Colorimetric and fluorescence quenching aptasensors for detection of streptomycin in blood serum and milk based on double-stranded DNA and gold nanoparticles

Selection and identification of the ssDNA aptamer against polymyxin B sulfate

BACKGROUND

Polymyxin B (PMB) is a potent antibiotic, and its sulfate form, Polymyxin B Sulfate (PMBS), is widely used. When PMBS is used as a veterinary drug, excessive use can lead to drug residues in animal bodies, which is a significant food safety issue and raises serious concerns. Therefore, there is an urgent need to strengthen research in this area. In this study, we obtained a ssDNA aptamer against PMBS using the Capture-SELEX method, which has notable advantages in small molecule selection. Then, we integrated the obtained aptamer with a biosensor based on the CRISPR/Cas14a system for a series of validations.

RESULTS

In this study, specific aptamers against PMBS were discovered via the Capture-SELEX process. The selection process consisted of ten rounds. The affinity of the candidate sequences was determined by Isothermal Titration Calorimetry (ITC), and the PMBS24 aptamer with the highest affinity was ultimately identified, with a dissociation constant (Kd) of 3.89 ± 0.46 μM. To further obtain high-affinity aptamers, we attempted to truncate the PMBS24 aptamer. However, the results demonstrated that the aptamer with the full-length sequence exhibited superior affinity. Subsequently, it was applied in the CRISPR/Cas14a-based sensor for the detection of PMBS. This method had a LOD of 0.99 ng mL-1, with good specificity, and was successfully used for the detection in milk.

SIGNIFICANCE

An important recognition element of PMBS has been successfully obtained, filling a part of the gap in the detection of PMBS. Moreover, the aptamer has been applied to the CRISPR/Cas14a-based sensor for amplification-free PMBS detection, yielding favorable detection results. This also opens up the possibility of applying the aptamer to other similar sensors.

Breaking barrier of binding buffer in colorimetric aptasensing of tetracycline in food fish using peroxidase mimic gold NanoZyme

Tetracycline is extensively used in aquaculture as a therapeutic agent that needs to be monitored due to food safety concerns. Aptasensing has been revealed as a suitable diagnostic platform for tetracycline sensing in food matrix due to its quick, low cost and robust nature. But, the colorimetric aptasensing of tetracycline employing the peroxidase activity of gold nanoparticles (AuNPs) to 3,3,5,5-tetramethylbenzidine (TMB) was unsuitable until now owing to the aptamer-specific alkaline binding buffer. The present study developed a method with an optimized reaction protocol diminishing the inhibitory effect of binding buffer on the sensor probe (AuNPs-aptamer + TMB + H2O2). The overall peroxidase activity of the sensor probe was only inhibited by tetracycline through selective adsorption on the AuNPs-aptamer complex. The peroxidase inhibition percentage in the test range of 0.01 to 0.5 mg L-1 tetracycline gave a logarithmic response (R2, 0.99) with a detection limit of 0.017 mg L-1 which is less than the prescribed limit (0.1 mg L-1) set by EU and FSSAI. The developed sensing system in fish muscle showed high recovery (111-115 %) with great potential for rapid detection of tetracycline in fish muscle.

Illuminating the future of food microbial control: From optical tools to Optogenetic tools

Light as an environmental signal can effectively regulate various biological processes in microbial systems. Optical and optogenetic tools are able to utilize light for precise control methods with minimal interference. Recently, research on these tools has extended to the field of microbiology. Distinguishing from existing reviews, this review narrows the scope of application into food sector, focusing on advances in optical and optogenetic tools for microbial control, including optical tools targeting pathogenic or probiotic bacteria for non-thermal sterilization, antimicrobial photodynamic therapy, or photobiomodulation, combined with nanomaterials as photosensors for food analysis. As well as using optogenetic tools for more convenient and precise control in food production processes, covering reversible induction, metabolic flux regulation, biofilm formation, and inhibition. These tools offer new solutions to goals that cannot be achieved by traditional methods, and they are still maturing to explore other uses in the food field.

Nanophotonic biosensors for COVID-19 detection: advances in mechanisms, methods, and design

The growing societal impact of coronavirus disease 2019 (COVID-19) has underscored the urgent need for innovative strategies to address the ongoing challenges posed by the pandemic. While rapid therapeutic interventions remain critical for short-term mitigation, equally vital is the development of accessible and efficient diagnostic tools to curb viral transmission. In this context, optical sensing technologies have emerged as foundational tools for detection and diagnosis, owing to their rapid response, user-friendliness, and adaptability. These attributes strengthen their indispensable role in identifying severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19. This review systematically outlines the structural components of SARS-CoV-2 virions and their respective biological functions, classifies optical biosensors according to their underlying principles and evaluates the advantages and limitations of each methodology in real-world diagnostic applications. By addressing current detection challenges, these optical platforms not only enhance our capacity to manage SARS-CoV-2 but also establish a framework for deploying optical sensing technologies in future pandemic scenarios.

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.

Photoelectrochemical sensing of isoniazid and streptomycin based on metal Bi-doped BiOI microspheres grown on book-shape layers of Ti3C2 heterostructures

Isoniazid and streptomycin are vital drugs for treating tuberculosis, which are utilized as efficient anti-tuberculosis agents. This paper presents a novel visible-light-driven composite photocatalyst Ti3C2/Bi/BiOI, which was built from Ti3C2 nanosheets and Bi/BiOI microspheres. Photoelectrochemical (PEC) sensors based on Ti3C2/Bi/BiOI were synthesized for isoniazid identification, which showed a linear concentration range of 0.1-125 μM with a detection limit of 0.05 μM (S/N = 3). Moreover, we designed a PEC aptasensors based on aptamer/Ti3C2/Bi/BiOI to detect streptomycin in 0.1 M PBS covering the electron donor isoniazid, because the isoniazid consumes photogenerated holes thus increasing the photocurrent effectively and preventing photogenerated electron-hole pairs from being recombined. Furthermore, PEC aptasensors based on aptamer/Ti3C2/Bi/BiOI were synthesized for streptomycin identification, which exhibited a linear concentration range of 0.01-1000 nM with a detection limit of 2.3 × 10-3 nM (S/N = 3), and are well stable in streptomycin sensing.

Aptamer Clicked Poly(ferrocenylsilanes) at Au Nanoparticles as Platforms with Multiple Function[†]

Aptamers are widely used in biosensing due to their specific sensitivity toward many targets. Thus, gold nanoparticle (AuNP) aptasensors are subject to intense research due to the complementary properties of aptamers as sensing elements and AuNPs as transducers. We present herein a novel method for the functional coupling of thrombin-specific aptamers to AuNPs via an anionic, redox-active poly(ferrocenylsilane) (PFS) polyelectroyte. The polymer acts as a co-reductant and stabilizer for the AuNPs, provides grafting sites for the aptamer, and can be used as a redox sensing element, making the aptamer-PFS-AuNP composite (aptamer-AuNP) a promising model system for future multifunctional sensors. The aptamer-AuNPs exhibit excellent colloidal stability in high ionic strength environments owing to the combined electrosteric stabilizing effects of the aptamer and the PFS. The synthesis of each assembly element is described, and the colloidal stability and redox responsiveness are studied. As an example to illustrate applications, we present results for thrombin sensitivity and specificity using the specific aptamer.

