Fast and sensitive screening detection of tetracyclines with a paper-based analytical device

Development and application of a CNT-Ag-Cu-Al/PS-based paper electrode for detecting diverse analytes in complex matrices

Electrochemical sensors play a crucial role in the detection of different analytes in complex matrices, and their performance is highly dependent on the electrode capacity. However, most of the available electrodes can only be used for single-component detection, so it is urgent to develop electrodes with high sensitivity and selectivity for different components. Herein, we report an amphiprotic amino-bonded carbon nanotube-Ag/Cu/Al nanoparticle/polystyrene-coated paper electrode (CNT-Ag-Cu-Al/PS electrode), which can be used for the measurement of glucose (Glc), oxytetracycline (OTC), and hydroquinone (HQ), respectively. The results showed that the analytical sensitivity and selectivity of the CNT-Ag-Cu-Al/PS electrode were comparable to those of single metal-coated paper substrate. The developed electrode also exhibited excellent linear responses for Glc, OTC, and HQ in the ranges of 1.0-1000.0 μM, 1.0 × 10-2 to 10.0 μM, and 5.0 × 10-3 to 50.0 μM, and the limits of detection (LODs) were 0.2055 μM (Glc), 0.0074 μM (OTC), and 0.0048 μM (HQ). Owing to the characteristics of good selectivity, anti-interference, stability, and reproducibility, the CNT-Ag-Cu-Al/PS paper electrode has been successfully applied to the detection of these analytes in complex human body fluids, food, and environmental waters. The paper electrode is promising for the detection of target compounds in complex matrices.

Electrochemical assisted enhanced nanozymatic activity of functionalized borophene for H2O2 and tetracycline detection

This study unveils the electrochemically-enhanced nanozymatic activity exhibited by borophene during the reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2. Herein, the surface of the pristine borophene was first modified with the addition of thiocyanate groups to improve hydroxyl radical (•OH) scavenging activity. Then, the oxidation reaction of TMB was accelerated under applied electrochemical potential. Both factors significantly improved the detection limit and drastically decreased the detection time. DPPH testing revealed that the radical scavenging nature of borophene was more than 70%, boosting its catalytic activity. In the presence of H2O2, borophene catalyzed the oxidation of TMB and produced a blue-colored solution that was linearly correlated with the concentration of H2O2 and allowed for the detection of H2O2 up to 38 nM. The present finding was further extended to nanozymatic detection of tetracyclines (TCs) using a target-specific aptamer, and the results were colorimetrically quantifiable up to 1 μM with a LOD value of 150 nM. Moreover, transferring the principles of the discussed detection method to form a portable and disposable paper-based system enabled the quantification of TCs up to 0.2 μM. All the sensing experiments in this study indicate that the nanozymatic activity of borophene has significantly improved under electrochemical potential compared to conventional nanozyme-based colorimetric detection. Hence, the present discovery of electrochemically-enhanced nanozymatic activity would be promising for various sensitive and time-dependent colorimetric sensor development initiatives in the future.

Multi-excitation wavelength of gold nanocluster-based fluorescence sensor array for sulfonamides discrimination

Sulfonamides (SAs) are widely used in many fields because of their advantages, including low price, wide antibacterial spectrum, and high stability. However, their accumulation in the human body leads to a variety of serious diseases. Therefore, it is necessary to design a convenient, effective, and sensitive method to detect SAs. Moreover, the fluorescence excitation spectrum has rich information characteristics, especially for the interaction between fluorophore and quencher via various mechanisms. However, the excitation wavelength-guided sensor array construction does not draw proper attention. To address these issues, we used BSA-AuNCs as a single probe to construct a sensor array for the detection of five SAs. The selected SAs showed different quenching effects on the fluorescence intensities of BSA-AuNCs. The changes in the fluorescence intensity at different excitation wavelengths (λ = 230, 250, and 280 nm) have been applied to construct our sensor array and address the distinguishability between the selected SAs. With helping of pattern recognition methods, five different SAs have been identified at three different concentrations. Additionally, qualitative analysis at different moral ratios and quantitative analysis at nanogram concentrations have been considered. Moreover, the proposed sensor array was successfully used to distinguish between different SAs in commercial milk with an accuracy of 100 %. This study provides a simple and powerful approach to SAs detection. Also, it shows a broad application prospect in the field of food and drug monitoring.

