CRISPR-Cas systems mediated biosensing and applications in food safety detection

A pH-responsive dual-emission composite for fast detection of BAs and visual monitoring seafood freshness with large luminescence color difference

Sensing biogenic amine (BAs) content is very important for assessing food freshness. To address the limitations such as small color difference values (ΔE) and complex preparation of probes for visualizing the freshness of seafood, a pH-responsive ratiometric fluorescent probe (EnEB) was prepared by Eu(NO3)3, trimeric acid (BTC), and hydrochloric acid norepinephrine (Enr). EnEB emitted blue (446 nm) and red fluorescence (616 nm) originating from Enr and Eu3+, respectively, and exhibiting a fluorescence wavelength difference up to 170 nm. The ratiometric fluorescent signals of EnEB showed a linear correlation with pH in the range of 5.5-8.0. Thus, EnEB can rapidly and precisely detect BAs, such as histamine, tyramine, and spermine, with detection limits and response times of 1.14 μmol/L (3 s), 1.04 μmol/L (8 s), and 0.41 μmol/L (2 s), respectively. Furthermore, an EnEB aerogel was prepared by loading EnEB in a matrix formed by polyvinyl alcohol (PVA) and agarose (AG). EnEB aerogel exhibited excellent acid-base gas-sensing properties. The fluorescence color of EnEB aerogel can change significantly with the deterioration of seafood. When seafood changed from fresh to decayed, the ΔE value of EnEB aerogel was as high as 80.9. Importantly, the results of seafood freshness by naked eye using EnEB aerogel was consistent well with the TVB-N content and the freshness standard stipulated by national food standard, indicating EnEB aerogel can accurately visually and real-time monitor seafood freshness. Furthermore, the strategy for sensing food freshness based on EnEB aerogel also offered multiple color variations to indicate fine freshness levels of seafood. This work provided a convenient, efficient, and accurate approach to assessing the freshness of seafood. Additionally, EnEB also has promising applications in security and anti-counterfeiting.

A CRISPR/Cas12a-based direct transverse relaxation time biosensor via hydrogel sol-gel transition for Salmonella detection

This research developed a magnetic relaxation switching (MRS) biosensor based on hydrogel sol-gel transition and the CRISPR/Cas12a system (MRS-CRISPR) to detect Salmonella. Herein, the alkaline phosphatase (ALP) labeled with streptavidin was captured by the biotin-modified DNA on magnetic nanoparticles (MNPs) surface, which generated an acidic environment via enzymatic reaction to release Ca2+ and induced the transformation of alginate sol to hydrogels. In contrast, Salmonella activated the trans-cleavage activity of the CRISPR/Cas12a system, interrupting the capture of ALP and the subsequent sol-gel transition. Then, transverse relaxation time (T2), which was regulated by the hydrogelation process was measured for Salmonella detection. The MRS-CRISPR biosensor enables sensitive detection of Salmonella with a detection limit of 158 CFU/mL. It directly alters the state of water molecules, overcoming the disadvantages of traditional MRS sensors that rely on MNPs to produce T2 signals indirectly. This method offers innovative insights for the application of the MRS technology in food safety analysis.

Machine Learning-Assisted, Dual-Channel CRISPR/Cas12a Biosensor-In-Microdroplet for Amplification-Free Nucleic Acid Detection for Food Authenticity Testing

The development of novel detection technology for meat species authenticity is imperative. Here, we developed a machine learning-supported, dual-channel biosensor-in-microdroplet platform for meat species authenticity detection named CC-drop (CRISPR/Cas12a digital single-molecule microdroplet biosensor). This strategy allowed us to quickly identify and analyze animal-derived components in foods. This biosensor was enabled by CRISPR/Cas12a-based fluorescence lighting-up detection, and the nucleic acid signals can be recognized by a Cas12a-crRNA binary complex to trigger the trans-cleavage of any by-stander reporter single-stranded (ss) DNA, in which nucleic acid signals can be converted and amplified to fluorescent readouts. The ultralocalized microdroplet reactor was constructed by reducing the reaction volume from up to picoliter to accommodate the aforementioned reaction to further enhance the sensitivity to even render an amplification-free nucleic acid detection. Moreover, we established a smartphone App coupled with a random forest machine learning model based on parameters such as area, fluorescent intensity, and counting number to ensure the accuracy of image recording and processing. The sample-to-result time was within 80 min. Importantly, the proposed biosensor was able to accurately detect the ND1 (pork-specific) and IL-2 (duck-specific) genes in deep processed meat-derived foods that usually had truncated DNA, and the results were more robust and practical than conventional real-time polymerase chain reaction after a side-by-side comparison. All in all, the proposed biosensor can be expected to be used for rapid food authenticity and other nucleic acid detections in the future.

Recent advances of food safety detection by nucleic acid isothermal amplification integrated with CRISPR/Cas

Food safety problems have become one of the most important public health issues worldwide. Therefore, the development of rapid, effective and robust detection is of great importance. Amongst a range of methods, nucleic acid isothermal amplification (NAIA) plays a great role in food safety detection. However, the widespread application remains limited due to a few shortcomings. CRISPR/Cas system has emerged as a powerful tool in nucleic acid detection, which could be readily integrated with NAIA to improve the detection sensitivity, specificity, adaptability versatility and dependability. However, currently there was a lack of a comprehensive summary regarding the integration of NAIA and CRISPR/Cas in the field of food safety detection. In this review, the recent advances in food safety detection based on CRISPR/Cas-integrated NAIA were comprehensively reviewed. To begin with, the development of NAIA was summarized. Then, the types and working principles of CRISPR/Cas were introduced. The applications of the integration of NAIA and CRISPR/Cas for food safety were mainly introduced and objectively discussed. Lastly, current challenges and future opportunities were proposed. In summary, this technology is expected to become an important approach for food safety detection, leading to a safer and more reliable food industry.