Aptamer-Based fluorescent DNA biosensor in antibiotics detection

The inappropriate employment of antibiotics across diverse industries has engendered profound apprehensions concerning their cumulative presence within human bodies and food commodities. Consequently, many nations have instituted stringent measures limiting the admissible quantities of antibiotics in food items. Nonetheless, conventional techniques employed for antibiotic detection prove protracted and laborious, prompting a dire necessity for facile, expeditious, and uncomplicated detection methodologies. In this regard, aptamer-based fluorescent DNA biosensors (AFBs) have emerged as a sanguine panacea to surmount the limitations of traditional detection modalities. These ingenious biosensors harness the binding prowess of aptamers, singular strands of DNA/RNA, to selectively adhere to specific target antibiotics. Notably, the AFBs demonstrate unparalleled selectivity, affinity, and sensitivity in detecting antibiotics. This comprehensive review meticulously expounds upon the strides achieved in AFBs for antibiotic detection, particularly emphasizing the labeling modality and the innovative free-label approach. It also elucidates the design principles behind a diverse array of AFBs. Additionally, a succinct survey of signal amplification strategies deployed within these biosensors is provided. The central objective of this review is to apprise researchers from diverse disciplines of the contemporary trends in AFBs for antibiotic detection. By doing so, it aspires to instigate a concerted endeavor toward the development of heightened sensitivity and pioneering AFBs, thereby contributing to the perpetual advancement of antibiotic detection methodologies.

Graphene-based gel electromembrane extraction coupled with modified screen-printed carbon electrode for detecting streptomycin in honey samples: Greener strategy for food analysis

This paper presents a greener methodology for the first time to determine streptomycin in honey based on the modification of gel in the gel electromembrane extraction (G-EME) technique using exfoliated graphene (EG). Differential pulse voltammetry (DPV) with a modified screen-printed carbon electrode was used as a detection technique. The EG was prepared by applying an electrochemical exfoliation of pencil graphite as an environmentally friendly and simple method. EG has conductivity properties, large specific surface areas, and the possibility of noncovalent π-π stacking. The addition of EG to G-EME could enhance the extraction efficiency by increasing the transfer rate of streptomycin, resulting in better LOQ. Out of several materials tested (AuNPs, AgNPs, graphene oxide, graphite, EG of pencil graphite 6B), EG powder of 6B was the best nanomaterial for carrying out G-EME. Furthermore, the problem associated with increasing electric current and electroendosmosis due to addition of graphene-based nanomaterial has been totally solved by tuning the acceptor phase's volume. Under the optimal conditions to perform EG@G-EME and DPV in the honey matrix, a good linearity was obtained between 20 and 580 μg kg-1 (R2 > 0.9964) with LOD and LOQ equal to 4.9 and 16.4 μg kg-1, respectively, in the honey matrix. Inter- and intra-assay results showed relative standard deviations of about 5 %. Compare to the conventional G-EME, our developed method showed better sensitivity.

Fluorescence detection of three types of pollutants based on fluorescence resonance energy transfer and its comparison with colorimetric detection

This study aimed at three representative pollutants, benzidine, cyromazine, and streptomycin, which were commonly used and posed a great threat to both environment and human health, mainly to explore a fast, simple, sensitive, visible naked-eye detection method. Colorimetric detection by gold nanoparticles (AuNPs) was first attempted. The cross-linking reaction occurred owing to the strong forces between the targets and AuNPs, leading to aggregation and color change. However, large-scale aggregation was easily formed and settled, which failed to achieve accurate quantification. Thus, AuNPs are considered to be used in fluorescence detection as reaction bridges. The introduction of AuNPs could effectively quench the fluorescence of Rhodamine B based on fluorescence resonance energy transfer (FRET). Moreover, a classical "on-off-on" fluorescence detection system was constructed based on nanomaterials. When AuNPs were added, the red fluorescence of the Rhodamine B solution could be effectively quenched (the "off" reaction). However, the tight cross-linking reaction between the three targets and AuNPs occurred through the strong affinity, causing Rhodamine B to dissociate in the solution. The fluorescence was rapidly restored, accompanied by a significant enhancement of fluorescence intensity (the "on" reaction). The fluorescent responses toward the three targets were established, resulting in good linearity in a wide range with low detection limits. Moreover, through the investigation of specificity, the fluorescence sensor exhibited satisfying selectivity and high binding affinity to the detected targets among the same types of inferences, indicating great potential for practical application. This simple, fast and sensitive fluorescence detection system was first used for simultaneously detecting three types of pollutants and finally successfully applied to real samples.

Metabolic Footprinting-Based DNA-AuNP Encoders for Extracellular Metabolic Response Profiling

Metabolic footprinting as a convenient and non-invasive cell metabolomics strategy relies on monitoring the whole extracellular metabolic process. It covers nutrient consumption and metabolite secretion of in vitro cell culture, which is hindered by low universality owing to pre-treatment of the cell medium and special equipment. Here, we report the design and a variety of applicability, for quantifying extracellular metabolism, of fluorescently labeled single-stranded DNA (ssDNA)-AuNP encoders, whose multi-modal signal response is triggered by extracellular metabolites. We constructed metabolic response profiling of cells by detecting extracellular metabolites in different tumor cells and drug-induced extracellular metabolites. We further assessed the extracellular metabolism differences using a machine learning algorithm. This metabolic response profiling based on the DNA-AuNP encoder strategy is a powerful complement to metabolic footprinting, which significantly applies potential non-invasive identification of tumor cell heterogeneity.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Enhanced detection of ascorbic acid with cascaded fluorescence recovery of a dual-nanoquencher system

An innovative strategy with target-triggered cascade fluorescence recovery of a dual-nanoquencher system was developed to detect ascorbic acid (AA). Herein, manganese dioxide (MnO₂) nanosheets and gold nanoparticles (AuNPs) were used as nanoquenchers simultaneously. Owing to their synergistic effects, the fluorescence of 2,3-diaminophenazine (DAP) was decreased efficiently, thus minimizing the background fluorescence. The introduction of AA triggered the decomposition of MnO₂ into Mn²⁺, which induced the aggregation of AuNPs. Both the decomposed MnO₂ and aggregated AuNPs possess weak quenching abilities towards DAP. Such a cascade amplification strategy enhanced the detection sensitivity for AA with a LOD as low as 6.7 nM, which was two orders of magnitude lower than that of MnO₂-based fluorescence assay. Furthermore, this amplification strategy was successfully applied to detect AA in food samples.

