Tap Water Samples Research Articles

Silver nanoparticles from orange peel extract: Colorimetric detection of Pb2+ and Cd2+ ions with a chemometric approach

Green silver nanoparticles (AgNPs@OPE) were obtained by using orange (citrus sinensis) peel water extract (OPE) that acts as a reducing and capping agent. This procedure permits the valorisation of waste as orange peel, and lowers the environmental impact of the process, with respect to the conventional synthetic procedure. The OPE extract reduced Ag(I) to Ag(0) in alkaline conditions, and stabilised the produced nanoparticles as a capping agent. The AgNPs@OPE were deeply characterized by UV–Vis spectroscopy, FT-IR, SEM analysis and DLS analysis and successively used as colorimetric sensors for different metals in aqueous solution. The colourimetric assay showed that AgNPs@OPE were able to detect Pb2+ and Cd2+, as demonstrated by the splits of surface plasmon resonance (SPR) band accompanied by the formation of a second new band; these spectral modification resulted in a colour change, from pristine nanoparticles’ yellow to brown, due to the aggregation process. For the quantification of each of the two target cations, a calibration was performed by using the univariate linear regression, within the linearity ranges, exploiting the absorbance ratio between the main SPR band and the new band relative to the aggregate formation. Then a multivariate approach was followed to perform both Cd2+ and Pb2+ quantification by means of Partial Least Square regression (PLS) and target cations distinction by Linear Discriminant Analysis (LDA) applied on Principal Components Analysis (PCA) outputs, in both cases using the entire UV–Vis spectra (350–800 nm) as input data. Finally, the ability to quantify and distinguish between Cd2+ and Pb2+ was tested in tap water samples spiked with the two cations in order to confirm the application of the AgNPs@OPE as selective sensor in real samples.

A Fluorescent Probe Derived from L‐Tryptophan for Copper (II) Ion Detection in Aqueous Media

AbstractCopper (Cu2+) is a transition metal ion extensively distributed in numerous foodstuffs of both animals and vegetables. An excess intake of Cu2+ ions cause injury, pneumonitis, a disorder in the nervous system, and gastrointestinal problems. Hence, we have developed a simple and novel Schiff base‐based fluorescence sensor for the detection of Cu2+ ions. The sensor, ‐3‐(1H‐indol‐3‐yl)‐2‐((4‐nitrobenzylidene) amino)propanoic acid (INAP), was synthesized from tryptophan and nitrobenzaldehyde by the reflux method and characterized by various analytical methods. The prepared INAP acted as a chemical sensor and displayed outstanding sensitivity and choosiness characteristics for Cu2+ ions an aqueous solvent. In the presence of Cu2+, it demonstrated a fluorescence change in an aqueous medium with a “turn‐off” phenomenon via complex‐mediated energy transfer characteristics, and the method of continuous variation suggested a 1 : 2 complex formation of the metal ion with INAP. The LOD of the sensor system was calculated to be 1.3 μM for the Cu2+ ion. In addition, the INAP fluorescent probe was applied to tap water samples and found acceptable recoveries. These results suggest that the newly fabricated sensor system would be explored as a chemosensor for the recognition of Cu2+ ions in environmental samples.

Superparamagnetic hydrophilic molecularly imprinted nanoparticles for an efficient and selective removal of tetracycline from water

In this work, a novel superparamagnetic hydrophilic molecularly imprinted nanomaterial for the removal of tetracycline (TC) was synthesized utilizing magnetite (Fe3O4) as the magnetic core, TC as the template molecule, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. Initially, Fe3O4 magnetic nanoparticles (MNP) coated with SiO2 (MNP@SiO2) were synthesized, followed by TC molecular imprinting on the nanoparticles. Initially, Fe3O4 MNP coated with SiO2 (MNP@SiO2) were synthesized, followed by TC molecular imprinting on the nanoparticles. The synthesis method for MNP@SiO2 was optimized, and DLS analysis of 10 replicates showed a nanoparticle size of 70.1 ± 5.8 nm, indicating high method reproducibility. The MNP@SiO2, as well as the imprinted (MNP@SiO2-MIP) and non-imprinted (MNP@SiO2–NIP) nanomaterials, were characterized by FTIR, TEM, VSM, XRD, DLS, Z potential, and BET analysis. The saturation magnetization (Ms) values were 43 emu/g for MNP@SiO2 and 32 emu/g for both MNP@SiO2-MIP and MNP@SiO2–NIP, confirming suitability for magnetic separation using external magnets. Batch binding experiments conducted in water and methanol assessed adsorption isotherms and binding kinetics, with data fitting the Langmuir isotherm model better than the Freundlich model. The developed MIP exhibited significant selectivity against other molecules with similar functional groups and size. In water, the adsorption capacity of the MNP@SiO2-MIP was 23 mg/g, with an imprinting factor of 2.2. Furthermore, the MIP demonstrated good regeneration performance. The material was tested on TC-spiked tap water samples, achieving 80.1 % TC removal with high reproducibility (3.2 %, n = 3). Combining hydrophilic superparamagnetic nanoparticles with molecular imprinting enhances their potential applications in environmental remediation, antibiotic purification, and drug delivery.

