A fluorometric assay for oxytetracycline based on the use of its europium(III) complex and aptamer-modified silver nanoparticles

Signal-off nanozyme-based colorimetric aptasensor for sensitive detection of ampicillin using MnO2 nanoflowers and gold nanoparticles

The combination of nanomaterials possessing distinct characteristics and the precision of aptamers facilitates the creation of biosensors that exhibit exceptional selectivity and sensitivity. In this manuscript, we present a highly sensitive aptasensor that utilizes the distinctive characteristics of MnO2 nanoflowers and gold nanoparticles to selectively detect ampicillin (AMP). In this aptasensor, the mechanism of signal change is attributed to the difference in the oxidase-mimicking activity of MnO2 nanoflowers in the presence of a free sequence. The inclusion of AMP hindered the creation of a double-stranded DNA configuration through its binding to the aptamer, resulting in an observable alteration in absorbance. The relative absorbance varied linearly with the concentration of AMP in the range of 70 pM to 10 nM with a detection limit of 21.7 pM. In general, the colorimetric aptasensor that has been developed exhibits exceptional selectivity and remarkable stability. It also demonstrates favorable performance in human serum, making it a highly reliable diagnostic tool. Additionally, its versatility is noteworthy as it holds great potential for detecting various antibiotics present in complex samples by merely replacing the utilized sequences with new ones.

Label-free competitive time-resolved fluorescent aptasensor for the detection of Pb2+ using ssDNA-sensitized fluorescence of Tb3+ ions

Lead (Pb2+) is one of the most toxic heavy metals, and its environmental pollution and serious damages is a global concern. Therefore, it is necessary to develop effective sensing methods. This study describes a new strategy for the design of label-free competitive time-resolved fluorescent (TRF) aptasensor for detecting Pb2+ ions. The sensing principle of this aptasensor is the competition between Pb2+ and Tb3+ ions to bind to the guanine/thymine-rich sequence (lead aptamer) and the sensitized luminescence of Tb3+ by this sequence. The developed TRF aptasensor demonstrated a good linear detection range from 2.5 nM to 150 nM and a limit of detection (LOD) of 645 pM. In addition, the proposed TRF aptasensor has a high selectivity towards Pb2+, and it has also been successfully utilized to detect this ion in milk and human serum samples. This TRF aptasensor offers advantages such as short analysis time, simple operation, low cost, being label-free, and surpassing the interference of background fluorescence of biological samples due to its TRF characteristic. In this paper, we propose a Tb3+/guanine/thymine-rich sequence system for designing different aptasensors against diverse targets by applying a proper guanine-rich sequence.

Time-resolved Fluorescence DNA-based Sensors for Reducing Background Fluorescence of Environment

The fluorescence assay is one of the popular methods that is applied for detection of different targets. However, this method may show low sensitivity and high background in biological samples due to the natural fluorescence of different compounds in complicated samples. In addition, it inevitably affects the detection results accuracy. A fundamental solution to this problem is the use of the time-resolved fluorescence technique (TRF). The main component of this technique is the use of long fluorescence lifetime reagents. In this review, various time-resolved fluorescent reagents such as complexes of lanthanide ions, lanthanide-doped inorganic nanoparticles; Mn-doped ZnS quantum dots (QDs) and pyrene excimer are introduced. Moreover, TRF sensors, especially TRF aptasensors (DNA-based sensors) are discussed. This review will give new ideas for researchers to develop novel high-sensitive TRF sensors that can remove or decrease background fluorescence and use them for the detection of various targets in complicated samples without treatment.

Recent advances in luminescence and aptamer sensors based analytical determination, adsorptive removal, degradation of the tetracycline antibiotics, an overview and outlook

Tetracycline antibiotics (TCs), one of the important antibiotic groups, have been widely used in human and veterinary medicines. Their residues in foodstuff, soil and sewage have caused serious threats to food safety, ecological environment and human health. Here, we reviewed the potential harms of TCs residues to foodstuff, environment and human beings, discussed the luminescence and aptamer sensors based analytical determination, adsorptive removal, and degradation strategies of TCs residues from a recent 5-year period. The advantages and intrinsic limitations of these strategies have been compared and discussed, the potential challenges and opportunities in TCs residues degradation have also been deliberated and explored.

