A novel Nb2C MXene based aptasensor for rapid and sensitive multi-mode detection of AFB1

A multifunctional biosensor for linked monitoring of inflammation indicators in hypertension drug evaluation and companion diagnostics

Hypertension, often called the "silent killer", is a prevalent chronic disease closely linked to inflammation. However, most current methods monitor only single indicator, providing a limited view of inflammation in hypertension progression. To address this, we developed a multifunctional biosensor featuring a dual target linked monitoring (DTLM) Probe for the simultaneous detection of IL-6 and CRP, two key inflammatory markers in hypertension progression. The DTLM Probe, based on NH2-UiO-66@AuNPs with mutually non-interfering signal chains, was optimized for high performance in tracking both indicators simultaneously. The dual outputs operate independently, enabling IL-6 and CRP to be detected together or individually within a single sample injection. Under optimized conditions, the biosensor demonstrated excellent specificity and sensitivity, with detection limits of 355 fg/mL for IL-6 and 367 fg/mL for CRP. Applied to a rat model, the biosensor effectively explored the anti-inflammatory effects of Qishenyiqi, a traditional Chinese medicine, assessing its efficacy in reducing hypertensive heart damage. Additionally, it distinguished IL-6 and CRP levels between healthy and hypertensive individuals, capturing subtle changes after treatments. This ensured targeted anti-inflammatory therapies for patients who would benefit most. This biosensor provides a powerful and versatile platform for dual markers tracking, supporting both drug evaluation and companion diagnostics for tailor treatments in hypertension management.

Signal-on aptasensors on paper-based platform: Application of multilayer MXene nanoquencher and stabilized luminescent carbon dots

Antibiotics are emerging hazardous small molecules, requiring urgent need for fast signal-on analytical methods to control antibiotic abuse. Signal-on fluorescence sensing strategies utilizing nanoquenchers and aptamers are fascinating but rarely accomplished on paper-based platforms. Here, a novel multilayer MXene sensing platform was established by leveraging Nb2C-MXene as a multilayer nanoquencher and zero-dimensional carbon dots-labeled aptamer (B-CDs@Apt) as a stable and bright recognition probe. The Nb2C-MXene has a multilayer nanosheet stack-like structure and efficient mass transfer channels. It can efficiently adsorb abundant B-CDs@Apt probes and quench their fluorescence. Importantly, the Nb2C-MXene/B-CDs@Apt system can release the B-CDs@Apt in response to the analyte with high sensitivity, thereby restoring the fluorescent signal. The developed aptasensor achieved sensitive and selective detection of chloramphenicol (CAP) and showed satisfactory anti-interference ability, stability, and practicability. Notably, the multilayer Nb2C-MXene/B-CDs@Apt system was successfully transferred to a paper-based sensing platform, with a low-density distribution of multilayer nanoquenchers carrying sufficient aptamer probes for analyte access. In comparison, the monolayer Nb2C nanosheets were unable to adsorb enough probes to output analyte-induced signals. The established paper-based analytical device (PAD) showed a LOD of 0.360 ng mL-1 for CAP, which is the first paper-based MXene aptasensor reported for fluorescence detection. By replacing the aptamer and carbon dot, the strategy was further extended to detect another analyte oxytetracycline (OTC), with LODs of 0.399 in tube and 0.867 ng mL-1 on PAD, respectively. Furthermore, concurrent detection of CAP and OTC was achieved using a dual-color PAD, demonstrating the potential to meet multi-target analytical requirements.

Defective UIO66 metal-organic framework nanoparticles assisted by cascade isothermal amplification technology for the detection of aflatoxin B1