Recent Advances and Perspectives on the Sources and Detection of Antibiotics in Aquatic Environments

Water quality and safety are vital to the ecological environment, social development, and ecological susceptibility. The extensive use and continuous discharge of antibiotics have caused serious water pollution; antibiotics are widely found in freshwater, drinking water, and reservoirs; and this pollution has become a common phenomenon and challenge in global water ecosystems, as water polluted by antibiotics poses serious risks to human health and the ecological environment. Therefore, the antibiotic content in water should be identified, monitored, and eliminated. Nevertheless, there is no single method that can detect all different types of antibiotics, so various techniques are often combined to produce reliable results. This review summarizes the sources of antibiotic pollution in water, covering three main aspects: (1) wastewater discharges from domestic sewage, (2) medical wastewater, and (3) animal physiology and aquaculture. The existing analytical techniques, including extraction techniques, conventional detection methods, and biosensors, are reviewed. The electrochemical biosensors have become a research hotspot in recent years because of their rapid detection, high efficiency, and portability, and the use of nanoparticles contributes to these outstanding qualities. Additionally, the comprehensive quality evaluation of various detection methods, including the linear detection range, detection limit (LOD), and recovery rate, is discussed, and the future of this research field is also prospected.

Application of Nanomaterial Modified Aptamer-Based Electrochemical Sensor in Detection of Heavy Metal Ions

Heavy metal pollution resulting from significant heavy metal waste discharge is increasingly serious. Traditional methods for the detection of heavy metal ions have high requirements on external conditions, so developing a sensitive, simple, and reproducible detection method is becoming an urgent need. The aptamer, as a new kind of artificial probe, has received more attention in recent years for its high sensitivity, easy acquisition, wide target range, and wide use in the detection of various harmful substances. The detection platform that an aptamer-based electrochemical biosensor (E-apt sensor) provides is a new approach for the detection of heavy metal ions. Nanomaterials are particularly important in the construction of E-apt sensors, as they can be used as aptamer carriers or sensitizers to stimulate or inhibit electrochemical signals, thus significantly improving the detection sensitivity. This review summarizes the application of different types of nanomaterials in E-apt sensors. The construction methods and research progress of the E-apt sensor based on different working principles are systematically introduced. Moreover, the advantages and challenges of the E-apt sensor in heavy metal ion detection are summarized.

Nano-engineered materials for sensing food pollutants: Technological advancements and safety issues

Food spoilage and safety are key concerns of the modern food sector. Among them, several types of polluting agents are the prime grounds of food deterioration. In this context, nanotechnology-based measures are setting new frontiers to strengthen food applications. Herein, we summarize the nanotechnological dimension of the food industry for both processing and packaging applications. Active bioseparation, smart delivery, nanoencapsulation, nutraceuticals, and nanosensors for biological detection are a few emerging topics of nanobiotechnology in the food sector. The development of functional foods is another milestone set by food nanotechnology by building the link between humans and diet. However, the establishment of optimal intake, product formulations, and delivery matrices, the discovery of beneficial compounds are a few of the key challenges that need to be addressed. Nanotechnology provides effective solutions for the aforementioned problem giving various novel nanomaterials and methodologies. Various nanodelivery systems have been designed, e.g., cochleate, liposomes, multiple emulsions, and polysaccharide-protein coacervates. However, their real applications in food sciences are very limited. This review also provides the status and outlook of nanotechnological systems for future food applications.

Three-dimensional modeling of streptomycin binding single-stranded DNA for aptamer-based biosensors, a molecular dynamics simulation approach

Streptomycin (STR) an aminoglycoside antibiotic which is used against bacteria in human and animal infection, have serious side effects on different parts of human body. Therefore, there is a crucial need to detect trace amount of it in serum and food products. Aptamers are oligonucleotides or peptides, which bind their targets with high affinity and specificity. These properties make aptamers as suitable candidates for biosensing applications. A 79-mer ss-DNA aptamer was applied for the detection of small amount of STR in various aptasensors. But there is no structural information on the STR-binding aptamer and molecular details underlying the aptamer-STR binding remain unexplored. In this study we provided a 3D-structural model for 79-mer ss-DNA aptamer from the sequence. Using docking program and molecular dynamics (MD) simulation we predicted the binding pocket of ss-DNA aptamer. Our results show STR streptose ring is buried within the groove of DNA model and capped by non Watson-Crick bases. STR interacts with aptamer through forming stable hydrogen bonds. Our computational findings are in fair agreement with experimental results. With the atomic structural details, we gained new insight into the Apt-STR binding interaction that can help to further optimize aptamer efficiency in biosensing applications.Communicated by Ramaswamy H. Sarma.

A Simple Yet Effective Preanalytical Strategy Enabling the Application of Aptamer-Conjugated Gold Nanoparticles for the Colorimetric Detection of Antibiotic Residues in Raw Milk

The misuse of antibiotics in the cattle sector can lead to milk contamination, with concomitant effects on the dairy industry and human health. Biosensors can be applied in this field; however, the influence of the milk matrix on their activity has been poorly studied in light of the preanalytical process. Herein, aptamer-conjugated gold nanoparticles (nanoaptasensors) were investigated for the colorimetric detection in raw milk of four antibiotics used in cattle. The effect of milk components on the colorimetric response of the nanoaptasensors was analyzed by following the selective aggregation of the nanoparticles, using the absorption ratio A₅₂₀/A₇₂₀. A preanalytical strategy was developed to apply the nanoaptasensors to antibiotic-contaminated raw milk samples, which involves a clarification step with Carrez reagents followed by the removal of cations through dilution, chelation (EDTA) or precipitation (NaHCO₃). The colorimetric signals were detected in spiked samples at concentrations of antibiotics as low as 0.25-fold the maximum residue limits (MRLs) for kanamycin (37.5 μg/L), oxytetracycline (25 μg/L), sulfadimethoxine (6.25 μg/L) and ampicillin (1 μg/L), according to European and Chilean legislation. Overall, we conclude that this methodology holds potential for the semiquantitative analysis of antibiotic residues in raw milk obtained directly from dairy farms.

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.

Cytochrome c/Multi-walled Carbon Nanotubes Modified Glassy Carbon Electrode for the Detection of Streptomycin in Pharmaceutical Samples

A novel electrochemical glassy carbon electrode modified with a multi-walled carbon nanotube, cytochrome c (Cyt c) and zinc oxide nanoparticles (ZnONPs) was fabricated to increase the sensitivity of electrode for the detection of streptomycin (STN) in certain pharmaceutical samples. Cyclic voltammetry (CV) and differential pulse voltammetry techniques were used for an electrochemical characterization of the electrode. Furthermore, the electrochemical biosensor construction phases were examined by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, the electrode offers a high selectivity and sensitivity signaling in the co-existence method of STN with the linear concentration ranging from 0.02 to 2.2 μM. The detection limits (LOD) and limit of quantification (LOQ) were found to be 0.0028 and 0.0562 μM, respectively. The fabricated sensing electrode has good stability, reproducibility and sensitivity towards STN in the pharmaceutical samples. Preliminary determinations of binding sites within the specified grid box size, which covers both Cyt c and STN, were done by molecular docking analysis. Moreover, density functional theory (DFT) computations were performed to provide insightful information into the optimized geometry of STN.

