Ions In Water Samples Research Articles

Persistent luminescent nanoparticles with enhanced afterglow through polydopamine modification for separation-free and visual detection of iron ions in water

Fluorescence analysis is one of the most popular methods in metal ions detection, but the background interference is an unavoidable obstacle in the fluorescence analysis of complex samples. In this work, a persistent luminescence nanoprobe was designed to detect iron ions in real samples by avoiding background interference. First, the Sr4Al14O25:Eu2+, Dy3+ persistent luminescent nanoparticles (PLNPs) were prepared by solid-state reaction protocols and polydopamine (PDA) encapsulation. After modification, these PLNPs@PDA showed better afterglow performance. More importantly, the PLNPs@PDA are highly selective toward iron ions, and could serve as an afterglow “turn off” nanoprobe for selective detection of iron ions through a dynamic quenching mechanism, with a detection limit of 2.86 μM. To further realize rapid and on-site detection, a test strip based on PLNPs@PDA was prepared and applied, which also showed good detection performance in real water samples. Compared with other detection methods, this afterglow imaging detection does not depend on expensive instruments, and can effectively shield the interference of background fluorescence from complex water samples, which has a good application prospects in the actual water sample. This work opens a new avenue for developing afterglow probe for the detection of metal ion in water samples without background interference.

Antioxidant and Antibacterial Screening and Hg(II) Sensing, Activities of Cu(II)pyridine-2,6-dicarboxylate Complexes.

In this study five different complexes of Cu(II) were synthesized for the purpose of environmentally notorious mercury sensing and preliminary biological screening. Pyridine-2,6-dicarboxylic acid (also known as dipicolinic acid, and abbreviated as H2DPA), 3-phenyl pyrazole (3-ppz), 4-iodo-1H-pyrazole (4-ipz), 4-nitropyrazole (4-npz), 4-bromopyrazole (4-bpz), and 4-chloropyrazole (4-cpz) were chosen as potential ligands. The synthesized complexes labelled as 1-5, namely [Cu(DPA)(3-ppz)], [Cu(DPA)(4-ipz)], [Cu(DPA)(4-npz)], [Cu(DPA)(4-bpz)], [Cu(DPA)(4-cpz)], were proposed based on spectroscopic data (FTIR, TGA, and UV-visible spectroscopy). These complexes feature C=O functionalities that are not involved in coordination and may be used for further applications. The isolated complexes were utilized for detecting Hg(II) ions in water samples. Various concentrations of Hg(II) ions were prepared for detection purposes, and changes in absorption concerning complexes 1-5 were determined using UV-Visible spectroscopy. It was found that complexes 3 and 4 exhibit efficient sensing abilities towards Hg(II) ions. The antibacterial activities of complexes 1-5 were assessed against S. typhi and E. coli. The complexes 1 and 3 displayed good antibacterial activities against S. typhi (13.67, and 13.56 mm, respectively) while complexes 1, 2 and 4 were found to be efficient against E. coli (11.6, 12.66, 11.31 mm, respectively). The absorption maxima of 2,2-diphenyl-1-picryhydrazyl (DPPH) at 517 nm, considerably shifted upon addition of complexes 1-5. The results reveal that the complexes possess potential free radical scavenging abilities.

Facile synthesis of Co/rGO, Au/rGO, and CoAu/rGO nanocomposites for precise determination of Arsenic(III) in water systems

Cobalt (Co), gold (Au), and cobalt-gold (CoAu) nanoparticles were deposited on reduced graphene oxide (rGO) by a facile and scalable procedure. The synthesised nanocomposites (Co/rGO, Au/rGO, and CoAu/rGO) were used as electrode materials for detecting trace amounts of arsenic (As(III)) ions in water samples. All three electrodes responded to the presence of As(III) in an acidic medium (different acids of the same concentration, then chosen acid at different concentrations). A detailed optimization of the conditions was continued with the CoAu/rGO electrode which showed the best response in terms of the best defined peak indicating the oxidation of As(0) to As(III) and the highest current. The electrode was tested in a wide range of concentrations (30–1000 µM), where two areas of linearity and limits of detection were obtained (for low- and high- concentrations). Moreover, this electrode showed the ability to detect As(III) ions in the presence of Cu(II), as an interference model as well as a satisfactory electrochemical response, in terms of a clear peak corresponding to the oxidation of As(0) to As(III) in a real sample.