Aflatoxin B1 (AFB1) exhibits significant toxicity and pose a serious threat to food safety, environmental hygiene, and public health even in trace amounts. Hence, the development of a rapid, accurate, and sensitive detection technology has become a pivotal aspect of ensuring control standards. In this study, we introduce the UIO66 and two defective dichloroacetic acid@UIO66 (DCA@UIO66, DU) metal-organic framework nanoparticles, named DU1 and DU2, characterized by different defect levels. It is noteworthy that DU1 exhibits superior DNA sensing capability compared to UIO66 and DU2. With a fluorescence quenching efficiency of 92.66 % and a recovery efficiency of 1256.75 %, DU1 demonstrates the substantial potential in the detection field. Furthermore, we employ cascade isothermal amplification to assist DU1-mediated fluorescence sensors in detecting AFB1. AFB1 is efficiently identified through an aptamer competition process facilitated by magnetic nanoparticles, which initiates the exponential amplification triggered rolling circle amplification reaction, and converts trace amounts of toxin signal into a large number of long single-stranded DNA molecules. Upon recognition of the amplification product by the fluorescent probe on DU1, a more stable double-stranded DNA is formed and leaves the surface of DU1, leading to a significant change in fluorescence intensity. This method exhibits acceptable sensitivity, with a detection limit of 0.09 pg mL-1 and a wide detection range spanning from 0.2 pg mL-1 to 20 pg mL-1. Additionally, this assay exhibits satisfactory specificity and high accuracy in practical sample applications. Our proposed method offers a solid theoretical framework and technical backing, thereby facilitating the establishment of a new generation of mycotoxin detection standards.

Developing a Ni-grafted magnetic nanoparticle for direct CotA capture in rapid detoxification of aflatoxin B1

Aflatoxin B1 (AFB1) exposure often causes serious food safety problems and illnesses in humans and animals, even at extremely low content. Therefore, effective degradation of AFB1 is vitally significant. Biodegradation by enzymes is an effective method to eliminate hazardous toxins, but the degradation efficiency and cost of the enzyme limit its wide application. In this work, we found that CotA derived from Bacillus subtilis can rapidly degrade AFB1 into small molecules with low toxicity. Molecular docking analysis was used to evaluate the feasibility of rapid degradation of AFB1 by CotA, and the UPLC-Q-TOF-MS was used to deduce the degradation products and pathways. Two biotransformation pathways were proposed based on the structures of these degradation products. Inspired by commercial Ni-NTA purification media, Ni-grafted magnetic nanoparticles (PNMP) were designed to capture CotA from cell-lysis buffer onto the PNMP surface, enabling direct immobilization of CotA to form PNMP@CotA. The PNMP@CotA exhibits higher activity, good tolerance to temperature and pH than free CotA. Furthermore, in vitro and in vivo experiments revealed a significant reduction in the toxicity of AFB1 degradation products.

Supramolecular Coassembly Activated Dual-Excitation Fluorescent Sensing Platform for Precise Detection of Aflatoxin B1

The development of a sensory signal amplification approach is very crucial for rapid and precise detection of aflatoxin B1 (AFB1). However, such approaches remain scarce due to the weak interactions between AFB1 and the sensing probes. Herein, the first example of a dual-excitation fluorescent platform for antibody-free AFB1 detection is reported, which is assembled by an ordered π-π stack of cationic perylene derivative (PTHA) and tris(2,2'-bipyridine)ruthenium(II) [Ru(bpy3)2+]. Taking advantage of stepwise assembly and multiple binding sites of the nanoprobe, its ability for capturing AFB1 is significantly improved driven by multiple noncovalent interactions. Interestingly, dual-excitation fluorescent sensing mode with signal superposition and self-calibration is activated in the supramolecular coassembly process. Under excitation of 365 nm and 440 nm, the platform exhibits specific recognition toward AFB1 and the limit of detection is determined to be 0.12 ng mL-1. Notably, the dual-excitation platform demonstrates exceptional sensitivity enhancements of 106-fold, revealing that the self-calibrated reference improves the sensitivity and accuracy of analytical method significantly. The applications of our platform not only crack the problem of precise AFB1 detection via supramolecular coassembly strategy but also provide a universal sensitization strategy for ultrasensitive analysis in complex environments.

Enhancing resolution in DNA staining dye-based label-free visual fluorescence aptasensor: Strategy for eliminating non-specific binding-induced signal interference