Cu(II)-induced magnetic resonance tuning and enhanced magnetic relaxation switching immunosensor for sensitive detection of chlorpyrifos and Salmonella

Magnetic relaxation switching (MRS) biosensors have been recognized as useful analytical tools for a range of targets; however, traditional MRS biosensors are limited by the "prozone effect", resulting in a narrow linear range and low sensitivity. Herein, we proposed a paramagnetic Cu2+-induced magnetic resonance tuning (MRET) strategy, based on which Cu2+ ions and magnetic nanoparticles (MNPs) were adopted to construct a Cu-MNP-mediated MRS (Cu-M-MRS) immunosensor with Cu2+ ions acting as a quencher and MNPs as an enhancer. An Fe3O4@polydopamine-secondary antibody conjugate was prepared and used to correlate the amount of Cu2+ ions to the target concentration through an immunoassay. Based on the immunoreaction, the Cu-M-MRS immunosensor enabled the sensitive detection of chlorpyrifos (0.05 ng/mL, a 77-fold enhancement in sensitivity compared with the traditional MRS immunosensor) and Salmonella (50 CFU/mL). The proposed MRET strategy effectively improved the sensitivity and accuracy of the MRS immunosensor, offering a promising and versatile platform for food safety detection.

Hydrogel-integrated sensors for food safety and quality monitoring: Fabrication strategies and emerging applications

Food safety is a global issue in public hygiene. The accurate, sensitive, and on-site detection of various food contaminants performs significant implications. However, traditional methods suffer from the time-consuming and professional operation, restricting their on-site application. Hydrogels with the merits of highly porous structure, high biocompatibility, good shape-adaptability, and stimuli-responsiveness offer a promising biomaterial to design sensors for ensuring food safety. This review describes the emerging applications of hydrogel-based sensors in food safety inspection in recent years. In particular, this study elaborates on their fabrication strategies and unique sensing mechanisms depending on whether the hydrogel is stimuli-responsive or not. Stimuli-responsive hydrogels can be integrated with various functional ligands for sensitive and convenient detection via signal amplification and transduction; while non-stimuli-responsive hydrogels are mainly used as solid-state encapsulating carriers for signal probe, nanomaterial, or cell and as conductive media. In addition, their existing challenges, future perspectives, and application prospects are discussed. These practices greatly enrich the application scenarios and improve the detection performance of hydrogel-based sensors in food safety detection.

Recent advances in nucleic acid signal amplification-based aptasensors for sensing mycotoxins

Mycotoxin contamination in food products may cause serious health hazards and economic losses. The effective control and accurate detection of mycotoxins have become a global concern. Even though a variety of methods have been developed for mycotoxin detection, most conventional methods suffer from complicated operation procedures, low sensitivity, high cost, and long assay time. Therefore, the development of simple and sensitive methods for mycotoxin assay is highly needed. The introduction of nucleic acid signal amplification technology (NASAT) into aptasensors significantly improves the sensitivity and facilitates the detection of mycotoxins. Herein, we give a comprehensive review of the recent advances in NASAT-based aptasensors for assaying mycotoxins and summarize the principles, features, and applications of NASAT-based aptasensors. Moreover, we highlight the challenges and prospects in the field, including the simultaneous detection of multiple mycotoxins and the development of portable devices for field detection.

A Multichannel Fluorescence Isothermal Amplification Device with Integrated Internet of Medical Things for Rapid Sensing of Pathogens through Deep Learning

The landscape of diagnostic assessments has experienced a paradigm shift driven by the advent of isothermal amplification techniques on point-of-care testing (POCT). The development of compact, portable isothermal amplification devices further emphasizes their transformative influence on diagnostic approaches. However, in prioritizing portability, these devices may exhibit limitations in functionality, rendering them less effective in addressing urgent public health emergencies during sudden pathogen outbreaks. In this paper, an efficient isothermal fluorescence amplification device has been fabricated for the rapid detection of pathogens during public health crises. The device features multichannel capability for simultaneous detection of various targets, integrates with the Internet of Medical Things (IoMT) for remote control and data uploading, and includes a deep learning-based batch processing system for rapid (9.4 ms) and accurate discrimination of pathogen type with excellent accuracy. The device has been successfully employed to simultaneously detect Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) with limits of detection (LODs) of 18 CFU/mL (SA) and 20 CFU/mL (MRSA) within 35 min by multiplex RPA assay and CRISPR/Cas12a-mediated nucleic acid detection assay.

CRISPR/Cas System: The Accelerator for the Development of Non-nucleic Acid Target Detection in Food Safety

Non-nucleic acid targets have posed a serious challenge to food safety. The detection of non-nucleic acid targets can enable us to monitor food contamination in a timely manner. In recent years, the CRISPR/Cas system has been extensively explored in biosensing. However, there is a lack of a summary of CRISPR/Cas-powered detection tailored to non-nucleic acid targets involved in food safety. This review comprehensively summarizes the recent advances on the construction of CRISPR/Cas-powered detection and the promising applications in the field of food safety related non-nucleic acid targets. The current challenges and futuristic perspectives are also proposed accordingly. The rapidly evolving CRISPR/Cas system has provided a powerful propellant for non-nucleic acid target detection via integration with aptamer and/or DNAzyme. Compared with traditional analytical methods, CRISPR/Cas-powered detection is conceptually novel, essentially eliminates the dependence on large instruments, and also demonstrates the capability for rapid, accurate, sensitive, and on-site testing.