Paper-Based Electrochemical Biosensors for Food Safety Analysis

Nowadays, foodborne pathogens and other food contaminants are among the major contributors to human illnesses and even deaths worldwide. There is a growing need for improvements in food safety globally. However, it is a challenge to detect and identify these harmful analytes in a rapid, sensitive, portable, and user-friendly manner. Recently, researchers have paid attention to the development of paper-based electrochemical biosensors due to their features and promising potential for food safety analysis. The use of paper in electrochemical biosensors offers several advantages such as device miniaturization, low sample consumption, inexpensive mass production, capillary force-driven fluid flow, and capability to store reagents within the pores of the paper substrate. Various paper-based electrochemical biosensors have been developed to enable the detection of foodborne pathogens and other contaminants that pose health hazards to humans. In this review, we discussed several aspects of the biosensors including different device designs (e.g., 2D and 3D devices), fabrication techniques, and electrode modification approaches that are often optimized to generate measurable signals for sensitive detection of analytes. The utilization of different nanomaterials for the modification of electrode surface to improve the detection of analytes via enzyme-, antigen/antibody-, DNA-, aptamer-, and cell-based bioassays is also described. Next, we discussed the current applications of the sensors to detect food contaminants such as foodborne pathogens, pesticides, veterinary drug residues, allergens, and heavy metals. Most of the electrochemical paper analytical devices (e-PADs) reviewed are small and portable, and therefore are suitable for field applications. Lastly, e-PADs are an excellent platform for food safety analysis owing to their user-friendliness, low cost, sensitivity, and a high potential for customization to meet certain analytical needs.

Heteroatom-free conjugated tetraphenylethylene polymers for selectively fluorescent detection of tetracycline

The antibiotic tetracycline (Tc) is a major contaminant in food and water, with adverse effects on both ecosystems and human health. The development of novel sensors for tetracycline detection is of great importance. In this work, we develop a novel heteroatom-free conjugated tetraphenylethylene polymer (TPE-CMP) fluorescence sensor for the detection of tetracycline. In the presence of Tc, the emission fluorescence of TPE-CMP was quenched by the photoinduced electron transfer mechanism to achieve high sensitivity. The polymers can detect tetracycline at a concentration of 0-100 μg/mL with a good linear correlation (0.99), and the limit of detection (LOD) is 1.23 μg/mL. Furthermore, TPE-CMP has excellent selectivity in detecting Tc in the presence of various anti-interference analytes, including ions and antibiotics. In addition, the practical feasibilities of TPE-CMP for Tc sensing were further investigated in milk, urine and wastewater samples with satisfactory recoveries (from 94.96% to 112.53% for milk, from 96.41% to 99.31% for urine and from 98.54% to 100.52% for wastewater). We have designed and synthesized TPE-CMP based on heteroatom-free for the specific fluorescence detection of tetracycline, expanding the range of fluorescence detection sensors and offering great promise for practical applications.

Spot tests: past and present

Microchemistry, i.e., the chemistry performed at the scale of a microgram or less, has its roots in the late eighteenth and early nineteenth centuries. In the first half of the twentieth century a wide range of spot tests have been developed. For didactic reasons, they are still part of the curriculum of chemistry students. However, they are even highly important for applied analyses in conservation of cultural heritage, food science, forensic science, clinical and pharmacological sciences, geochemistry, and environmental sciences. Modern pregnancy tests, virus tests, etc. are the most recent examples of sophisticated spot tests. The present ChemTexts contribution aims to provide an overview of the past and present of this analytical methodology.

Development of an Electrochemical Sensor Based on Nanocomposite of Fe3O4@SiO2 and Multiwalled Carbon Nanotubes for Determination of Tetracycline in Real Samples

In this work, an electrochemical sensor (GCE/MWCNT/Fe3O4@SiO2) based on a composite of multiwalled carbon nanotubes (MWCNT) and an Fe3O4@SiO2 (MMN) nanocomposite on a glassy carbon electrode (GCE) was developed for the detection of tetracycline (TC). The composite formed promoted an increased electrochemical signal and the stability of the sensor, combining its individual characteristics such as high electrical conductivity and large surface area. The composite material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, and scanning electron microscope (SEM). The adsorptive stripping differential pulse voltammetry (AdSDPV) promoted better performance for the electrochemical sensor and greater sensitivity for TC detection. Under optimized conditions, the currents increased linearly with TC concentrations from 4.0 to 36 µmol L−1 (0.997) and from 40 to 64 µmol L−1 (0.994) with detection and quantification limits of 1.67 µmol L−1 and 4.0 µmol L−1, respectively. The sensor was applied in the analysis of milk and river water samples, obtaining recovery values ranging from 91–117%.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.

