Spiked Tap Water Samples Research Articles

Transforming Food Biowaste into Selective and Reusable Adsorbents for Pesticide Removal from Water

With growing concerns regarding environmental pollution and the need for sustainable waste management practices, this study investigates the potential of utilizing spent coffee grounds (SCG) as a precursor for producing functional carbon materials aimed at organophosphorus pesticide remediation under environmentally relevant conditions. Carbonization of SCG is followed by various activation methods, including treatment with potassium hydroxide, phosphoric acid, and carbon dioxide, individually or in combination. The resulting biochars are systematically analyzed for their adsorption performance towards malathion and chlorpyrifos. Screening tests revealed a selective adsorption preference towards aromatic chlorpyrifos over aliphatic malathion. Activation processes significantly influence adsorption kinetics and efficiency, with physical activation showing notable adsorption rates and capacity enhancements. Moreover, the SCG-derived biochars exhibit a pronounced dependency on adsorption temperature. Adsorption, regeneration, and reuse of the most promising material are tested in a real, spiked tap water sample, proving that the presence of ions in tap water did not affect the adsorption and that the material has the potential to be reused more than ten times. This work proposes a straightforward approach for recycling SCG by converting it into functional carbon materials, underscoring the importance of selecting the appropriate activation processes and conditions for practical applications in pesticide remediation.

Electroanalysis of bromate at riboflavin impregnated Ketjen black porous electrode via an autocatalytic cycle with finite length diffusion

The emergence of elevated concentrations of bromate, classified as a 2B type carcinogen, in drinking water following the treatment of water supplies with ozonation and other oxidation methods has underscored the importance of developing methods for reliable and rapid screening of drinking water. In this work, we report the use of electro activated riboflavin (RF) impregnated Ketjen black (KB) modified screen-printed electrode (elRF@KB-SPE) for the determination of bromate. The sensing surfaces were subjected to morphological and structural characterization using scanning electron microscopy and Raman spectroscopy. These analyses confirmed the successful modification of the electrode with an extended elRF@KB porous coating. Based on cyclic voltammetry (CV) and electrochemical impedance spectroscopy measurements, the response of elRF@KB-SPE towards bromate can be described through a dual mechanism involving i) an autocatalytic chemical/electrochemical process that predominantly occurs in the finite length pores of KB, and ii) an RF-mediated electrocatalytic process. Notably, the data demonstrated that the advanced electrocatalytic properties of the otherwise electrocatalytically inactive absorbed RF molecules are endowed after a simple electro activation process (three CV scans). Amperometric measurements at −0.05 V vs. Ag/AgCl revealed a linear relationship between the current response and the concentration of bromates over the concentration range 0.50−18.0 μM, achieving a limit of detection (3σ/slope) of 0.04 μM. The interference effect of various electroactive species was investigated demonstrating that elRF@KB-SPE is highly selective to bromate. The analytical utility of the method was evaluated in spiked tap water samples. Recoveries were 91.2 − 106.4 %.

Electrochemical Sensor Based on Glassy Carbon Electrode Modified with Carbon Nanohorns (SWCNH) for Determination of Cr(VI) via Adsorptive Cathodic Stripping Voltammetry (AdCSV) in Tap Water

In this study, a new and simple glassy carbon electrode modified with carbon nanohorns (SWCNH/GCE) was used for the determination of Cr(VI) in aqueous matrices via adsorptive cathodic stripping voltammetry (AdCSV). The modified electrode was characterized via field emission scanning electron microscopy and cyclic voltammetry, which revealed a homogeneous distribution of spherical agglomerates of SWCNH on the electrode surface. The modification increased the electrochemically active area from 0.10 cm2 ± 0.01 (GCE) to 0.16 cm2 ± 0.01 (SWCNH/GCE). The optimized analytical conditions were as follows: a supporting electrolyte (0.15 mol L−1 HCl), an accumulation potential of 0.8 V versus Ag/AgCl, and an accumulation time of 240 s. Validation of the analytical methodology was performed, obtaining a linear range between 20 and 100 µg L−1, a limit of detection of 3.5 µg L−1, and a limit of quantification of 11.6 µg L−1 with good accuracy and precision. The method was applied to the analysis of spiked tap water samples, and the results were compared using a flame atomic absorption spectrophotometer (FAAS) with no significant statistical differences.