Technological Advancements for the Detection of Antibiotics in Food Products

Antibiotics, nowadays, are not only used for the treatment of human diseases but also used in animal and poultry farming to increase production. Overuse of antibiotics leads to their circulation in the food chain due to unmanaged discharge. These circulating antibiotics and their residues are a major cause of antimicrobial resistance (AMR), so comprehensive and multifaceted measures aligning with the One Health approach are crucial to curb the emergence and dissemination of antibiotic resistance through the food chain. Different chromatographic techniques and capillary electrophoresis (CE) are being widely used for the separation and detection of antibiotics and their residues from food samples. However, the matrix present in food samples interferes with the proper detection of the antibiotics, which are present in trace concentrations. This review is focused on the scientific literature published in the last decade devoted to the detection of antibiotics in food products. Various extraction methods are employed for the enrichment of antibiotics from a wide variety of food samples; however, solid-phase extraction (SPE) techniques are often used for the extraction of antibiotics from food products and biological samples. In addition, this review has scrutinized how changing instrumental composition, organization, and working parameters in the chromatography and CE can greatly impact the identification and quantification of antibiotic residues. This review also summarized recent advancements in other detection methods such as immunological assays, surface-enhanced Raman spectroscopy (SERS)-based assays, and biosensors which have emerged as rapid, sensitive, and selective tools for accurate detection and quantification of traces of antibiotics.

[Application of carbon dots in analysis and detection of antibiotics]

Antibiotics have been overused in recent years because of their remarkable curative effect, but this has led to considerable environmental pollution. Therefore, the development of approaches aimed at the effective detection and control of the antibiotics is vital for protecting the environment and human health. Many conventional strategies (such as high-performance liquid chromatography (HPLC), gas chromatography (GC), high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)) are currently in use for the detection of antibiotics. These strategies have aroused a great deal of interest because of their outstanding features of high efficiency and speed, good reproducibility, automation, etc. However, various problems such as tedious sample pretreatment, low detection sensitivity, and high cost must be overcome for the effective detection of antibiotics in environmental samples. Consequently, it is of great significance to improve the detection sensitivity of antibiotics. The development of new materials combined with the existing detection technology has great potential to improve the detection results for antibiotics. Carbon dots (CDs) are a new class of nanomaterials with particle sizes in the range of 0-10 nm. In addition, CDs have desirable properties such as small particle effect, excellent electrical properties, unique optical properties, and good biocompatibility. Hence, they have been widely utilized for the detection of antibiotics in environmental samples. In this review, the application of CDs combined with sensors and chromatographic technology for the detection of antibiotics in the last five years are summarized. The development prospects of CD-based materials and their application to the analysis and detection of antibiotics are presented. In this review, many new sensors (CDs combined with molecularly imprinted polymer sensors, aptamer sensors, electrochemiluminescence sensors, fluorescence sensors, and electrochemical sensors) combined with CD-based materials and their use in the detection of antibiotics are summarized. Furthermore, advanced analysis methods such as ratiometric sensor and array sensor methods are reviewed. The novel analysis methods provide a new direction toward the detection of antibiotics by CDs combined with a sensor. Moreover, CD-based chromatographic stationary phases for the separation of antibiotics are also summarized in this manuscript. It is reported that the detection sensitivity for antibiotics can be greatly improved by the combination of CDs and a sensor. Nevertheless, a literature survey reveals that the detection of antibiotics in complex environmental samples is confronted with numerous challenges, including the fabrication of highly sensitive sensors in combination with CDs. Furthermore, the development of novel high-performance materials is of imperative. In addition, it is important to develop new methods for effective data processing. The separation of antibiotics with CDs as the chromatographic stationary phases is in the preliminary stage, and the separation mechanism remains to be clarified. In conclusion, there are still many problems to be overcome when using CDs as novel materials for the detection of antibiotics in environmental samples. Nowadays, CD-based materials are being intensively studied, and various analytical detection technologies are being rapidly developed. In the future, CD-based materials are expected to play an important role in the detection of antibiotics and other environmental pollutants.

Establishment of a dual-aptasensor for simultaneous detection of chloramphenicol and kanamycin

Aptamers, as single-stranded DNA or RNA fragments, have been widely applied as the bio-recognition element for fabrication of flexible and reliable aptasensors to be used in food safety control, clinical therapy and diagnosis and environment monitoring fields. With increasingly fierce antibiotics resistance appearing as a worldwide problem, a highly efficient method is urgently needed to detect antibiotics residues in animal-sourced food. Herein, a simply operated aptasensor based on quantitative real-time PCR (qRT-PCR) was fabricated to realise the simultaneous detection of two antibiotics (i.e. chloramphenicol and kanamycin). The limit of detection (LOD) of 6.13 ng/mL for chloramphenicol and of 19.17 ng/mL for kanamycin of this dual-aptasensor were achieved. Actually, such LOD values were not as good as that of an aptasensor individually established for each antibiotic. The circular dichroism analysis suggested that in the dual-aptasensor, adjacent aptamers might disturb each other's binding with their respective target. Although certain detection sensitivity was lost, the dual-aptasensor could still fulfil the detection requirements, and more importantly, it would improve the detection efficiency. Finally, this dual-aptasensor was applied for detecting chloramphenicol and kanamycin in real spiked food samples, and results indicated good recovery rates. These results demonstrated this developed dual-aptasensor to be a promising highly efficient method with low cost for simultaneous detection of chloramphenicol and kanamycin residues in animal-sourced food samples.

A colorimetric and electrochemical dual-mode biosensor for thrombin using a magnetic separation technique

In general, protein detection relies primarily on enzyme-linked immunosorbent assays. Here, we constructed a colorimetric and electrochemical dual-mode biosensor for thrombin detection based on the mechanism of aptamer recognition. Magnetic nanobeads (MBs) were used as carriers for separation and enrichment to quickly capture thrombin (TB) in the complex matrix. Also, the combination of MBs and the magnetic electrode array (MEA) effectively avoided the poisoning of the electrode by biological samples. Furthermore, hybridization chain reaction (HCR) was indirectly used to achieve amplification of TB. A large number of horseradish peroxidases (HRPs) were coupled with the amplified long nucleic acid fragments. Based on the color and current response of the substrate TMB catalyzed by HRP, a dual-mode detection system for thrombin was established to ensure the accuracy of the test results. The method had a minimum resolution of 10 nM to the naked eye and an electrochemical detection limit as low as 0.35 nM. In addition, the sensor provided good anti-interference ability in a complex matrix and showed great potential to detect TB in complex samples.

