A novel M-shape electrochemical aptasensor for ultrasensitive detection of tetracyclines

An aptamerelectrochemical sensor based on functional carbon nanofibers for tetracycline determination

Fe-Co@CNF was synthesized by electrospinning technology, and AuNPs was loaded onto Fe-Co@CNF by in-situ reduction to obtain Fe-Co@CNF@AuNPs composite material, which was used as the working electrode based on Au-S bond cooperation. The tetracycline electrochemical sensing interface Fe-Co@CNF@AuNPs@Apt was constructed by connecting mercaptoylated tetracycline (TC) aptamers on Fe-Co@CNF@AuNPs surface. The morphology and composition of Fe-Co@CNF@AuNPs composites were characterized by SEM, TEM, EDS, XRD and XPS, and the electrochemical properties of tetracycline were evaluated by CV and DPV. The results showed that the addition of Fe and Co did not destroy the structure of the original carbon nanofibers, and their synergistic effect enhanced the electrocatalytic performance, effective electrode area and electron transfer ability of carbon nanofibers. AuNPs are evenly distributed over the fibers, which effectively improves the electrical conductivity of the material. Under the optimal conditions, the theoretical detection limit of tetracycline was 0.213 nM, and the linear detection range was 5.12-10 mM, which could successfully detect tetracycline in milk.

A miniaturized biosensor for rapid detection of tetracycline based on a graphene field-effect transistor with an aptamer modified gate

Tetracycline is a broad-spectrum antibiotic for human, poultry and livestock that may cause health damage when enriched in humans. Therefore, it is essential to create a rapid tetracycline assay with high sensitivity, specificity and portability. In this study, a miniaturized tetracycline biosensor based on aptamer-modified graphene field-effect transistor (Apt-SGGT) was fabricated and two detection strategies using transfer characteristic curves and real-time channel current were established for different circumstances. The detection limits of the two strategies were 2.073 pM and 100 pM, respectively. The biosensor also demonstrated outstanding stability, anti-interference and specificity ability. Finally, the biosensor was employed to detect the content of tetracycline in Skim Milk with outstanding recovery rate. We believe that the miniaturized Apt-SGGT biosensor with appropriate detection strategies will provide an ideal portable sensing platform for many important analytes in food with superior selectivity and sensitivity.

Aggregation-induced emission carbon dots as Al3+-mediated nanoaggregate probe for rapid and selective detection of tetracycline

Worldwide abuse of tetracycline (TC) seriously threatens environmental safety and human health. Metal-TC complexes formed by residual TC in the environment can also contribute to the spread of antibiotic resistance. Therefore, monitoring of TC residues is still required. Here, we report novel aggregation-induced emission carbon dots (AIE-Cdots) as nanoaggregate probes for the rapid and selective detection of TC residue. Riboflavin precursors with rotational functional groups led to the development of AIE-Cdots. The aggregation of AIE-Cdots was induced selectively for Al3+, amplifying the fluorescence signals owing to the restricted rotation of the side chains on the AIE-Cdot surface. The fluorescence signal of such Al3+-mediated nanoaggregates (Al3+-NAs) was further triggered by the structural fixation of TC at the Al3+ active sites, suggesting the formation of TC-coordinated Al3+-NAs. A linear correlation was observed in the TC concentration range of 0-10 μM with a detection limit of 42 nM. In addition, the strong Al3+ binding affinity of AIE-Cdots produced similar NAs and enhanced fluorescence signals in Al3+-TC mixtures. These AIE-Cdots-based nanoplatforms have a rapid response, good selectivity, and reliable accuracy for detecting TC or aluminum complexes, meeting the requirements for hazardous substance monitoring and removal in environmental applications.

Yb-TCPP metal-organic framework as fluorescence sensor for detecting tetracycline in milk

Developing effective means for detecting contamination in milk during production, processing, and storage is both important and challenging. Tetracycline (TC), due to its use in treating animal infections, is among the most prevalent organic pollutants in milk, posing potential and significant threats to human health. However, efficient and in situ monitoring of TC remains lacking. Nevertheless, we have successfully developed a highly sensitive and selective fluorescence method for detecting TC in milk using a metal-organic framework material made from Yb-TCPP (ytterbium-tetra(4-carboxyphenyl)porphyrin). The calculated Stern-Volmer constant (KSV) was 12,310.88 M-1, and the detection limit was 2.44 × 10-6 M, surpassing previous reports. Crucially, Yb-TCPP fluoresces in the near-infrared region, promising its development into a specific fluorescence detection product for practical TC detection in milk, offering potential application value.

A smartphone-assisted paper-based ratio fluorescent probe for the rapid and on-site detection of tetracycline in food samples

Rapid, sensitive and portable analytical methods for on-site detection of tetracycline (TC) in food samples is of critical importance for food safety and public health. In this study, a dual-emission ratio fluorescent probe (Gd0.9@Eu0.1) was prepared and utilized for the detection of tetracycline (TC) by observing the fluorescence color change from blue to red. The detection process exhibits a wide linear range (0-52.0 μM), good selectivity and low detection limit (14 nM). A paper-based probe and a colorimetric card was constructed for the visual detection of TC. Furthermore, a novel and portable detection platform combining smartphone and test strip was exploited for the quantitative and on-site detection of TC in real pork sample. The developed method was validated through intra- (n = 5) and inter-day (n = 2) measurements, as well as comparison with a traditional HPLC method. These statistical result validate the reliability and accuracy of the developed method. This intelligent detection platform represents a promising approach for the rapid, sensitive and visual detection of TC in food samples.