Nanomaterial-based fluorescent biosensors for the detection of antibiotics in foodstuffs: A review

Antibiotics are widely used as bacteriostatic or bactericidal agents against various microbial infections in humans and animals. The excessive use of antibiotics has led to an accumulation of their residues in food products, which ultimately poses a threat to human health. In light of the shortcomings of conventional methods for antibiotic detection (primarily cost, proficiency, and time-consuming procedures), the development of robust, accurate, on-site, and sensitive technologies for antibiotic detection in foodstuffs is important. Nanomaterials with amazing optical properties are promising materials for developing the next generation of fluorescent sensors. In this article, advances in detecting antibiotics in food products are discussed with respect to their sensing applications, with a focus on fluorescent nanomaterials such as metallic nanoparticles, upconversion nanoparticles, quantum dots, carbon-based nanomaterials, and metal-organic frameworks. Furthermore, their performance is evaluated to promote the continuation of technical advances.

Photoelectrochemical aptasensing of oxytetracycline based on a BiVO4-carboxylated graphene-WO3 Z-scheme heterojunction

A new BiVO₄-carboxylated graphene (cG)-WO₃ Z-scheme heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode by ultrasonic mixing and cast-coating for determination of oxytetracycline (OTC). Since cG can absorb visible light and well match with the energy levels of WO₃ and BiVO₄ to promote the charge separation and transfer, the photocurrent on the BiVO₄-cG-WO₃/FTO photoelectrode is 4.4 times that on the control BiVO₄-WO₃/FTO photoelectrode. An amino-functionalized OTC aptamer was fixed on the BiVO₄-cG-WO₃/FTO photoelectrode by the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide mediated amide reaction, and then hexaammonium ruthenium(III) (Ru(NH₃)₆³⁺) was attached to the OTC aptamer to increase the photocurrent response to the OTC binding. Under the optimized conditions, the photocurrent on the BiVO₄-cG-WO₃/FTO photoelectrode at 0 V vs SCE was linear with the common logarithm of OTC concentration from 0.01 nM to 500 nM, with a limit of detection of 3.1 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of real water samples.

Bibliometrics Analysis of Research Progress of Electrochemical Detection of Tetracycline Antibiotics

Tetracycline is a broad-spectrum class of antibiotics. The use of excessive doses of tetracycline antibiotics can result in their residues in food, posing varying degrees of risk to human health. Therefore, the establishment of a rapid and sensitive field detection method for tetracycline residues is of great practical importance to improve the safety of food-derived animal foods. Electrochemical analysis techniques are widely used in the field of pollutant detection because of the simple detection principle, easy operation of the instrument, and low cost of analysis. In this review, we summarize the electrochemical detection of tetracycline antibiotics by bibliometrics. Unlike the previously published reviews, this article reviews and analyzes the development of this topic. The contributions of different countries and different institutions were analyzed. Keyword analysis was used to explain the development of different research directions. The results of the analysis revealed that developments and innovations in materials science can enhance the performance of electrochemical detection of tetracycline antibiotics. Among them, gold nanoparticles and carbon nanotubes are the most used nanomaterials. Aptamer sensing strategies are the most favored methodologies in electrochemical detection of tetracycline antibiotics.

Dual fluorescent aptasensor for simultanous and quantitative detection of sulfadimethoxine and oxytetracycin residues in animal-derived foods tissues based on mesoporous silica

