₂ nanosheets, which acted as a catalyst for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu²⁺, the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu²⁺ concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu²⁺. Moreover, the system has been efficaciously implemented for Cu²⁺ detection in actual tap water samples. The layered-nanostructures of MnO₂ nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO₂ nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H₂O₂ and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO₂ nanosheets is promising for real-time, rapid and highly sensitive detection of Cu²⁺ under practical conditions.

l-cysteine-modified chiral gold nanoparticles promote periodontal tissue regeneration

Gold nanoparticles (AuNPs) with surface-anchored molecules present tremendous potential in tissue regeneration. However, little is known about chiral-modified AuNPs. In this study, we successfully prepared L/D-cysteine-anchored AuNPs (L/D-Cys-AuNPs) and studied the effects of chiral-modified AuNPs on osteogenic differentiation and autophagy of human periodontal ligament cells (hPDLCs) and periodontal tissue regeneration. In vitro, more L-Cys-AuNPs than D-Cys-AuNPs tend to internalize in hPDLCs. L-Cys-AuNPs also significantly increased the expression of alkaline phosphatase, collagen type 1, osteocalcin, runt-related transcription factor 2, and microtubule-associated protein light chain 3 II and decreased the expression of sequestosome 1 in hPDLCs compared to the expression levels in the hPDLCs treated by D-Cys-AuNPs. In vivo tests in a rat periodontal-defect model showed that L-Cys-AuNPs had the greatest effect on periodontal-tissue regeneration. The activation of autophagy in L-Cys-AuNP-treated hPDLCs may be responsible for the cell differentiation and tissue regeneration. Therefore, compared to D-Cys-AuNPs, L-Cys-AuNPs show a better performance in cellular internalization, regulation of autophagy, cell osteogenic differentiation, and periodontal tissue regeneration. This demonstrates the immense potential of L-Cys-AuNPs for periodontal regeneration and provides a new insight into chirally modified bioactive nanomaterials.

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L/D-Cys-AuNPs exert a chirality-dependent effect on hPDLCs.

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L-Cys-AuNPs efficiently induced osteogenic differentiation in hPDLCs.

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L-Cys-AuNPs significantly improved periodontal tissue regeneration.

Gold Nanoparticles Combined Human β-Defensin 3 Gene-Modified Human Periodontal Ligament Cells Alleviate Periodontal Destruction via the p38 MAPK Pathway

Periodontitis is a chronic inflammatory disease with plaques as the initiating factor, which will induce the destruction of periodontal tissues. Numerous studies focused on how to obtain periodontal tissue regeneration in inflammatory environments. Previous studies have reported adenovirus-mediated human β-defensin 3 (hBD3) gene transfer could potentially enhance the osteogenic differentiation of human periodontal ligament cells (hPDLCs) and bone repair in periodontitis. Gold nanoparticles (AuNPs), the ideal inorganic nanomaterials in biomedicine applications, were proved to have synergetic effects with gene transfection. To further observe the potential promoting effects, AuNPs were added to the transfected cells. The results showed the positive effects of osteogenic differentiation while applying AuNPs into hPDLCs transfected by adenovirus encoding hBD3 gene. In vivo, after rat periodontal ligament cell (rPDLC) transplantation into SD rats with periodontitis, AuNPs combined hBD3 gene modification could also promote periodontal regeneration. The p38 mitogen-activated protein kinase (MAPK) pathway was demonstrated to potentially regulate both the in vitro and in vivo processes. In conclusion, AuNPs can promote the osteogenic differentiation of hBD3 gene-modified hPDLCs and periodontal regeneration via the p38 MAPK pathway.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

A novel imidazole derived colorimetric and fluorometric chemosensor for bifunctional detection of copper (II) and sulphide ions in environmental water samples

Herein, a novel "ON-OFF" colorimetric and fluorometric chemosensor; 1N-allyl-2-(2, 5-dimethoxyphenyl)-4, 5-diphenyl-1H-imidazole (ADPPI), was constructed for sequential determination of Cu²⁺ and S^2- ions in aqueous media. The interaction between chemosensor ADPPI and different metal cations was investigated using UV-VIS and fluorimetric spectroscopy. ADPPI showed a favorable and good interaction with Cu²⁺ ions producing blue colored solution peaked at 610 nm with blue fluorescence at λ_em. = 447 nm. The produced complex between Cu²⁺ ions and ADPPI can be used as a cascade probe for detection of S^2- ions. The detection limits (LODs) were 1.01 nM and 1.25 μM for Cu²⁺ and S^2- ions, respectively (the lowest between the family of colorimetric and fluorometric chemosensors). To further increase the applicability of the proposed method, Cu²⁺ and S^2- ions concentrations were measured in environmental water samples.