Recent advances in aptamer-based sensors for aminoglycoside antibiotics detection and their applications

Aminoglycoside antibiotics (AAs) have been extensively applied in medical field and animal husbandry owing to desirable broad-spectrum antibacterial activity. Excessive AAs residues in the environment can be accumulated in human body through food chain and cause detrimental effect on human health. The establishment of highly specific, simple and sensitive detection methods for monitoring AAs residues is highly in demand. Aptasensor using aptamer as the biological recognition element is the efficient and promising sensing method for detection of AAs. In this review, we have made a summary of specific aptamers sequences against AAs. Subsequently, we provide a systematical and comprehensive overview of modern techniques in aptasensors for detection of AAs according to optical aptasensors as well as electrochemical aptasensors and further summarize their advantages and disadvantages to compare their applications. In addition, we present an overview of practical applications of aptasensors in sample detection of AAs. Moreover, the current challenges and future trends in this field are also included to reveal a promising perspective for developing novel aptasensors for AAs.

Advances in Gold Nanoparticles-Based Colorimetric Aptasensors for the Detection of Antibiotics: An Overview of the Past Decade

Misuse of antibiotics has recently been considered a global issue because of its harmful effects on human health. Since conventional methods have numerous limitations, it is necessary to develop fast, simple, sensitive, and reproducible methods for the detection of antibiotics. Among numerous recently developed methods, aptasensors are fascinating because of their good specificity, sensitivity and selectivity. These kinds of biosensors combining aptamer with colorimetric applications of gold nanoparticles to recognize small molecules are becoming more popular owing to their advantageous features, for example, low cost, ease of use, on-site analysis ability using naked eye and no prerequisite for modern equipment. In this review, we have highlighted the recent advances and working principle of gold nanoparticles based colorimetric aptasensors as promising methods for antibiotics detection in different food and environmental samples (2011–2020). Furthermore, possible advantages and disadvantages have also been summarized for these methods. Finally, the recent challenges, outlook, and promising future perspectives for developing novel aptasensors are also considered.

Aggregation-based fluorescence amplification strategy: "turn-on" sensing of aminoglycosides using near-IR carbocyanine dyes and pre-micellar surfactants

This study is aimed at developing sensing schemes without obtaining selective receptors. A series of simple carbocyanine dyes was synthesized, whose emission was quenched in water with formation of nanoparticles in the range of 20-100 nm. Fluorescence in near-IR region is "turned on" in the presence of a drug cation of middle molecular weight (400-700 Da) and sodium dodecyl sulfate (SDS), as well as anionic drugs and a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Aggregates (clusters) up to 100-200 nm in size were detected using dynamic light scattering (DLS) and Rayleigh light scattering (RLS) techniques in the systems: cationic analyte-SDS, carbocyanine dye-CTAB, and in all brightly fluorescent ternary systems dye-surfactant-analyte. Small ions (<200 Da) incapable of multi-point binding do not form the aggregates or cause the emission enhancement. The "turn-on" signal is only observed at the surfactant submicellar concentrations insufficient to solubilize the dye nanoparticles. Based on these findings, we suggest a rapid and simple method for the detection of ≥4·10^-5 mol/L of neomycin in urine. The proposed strategy paves the way for developing more selective methods.

Dynamic light scattering and fluorescence dual-signal sensing of cancer antigen-125 via recognition of the polymerase chain reaction product with gold nanoparticle probe

Cancer antigen 125 (CA - 125) is an important biomarker for the diagnosis of ovarian cancer. In this paper, oligonucleotide 5'-GACAGGCCCGAAGGAATAGATAATACGACTCACTATAGGGAGACAAGAATAAACGCTCAA-3' (oligo 1) contains an aptamer of CA - 125, and was designed partly complementary to oligonucleotide 5'-CTCTCTCTCCACCTTCTTCTTTGAGCGTTTATTCTTGTCT-3' (oligo 2). Oligo 1 · oligo 2 was extended with the Klenow fragment (exo^-) polymerase for further polymerase chain reaction (PCR) processes in the presence of two primers: deoxyribose nucleoside triphosphate and Taq polymerase. Single-stranded DNA was produced at two sides of the PCR product by introducing a C₁₈ spacer into the two primers, which could hybridize with AuNPs-DNA probes, investigated by dynamic light scattering and fluorescence. The addition of CA - 125 can interrupt the hybridization between oligo 1 and oligo 2, causing the average diameter of AuNPs-DNA probes to decrease with the increase of CA-125 within the range of 5 fg mL^-1 - 50 ng mL^-1. The linear regression equation of this relationship was D = 430.48-49.60 log₁₀C, with a detection limit of 1.1 fg mL^-1. Fluorescein molecules were modified at the end of the forward primer. The fluorescence intensity of the PCR product can be measured simultaneously, with the fluorescence intensity increasing linearly with the logarithm of CA-125 concentration within a linear range from 10 fg mL^-1 to 50 ng mL^-1, with a detection limit of 1.5 fg mL^-1.

A split aptamer (SPA)-based sandwich-type biosensor for facile and rapid detection of streptomycin

As antibiotic pollution is gaining prominence as a global issue, the demand for detection of streptomycin (STR), which is a widely used antibiotic with potential human health and ecological risks, has attracted increasing attention. Aptamer-based biosensors have been developed for the detection of STR in buffers and samples, however, the non-target signals due to the conformational variation of free aptamers possibly affect their sensitivity and stability. In this study, by introducing the STR-specific split aptamer (SPA), a sensitive evanescent wave fluorescent (EWF) biosensor is developed for the sandwich-type based detection of STR. The standard calibration curve obtained for STR has a detection limit of 33 nM with a linear range of 60-526 nM. This biosensor exhibited good selectivity, reliable reusability for at least 100 times measurements, and high recovery rates for spiked water samples; moreover, all detection steps are easy-to-operate and can be completed in 5 min. Therefore, it exhibits great promise for actual on-site environmental monitoring. Additionally, without introducing any other oligonucleotides or auxiliary materials, this SPA-based biosensing method shows potential as a simple, sensitive, and low-cost manner for the detection of other small molecular targets.

A Paper-Based Colorimetric Aptasensor for the Detection of Gentamicin

Antibiotics are classes of antimicrobial substances that are administered widely in the field of veterinary science to promote animal health and feed efficiency. Cattle-administered antibiotics hold a risk of passing active residues to milk, during the milking process. This becomes a public health concern as these residues can cause severe allergic reactions to sensitive groups and considerable economic losses to the farmer. Hence, to ensure that the produced milk is safe to consume and adheres to permissible limits, an on-farm quick and reliable test is essential. This study illustrates the design and development of a microfluidic paper biosensor as a proof-of-concept detection system for gentamicin in milk. Localized surface plasmon resonance (LSPR) properties of gold nanoparticles have been explored to provide the user a visual feedback on the test, which was also corroborated by RGB analysis performed using Image J. The assay involves the use of a short stretch of single stranded DNA, called aptamer, which is very specific to the gentamicin present in the milk sample. The camera-based LOD for the fabricated paper device for milk samples spiked with gentamicin was calculated to be 300 nM, with a reaction time of 2 min.