A Molecularly Imprinted Electrochemical Sensor Based on TiO2@Ti3C2Tx for Highly Sensitive and Selective Detection of Chlortetracycline

In view of the serious side effects of chlortetracycline (CTC) on the human body, it is particularly important to develop rapid, sensitive, and selective technologies for the detection of CTC in food. In this work, a molecularly imprinted electrochemical sensor with [Fe(CN)6]3-/4- as signal probe was proposed for the highly sensitive and selective detection of CTC. For this purpose, TiO2, which acts as an interlayer scaffold, was uniformly grown on the surface of Ti3C2Tx sheets through a simple two-step calcination process using Ti3C2Tx as the precursor to effectively avoid the stacking of Ti3C2Tx layers due to hydrogen bonding and van der Waals forces. This endowed TiO2@Ti3C2Tx with large specific surface, abundant functional sites, and rapid mass transfer. Then, polypyrrole molecularly imprinted polymers (MIPs) with outstanding electrical conductivity were modified on the surface of TiO2@Ti3C2Tx via simple electro-polymerization, where the pyrrole was employed as a polymeric monomer and the CTC provided a source of template molecules. This will not only provide specific recognition sites for CTC, but also facilitate electron transport on the electrode surface. The synergistic effects between TiO2@Ti3C2Tx and polypyrrole MIPs afforded the TiO2@Ti3C2Tx/MIP-based electrochemical sensor excellent detection properties toward CTC, including ultra-low limits of detection (LOD) (0.027 nM), a wide linear range (0.06-1000 nM), and outstanding stability, reproducibility, selectivity, and feasibility in real samples. The results indicate that this strategy is feasible and will broaden the horizon for highly sensitive and selective detection of CTC.

An efficient deep eutectic magnetic nano gel for rapid ultrasound-assisted dispersive µ-solid phase extraction of residue of tetracyclines in food samples

In the present study, a magnetic nano gel as the sorbent which is the combination of octatonic acid: cumarin as eutectic solvent and Fe3O4@SiO2 was introduced as the sorbent in ultrasound-assisted dispersive µ-solid phase extraction process coupled with high performance liquid chromatography with photo diode array detector for simultaneous separation and determination of tetracyclines residues in food samples. FT-IR, SEM, VSM were used for the characterization of the synthetized magnetic nano gel. Under obtained optimum conditions, the obtained linear ranges were 1.5-500 (µg L-1), 2.5-750 (µg L-1), 2-750 (µg L-1), and 2.5-500 (µg L-1) for tetracycline, oxytetracycline, chlortetracycline, and doxycycline, respectively. Moreover, the below level of quantification (BLQ) (based on S/N = 3) of 0.47 µg L-1, 0.11 µg L-1, 0.85 µg L-1, 0.66 µg L-1, 0.81 µg L-1 and the limit of quantification (based on S/N = 10) of 1.61, 2.74, 2.23 (µg L-1), and 2.66 were achieved for tetracycline, oxytetracycline, chlortetracycline, and doxycycline, respectively. The intra-day and inter-day precision (%) of the procedure were less than 3.2 and 3.8, respectively. The recoveries over 95% confirmed high sufficiency of the proposed method for application in complex matrices such as honey, milk, and egg.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05798-w.

Optical sensing of tetracycline concentration using a liquid crystal-based platform targeting the chelating properties of tetracycline

In this study, a liquid crystal (LC)-based assay for the real-time detection of tetracycline (Tc) was developed. The sensor was constructed by implementing an LC-based platform that utilized the chelating properties of Tc to target Tc metal ions. This design enabled Tc-dependent induction of changes in the optical image of the LC; these modifications could then be observed in real-time with the naked eye. The performance of the sensor in detecting Tc was investigated with various metal ions to identify the most effective metal ion for Tc detection. In addition, the selectivity of the sensor was evaluated using different antibiotics. A correlation between Tc concentration and the optical intensity of the LC optical images was established, which enabled the quantification of Tc concentrations. The proposed method can detect Tc concentrations with a detection limit as low as 2.67 pM. Tests were conducted on milk, honey, and serum samples, which demonstrated that the proposed assay is highly accurate and reliable. The high sensitivity and selectivity of the proposed method make it a promising tool for real-time Tc detection, with potential applications in fields ranging from biomedical research to agriculture.

"Click" Reaction-Mediated Silk Fibroin-Functionalized Thiol-Branched Graphene Oxide Quantum Dots for Smart Sensing of Tetracycline

The abuse of tetracycline (TC) antibiotics causes the accumulation of their residue in the environment, which has an irreversible impact on food safety and human health. In light of this, it is vital to offer a portable, quick, efficient, and selective sensing platform to detect TC instantly. Herein, we have successfully developed a sensor using silk fibroin-decorated thiol-branched graphene oxide quantum dots through a well-known thiol-ene click reaction. It is applied to ratiometric fluorescence sensing of TC in real samples in the linear range of 0-90 nM, with the detection limit of 49.69, 47.76, 55.25, 47.90, and 45.78 nM for deionized water, chicken sample, fish sample, human blood serum, and honey sample, respectively. With the gradual addition of TC to the liquid media, the sensor develops a synergetic luminous effect in which the fluorescence intensity of the nanoprobe steadily declines at 413 nm, while the intensity of a newly emerging peak increases at 528 nm, maintaining a ratio that is dependent on the analyte concentration. The increase of luminescence properties in the liquid media is clearly visible by naked eyes in the presence of 365 nm UV light. The result helps us in building a filter paper strip-based portable smart sensor using an electric circuit comprising a 365 nm LED (light-emitting diode) powered by a mobile phone battery which is attached just below the rear camera of a smartphone. The camera of the smartphone captures the color changes that occur throughout the sensing process and translates into readable RGB data. The dependency of color intensity with respect to the concentration of TC was evaluated by deducing a calibration curve from where the limit of detection was calculated and found to be 0.125 μM. These kinds of gadgets are important for the possible real-time, on-the-spot, quick detection of analytes in situations where high-end approaches are not easily accessible.

