Aggregation-induced-emission red carbon dots for ratiometric sensing of norfloxacin and anti-counterfeiting.

The detection of trace antibiotic residues holds significant importance because it's related to food safety and human health. In this study, we developed a new high-yield red-emitting carbon dots (R-CDs) with aggregation-induced emission properties for ratiometric sensing of norfloxacin. R-CDs were prepared in 30 min using an economical and efficient microwave-assisted method with tartaric acid and o-phenylenediamine as precursors, achieving a high yield of 34.4 %. R-CDs showed concentration-dependent fluorescence and aggregation-induced-emission properties. A ratiometric fluorescent probe for detecting the norfloxacin was developed. In the range of 0-40 µM, the intensity ratio of two emission peaks (I445 nm/I395 nm) towards norfloxacin show good linear relationship with its concentrations and a low detection limit was obtained (36.78 nM). In addition, complex patterns were developed for anti-counterfeiting based on different emission phenomenon at different concentrations. In summary, this study designed a novel ratiometric fluorescent probe for detection of norfloxacin, which greatly shortens the detection time and improves efficiency compared with high-performance liquid chromatography and other methods. The study will promote the application of carbon dots in anti-counterfeiting and other related fields, laying the foundation for the preparation of low-cost photosensitive anti-counterfeiting materials.

Iron-driven self-assembly of dopamine into dumbbell-shaped nanozyme for visual and rapid detection of norfloxacin on a smartphone-assisted platform.

Antibiotics in aquatic environments raise health concerns. Therefore, the rapid, on-site, and accurate detection of antibiotic residues is crucial for protecting the environment and human health. Herein, a dumbbell-shaped iron (Fe3+)-dopamine coordination nanozyme (Fe-DCzyme) was developed via an iron-driven self-assembly strategy. It exhibited excellent peroxidase-like activity, which can be quenched by adding l-cysteine to prevent Fe3+/Fe2+ electron transfer but restored by adding norfloxacin. Given the 'On-Off-On' effect of peroxidase-like activity, Fe-DCzyme was used as a colourimetric sensor for norfloxacin detection, and showed a wide linear range from 0.05 to 6.00 µM (R2 = 0.9950) and LOD of 27.0 nM. A portable smartphone-assisted detection platform using Fe-DCzyme was also designed to convert norfloxacin-induced color changes into RGB values as well as to realise the rapid, on-site and quantitative detection of norfloxacin. A good linear relation (0.10-6.00 µM) and high sensitivity (LOD = 79.3 nM) were achieved for the smartphone-assisted Fe-DCzyme detection platform. Its application was verified using norfloxacin spiking methods with satisfactory recoveries (92.66%-119.65%). Therefore, the portable smartphone-assisted Fe-DCzyme detection platform with low cost and easy operation can be used for the rapid, on-site and visual quantitative detection of antibiotic residues in water samples.

Environmental remediation of the norfloxacin in water by adsorption: Advances, current status and prospects.

Antibiotics are considered as the new generation water pollutants as these disturb endocrine systems if water contaminated with antibiotics is consumed. Among many antibiotics norfloxacin is present in various natural water bodies globally. This antibiotic is considered an emerging pollutant due to its low degradation in aquatic animals. Besides, it has many side effects on human vital organs. Therefore, the present article discusses the recent advances in the removal of norfloxacin by adsorption. This article describes the presence of norfloxacin in natural water, consumption, toxicity, various adsorbents for norfloxacin removal, optimization factors for norfloxacin removal, kinetics, thermodynamics, modeling, adsorption mechanism and regeneration of the adsorbents. Adsorption takes place in a monolayer following the Langmuir model. The Pseudo-second order model represents the kinetic data. The adsorption capacity ranged from 0.924 to 1282 mg g-1. In this sense, the parameters such as the NFX concentration added to the adsorbent textural properties exerted a great influence. Besides, the fixed bed-based removal at a large scale is also included. In addition to this, the simulation studies were also discussed to describe the adsorption mechanism. Finally, the research challenges and future perspectives have also been highlighted. This article will be highly useful for academicians, researchers, industry persons, and government authorities for designing future advanced experiments.

