Selective Determination Research Articles

Novel disposable screen-printed sensors based on copper oxide nanoparticles for sensitive voltammetric assay of antazoline

The fabrication and electroanalytical validation of a novel homemade screen-printed carbon electrode enriched with copper oxide nanoparticles (CuONPs/SPCEs) were demonstrated for sensitive and selective voltammetric determination antazoline (ANT) in eye drop solution and spiked serum samples. With a reported electrocatalytic activity, CuONPs catalyzed the oxidation of ANT at the electrode surface showing an irreversible anodic oxidation peak at 0.9 V under a diffusion-controlled electrode reaction. Based on the electroanalytical and molecular orbital calculation studies, oxidation of ANT molecule undergoes via oxidation of the aliphatic nitrogen atom within the ANT moiety. Linear calibration curves were illustrated covering the ANT concentration ranged from 0.01 to 3.819 µg mL−1 with and limit of detection 3 ng mL−1. The fabricated sensors enriched with CuONPs exhibited high fabrication and measurement reproducibility with a prolonged shelf lifetime (6 months). The electroanalytical approach presented adequate sensitivity and selectivity with a short analysis time, applying low-cost instrumentation and simple pretreatment protocol avoiding handling hazardous organic solvents. Trace ANT was monitored in the presence of different interfering species, degradation products, and xylometazoline hydrochloride (ZYL) in the co-formulated ophthalmic pharmaceutical samples. The CuONPs based voltammetric sensors were introduced as a reliable eco-friendly analytical tool for monitoring ANT in ophthalmic solutions and biological fluids with acceptable recovery values.

A novel potentiometric screen-printed electrode based on crown ethers/nano manganese oxide/Nafion composite for trace level determination of copper ion in biological fluids.

Copper levels in biological fluids are associated with Wilson's, Alzheimer's, Menke's, and Parkinson's diseases, making them good biochemical markers for these diseases. This study introduces a miniaturized screen-printed electrode (SPE) for the potentiometric determination of copper(II) in some biological fluids. Manganese(III) oxide nanoparticles (Mn2O3-NPs), dispersed in Nafion, are drop-casted onto a graphite/PET substrate, serving as the ion-to-electron transducer material. The solid-contact material is then covered by a selective polyvinyl chloride (PVC) membrane incorporated with 18-crown-6 as a neutral ion carrier for the selective determination of copper(II) ions. The proposed electrode exhibits a Nernstian response with a slope of 30.2 ± 0.3mV/decade (R2 = 0.999) over the linear concentration range 5.2 × 10-9 - 6.2 × 10-3mol/l and a detection limit of 1.1 × 10-9mol/l (69.9ng/l). Short-term potential stability is evaluated using constant current chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). A significant improvement in the electrode capacitance (91.5 μF) is displayed due to the use of Mn2O3-NPs as a solid contact. The presence of Nafion, with its high hydrophobicity properties, eliminates the formation of the thin water layer, facilitating the ion-to-electron transduction between the sensing membrane and the conducting substrate. Additionally, it enhances the adhesion of the polymeric sensing membrane to the solid-contact material, preventing membrane delamination and increasingthe electrode's lifespan. The high selectivity, sensitivity, and potential stability of the proposed miniaturized electrode suggests its use for the determination of copper(II) ions in human blood serum and milk samples. The results obtained agree fairly well with data obtained by flameless atomic absorption spectrometry.

Two-dimensional hydrophilic imprinted resin–graphene oxide composite for selective extraction and rapid determination of gibberellin traces in licorice samples

This study presents novel methodologies and materials for selectively and sensitively determining gibberellin traces in licorice to address food safety concerns. A novel hydrophilic imprinted resin–graphene oxide composite (HMIR–GO) was developed with fast mass transfer, high adsorption capacity, and exceptional aqueous recognition performance for gibberellin. Leveraging the advantages of molecular imprinting, hydrophilic resin synthesis, and rapid mass transfer characteristics of GO, HMIR–GO was employed as an adsorbent, showing resistance to matrix interference. Coupled with HPLC, a rapid and selective method for determining gibberellin was established. Under optimal conditions, the method exhibited a wide linear range (0.02–5.00 μg g−1, r = 0.9999), low detection limits (3.3 ng g−1), and satisfactory recoveries (92.0–98.4%), enabling the accurate and rapid detection of gibberellin in licorice. This study introduces a pioneering strategy for the selective extraction and determination of trace gibberellin levels, offering insights for similar applications in functional foods.