Construction of nitrite electrochemical sensor by in-situ deposition of FeOOH nanomaterials on carbon cloth modified with green DBD technology

The treatment of carbon cloth with concentrated or dilute acid to produce hydrophilic carbon-based flexible electrodes raises environmental pollution concerns. This study utilized a green, rapid, and cost-effective dielectric barrier discharge (DBD) technique was utilized for the hydrophilic modification of conductive hydrophobic carbon cloth. A nitrite electrochemical sensor was constructed by depositing high specific surface area pom-pom FeOOH on modified carbon cloth through a constant potential electrochemical in-situ deposition method. The FeOOH/CC binder-free self-supporting electrode demonstrates nitrite detection capabilities within linear ranges of 0.5–900 µM and 1 mM–10 mM, boasting a detection limit of 0.154 µM (S/N = 3). This sensor exhibits excellent interference immunity, stability, and reproducibility. Its application in detecting nitrite in ham sausage and tap water samples yields 97.00 % to 101.33 % recovery rates, respectively, comparable to UV spectrophotometry results, affirming the sensor’s accuracy and practical feasibility. This straightforward and swift carbon material modification technique presents a novel approach for crafting carbon cloth electrochemical sensors.

Enhancing Analytical Sensitivity and Selectivity for Methylene Blue Determination in Water Samples by Using Multiphase Electroextraction Coupled with Optical Absorption Spectroscopy and Surface-Enhanced Raman Scattering.

While optical analysis spectroscopy offers operational ease and low cost, it suffers from limitations regarding sensitivity when it comes to analyzing analytes at low concentrations. On the other hand, surface-enhanced Raman spectroscopy (SERS) offers high sensitivity but low selectivity in complex matrices. In this study, we have effectively addressed these challenges by integrating multiphase electroextraction (MPEE) as a sample preparation technique with these two spectroscopic methods for determining methylene blue (MB) dye in tap water samples. A Box-Behnken design was utilized for optimizing electroextraction parameters such as extraction time, pH, and acetonitrile percentage in the donor phase. After optimization, optical absorption spectroscopy results in a linear analytical curve within the range of 30 to 375 mg L-1 of MB, with method validation demonstrating high precision (relative standard deviation between 3.0 and 9.9%), recovery (99-105%), and detection and quantification limits of 1.3 and 4.0 μg L-1, respectively. On the other hand, using SERS, it was possible to detect MB in concentrations as low as 0.05 μg L-1. The extremely low concentrations of MB detected (in the range of a few ppb and ppt) and the acceptable validation performance parameters obtained highlight the potential of MPEE to enhance the applicability of spectroscopic techniques in routine analyses, especially when dealing with complex and challenging samples.

Green modified electrode for sensitive simultaneous heavy metal ions electrodetection

The detection of heavy metals (HM) is of particular importance in terms of human health and environmental protection. Electrochemical sensors are usually limited by the interference of various cations that coexist in real samples. These shortcomings are usually solved by incorporating various particles into the electrode material, which represents another source of pollution, thus being unsustainable. In this study, it was demonstrated that the new investigated natural clay (nc), used without processing, and immobilized with chitosan (Chi) matrix on the surface of a GCE in order to obtain nc-Chi/GCE modified electrode can detect, separately and simultaneously, four heavy metals (i.e. Zn2+, Cd2+, Pb2+ and Cu2+). The electrochemical behavior of the new eco-friendly modified electrode and its capacity to detect heavy metals has been investigated by electrochemical impedance spectroscopy (EIS) and square wave anodic stripping voltammetry (SWASV). The obtained electroanalytical performances (i.e., a detection limit of 43.1 nM for Zn2+, 19.1 nM for Cd2+, 4.3 nM for Pb2+ and 57.3 nM for Cu2+) corroborated with the reproducibility and stability of the modified electrode successfully recommends it as a suited device for heavy metals ions detection. The nc-Chi/GCE modified electrode was validated by measurements performed in real samples of tap water.