3D rhombohedral microcrystals metal-organic frameworks for electrochemical and fluorescence sensing of tetracycline

Zirconium-based metal-organic frameworks (MOF) exhibiting 3D rhombohedral microcrystals were synthesized by the solvothermal method. The structure, morphology, composition, and optical properties of the synthesized MOF were carried out using different spectroscopic, microscopic, and diffraction techniques. Synthesized MOF was rhombohedral in shape and the cage structure of these crystalline molecules was the active binding site of the analyte, tetracycline (TET). The electronic property and size of the cages are chosen such that a specific interaction with TET was observed. Sensing of the analyte was demonstrated by both the electrochemical and fluorescent techniques. The MOF had significant luminescent properties and exhibited excellent electro-catalytic activity due to embedded zirconium metal ions. An electrochemical and fluorescence sensor was fabricated towards TET where TET binds via hydrogen bond to MOF, and causes fluorescence quenching due to the transfer of electrons. Both approaches exhibited high selectivity and good stability in the presence of interfering molecules such as antibiotics, biomolecules, and ions; and showed excellent reliability in tap water and wastewater sample analysis.

A tag-free fluorescent aptasensor for tobramycin detection using a hybridization of three aptamer strands and SYBR Green I dye

In this study, a sensitive fluorescent method is designed to detect tobramycin (TOB) drug applying a hybrid structure of three aptamer strands and SYBR Green I (SGI) fluorescent dye as the bioreceptor segment and signal indicator, respectively. The preferential binding of the aptamers to TOB resulted in the collapse of the hybridized aptamer skeleton to the single strands. So, the intercalation of SGI molecules reduced that quenched the fluorescence response. The aptasensing assay provided the superior target specificity with a detection limit (LOD) of 0.153 pM and a wide linear dynamic range over 0.5 pM-300 μM. The aptasensor could successfully quantify TOB in human serum samples. The tag-free sensor with the remarkable advantages of simplicity, easy-to-use, cost-effectiveness, and high sensitivity is superior to be applicable for clinical samples.

Copper nanoclusters stabilized by D-penicillamine for ultrasensitive and visual detection of oxytetracycline

Copper nanoclusters (DPA@CuNCs) with red fluorescence were successfully synthesized by a one-step method based on D-penicillamine (DPA), which acted not only as a reducing agent but also as a stabilizer. The products were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, particle-size analysis, ultraviolet-visible spectrophotometry, and fluorescence spectrometry. When the excitation wavelength was 280 nm, DPA@CuNCs emitted bright red fluorescence at 640 nm with a fluorescence quantum yield of 5.8 %. Due to the inner filter effect, oxytetracycline (OTC) effectively quenched the fluorescence of DPA@CuNCs, and then DPA@CuNCs were applied to the trace detection of OTC. The method showed a good linear range for OTC from 5 to 60 μmol/L, with a detection limit of 0.026 μmol/L and a correlation coefficient R² of 0.9983. Moreover, a paper-based sensor for the visual detection of OTC has been developed, which can conveniently and rapidly distinguish the concentration ranges of OTC through the color changes of the test papers.

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.

Aptamer-based NanoBioSensors for seafood safety

Chemical and biological contaminants are of primary concern in ensuring seafood safety. Rapid detection of such contaminants is needed to keep us safe from being affected. For over three decades, immunoassay (IA) technology has been used for the detection of contaminants in seafood products. However, limitations inherent to antibody generation against small molecular targets that cannot elicit an immune response, along with the instability of antibodies under ambient conditions greatly limit their wider application for developing robust detection and monitoring tools, particularly for non-biomedical applications. As an alternative, aptamer-based biosensors (aptasensors) have emerged as a powerful yet robust analytical tool for the detection of a wide range of analytes. Due to the high specificity of aptamers in recognising targets ranging from small molecules to large proteins and even whole cells, these have been suggested to be viable molecular recognition elements (MREs) in the development of new diagnostic and biosensing tools for detecting a wide range of contaminants including heavy metals, antibiotics, pesticides, pathogens and biotoxins. In this review, we discuss the recent progress made in the field of aptasensors for detection of contaminants in seafood products with a view of effectively managing their potential human health hazards. A critical outlook is also provided to facilitate translation of aptasensors from academic laboratories to the mainstream seafood industry and consumer applications.

A luminescent Eu3+-functionalized MOF for sensitive and rapid detection of tetracycline antibiotics in swine wastewater and pig kidney

Tetracyclines (TCs), a type of antibiotics, are widely used in human therapy and animal husbandry. Public concerns about tetracyclines residues have been raised due to their negative impact on the environment and food, causing bacterias drug resistance and human health concerns. In this work, a luminescent europium MOF (EuUCBA) is constructed via post-synthetic attachment of Eu³⁺ into a UiO-66 type MOF. The luminescent of EuUCBA exhibits high stability in aqueous media in the pH range of 4-11. Among 36 common veterinary drugs, the synthesized probe is highly selective and sensitive to six tetracyclines with low detection limits of 0.118 μM, 0.228 μM, 0.102 μM, 0.138 μM, 0.206 μM, and 0.078 μM for oxytetracycline (OTC), chlortetracycline (CTC), methylenetetracycline (MTC), minocycline (MOC), tetracycline (TC), and doxycycline (DOXY), respectively. Furthermore, the probe shows good anti-interference ability and fast response. Finally, EuUCBA was successfully to detect DOXY in swine wastewater and pig kidney with good recoveries. This work provides an excellent fluorescent sensor for highly selective and rapid detection of TCs residues in wastewater and complex biological samples.