Selective and invisible separation and determination of Rhodamine B in diverse industrial samples using aqueous biphasic switchable hydrophilicity solvent-like based microextraction method

An effective and selective aqueous biphasic switchable hydrophilicity solvent-like based microextraction method (ABSHS-ME) combined with UV–vis spectrophotometry was established for the first time to monitor Rhodamine B (RhB) at 550 nm in soaps, lipsticks, anti-freezes and match tips. RhB was extracted firstly as its invisible form into immiscible hydrophobic phase and then converted to its UV–vis active form using acidified ethanol. The essential extraction parameters (pH, SHS volume, and vortex time) were optimized by Box-Behnken Design of Response Surface Methodology. Quadratic model with R2 = 0.9893 was found as favourable chemometric design for ABSHS-ME method. Preconcentration factor was obtained to be 25. Effect of matrix ions and dyes were examined in detail. 7 and 24 µg/L of Rhb were determined for limit of detection and limit of quantitation, respectively. RhB was determined linearly between 24 and 2500 µg/L. Relative standard deviations were lower than 7 %. ABSHS-ME method was validated determining the RhB concentrations of industrial samples with analyte addition-recovery tests. RhB contents of the real samples analyzed were found between 0.26–1.07 µg/g and 1.53–4.73 µg/mL with recovery values ranging from 95 to 101 %. The environmentally friendly index of the method was evaluated using the new generation AGREE tool.

Determinants of the optimal selection of vascular access devices: A systematic review underpinned by the COM-B behavioural model.

Optimal selection of vascular access devices is based on multiple factors and is the first strategy to reduce vascular access device-related complications. This process is dependent on behavioural and human factors. The COM-B (Capability, Opportunity, Motivation, Behaviour) model was used as a theoretical framework to organize the findings of this systematic review. To synthesize the evidence on determinants shaping the optimal selection of vascular access devices, using the COM-B behavioural model as the theoretical framework. Systematic review of studies which explore decision-making at the time of selecting vascular access devices. The Medline, Web of Science, Scopus and EbscoHost databases were interrogated to extract manuscripts published up to 31 December 2021, in English or Spanish. Among 16 studies included in the review, 8/16 (50%) focused on physical capability, 8/16 (50%) psychological capability, 15/16 (94%) physical opportunity, 12/16 (75%) social opportunity, 1/16 (6%) reflective motivation and 0/16 (0%) automatic motivation. This distribution represents a large gap in terms of interpersonal and motivational influences and cultural and social environments. Specialist teams (teams created for the insertion or maintenance of vascular access devices) are core for the optimal selection of vascular access devices (75% physical capability, 62% psychological capability, 80% physical opportunity and 100% social opportunity). Specialist teams predominantly lead all actions undertaken towards the optimal selection of vascular access devices. These actions primarily centre on assessing opportunity and capability, often overlooking motivational influences and social environments. A more implementation-focused professional approach could decrease inequity among patients and complications associated with vascular access devices. Optimal selection of vascular access devices is the primary strategy in mitigating complications associated with these devices. There is a significant disparity between interpersonal and motivational influences and the cultural and social environments. Furthermore, specialized teams play a pivotal role in facilitating the optimal selection of vascular access devices. The study can benefit institutions concerned about vascular access devices and their complications. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. No Patient or Public Contribution. WHAT DOES THIS ARTICLE CONTRIBUTE TO THE WIDER GLOBAL CLINICAL COMMUNITY?: Optimal selection of vascular devices remains a growing yet unresolved issue with costly clinical and patient experience impact. Interventions to improve the optimal selection of vascular devices have focused on training, education, algorithms and implementation of specialist vascular teams; alas, these approaches do not seem to have substantially addressed the problem. Specialist vascular teams should evolve and pivot towards leading the implementation of quality improvement interventions, optimizing resource use and enhancing their role.