By optimizing the quenching capabilities of diverse two-dimensional (2D) nanomaterials such as graphene oxide (GO), Ti3C2 MXene, and MoS2, we have pioneered a label-free fluorescence aptasensor with near-zero background signal, enabling highly sensitive detection of aflatoxin B1 (AFB1). This aptasensor was equipped with a newly synthesized dicationic fluorophore, VLM, which exhibited binding-induced turn-on fluorescence properties. Among the evaluated 2D nanosheets, MoS2 nanosheets were found to exhibit exceptional quenching efficiency for the background emission of the cDNA/VLM complex (cDNA was the complementary DNA of the aptamer), further enhancing the overall performance of our aptasensor. Upon exposure to AFB1, the aptamers underwent conformational switching and target binding, leading to the formation of aptamer/AFB1 complex. Additionally, the aptamers bound complementarily to cDNA, creating aptamer-cDNA duplexes that interacted with VLM, resulting in a robust fluorescence signal. Despite the presence of a weakly fluorescent cDNA/VLM background, this fluorescence could be effectively quenched by the addition of MoS2 nanosheets. Consequently, the label-free fluorescence aptasensor exhibited excellent linearity with AFB1 concentration within 2-3000 ng mL-1, achieving a limit of detection (LOD) of 0.006 ng mL-1. Remarkably, the visual fluorescence captured by a smartphone camera can be processed using extracted grayscale values, consistently revealing a linear relationship with the AFB1 concentration within 2-3000 ng mL-1, with a LOD of 0.197 ng mL-1. This aptasensor demonstrated exceptional sensitivity and a remarkably rapid sample-to-answer detection time of 74 min, showcasing its immense potential as a straightforward, sensitive, and visually intuitive method for rapid AFB1 detection with enhanced resolution.

Competitive Electrochemical Apta-Assay Based on cDNA-Ferrocene and MXenes for Staphylococcus aureus Surface Protein A Detection

Staphylococcus aureus (S. aureus) represents one of the most frequent worldwide causes of morbidity and mortality due to an infectious agent. It is a part of the infamous ESKAPE group, which is highly connected with increased rates of healthcare-associated infections and antimicrobial resistance. S. aureus can cause a large variety of diseases. Protein A (PrA) is a cell-wall-anchored protein of S. aureus with multiple key roles in colonization and pathogenesis and can be considered as a marker of S. aureus. The development of aptasensors, having an aptamer as a specific biorecognition element, increases selectivity, especially when working with complex matrices. The association with state-of-the-art materials, such as MXenes, can further improve the analytical performance. A competitive aptasensor configuration based on a ferrocene (Fc)-labeled cDNA hybridized (cDNA-Fc S13) on a specific aptamer (APT) for PrA in the presence of MXene nanosheets was designed for the indirect detection of S. aureus. The aptasensor displayed a linear range of 10-125 nM, an LOD of 3.33 nM, and a response time under 40 min. This configuration has been tested in real samples from volunteers diagnosed with S. aureus infections with satisfactory results, enabling the perspective to develop decentralized devices for the rapid detection of bacterial strains.

Fluorescence/colorimetric sensor based on aptamers-molecular imprinted polymers synergistic recognition for ultrasensitive and interference-free detection of aflatoxin B1

This work aimed to develop a fluorescence/colorimetric sensor for the ultrasensitive detection of AFB1 based on the aptamers and molecular imprinted polymers (MIPs). The polydopamine on Fe3O4 (Fe3O4@MIP) was used to achieve efficient separation of AFB1. The aptamer-modified carbon dots and metal-organic frameworks (Apt-CDs@MOF) were used to form sandwich particles (Fe3O4@MIP-AFB1-Apt-CDs@MOF). The sandwich particles were separated and removed using magnets, and the remaining Apt-CDs@MOF in suspension was used for both fluorescence and colorimetric detection. The sensor reached the linear range of 0.05-150 ng mL-1 (fluorescence channel) and 0.1-100 ng mL-1 (colorimetric channel). The detection limit can be as low as 37.0 pg mL-1 (fluorescence channel) and 13.0 pg mL-1 (colorimetric channel). Through the clever use of sandwich structure, the sensor represents a novel method for interference-free detection of AFB1. The proposed sensor effectiveness was further validated by quantifying AFB1 in untreated edible oil, which shows great potential for application.

The potential of MXene-based materials in fluorescence-based sensing/biosensing of ionic and organic contaminants in environment and food samples: Recent advancements and challenges

MXenes belong to one of the recently developed advanced materials with tremendous potential for diverse sensing applications. To date, various types of MXene-based materials have been developed to generate direct/indirect ultrasensitive sensing signals against various forms of analytes via fluorescence quenching or enhancement. In this work, the fluorescence sensing/biosensing capabilities of the MXene-based materials have been explored and evaluated against a list of ionic/emerging pollutants in environment and food matrices. The suitability of an MXene-based sensing approach is also validated through the assessment of the performance based on the basic quality assurance parameters, e.g., limit of detection (LOD), sensing range, and response time. Accordingly, the best performing MXene-based materials are selected and recommended for the given target(s) to help facilitate their scalable applications under real-world conditions.