Self-assembled gold nanoparticles and amphiphile peptides: a colorimetric probe for copper(ii) ion detection

We show that arginine/phenylalanine based peptides can be used to control the aggregation of gold nanoparticles in different ways. The arrangement provides a colorimetric approach to detect Cu²⁺ ions in water.

A unimolecular DNA fluorescent probe for determination of copper ions based on click chemistry

A homogenous fluorescence method was constructed for Cu²⁺ detection by employing DNA-templated click chemistry and exonuclease reaction. In this strategy, a dumbbell shaped DNA probe, which contained an alkyne group and an azide group at its ends, was designed as the template for the click chemistry reaction, and also the signal probe. In the absence of Cu²⁺, the DNA probe was digested into small oligonucleotide fragments by exonuclease, resulting in a low fluorescence background. However, this DNA probe can be sealed at its two ends by Cu²⁺-induced click chemistry ligation in the presence of Cu²⁺. This closed structure of DNA would remain stable after addition of exonuclease, and could then be stained by SYBR Green I. A strong fluorescence signal was observed, which was related to the concentration of Cu²⁺. This assay showed high selectivity and reached the detection limit of 39 nM. Moreover, the proposed strategy exhibited satisfactory detection results in real complex sample analysis, and has promising application in environmental monitoring and food safety.

A homogenous fluorescence method was constructed for Cu²⁺ detection by employing DNA-templated click chemistry and exonuclease reaction.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

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.

Yolk–shell structured Au@Ag@mSiO2 as a probe for sensing cysteine enantiomers and Cu2+ based on circular dichroism

Novel yolk–shell structured Au@Ag@mSiO₂ was fabricated and used as a probe for recognition and quantification of cysteine enantiomers and Cu²⁺.

Developing on-site paper colorimetric monitoring technique for quick evaluating copper ion concentration in mineral wastewater

With the reinforce of the copper mining, the on-site monitoring of the accompanied effluent discharge is highly demanded for the emergency response to minimize the negative effect of the effluent on the surrounding ecosystem. On the basis of the specific interaction between Cu²⁺ and l-Cysteine (l-Cys), which was modified on gold nanoparticles (Au NPs), and the aggregation dependent surface plasmon resonance (SPR) of Au NPs, we developed an easy-on-going paper colorimetric method for the quick evaluating the copper ion concentration in the waste water excreted from the copper mine. The color change of l-Cys modified Au NPs (l-Cys-Au NPs)immobilized on a filter paper was very sensitive to the Cu²⁺ concentration and free of interference from other metal ions typically in waste water. The proposed paper colorimetry has the LOD of 0.09mg/L and the linear range of 0.1-10mg/L, respectively, with the RSD (n=5) was 6.6% for 1mg/L Cu²⁺ and 3.5% for 5mg/L Cu²⁺. The quantitative analysis results for the mineral wastewater is in good agreement the China National Environmental Protection Standards HJ485-2009, which indicates the current method could be developed to the on-site detection technique for the emergency response in monitoring Cu²⁺ in industrial wastewater or polluted water.

Gly–Gly–His tripeptide- and silver nanoparticle-assisted electrochemical evaluation of copper(ii) ions in aqueous environment

A sensitive and selective electrochemical sensor for Cu²⁺ assay is developed using tripeptide-based recognition and silver nanoparticle-modified electrode.

Nanotechnology for Food Packaging and Food Quality Assessment

Nanotechnology has paved the way to innovative food packaging materials and analytical methods to provide the consumers with healthier food and to reduce the ecological footprint of the whole food chain. Combining antimicrobial and antifouling properties, thermal and mechanical protection, oxygen and moisture barrier, as well as to verify the actual quality of food, e.g., sensors to detect spoilage, bacterial growth, and to monitor incorrect storage conditions, or anticounterfeiting devices in food packages may extend the products shelf life and ensure higher quality of foods. Also the ecological footprint of food chain can be reduced by developing new completely recyclable and/or biodegradable packages from natural and eco-friendly resources. The contribution of nanotechnologies to these goals is reviewed in this chapter, together with a description of portable devices ("lab-on-chip," sensors, nanobalances, etc.) which can be used to assess the quality of food and an overview of regulations in force on food contact materials.