Bifunctional Sensors Based on Phosphomolybdates for Detection of Inorganic Hexavalent Chromium and Organic Tetracycline

Exploring effective sensors for detecting possible hazards in a water system are greatly significant. This work proposed a strategy for stable and effective bifunctional sensors via incorporating hourglass-type phosphomolybdates into metal-organic fragments to construct a high-dimensional framework. Two hourglass-type phosphomolybdate-based electrochemical sensors toward heavy metal ion Cr(VI) and tetracycline (TC) detection were designed with the formula [Co^II₂(H₂O)₄Na^I₂][Co^II(Hbpe)][Na^I(bpe)_1.5]{Co^II[P^V₄Mo^V₆O₃₁H₆]₂}·9H₂O (1) and [Co^II(H₂O)₄Na^I₃][Co^II(Hbpe)][Co^II(bpe)]{Co^II[P^V₄Mo^V₆O₃₁H₆]₂}·9H₂O (2) [bpe = 1,2-di(4-pyridyl)ethylene]. Structural analysis showed that hybrids 1 and 2 possess three-dimensional POM-supported network features with favorable stability and exhibit reversible redox properties. Experiments found that this kind of hybrids as efficient sensors have excellent electrochemical performance toward Cr(VI) detection with high sensitivities of 0.111 μA·μM^-1 for 1 and 0.141 μA·μM^-1 for 2, fast response time of 1 s, and low detection limits of 30 nM for 1 and 27 nM for 2, which far meet the standard of WHO for drinking water. Moreover, hybrids 1-2 also exhibit fast responses to TC detection with sensitivities of 0.0073 and 0.022 μA·mM^-1 and detection limits of 0.426 and 0.084 mM. This work offers a novel strategy for the purposeful design of efficient POM-based electrochemical sensors for accurate determination of contaminants in a practical water system.

Biomass-derived carbon dots as a sensitive and selective dual detection platform for fluoroquinolones and tetracyclines

A novel carbon dot (CD) was synthesized through the facile and simple hydrothermal method from Curcuma amada, as the precursor for the first time. These CDs with an average diameter of 4.6 nm display blue fluorescence, with excitation/emission maxima at 360/445 nm and a quantum yield of 14.1%. It exhibited high stability under different conditions and was characterized using various techniques. These CDs can be employed as a dual-sensing platform to detect tetracyclines and fluoroquinolones, two antibiotic classes. Even though antibiotics are regarded as an inevitable commodity, overuse and improper management of discarded antibiotics pose a severe threat to the environment. Herein, we developed a dual-sensing, biocompatible sensor with high selectivity and sensitivity to detect antibiotics. CD was employed as a fluorescence probe and detected tetracycline and fluoroquinolone antibiotic through inner filter effect-based fluorescence quenching and hydrogen bonding-based enhancement process, respectively. The linear range was 0-16 μM and the detection limit was 33 nM for tetracycline and 2 nM for fluoroquinolone antibiotic. As an electrochemical probe, CD selectively detected tetracycline with a lower detection limit of 0.5 nM over a linear range of 0-16 μM. Using both methods, a real sample analysis of the developed sensor exhibited accurate reliability and precision.

A ratiometric fluorescent sensor for tetracyclines detection in meat based on pH-dependence of targets with lanthanum-doped carbon dots as probes

Although some ratiometric fluorescent sensors have been reported to detect tetracyclines, most of ratiometric fluorescent sensors were established based on europium ion with a narrow linear range. In this work, a ratiometric fluorescent sensor for tetracyclines detection was established based on the dual-emission lanthanum-doped carbon dots (La-CDs) as probes combining with the characteristic pH-response of tetracyclines. The fluorescence intensity of tetracyclines will be enhanced in high pH, and the emission peak of tetracyclines overlapped with the peak of probes. The superposition effect of tetracyclines and probes at 515 nm greatly improved the sensitivity of the ratiometric fluorescent sensor and widened the detection range, and linear ranges for oxytetracycline (OTC) and tetracycline (TC) were respectively 0.00-805.20 μM and 0.00-1039.50 μM. Moreover, the preparation procedure of the La-CDs was simple and time saving and the coupling agent was not required. A comparison of La-CDs with undoped carbon dots (un-CDs) showed that the optical performance and sensing performance of La-CDs were improved. In addition, a portable paper sensor with La-CDs as probes was preliminarily explored in this work, and the sensor has been applied to detect OTC and TC in pork and fish with satisfactory results.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers’ health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

Aptamer-Target Recognition-Promoted Ratiometric Electrochemical Strategy for Evaluating the Microcystin-LR Residue in Fish without Interferences

Given the significance of food safety, it is highly urgent to develop a sensitive yet reliable sensor for the practical analysis of algal toxins. As most of the developed sensors are disturbed by interfering substances and the target toxin is detected in a single-signal manner based on the immunoassay technology. Herein, we developed an aptamer-based dual-signal ratiometric electrochemical sensor for the sensitive and accurate analysis of microcystin-LR (MC-LR), using it as a proof-of-concept analyte. Methylene blue-tagged ssDNA (MB-ssDNA) was immobilized at the gold electrode surface accompanied with the absence of ferrocene-tagged ssDNA (Fc-ssDNA), resulting in a high differential pulse voltammetry (DPV) current of MB and a low DPV current of Fc. The recognition of MB-ssDNA by MC-LR stimulated the formation of MC-LR@MB-ssDNA, which induced the removal of MB-ssDNA from the electrode and the exposure of SH-ssDNA, enabling Fc-ssDNA to be captured at the electrode surface via nucleic acid hybridization. In comparison with MC-LR deficiency, the DPV signal of MB dropped along with an improved DPV signal of Fc, contributing to the ratiometric detection of MC-LR, with the limit of detection down to 0.0015 nM. Furthermore, this ratiometric electrochemical sensor was successfully explored to assess the bioaccumulated amount of MC-LR in the liver and meat of fish. The aptamer-based ratiometric strategy to develop an electrochemical MC-LR assay will offer a promising avenue to develop high-performance sensors, and the sensor will find more useful application in MC-LR-related aquatic product safety studies.