Reproducible, Accurate, and Sensitive Food Toxin On-Site Detection with Carbon Nanotube Transistor Biosensors

Field-effect transistor (FET) biosensors based on nanomaterials are promising in the areas of food safety and early disease diagnosis due to their ultrahigh sensitivity and rapid response. However, most academically developed FET biosensors lack real-world reproducibility and comprehensive methodological validation to meet the standards of regulatory bodies. Here, highly uniform and well-packaged semiconducting carbon nanotube (CNT) FET biosensor chips were developed and assessed for the plug-and-play sensing for the rapid and highly sensitive detection of aflatoxin B1 (AFB1) in real food samples to meet international standards. In order to meet the requirements for reproducibility and stability, a scalable residual-free passivation and packaging process was developed for CNT FET biosensors. Portable detection systems were then constructed for on-site detection. The resulting packaged chips were functionalized with nucleic aptamers to enable highly selective detection of AFB1 in food samples with a detection limit (LOD) of 0.55 fg/mL (standard) for AFB1 and cross-reactivity coefficients to interferences as low as 1.8 × 10-7 in simulated solutions. Utilizing the portable detection system, on-site real food detection was achieved with a rapid response time less than 60 s, and LOD of 0.25 pg/kg (standard) in complex corn sample matrices. Single-blind tests demonstrated the ability of the chips to detect AFB1-positive food with 100% accuracy, using a set of 30 peanut samples. Validation experiments confirmed that the detection range, stability, and repeatability met international standards. This study showcased the accuracy, reliability, and potential practical applications of CNT FET biosensor chips in areas such as food safety and rapid biomedical testing.

Decentralized food safety and authentication on cellulose paper-based analytical platform: A review

Food safety and authenticity analysis play a pivotal role in guaranteeing food quality, safeguarding public health, and upholding consumer trust. In recent years, significant social progress has presented fresh challenges in the realm of food analysis, underscoring the imperative requirement to devise innovative and expedient approaches for conducting on-site assessments. Consequently, cellulose paper-based devices (PADs) have come into the spotlight due to their characteristics of microchannels and inherent capillary action. This review summarizes the recent advances in cellulose PADs in various food products, comprising various fabrication strategies, detection methods such as mass spectrometry and multi-mode detection, sampling and processing considerations, as well as applications in screening food safety factors and assessing food authenticity developed in the past 3 years. According to the above studies, cellulose PADs face challenges such as limited sample processing, inadequate multiplexing capabilities, and the requirement for workflow integration, while emerging innovations, comprising the use of simplified sample pretreatment techniques, the integration of advanced nanomaterials, and advanced instruments such as portable mass spectrometer and the innovation of multimodal detection methods, offer potential solutions and are highlighted as promising directions. This review underscores the significant potential of cellulose PADs in facilitating decentralized, cost-effective, and simplified testing methodologies to maintain food safety standards. With the progression of interdisciplinary research, cellulose PADs are expected to become essential platforms for on-site food safety and authentication analysis, thereby significantly enhancing global food safety for consumers.

DNA-functionalized cryogel based colorimetric biosensor for sensitive on-site detection of aflatoxin B1 in food samples

Hydrogel biosensors present numerous advantages in food safety analysis owing to their remarkable biocompatibility, cargo-loading capabilities and optical properties. However, the current drawbacks (slow target responsiveness and poor mechanical strength) restricted their further utilization at on-site detection of targets. To address these challenges, a DNA-functionalized cryogel with hierarchical pore structures is constructed to improve the reaction rate and the robustness of hydrogel biosensor. During cryogel preparation, ice crystals serve as templates, shaping interconnected hierarchical microporous structures to enhance mass transfer for faster responses. Meanwhile, in the non-freezing zone, concentrated monomers create a dense cross-linked network, strengthening cryogel matrix strength. Accordingly, a colorimetric biosensor based on DNA cryogel has been developed as a proof of concept for rapid detection of aflatoxin B1 (AFB1) in food samples, and an excellent analytical performance was obtained under the optimized conditions with a low detection limit (1 nM), broad detection range (5-100 nM), satisfactory accuracy and precision (recoveries, 81.2-112.6 %; CV, 2.75-5.53 %). Furthermore, by integrating with a smartphone sensing platform, a portable device was created for rapid on-site measurement of target within 45 min, which provided some insight for hydrogel biosensors design.