Fe3O4@PS-DVB microspheres modified with urea functional groups for rapid and green extraction of fluorinated aromatic carboxylic acids from tap and formation water

The present study describes the trace analysis of 23 fluorinated aromatic carboxylic acids based on the dispersive magnetic solid phase extraction (m-SPE) technique coupled with the gas chromatography coupled with mass spectrometry (GC–MS) electron ionization (EI) technique. A commercial hydrophilic-lipophilic balanced (HLB) material polystyrene divinyl benzene having urea functional groups was modified with magnetite nanoparticles and employed as a sorbent for dispersive m-SPE of fluorobenzoic acids (FBAs) from the tap and formation water samples. The extraction occurred due to π- π interaction between the aromatic ring of synthesized sorbent and the aromatic ring of FBAs, the hydrogen bond formation between the urea functional group of the sorbent and carbonyl oxygen, fluorine of the FBAs. As a result, the method was precise, rapid, reproducible, and calibrated with the coefficient of variation (R2) greater than 0.98 for all 23 compounds. The instrument detection limit (IDL) and method detection limit (MDL) were found in the range of 2.60 – 8.25 ng/mL and 0.08 – 0.28 ng/mL respectively. Extraction efficiencies were found in the range of 83.80–100 % for tap water samples and 78.41–98.92 % for formation water samples, respectively, with an enrichment factor of 33.33–66.66 and a maximum RSD of 7.07 %. The recyclability and magnetic properties of the synthesized material were also investigated, resulting in the material being reused for six cycles without impacting its performance; hence, the method offers rapid determination and high throughput analysis of FBAs. In addition, simulation studies were performed using the adsorption location tool of Material Studio, confirming the interaction sites of sorbent with FBAs. AGREE evaluated the analytical greenness of the method, and the score was found to be 0.51.

Anthocyanin‐Enhanced Bacterial Cellulose Nanofibers for Sustainable Hg(II) Ion Sensing

AbstractHg(II), poses a significant threat to both the environment and overall well‐being. The present indicator utilizes anthocyanin extract from roselle (Hibiscus sabdariffa), RSE, and incorporates it into bacterial cellulose nanofibers (BCNF) to detect Hg(II) ions. Through examination of the CIE Lab color variables, it is determined that the binding of Hg(II) leads to a discernible alteration in the color. The visible color changes as the Hg(II) concentration increases. ATR‐FTIR(Attenuated Total Reflectance‐Fourier transform infrared spectroscopy) and SEM(scanning electron microscopy) are utilized to analyze the bacterial cellulose nanofibers containing anthocyanin. The selectivity of the proposed sensor is assessed by conducting experiments with different types of metal ions including Co2+, Al3+, Na+, Ba2+, Ni2+, Mg2+, Cd2+, Pb2+, Fe2+, Fe3+, and Cu2+. The outcomes indicate that the sensor exhibits a remarkable ability to distinguish and respond specifically to Hg(II) ions. This particular sensing technique allows for the precise and reliable detection of Hg(II), with a detection limit of 0.72 ppm, by simply observing with the naked eye. For the effective treatment of a tap water sample, the BCNF‐RSE film provides successful results in the detection of Hg(II) ions. This innovative metallochromic sensor offers a promising solution for the on‐site, cost‐effective, portable, easy to use, and real‐time detection of Hg(II) ions.

Label-free and ultrasensitive detection of environmental lead ions based on spatially localized DNA nanomachines driven by hyperbranched hybridization chain reaction

A label-free fluorescent sensing strategy for the rapid and highly sensitive detection of Pb2+ was developed by integrating Pb2+ DNAzyme-specific cleavage activity and a tetrahedral DNA nanostructure (TDN)-enhanced hyperbranched hybridization chain reaction (hHCR). This strategy provides accelerated reaction rates because of the highly effective collision probability and enriched local concentrations from the spatial confinement of the TDN, thus showing a higher detection sensitivity and a more rapid detection process. Moreover, a hairpin probe based on a G-triplex instead of a G-quadruplex or chemical modification makes hybridization chain reaction more controlled and flexible, greatly improving signal amplification capacities and eliminating labeled DNA probes. The enhanced reaction rates and improved signal amplification efficiency endowed the biosensors with high sensitivity and a rapid response. The label-free detection of Pb2+ based on G-triplex combined with thioflavin T can be achieved with a detection limit as low as 1.8 pM in 25 min. The proposed Pb2+-sensing platform was also demonstrated to be applicable for Pb2+ detection in tap water, river water, shrimp, rice, and soil samples, thus showing great potential for food safety and environmental monitoring.