Development of electrochemical sensors based on silver nanoparticles electrodeposited on gold screen-printed electrodes: application to nitrate trace analysis in water

Abstract. A simple, reusable and sensitive electrochemical sensor based on a gold screen-printed electrode modified with silver nanoparticles has been developed for the detection of nitrate in water. Scanning electron microscopy, square wave voltammetry and electrochemical impedance spectroscopy were used to characterize the modification of the electrode surface. The modified electrode with different silver nanoparticle loadings was also tested, as well as the influence of scan rate on the reduction of nitrate. The sensor exhibited a wide linear response to nitrate from 100 to 1500 µM and a detection limit of 7.7 µM, which is significantly less than the maximum contaminant level admitted in drinking water (800 µM). The reproducibility, repeatability and selectivity of the sensor have also been examined. The suitability of the proposed sensor for real sample detection was successfully demonstrated via recovery studies performed in spiked tap water samples. The proposed approach was used to determine nitrate in freshwater, and the results were in good agreement with those obtained from a commercial nitrate sensor. These advantages make the developed sensor a promising alternative approach for integration into an online monitoring system for water monitoring.

Thymol-based Dual Chemosensor for Optical Detection of Cu2+ and Pb2+ ions and Evaluation of its Toxicity Against Plant Growth Promoting Rhizobacteria

Abstract: Thymol is a naturally occurring monoterpenoid phenol, and its derivatives may emerge as eco-friendly materials for the development of chemosensing probes. To prepare a non-toxic chemosensing probe based on thymol moiety for the detection of metal ions. : A chemosensor (TPC) based on thymol was afforded by the reaction of thymol and piperidine in methanol. The structure elucidation of TPC was carried out with UV-Vis, 1H-NMR, 13C-NMR, and FT-IR analysis. The chemosensing properties of the synthesized probe were determined with UVvisible spectroscopy, and further, it was exploited for the determination of the concentration of Cu2+ and Pb2+ ions in spiked tap water samples. The toxicity studies of the chemosensing probe were conducted against the plant growth-promoting rhizobacteria (PGPR), i.e., Rhizobium sp., Pseudomonas sp., and Azospirillum sp. The absorption spectrum of TPC showed a band at 277 nm. The presence of Cu2+ and Pb2+ ions induced an increase in the absorption intensity at 277 nm by 2-fold and 1.5-fold, respectively. The binding constant for both TPC-Cu2+ and TPC-Pb2+ was calculated as 1.55 × 105 M-1 and 1.47 × 105 M-1, respectively. The respective limit of detection (LOD) and limit of quantification (LOQ) for Cu2+ were 623.64 × 10-6 mol L-1 and 1889.85 × 10-6 mol L-1. For Pb2+ ions, LOD and LOQ were calculated as 676.70 × 10-6 mol L-1 and 2050.60 × 10-6 mol L-1, respectively. In spiked tap water samples, percent recovery was observed in the range of 80.1 to 81.0 % and 80.1 to 81.9 % for Cu2+ and Pb2+ ions, respectively. Toxicity studies of the synthesized probe inferred that TPC was non-toxic against the tested PGPR at all the tested concentrations. In this work, we have synthesized a thymolbased chemosensor, which has been evaluated as a non-toxic sensor for Pb2+ and Cu2+ ions.

A Cyanoalkyl Silicone GC Stationary-Phase Polymer as an Extractant for Dispersive Liquid–Liquid Microextraction

