New Fluorescent Probes for the Sensitive Determination of Glyphosate in Food and Environmental Samples

In this paper, a dual-functional probe, 2-(benzothiazol)-4-(3-hydroxy-4-methylphenyl) imino phenol (BHMH), was synthesized and characterized for the simultaneous detection of Cu2+ and Fe3+ in dimethyl sulfoxide/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (DMSO/HEPES) (1:4, v/v, pH = 6.0). The limits of detections (LODs) for Cu2+ and Fe3+ were 9.05 and 48 nM, respectively. Based on the competitive coordination, the complex BHMH-Cu2+/Fe3+ exhibited good sensitivity and selectivity for glyphosate. The LODs of BHMH-Cu2+ and BHMH-Fe3+ for glyphosate were 0.41 and 0.63 μM, respectively. The probe quantitatively detected glyphosate in tap water, Songhua River water, local water and soil, and food samples. The colorimetric on-site glyphosate sensing through the probe BHMH-Cu2+ was also studied based on smartphones. BHMH and BHMH-Cu2+/Fe3+ exhibited outstanding imaging capabilities for Cu2+, Fe3+, and glyphosate in living cells with low cytotoxicity, especially the first time for glyphosate.

Simultaneous Visual Detection and Removal of Cu2+ with Electrospun Self-Supporting Flexible Amidated Polyacrylonitrile/Branched Polyethyleneimine Nanofiber Membranes

Sensitive detection and effective removal of copper ions (Cu²⁺) from water are still arduous tasks required to protect public health and environmental safety because of the serious impacts of Cu²⁺ on humans and other organisms. Herein, we report the design and fabrication of self-supporting flexible amidated polyacrylonitrile/branched polyethyleneimine nanofiber membranes (abbreviated as aPAN/BPEI NMs) via facile electrospinning and a subsequent hydrothermal method, which are used not only as strips for the visual detection of Cu²⁺ but also as effective adsorbents for the removal of Cu²⁺ from water. Because aPAN/BPEI NMs are self-supporting, they can be easily removed from the solution to reduce secondary pollution to the environment. Based on the high Cu²⁺ binding capacity of BPEI, Cu²⁺ ions are adsorbed on the aPAN/BPEI NMs, which leads to the appearance of new absorbance bands at 280 and 636 nm and a color change from yellow to blue. aPAN/BPEI NMs are utilized for the visual detection of Cu²⁺ with a linear range of 50-700 μM and limits of detection of 11.5 and 4.8 μM (absorption peaks at 280 and 636 nm). More importantly, aPAN/BPEI NMs exhibit excellent selectivity and certain recovery with a simple treatment. Furthermore, by utilizing the adsorption characteristics of Cu²⁺ in aqueous media, it can be effectively removed by aPAN/BPEI NMs with a remarkable adsorption capacity of 209.53 mg·g^-1. Additionally, the removal of Cu²⁺ by aPAN/BPEI NMs does not exhibit interference by other foreign ions. The adsorption process conforms well to the pseudo-second order (PSO) kinetic model and Jovanovich model, proving that adsorption occurs via chemical and monolayer adsorption mechanisms. Accordingly, this work will provide theoretical and technical support for the design and fabrication of novel heavy metal ion detection-removal integrated materials exhibiting high sensitivity and strong adsorption.

Antibacterial Activity and Mechanism of ZnO/Cu2+-Chitosan/Montmorillonite

A new composite antibacterial material ZnO/Cu²⁺-Chitosan/Montmorillonite (ZCCM) was prepared with montmorillonite as carrier, Zn(Ac)₂•2H₂O, Cu(NO₃)₂•3H₂O and chitosan as raw materials. ZCCM was characterized by X-ray diffraction, nitrogen physical adsorption, scanning electron microscopy and energy dispersion spectrometry. The antibacterial activity of ZCCM against Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus was evaluated by minimal inhibitory concentration, minimum bactericidal concentration and the influence of growth curves. ZCCM displays excellent antibacterial activity which is higher than ZnO-Montmorillonite, Cu²⁺-Montmorillonite and ZnO/Cu²⁺-Montmorillonite. In addition, the antibacterial mechanism of ZCCM was investigated by analyzing bacterial morphology, integrity of cell membrane, lipid peroxidation and the effect of histidine on antibacterial activity of materials. It is found that cell morphologies of bacteria are damaged and bacterial cells are shrunken. With the increase of cell membrane permeability, the intracellular dissolved matters leak continuously. What's more, the reactive oxygen species are generated and biomacromolecules are oxidized.