A multifunctional near-infrared fluorescent probe based on benzothiazole structure for fluoride-ion detection

Fluoride ions (F−) are one of the essential trace elements for the human body and are widely existed in nature. In this study, we present a novel fluorescent probe (YF-SZ-F) designed and synthesized for the specific detection of F−. The probe exhibits high sensitivity, excellent selectivity, and low cytotoxicity, making it a promising tool for biomedical applications. Imaging experiments conducted on zebrafish and Arabidopsis roots demonstrate the probe’s remarkable cellular permeability and biocompatibility, laying a solid foundation for its potential biomedical utility. Furthermore, the probe holds potential for practical applications in environmental monitoring and public health through its capability to detect fluoride ions in water samples and via mobile phone software. This multifaceted functionality underscores the broad applicability and significance of the fluorescent probe, not only in scientific research but also in real-world scenarios, contributing to the development of more convenient and precise methods for fluoride detection.

Au nanoparticles decorated graphitic carbon nitride nanosheets as a sensitive and selective fluorescence probe for Fe3+ and dichromate ions in aqueous medium

Graphitic carbon nitride mutated with metal nanoparticles has captivated great interest as an effective fluorescent sensor for the detection of harmful ions present in water. In the present work, bulk-gCN was synthesized using melamine as precursor, and further Au-gCN nanocomposite were fabricated via in-situ direct reduction deposition method. The structural, morphological, compositional, stability and optical properties of bulk gCN and Au-gCN nanocomposite were examined using various scattering and spectroscopic techniques such as HRTEM, XPS, XRD and SEM. The synthesized bulk gCN straggles during selectivity studies with different cations and anions because of its uneven surface morphology, however in Au-gCN gold nanoparticles are uniformly distributed on the gCN sheets which results in its enhanced selectivity over bulk gCN. This leads to the fabrication of an optical sensor for Fe3+ and Cr2O72− ions with limit of detection of 4.62 and 2.77 μM, respectively. The sensing of Fe3+ ions corresponds to the photoinduced electron transfer (PET) mechanism, while the detection of chromate species is associated with an inner filter effect (IFE). The practical applicability of the sensor was also evaluated for different environmental water samples. The high stability, sensitivity, and specificity of Au-gCN nanocomposite make it a potential fluorescent probe for Fe3+ and Cr2O72− ions in water samples.

Microwave assisted facile one pot synthesis of novel pyrazole derivative for multi-analyte detection (Fe3+ and Zn2+) and its solvatochromic studies

A novel heterocyclic pyrazole-based probe Ph-DB was synthesised by microwave assisted concatenation of phenyl hydrazine and 2,5-dibromo-3-thiophenecarboxylaldehyde. The veracity of synthesized pyrazole derivative was established using 1H NMR,13C NMR, HRMS and FT-IR. ICT studies were conducted in different organic solvents of varying polarity to comprehend the solvatochromic nature of compound. DFT studies were performed to elucidate the intricacies of the Ph-DB’s electronic structure. The electrochemical band gap and optical band gap were calculated using cyclic voltammetry and Tauc's plot respectively. SEM analysis was carried out to explore the surface morphology of Ph-DB which was found to show small microwires like structures which supports optoelectrical properties of Ph-DB. The photophysical studies were carried out to check the chromogenic and fluorogenic response of Ph-DB towards different metal ions. It was observed that Ph-DB shows noticeable fluorescence enhancement with Zn2+ ions with the detection limit of 6.1 µM and chromogenic change with Fe3+ with a detection limit of 6.6 µM. Additionally quantum yield, binding constant and recovery experiment of Ph-DB probe were performed. Ph-DB probe was utilised for precise monitoring of Zn2+ and Fe3+ ions in water samples.