Tandem Förster resonance energy transfer induced visual ratiometric fluorescence sensing of tetracyclines based on zeolitic imidazolate framework-8 incorporated with carbon dots and safranine T

With increasing TC concentration, tandem FRET1 from CDs to TC, then FRET2 from TC to safranine T were occurred. TC could be easily recognized by naked eye. Besides, we could perform on-site detection of TC with the help of a mobile phone.

Self-Assembling Nucleic Acid Nanostructures Functionalized with Aptamers

Researchers have worked for many decades to master the rules of biomolecular design that would allow artificial biopolymer complexes to self-assemble and function similarly to the diverse biochemical constructs displayed in natural biological systems. The rules of nucleic acid assembly (dominated by Watson-Crick base-pairing) have been less difficult to understand and manipulate than the more complicated rules of protein folding. Therefore, nucleic acid nanotechnology has advanced more quickly than de novo protein design, and recent years have seen amazing progress in DNA and RNA design. By combining structural motifs with aptamers that act as affinity handles and add powerful molecular recognition capabilities, nucleic acid-based self-assemblies represent a diverse toolbox for use by bioengineers to create molecules with potentially revolutionary biological activities. In this review, we focus on the development of self-assembling nucleic acid nanostructures that are functionalized with nucleic acid aptamers and their great potential in wide ranging application areas.

Recent advances in developing optical and electrochemical sensors for analysis of methamphetamine: A review

Recognition of misused stimulant drugs has always been a hot topic from a medical and judicial perspective. Methamphetamine (MAMP) is an addictive and illegal drug that profoundly affects the central nervous system. Like other illicit drugs, the detection of MAMP in biological and street samples is vital for several organizations such as forensic medicine, anti-drug headquarters and diagnostic clinics. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of analytical sensors in MAMP tracing. For the first time, this study has briefly reviewed all the optical and electrochemical sensors in MAMP detection from earlier so far. How various receptors with engineering nanomaterials allow developing novel approaches to measure MAMP have been studied. Fundamental concepts related to optical and electrochemical recognition assays in which nanomaterials have been used and relevant MAMP sensing applications have been comprehensively covered. Challenges, opportunities and future outlooks of this field have also been discussed at the end.

Tetracycline Antibiotics: Elucidating the Electrochemical Fingerprint and Oxidation Pathway

Herein, a complete study of the electrochemical behavior of the most commonly used tetracycline antibiotics (TCs) on unmodified carbon screen-printed electrodes (SPEs) is presented. In addition, the oxidation pathway of TCs on SPE is elucidated, for the first time, with liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Square wave voltammetry (SWV) was used to study the electrochemical fingerprint (EF) of the antibiotics shaping the different oxidation processes of the TCs in a pH range from 2 to 12. Their characteristic structure and subsequent EF offer the possibility of distinguishing this class of antibiotics from other types. Under the optimized parameters, calibration curves of tetracycline (TET), doxycycline (DOXY), oxytetracycline (OXY), and chlortetracycline (CHL) in a Britton Robinson buffer solution (pH 9) exhibited a linear range between 5 and 100 µM with excellent reproducibilities (RSDTET = 3.01%, RSDDOXY = 3.29%, RSDOXY = 9.78% and RSDCHL = 6.88% at 10 µM, N = 3) and limits of detection (LOD) of LODTET = 4.15 µM, LODDOXY = 2.14 µM, LODOXY = 3.07 µM and LODCHL = 4.15 µM. Furthermore, binary, tertiary, and complex mixtures of all TCs were analyzed with SWV to investigate the corresponding EF. A dual pH screening (pH 4 and pH 9), together with the use of a custom-made Matlab script for data treatment, allowed for the successful confirmation of a single presence of TCs in the unknown samples. Overall, this work presents a straightforward study of the electrochemical behavior of TCs in SPE, allowing for the future on-site identification of residues of tetracycline antibiotics in real samples.

Emerging Electrochemical Sensors for Real-Time Detection of Tetracyclines in Milk

Antimicrobial drug residues in food are strictly controlled and monitored by national laws in most territories. Tetracyclines are a major broad-spectrum antibiotic class, active against a wide range of Gram-positive and Gram-negative bacteria, and they are the leading choice for the treatment of many conditions in veterinary medicine in recent years. In dairy farms, milk from cows being treated with antibiotic drugs, such as tetracyclines, is considered unfit for human consumption. Contamination of the farm bulk tank with milk containing these residues presents a threat to confidence of supply and results in financial losses to farmers and dairy. Real-time monitoring of milk production for antimicrobial residues could reduce this risk and help to minimise the release of residues into the environment where they can cause reservoirs of antimicrobial resistance. In this article, we review the existing literature for the detection of tetracyclines in cow's milk. Firstly, the complex nature of the milk matrix is described, and the test strategies in commercial use are outlined. Following this, emerging biosensors in the low-cost biosensors field are contrasted against each other, focusing upon electrochemical biosensors. Existing commercial tests that identify antimicrobial residues within milk are largely limited to beta-lactam detection, or non-specific detection of microbial inhibition, with tests specific to tetracycline residues less prevalent. Herein, we review a number of emerging electrochemical biosensor detection strategies for tetracyclines, which have the potential to close this gap and address the industry challenges associated with existing tests.