Copper ions impair zebrafish skeletal myofibrillogenesis via epigenetic regulation

Unbalanced copper (Cu²⁺ ) homeostasis is associated with the developmental defects of vertebrate myogenesis, but the underlying molecular mechanisms remain elusive. In this study, it was found that Cu²⁺ stressed zebrafish embryos and larvae showed reduced locomotor speed as well as loose and decreased myofibrils in skeletal muscle, coupled with the downregulated expression of muscle fiber markers mylpfa and smyhc1l and the irregular arrangement of myofibril and sarcomere. Meanwhile, the Cu²⁺ stressed zebrafish embryos and larvae also showed significant reduction in the expression of H3K4 methyltransferase smyd1b transcripts and H3K4me3 protein as well as in the binding enrichment of H3K4me3 on gene mylpfa promoter in skeletal muscle cells, suggesting that smyd1b-H3K4me3 axis mediates the Cu²⁺ -induced myofibrils specification defects. Additionally, whole genome DNA methylation sequencing unveiled that the gene smyd5 exhibited significant promoter hyper-methylation and increased expression in Cu²⁺ stressed embryos, and the ectopic expression of smyd5 in zebrafish embryos also induced the myofibrils specification defects as those observed in Cu²⁺ stressed embryos. Moreover, Cu²⁺ was shown to suppress myofibrils specification and smyd1b promoter transcriptional activity directly independent of the integral function of copper transporter cox17 and atp7b. All these data may shed light on the linkage of unbalanced copper homeostasis with specific gene promoter methylation and epigenetic histone protein modification as well as the resultant signaling transduction and the myofibrillogenesis defects.

Probing the Structure of Toxic Amyloid-β Oligomers with Electron Spin Resonance and Molecular Modeling

Structural models of the toxic species involved in the development of Alzheimer's disease are of utmost importance to understand the molecular mechanism and to describe early biomarkers of the disease. Among toxic species, soluble oligomers of amyloid-β (Aβ) peptides are particularly important, because they are responsible for spreading cell damages over brain regions, thus rapidly impairing brain functions. In this work we obtain structural information on a carefully prepared Aβ(1-42) sample, representing a toxic state for cell cultures, by combining electron spin resonance spectroscopy and computational models. We exploited the binding of Cu²⁺ to Aβ(1-42) and used copper as a probe for estimating Cu-Cu distances in the oligomers by applying double electron-electron resonance (DEER) pulse sequence. The DEER trace of this sample displays a unique feature that fits well with structural models of oligomers formed by Cu-cross-linked peptide dimers. Because Cu is bound to the Aβ(1-42) N-terminus, for the first time structural constraints that are missing in reported studies are provided at physiological conditions for the Aβ N-termini. These constraints suggest the Aβ(1-42) dimer as the building block of soluble oligomers, thus changing the scenario for any kinetic model of Aβ(1-42) aggregation.