Comparative analysis of SilA-laccase mediated degradation of ciprofloxacin, norfloxacin and ofloxacin and interpretation of the possible catalytic mechanism.

Fluoroquinolones (FQs) are the most commonly used antimicrobial drugs and regardless of their advantages in the healthcare sector, the pollution of these antimicrobial drugs in the environment has big concerns about human and environmental health. The presence of these antibiotic drugs even at the lowest concentrations in the environment has resulted in the emergence and spread of antibiotic resistance. Hence, it is necessary to remediate these pollutants from the environment. Previously alkaline laccase (SilA) from Streptomyces ipomoeae has been demonstrated to show degrading potentials against two of the FQs, Ciprofloxacin (CIP) and Norfloxacin (NOR); however, the molecular mechanism was not elucidated in detail. In this study, we have analyzed the possible molecular catalytic mechanism of FQ degrading SilA-laccase for the degradation of the FQs, CIP, NOR and Ofloxacin (OFL) using three-dimensional protein structure modeling, molecular docking and molecular dynamic (MD) studies. The comparative protein sequence analysis revealed the presence of tetrapeptide conserved catalytic motif, His102-X-His104-Gly105. After evaluating the active site of the enzyme in depth using CDD, COACH and S-site tools, we have identified the catalytic triad composed of three conserved amino acid residues, His102, Val103 and Tyr108 with which ligands interacted during the catalysis process. By analyzing the MD trajectories, it is revealed that the highest degradation potential of SilA is for CIP followed by NOR and OFL. Ultimately, this study provides the possible comparative catalytic mechanism for the degradation of CIP, NOR and OFL by the SilA enzyme.Communicated by Ramaswamy H. Sarma.

Study of degradation of norfloxacin antibiotic and their intermediates by natural solar photolysis.

In this work, the photolysis of the antibiotic norfloxacin (NOR) and the formation of its photodegradation products were studied using UV and solar radiation. Their extraction was also assessed in Milli-Q water and secondary effluents from a wastewater treatment plant. The photolysis of NOR was chromatographically monitored. The structure of each degradation product is related to the reaction of NOR with reactive oxygen species (ROS), as confirmed using radical quenchers and mass spectrometry. Additionally, the feasibility of extracting NOR and its degradation products was assessed using a commercial solid phase extraction system. Photolysis results showed the formation of five degradation products, generated under exposure to both types of radiation. The decays in NOR concentrations for the solar and UV treatments were adjusted to pseudo first-order kinetics with apparent constant values of ksolar = 1.19 × 10-3 s-1 and kUV = 3.84 × 10-5 s-1. Furthermore, the superoxide radical was the main participant species in the formation of the degradation products P3, P4, and P5. Species P1 and P2 do not need this radical for their formation. The presence of NOR in water opens the possibility of its photolysis by solar radiation. This work contributes to the understanding of the mechanisms that mediate its photodegradation, in addition to studying potential options for its determination and its photodegradation products in the sample treatment.

A high-precision prediction for spatiotemporal distribution and risk assessment of antibiotics in an urban watershed using a hydrodynamic model.