A novel liquid crystal-based aptasensor for ultra-low detection of ochratoxin a using a π-shaped DNA structure: Promising for future on-site detection test strips

Ochratoxin A (OTA) as the most dangerous mycotoxin is produced by Aspergillus Ochraceus and Penicillium verrucosum. OTA can be found in beverages and foodstuffs that induces the teratogenic, nephrotoxic, carcinogenic, and immunosuppressive effects on humans. Hence, developing highly sensitive methods for its detection is of great importance. Herein, a novel aptasensor was designed for the label-free monitoring of the ultra-low OTA levels by a combination of the superiority of aptamers and long-range orientational order of liquid crystals (LCs). The aptasensing strategy was based on the conformational switch of the immobilized π-shaped DNA structure on the glass substrate in presence of the target. A shift in the orientation of LCs from random to homeotropic state led to the apparent alteration of the optical appearance of the aptasensor platform from bright to dark. The LC-based aptasensor especially detects OTA at the ultra-trace level as low as 0.63 aM with comparable selectivity. The aptasensor could detect OTA successfully in the grape juice, coffee, and human serum samples. The LC-based aptasensor paves a way for developing portable and real-time sensing probes with high performance for food safety control and clinical application.

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.

Ilies) S, Orha C, Manea F. Graphene Oxide Electroreduced onto Boron-Doped Diamond and Electrodecorated with Silver (Ag/GO/BDD) Electrode for Tetracycline Detection in Aqueous Solution

A new electrochemical sensor designed by modifying the commercial boron-doped diamond (BDD) electrode with graphene oxide (GO) reduced electrochemically and further electrodecorated with silver (Ag), named the Ag/GO/BDD electrode, was selected among a series of the BDD, GOelectroreduced onto BDD (GO/BDD) and silver electrodeposited onto BDD (Ag/BDD) electrodes for the detection of tetracycline (TC) in aqueous solution. The best results regarding the sensitivity of 46.6 µA·µM-1·cm-2 and the lowest limit of detection of 5 nM was achieved using square-wave voltammetry (SWV) operated at the step potential of 5 mV, modulation amplitude of 200 mV and the frequency of 10 Hz in alkaline medium. The application of the alkaline supporting electrolyte-based procedure is limited for water monitoring due to the presence of chloride that interferes with TC detection; however, it can be applied for quantitative determination of pharmaceutical formulations. 0.1 M Na2SO4 supporting electrolyte eliminated chloride interference and can be used for the application of Ag/GO/BDD in practical detection of TC in water.

Ultrasensitive and visual detection of tetracycline based on dual-recognition units constructed multicolor fluorescent nano-probe

Ultrasensitive and visual detection of tetracycline antibiotic (TC) residues is of great significance to public health and environmental safety. A novel dual-response ratiometric fluorescent nano-probe (SiQDs-Cit-Eu) has been elaborately tailored for the determination and on-site visual assay of tetracycline, by grafting citric acid and europium (Eu³⁺) ions onto the surface of silicon quantum dots (SiQDs). The blue-emissive SiQDs (λ_em = 455 nm) fabricated by a one-step facile method act as both scaffold for coordination with Eu³⁺ ions and recognition unit for TC owing to the inner filter effect (IFE). The coordinate unsaturated red-fluorescent Eu³⁺ ions (λ_em = 617 nm) bond to the surface of SiQDs, serving as the specific recognition element for TC due to the antenna effect. In the presence of TC, the as-synthesized nano-probe exhibits double (λ_em = 455 and 617 nm) and reverse response signals which are accompanied by a marked color change from blue to purple, and then red, thus achieving ultra-high sensitivity with a detection limit of 7.1 nM and instant visual detection of TC in real samples (milk, honey, lake and river water). Furthermore, smartphone-assisted point-of-care testing platform is also constructed based on nano-probe-immobilized test paper by using the color scanning APP.

Contribution of Nanomaterials to the Development of Electrochemical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The detection of antimicrobial residues in food products of animal origin is of utmost importance. Indeed antimicrobial residues could be present in animal derived food products because of animal treatments for curative purposes or from illegal use. The usual screening methods to detect antimicrobial residues in food are microbiological, immunological or physico-chemical methods. The development of biosensors to propose sensitive, cheap and quick alternatives to classical methods is constantly increasing. Aptasensors are one of the major trends proposed in the literature, in parallel with the development of immunosensors based on antibodies. The characteristics of electrochemical sensors (i.e., low cost, miniaturization, and portable instrumentation) make them very good candidates to develop screening methods for antimicrobial residues in food products. This review will focus on the recent advances in the development of electrochemical aptasensors for the detection of antimicrobial residues in food products. The contribution of nanomaterials to improve the performance characteristics of electrochemical aptasensors (e.g., Sensitivity, easiness, stability) in the last ten years, as well as signal amplification techniques will be highlighted.

A dual-response ratiometric fluorescent sensor by europium-doped CdTe quantum dots for visual and colorimetric detection of tetracycline

Residues in animal food and drinking water caused by the abuse of antibiotics lead to cell resistance and many chronic diseases in the human body. Therefore, it has become an inevitable trend to develop a fast, easy-to-use, on-site/real-time visualization method for the detection of antibiotics. Herein, we report a dual-response ratiometric fluorescence sensor which is fabricated by chelating europium ions (Eu³⁺) onto cadmium telluride quantum dots (CdTe QDs) for real-time and visible detection of tetracycline (TC). With the TC addition, the fluorescence of probe can be seen by the naked eye, from green to yellow and finally to red, exhibiting a dosage-sensitive and broad-chromatic detection strategy for TC. The fluorescence intensity ratio of I₆₁₆/I₅₁₂ of Eu/CdTe QDs sensor displays a good linear relation to TC concentrations in the range of 0-80 μM with a limit of detection (LOD) of 2.2 nM. In addition, the sensor can visually detect 200 nM TC in actual samples, which is lower than the maximum residue limit (MRL) of the safety standard. The methodology reported here opens a window toward the real applications of fluorescent and shows the wide applicability in pursuing the concepts simple, rapid, visual, and real-time for food safety and environmental protection.