L-cysteine modified N-doped carbon quantum dots derived from peach palm (Bactris gasipaes) peels for detection of mercury ions

Establishing an effective strategy for Hg2+ determination with good sensitivity and high selectivity is of particular concern. In this work, N-doped carbon quantum dots (NCQDs) were obtained for the first time from peels of peach palm fruit (Bactris gasipaes) through microwave-assisted one-pot synthesis. Surface NCQDs was modified with l-cysteine (NCQDs/CYS) by a chemical reaction (known as amide coupling) between the nitrogen-containing groups (amine group) of l-cysteine ligand and the carboxyl groups of NCQDs. The chemical bonding was examined by Fourier Transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). NCQDs/CYS nanoparticles exhibited a quantum yield of fluorescence (ΦFL) of 25.4%, high solubility in water, and a surface with thiol groups from l-cysteine. Mercury ions induced quenching of fluorescence of NCQDs/CYS at low concentrations (Limit of Detection, LOD = 0.19 μM) with great sensitivity. A significant preference for Hg2+ ions was found because of the high affinity between the thiolate groups of NCQDs/CYS and the analyte. Time-resolved fluorescence measurements were done to study the way that led to fluorescence quenching when Hg2+ ions were present, evidencing a static quenching fluorescence mechanism. The new NCQDs/CYS material could be applied to accurately measure the concentration of Hg2+ ions in water samples in a fast and cost-effective way.

In Situ Ni(II) Complexation Induced Deprotonation of Bis-Thiourea-Based Tweezers in DMSO-Water Medium: An Approach toward Recognition of Fluoride Ions in Water with Organic Probe Molecules.

Recognition of fluoride in water through the fluoride-induced Brönsted acid-base deprotonation reaction of an organic probe molecule is still a challenging task owing to the lower basicity of fluoride ions and the instability of the conjugate base of the probe molecules in aqueous medium. Herein, we report a complementary strategy in which the conjugate base of the studied bis-thiourea molecule in dimethyl sulfoxide (DMSO) medium is simultaneously stabilized through chelation of the Ni(II) ion, which eventually facilitates the recognition of the fluoride ion in water samples. The recognition methodology is validated colorimetrically and electrochemically, and finally, the applicability of the approach is explored with water samples collected from fluoride-affected areas. The limit of detection value for the fluoride ion in water medium was found to be 0.2 and 0.3 ppm with UV-visible spectroscopy and differential pulse voltammetry measurements, respectively. The methodology is also demonstrated on a paper strip for the detection of the fluoride ion with the naked eye and a smartphone-based RGB sensor. The scheme has been shown to be effective in enhancing the aqueous fluoride recognition ability of the organic probe molecules with acidic hydrogen prone to deprotonation by the fluoride ion.

Aggregation-induced emission active multianalyte sensor: Detection of pH, carbonate, bi-carbonate and nitroaromatics in water

An aggregation-induced emission (AIE) based multi-tasking probe DAAQ (5-(dimethylamino)-N-(9,10-dioxo-9,10-dihydroanthracen-2-yl)naphthalene-1-sulfonamide) has been reported for detecting multiple analytes such as anions (carbonate and bicarbonate ions) and nitroaromatic compounds (2,4-DNP and TNP). Probe DAAQ displayed the photophysical properties of aggregation-induced emission (AIE) in DMSO-water mixture, acidochromism and detected various analytes, making DAAQ a multi-tasking probe. DAAQ respond to carbonate and bicarbonate (CO32− and HCO3−) with a colour change from pale yellow to dark orange. The limit of detections (LOD) was estimated as 0.486 mg/L and 41.35 mg/L for CO32− and HCO3−, respectively. The applications of DAAQ were also explored to detect CO32− ions in water samples collected from various sources and soft drinks. Further, the probe also explored detecting neural aromatic compounds such as 2,4-DNP and TNP by a naked eye colour change and the LODs were calculated as 12.6 µM and 8.19 µM, respectively. DFT calculations were applied for the confirmation binding studies of DAAQ with multiple analytes. The sensing of 2,4-DNP and TNP were achieved through PET with a Turn-Off response. The sensing mechanisms were confirmed with 1H NMR experiments.

