Novel label-free fluorescence aptasensor for chloramphenicol detection based on a DNA four-arm junction-assisted signal amplification strategy

Bidirectional hybridized hairpin DNA fluorescent aptasensor based on Au-Pd NPs and CDs for ratiometric detection of AFB1

A novel and simple ratiometric fluorescent aptasensor was developed for the sensitive detection of aflatoxin B1 (AFB1). A hairpin DNA (h-DNA) was independently synthesized as the basic skeleton, and the bidirectional hybridization of h-DNA can increase the load of aptamer and signal probes, thereby realizing signal amplification. The high-efficiency fluorescence resonance energy transfer interaction between gold-palladium nanoparticles (Au-Pd NPs) and the self-synthesized fluorescent probe carbon dots (CDs) was utilized. Moreover, the label-free probe SYBR Green I (SG I) dye was introduced to form a double-signal probe with CDs, and a ratiometric sensor with FCDs/FSG I as a response signal was constructed. The ratio strategy can eliminate the fluctuation of external factors, thus improving the accuracy and reliability of the sensor. The quenching effect of Au-Pd NPs on CDs was 1.4 times that of AuNPs and 3.4 times that of Pd NPs, respectively. In the range 1-100 ng/mL, FCDs/FSG I showed a good linear relationship with the logarithm of the concentration of AFB1, and the limit of detection was as low as 0.07 ng/mL. The sensor was used to detect AFB1 in spiked peanuts and wine samples, and the recovery was between 91 and 115%, indicating that the sensor has high application potential in real sample analysis.

Fluorescent immunoassay for chloramphenicol based on the label-free polyadenine-mediated spherical nucleic acids triggered signal amplification

A fluorescent immunosorbent assay incorporating signal amplification away from the surface of spherical nucleic acid (SNA) was developed for the detection of chloramphenicol (CAP). Through the conjugation of antibodies and poly-adenine (polyA) DNA onto the surface of gold nanoparticles (AuNPs), the fabrication of the nano-immunoprobe was achieved in a more straightforward and cost-effective manner. Moreover, a strategy utilizing the hybridization chain reaction (HCR) in the amplification step was devised, with particular attention given to the enzyme inhibition associated with SNA. The results demonstrated good performance on CAP detection with a linear range of 0.01-5 ng/L with a detection limit of 0.005 ng/L. The significance of this work mainly lies in the polyA-SNA-based immunoprobe and the thoughtful design to prevent enzyme inhibition.

A reusable screen-printed carbon electrode-based aptasensor for the determination of chloramphenicol in food and environment samples

An electrochemical aptasensor was developed for the determination of chloramphenicol (CAP) in fresh foods and food products. The aptasensor was developed using Prussian blue (PB) and chitosan (CS) film. PB acts as a redox probe for detection and CS acts as a sorption material. The aptamer (Apt) was immobilized on a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs). Under optimum conditions, the linearity of the aptasensor was between 1.0 and 6.0 × 106 ng L-1 with a detection limit of 0.65 and a quantification limit of 2.15 ng L-1. The electrode could be regenerated up to 24 times without the use of chemicals. The aptasensor showed good repeatability (RSD <11.2%) and good reproducibility (RSD <7.7%). The proposed method successfully quantified CAP in milk, shrimp pond water and shrimp meat with good accuracy (recovery = 88.0 ± 0.6% to 100 ± 2%). The proposed aptasensor could be especially useful in agriculture to ensure the quality of food and the environment and could be used to determine other antibiotics.

Establishment of a Dual-Signal Enhanced Fluorescent Aptasensor for Highly Sensitive Detection of Ochratoxin A

A robust and versatile dual-signal enhanced fluorescent aptasensor was developed for ochratoxin A (OTA) detection based on fluorescence resonance energy transfer between 5-carboxyfluorescein (FAM) and Super Green I (SG) fluorophores as the donor and graphene oxide (GO) nanosheet as the acceptor. Abundant SG probes were adsorbed into the FAM-complementary DNA (cDNA)-aptamer double-stranded structure to achieve remarkably enhanced fluorescence responses. Without OTA, the FAM-cDNA-SG conjugates coexisted with GO nanosheets, exhibiting strong fluorescence signals. In the presence of OTA, it was captured by the aptamers to release cDNA-FAM and SG probes, which were adsorbed by GO, leading to OTA-dependent fluorescence quenching. The changed fluorescence intensity was measured for accurate quantitation of OTA. Under optimum conditions, the dual-signal enhanced fluorescent aptasensor realized fascinating sensitivity with a limit of detection of 0.005 ng/mL and a wide concentration range of 0.02-20 ng/mL, as well as high selectivity for OTA over other interfering substances, excellent accuracy with average recoveries of 91.37-116.83% in the fortified malt matrices, and superior reliability and practicability in actual samples. This FAM-cDNA-aptamer-SG/GO nanosheet-based aptasensing platform could be extended to monitor other contaminants or trace molecules in food, environmental, and diagnostic fields by altering the corresponding aptamers.