Polar modified dendritic post-cross-linked polymer for Cu2+ adsorption

The polar modified dendritic post-cross-linked polymer, namely HCPD was synthesized and used for adsorptive removal of Cu²⁺ from aqueous solution. The results showed that 5.12 mmol/g of amino and 2.25 mmol/g of carbonyl groups were uploaded on the polymer and these groups were significantly beneficial for Cu²⁺ removal. The maximum capacity reached 157.8 mg/g at 313 K and increased as the temperature increased. The Langmuir model characterized the equilibrium data well and a chemical interaction was involved with the enthalpy change of 49.50 kJ/mol. The pseudo-second-order kinetic model described the kinetic data well and the intra-particle diffusion model was appropriate for characterizing the kinetic adsorption. HCPD could be easily regenerated and the regenerated polymers were effectively recycled for five times without significant loss of the equilibrium capacity. Moreover, Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) results revealed that the chelating coordination of the amino and carbonyl groups with Cu²⁺ was the main driving force for the adsorption.

[12]aneN3-based multifunctional compounds as fluorescent probes and nucleic acids delivering agents

A series of multifunctional compounds (MFCs) 1a-1e based on 1,8-naphthalimide and [12]aneN3 building blocks were designed and synthesized. They were used as not only fluorescent probes for recognition of Cu2+ ions but also as non-viral gene vectors for DNA and RNA delivery. Furthermore, their complexes with Cu2+ (1-Cu) could also selectively stain lysosome in HeLa cells. In order to achieve high performance multifunctional materials, structure-performance relationship of MFCs 1a-1e was studied. It was found that MFCs 1a-1e exhibited highly selective fluorescence turn-off for Cu2+, without interference by other metal ions in aqueous solution. The fluorescence emission of 1a-1e was quenched by a factor of 10-fold, 47-fold, 6-fold, 64-fold, and 15-fold respectively in the presence of Cu2+ ions. Due to high sensitivity, good water solubility, and low cytotoxicity, MFCs 1a-1d were successfully applied in the recognition of Cu2+ and selectively staining lysosome in HeLa cells. Most importantly, MFCs 1a and 1b had excellent HeLa cell selectivity in RNA delivery, and their performances were far better than lipofectamine 2000 and 25 kDa PEI.

Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu2+ and l-Cysteine and Their Logic Gate Operation

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu²⁺ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu²⁺ complex exhibited selective fluorescence recovery and color disappearance on exposure to l-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu²⁺ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu²⁺ causes the detachment of Cu²⁺ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu²⁺ in the linear range of 0-280 μM. A detection limit of 4.75 μM is achieved using fluorescence spectroscopy and 4.74 μM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0-800 μM with detection limits of 28.11 μM (fluorescence determination) and 19.74 μM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu²⁺ system exhibits distinguishable responses to other biothiols such as l-glutathione (GSH) and dl-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu²⁺, Fe³⁺ can also quench the fluorescence of PQDs and the PQD-Fe³⁺ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu²⁺ and Cys in some real samples.

A Coumarin-Based Fluorescent Probe for Ratiometric Detection of Cu2+ and Its Application in Bioimaging

The fluorescent probe L, based on naphthalimide-modified coumarin, was designed, synthesized, and characterized, which could recognize Cu2+ from other cations selectively and sensitively in HEPES buffer (10 mM, Ph = 7. 4)/CH3CN (1:4, V/V). When the probe L interacted with Cu2+, the color and the fluorescent intensity changed obviously and it provided the naked-eye detection for Cu2+. The recognition mode between them was achieved by Job's plot, IR, MS, SEM, and 1HNMR. In addition, test strips made from L could still interact with Cu2+ in tap water effectively. The limit of detection (LOD) of L was 3.5 × 10-6 M. Additionally, the density functional theory (DFT) calculation method was used to analyze the action mechanism of L toward Cu2+. Importantly, the fluorescent probe L could demonstrate favorable selectivity toward Cu2+ in Caenorhabditis elegans. Thus, L was considered to have some potential for application in bioimaging.

A New bis(rhodamine)-Based Colorimetric Chemosensor for Cu2

A novel sensor (RD) bearing rhodamine B and 4-tert-Butyl phenol unit have been designed and synthesized using microwave irradiation. The sensor allows selective detection of Cu2+ by forming absorptive complex and trigger the formation of highly colored ring-open spirolactam. The recognition ability of the sensor was investigated by absorbance, Job's plot, infrared (IR) and time dependent-density functional theory (TD-DFT) calculations.