A methodology for the high-precision prediction and risk assessment of antibiotics at the watershed scale was established. Antibiotic emission inventory and attenuation processes were integrated into the MIKE 11 model to predict the spatiotemporal distribution of norfloxacin, ofloxacin, enrofloxacin, erythromycin, roxithromycin, and sulfamethoxazole in the Nanfei River watershed, China. Considering the variations in antibiotic removal in sewage treatment plants, manure composting, and lagoon systems, the high, medium, and low removal efficiencies of selected antibiotics across China were obtained and used as the best, expected, and worst scenarios, respectively, to evaluate the uncertainty of antibiotic emissions. The predicted concentrations were comparable to antibiotic measurements after flow calibration. The prediction results showed that the highest concentration exposures were mainly concentrated in urban areas with a dense population. Flow variations controlled the temporal distribution characteristics of antibiotics via the dilution effect, and the concentrations of antibiotics in the dry season were 3.1 times higher than those in the wet season. The median concentrations of norfloxacin and erythromycin ranged from 111.36 ng/L to 592.33 ng/L and 106.63 ng/L to 563.01 ng/L, respectively, which both posed a high risk to cyanobacteria and a medium risk to spreading antibiotic resistance. Scenario analysis further demonstrated that high removal efficiencies of these antibiotics can considerably reduce the potential ecotoxicity risks and bacterial resistance selection. The developed methodology for predicting the distribution and risk of antibiotics was suitable for the risk assessment and control strategy of human- and livestock-sourced pollutants.

Simulation and risk assessment of typical antibiotics in the multi-media environment of the Yangtze River Estuary under tidal effect.

Frequent human activities in estuary areas lead to the release of a large number of antibiotics, which poses a great threat to human health. However, there are very limited studies about the influence of the special natural phenomena on the occurrence and migration of antibiotics in the environment. In this study, we simulated the migration and transformation of six typical antibiotics, including oxytetracycline (OTC), tetracycline (TC), norfloxacin (NOR), ofloxacin (OFX), erythromycin (ETM), and amoxicillin (AMOX), in the environmental media from 2011 to 2019 in the Yangtze River Estuary, by using the level III multi-media fugacity model combined with the factor of tides. The simulation results showed that the most antibiotics mainly existed in soil and sediment while erythromycin were found mainly in water. The concentrations of antibiotics in air, freshwater, seawater, groundwater, sediment, and soil were 10-23-10-25, 0.1-12 ng/L, 0.02-7 ng/L, 0.02-16 ng/L, 0.1-13 ng/g, and 0.1-15 ng/g respectively. Sensitivity analysis showed that the degradation rate (Km) and the soil-to-water runoff coefficient (Kl) were important model parameters, indicating that hydrodynamic conditions had a significant impact on the migration of antibiotics in various environmental phases in estuarine areas. Tide can enhance the exchange between water bodies and cause the transformation of the antibiotics from freshwater to seawater and groundwater, which improved the accuracy of the model, especially the seawater and soil phase. Risk assessments showed that amoxicillin, erythromycin, ofloxacin, and norfloxacin posed a threat to the estuarine environment, but the current source of drinking water did not affect human health. Our findings suggested that, when one would like to exam the occurrence and migration of antibiotics in environment, more consideration should be given to the natural phenomena, in addition to human activities and the nature of antibiotics.

Sensitive determination of Norfloxacin in milk based on ß-cyclodextrin functionalized silver nanoparticles SERS substrate.

The norfloxacin (NFX) residue in milk will increase human resistance to drugs and pose a threat to public health. In this work, a highly sensitive method for detection of NFX was developed based on surface enhanced Raman spectroscopy (SERS) using ß-cyclodextrin functionalized silver nanoparticles (ß-CD-AgNPs) as substrate. The unique spatial size and hydrophilicity of ß-CD on the surface of AgNPs could selectively capture the target molecule (NFX) through some weak interactions, including hydrogen-bond interaction, electrostatic interaction, etc. The interactions were characterized by the UV-Vis absorption spectroscopy, fluorescence spectroscopy, Zeta potential and DLS. The Raman signal of NFX is largely enhanced when anchored by ß-CD on the surface of AgNPs due to SERS effect. Through a series of experiments and analysis, the limit of detection (LOD) in standard solution and spiked milk were calculated to be 3.214 pmol/L and 5.327 nmol/L. The correlation coefficients (R2) were 0.986 and 0.984, respectively. For milk sample determination of NFX, the recovery was 101.29% to 104.00% with the relative standard deviation (RSD) from 2.986% to 9.136%. To sum up, this developed SERS strategy is sensitive and specific to detect NFX in milk, it has practical application value and prospects.