Herein, we developed a dual fluorescent aptasensor based on mesoporous silica to simultaneously detect sulfadimethoxine (SDM) and oxytetracycline (OTC) in animal-derived foods. We immobilized two types of aptamers modified with FAM and CY5 on the silica surface by base complementary pairing reaction with the cDNA modified with a carboxyl group and finally formed the aptasensor detection platform. Under optimal conditions, the detection range of the aptasensor for SDM and OTC was 3-150 ng/mL (R ² = 0.9831) and 5-220 ng/mL (R ² = 0.9884), respectively. The limits of detection for SDM and OTC were 2.2 and 1.23 ng/mL, respectively. The limits of quantification for SDM and OTC were 7.3 and 4.1 ng/mL, respectively. Additionally, the aptasensor was used to analyze spiked samples. The average recovery rates ranged from 91.75 to 114.65% for SDM and 89.66 to 108.94% for OTC, and all coefficients of variation were below 15%. Finally, the performance and practicability of our aptasensor were confirmed by HPLC, demonstrating good consistency. In summary, this study was the first to use the mesoporous silica-mediated fluorescence aptasensor for simultaneous detection of SDM and OTC, offering a new possibility to analyze other antibiotics, biotoxins, and biomolecules.

Electrospun chitosan/polyethylene oxide nanofibers mat loaded with copper (II) as a new sensor for colorimetric detection of tetracycline

Using electrospun chitosan/polyethylene oxide nanofibers mat (CS/PEO NFM) as carrier, Cu@CS/PEO NFM, a new tetracycline (TC) solid-state colorimetric sensor, were simply prepared by directly immobilizing Cu²⁺ on surface of CS/PEO NFM. After immersing in TC solutions, Cu@CS/PEO NFM can display visible color changes to the naked eye within 5.0 min, and the TC concentration-dependent color changes can also be quantitatively analyzed with a smartphone. Because Cu²⁺ can enhance the adsorption of CS/PEO NFM for TC, Cu@CS/PEO NFM possess a more sensitive response ability to TC, ensuring that the colorimetric sensing detection will not be interfered by other coexisting drugs. Due to the reversible combination of chitosan and Cu²⁺, the colorimetric sensing ability of Cu@CS/PEO NFM can be regenerated even after being reused at least 4 times. In addition, the naked eye detection limit of Cu@CS/PEO NFM-based colorimetric sensing is 65 μg kg^-1, which does not exceed the maximum residue limit in milk samples set by China (100 μg kg^-1). The obtained results fully indicated the practical application value of this method in preventing the hazard of TC residues.

Advances and perspectives of aptasensors for the detection of tetracyclines: A class of model compounds of food analysis

The residual tetracyclines in food are frequently applied as the model compounds to develop aptasensors. Until now, more than 100 advanced aptasensors towards tetracyclines have been developed and published in English. This review summarizes and discusses comprehensively these advanced aptasensors, in terms of the principle designs, applied frontier transducers/materials, working performance, and advantages/disadvantages. The aptasensors are classified according to the inherent transduction techniques, i.e., optics, optics-electricity, optics-mass, and electricity-mass. Moreover, the present challenges such as the limited specificity and limited affinity of the aptamers, the future prospects and trends such as further combination with other advanced materials and technologies, and the urgent need of expanding the practical application were discussed and prospected. We hope this review can serve as a powerful tool for both tracing the development progresses of aptasensors and providing adequate references for further development of aptasensing methods for food-related analytes.

Molecularly imprinted fluoroprobes doped with Ag nanoparticles for highly selective detection of oxytetracycline in real samples

A molecularly imprinted polymer (MIP), which is synthesized by a nanomolding process around a template, has emerged as a promising analytical tool for environmental quality monitoring and food safety test. In this work, a fluoroprobe with Ag-doped MIP nanolayer (16 nm thickness) is successfully prepared for the highly selective detection of oxytetracycline (OTC) in real samples (i.e. Yangtze River water, swine urine). In the MIP nanolayer, two functional monomers (i.e. 4-(2-acrylamidoethylcarbamoyl)-3-fluorophenylboronic acid, methacrylic acid) synergistically constitute the specific recognition sites. Meanwhile, the doped Ag enhances the detection sensitivity (with a detection limit of 5.38 nM) and accelerates the detection rate (within 2.5 min) even in real samples. Therefore, the present study paves the way for the preparation of MIP-based fluoroprobes, showing great prospects in environmental quality and food safety tests.