A ratiometric and selective fluorescent nanosensor for determining Hg2+ ions based on a novel functionalized metal–organic framework

A new method using fluorescence was developed to detect Hg2+ ions in water. This method relied on the reaction between NH2‐MIL‐53(Al) and 5‐bromo‐2‐hydroxyacetophenone. The method was carefully fine‐tuned for optimal reaction conditions and analytical parameters like pH levels, nanosensor quantity, and detection limits. It showed great linearity in detecting Hg2+ ions in the range of 0.0–3.0 ppm (0.0–1.50 × 10−5 M), with a very low detection limit of 1.65 × 10−2 ppm (8.23 × 10−8 M). We tested how well the method can distinguish between different substances by investigating whether other common substances in water samples would interfere. The results were positive, as the presence of these substances did not significantly affect the accuracy of detecting Hg2+ ions, confirming the method's reliability. In order to confirm its dependability, we conducted a quantitative test to detect Hg2+ ions in water samples. The recovery rates obtained ranged from 97.16% to 103.2%, demonstrating the method's precision and accuracy. A comparison with inductively coupled plasma optical emission spectrometry (ICP‐OES), a well‐known method for analyzing trace metals, produced similar results, further instilling confidence in the 5Br2HA = N‐Al‐MOF nanosensor that was developed. In general, this research emphasizes the exciting potential of the new nanosensor in detecting Hg2+ ions in various water and cosmetic samples. It provides a strong and dependable alternative to traditional detection methods.

Physicochemical attributes and bacteriome diversity of Lake Tunari, Taraba State, Nigeria

Physicochemical parameters of aquatic habitats can play an influential part in shaping the microbial communities of water bodies. In this study, water samples from Lake Tunari were analysed for its microbiome and physicochemical attributes, using spectrophotometric and culture-dependent methodologies respectively. The temperature of the lake ranged from 28.00 – 29.00 (°C), while the pH ranged from 6.50 – 7.20. Heavy metals such as Manganese (0.48 ppm), Lead (0.14 ppm) and Selenium (0.10 ppm) showed significantly high values in selected parts of the lake, surpassing limits set by the World Health Organisation. Microbiome analysis revealed the largest phylum across sample sites as Proteobacteria, Firmicutes, and Planctomycetota with peak relative abundance values of 64.13%, 45.29% and 16.11% respectively. Bacterial genera such as Exiguobacterium, Methylocystis and Rhodoferax were detected from designated sites. The presence of these genera capable of tolerating, utilizing or degrading metal ions in water samples of the Lake might be indicative of chemical and metal trickles into the water body. In addition, relatively new and understudied bacterial phyla such as Gemmatimonadota, as well as unknown bacterial clades were identified from water samples of the lake. This study has revealed that Lake Tunari is not impervious to pollution, caused by either anthropogenic activities or from adjoining water channels. Environmental health awareness programs can be introduced to enlighten the populace, while scheduled microbial and physicochemical surveillance can be adopted, to control microbial contamination and curtail toxic material inflow into the Lake.