In situ SERS detection of quinolone antibiotic residues in a water environment based on optofluidic in-fiber integrated Ag nanoparticles.

In this paper, we present a microstructured optofluidic in-fiber Raman sensor for the detection of quinolone antibiotic residue in a water environment based on Ag surface-enhanced Raman scattering (SERS) substrate grown on the surface of the suspended core of micro-hollow optical fiber (MHF). Here, MHF has a special structure with a suspended core and a microchannel inside, which can become a natural in-fiber optofluidic device. Meanwhile, the self-assembled Ag SERS substrate can be grown on the suspended core's surface through chemical bonds, forming a microstructured optofluidic device with a Raman enhancement effect. Therefore, it can effectively detect the Raman signal of unlabeled trace quinolone antibiotic residue (ciprofloxacin and norfloxacin) inside the optical fiber. The results show that the ciprofloxacin and norfloxacin detection limits (LOD) are 10-10M and 10-11M, respectively. Compared with the maximum residue limit (3.01×10-7mol/L) stipulated by the European Union, the results are much lower, and an ideal quantitative relationship can be obtained within the detection range. Significantly, this study provides an in-fiber microstructured optofluidic Raman sensor for the label-free detection of quinolone antibiotic residue, which will have good development prospects in the field of antibiotic water pollution environmental detection.

Toward broader applications of iron ore waste in pollution control: Adsorption of norfloxacin.

Norfloxacin, a kind of antibiotic frequently detected in environments, represents a group of non-persistent organic pollutants with latent risks to the ecosystem. Iron ore waste, generated and accumulated in large quantities from the iron/steel industry, was evaluated as a potential sorbent for norfloxacin removal. Kinetics analysis showed that the adsorption process reached equilibrium at 72 h, and the adsorption process could be best defined by the pseudo-second-order kinetics with the primary mechanism of norfloxacin adsorption suggested to be cation exchange. Further, adsorption of norfloxacin to iron ore waste was shown to be facilitated by the pH range of 2-10, low cation concentration, and low temperature, which are characteristic of natural surface waters, suggesting the potential of practical applications in aquatic environments. These findings provide new insight into the potentials of beneficial reuse for iron ore waste in the adsorptive removal of environmental pollutants.

The influence mechanism of the molecular structure on the peak current and peak potential in electrochemical detection of typical quinolone antibiotics.

Antibiotic pollution in water has become an increasingly serious problem, posing a potentially huge threat to human health. Ofloxacin (OFL), norfloxacin (NOR), and enoxacin (ENX) are typical broad-spectrum quinolone antibiotics, which are frequently detected in various water environments. An electrochemical sensor is a rapid and effective tool to detect antibiotics in the aquatic environment. The molecular structure of target pollutants is an important factor affecting the detection performance of electrochemical sensors. Based on the electrochemical detection results of antibiotics (OFL, NOR, and ENX), we first used the molecular structure analysis method based on quantum chemistry to accurately identify the electronegativity and the electrocatalytic degree of the oxidizable (and non-oxidizable) functional groups of pollutants. We also clarified the influence mechanism of the molecular structure on the peak current and peak potential. These results can provide theoretical support for rapidly selecting electrodes with a suitable electrochemical window to efficiently detect trace organic pollutants (such as antibiotics) in water based on the molecular structure of the target pollutant.

Preparation of Ce0.9Zr0.1O2/SnIn4S8 composite photocatalyst and its degradation of typical antibiotic pollutants.