Cu2+ in liquid ammonia-The impact of solvent flexibility and electron correlation in ab initio quantum mechanical charge field molecular dynamics

The impact of solvent flexibility and electron correlation on the simulation results of Cu²⁺ in liquid ammonia has been investigated via an ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach. To achieve this, three different simulation systems were considered in this study, namely Cu²⁺ in rigid and flexible ammonia at Hartree-Fock (HF) level of theory, as well as resolution of identity second order Møller-Plesset (MP2) perturbation theory in the rigid body case. In all cases, a stable octahedral [Cu(NH₃ )₆ ]²⁺ complex subject to dynamic Jahn-Teller distortions without the occurrence of ligand exchange was observed. The Cu²⁺  - NH₃ distance in the first shell agrees well with the experimental and other theoretical data. In all three cases, the structural data shows that the rigid-body ammonia model in conjunction with the HF level of theory provides accurate data for the first solvation shell, while at the same time, the computational demand and thus the achievable simulation time are much more beneficial. The vibrational analysis of the Cu²⁺  - NH₃ interaction yields similar force constants in the three investigated systems indicating that there is no distinct difference on the dynamical properties of the first solvation shell. In addition to the QMCF MD simulations, a number of natural bond orbital (NBO) analyses were carried out, confirming the strong electrostatic character of the Cu²⁺  - NH₃ interaction.

Characterization of a Cu2+, SDS, alcohol and glucose tolerant GH1 β-glucosidase from Bacillus sp. CGMCC 1.16541

A β-glucosidase gene (bsbgl1a) from Bacillus sp. CGMCC 1.16541 was expressed in Escherichia coli BL21 and subsequently characterized. The amino acid sequence shared 83.64% identity with β-glucosidase (WP_066390903.1) from Fictibacillus phosphorivorans. The recombinant β-glucosidase (BsBgl1A) had a molecular weight of 52.2 kDa and could hydrolyze cellobiose, cellotriose, cellotetrose, p-nitrophenyl-β-D-glucopyranoside (pNPG), and p-nitrophenyl-β-D-xylopyranoside (pNPX). Optimal activity for BsBgl1A was recorded at 45 °C with a pH between 5.6 and 7.6, and 100% of its activity was maintained after a 24 h incubation between pH 4 and 9. Kinetic characterization revealed an enzymatic turnover (Kcat) of 616 ± 2 s^-1 (with cellobiose) and 3.5 ± 0.1 s^-1 (with p-nitrophenyl-β-D-glucopyranoside). Interestingly, the recombinant enzyme showed cupric ion (Cu²⁺), sodium dodecyl sulfate (SDS) and alcohol tolerance at 10 mM for Cu²⁺ and 10% for both SDS and alcohol. Additionally, BsBgl1A had high tolerance for glucose (Ki = 2095 mM), which is an extremely desirable feature for industrial applications. Following the addition of BsBgl1A (0.05 mg/ml) to a commercial cellulase reaction system, glucose yields from sugarcane bagasse increased 100% after 1 day at 45 °C. This work identifies a Cu²⁺, SDS, alcohol, and glucose tolerant GH1 β-glucosidase with potential applications in the hydrolysis of cellulose for the bioenergy industry.

Coumarin-Based Reversible Fluorescent Probe for Selective Detection of Cu2+ in Living Cells

Copper ion plays an important role in many biological processes in human body. H₂S is considered as the third gasses transmitter after carbon monoxide and nitric oxide. Here a novel ICT-based fluorescent ON-OFF-ON probe for Cu²⁺ and H₂S detection was developed. Selectivity and sensitivity of probe was confirmed in aqueous Tris-HCl buffer (10 mM, pH 7.4, containing 90% acetonitrile). Probe DF-CU shows high selectivity over other analytes. The degree of fluorescence quenching is linearly associated with the concentration of Cu²⁺ (R² = 0.9919). The limit of detection (LOD, calculated according to the 3σ/slope) for Cu²⁺ was 6.4 μM. Probe can work in almost all pH. The probe shows a very fast response to Cu²⁺ (within 10 s). Its response to copper ion could be reversed by H₂S. The complex of probe with Cu²⁺ could be used for H₂S detection. Furthermore, this ON-OFF-ON fluorescent probe successfully applied in the living cells for the detection of Cu²⁺ and H₂S.