Fluorescence/visual aptasensor based on Au/MOF nanocomposite for accurate and convenient aflatoxin B1 detection

A dual-mode fluorescence/visual aptasensor was developed for straightforward and accurate determination of aflatoxin B1 (AFB1) based on an Au/metal-organic framework (Au/MOF) composite. Aptamer-modified Au/Fe3O4 (Apt/Au/Fe3O4) served as the recognition element, and Au/MOF modified with complementary chains and 3,3',5,5'-tetramethylbenzidine (cDNA/TMB/Au/MOF) acted as the fluorescence and visual probes. These components are integrated to form conjugates (Apt/Au/Fe3O4-cDNA/TMB/Au/MOF). Upon the introduction of AFB1, some cDNA/TMB/Au/MOF dissociated from Apt/Au/Fe3O4, enabling the use of detached probes for visual detection. The undecomposed conjugates were isolated magnetically for use in fluorescence detection. As the AFB1 concentration increases, the visual signal intensifies and fluorescence intensity diminishes. Thus, the proposed aptasensor achieves the simultaneous fluorescence and visual determination of AFB1, obviating the need for material and reagent substitutions. The detection limits were established at 0.07 ng mL-1 for the fluorescence mode and 0.08 ng mL-1 for the visual mode. The effectiveness of the aptasensor was further validated by quantifying AFB1 in real samples.

Multi-MXene assisted large-scale manufacturing of electrochemical biosensors based on enzyme-nanoflower enhanced electrodes for the detection of H2O2 secreted from live cancer cells

In situ monitoring of H2O2 in cellular microenvironments plays a critical role in the early diagnosis and pretreatment of cancer, but is limited by the lack of efficient and low-cost strategies for the large-scale preparation of real-time biosensors. Herein, a universal strategy for MXene-based composite inks combined with a scalable screen-printing process is validated in large-scale manufacturing of electrochemical biosensors for in situ detection of H2O2 secreted from live cells. Compositing biocompatible carboxymethyl cellulose (CMCS) with excellent conductive MXene, a water-based ink electrode (MXene/CMCS) with tunable viscosity is efficiently printed with desirable printing accuracy. Subsequently, the MXene/CMCS@HRP electrochemical biosensor exhibits stable electrochemical performance through HRP nanoflower modification, showing rapid electron transport and high electrocatalytic capacity, and demonstrating a low limit of detection (0.29 μM) with a wide linear detection range (0.5 μM-3 mM), superior sensitivity (56.45 μA mM-1 cm-2), long-term stability and high anti-interference ability. Moreover, this electrochemical biosensor is effectively employed for in situ detection of H2O2 secreted from HeLa cells, revealing good biocompatibility and outstanding biosensing capability. This proposed strategy not only extends the possibility of low-cost biomedical devices, but also provides a promising approach for early diagnosis and treatment of cancer.

A dual-signal aptasensor based on cascade amplification for ultrasensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is considered as a serious carcinogenic mycotoxin that was widely detected in grains and foods, and its sensitive analysis is of key importance to avoid the health threats for consumers. In this study, a dual-signal aptasensor based on cascade of entropy-driven strand displacement reaction (ESDR) and linear rolling circle amplification (LRCA) was fabricated for ultrasensitive determination of AFB1. At the sensing system, the complementary strand would be released after the aptamer combined with AFB1, which will bring about the functional domains exposed, triggering the subsequent ESDR. Meanwhile, the two strands that were outputted by ESDR would incur the downstream LRCA reaction to produce a pair of long strands to assist in the generation of fluorescence and absorbance signals. Under the optimized conditions, the proposed aptasensor could achieve excellent sensitivity (limit of detection, 0.427 pg/mL) with satisfactory accuracy (recoveries, 92.8-107.9 %; RSD, 2.4-5.0 %), mainly ascribed to the cascade amplification. Importantly, owing to the flexibility design of nucleic acid primer, this analytical method can be applied in monitoring various hazardous substances according to the specific requirements. Our strategy provides some novel insights at signal amplification for rapid detection of AFB1 and other targets.