Size-dependent Effects of Gold Nanoparticles on Osteogenic Differentiation of Human Periodontal Ligament Progenitor Cells

Gold nanoparticles (AuNPs) have been reported to promote osteogenic differentiation of mesenchymal stem cells and osteoblasts, but little is known about their effects on human periodontal ligament progenitor cells (PDLPs). In this study, we evaluated the effects of AuNPs with various diameters (5, 13 and 45 nm) on the osteogenic differentiation of PDLPs and explored the underlying mechanisms. 5 nm AuNPs reduced the alkaline phosphatase activity, mineralized nodule formation and expression of osteogenic genes, while 13 and 45 nm AuNPs increased these osteogenic markers. Compared with 13 nm, 45 nm AuNPs showed more effective in promoting osteogenic differentiation. Meanwhile, autophagy was up-regulated by 13 and 45 nm AuNPs but blocked by 5 nm AuNPs, which corresponded with their effects on osteogenic differentiation and indicated that autophagy might be involved in this process. Furthermore, the osteogenesis induced by 45 nm AuNPs could be reversed by autophagy inhibitors (3-methyladenine and chloroquine). These findings revealed that AuNPs affected the osteogenic differentiation of PDLPs in a size-dependent manner with autophagy as a potential explanation, which suggested AuNPs with defined size could be a promising material for periodontal bone regeneration.

Selective and sensitive colorimetric determination of cobalt ions using Ag–Au bimetallic nanoparticles

Selective and sensitive colorimetric detection of Co²⁺based on the aggregation of Ag–Au BNPs is due to the formation of positively charged (en)₂CoS₂O₃⁺on the negative nanoparticle surface.

Glutathione Modified Gold Nanoparticles for Sensitive Colorimetric Detection of Pb2+ Ions in Rainwater Polluted by Leaking Perovskite Solar Cells

In the past few years, the advent of lead halide perovskite solar cells (PSCs) has revolutionized the prospects of the third- generation photovoltaics and the reported power conversion efficiency (PCE) has been updated to 22%. Nevertheless, two main challenges, including the poisonous content of Pb and the vexing instability toward water, still lie between the lab-based PSCs technology and large scale commercialization. With this background, we first evaluated Pb²⁺ concentration from the rainwater samples polluted by three types of markets promising PSCs with inductively coupled plasma mass spectrometry measurements (ICP-MS) as a case study. The influence of possible conditions (pH value and exposure time) on the contents of Pb²⁺ from the three PSCs was systematically compared and discussed. Furthermore, an optimized glutathione functionalized gold nanoparticles (GSH-AuNPs) colorimetric sensing assay was used to determine Pb²⁺ leaking from PSCs for the first time. The Pb²⁺-induced aggregation of sensing assay could be monitored via both naked eye and UV-vis spectroscopy with a detection limit of 15 and 13 nM, which are all lower than the maximum level in drinking water permitted by WHO. The quantitative detection results were compared and in good agreement with that of ICP-MS. The results indicate that the content of Pb²⁺ from three PSCs are in the same order of magnitude under various conditions. By the use of the prepared GSH-AuNPs self-assembled sensing assay, the fast and on-site detection of Pb²⁺ from PSCs can be realized.

Chiral Imidazolium-Functionalized Au Nanoparticles: Reversible Aggregation and Molecular Recognition

Gold nanoparticles (AuNPs) stabilized by imidazolium salts derived from amino acids [glycine (1), rac-alanine (2), l-phenylalanine (3), and rac-methionine (4)] were prepared. The AuNPs were stabilized the most by 4, which kept the particles dispersed in water for months at pH > 5.5. These AuNPs exhibited a well-defined absorption band at 517 nm and had an average particle size of 11.21 ± 0.07 nm. The 4-AuNPs were reversibly aggregated by controlling the pH of the solution. Chiral R,R-4-AuNPs and S,S-4-AuNPs were synthesized, and the chiral environment on the nanoparticle surface was confirmed using circular dichroism; these nanoparticles exhibited a molecular recognition of chiral substrates. Furthermore, they showed potential for separating racemic mixtures when supported on a layered double hydroxide.