Bifunctional MOFs-Based Ratiometric Electrochemical Sensor for Multiplex Heavy Metal Ions

In this study, a ratiometric electrochemical sensor based on metal-organic frameworks (MOFs) was developed for sensing of multiplex metal ions. The bifunctional MOFs were prepared in a way to integrate two signal tags and a detection probe. In the presence of target metal ions, the target metal ions can replace the framework metal-ion center in the original MOFs through an ion-exchange reaction, leading to ratiometric electrochemical signals under different applied potentials. One consisted of the Cu²⁺ signal generated from electroactive MOFs selected as internal reference signals. The other consisted of the signal induced by other target metal ions. Using the I_metal ions/I_Cu²⁺ signal as the output, the prepared ratiometric probe was able to eliminate disturbance caused by the sensing environment. Moreover, the large surface area and abundant active sites in MOFs produced a multiplex ratiometric electrochemical sensor with improved characteristics in terms of reproducibility, stability, and sensitivity. The sensor was also simple without sophisticated instrumentation, amplification processes, or an acid dissolution/preconcentration procedure, hence promising for practical applications.

Two water-soluble fluorescence probes based on 5(6)-carboxyl rhodamine for Cu2+ imaging in living cells

Two novel water-soluble fluorescence probes T1 and T2 based on 5(6)-carboxyl rhodamine were designed and synthesized using a regioselective reaction. The probes exhibited highly selective and sensitive recognition toward Cu²⁺ over other metal ions in acetonitrile/Tris-HCl buffer solution (2:98, v/v; pH 7.4). Detection limits were 0.4 μM for T1 and 4.50 μM for T2 based on fluorescence titration analysis. Furthermore, probe T1 was successfully applied in cell imaging experiments to monitor Cu²⁺ in cells.

Measured data of Drosophila melanogaster (Diptera Drosophilidae) development and learning and memory behaviour after copper exposition

This article presents the statistical analysis data from Drosophila melanogaster development (from larvae to adult) and learning and memory retention behavior of a Pavlovian conditioning in male and female flies exposed to copper. While the full data sets are available In the article: Copper decrease associative learning and memory in D. melanogaster, this data-in-brief article includes the detailed statistical analysis performed. Data demonstrates Statistica Software analysis between the subject part of the analysis: 2 treatments x 2 sexes x 2 ages and within subject part of the analysis: 2 treatments x 2 sex x 2 ages x 4 times, repeated measures.

Silk Fibroin-Confined Star-Shaped Decahedral Silver Nanoparticles as Fluorescent Probe for Detection of Cu2+ and Pyrophosphate

A green, one-step method for the fabrication of silk fibroin (SF) protected silver decahedral nanoparticles (SF@AgNPs) has been developed. High-resolution transmission electron microscopy characterization demonstrated that the silver decahedral nanoparticles can provide more binding sites with (111) facets. Moreover, a facile strategy based on Cu²⁺ mediated SF@AgNPs was reported as an on-off-on fluorescent system for the detection of Cu²⁺, and the SF@AgNPs can be also used for the determination of pyrophosphate ion (P₂O₇^4-, PPi). The fluorescence of SF@AgNPs was quenched by Cu²⁺ as a complex formed between SF and Cu²⁺ and was restored when PPi was introduced into the system due to the higher binding affinity between PPi and Cu²⁺. Herein, a novel SF@AgNPs-Cu²⁺ fluorescent probe for Cu²⁺ and PPi detection is presented. The proposed assay shows a linear relationship at a Cu²⁺ concentration range from 1 to 6 μM with a detection limit of 33.3 nM. This simple, reliable, selective, and environmentally friendly fluorescent probe also has a wide concentration range from 100 to 700 μM with a detection limit of 6.7 μM for PPi. The 16 types of anions lead to negligible changes in the SF@AgNPs-Cu²⁺ complexes, while restoring the fluorescence intensity of the complexes when added with PPi. Additionally, it is demonstrated that the SF@AgNPs-based fluorescent assay works in real biological samples. It suggests that this proposed method has the potential for application in the clinical detection of Cu²⁺ and PPi.