Machine learning approaches for simultaneous spectrophotometric determination of heavy metal ions in water samples

In this study, the simultaneous determination of Co, Cd, Ni, Cu, and Pb was carried out as a color complex with 4-(2-pyridylazo) resorcinol in an aqueous solution under the assesting of machine learning. A partial least-squares multivariate linear regression and artificial neuron network for the analysis of mixtures of metals were developed. MATLAB is a powerful software machine learning program that was used to support matrix calculations and displays. The benefit of MATLAB in the construction of the machine learning model allows the development of a rapid and highly effective analysis of multiple components in the mixtures without separation and enrichment. For individual determinations, the working ranges were discovered as the important information for choosing the initial concentration of each heavy metal in a mixture, r. The results of analysis of Ni2+, Pb2+, and Cd2+ by two methods Partial Least Squares - PLS and Artificial Neural Networks - ANN are sensitive and accurate for simultaneous determination of the concentration of these ions in the synthesis mixture with a high regression coefficient of 0.993, respectively, 0.997, 0.997 for Ni2+, Pb2+ and Cd2+. As for Cu2+ and Co2+, the accuracy is higher when using the ANN method.

Thiol-based chemically modified carbon screen-printed electrode for simultaneous quantification of trace level Pb(II) and Cd(II).

Present work reports, the development of a novel electrochemical sensor based on a diazonium-coupling reaction and covalent attachment of the -NH2 group of cysteamine (Cyst) on screen-printed carbon electrode (SPCE), for simultaneous determination of Pb(II) and Cd(II). Initially, the in-situ generated 4-carboxyphenyl (4-CP) diazonium salt was electro-grafted to generate 4-CP/SPCE, followed by covalent bonding of terminal carboxylic group of 4-CP with -NH2 group of Cyst to give Cyst/4-CP/SPCE. The modified electrode showed an enhanced selectivity and sensitivity toward the quantification of Pb(II) and Cd(II) using square wave anodic stripping voltammetry (SWASV) without mutual interference. Under optimal experimental conditions, the newly designed sensor showed a wide linear range of 0.01µM to 0.7µM. The limit of detection (LOD) obtained was 0.882nM (0.09 ppb) and 0.65nM (0.134ppb) for Cd(II) and Pb(II), respectively. The modified SPCE exhibited good stability, selectivity, and reproducibility. Furthermore, the sensor was successfully applied for the determination of Pb(II) and Cd(II) ions in water samples which illustrated excellent recoveries in different spiked samples and the results were in line with the standard ICP-AES analysis.

Aminosilane assisted deposition of gold nanoparticles on Zn(OH)2 nanosheets and their application in electrochemical sensor

A facile and efficient method for systematical deposition of gold nanoparticles (AuNPs) on Zn(OH)2 nanosheets (NS) with different Zn and Au ratios was established in the presence of N-[3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT silane), without adding any external reducing agents, at room temperature. Here, TPDT silane behaves as both a stabilizing and reducing agent. UV–vis absorption spectroscopy, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to confirm the formation of AuNPs on Zn(OH)2 NS. As the concentration of AuNPs increased, a proportional increase in both the number and size of deposited AuNPs on Zn(OH)2 NS was observed. To understand how the variation in the number and size of AuNPs affects their catalytic activity, the electrocatalytic activity of different composition ratios of Zn(OH)2-Au NS toward nitrite ions was studied using cyclic voltammetry and amperometric technique. The TPDT-stabilized Zn(OH)2-Au NS showed high electrocatalytic activity, attributed to the effective electron transfer from Zn(OH)2 NS to AuNPs, creating a synergistic effect that enhances the overall activity. The optimal Zn(OH)2-Au NS modified electrode showed an amperometric sensitivity of 5.72 nA/µM and a limit of detection of 1.2 µM for nitrite ions in water sample well below the guideline value of WHO. This demonstrates the practical applicability of this method for real-world water analysis.