Application of Multiplexed Aptasensors in Food Contaminants Detection

The existence of contaminants in food poses a serious threat to human health. In recent years, aptamer sensors (aptasensors) have been developed rapidly for the detection of food contaminants because of their high specificity, design flexibility, and high efficiency. However, the development of high-throughput, highly sensitive, on-site, and cost-effective methods for simultaneous detection of food contaminants is still restricted due to multiple signal overlap or mutual interference and cross-reaction between different analytes with similar molecular structures. To overcome these problems, this Review summarizes some effective strategies from the articles published in recent years about multiplexed aptasensors for the simultaneous detection of food contaminants. This work focuses on the application of multiplexed aptasensors to simultaneously detect antibiotics, pathogens, and mycotoxins in food. These aptasensors mainly contain fluorescent aptasensors, electrochemical aptasensors, surface-enhanced Raman scattering-based aptasensors, microfluidic chip aptasensors, and paper-based multiplexed aptasensors. In addition, this Review also covers the application of nucleic acid cycle amplification and nanomaterial amplification strategies to improve the detection sensitivity. Finally, the limitations and challenges in the design of multiplexed aptasensor are also taken into account.

Application of DNA-Nanosensor for Environmental Monitoring: Recent Advances and Perspectives

PURPOSE OF REVIEW

Environmental pollutants are threat to human beings. Pollutants can lead to human health and environment hazards. The purpose of this review is to summarize the work done on detection of environmental pollutants using DNA nanosensors and challenges in the areas that can be focused for safe environment.

RECENT FINDINGS

Most of the DNA-based nanosensors designed so far use DNA as recognition element. ssDNA, dsDNA, complementary mismatched DNA, aptamers, and G-quadruplex DNA are commonly used as probes in nanosensors. More and more DNA sequences are being designed that can specifically detect various pollutants even simultaneously in complex milk, wastewater, soil, blood, tap water, river, and pond water samples. The feasibility of direct detection, ease of designing, and analysis makes DNA nanosensors fit for future point-of-care applications.

SUMMARY

DNA nanosensors are easy to design and have good sensitivity. DNA component and nanomaterials can be designed in a controlled manner to detect various environmental pollutants. This review identifies the recent advances in DNA nanosensor designing and opportunities available to design nanosensors for unexplored pathogens, antibiotics, pesticides, GMO, heavy metals, and other toxic pollutant.

Impact of Protein Corona on Noncovalent Molecule-Gold Nanoparticle-Based Sensing

Gold nanoparticle (AuNP)-based sensors have been extensively applied for sensing or imaging. It is known that a protein shell named protein corona (PC) formed around the nanomaterials could not only block the desired function of nanomaterials but also affect their behavior, which is a hot and important issue needing consideration. Therefore, we hypothesize that the formation of PC around AuNPs could inevitably affect the AuNP-based target assay. In this work, the effects of PC on the detection results in sensors based on AuNPs were studied. Three types of noncovalent molecule-AuNP sensors including AuNP-dichlorofluorescein, AuNP-aptamer, and AuNP-antibody-DNA were constructed, and several typical proteins (bovine serum albumin, fibrinogen, hemoglobin, and β-lactoglobulin), milk, and fetal bovine serum were selected as models for the formation of PCs. This study shows that the PC could cause the loss of detection signals (up to 80%) and result in positive deviation of the measuring value compared with the true value. Moreover, the loss of detection signals could also increase the limits of detection (almost 10 times), decreasing the sensitivity of the three types of sensors, as proposed in this work compared to that without PC. Moreover, the polyethylene glycol backfilling strategy could not resolve the negative effects of PC on noncovalent molecule-AuNP sensors. The impacts of PC on detection results from noncovalent molecule-AuNP sensors would cause misdiagnosis or wasted production, which needs careful reconsideration of the AuNP-based detection in application fields like clinic diagnosis, food safety control, and so forth.

Recent Biosensors for Detection of Antibiotics in Animal Derived Food

Antibiotics are extensively employed as bacteriostatic agents for fighting against microbial infection in animals. However, inappropriate doses of antibiotic drugs may result in antibiotic residues in food of animal origin and may cause various side effects on human health. Moreover, the transferor of antibiotic-resistant bacteria to humans through the food chain may induce serious health hazards. Hence, it is vital to develop sensitive and selective methods for rapid screening and regular monitoring of antibiotic residues in animal-derived foods. The conventional different chromatographic and spectroscopic techniques are time-consuming, expensive and require skilled personnel. To overcome such limitations, biosensors have emerged as an innovative approach recently and integrated with nanotechnologies for sensitive, rapid and on-site monitoring of different antibiotic residues in animal origin foods. This mini-review aims to give an overview of the currently available biosensing techniques to detect antibiotic residue in foods.

DNA functionalized metal and metal oxide nanoparticles: principles and recent advances in food safety detection

The frequent occurrence of food safety incidents has given rise to unprecedented concern about food contamination issues for both consumers and the industry. Various contaminations in food pose serious threats to food safety and human health. Many detection methods were studied to address the challenge. Recently, biosensors relying on deoxyribonucleic acid (DNA)-functionalized nanoparticles have been developed as an efficient and effective detection method. In the current review, the strategies for DNA assembly metal and metal oxide nanoparticles are elaborated, recent applications of the sensors based on DNA-functionalized nanoparticles in food contaminant detection are discussed. Pathogenic bacteria, heavy metal ions, mycotoxins, antibiotics, and pesticides are covered as food contaminants. Additionally, limitations and future trends of functionalized nanoparticles-based technology are also presented. The current review indicates that DNA-functionalized metal and metal oxide nanoparticles are a novel nanomaterial with unique biological and physical properties for developing electrochemical, fluorescent, colourimetric and surface-enhanced Raman spectroscopy (SERS) sensors, etc. Compared with conventional detection techniques, DNA-functionalized metal and metal oxide nanoparticles have considerable advantages with high accuracy, high specificity, micro-intelligence, and low cost. Nevertheless, the stability of these sensors and the limitations of real-time detection are still under discussion. Therefore, more tolerant, portable, and rapid DNA sensors should be developed to better the real-time monitoring of harmful contaminants.

A Novel Turn on Fluorescence Sensor for Determination Enoxaparin, a Low Molecular Weight Heparin

A sensor system was designed for the detection of Enoxaparin (Enox), a low molecular weight heparin (LMWH) that was run over the fluorescence quenching mechanism of fluorescein (FL) dye. At nanomolar concentrations, FL probe was subjected to fluorescence quenching by Fe(III). Fluorescence quenching mechanism of FL by Fe(III) was examined using various analytical techniques such as UV-vis absorption, fluorescence, and Fourier transform Infrared spectroscopy techniques, as well as with scanning electron microscope. The results indicated that photoinduced electron transfer process occurred between FL and Fe and that FL was quenched both statically and dynamically. Thermodynamic parameters showed that the interactions between them were predominantly hydrophobic interactions. Enox caused FL to recover its lost fluorescence properties and an increase was observed in the intensity of the fluorescence. Enox was detected successfully with the turn on fluorescence sensor. The developed Enox biosensor exhibited linearity in the range of 0-1.1 μg/ml. For Enox detection, the limit of detection was measured as 255 ng/mL. Enox biosensor was presented as a practical, simple, and applicable sensor system with high sensitivity and good selectivity. Enox is a medication usually monitored indirectly over anticoagulation. This study was presented as an alternative method for monitoring Enox directly. HIGHLIGHTS: Fluorescence quenching of Fluorescein dye by Fe(III) was studied in detail. The presence of enoxaparin enhanced the fluorescence properties of the fluorescein dye. A sensitive, simple and effective sensor system for determination of Enoxaparin, a low molecular weight heparin was shaped in the aqueous media. It was presented as a new method for Enoxaparin to be followed directly.