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.

An all-in-one portable colorimetric detection platform for sensitive detection of bisphenol A based on target-mediated CeO2@ZIF-8/Apt biocomposites

BPA aptamers functionalized cerium oxide nanoparticles encapsulated in zeolitic imidazolate framework-8 (CeO2@ZIF-8/Apt) were developed to fabricate an all-in-one portable platform for on-site quantitative detection of BPA. By combining biocomposites with a 3,3',5,5'-tetramethylbenzidine (TMB)-based sodium alginate (SA) hydrogel and smartphone-based RGB analysis, highly sensitive and convenient monitoring of BPA was achieved. CeO2@ZIF-8 composites were constructed using a novel surfactant-modified concentration-controlled synthesis strategy. After being functionalized with BPA aptamers, CeO2@ZIF-8/Apt biocomposites were used as target-response colorimetric probes for target recognition and signal transduction. The oxidase-like activity of CeO2@ZIF-8 was effectively sealed by BPA aptamers and controllably released in a concentration-dependent manner through aptamer-BPA reactions. Utilizing SA hydrogels containing TMB in the caps, a one-step sample addition and one-pot detection can be conveniently achieved and reliably quantified by smartphone-based RGB analysis in an instrument-free way. The detection range of this portable detection platform is 50 pg/mL to 500 ng/mL with limit of detection calculated as 34.88 pg/mL, comparable to that of conventional detection in the solution system (4.57 pg/mL). The recoveries in tap water, apple juice, and milk ranged from 91.02 % and 106.75 %. This work contributes new insights into the design of all-in-one detection platforms for contaminants monitoring in resource-constrained regions.

Exonuclease-based aptasensors: Promising for food safety and diagnostic aims

As of today's requirement, developing cost-effective smart sensing tools with ultrahigh sensitivity for food safety insurance is of special importance. For this purpose, aptamer-based biosensors (aptasensors) powered by the superiorities of the recycling signal amplification strategies have been expanded especially. Target recycling supported by enzymes is an appealing approach for implementing signal amplification. As the supreme biocatalyst enzymes, exonucleases can inaugurate signal improvement by involving a single target in a process would result in appreciable repeating cycles of the cleavage of the phosphodiester bonds between the building blocks of the nucleic acid strands, and also, their terminals. Although there are diverse substances for catalyzing amplification strategies, including nanoparticles, carbon-based nanocomposites, and quantum dots (QDs), exonucleases are of superiority over them by simplifying the amplification process with no need for the complicated pre-treatment processes. The outstanding selectivity and great sensitivity of the aptasensors tuned by amplification potency of exonucleases nominate them as the promising sensing tools for label-free, ease-of-use, cost-effective, and real-time diagnosis of diverse targets. Here, we summarize the achievements and perspectives in the scientific branch of aptasensor design for the qualitative monitoring of diverse targets by cooperation of exonucleases with the conspicuous potential for the signal amplification. Finally, some results are expressed to provide a comprehensive viewpoint for developing novel nuclease-based aptasensors in the future.

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.

Ultrasensitive detection of ineradicable and harmful antibiotic chloramphenicol residue in soil, water, and food samples

Chloramphenicol (CAP) is a harmful antibiotic that inevitably enters our food chain through natural or manmade means. Its ineradicable residue pollutes soils and water, accumulates in plants and animal products, and eventually affects human health. An ultrasensitive method for detecting and monitoring CAP is therefore urgently required. Herein, we report an ultrafast extraction and amperometry detection method based on a graphite-sulfate-modified electrode for detecting CAP in soil, water, and food samples. The graphite sulfate is prepared by the oxidation method and its structural properties are comprehensively investigated. The developed sensor electrode showed a wider linear range of 0.3-32.0 μg kg^-1 and an ultralow detection limit of 0.1 μg kg^-1, both of which meet the European Commission Reg 1871/2019 reference points for action. The method works well with both meat and plant samples, achieving CAP recoveries ranging from 90.8 to 99.1% even at low concentrations. Moreover, the sensor electrode shows more than 95% selectivity toward CAP detection in the soil, water, and food matrices. The developed method exhibits good repeatability and reproducibility in the analysis of real samples.