Determination of Tree Type Selection in Park and Garden Construction by the Value Engineering Method: Sinanoba Beach Park Example

In order to achieve efficient projects when producing any product, the cost, quality, and production time need to be optimized. However, this is not always easy to achieve. The budgets of the projects may be exceeded, they may not be completed in the stipulated and committed time, or the products may not be produced with sufficient quality for various reasons. It is vital to analyze the project functions/steps very closely throughout the design phase to ensure that all feasible alternatives are studied and examined, and that the most appropriate alternative is picked for the functions that can meet the project criteria. Value engineering (DM) can be defined as an organized effort to analyze product features, functions and material selections; is designed to solve problems and/or reduce costs while maintaining or improving performance and quality requirements; and performs essential functions at the required quality, reliability, and life-cycle cost. In this study, value engineering was used for the selection of trees needed in the construction of parks. A value engineering team decided that the trees should be coniferous with the prerequisite that they can remain green without shedding their summer-winter leaves and determined which criteria the coniferous trees required to be located in the park should meet. The team members conducted value engineering after determining which trees met these criteria and were subsequently purchased. As a result, the team determined the most appropriate optimum cost solution with the value engineering method to meet all the criteria among the determined alternative tree species

A unique implementation of Hantzsch reaction for determination of natamycin in Yoghurt: Hyphenated with Box-Behnken-design for optimization

This study aims to develop a novel and selective method for the detection of natamycin (E235) in yoghurt. The suggested method adopts an application of Hantzsch reaction to turn on the fluorescence behavior of natamycin (blue fluorescence), allowing its sensitive and selective determination in yoghurt samples without any overlapping at 485 nm. The originality of the research lies in the fact that this application takes place for the first time, also the detection (LOD) and quantification (LOQ) limits were very low (0.02 and 0.06μg mL−1, respectively) with a linear concentration range of 0.1–1.0 μgmL-1. Moreover, the developed method was employed for the detection of E235 in yoghurt sample with a good recoveries (98.80 ± 1.20–99.20 ± 1.15 (%), over a concentration range of 0.5–1.0 μgmL-1, (LOD = 0.04 and LOQ = 0.12 μgmL-1). Furthermore, the specificity and convenient application of our intended method is an attempt to determine E235 in milk anddairy products with easily followable steps.

A novel enrichment and sensitive method for rapid determination of 4 sulfonamide antibiotics residues in fish

Sulfonamide antibiotics with superior performance are widely used in aquaculture. However, the residues of sulfonamide antibiotics in aquatic products may pose a threat to human health. In this work, a novel type of magnetic molecularly imprinted polymer (mMIP) was synthesized and coupled with ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) for the selective separation and determination of 4 sulfonamide antibiotics residues in tilapia. The structure and adsorption properties of the polymers were characterized and evaluated. The key mMIP variables were investigated to determine the optimal magnetic solid phase extraction conditions. Results showed that the mMIPs had saturated adsorption capacities of 137.4, 78.7, 65.2, and 58.4 mg/g for trimethoprim, sulfadiazine, sulfamethazine, and sulfamethoxazole, respectively. Under optimized conditions, the linear range of the method for the detection of the 4 sulfonamides was 0.1–100 ng mL−1 (R > 0.991), the detection limit was 0.015 μg kg−1 (S/N = 3), the recovery rate was 78.6–101%, and the relative standard deviation (RSD%) was 4.2–7.8%. This new rapid and ultra-sensitive pretreatment method was successfully applied to the monitoring of trace sulfonamide antibiotics residues in fish samples.

Magnetic Three-Dimensional Graphene: A Superior Adsorbent for Selective and Sensitive Determination of Nitrite in Water Samples by Ion-Pair Based-Surfactant-Assisted Solid-Phase Extraction Combined with Spectrophotometry

A straightforward, fast and efficient analytical method was developed which utilizes a magnetic composite called three-dimensional graphene (3D-G@Fe3O4) as an adsorbent to recover nitrite ions (NO2−) from environmental water samples. The investigation into the synthesized adsorbent contained an examination of its morphology, chemical composition, structural attributes, and magnetic properties. This comprehensive analysis was conducted using various instrumental techniques, including Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and vibrating sample magnetometry (VSM). The adsorbent surface was activated by adding cetyltrimethylammonium bromide (CTAB) to the sample solution. To improve the selectivity and sensitivity of the method, nitrite ions were reacted with sulfanilic acid and chromotropic acid sequentially. An orange-red azo-dye complex was formed in the presence of nitrite ions with a clear absorbance peak at 514 nm. The effect of the main experimental parameters such as the pH of the sample solution, adsorbent dosage, and CTAB dosage was explored, and the optimization process was performed using a central composite design (CCD). The linear dynamic range (20–100 ng mL−1) was determined under optimal experimental circumstances, yielding a reasonable determination coefficient (R2, 0.9993), a detection limit of 5.12 ng mL−1, an enrichment factor of 167, and precision values of 1.0% intraday and 2.9% inter-day. The methodology successfully identified minute nitrite ions in environmental water samples with relative recoveries that varied between 96.05 and 101.6 ng mL−1.