[Effects of copper and cadmium ions on protective enzyme activity in Oncomelania hupensis]

OBJECTIVE

To evaluate the effects of Cu²⁺ and Cd²⁺ at different concentrations on superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity in Oncomelania hupensis.

METHODS

Cu²⁺- and Cd²⁺-containing solutions were prepared at 7 concentrations, and O. hupensis snails were exposed to the solutions for 24 h, of 15 snails in each concentration. Then, the snail body was collected following removal of the snail shell and homogenated, and the SOD, CAT and POS activities were detected in the supernatants.

RESULTS

With the increase of the Cu²⁺ concentration, the SOD activity appeared a rise followed by a reduction in O. hupensis snails, and the CTA activity appeared a decline-rise-decline tendency, while the POD activity showed a tendency towards rise followed by decline. With the increase of the Cd²⁺ concentration, the SOD activity appeared a rise followed by a reduction in O. hupensis snails, and the CTA activity appeared a decline- rise- decline tendency, while the POD activity showed a decline-rise-decline tendency.

CONCLUSIONS

Exposure to Cu²⁺ and Cd²⁺ at high concentrations results in a decline in the activity of SOD, CAT and POD in O. hupensis at the same time.

[Acute toxicity of four heavy metal ions to Oncomelania hupensis]

OBJECTIVE

To assess the acute toxicity of Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ to Oncomelania hupensis.

METHODS

Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ solutions were prepared at five concentrations, and 10 snails were exposed to each concentration for 24, 48, 72 h and 96 h. Then, the inhibition of snail activity and snail death was observed, and the half maximal effective concentration (EC₅₀) and median lethal concentrations (LC₅₀) were estimated.

RESULTS

The 24, 48, 72 h and 96 h EC50 values of Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ were 0.74, 0.56, 0.46, 0.37 mg/L, 4.79, 3.52, 1.70, 1.26 mg/L, 1.90, 1.49, 0.83, 0.76 mg/L and 21.40, 9.98, 7.90, 5.42 mg/L for snails, respectively. The 96 h LC₅₀ values of Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ were 0.43, 2.96, 1.12 mg/L and 12.22 mg/L for snails, the safe concentrations were 0.004 3, 0.029 6, 0.011 2, 0.122 2 mg/L, respectively.

CONCLUSIONS

Cu²⁺ shows a high acute toxicity to snails, and Cd²⁺ and Hg²⁺ exhibit a moderate acute toxicity to snails, while Pb²⁺ is lowly toxic to snails.

Colorimetric and Fluorometric Paper-Based Assay for Cu2+ Detection Based on Green Synthesis of 2-Aminoterephthalic Acid-Derived Pigments

In this study, we developed a simple and economical method for the green synthesis of Cu²⁺ sensors based on betaxanthin pigments. Aminoisophthalic acid-betaxanthin was synthesized by coupling 2-aminoisophthalic acid and betalamic acid produced from DOPA-extradiol-4,5-dioxygenase in situ and in vitro. The resulting 2-aminoterephthalic acid-betaxanthin (2-AIPA-BX) presented a satisfying fluorescence quantum yield in water and a high degree of selectivity for Cu²⁺ over interfering metal ions. The bioproduction process of 2-AIPA-BX was scaled up from test tubes to 1 L-flasks, indicating the robustness and reproducibility of this method. Additionally, we successfully incorporated 2-AIPA-BX into paper-based analytical devices to facilitate simple, inexpensive, and portable setup with lower sample consumption for onsite monitoring of environmental and biological samples.