G-quadruplex specific thioflavin T-based label-free fluorescence aptasensor for rapid detection of tetracycline

A label-free fluorescence aptasensor was developed for the rapid detection of tetracycline (TET) based on G-quadruplex structure of TET aptamers and G-quadruplex specific dye Thioflavin T (ThT). The fluorescence of free ThT is essentially weak in aqueous solution, whereas it selectively identifies the G-quadruplex of aptamers to form the G-quadruplex/ThT conjugates, resulting in an enormous increase of the fluorescence intensity. However, the fluorescence intensity of G-quadruplex/ThT conjugates was drastically suppressed due to the release of free ThT from G-quadruplex/ThT conjugates after the addition of TET via specific binding with TET aptamers. The key factors affecting sensitivity and selectivity including the reaction medium, binding time of ThT to TET aptamers, incubation time between TET aptamers and TET, concentration of ThT and TET aptamers were investigated in detail. The optimal conditions were as follows: ultrapure water as reaction medium, binding time of 5 min, incubation time of 1 min, 9.0 μmol/L ThT and 0.03 μmol/L aptamers. A good linear relationship (correlation coefficient of 0.9973) was obtained between the fluorescence quenching efficiency (F₀ - F) / F₀ and the logarithm of TET concentration in the range of 0.01-1.0 μmol/L. The limit of detection was 0.001 μmol/L (S/N = 3). The proposed assay was applied for the detection of TET in the spiked honey and milk samples with recoveries ranging from 93.5% to 106.9%. The developed label-free fluorescence aptasensor showed advantages of high specificity, low cost and short time-consuming, illustrating potential application for on-site detection of TET in foodstuffs.

Label-free and enzyme-free one-step rapid colorimetric detection of DNA methylation based on unmodified gold nanoparticles

DNA methylation has been identified as one of the important causes of tumorigenesis, so it is important to develop some advanced methods for detecting and quantifying DNA methylation. In this study, a label-free and enzyme-free one-step rapid colorimetric detection of DNA methylation based on unmodified Au nanoparticles(Au NPs)has been proposed. This method can quickly, efficiently, economically and easily colorimetric detect methylated DNA only by the color change of unmodified Au NPs solution without the covalent modification of Au NPs in advance or complicated instruments for implementation with practical limitations or expensive biological enzymes or traditional organic dyes during the reaction. The strategy employed the difference in electrostatic attraction of single-stranded DNA and double-stranded DNA against salt-induced aggregation of Au NPs. The method has a DNA methylated detection limit of 8.47 nM and it is distinctly visible to detect methylated DNA with the naked eye as low as 20 nM. Furthermore, the strategy has an ability to detect methylated DNA in the presence of abundant unmethylated DNA with the detection limit of 0.13% and as low as 1% methylated DNA can be distinguished in heterogeneous samples with the naked eye. Also, the stratagem provides a convenient and rapid platform for methylated DNA detection of human serum samples in one step, which displays a huge potential for clinical diagnosis and treatment of oncological diseases.

Improved Antibiotic Detection in Raw Milk Using Machine Learning Tools over the Absorption Spectra of a Problem-Specific Nanobiosensor

In this article we present the development of a biosensor system that integrates nanotechnology, optomechanics and a spectral detection algorithm for sensitive quantification of antibiotic residues in raw milk of cow. Firstly, nanobiosensors were designed and synthesized by chemically bonding gold nanoparticles (AuNPs) with aptamer bioreceptors highly selective for four widely used antibiotics in the field of veterinary medicine, namely, Kanamycin, Ampicillin, Oxytetracycline and Sulfadimethoxine. When molecules of the antibiotics are present in the milk sample, the interaction with the aptamers induces random AuNP aggregation. This phenomenon modifies the initial absorption spectrum of the milk sample without antibiotics, producing spectral features that indicate both the presence of antibiotics and, to some extent, its concentration. Secondly, we designed and constructed an electro-opto-mechanic device that performs automatic high-resolution spectral data acquisition in a wavelength range of 400 to 800 nm. Thirdly, the acquired spectra were processed by a machine-learning algorithm that is embedded into the acquisition hardware to determine the presence and concentration ranges of the antibiotics. Our approach outperformed state-of-the-art standardized techniques (based on the 520/620 nm ratio) for antibiotic detection, both in speed and in sensitivity.

Selective enrichment of zein gene of maize from cereal products using magnetic support having pyrrolidinyl peptide nucleic acid probe

Here, we describe DNA enrichment of the zein gene from maize using pyrrolidinyl peptide nucleic acid (PNA) immobilized on a magnetic solid support as a capture element. Magnetite nanoparticles (MNP) with a capacity of 373 pmolPNA/mg and coated with poly(N-acryloylglycine) (PNAG) showed a good response to magnetic field. The PNA probe immobilized on the MNP discriminated between non-complementary and complementary DNA using fluorophore-tagged DNA as a model. We applied this system for the enrichment of the zein gene from maize in eight cereal product samples. After DNA desorption from the MNP, and its amplification via polymerase chain reaction (PCR), gel electrophoresis indicated that only cereal samples containing the zein gene from maize yielded positive results, indicating a high binding specificity between the PNA used and the complementary DNA. This PNA-functionalized MNP is potentially useful as an effective nano-solid support for DNA enrichment from other samples.

A self-powered aptasensor using the capacitor-amplified signal of a photofuel cell and a portable digital multimeter readout

A self-powered aptasensor for streptomycin detection was constructed with a photofuel cell combined with a capacitor and a digital multimeter. The sensitivity of the proposed sensor was 8.7 times of that without using a capacitor amplifier circuit.