Considering the high environmental risk, the remediation of antibiotic pollutants attracted numerous attentions. In this work, a novel photocatalyst, Ce0.9Zr0.1O2/SnIn4S8, was fabricated by in situ precipitation and hydrothermal method and then applied to the degradation of norfloxacin under the irritation of visible light. The SEM, TEM, XRD, XPS, and electrochemical results clearly showed that the n-type heterojunction between Ce0.9Zr0.1O2 and SnIn4S8 was successfully constructed, which greatly reduces the recombination of the photogenic electron and holes, leading to the improvement of photocatalytic performance and stability (recycled over eight times). Besides, the Ce0.9Zr0.1O2/SnIn4S8 composite also exhibited good ability to mineralize norfloxacin. Under the optimal condition (pH 3, 1 g L-1 of 10% Ce0.9Zr0.1O2/SnIn4S8, and 8 mg L-1 of initial norfloxacin concentration), norfloxacin could be fully and rapidly degraded in 60 min, and completely mineralized in 4 h (99.3 ± 1.7%). LC-QTOF-MS results evidently displayed eight intermediates during norfloxacin degradation. In addition, with the attack of the reactive oxygen species (h+, •OH, and •O2-), norfloxacin could be effectively decomposed via deoxygenation, hydroxylation, and carboxylation reactions. Notably, compared to photodegradation, the photocatalytic process could completely eliminate the norfloxacin from water because it could avoid the accumulation of toxic byproducts.

Norfloxacin detection based on the peroxidase-like activity enhancement of gold nanoclusters.

The use of nanomaterials as mimic enzymes provides a promising way to implement bio-molecule detection in living systems. However, to achieve highly efficient catalytic processes with gold nanocluster-based nanozymes is still challenging. In this study, a facile reduction method was utilized to synthesize gold nanoclusters with 1-methyl-D-tryptophan as the reducing and capping agent. The obtained gold nanoclusters exhibited a peroxidase-mimicking property in the redox reaction of 3,3',5,5'-tetramethylbenzidine to blue oxidized 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. The addition of norfloxacin endowed the nanozymes with a 10-fold enhancement in catalytic efficiency due to the surface charge-controlled electron transfer modulation. The colorimetric sensing system presented a high selectivity toward norfloxacin. The good linear relationship of norfloxacin monitoring was gained in the range of 1.25~8.0 µM (R2 = 0.996), with a detection limit of 0.2 µM. The practical application of the proposed protocol for the measurement of norfloxacin in capsules was realized. This demonstrates that on account of their significant catalytic efficiency enhancement, the gold nanocluster-based nanozymes hold great promise in realizing the selective detection of drugs. Graphical Abstract.

Norfloxacin adsorption on montmorillonite and carbon/montmorillonite hybrids: pH effects on the adsorption mechanism, and column assays.

The presence of norfloxacin antibiotic (NFX) in drinking water raises significant scientific concern due to the health and environmental problems that may cause. This study aimed to evaluate the NFX removal: 1) in batch adsorption at different pH values on montmorillonite (M) and montmorillonite-carbon hybrids (M-HC); 2) in continuous columns experiments, to assess the technological application of these hybrids as domestic filters, using one M-HC as adsorbent material ranging from 1% to 5%. Batch experiments showed that adsorption occurred in all the samples, being M the material with the highest adsorption capacity (95% of adsorption for cationic NFX). For the M-HC the adsorption seemed to be not strongly dependent of the pH (20%- 41% of adsorption). The characterization of adsorbents and NFX adsorption products (FTIR, XRD, and zeta potential analysis) disclosed that adsorption occurs at both the external surface and the interlayer space of M. For the M-HC synthesized without activation, the interlayer space seemed to be predominantly responsible; while for the activated M-HC the adsorption occurred at the external surface (its interlayer was destroyed). The column experiments revealed that the best adsorption capacity and highest flow were attained using 1% of adsorbent material in the column packing.

Efficient removal of norfloxacin in water using magnetic molecularly imprinted polymer.