In this work, three cyanoalkyl silicone GC stationary-phase polymers, namely OV-105, OV-225, and OV-275, were investigated as potential extractants for dispersive liquid–liquid microextraction (DLLME). The OV-225 polymer (cyanopropylmethyl-phenylmethylsilicone) exhibited the cleanest chromatographic background and was extensively studied. The proposed polymer was tested through the DLLME of four non-steroidal anti-inflammatory drugs from aqueous samples, followed by HPLC separation with UV detection at 230 nm. To achieve the maximum enrichment, the experimental conditions that influence the DLLME process were optimized using one-factor-at-a-time and design-of-experiment (DoE) approaches. The extraction variables (polymer mass, dispersive solvent volume, buffer pH, and mixing time) were screened by implementing a two-level full factorial design (FFD). Significant variables were fine-tuned using response surface methodology based on a face-centered central composite design (CCD). The optimum conditions were 10 mg of polymer (extraction medium); 50 µL of tetrahydrofuran (dispersive solvent); 100 µL of phosphate buffer pH 2.75 ([PO43−] = 100 mM); and 3 min of vortex mixing. The addition of salt had a minimal effect on the enrichment factors. In the optimum conditions, enrichment factors up to 46 were achieved using 1.5 mL samples. Calibration curves exhibited correlation coefficients > 0.999 using 4-pentylbenzoic acid as an internal standard. The limits of quantitation were 5 ng/mL for naproxen, 10 ng/mL for diflunisal, 25 ng/mL for indomethacin, and 75 ng/mL for ibuprofen. The analysis of spiked tap water samples showed adequate relative recoveries and precision. In conclusion, the proposed polymer (OV-225) is a potential greener alternative to traditional organic extractants used in DLLME.

Active site engineering of Zn-doped mesoporous ceria toward highly efficient organophosphorus hydrolase-mimicking nanozyme

Hydrolase-mimicking nanozymes have received increasing attention in recent years, but the effective rational design and development of these materials has not been realized, as they are not at present considered a critical research target. Herein, we report that Zn-doped mesoporous ceria (Zn-m-ceria) engineered to have an abundance of two different active sites with different functions—one that allows both co-adsorption binding of organophosphate (OP) and water and another that serves as a general base—has significant organophosphorus hydrolase (OPH)-like catalytic activity. Specifically, Zn-m-ceria exhibits a catalytic efficiency over 75- and 25-fold higher than those of m-ceria and natural OPH, respectively. First-principles calculations reveal the importance of Zn for the OPH-mimicking activity of the material, promoting substrate adsorption and proton-binding. The OPH-like Zn-m-ceria catalyst is successfully applied to detect a model OP, methyl paraoxon, in spiked tap water samples with excellent sensitivity, stability, and detection precision. We expect that these findings will promote research based on the rational engineering of the active site of nanozymes and efficient strategies for obtaining a diverse range of catalysts that mimic natural enzymes, and hence the utilization in real-world applications of enzyme-mimicking catalysts with properties superior to their natural analogs should follow.

Voltammetric determination of sulfamethoxazole using commercial screen-printed carbon electrodes

A differential pulse voltammetric (DPV) method using commercial screen-printed carbon electrodes (SPCE) is developed for a fast and cost-effective determination of the antibiotic sulfamethoxazole (SMX). Optimal measurements are carried out at pH 5.5 in acetate buffer and yield a detection limit of 15 µg/L and a linearity range of 50 – 600 µg/L with good repeatability (1.1%) and reproducibility (2.5%). The method is successfully applied to the analysis of a spiked tap water sample with very high reproducibility (0.4%) and good trueness (Recovery 95.2%).Additional considerations are made about the irreversible electrochemical oxidation of SMX, which is notoriously pH-dependent according to a process involving 2e- and 2H+, in agreement with several reported mechanisms in the literature. Besides, the analysis of other sulfonamide antibiotics is discussed, showing the key role of the free terminal amino group in oxidation, which makes almost undistinguishable voltammetric signals from different molecules sharing this moiety. In contrast, the acetylation of the mentioned group (e.g., in sulfonamide metabolites) drastically reduces the sensitivity of voltammetric measurements.