A Sensitive Fluorescent Assay for Tetracycline Detection Based on Triple-helix Aptamer Probe and Cyclodextrin Supramolecular Inclusion

Herein, an effective pyrene excimer signaled fluorescent biosensor for the determination of tetracycline based on triple-helix aptamer probe (TAP) and supramolecular inclusion of cyclodextrin was reported. The TAP was devised containing an aptamer loop, two DNA segment stems and a triplex-forming oligonucleotide (signal probe) labeled with pyrenes at 5' and 3' ends. The presence of target could result in its binding towards aptamer with a mighty affinity, leading to a conformation change of the TAP and whereupon the release of the signal probe. This liberty of signal probe enabled the formation of pyrene excimer, generating fluorescence signals. Further, signal amplification was fulfilled through the addition of γ-cyclodextrin which could interact with pyrene dimer, thus leading to an enhanced "on-state" of the sensing ensemble. In contrast, when the target was absent, the sensing ensemble remained "off-state" because of the long distance between two pyrene molecules. When the conditions were properly optimized, the increasing signal kept a linear dependence on target concentrations ranging from 5.0 nM to 100 nM, and the detection limit reached as low as 1.6 nM. In this way, a newly-constructed, simple, and economically affordable protocol enjoys desirable efficiency, sensitivity, specificity in biosensing. Also, its universality as another attractive behalf in assaying diverse targets was envisioned with only the need of matched aptamer replacement.

Interface engineering of zeolite imidazolate framework-8 on two-dimensional Al-metal-organic framework nanoplates enhancing performance for simultaneous capture and sensing tetracyclines

The increasing misgivings of environmental pollution derived from antibiotic residues make it imperative to explore a bifunctional platform for synchronous monitoring and removal of antibiotics. Herein, zeolite imidazolate framework-8 (ZIF-8) is anchored on two-dimensional (2D) amino-functionalized Al-metal organic framework (NH₂-MIL-53(Al)) nanoplates to construct a dual metal-organic frameworks smart platform (ZIF-8/NH₂-MIL-53(Al)) for simultaneous capture and fluorescence sensing of tetracyclines (TCs). ZIF-8 nanoparticles anchored on 2D nanoplates having a smaller size and a larger specific surface area boost the adsorption capabilities (561, 533, 526 and 578 mg g^-1 for doxycycline (DOX), tetracycline (TET), oxytetracycline (OTC) and chlortetracycline (CTC), respectively). Notably, the pyridine N of ZIF-8 cooperated with the abundant NH₂ on the surface of NH₂-MIL-53(Al) exhibits high affinity toward TCs, remarkably enhancing the sensitivity by facilitating the photo-induced electron transfer and the inner-filter effect. The LODs (1.2 μg L^-1 for TET, DOX, OTC and 2.2 μg L^-1 for CTC, respectively) are at least 10-fold lower than those of NH₂-MIL-53(Al) and are comparable or superior to those of reported sensors. The dual metal-organic frameworks smart platform presents satisfactory reliabilities and accuracies for detecting TCs in real samples, which anticipates new routes to develop integrated systems for simultaneous capture and detection of organic pollutants.

Development of an electrochemical biosensor for impedimetric detection of tetracycline in milk

Abstract

This study dealt with the fabrication of an impedimetric biosensor based on nanomaterial modified with pencil graphite electrode for the detection of tetracycline (TET) in milk samples. For response of the impedimetric aptasensor to be improved, the influence of different parameters (immobilization time of reduced grapheme oxide, time of aptamer, and TET binding, and concentration of aptamer) was optimized. In optimum conditions, the aptasensor provided a concentration range within 1 × 10^-16 - 1 × 10^-6 M and with a limit of detection of 3 × 10^-17 M TET. The proposed impedimetric aptasensor was then used in milk samples analysis, and the acceptable recovery was achieved ranging from 92.8 to 102.1%. According to this study, the combination of an aptamer and electrochemical impedance spectroscopy is a promising method for detection of TET in milk samples with high reproducibility and stability.

Graphic abstract

Highly sensitive detection of multiple antibiotics based on DNA tetrahedron nanostructure-functionalized magnetic beads

Functional DNAs-functionalized magnetic beads (MBs) offer great potential in bioanalysis field because of their target recognition and magnetic separation functions. However, the recognition capability and hybridization affinity of DNA probes often suffer from limited available space, poor probe conformation and non-selective adsorption. To overcome these limitations, we herein used aptamer-pendant DNA tetrahedron nanostructure-functionalized MBs (TETapt-tet MBs) to develop a target-response fluorescence method with tetracycline (TET) as a model. In the absence of TET, 6-carboxy-X-rhodamine-labeled complementary DNAs (ROX-cDNAs) were assembled on the surface of MBs. Upon the addition of target TET, the ROX-cDNAs were separated and released from the MBs to generate fluorescence signal. The limit of detection and limit of quantification for TET were found to be 6 pg mL^-1 and 20 pg mL^-1, respectively. Compared with ssDNA-functionalized MBs surface, the designed DNA tetrahedron nanostructure-based surface could decrease the hybridization time and reduce false positives, ensuring the accuracy of TET detection in complex samples. The presented method was successfully employed for TET detection in honey samples. Moreover, this functionalization strategy could be extended to detect multiple antibiotics by simply substituting different aptamer sequences. Therefore, the proposed method has great potential in the field of food safety and public health.