A Smartphone-Based Sensing System for On-Site Quantitation of Multiple Heavy Metal Ions Using Fluorescent Carbon Nanodots-Based Microarrays

The development of cost-effective and versatile sensing system for simultaneous and rapid quantitation of multiple targets is highly demanded for environmental surveillance, food safety inspection, home healthcare, etc. This work reports on (1) paper-based microarrays relying on fluorescence turn-off of carbon nanodots (CDs) for analyte recognition and (2) a stand-alone smartphone-based portable reader (SBR) installed with a custom-designed APP (SBR-App), which can accurately and reproducibly acquire fluorescence change from the microarray chip, automatically report the results, generate and share the reports via wireless network. Simultaneous detection of Hg²⁺, Pb²⁺, and Cu²⁺ in the Pearl River water samples was achieved with the reported sensing system. End-user operation is limited to pipet samples to the microarray chip, insert the chip to the SBR, and open the SBR-App to acquire an image 5 min after sample introduction. There is no requirement for complicated sample pre-treatment and expensive equipment except for a smartphone. This versatile and cost-effective smartphone-based sensing system featured with reliability and simplicity is ideally suited for user- and eco-friendly point-of-need detection in resource-constrained environments.

Spectroscopic and Structural Analysis of Cu2+-Induced Fluorescence Quenching of ZsYellow

Fluorescent proteins exhibit fluorescence quenching by specific transition metals, suggesting their potential as fluorescent protein-based metal biosensors. Each fluorescent protein exhibits unique spectroscopic properties and mechanisms for fluorescence quenching by metals. Therefore, the metal-induced fluorescence quenching analysis of various new fluorescent proteins would be important step towards the development of such fluorescent protein-based metal biosensors. Here, we first report the spectroscopic and structural analysis of the yellow fluorescent protein ZsYellow, following its metal-induced quenching. Spectroscopic analysis showed that ZsYellow exhibited a high degree of fluorescence quenching by Cu²⁺. During Cu²⁺-induced ZsYellow quenching, fluorescence emission was recovered by adding EDTA. The crystal structure of ZsYellow soaked in Cu²⁺ solution was determined at a 2.6 Å resolution. The electron density map did not indicate the presence of Cu²⁺ around the chromophore or the β-barrel surface, which resulted in fluorescence quenching without Cu²⁺ binding to specific site in ZsYellow. Based on these results, we propose the fluorescence quenching to occur in a distance-dependent manner between the metal and the fluorescent protein, when these components get to a closer vicinity at higher metal concentrations. Our results provide useful insights for future development of fluorescent protein-based metal biosensors.

Sequential colorimetric sensing of cupric and mercuric ions by regulating the etching process of triangular gold nanoplates

A triangular gold nanoplate (AuNPL)-based colorimetric assay is presented for ultrasensitive determination of cupric ions (Cu²⁺⁾ and mercuric ions (Hg²⁺) in sequence. AuNPLs were found to be etched efficiently when producing triiodide ions (I₃^-) by a redox reaction between Cu²⁺ and iodide ions (I^-), leading to a change of the shape of AuNPLs from triangular to sphere along with a color change from blue to pink. In the presence of Hg²⁺ the etching of AuNPLs was suppressed due to the consumption of I^- by the formation of HgI₂. With an increase of the concentration of the Hg²⁺ a transformation from sphere to triangular in the shape of AuNPLs occurred with a color change from pink to blue. The evolution of AuNPLs from etching to anti-etching state by sequential addition of Cu²⁺ and Hg²⁺ was accompanied with color variations and band shifts of localized surface plasmon resonance (LSPR), allowing for visual and spectroscopic determination of Cu²⁺ and Hg²⁺ successively within 15 min. In the range 0.01-1.5 μM for Cu²⁺ and 0.02-3.0 μM for Hg²⁺, the linear relationship between the band shift values and the target ions concentration was found good (R² > 0.996). The limit of detections (3S/k) was 19 nM for Cu²⁺ and 9 nM for Hg²⁺, respectively. The lowest visual estimation concentration was 80 nM for both Cu²⁺ and Hg²⁺ through the distinguishable color changes. This system exhibited desirable selectivity for Cu²⁺ and Hg²⁺ over other common ions tested. The method has been successfully applied to sequential determination of Cu²⁺ and Hg²⁺ in real water and food samples. Graphical abstract Scheme 1 Schematic illustration for sequential detection of Cu²⁺ and Hg²⁺ based on etching of AuNPLs.