Flexible electrochemical sensor constructed using an active copper center instead of unstable molybdenum carbide for simultaneous detection of toxic catechol and hydroquinone

A new electrochemical sensor based on a Cu-CuO@MoOx-modified polyethylene terephthalate electrode spin coated with PEDOT (Cu-CuO@MoOx-PEDOT/PET) was developed for simultaneous determination of catechol (CT) and hydroquinone (HQ). A zerovalent copper and copper(II) oxide intercalated molybdenum oxide MoOx (x = 2 or 3) hybrid nanomaterial (Cu-CuO@MoOx) by introducing active copper catalytic centers into the Mo2C@MoOx system based on unstable Mo2C, and replaced Mo2C using a simple hydrothermal method. At room temperature, the Cu-CuO@MoOx-PEDOT/PET electrode demonstrated the lowest detection limits of 0.216 and 0.221 μM for CT and HQ (S/N = 3), respectively. In addition, the applicability of this method was proven by the recovery of CT and HQ in spiked tap water samples. The Cu-CuO@MoOx-PEDOT/PET flexible electrode had strong anti-interference ability, good repeatability and long-term stability. It was used in the detection of CT and HQ in Nanjing tap water, the recoveries of CT and HQ calculated from the i–t curve were 99.36 % and 97.56 %, respectively. Most importantly, the flexible electrode could still maintain relatively stable electrochemical responses under different bending and folding conditions, and the obtained relative standard deviations (RSDs) were 2.78 % and 1.53 %, respectively. This flexible property holds promise for the construction of wearable electrochemical sensors.

Polyaniline Entrapped Water-Dispersible 3MPA-ZnSe Quantum Dots and Their Application for the Development of an Enzymatic Electrochemical Nanobiosensor for the Detection of 17β-Estradiol, an Endocrine-Disrupting Compound.

17β-estradiol is used as a growth and fertility stimulant in the agronomic sector to induce fertility and manipulate reproductive characteristics in animals. However, unintended or unregulated distribution and exposure to even significant low levels of 17β-estradiol estrogen have detrimental health implication that can lead to reproductive abnormalities and even cancer. This could have severe effect on the ecosystem imbalance, food safety, to such a degree that its health impact necessitates rapid methods to probe for its prevalence and occurrence in the environment. Herein a simple, robust, sensitive and once-off use electrochemical biosensor to detect 17β-estradiol is developed, using 3-mercaptopropionic acid capped zinc selenide quantum dots trapped within the polyaniline (PANI) framework structure. The biosensor's interaction with the substrate was based on the capability of the hemeprotein, horseradish peroxidase (HRP) enzyme (i.e., baroreceptor) to alternatively catalyze phenolic alcohols. The biosensor displayed a significantly low limit of detection limit (LOD) of value 0.2 × 10-6M towards 17β-estradiol. The Mechaelis-Menten constant (Km) with the magnitude of 0.64 × 10-6M was obtained; this indicates an outstanding affinity of the biosensing films towards 17β-estradiol. Subsequently, the developed biosensor was able to accurately and efficiently measure successive concentrations of 17β-estradiol from 0.2 × 10 to 4 × 10-6M. The fabricated biosensor showed good selectivity towards 17β-estradiol compared to the other estrogenic endocrine-disrupting compounds such as estrone (E1), ethnylstradiol (EE2), and estriol (E3). The biosensor was capable of detecting 17β-estradiol in spiked tap water samples with good recoveries, thus affirming its potential to be applied for real electro-analysis of 17β-estradiol in treated wastewater.

Large surface vanadium pentoxide nanosheet modified screen-printed electrode for nanomolar diclofenac determination

This work reports on the utilization of vanadium pentoxide nanosheet (V2O5 NS)-modified screen-printed electrodes (SPEs) for the nanomolar voltammetric determination of diclofenac (DCF). V2O5 NSs were produced with a facile bath sonication method in a blend of 75/25% v/v H2O/isopropyl alcohol. The morphological, structural, and electrochemical characteristics of exfoliated V2O5 NSs were evaluated via scanning electron microscopy, X-ray diffraction, infrared spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). V2O5 NSs showed a 2D low dimensional morphology with most layers having dimensions of a few micrometers. Diagnostics CV studies using 5-hydroxydiclofenac or 2-(2-hydroxyphenyl) acetic acid, which have been proposed in literature to be involved in the electro oxidation of DCF, suggested that the actual mechanism is more complicated and need to be further elucidated. CV and EIS data demonstrated that at pH>6 V2O5 NSs deprived of their characteristic pseudocapacitive properties offering low background signals and enhanced electrocatalytic properties toward DCF. Among different preconcentration treatments examined, a short (192 s) cyclic potentiodynamic treatment was found to exhibit a stable, semi reversible pair of peaks of increased magnitude with successive cycles, and low background signal. The quantification of DCF was conducted using differential pulse voltammetry. A well-defined oxidation peak at ca. 380 mV at pH 7 vs. Ag/AgCl/3 M KCl was recorded and its height was found to be linearly correlated with the concentration of DCF over the range 20–200 nmol L−1, while a limit of detection (3Sx/slope) of 3.1 nmol L−1 was achieved. The response of V2O5 NS/SPE was evaluated against common interfering compounds, while the accuracy of the method was evaluated in spiked tap water samples.