Effective and practical materials are important for the pollution control in the environment. A novel magnetic molecularly imprinted polymer (CoFe2O4@TiO2-MMIP) was prepared based on the surface molecular imprinting technology combined with photocatalytic degradation and magnetic separation. The adsorption rate constant and maximum adsorption capacity of CoFe2O4@TiO2-MMIP are 0.21 g mg-1 min-1 and 14.26 mg g-1, respectively. The effects of experimental factors on the adsorption properties of the magnetic molecularly imprinted polymer were investigated. CoFe2O4@TiO2-MMIP had selective adsorption ability towards fluoroquinolones. The adsorption efficiency was closely related to the molecular structure, molecular weight, polarity and functional groups of the target contaminant and the removal efficiency of norfloxacin was affected by another substance obviously in binary adsorption system. The adsorption-photocatalytic recycling experiment verified that CoFe2O4@TiO2-MMIP could simultaneously complete the degradation of pollutants and in-situ regeneration, indicating good reusability. This material with selective adsorption and photocatalytic regeneration would have substantial attraction for application in the removal of fluoroquinolones.

Comparison of visible light driven H2O2 and peroxymonosulfate degradation of norfloxacin using Co/g-C3N4.

As common advanced oxidation processes, Fenton-like and peroxymonosulfate (PMS) processes have received enormous attention due to their high efficiency in the pollutants degradation. In this study, the Co/g-C3N4 photocatalyst was prepared by facial calcination strategy and used to evaluate the behavior of the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems for norfloxacin (NOR) photocatalytic degradation under visible light irradiation. The composite photocatalysts exhibited better performance compared to that of pure g-C3N4 due to the efficient separation of electron-hole pairs and visible light absorption. The Co/g-C3N4/PMS system possessed better photocatalytic performance than the Co/g-C3N4/H2O2 system, where the degradation ratio of NOR and removal ratio of total organic carbon (TOC) were 96.4% and 54%, respectively, in 10 min. The photocatalytic mechanism was investigated using reactive species trapping experiments and electron spin-resonance spectroscopy (ESR). ⋅OH and SO4⋅- were the dominant reaction species in the Co/g-C3N4/H2O2 and Co/g-C3N4/PMS systems, respectively. According to the analysis of the NOR degradation path, SO4⋅- could attack the C-H bond on the piperazine ring or quinolone group of NOR, which resulted in it more active and accelerating the destruction of NOR with SO4⋅- and ⋅OH. The destruction of the quinolone group was the main pathway in the H2O2 process, while the destruction of the piperazine ring was the main pathway in the PMS process. In sum, the Co/g-C3N4/PMS process had a higher photocatalytic activity and economic applicability.

Occurrence, sources and risk assessment of fluoroquinolones in dumpsite soil and sewage sludge from Chennai, India.

Soil and sludge are major reservoirs of organic compounds such as fluoroquinolones (FQs) which are broad-spectrum antibacterial agents. Hence, we monitored three major FQs, namely, ciprofloxacin (CIP), norfloxacin (NOR), and ofloxacin (OFL), in surface soil from two major dumpsites and dry and wet sludge from sewage treatment plants in Chennai city. The mean concentration of FQs in soil and sludge samples were 20 µg/g and 26 µg/g, respectively. Nearly 50% of the total FQs in dumpsite soil was contributed by CIP followed by NOR (32%) and OFL (13%). Similarly, CIP was the major contributor in sludge samples followed by NOR and OFL. The concentration of FQs was two folds higher in wet sludge than dry sludge most likely indicating that water solubility of these compounds might play an important role for elevated level of FQs in wet sludge. Solid waste from pharmaceutical industries, households, and sludge from wastewater treatment plants were expected to be the major source of FQs in dumpsite soil. Predicted risk assessment using soil to water migration concentrations via surface run off indicated high risk to aquatic organisms. However, risk quotient (RQ) was found less to earthworm in most of the soil samples. The findings from this study might help in future policies on disposal of household antibiotics in the solid waste stream.

Novel synthesis of orange-red emitting copper nanoclusters stabilized by methionine as a fluorescent probe for norfloxacin sensing.