A single excitation dual emission semi-salamo type multi-functional probe for sensitive pH and Cu2+ detection

pH and Cu2+ ion concentration changes are linked to disorders like Alzheimer's and cancer. Rapid detection of pH and Cu2+ ions is critical for public health and environmental concerns. The semi-salamo-type probe (E)-2-hydroxy-1-naphthaldehyde O-(2-(aminooxy)ethyl) oxime (NSS) demonstrated substantial dual-functional performance, sensing pH change and Cu2+ ions. A single excitation and double emission characteristic on the probe NSS made it distinctive. Probe NSS exhibits pH-dependent excited state intramolecular proton transfer (ESIPT), and its optical properties vary based on the pH environment. Probe NSS detects pH changes from 2 to 11 by changing the “off-on-off” of the excited state intra-molecular proton transfer (ESIPT) mechanism, exhibiting rapid, reversible, and selective responses. In addition, the luminescent salamo-like naphthalene-based probe NSS can coordinate with Cu2+ ions, achieving great selectivity and sensitivity to identify Cu2+ ions with a detection limit of 0.84 ppb (13.2 nM) Probe NSS can detect Cu2+ ions in actual water samples such as tap water and yellow river water. The test strip loaded with probe NSS enabled quick and accurate detection of Cu2+ ions in water samples. Consequently, the versatile salamo-type probe NSS lays the foundation for developing high sensitivity and fast-response dual-mode pH meters as well as Cu2+ sensing.

A carboethoxy quinoline-Derived Schiff base chemosensor: Crystal structure, selective Hg2+ ion detection and its computational study

Environmental monitoring of mercury (Hg2+) ions has become increasingly important as a result of their detrimental effects on biological organisms at all levels. To recognize toxic metal ions, utmost effort has been devoted to developing new materials that are highly selective, ultra-sensitive, and provide rapid response. In this context, a new chemosensor, 2-imino [N - (N-amido phenyl)]-6-methoxy-3-carbethoxy quinoline (L), has been synthesized by combining 2-formyl-6-methoxy-3-carbethoxy quinoline and benzhydrazide and it has been extensively characterized by NMR, FTIR, ESI-Mass and SCXRD analysis. Probe L has excellent specificity and sensitivity toward Hg2+ ions in semi-aqueous solutions, with a detection limit of 0.185 μM, regardless of the presence of other interfering cations. Chromogenic behavior was demonstrated by the L when it changed the color of the solution from colorless to light yellow, a change that can be observed visually. The probe L forms a 1:1 stochiometric complex with an estimated association constant (Ka) of 6.74 × 104 M−1. The 1H NMR change and density functional theory calculations were analyzed to improve our understanding of the sensing mechanism. Also, an inexpensive and simple paper-based test kit has been developed for the on-site detection of mercury ions in water samples.

Evaluation of PVC@Silver Nanocomposite as Sensor for Low Limit Detection of Cadmium Ion By Surface Plasmon Resonance Based Method

This study explores the development of a PVC@Silver nanocomposite for enhanced detection of cadmium ions in water samples. Various characterization techniques confirmed the successful incorporation of silver nanoparticles into the polyvinyl chloride (PVC) matrix across different concentrations (1–4%). X-ray diffraction revealed the face-centered cubic crystalline structure of the silver nanoparticles, with the intensities of the (111), (200), (220), and (311) peaks increasing with higher Ag concentrations. The average crystallite sizes ranged from 26.1 nm (3% Ag) to 30.0 nm (2% Ag). Dynamic light scattering showed nanoparticle sizes of 24–43 nm, while zeta potential values of -24 to -40 mV indicated reasonable colloidal stability. Brunauer–Emmett–Teller (BET) surface area analysis demonstrated a decreasing surface area from 30.09 m2/g (1% Ag) to 25.27 m2/g (3% Ag), attributed to pore filling by silver nanostructures. Significantly, the PVC@Silver nanocomposite facilitated sensitive detection of Cd(II) ions using surface plasmon resonance (SPR), exhibiting an SPR angle shift of 26.30° with intensity values ranging from 10.80 (4% Ag) to 12.19 (3% Ag). UV–vis spectra revealed a prominent surface plasmon resonance band at 420–430 nm, indicating the presence of silver nanoparticles. The optical band gap varied from 4.51eV (1% Ag) to 4.12eV (4% Ag).