Rapid warning microanalyzer for heavy metals monitoring in natural waters

A warning microanalyzer for the rapid monitoring of different heavy metals in water using Carbon Dots (CDs) as selective optical reagents is presented. The synthesized CDs have different surface functionalization and exhibit selective fluorescence quenching by heavy metal ions, that combined with the use of microfluidics, provide sensitivity, ease of automation and reproducibility to the method. Moreover, they present maximum excitation wavelengths around 350 nm, allowing multiparametric analysis with a single light source. Although quantum yields range from 16 % to 78 % depending on the type of CDs, enough sensitivity is achieved for each heavy metal using the same measurement conditions of the optical detection system (lock-in modulating frequency, signal amplitude and measurement frequency). The microanalyzer is composed of a Cyclic Olefin Copolymer (COC) analytical microsystem, a flow management system, and a miniaturized customized optical detection system. In this paper, we demonstrate that our proposed system can be used as a toxicity control system by selectively measuring five different heavy metal ions (Co2+, Cu2+, Hg2+, Ni2+, and Pb2+) with detection limits ranging from 2 to 12 ppb. Spiked tap water samples were analyzed, giving recoveries from 98 % to 134 %. Polluted samples containing four of the five heavy metal ions studied (Co2+, Cu2+, Ni2+, and Pb2+) were also analyzed with no significant differences observed between both methods, the proposed microanalyzer and the reference method (ICP-OES).

Electropolymerized, Molecularly Imprinted Polymer on a Screen-Printed Electrode-A Simple, Fast, and Disposable Voltammetric Sensor for Trazodone.

In recent years, analytical chemistry has been facing new challenges, particularly in developing low-cost, green, and easy-to-reproduce methods. In this work, a simple, reproducible, and low-cost electrochemical (voltammetric) molecularly imprinted polymer (MIP) sensor was designed specifically for the detection of trazodone (TZD). Trazodone (TZD) is an antidepressant drug consumed worldwide since the 1970s. By combining electropolymerization (surface imprinting) with screen-printed electrodes (SPCEs), the sensor is easy to prepare, is environmentally friendly (uses small amounts of reagents), and can be used for in situ analysis through integration with small, portable devices. The MIP was obtained using cyclic voltammetry (CV), using 4-aminobenzoic acid (4-ABA) as the functional monomer in the presence of TZF molecules in 0.1 M HCl. Non-imprinted control was also constructed in the absence of TZD. Both polymers were characterized using CV, and TZD detection was performed with DPV using the oxidation of TZD. The polymerization conditions were studied and optimized. Comparing the TZD signal for MIP/SPCE and NIP/SPCE, an imprinting factor of 71 was estimated, indicating successful imprinting of the TZD molecules within the polymeric matrix. The analytical response was linear in the range of 5–80 µM, and an LOD of 1.6 µM was estimated. Selectivity was evaluated by testing the sensor for molecules with a similar structure to TZD, and the ability of MIP/SPCE to selectively bind to TZD was proven. The sensor was applied to spiked tap water samples and human serum with good recoveries and allowed for a fast analysis (around 30 min).