Fluorescence-based aptasensors for small molecular food contaminants: From energy transfer to optical polarization

Small molecular food contaminants, such as mycotoxins, pesticide residues and antibiotics, are highly probable to be passively introduced in food at all stages of its processing, including planting, harvest, production, transportation and storage. Owing to the high risks caused by the unknowing intake and accumulation in human, there is an urgent need to develop rapid, sensitive and efficient methods to monitor them. Fluorescence-based aptasensors provide a promising platform for this area owing to its simple operation, high sensitivity, wide application range and economical practicability. In this paper, the common sorts of small molecular contaminants in foods, namely mycotoxins, pesticides, antibiotics, etc, are briefly introduced. Then, we make a comprehensive review, from fluorescence resonance energy transfer (in turn-on, turn-off, and ratiometric mode, as well as energy upconversion) to fluorescence polarization, of the fluorescence-based aptasensors for the determination of these food contaminants reported in the last five years. The principle of signal generation, the advances of each sort of fluorescent aptasensors, as well as their applications are introduced in detail. Additionally, we also discussed the challenges and perspectives of the fluorescent aptasensors for small molecular food contaminants. This work will offer systematic overview and inspiration for amateurs, researchers and developers of fluorescence-based aptasensors for the detection of small molecules.

Advances in Biosensing of Chemical Food Contaminants Based on the MOFs-Graphene Nanohybrids

Food safety issue is becoming an international challenge for human health owing to the presence of contaminants. In this context, reliable, rapid, and sensitive detecting technology is extremely demanded to establish food safety assurance systems. MOFs (Metal-organic frameworks) are a new type of porous crystalline material with particular physical and chemical characteristics presented in food safety requirements. (Bio)sensors driven MOF materials have emerged as a promising alternative and complementary analytical techniques, owing to their great specific area, high porosity, and uniform and fine-tunable pore buildings. Nevertheless, the insufficient stability and electrical conductivity of classical MOFs limit their utilization. Employing graphene-derived nanomaterials with high functional elements as patterns for the MOF materials not only improves the structural instability and poor conductivity but also impedes the restacking and aggregation between graphene layers, thus significantly extending the MOFs application. A review of MOFs-graphene-based material used in food contamination detection is urgently needed for encouraging the advance of this field. Herein, this paper systematically outlines current breakthroughs in MOF-graphene-based nanoprobes, outlines their principles, and illustrates their employments in identifying mycotoxins, heavy metal ions, pathogens, antibiotics, and pesticides, referring to their multiplexing and sensitivity ability. The challenges and limitations of applying MOF-graphene composite for precise and efficient assessment of food were also debated. This paper would maybe offer some inspired concepts for an upcoming study on MOF-based composites in the food security context.

Nanomaterial-Based Fluorescent Biosensor for Food Safety Analysis

Food safety issues have become a major threat to public health and have garnered considerable attention. Rapid and effective detection methods are crucial for ensuring food safety. Recently, nanostructured fluorescent materials have shown considerable potential for monitoring the quality and safety of food because of their fascinating optical characteristics at the nanoscale. In this review, we first introduce biomaterials and nanomaterials for food safety analysis. Subsequently, we perform a comprehensive analysis of food safety using fluorescent biosensors based on nanomaterials, including mycotoxins, heavy metals, antibiotics, pesticide residues, foodborne pathogens, and illegal additives. Finally, we provide new insights and discuss future approaches for the development of food safety detection, with the aim of improving fluorescence detection methods for the practical application of nanomaterials to ensure food safety and protect human health.

Enhanced adsorptional-photocatalytic degradation of chloramphenicol by reduced graphene oxide-zinc oxide nanocomposite

Improper discharge of waste dry cell batteries and untreated antibiotics laden effluents to the environment pose serious threat to the sustenance of the ecosystem. In this study, synthesis of reduced graphene oxide-ZnO (rGO-ZnO) nanocomposite was achieved via a bioreduction process using waste dry cell battery rod as graphene oxide (GO) precursor. The nanocomposite was applied in the ultraviolet photocatalytic degradation of chloramphenicol (CAP) at 290 nm in the presence of hydrogen peroxide. RGO-ZnO nanocomposite was characterized by SEM, TEM, XRD, BET and FTIR. TEM image of the nanocomposite revealed a polydispersed, quasi-spherical zinc oxide on a coarse reduced graphene oxide surface. XRD patterns showed sharp, prominent crystalline wurtzite hexagonal phases of ZnO and rGO. BET surface area of the nanocomposite was 722 m²/g with pore size of 2 nm and pore volume of 0.4 cc/g. % photo-removal efficiency increased with increasing irradiation time but diminished at higher pH, temperature and CAP concentration. Photocatalytic adsorption process fitted more accurately into the Freundlich model (R² = 0.99) indicating a multilayer adsorption mechanism. 92.74% reduction in chemical oxygen demand (COD) level of veterinary effluent was obtained after treatment with the nanocomposite thus affirming its effectiveness in real waste water samples.