Paper-based analytical device for high-throughput monitoring tetracycline residue in milk

A low-cost and portable paper-based analytical device has been developed for high throughput and on-site monitoring TC residue in milk through visualized colorimetric reaction. The filtration and concentration effect induced by the porous nature of paper contribute to strengthen the color intensity, leading to quantitative and sensitive detection of tetracycline reaching 1 ppm detection limit, with the linear range of 1-100 ppm both in water and milk samples. The applicability was demonstrated by detection of TC in 18 different types of real milk samples with good recovery ranging from 88% to 113%. Furthermore, the dynamic degradation behavior of tetracycline was monitored through the device. To the best of our knowledge, this is the first report of colorimetric detection of tetracycline in milk using the paper-based device. This simple, fast, cost-effective (~$0.50 per device) and equipment-free paper-based platform provides a promising tool for future application in food and environmental safety.

DNA-Gold Nanozyme-Modified Paper Device for Enhanced Colorimetric Detection of Mercury Ions

In this work, a paper device consisted of a patterned paper chip, wicking pads, and a base was fabricated. On the paper chip, DNA–gold nanoparticles (DNA–AuNPs) were deposited and Hg²⁺ ions could be adsorbed by the DNA–AuNPs. The formed DNA–AuNP/Hg²⁺ nanozyme could catalyze the tetramethylbenzidine (TMB)–H₂O₂ chromogenic reaction. Due to the wicking pads, a larger volume of Hg²⁺ sample could be applied to the paper device for Hg²⁺ detection and therefore the color response could be enhanced. The paper device achieved a cut-off value of 50 nM by the naked eye for Hg²⁺ under optimized conditions. Moreover, quantitative measurements could be implemented by using a desktop scanner and extracting grayscale values. A linear range of 50–2000 nM Hg²⁺ was obtained with a detection limit of 10 nM. In addition, the paper device could be applied in the detection of environmental water samples with high recoveries ranging from 85.7% to 105.6%. The paper-device-based colorimetric detection was low-cost, simple, and demonstrated high potential in real-sample applications.

Miniaturized analytical methods for determination of environmental contaminants of emerging concern - A review

The determination of contaminants of emerging concern (CECs) in environmental samples has become a challenging and critical issue. The present work focuses on miniaturized analytical strategies reported in the literature for the determination of CECs. The first part of the review provides brief overview of CECs whose monitoring in environmental samples is of particular significance, namely personal care products, pharmaceuticals, endocrine disruptors, UV-filters, newly registered pesticides, illicit drugs, disinfection by-products, surfactants, high technology rare earth elements, and engineered nanomaterials. Besides, an overview of downsized sample preparation approaches reported in the literature for the determination of CECs in environmental samples is provided. Particularly, analytical methodologies involving microextraction approaches used for the enrichment of CECs are discussed. Both solid phase- and liquid phase-based microextraction techniques are highlighted devoting special attention to recently reported approaches. Special emphasis is placed on newly developed materials used for extraction purposes in microextraction techniques. In addition, recent contributions involving miniaturized analytical flow techniques for the determination of CECs are discussed. Besides, the strengths, weaknesses, opportunities and threats of point of need and portable devices have been identified and critically compared with chromatographic methods coupled to mass chromatography. Finally, challenging aspects regarding miniaturized analytical methods for determination of CECs are critically discussed.

Chlortetracycline and melanin biopolymer - The risk of accumulation and implications for phototoxicity: An in vitro study on normal human melanocytes

Tetracyclines belong to antimicrobial classes with the highest consumption in veterinary medicine and agriculture, which leads to the contamination of the environment and food products, as well as to antibiotic resistance and adverse drug reactions. Chloro-derivatives of tetracyclines are thought to be relatively more phototoxic than others and belong to the most frequently cited drugs as photosensitizers. Melanins are heterogenous biopolymers determining skin, hair and eye colour. They are biosynthesized in a multistep process in melanocytes. Melanins, besides photoprotective and antioxidant properties, may also contribute to adverse skin drug reactions, which involve e.g. hyperpigmentation disorders and phototoxic reactions. Furthermore, they have the ability to form a drug-melanin complex, which leads to deposition of the drug or its metabolites in pigmented tissues. The aim of the study was to examine the ability of chlortetracycline to form a complex with melanin, as well as the effect of the drug on viability, antioxidant defence system and melanogenesis in normal human epidermal melanocytes exposed to the UVA radiation. The obtained results show for the first time that chlortetracycline forms a complex with melanin polymers, which creates a possibility of the drug accumulation in pigmented tissues. A simultaneous exposition of normal melanocytes to chlortetracycline and to the UVA radiation decreases cell viability, proportionally to the drug concentration and the irradiation time. The phototoxic effect appears to be related to the induction of oxidative stress in melanocytes, mainly through an increase of SOD and a decrease of the CAT activity. Chlortetracycline itself does not influence the melanin content or the activity of tyrosinase. The UVA radiation appeared to be a conditioning factor stimulating melanogenesis, whereas the presence of the drug augmented this effect.