Evaluation of solution anode glow discharge as a vapor generator in ICP-OES procedures: Application to highly sensitive determination of Cd and Hg

Herein, we developed a novel microplasma-assisted vapor generation technique based on solution anode glow discharge (SAGD) as a substitute for the pneumatic nebulization (PN) routinely used in inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimal state of the newly proposed SAGD-ICP-OES system, the detection limits (DLs) of Cd and Hg were reduced by some 12- and 90-fold respectively, and an average of 2 times for other elements (Ag, Bi, Pb, Tl and Zn) in comparison with conventional PN. This system not only obtained the good detection limits amenable to the ultra-trace determination of Cd (DL = 0.3 μg L−1) and Hg (DL = 0.2 μg L−1), but also retained the ability of multi-element analysis. Its accuracy was demonstrated by the determination of Cd and Hg using GBW07312 (stream sediments) and GBW10029 (fish) certified reference materials (CRMs) and spiked tap water samples. The results showed good consistency with the certified values and the values obtained using inductively coupled plasma−mass spectrometry.

Viscose-Derived Activated Carbons Fibers as Highly Efficient Adsorbents for Dimethoate Removal from Water.

Extensive use of pesticides resulting in their accumulation in the environment presents a hazard for their non-target species, including humans. Hence, efficient remediation strategies are needed, and, in this sense, adsorption is seen as the most straightforward approach. We have studied activated carbon fibers (ACFs) derived from viscose fibers impregnated with diammonium hydrogen phosphate (DAHP). By changing the amount of DAHP in the impregnation step, the chemical composition and textural properties of ACFs are effectively tuned, affecting their performance for dimethoate removal from water. The prepared ACFs effectively reduced the toxicity of treated water samples, both deionized water solutions and spiked tap water samples, under batch conditions and in dynamic filtration experiments. Using the results of physicochemical characterization and dimethoate adsorption measurements, multiple linear regression models were made to reliably predict performance towards dimethoate removal from water. These models can be used to quickly screen among larger sets of possible adsorbents and guide the development of novel, highly efficient adsorbents for dimethoate removal from water.

Optimization of Square Wave Voltammetry (SWV) Parameters by Design of Experiment (DoE) Methodologies for the Determination of Mifepristone at Glassy Carbon Electrode (GCE)

AbstractIn the present study, an electroanalytical method that permits the optimization of factors affecting SWV for sensitive detection of mifepristone at glassy carbon electrode (GCE) using response surface methodology (RSM) with desirability function (DF) is presented. Factors selected for optimization after screening using full factorial design were frequency (X1), amplitude (X2), and pH (X3). The central composite design as a response surface methodology with desirability function (DF) was applied for obtaining the optimum level. The optimum conditions were obtained as follows: Frequency (X1=50 Hz), amplitude (X2=33.4 mV), and pH (X3=9.4), with an overall desirability function of 0.97. Subsequently, confirmatory experiments were performed in triplicates to validate the optimum conditions. The results obtained were satisfactory and agreed well with less only 11.9 % deviation from the values predicted by the model. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.54 and 1.80 ppm, respectively. The proposed method was applied for a quantitative determination of mifepristone in spiked tap water samples. The recovery tests showed that the detection of mifepristone at GC could be evaluated on environmental samples.

Viscose-derived activated carbons as adsorbents for malathion, dimethoate, and chlorpyrifos-screening, trends, and analysis.

The release and accumulation of pesticides in the environment require the development of novel sustainable technologies for their removal. While adsorption is a classical approach, the design of new materials with enhanced adsorption properties could rationalize the remediation routes and decrease potential risks for their non-target organisms, including humans. More importantly, the use of adsorbents and their synthesis should be implemented in a sustainable and environmentally friendly manner. In this contribution, we studied the adsorption of organophosphorus pesticides (OPs) dimethoate, malathion, and chlorpyrifos on viscose fiber-derived activated carbon fibers (ACFs). The most efficient adsorption was found for chlorpyrifos, followed by malathion and dimethoate, while material properties were correlated with OP uptake. These ACFs are extremely efficient for chlorpyrifos adsorption, with experimentally observed adsorption capacitances reaching 240mgg-1. Detailed analysis suggests that chlorpyrifos is physisorbed on ACF surfaces and that increased surface hydrophilicity reduces the uptake. Studied ACFs have great potential for practical application. They can reduce OPs' concentrations to such levels that no acute neurotoxic effects of the studied OPs in spiked tap water samples are seen, even for starting concentrations up to 104 times higher than the allowed ones. Finally, this study presents possible guidance for developing even more efficient and environmentally friendly adsorbents for chlorpyrifos, the most toxic among studied OPs.