Onsite/on-field analysis of pesticide and veterinary drug residues by a state-of-art technology: A review

Pesticides and veterinary drugs are generally employed to control pests and insects in crop and livestock farming. However, remaining residues are considered potentially hazardous to human health and the environment. Therefore, regular monitoring is required for assessing and legislation of pesticides and veterinary drugs. Various approaches to determining residues in various agricultural and animal food products have been reported. Most analytical methods involve sample extraction, purification (cleanup), and detection. Traditional sample preparation is time-consuming labor-intensive, expensive, and requires a large amount of toxic organic solvent, along with high probability for the decomposition of a compound before the analysis. Thus, modern sample preparation techniques, such as the quick, easy, cheap, effective, rugged, and safe method, have been widely accepted in the scientific community for its versatile application; however, it still requires a laboratory setup for the extraction and purification processes, which also involves the utilization of a toxic solvent. Therefore, it is crucial to elucidate recent technologies that are simple, portable, green, quick, and cost-effective for onsite and infield residue detections. Several technologies, such as surface-enhanced Raman spectroscopy, quantum dots, biosensing, and miniaturized gas chromatography, are now available. Further, several onsite techniques, such as ion mobility-mass spectrometry, are now being upgraded; some of them, although unable to analyze field sample directly, can analyze a large number of compounds within very short time (such as time-of-flight and Orbitrap mass spectrometry). Thus, to stay updated with scientific advances and analyze organic contaminants effectively and safely, it is necessary to study all of the state-of-art technology.

Concentration-dependent photoluminescence carbon dots for visual recognition and detection of three tetracyclines

Concentration-dependent photoluminescence carbon dots (CDs) have been successfully synthesized through the one-step hydrothermal treatment of o-phthalic acid and ethylenediamine. The CDs possessed higher fluorescence quantum yield, up to 39.22%, exhibiting distinguished optical property, water solubility, and stability. The CDs that emit strong blue-green fluorescence can visually identify and determine tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC). TC quenched the fluorescence of CDs at 500 nm owing to the inner filter effect; OTC behaved similarly, but the emission wavelength of CDs was red-shifted to 515 nm. Inversely, once CTC was introduced to CDs solution, the fluorescence increased and the emission peak was blue-shifted to 450 nm. Bandgap transition and electrostatic interaction were proposed to be the mechanisms for the detection of OTC and CTC by CDs. Wide linear relationships were established for TC, OTC, and CTC with the limits of detection to be 50 nM, 36 nM, and 373 nM, respectively. Furthermore, the nanoscale probe constructed by this system has been applied to detect tetracyclines (TCs) in complex samples with satisfying recoveries (93.2-114%) and was designed as a portable test strip sensor for visually on-site TCs of honey sample screening. Accordingly, the preparation process of the nano fluorescent probe is simple and environmentally friendly, and the probe has a specific recognition ability for tetracyclines. The synthesized CDs in this work provide a new orientation for fast, effective, and visual real-time detection of tetracycline in actual samples.

Recent development of antibiotic detection in food and environment: the combination of sensors and nanomaterials

In recent years, the abuse of antibiotics has led to the pollution of soil and water environment, not only poultry husbandry and food manufacturing will be influenced to different degree, but also the human body will produce antibody. The detection of antibiotic content in production and life is imperative. In this review, we provide comprehensive information about chemical sensors and biosensors for antibiotic detection. We classify the currently reported antibiotic detection technologies into chromatography, mass spectrometry, capillary electrophoresis, optical detection, and electrochemistry, introduce some representative examples for each technology, and conclude the advantages and limitations. In particular, the optical and electrochemical methods based on nanomaterials are discussed and evaluated in detail. In addition, the latest research in the detection of antibiotics by photosensitive materials is discussed. Finally, we summarize the pros and cons of various antibiotic detection methods and present a discussion and outlook on the expansion of cross-scientific areas. The synthesis and application of optoelectronic nanomaterials and aptamer screening are discussed and prospected, and the future trends and potential impact of biosensors in antibiotic detection are outlined.Graphical abstract.