Fluorescent and colorimetric dual-mode chemosensor for easy detection of Cu2+: Practical and smartphone-based application to test strip and water sample

A fluorescent and colorimetric dual-mode chemosensor HNHQ, based on the julolidine and naphthol moieties, was synthesized. Compound HNHQ exhibited unique photophysical properties of an intense fluorescence with a high quantum yield (Φ = 0.363) and a light yellow color through the ICT mechanism. HNHQ could detect Cu2+ through both a fluorescence turn-off and a colorimetry variation of light yellow to yellowish brown. HNHQ reacted with Cu2+ with a binding ratio of 1:1. The detection limit for Cu2+ was analyzed to be 1.60 μM for fluorescence and 1.32 μM for UV–vis, considerably below the safe value of 31.5 μM established by the World Health Organization (WHO). HNHQ analyzed Cu2+ in the pH range of 6–8 and reversibly identified Cu2+ by using ethylenediaminetetraacetic acid (EDTA). Moreover, HNHQ could effectively detect Cu2+ in mineral and tap water samples, in addition to test strips through fluorescent and colorimetric changes. As a portable probe, HNHQ was successfully applied to a smartphone-based RGB analysis for the quantitative examination of Cu2+. The detection mechanism of HNHQ for Cu2+ was illustrated by 1H NMR titration, ESI-MS analysis, and density functional theory (DFT) calculations.

Boron, nitrogen, and sulfur co‐doped carbon dots as a fluorescence probe for label‐free analysis of Hg2+

AbstractHg2+ is one of the most toxic heavy metals, posing a serious threat to the human body and the environmental ecosystem. In order to detect Hg2+ rapidly, accurately, and sensitively, a kind of boron, nitrogen, and sulfur co‐doped carbon dots (B,N,S‐CDs) were synthesized by a simple, economical, and direct hydrothermal method. The average size of the prepared B,N,S‐CDs is 2.7 ± 0.7 nm, and the high photoluminescence quantum yield is 67.6%. Furthermore, due to the efficient quenching effect of Hg2+, such B,N,S‐CDs are considered to serve as an efficient fluorescence sensing platform for label‐free and sensitive detection of Hg2+ with a detection limit of 72 nM. The selectivity experiments reveal that the B,N,S‐CDs are selective and specific for Hg2+ even in the presence of other interfering substances. Most importantly, the Hg2+ sensing platform based on B,N,S‐CDs can be successfully applied to the determination of Hg2+ in tap water and real lake water samples. This stable and inexpensive carbon material exhibits excellent sensitivity and selectivity, potentially suitable for Hg2+ monitoring in environmental applications.

Dye-sensitized lanthanide-doped upconversion nanoprobe for enhanced sensitive detection of Fe3+ in human serum and tap water

Iron ion (Fe3+) detection is crucial for human health since it plays a crucial role in many physiological activities. In this work, a novel Schiff-base functionalized cyanine derivative (CyPy) was synthesized, which was successfully assembled on the surface of upconversion nanoparticles (UCNPs) through an amphiphilic polymer encapsulation method. In the as-designed nanoprobe, CyPy, a recognizer of Fe3+, is served as energy donor and β-NaYF4:Yb,Er upconversion nanoparticles are adopted as energy acceptor. As a result, a 93-fold enhancement of upconversion luminescence is achieved. The efficient energy transfer from CyPy to β-NaYF4:Yb,Er endows the nanoprobe a high sensitivity for Fe3+ in water with a low detection limit of 0.21 μM. Moreover, the nanoprobe has been successfully applied for Fe3+ determination in human serum and tap water samples with recovery ranges of 95 %-105 % and 97 %-106 %, respectively. Moreover, their relative standard deviations are all below 3.72 %. This work provides a sensitive and efficient methodology for Fe3+ detection in clinical and environmental testing.

Sensitive and rapid determination of tetracycline antibiotic by carrot juice-derived carbon dots as a fluorescent probe.