An ESIPT active coumarin-diphenyl azine-based AIEgen: Nanomolar Cu2+ ion sensing, Latent Fingerprinting, live-cell imaging, and real sample analysis

Designing economical and sensitive chemosensors for detecting important metal ions, like Cu2+ ions, is essential and remains a hot topic worldwide. In this investigation, we extended our investigation to design a specific diphenyl-azine-based skeletal system for the selective and sensitive detection of Cu2+ions. We reported a coumarin-diphenyl-azine-based AIEgen (C-1) using an improvised methodology with a large Stoke's shift (∼245 nm) for precisely sensing copper ions in solid, solution, and biological cells. The AIE-ESIPT properties of C-1 were validated using various sophisticated techniques. C-1 was found to be a promising selective and sensitive sensor of Cu2+ ions (nanomolar LOD value ∼10.38 nM) via colorimetric and TURNOFF fluorometric ways. The practical applicability of C-1 was analyzed via real-time estimation of copper ions in water samples (obtained from three varied locations) and in biological samples (urine and serum). The satisfactory recovery with a low RSD value indicates the potential of C-1 in detecting copper ions in actual samples. Estimating copper ions in urine and blood samples demonstrates the usefulness of C-1 in diagnosing disorders like Wilson's disease, which is caused by high concentrations of copper ions in the body. Additionally, we have detected Cu2+ions in live cells (HeLa cells) and carried out Latent Fingerprinting (Level 1 and Level 2) to validate its versatility in physiological and forensic applications. Overall, the proposed C-1 AIEgen is an ultrasensitive Cu2+ions sensor with innumerable applications in the physical world.

Controllable detection threshold achieved through the toehold switch system in a mercury ion whole-cell biosensor

Due to the toxicity of mercury and its harmful effects on human health, it is essential to establish a low-cost, highly sensitive and highly specific monitoring method with a wide detection range, ideally with a simple visual readout. In this study, a whole-cell biosensor with adjustable detection limits was developed for the detection of mercury ions in water samples, allowing controllable threshold detection with an expanded detection range. Gene circuits were constructed by combining the toehold switch system with lactose operon, mercury-ion-specific operon, and inducible red fluorescent protein gene. Using MATLAB for design and selection, a total of eleven dual-input single-output sensing logic circuits were obtained based on the basic logic of gene circuit construction. Then, biosensor DTS-3 was selected based on its fluorescence response at different isopropyl β-D-Thiogalactoside (IPTG) concentrations, exhibiting the controllable detection threshold. At 5–20 μM IPTG, DTS-3 can achieve variable threshold detection in the range of 0.005–0.0075, 0.06–0.08, 1–2, and 4–6 μM mercury ion concentrations, respectively. Specificity experiments demonstrated that DTS-3 exhibits good specificity, not showing fluorescence response changes compared with other metal ions. Furthermore spiked sample experiments demonstrated its good resistance to interference, allowing it to distinguish mercury ion concentrations as low as 7.5 nM by the naked eye and 5 nM using a microplate reader. This study confirms the feasibility and performance of biosensor with controllable detection threshold, providing a new detection method and new ideas for expanding the detection range of biosensors while ensuring rapid and convenient measurements without compromising sensitivity.

A novel tryptanthrin-based "on-off-on" probe for sequential sensing Cu2+/S2- in water samples.

Copper ions (Cu2+) and sulfide (S2-) play essential roles in many physiologies and pathologic processes. Herein, a new "on-off-on" tryptanthrin-based probe TR-1 (TR-1) has been designed and synthesized inafacileandeconomicalway. TR-1 exhibited highly selective and sensitive response to Cu2+ without any interference over 14 competitive metal ions and the detection limit downs to 24nM, which is far below the Chinese standard of fishery water quality (157nM). The 'in situ' prepared complex TR-1 + Cu2+ could also be applied to detect S2- with the detection limit of 62nM. Further, TR-1 was potentially applied for the analysis of copper ions in water samples.