A Novel Fluorescent Aptasensor for Sensitive Detection of Oxytetracycline Based on Gold Nanoparticles and OTC-Eu3+ Complex Using Two Different Methods for Modification of Gold Nanoparticles

We developed a simple and selective fluorescent aptasensor for the detection of oxytetracycline (OTC) using aptamer-conjugated gold nanoparticles (AuNPs) and a complex formed between oxytetracycline and a europium cation. In this study, AuNPs were modified with an OTC aptamer using two methods (Tween and NaCl methods). In the absence of OTC, an OTC-Eu3+ complex binds to the aptamer in the aptamer-conjugated AuNPs to give weak fluorescence emission. However, in the presence of OTC, the aptamer interacts with its target, causing a strong fluorescence emission. Under optimum conditions, the designed method showed high selectivity for OTC and a good linear range to OTC concentration from 15 to 500 nM with a limit of detection (LOD) of 10.6 nM for the NaCl method and linear range over 15–500 nM with an LOD of 8.8 nM for the Tween method. This biosensor was successfully employed to quantify OTC in milk and tablet samples.

A novel turn-off fluorescent aptasensor for ampicillin detection based on perylenetetracarboxylic acid diimide and gold nanoparticles

Herein, a novel turn-off fluorescent aptasensor was developed for selective detection of ampicillin (AMP) at picomolar level based on 3,4,9,10-perylenetetracarboxylic acid diimide (PTCDI) as an affordable and low-cost fluorophore. This aptasensor was designed using aptamer, its complementary strand (CS) and gold nanoparticles (AuNPs). The principle of the sensing method is a decrease in the fluorescence intensity of PTCDI in the presence of free CS. Following the addition of AMP, Aptamer/CS-modified AuNPs releases CS and so, the fluorescence intensity of PTCDI is reduced. The designed analytical method indicated a good linear range from 100 pM to 1000 pM and a limit of detection (LOD) of 29.2 pM was obtained. Furthermore, the sensing strategy indicated satisfactory results for the detection of AMP in the spiked human serum samples. By changing the sequences of aptamer and its CS, the presented analytical approach can be easily applied for detection of other antibiotics.

Optical sensors based on silver nanoparticles for determination of pharmaceuticals: An overview of advances in the last decade

This review focuses on optical nanosensors based on silver nanoparticles (Ag NPs) and demonstrates their applications in the determination of pharmaceutical compounds in the last decade. Such optical sensors have received high attention in the analytical field owing to their low cost and simplicity since they do not require any complex or expensive instrumentation. This article reviews Ag NP-based optical methods for the determination of pharmaceutical compounds from 2010 to 2020. The reported optical methods are classified into four types: spectrophotometry, spectrofluorimetry, scattering and chemiluminescence. Ag NPs play different roles in the different sensing platforms used by these methods, the details of which are carefully explained in this review. Moreover, the relevant analytical parameters of the developed methods are categorized by role and tabulated. It is hoped that this review will stimulate further research in this field with similar nanostructures.

Portable ratiometric probe based on the use of europium(III) coordination polymers doped with carbon dots for visual fluorometric determination of oxytetracycline

A novel ratiometric fluorescent probe for the determination of oxytetracycline (OTC) was developed. The method is based on the use of adenosine monophosphate/Eu(III) nanoscale coordination polymers doped with carbon dots (CDs) (CD@AMP/Eu NCPs). These were fabricated by self-assembly of Eu³⁺ and AMP on the surface of CDs containing large amounts of hydroxyl and carbonyl groups. Under the excitation at 310 nm wavelength, the doped NCPs display strong pink emission of Eu³⁺ at 615 nm and blue emission of the CDs at 430 nm on exposure to OTC. The ratio of fluorescence intensity (F₆₁₅/F₄₃₀) of such NCPs displays excellent linear relationship with OTC concentration ranging from 0.2 to 60 μM and the limit of detection (LOD) is 25 nM (3σ). The doped NCPs were evenly immobilized on common filter paper to prepare a visual ratiometric probe for the determination of OTC. Assisted by a digital camera with an APP color detector, the paper-based test strip was applied for the quantitative determination of OTC with a LOD of 0.5 μM and a wide linear scope of 1-100 μM. The method was applied to the determination of OTC in milk samples. Graphical abstractSchematic representation of the principle for oxytetracycline (OTC) determination using carbon dots (CD)@adenosine monophosphate (AMP)/Europium (Eu³⁺) paper-based ratiometic probe.