The antibiotic tetracycline can be efficiently used as medicine for the deterrence of bacterial infections in humans, animals, and plants. However, the unprecedented use of tetracycline is of great concern owing to its low biodegradability, extensive usage, and adverse impacts on the environment and water quality. In this study, a sensitive spectrofluorometric method was proposed for the direct determination of tetracycline, based on biocompatible fluorescent carbon dots (CDs). The synthesis of CDs was performed by adopting a green hydrothermal procedure from carrot juice without requiring surface passivation or outflowing any environmentally hazardous waste. X-ray diffraction analysis and transmission electron microscopy revealed amorphous spherical-shaped CDs that exhibited blue emission under blue illumination. The fabricated fluorescent probe directly detected tetracycline in the concentration range of 4.00 ×10-6 to 1.55 ×10-5mol L-1 with an LOD of 1.33 ×10-6mol L-1. The performance of the probe was assessed in a tap water sample, with recovery values between 80.70 and 103.60%. The method's greenness was evaluated using the Analytical Green metric approach (AGREE) and confirmed to be within the green range. The developed method is facile, rapid, cost-effective, and offers a wide linear range and satisfactory selectivity, making it potentially suitable for determining tetracycline in water applications.

A Novel Electrochemical Sensing Based on Cerium Oxide/Nitrogen-Doped Reduced Graphene Oxide for Sensitive Detection of Acetaminophen

Acetaminophen (ACP), a common analgesic and antipyretic medication, can harm the liver when overdosed and its metabolites can contaminate the environment, so it is necessary to monitor the concentration precisely and reliably. In this work, we successfully synthesized cerium oxide/nitrogen-doped reduced graphene oxide (CeO2/N-rGO) composite nanomaterials using a one-step hydrothermal method. Using composite nanomaterials, we created an electrochemical sensing detection platform for ACP detection. The synthesized materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The constructed electrochemical sensor exhibits good ACP detection ability under the synergistic effect of CeO2 and N-rGO. Under optimal experimental conditions, the sensor displayed a linear range for the detection of ACP of 1 ∼ 200 μM and the lowest detection limit of 0.79 μM, exhibiting outstanding selectivity, stability, and repeatability. Furthermore, the sensor was effectively applied to detect ACP in tap water samples, which offers a wide range of possible applications in actual sample testing.

Per- and polyfluoroalkyl substances (PFAS) in paired tap water and house dust from United States homes

Most people in the United States have been exposed to per- and polyfluoroalkyl substances (PFAS) which have been linked to a wide array of adverse health conditions in adults and children. The consumption of contaminated drinking water is an important human exposure pathway to PFAS. Residential sources also contribute to PFAS exposure through dermal contact and ingestion of house dust, which acts as an aggregate of chemicals from sources like furnishing materials and consumer products. The U.S. Department of Housing and Urban Development (HUD) conducted the first nationwide survey of residential hazards called the American Healthy Homes Survey (AHHS) in 2005, followed by a second survey (AHHS II) in 2017. The U.S. Environmental Protection Agency (EPA) collaborated with HUD on both efforts and subsequently analyzed PFAS in household tap water and house dust collected from the same homes during the AHHS II study. This study leverages these paired samples to investigate potentially important exposure sources and pathways in the residential environment. Here we report results for paired household tap water and house dust samples from 241 homes for 13 and 16 PFAS chemicals, respectively. All 13 targeted chemicals were detected in the household tap water samples with detections ranging from 100 % for PFBS to 1 % for PFNS, and all 16 targeted chemicals were detected in the house dust samples with detections ranging from 97 % for PFOA to 9 % for PFNS. Four chemicals (PFOA, PFOS, PFHxS, and PFHpA) were measured above the limit of detection in at least 50 % of the samples in both media. All households had at least one of the targeted PFAS detected in both their tap water and house dust. Results provided evidence that geographical factors, such as proximity to ambient contamination sources, were main drivers of PFAS contamination in tap water, while PFAS contamination in house dust was driven mainly by within-home sources. Exposure estimates calculated from the measured PFAS concentrations highlight the importance of addressing potential sources of exposure to PFAS within homes in addition to ambient sources affecting communities’ drinking water, particularly to reduce children’s exposure to these chemicals.