A new cognate aptamer pair-based sandwich-type electrochemical biosensor for sensitive detection of Staphylococcus aureus

A pair of aptamers for Staphylococcus aureus (S. aureus) is immensely needed for developing sandwich-type signal-on electrochemical aptasensors. In this study, we have successfully developed a cognate pair of aptamers that bind to S. aureus simultaneously, among many aptamer candidates screened out after a total of ten rounds of bacterial cell-based systemic evolution of ligands by exponential enrichment (SELEX). The obtained aptamer candidates have been estimated by using flow cytometry and confocal microscope, to evaluate their binding affinity and specificity to the target cells. The screening for sandwich-type binding of cognate pair of aptamers with S. aureus was conducted by enzyme-based colorimetric assay and confirmed by circular dichroism (CD), two-color fluorescence imaging analysis, additionally. The cognate pair of two aptamers, named SA37 and SA81, showed very good affinity and specificity to S. aureus with their dissociation constants (Kd) of 16.5 ± 3.4 nM and 14.47 ± 8.18 nM, respectively. These newly discovered cognate pair of aptamers have been very successfully implemented to develop a sandwich-type signal-on electrochemical biosensor with the limit of detection (LOD) of 39 CFUs and 414 CFUs in buffer and spiked tap water samples, respectively. This study showed that this cognate pair of aptamers-based detection of S. aureus enables simple, rapid, and robust biosensors for food safety management.

One-Pot Hydrothermal Synthesis of Carbon Dots as Fluorescent Probes for the Determination of Mercuric and Hypochlorite Ions.

Nitrogen and sulfur codoped carbon dots (NSCDs) were synthesized via a one-pot hydrothermal method, and citric acid, ethylenediamine, and methyl blue were used as precursors. The obtained NSCDs were spherical with an average size of 1.86 nm. The fluorescence emission spectra of the NSCDs were excitation independent and emitted blue fluorescence at 440 nm with an excitation wavelength at 350 nm. The quantum yield of the NSCDs was calculated to be 68.0%. The NSCDs could be constructed as fluorescent probes for highly selective and sensitive sensing mercuric (Hg2+) and hypochlorite (ClO−) ions. As the addition of Hg2+ or ClO− ions to the NSCDs, the fluorescence intensity was effectively quenched due to dynamic quenching. Under the optimal conditions, the linear response of the fluorescence intensity ranged from 0.7 μM to 15 μM with a detection limit of 0.54 μM and from 0.3 μM to 5.0 μM with a limit of detection of 0.29 μM for Hg2+ and ClO− ions, respectively. Finally, the proposed method was successfully used for quantifying Hg2+ and ClO− ions in spiked tap water samples.

Carbon-stabilized porous silicon as novel voltammetric sensor platforms

The use of carbon-stabilized porous silicon (pSi) as a voltammetric sensing platform able to discriminate the detection of various electroactive species with similar redox potentials is demonstrated for the first time. For this purpose, the voltammetric responses to the presence of the three dihydroxybenzene isomers hydroquinone, catechol and resorcinol were studied using thermally hydrocarbonized pSi (THCpSi) and thermally carbonized pSi (TCpSi), as well as a glassy carbon electrode (GCE) as a benchmark. Both THCpSi and TCpSi outperformed the electrochemical performance of a GCE, as shown by the electrochemical characterization performed in the presence of the redox pair [Fe(CN)6]3-/4-. Cyclic voltammetry results demonstrated that both THCpSi and TCpSi exhibited fast electron transfer kinetics, with TCpSi showing a slightly improved electrochemical performance. The electrode catalytic enhancement shown by these carbon-stabilized nanostructures was harnessed to allow the simultaneous voltammetric determination of hydroquinone, catechol and resorcinol. The analytical performance of TCpSi to the detection of the three dihydroxybenzene isomers was studied using differential pulse voltammetry, revealing good reproducibility, high sensitivity, low limits of detection (all below 5 µmol L−1) and good recoveries (between 98 and 102%) in the analysis of spiked tap water samples.