Gold-Planet-Silver-Satellite Nanostructures Using RAFT Star Polymer

The hierarchical self-assembly of distinct nanoelements into precisely ordered nanostructures requires efficient and flexible fabrication strategies. Herein, we report the precise fabrication of bimetallic gold-planet-silver-satellite nanoparticle-arrangements employing RAFT star polymers as particle linker connecting gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) with judiciously modified surface activity. The strengths of this approach include the adjustability of interparticle distances by tailoring the star polymer molar mass. The prepared nanoassemblies have well-defined structures in which a planet AuNP (∼13 nm) is encompassed by several satellite AgNPs (∼8 nm), thus incorporating the properties of both AuNPs and AgNPs, as confirmed by transmission electron microscopy and UV-vis spectra. Our results highlight the general applicability of RAFT star polymers as a nanosynthesis platform for synthesizing noble metal nanocomposites.

Detection of Copper(II) Ions Using Glycine on Hydrazine-Adsorbed Gold Nanoparticles via Raman Spectroscopy

A facile, selective, and sensitive detection method for the Cu²⁺ ions in environmental and biological solutions has been newly developed by observing the unique CN stretching peaks at ~2108 cm⁻¹ upon the dissociative adsorption of glycine (GLY) in hydrazine buffer on gold nanoparticles (AuNPs). The relative abundance of Cu species on AuNPs was identified from X-ray photoelectron spectroscopy analysis. UV-Vis spectra also indicated that the Au particles aggregated to result in the color change owing to the destabilization induced by the GLY-Cu²⁺ complex. The CN stretching band at ~2108 cm⁻¹ could be observed to indicate the formation of the CN species from GLY on the hydrazine-covered AuNP surfaces. The other ions of Fe³⁺, Fe²⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺, Cr³⁺, Co²⁺, Cd²⁺, Pb²⁺, Ca²⁺, NH₄⁺, Na⁺, and K⁺ at high concentrations of 50 µM did not produce such spectral changes. The detection limit based on the CN band for the determination of the Cu²⁺ ion could be estimated to be as low as 500 nM in distilled water and 1 µM in river water, respectively. We attempted to apply our method to estimate intracellular ion detection in cancer cells for more practical purposes.

Self-Assembled Core-Satellite Gold Nanoparticle Networks for Ultrasensitive Detection of Chiral Molecules by Recognition Tunneling Current

Chirality sensing is a very challenging task. Here, we report a method for ultrasensitive detection of chiral molecule l/d-carnitine based on changes in the recognition tunneling current across self-assembled core-satellite gold nanoparticle (GNP) networks. The recognition tunneling technique has been demonstrated to work at the single molecule level where the binding between the reader molecules and the analytes in a nanojunction. This process was observed to generate a unique and sensitive change in tunneling current, which can be used to identify the analytes of interest. The molecular recognition mechanism between amino acid l-cysteine and l/d-carnitine has been studied with the aid of SERS. The different binding strength between homo- or heterochiral pairs can be effectively probed by the copper ion replacement fracture. The device resistance was measured before and after the sequential exposures to l/d-carnitine and copper ions. The normalized resistance change was found to be extremely sensitive to the chirality of carnitine molecule. The results suggested that a GNP networks device optimized for recognition tunneling was successfully built and that such a device can be used for ultrasensitive detection of chiral molecules.

Surface-site reactivity in small-molecule adsorption: A theoretical study of thiol binding on multi-coordinated gold clusters

BACKGROUND

The adsorption of organic molecules on metal surfaces has a broad array of applications, from device engineering to medical diagnosis. The most extensively investigated class of metal-molecule complexes is the adsorption of thiols on gold.

RESULTS

In the present manuscript, we investigate the dependence of methylthiol adsorption structures and energies on the degree of unsaturation at the metal binding site. We designed an Au20 cluster with a broad range of metal site coordination numbers, from 3 to 9, and examined the binding conditions of methylthiol at the various sites.

CONCLUSION

We found that despite the small molecular size, the dispersive interactions of the backbone are a determining factor in the molecular affinity for various sites. Kink sites were preferred binding locations due to the availability of multiple surface atoms for dispersive interactions with the methyl groups, whereas tip sites experienced low affinity, despite having low coordination numbers.

Portable Nanoparticle-Based Sensors for Food Safety Assessment

The use of nanotechnology-derived products in the development of sensors and analytical measurement methodologies has increased significantly over the past decade. Nano-based sensing approaches include the use of nanoparticles (NPs) and nanostructures to enhance sensitivity and selectivity, design new detection schemes, improve sample preparation and increase portability. This review summarizes recent advancements in the design and development of NP-based sensors for assessing food safety. The most common types of NPs used to fabricate sensors for detection of food contaminants are discussed. Selected examples of NP-based detection schemes with colorimetric and electrochemical detection are provided with focus on sensors for the detection of chemical and biological contaminants including pesticides, heavy metals, bacterial pathogens and natural toxins. Current trends in the development of low-cost portable NP-based technology for rapid assessment of food safety as well as challenges for practical implementation and future research directions are discussed.