In-syringe homogeneous liquid–liquid microextraction as an economical, convenient, and one-step analytical method for the extraction and preconcentration of five plasticizers and one antioxidant from different city tap water samples

In this study, an analytical method called in-syringe homogeneous liquid–liquid microextraction was developed and applied for the extraction and preconcentration of plasticizers including di ethyl phthalate, di isobutyl phthalate, di-n-butyl phthalate, di(2-ethylhexyl) adipate, and di(2-ethylhexyl) phthalate and one antioxidant, (butylated hydroxytoluene). Only a few microliters of dibutyl amine was used as the extraction solvent. This switchable solvent became miscible in the solution of interest by adding acetic acid at µL-level to extract the analytes. Also, the addition of sodium carbonate (in mg-level) into the solution led to the release of carbon dioxide, which facilitated the extraction of plasticizers into the extractant. Also, sodium carbonate caused to the regeneration of the extractant in the upper narrow bore of the syringe. The enriched analytes were determined by a gas chromatographic equipped with a flame ionization detector. Under the optimum conditions, extraction recoveries and enrichment factors were obtained in the ranges of 39–78 % and 196–394, respectively. Also, the limits of detection and quantification were in the ranges of 1.76–12.51 µg/L and 5.80–41.28 µg/L, respectively, and the r2 values were equal to or better than 0.991. Development of the method as a one-step analysis processed which was electrically independent in extraction and preconcentration stage (no centrifugation or vortexing) and inexpensive. The use of only µL-level of organic solvent, convenient operation, and short extraction time are the other highlights of the method. This method was successfully applied to the extraction, preconcentration, and determination of several plasticizers in eight different city water samples.

Assessment of Indoor and Water Radon Concentrations in Esenyurt and Beylikdüzü Districts of Istanbul, Marmara Region, Turkey

The radon activity concentration measurements for indoor and tap water were studied in Esenyurt and Beylikdüzü districts of Istanbul Province, Turkey. The mean radon concentration value received from thirty-six passive radon detectors was obtained as 63.56 Bq/m3. The mean annual effective dose for indoor radon measurements is 1.60 mSv/y in this measurement period. The radon activity results of calculated tap water samples were under 0.8 Bq/L. The annual effective doses resulting from ingestion and inhalation were calculated to evaluate the health risk across various age groups. All radon measurement results, and the associated calculated data for ingestion and inhalation remained below the threshold values established by international organizations

Carbon quantum dots with ultra-high quantum yield for versatile turn-on sensor of gluten and cyanide Ions

In this work, we reported the synthesis of carbon quantum dots (CQDs) with high fluorescent quantum yield (90.7 %). These nanoparticles were applied in a turn-off/turn-on sensor able to detect cyanide ions. In this sensing strategy, Fe3+ ions were added to the aqueous suspension of CQDs to quench the fluorescence of the system, which was recovered from the presence of cyanide ions. Furthermore, a sensor array was developed using the LDA chemometric tool, to classify different species present in cookie formulations, including gluten. The turn-off/turn-on sensor proved to be sensitive and effective for detecting cyanide ions, with a detection limit of 3.77 ppm. This high sensibility and selectivity allowed quantifying the analyte in a real sample of tap water.

Photocurrent polarity switching photoelectrochemical aptasensor for oxytetracycline based on BiOBr/Ag2S/PDA//CuO: CuO-induced II-type to dual Z-scheme system

BackgroundAs a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC.Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag2S/PDA (Polydopamine) photocurrent polarity reversal. ResultsBiOBr/Ag2S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu–S2) was got through Cu–S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag2S/PDA through the specific binding of OTC to S2. This identification process formed dual Z-type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM ∼ 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application. SignificanceThis work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag2S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag2S, PDA and CuO.

Synthesis of non-modified near-infrared carbon dots for hypochlorite detection and cell membrane imaging

Devising carbon dots with long wavelength emission (red light or near infrared), high selectivity and good bio-compatibility is critical in fluorescence detection and imaging, but achieving this goal remains a great challenge. Herein, near-infrared emissive carbon dots (NIR-CDs) with obvious emission characteristic of 653 nm were synthesized through hydrothermally treatment of toluidine bule and gallic acid. Noticeably, the NIR-CDs exhibited excellent selectivity and sensitivity to hypochlorite (ClO−), and the limit of detection is as low as 42.7 nM. The selective recognition reaction between ClO− and the surface functional groups of NIR-CDs inhibits the fluorescence from NIR-CDs. The quenching mechanism was confirmed by fluorescence lifetime decays, FT-IR spectroscopy and UV–vis absorption spectra. More remarkably, the NIR-CDs have rich hydrophilic groups showed lower cytotoxicity, excellent bio-compatibility and specific cell membrane localization ability. The established spectrofluorometric method based on NIR-CDs has been used to determination of ClO− level in tap water sample, the recoveries were 97.7 %–103.3 %. In addition, the NIR-CDs also has been successfully applied for the imaging of cell membrane. The study provides a novel idea for developing NIR ClO− probe as well as cell membrane localization probe based on CDs, which present bright prospects in real water samples monitoring and cell membrane imaging.