Lentils/urea as precursors for profound S and N doping of carbon dots for selective sequential determination of Hg(II) and S(II) in food and environmental samples

In this article, we described a new platform for probing toxic pollutants, namely Hg2+ and S2-, in aquatic environment by tracing the “on–off-on” fluorescence signals of quantum dots. To achieve this, red lentils and urea, as natural precursors, were utilized as sources of S and N doping, respectively, to fabricate blue fluorescent carbon quantum dots, namely, lentils/urea quantum dots (LUQDs) with good quantum yield and plentiful S-doping. In the present work, the quality-by-design (QbD) strategy was applied to control and select the optimum conditions for the microwave-aided synthesis of the carbon dots. LUQDs exhibit excitation-dependent emissions, where the maximum fluorescence emission was at 360 nm after excitation at 300 nm. During the detection step, the fluorescence of LUQDs is quenched by the incorporation of Hg2+ over the range of 0.50–70.0 μM. Next, S2- reacts with Hg2+, resulting in turning on the fluorescence emission of LUQDs in the range of 10.0–150.0 µM.The method was applied for the detection of both Hg2+ and S2- in tap, sewage, and river water samples with a recovery rate ranging between 98.96 % and 101.26 %; in addition, Hg2+ was detected in canned Tuna samples with a recovery of 98.70 %. Furthermore, the greenness of the developed method was confirmed through various greenness metrics.

Portable wireless electrochemical sensing of breviscapine using core-shell ZIFs-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra-modified electrode.

Acore-shell ZIF-67@ZIF-8-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra (Co/C-NCNP) hybrid nanostructure was preparedby a pyrolysis method. The synthesized Co/C-NCNP was modified on the screen-printed carbon electrode and used for the portable wireless sensitive determination of breviscapine (BVC) by differential pulse voltammetry. The Co/C-NCNP had a large surface area and excellent catalytic activity with increasing Co sites to combine with BVC for selective determination, which led to the improvement of the sensitivity of the electrochemical sensor. Under optimized conditions, the constructed sensor had linear ranges from 0.15 to 20.0µmol/L and 20.0 to 100.0µmol/L with the limit of detection of 0.014µmol/L (3S0/S). The sensor was successfully applied to BVC tablet sample analysis with satisfactory results. This work provided the potential applications of zeolitic imidazolate framework-derived nanomaterials in the fabrication of electrochemical sensors for the sensitive detection of drug samples.

Determinants for Supplier Selection Based on Hybrid Grey Theory: Case Study of the Vietnamese Coffee Industry

Coffee is not merely a refreshing beverage but also invigorates people, provides relaxation, contributes to human health, and fosters closer social connections. Coffee is one of the most widely consumed beverages worldwide and the most traded commercial commodity. Moreover, the rapid development of the Vietnamese coffee industry caused some concerns due to its insufficient performance and the fierce competition within the industry. It is significant to establish an efficient supply network; notwithstanding, supplier selection has always been a challenge for companies. Therefore, this paper employs a hybrid model to determine the supplier selection criteria, a vital factor for a manufacturer under practical operating conditions. Firstly, a combined model of Grey forecasting and the Grey Fourier series is applied to forecast future rainfall and temperature data for six consecutive years. Secondly, based on the criteria, strategies, and buyer requirements, the single-objective linear programming model helps identify the outperformed suppliers. The results found that prices and location change are determinants of supplier selection, and supplier shortage is an enormous barrier for the industry. In this study, these price forecasts allow supply chain management to make informed decisions about inventory levels, transportation routes, and resource allocation to ensure smooth operation and optimize coffee supply chain management.

Electrocatalytic sensing of propyl gallate in real-time food samples using a synergistic Sm-MOF@GCN composite modified glassy carbon electrode