In the present work, we report a novel chemical approach for the synthesis of orange-red emitting copper nanoclusters (Cu NCs) using L-methionine as stabilizing agent at room temperature for the first time. The synthetic route is facile, economical and viable. The methionine stabilized copper nanoclusters (Cu NCs/Met) were thoroughly characterized by TEM, FT-IR, XPS, UV-Vis, steady state and transient fluorescence spectroscopy. The results show the synthesized Cu NCs/Met with a fluorescence quantum yield of 4.37% possessed high stability and excellent optical features such as large Stokes shift and long fluorescence lifetime (8.3 µs). Significantly, the fluorescence intensity of Cu NCs/Met could be efficiently quenched by norfloxacin (NOR) pharmaceutical. A fast and cost-effective NOR sensor was proposed employing Cu NCs/Met as the fluorescent nanoprobe, and the quenching mechanisms were attributed to inner filter effect and agglomeration-induced quenching. The developed sensor exhibited a high sensitivity and selectivity towards NOR in a wide linear range from 0.05 to 250 µM with a detection limit as low as 17 nM. Moreover, the practicability of the developed NOR sensor for real sample assay was validated with satisfactory recoveries, indicating this sensing platform with great potential for label-free pharmaceutical detection in complex systems.

Effect of the CuO addition on a Sb-doped SnO2 ceramic electrode applied to the removal of Norfloxacin in chloride media by electro-oxidation.

Norfloxacin is employed as in veterinary and human medicine against gram-positive and gram-negative bacteria. Due to the ineffective treatment at the wastewater treatment plants it becomes an emergent pollutant. Electro-oxidation appears as an alternative to its effective mineralization. This work compares Norfloxacin electro-oxidation on different anodic materials: two ceramic electrodes (both based on SnO2 + Sb2O3 with and without CuO, named as CuO and BCE, respectively) and a boron doped diamond (BDD). First, the anodes were characterized by cyclic voltammetry, revealing that NOR direct oxidation occurred at 1.30 V vs. Ag/AgCl. The higher the scan rate the higher both the current density and the anodic potential of the peak. This behavior was analyzed using the Randles-Sevcik equation to calculate the Norfloxacin diffusion coefficient in aqueous media, giving a value of D = 7.80 × 10-6 cm2 s-1 at 25 °C), which is close to the predicted value obtained using the Wilke-Chang correlation. The electrolysis experiments showed that both NOR and TOC decay increased with the applied current density, presenting a pseudo-first order kinetic. All the anodes tested achieved more than 90% NOR degradation at each current density. The CuO is not a good alternative to BCE because although it acts as a catalyst during the first use, it is lost from the anode surface in the subsequent uses. According to their oxidizing power, the anodes employed are ordered as follows: BDD > BCE > CuO.

Determination of norfloxacin residues in foods by exploiting the coffee-ring effect and paper-based microfluidics device coupling with smartphone-based detection.

By utilizing the coffee-ring effect and microfluidic paper-based analytical devices (µPADs), this study improved the sensitivity of the determination of norfloxacin in four different food matrices. Micro-PADs in this study were fabricated by designing and embedding wax channels onto cellulose-based filter paper through printing and subjecting the paper to heat to allow the wax to penetrate the paper. Determination of norfloxacin concentration in food samples was achieved by monitoring the colorimetric reaction that occurred between norfloxacin and the added iron (III) nitrate nonahydrate in 5 mM ammonia in each reaction chamber. A transition metal hydroxide was formed through this reaction that resulted in the formation of a solid precipitate to enable the antibiotic to bind to the iron molecule via coordination chemistry. This metal ion-antibiotic complex generated a visible color change. Following the colorimetric reaction, images were taken and subsequently analyzed via ImageJ to determine the relative pixel intensity that was used to infer norfloxacin concentration. The analytical sensitivity of this device was determined to be as low as 50 ppm when analyzing the inner-ring reaction, and as low as 5 ppm when analyzing the outer coffee ring thereby allowing for an alternative cheaper, faster, and more user-friendly method to detect norfloxacin than the conventional methods. PRACTICAL APPLICATION: This novel paper-based microfluidic device can achieve the detection of antibiotic residues in agrifoods in a faster, cheaper, and more user-friendly manner.