Dual Fluorescence-colorimetric Silver Nanoparticles Based Sensor for Determination of Olanzapine: Analysis in Rat Plasma and Pharmaceuticals

The present work describes a dual-readout assay for the determination of an antipsychotic drug olanzapine using Rhodamine B modified silver nanoparticles (AgNPs). AgNPs, when mixed with Rhodamine B, quenched its fluorescence emission with high quenching efficiency as evident from the Stern Volmer plot. Transmission electron microscopy image and Dynamic Light Scattering histogram of Rhodamine B bound AgNPs showed a stable monodispersed nanosuspension. Addition of olanzapine to Rhodamine B-bound AgNPs resulted in reappearance of fluorescence, which was dependent on the amount of olanzapine added to the system. Besides displacing the surface bound Rhodamine B molecules, it caused aggregation of AgNPs which formed the basis of dual-readout sensor. Several parameters such as pH, reaction time and order of addition of the three components which may influence the analytical signal were studied and optimized. The method was validated for linearity, sensitivity, selectivity, accuracy, precision and recovery. Based on this dual-readout system, linear concentration range was established from 0.05 to 10 µM (fluorescence measurement) and 5.0 to 50 µM (colorimetric response) for olanzapine. The limit of detection (LOD) using fluorescence and colorimetric approach was 0.013 µM and 1.25 µM, respectively. The proposed method showed excellent selectivity for olanzapine in presence of several antipsychotic drugs, cations, sugars and amino acids. Finally, the method was successfully applied to a pharmacokinetic study of olanzapine in rats and also for analyzing pharmaceutical formulations.

Khattab T. Recent Advances in Cellulose-Based Biosensors for Medical Diagnosis

Cellulose has attracted much interest, particularly in medical applications such as advanced biosensing devices. Cellulose could provide biosensors with enhanced biocompatibility, biodegradability and non-toxicity, which could be useful for biosensors. Thus, they play a significant role in environmental monitoring, medical diagnostic tools, forensic science, and foodstuff processing safety applications. This review summarizes the recent developments in cellulose-based biosensors targeting the molecular design principles toward medical detection purposes. The recognition/detection mechanisms of cellulose-based biosensors demonstrate two major classes of measurable signal generation, including optical and electrochemical cellulosic biosensors. As a result of their simplicity, high sensitivity, and low cost, cellulose-based optical biosensors are particularly of great interest for including label-free and label-driven (fluorescent and colorimetric) biosensors. There have been numerous types of cellulose substrates employed in biosensors, including several cellulose derivatives, nano-cellulose, bacterial cellulose, paper, gauzes, and hydrogels. These kinds of cellulose-based biosensors were discussed according to their preparation procedures and detection principle. Cellulose and its derivatives with their distinctive chemical structure have demonstrated to be versatile materials, affording a high-quality platform for accomplishing the immobilization process of biologically active molecules into biosensors. Cellulose-based biosensors exhibit a variety of desirable characteristics, such as sensitivity, accuracy, convenience, quick response, and low-cost. For instance, cellulose paper-based biosensors are characterized as being low-cost and easy to operate, while nano-cellulose biosensors are characterized as having a good dispersion, high absorbance capacity, and large surface area. Cellulose and its derivatives have been promising materials in biosensors which could be employed to monitor various bio-molecules, such as urea, glucose, cell, amino acid, protein, lactate, hydroquinone, gene, and cholesterol. The future interest will focus on the design and construction of multifunctional, miniaturized, low-cost, environmentally friendly, and integrated biosensors. Thus, the production of cellulose-based biosensors is very important.

Chlortetracycline-Functionalized Silver Nanoparticles as a Colorimetric Probe for Aminoglycosides: Ultrasensitive Determination of Kanamycin and Streptomycin

Aminoglycosides (AMGs) have been extensively used to treat infectious diseases caused by Gram-negative bacteria in livestock and humans. A selective and sensitive colorimetric probe for the determination of streptomycin and kanamycin was proposed based on chlortetracycline-coated silver nanoparticles (AgNPs-CTC) as the sensing element. Almost all of the tested aminoglycoside antibiotics can rapidly induce the aggregation of AgNPs, along with a color change from yellow to orange/red. The selective detection of aminoglycoside antibiotics, including tobramycin, streptomycin, amikacin, gentamicin, neomycin, and kanamycin, with other types of antibiotics, can be achieved by ultraviolet (UV) spectroscopy. This developed colorimetric assay has ability to detect various AMGs using in-depth surface plasmon resonance (SPR) studies. With this determination of streptomycin and kanamycin was achieved at the picomolar level (pM) by using a UV-visible spectrophotometer. Under aqueous conditions, the linear range of the colorimetric sensor for streptomycin and kanamycin was 1000-1,1000 and 120-480 pM, respectively. The corresponding limit of detection was 2000 pM and 120 pM, respectively. Thus, the validated dual colorimetric and ratiometric method can find various analytical applications for the ultrasensitive and rapid detection of AMG antibiotics in water samples.

The Growing Interest in Development of Innovative Optical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The presence of antimicrobial residues in food-producing animals can lead to harmful effects on the consumer (e.g., allergies, antimicrobial resistance, toxicological effects) and cause issues in food transformation (i.e., cheese, yogurts production). Therefore, to control antimicrobial residues in food products of animal origin, screening methods are of utmost importance. Microbiological and immunological methods (e.g., ELISA, dipsticks) are conventional screening methods. Biosensors are an innovative solution for the development of more performant screening methods. Among the different kinds of biosensing elements (e.g., antibodies, aptamers, molecularly imprinted polymers (MIP), enzymes), aptamers for targeting antimicrobial residues are in continuous development since 2000. Therefore, this review has highlighted recent advances in the development of aptasensors, which present multiple advantages over immunosensors. Most of the aptasensors described in the literature for the detection of antimicrobial residues in animal-derived food products are either optical or electrochemical sensors. In this review, I have focused on optical aptasensors and showed how nanotechnologies (nanomaterials, micro/nanofluidics, and signal amplification techniques) largely contribute to the improvement of their performance (sensitivity, specificity, miniaturization, portability). Finally, I have explored different techniques to develop multiplex screening methods. Multiplex screening methods are necessary for the wide spectrum detection of antimicrobials authorized for animal treatment (i.e., having maximum residue limits).

Label-free electrochemical aptasensor for progesterone detection in biological fluids

A label-free electrochemical progesterone (P4) aptasensor was successfully developed by covalently immobilizing NH₂-functionalized P4-specific aptamer on the electrode surface. The NiO-Au hybrid nanofibers were synthesized by the electrospinning technique. GQDs-NiO-AuNFs nanocomposite was prepared by dispersing of electrospun NiO-AuNFs in the as-synthesized graphene quantum dots (GQDs) solution and stirring for 24 h. Novel GQDs-NiO-AuNFs nano-architecture in combination with functionalized multiwalled carbon nanotubes (f-MWCNTs) were further utilized to modify screen printed carbon electrode (SPCE) in order to construct an effective immobilization matrix with plenty of carboxylic functional groups. The stepwise assembly process of the designed aptasensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The aptamer-progesterone complex formation led to a hindered electron transfer reaction on the sensing interface, which decreased the redox probe peak current. Based on of this, progesterone could be quantitatively detected by monitoring the decrease of differential pulse voltammetric (DPV) responses of [Fe(CN)₆]^3-/4- peak current with increasing the progesterone concentration. Under optimized experimental parameters, the aptasensor exhibited a dynamic concentration range from 0.01 to 1000 nM and a detection limit of 1.86 pM. The proposed aptasensor was successfully employed for the determination of progesterone in human serum samples and pharmaceutical formulations.