A novel electrochemical sensor has been developed using the sonochemically synthesized samarium metal–organic framework (Sm-MOF) and the graphitic carbon nitride (GCN) composite for the selective determination of propyl gallate (PG). The as-synthesized Sm-MOF@GCN composite was characterized by XRD, XPS, and FESEM. The morphological studies of the prepared Sm-MOF@GCN composite revealed the bar-shaped Sm-MOF and porous sheet-like morphology of GCN. The combined effect of the Sm-MOF and GCN enhance the current density response and lowers the oxidation potential, which was beneficial for the electrochemical sensing of PG. Moreover, the high electrochemical active surface area (EASA) (0.0649 cm2) and the rate constant value (Ko) of 1.44x10-5 cm s−1 confirm the faster electron transfer kinetics at the interface of Sm-MOF@GCN composite. However, the developed Sm-MOF@GCN composite possesses linear range from 0.02 to 60 µM with a nanomolar detection level (2.05 nM), high sensitivity (0.1914 μA μM−1 cm−2), excellent reproducibility, repeatability, and stability for up to 30 days towards the PG detection. Finally, the Sm-MOF@GCN composite-modified electrocatalyst was utilized for the quantification of PG in foodstuffs such as instant noodles, cookies, cakes, and oils. The result of the study, the Sm-MOF@GCN composite displayed good recovery results, making it a promising candidate for detecting PG in real-world samples in view of its binder-free approach and facile fabrication process.

Fabrication of two-dimensional fluorescent stanene oxide nanosheets for the detection of cortisone in biofluids

The current work provides a new approach for the fabrication of two-dimensional blue fluorescent guanidine acetic acid templated stanene oxide nanosheets (GAA-SnO2 NSs) for selective determination of cortisone. The GAA-SnO2 NSs displayed blue fluorescence with a quantum yield of 21.16 %. Under excitation wavelength of 370 nm, the GAA-SnO2 NSs responded to cortisone by exhibiting noticeably decrease in the emission peak at 454 nm. The introduction of cortisone to GAA-SnO2 NSs significantly altered fluorescence emission, leading to achieve desirable linear relationship between the intensity ratio (I0/I) and the concentration (0.5–10 μM). The detection limit was found to be 41.74 nM for cortisone. The GAA-SnO2 NSs were decorated on paper for the development of embedded analytical probe for cortisone detection. Furthermore, the method was successfully demonstrated to assay cortisone in biofluid (plasma and urine) samples with good recoveries.

Turn-on fluorescence of mirabegron for its sensitive detection in human plasma: Box-Behnken-Design for optimization

Here, a novel fluorescence strategy was established for the detection of mirabegron (MBG) sensitively on the basis of hantzsch dihydropyridine synthesis. The developed method adopts turn-on fluorescence of MBG for the first time, permitting its selective determination in spiked human plasma at 486 nm after excitation at 410 nm. The developed method exhibited a good linear range from 0.5 μgmL-1 to 2.0 μgmL-1 with detection and quantification limits of 0.05 and 0.2 (μgmL-1), respectively. The profitable applicability of the developed method in spiked human plasma samples was demonstrated, achieving limit of detection below the previously levels reported by spectroscopic methods, allowing application of the developed method for selective determination of MBG in its tablets and spiked human plasma samples with good recovery.

The determinants of political selection: a citizen-candidate model with valence signaling and incumbency advantage

AbstractWe expand the theory of politician quality in electoral democracies with citizen candidates by supposing that performance while in office sends a signal to the voters about the politician’s valence. Individuals live two periods and decide to become candidates when young, trading off against type-specific private wages. The valence signal increases the reelection chances of high valence incumbents (screening mechanism of reelection), and thus their expected gain from running for office (self-selection mechanism). Since self-selection improves the average quality of challengers, voters become more demanding when evaluating the incumbent’s performance. This complementarity between the self-selection and the screening mechanisms may lead to multiple equilibria. We show that more difficult and/or less variable political jobs increase the politicians’ quality. Conversely, societies with more wage inequality have lower quality polities. We also show that incumbency advantage blurs the screening mechanism by giving incumbents an upper-hand in electoral competition and may wipe out the positive effect of the screening mechanism on the quality of the polity.

The Impact of Social Determinants of Maternal Mental Health in Marginalized Mothers.