A long lifetime ratiometrically luminescent tetracycline nanoprobe based on Ir(III) complex-doped and Eu3+-functionalized silicon nanoparticles

Different from fluorescent dyes-doped or carbon materials-based ratiometric tetracycline nanoprobes, herein, a new Ir(III) complex-doped and europium(III) ion (Eu³⁺)-functionalized silicon nanoparticles (Ir(III)@SiNPs-Eu³⁺) with long luminescent lifetimes was firstly fabricated for selective detection of tetracycline (TC) in complex systems through time-resolved emission spectra (TRES) measurement. In the presence of TC, the red phosphorescence of Eu³⁺ is greatly enhanced by adsorption energy transfer emission (AETE) of TC, while the strong green luminescence of Ir(III)@SiNPs is quenched by the inner filtration effect (IFE) of TC. Based on these striking emission changes, Ir(III)@SiNPs-Eu³⁺ can sensitively detect TC in the linear range of 0.01-20 μM with a detection limit of 4.9 × 10^-3 μM. Benefitting from the long lifetime of Ir(III)@SiNPs-Eu³⁺, the nanoprobe demonstrates excellent TC detection performance through TRES in high background system of 5 % human serum. Furthermore, the formed Ir(III)@SiNPs-Eu³⁺/TC complex can be used to sensitively recognize Hg²⁺ via a ratiometric luminescence mode. Notably, the cytotoxicity of Ir(III)@SiNPs-Eu³⁺ is very low and thus the sensitive monitoring the detection of Ir(III)@SiNPs-Eu³⁺ to TC and Hg²⁺ also works well in porcine renal cells, demonstrating high application potential in real samples.

Simultaneous electrochemical determination of ochratoxin A and fumonisin B1 with an aptasensor based on the use of a Y-shaped DNA structure on gold nanorods

A complementary DNA (cDNA) was designed to simultaneously hybridize with the ochratoxin A (OTA) aptamer and the fumonisin B1 (FB1) aptamer to form a unique Y-shaped DNA structure and to achieve simultaneous detection. Gold nanorods (AuNRs) were used to immobilize thionine (Th), thiolated ferrocene (Fc), thiolated OTA aptamer (Apt1), and thiolated FB1 aptamer (Apt2), to form an amplified signal element and a recognition element. The Apt1-AuNRs-Th complex and the Apt2-AuNRs-Fc complex hybridize with cDNA to form a unique Y-DNA structure on a gold electrode. This produces two initial electrochemical signals [with 177 μΑ cm^-2 near -0.2 V, and 3121 μΑ cm^-2 near +0.46 V (vs. Ag/AgCl)] by differential pulse voltammetry. Upon addition of 0.1 ng mL^-1 OTA and 0.1 ng mL^-1 FB1, the aptamers bind the two toxins. This results in the release of Apt1-AuNRs-Th and Apt2-AuNRs-Fc, so the peak currents densities decrease to 115 μΑ cm^-2 and 209 μΑ cm^-2. The assay allows simultaneous determination of OTA and FB1 in the 1.0 pg·mL^-1 to 100 ng·mL^-1 concentration ranges, with LODs of 0.47 and 0.26 pg·mL^-1. The assay is reproducible, stable and specific. It was applied to the determination of OTA and FB1 in spiked beer, with recoveries between 89.0% and 102.0%. Graphical abstractSchematic representation of OTA and FB₁ detection based on Apt₂-AuNRs-Fc/Apt₁-AuNRs-Th/cDNA/AuE. (AuNRs: Gold nanorods; Th: thionine; Fc: ferrocene; SH: thiol; BSA: Bovine serum albumin; cDNA: Complementary DNA; Apt₁: Aptamer1; Apt₂: Aptamer2; OTA: Ochratoxin A; FB₁: Fumonisin B₁).

A novel fluorescent "turn-on" aptasensor based on nitrogen-doped graphene quantum dots and hexagonal cobalt oxyhydroxide nanoflakes to detect tetracycline

In this study, a novel fluorescent "turn-on" aptasensor was developed for sensitive and rapid detection of tetracycline (TC) in animal-derived food. It is based on aptamer-functionalized nitrogen-doped graphene quantum dots (N-GQDs-aptamer) coupled with cobalt oxyhydroxide (CoOOH) nanoflakes. The CoOOH nanoflakes are efficient fluorescence quenchers in homogeneous solutions, and this is due to their advantages of excellent optical properties, superior flexibility, and water dispersibility. The proposed method's mechanism is driven by quenching based on the fluorescence resonance energy transfer (FRET) between the donor (N-GQDs) and the acceptor (CoOOH nanoflakes). On the other hand, fluorescence recovery is caused by the structure switching behavior of the aptamer. Compared with previous methods, our developed method exhibits better behavior in terms of being easy to fabricate and being simple in detection procedure and maintains the detection limit low enough in TC determination: a linear range from 1 to 100 ng mL^-1 and a detection limit of 0.95 ng mL^-1 (S/N = 3). Furthermore, the proposed method was applied to five animal-derived food samples (milk, honey, fish, eggs, and chicken muscle) and demonstrated practical applicability. As well, the method has the advantages of simplicity in pre-treatment and convenience in instruments, saves times, and is cost-effective. Finally, the proposed method demonstrates significant potential for sensitive and rapid detection of specific components in real samples. Graphical abstract.