Spectroscopic and Magneto-Optical Signatures of Cu1+ and Cu2+ Defects in Copper Indium Sulfide Quantum Dots

Colloidal quantum dots (QDs) of I-III-VI ternary compounds such as copper indium sulfide (CIS) and copper indium selenide (CISe) have been under intense investigation due to both their unusual photophysical properties and considerable technological utility. These materials feature a toxic-element-free composition, a tunable bandgap that covers near-infrared and visible spectral energies, and a highly efficient photoluminescence (PL) whose spectrum is located in the reabsorption-free intragap region. These properties make them attractive for light-emission and light-harvesting applications including photovoltaics and luminescent solar concentrators. Despite a large body of literature on device-related studies of CISe(S) QDs, the understanding of their fundamental photophysical properties is surprisingly poor. Two particular subjects that are still heavily debated in the literature include the mechanism(s) for strong intragap emission and the reason(s) for a poorly defined (featureless) absorption edge, which often "tails" below the nominal bandgap. Here, we address these questions by conducting comprehensive spectroscopic studies of CIS QD samples with varied Cu-to-In ratios using resonant PL and PL excitation, femtosecond transient absorption, and magnetic circular dichroism measurements. These studies reveal a strong effect of stoichiometry on the concentration of Cu¹⁺ vs Cu²⁺ defects (occurring as Cu_In^″ and Cu_Cu^• species, respectively), and their effects on QD optical properties. In particular, we demonstrate that the increase in the relative amount of Cu²⁺ vs Cu¹⁺ centers suppresses intragap absorption associated with Cu¹⁺ states and sharpens band-edge absorption. In addition, we show that both Cu¹⁺ and Cu²⁺ centers are emissive but are characterized by distinct activation mechanisms and slightly different emission energies due to different crystal lattice environments. An important overall conclusion of this study is that the relative importance of the Cu²⁺ vs Cu¹⁺ emission/absorption channels can be controlled by tuning the Cu-to-In ratio, suggesting that the control of sample stoichiometry represents a powerful tool for achieving functionalities (e.g., strong intragap emission) that are not accessible with ideal, defect-free materials.

Responses of Periphyton Microbial Growth, Activity, and Pollutant Removal Efficiency to Cu Exposure

Periphyton is an effective matrix for the removal of pollutants in wastewater and has been considered a promising method of bioremediation. However, it still needs to be verified whether periphyton can maintain microbial activity and pollutant removal efficiency when dealing with the influence with complex components, and the underlying mechanisms of periphyton need to be revealed further. Herein, this study investigated the microbial growth, activity and functional responses of periphyton after removal of Cu from wastewater. Results showed that the cultivated periphyton was dominated by filamentous algae, and high Cu removal efficiencies by periphyton were obtained after 108 h treatments. Although 2 mg/L Cu²⁺ changed the microalgal growth (decreasing the contents of total chlorophyll-a (Chla), the carbon source utilization and microbial metabolic activity in periphyton were not significantly affected and even increased by 2 mg/L Cu²⁺. Moreover, chemical oxygen demand (COD) removal rates were sustained after 0.5 and 2 mg/L Cu²⁺ treatments. Our work showed that periphyton had strong tolerance and resistance on Cu stress and is environmentally friendly in dealing with wastewater containing heavy metals, as the microbial functions in pollutant removal could be maintained.