Background: A deeper understanding of the key determinants of maternal mental health is important for improving care for women, especially women who are at an economic disadvantage. Objectives: To explore the associations of select social determinants: access, social support, and stress, with the onset of antepartum depression in low-income mothers. Participants: The Pregnancy Risk Assessment Monitoring System (PRAMS) is an ongoing, population-based surveillance system with selected data from 2016 to 2019, establishing a randomly selected sample of women with a recent live birth at most 4 months postdelivery, between 1,300 and 3,400 women per state (n ∼ 162,558). Methods: In this cross-sectional study, the phase 8 PRAMS was adapted to measure social support, access, stress, and their relationships with the onset of antepartum depression in low-income mothers. To assess low-income marginalization, a threshold was established based on income levels within 130% of the federal poverty level; antepartum (n ∼ 41,289). Results: The defined access, social support, and stress factors showed a statistically significant association with the onset of antepartum depression among low-income mothers. Of women in this sample, 22.6% indicated antepartum depression (p < 0.001; R2 = 0.066). Negative social support indicators were associated with an increased likelihood of antepartum depression; 3.71 increased odds of depression for abuse during pregnancy, and 0.79 decreased odds with positive acknowledgment of paternity. Access indicator terms showed an association with the decreased likelihood of antepartum depression through breastfeeding information support (Info from Baby Doc, odds ratio [OR] = 0.86), prenatal care utilization (12+ visits, OR = 0.82), and specific insurance type (insurance by job, OR = 0.82). All instances of stressful life events showed an increased likelihood of depression during pregnancy (for majority of stressful life events: OR >1.12). Conclusions: Economically marginalized mothers face unmet social and health care needs leading to poorer outcomes during pregnancy. These findings provide additional support for improved policy and public health efforts, such as assessment, education, and interventions, to decrease prevalence and improve treatment for antepartum depression among marginalized mothers.

Enzyme-integrated metal-organic framework platform for cascade detection of α-amylase

As one of the most important industrial enzymes, α-amylase is widely used in food processing, such as starch sugar and fermentation, bringing high added value to industry of more than a trillion dollars. We developed a multi-enzyme system (Glu&Gox@Cu-MOF-74) prepared by embedding α-glucosidase (Glu) and glucose oxidase (Gox) into the biomimetic metal-organic framework Cu-MOF-74 using in situ encapsulation within 15 min at room temperature for efficient and sensitive detection of α-amylase activity. Benefitting from the remarkable peroxidase-mimicking property and rigid skeleton of Cu-MOF-74, the biocatalytic platform exhibited excellent cascade activity and tolerance in various extremely harsh environments compared to natural enzymes. On this basis, a cascade biocatalytic platform was constructed for the detection of α-amylase activity with wide linear range (5–100 U/L) and low limit of detection (1.45 U/L). The colorimetric cascade scheme is important for the sensitive and selective determination of α-amylase in complex fermentation samples, and the detection time is short (∼0.5 h). This work provides new ideas for the detection of α-amylase based on the cascade amplification method.

N/S co-doped carbon dots-based solution-gated graphene transistors (SGGT) for ultra-sensitive and selective determination of Hg (II) ions in real water and serum samples

The conventional methods for detecting Hg2+ ions are generally impaired by low sensitivity, a high limit of detection (LOD), and the long detection time required. In this work, we develop a novel solution gated graphene transistor (SGGT) based on carbon dots doped with N and S elements (N/S CDs) as gate electrode probes. The prepared N/S CDs, which are 3–5 nm in diameter, are first modified at the gate of the SGGT through covalent bonding that specifically recognizes Hg2+ ions. The SGGT is then used as a Hg2+ sensor, exhibiting good selectivity, ultrahigh sensitivity, good reproducibility, and a short detection time. The SGGT sensor has an excellent linear detection range, from 0.1 fM to 1 nM. The LOD can reach 28 aM, which is far lower than that of conventional detection methods. Moreover, the SGGT sensor also has a rapid response time of ∼ 40 s. Finally, the ability to analyze real water samples and serum samples is demonstrated.

Nitrogen-doped carbon dots as fluorescent probes for sensitive and selective determination of Fe3+

At present, the contamination of water resources by heavy metal ions has posed a significant threat to human survival. Therefore, it is particularly critical to develop low-cost, easy-to-use, and highly efficient heavy metal detection technologies. In this work, a fast and cost-effective fluorescent probe for nitrogen-doped carbon dots (N-CDs) was prepared using one-step hydrothermal method with citric acid (CA) as carbon source, and melamine as nitrogen source. The structural and optical characterizations of the resulting N-CDs were investigated in details. The results showed that the quantum yield of the prepared fluorescent probe was as high as 45 %, and an average fluorescence lifetime was about 7.80 ns. N-CDs have excellent water solubility and dispersibility, with an average size of 2.58 nm. N-CDs exhibited excellent specific responsiveness to Fe3+ and can be used as an effective method for detecting Fe3+ at low-concentrations (the concentrations of N-CDs as low as 0.24 μg/mL) using fluorescent probes. The linear response of the fluorescent probe N-CDs to Fe3+ was formed in the concentration range of 20–80 μM, and the detection limit was 3.18 μM. In addition, in the actual water samples analysis, the recovery rate reached 97.05–100.58 %. The prepared of N-CDs provide available Fe3+ fluorescent probes in the environment.