Single glass nanopore-based regenerable sensing platforms with a non-immobilized polyglutamic acid probe for selective detection of cupric ions

A single glass capillary nanopore-based sensing platform for rapid and selective detection of cupric ions is demonstrated by utilizing polyglutamic acid (PGA) as a non-immobilized probe. The detection is based on the significant decrease of ionic current through nanopore and the reversal of ion current rectification responses induced by the chelated cupric ions on the probes when in the presence of cupric ions. PGA shows high selectivity for detecting cupric ions rather than other metal ions. The sensitivity of the sensing platform can be improved about 1-2 orders of magnitude by employing asymmetric salt gradients during the measurements. And the PGA-based nanopore sensing platform shows excellent regenerability for Cu(2+) sensing applications. In addition, the method is found effective and reliable for the detection of cupric ions in real samples with small volume down to 20 μL. This nanopore-based sensing platform will find promising practical applications for the detection of cupric ions.

Colorimetric magnetic microspheres as chemosensor for Cu(2+) prepared from adamantane-modified rhodamine and β-cyclodextrin-modified Fe3O4@SiO2 via host-guest interaction

Adamantane-modified salicylrhodamine B and β-cyclodextrin-modified Fe3O4@SiO2 were assemblied by host-guest interactions which induced novel inclusion complex magnetic nanoparticles (SFIC MNPs) colorimetric sensitive for Cu(2+) being prepared. The MNPs exhibit a clear color change from colorless to pink selectively and sensitively with the addition of Cu(2+) in the experiments of UV-visible spectra, and the detection limit measures up to 5.99×10(-6)M in solutions of CH3CN-H2O =1:10. The SFIC magnetic nanoparticles are superparamagnetic according to magnetic measurements and can be separated and collected easily with a commercial magnet in nine seconds. In addition, the microspheres have also showed good ability of separating for other ions from aqueous solutions due to a large number of hydroxyl groups on the surface.

Highly selective and sensitive paper-based colorimetric sensor using thiosulfate catalytic etching of silver nanoplates for trace determination of copper ions

A novel, highly selective and sensitive paper-based colorimetric sensor for trace determination of copper (Cu(2+)) ions was developed. The measurement is based on the catalytic etching of silver nanoplates (AgNPls) by thiosulfate (S2O3(2-)). Upon the addition of Cu(2+) to the ammonium buffer at pH 11, the absorption peak intensity of AuNPls/S2O3(2-) at 522 nm decreased and the pinkish violet AuNPls became clear in color as visible to the naked eye. This assay provides highly sensitive and selective detection of Cu(2+) over other metal ions (K(+), Cr(3+), Cd(2+), Zn(2+), As(3+), Mn(2+), Co(2+), Pb(2+), Al(3+), Ni(2+), Fe(3+), Mg(2+), Hg(2+) and Bi(3+)). A paper-based colorimetric sensor was then developed for the simple and rapid determination of Cu(2+) using the catalytic etching of AgNPls. Under optimized conditions, the modified AgNPls coated at the test zone of the devices immediately changes in color in the presence of Cu(2+). The limit of detection (LOD) was found to be 1.0 ng mL(-1) by visual detection. For semi-quantitative measurement with image processing, the method detected Cu(2+) in the range of 0.5-200 ng mL(-1)(R(2)=0.9974) with an LOD of 0.3 ng mL(-1). The proposed method was successfully applied to detect Cu(2+) in the wide range of real samples including water, food, and blood. The results were in good agreement according to a paired t-test with results from inductively coupled plasma-optical emission spectrometry (ICP-OES).

Tunnelling current recognition through core–satellite gold nanoparticles for ultrasensitive detection of copper ions

The addition of copper ions induces the formation of GNP/l-cysteine/Cu²⁺/l-cysteine/GNP molecular junctions and generates a significant decrease in the resistance through the networks.

Monolayer protected gold nanoparticles with metal-ion binding sites: functional systems for chemosensing applications

Au NPs containing binding sites for metal ions in the monolayer are attractive components of sensing assays.

A robust site-specific Au@SiO2@AgPt nanorod/nanodots superstructure for in situ SERS monitoring of catalytic reactions

A site-specific trimetallic Au@SiO₂@AgPt nanorod/nanodots superstructure can be fabricated to provide real-time SERS monitoring of catalytic reactions.