A novel multimode biosensor for sensitive detection of AFB1 in food based on Mxenes nano enzymes

Interactions of metal-based nanozymes with aptamers, from the design of nanozyme to its application in aptasensor: Advances and perspectives

Nanozymes, characterized by enzyme-like activity, have been extensively used in quantitative analysis and rapid detection due to their small size, batch fabrication, and ease of modification. Researchers have combined aptamers, an emerging molecular probe, with nanozymes for biosensing to address the limited reaction specificity of nanozymes. Nanozyme aptasensors are currently experiencing significant growth, offering a promising solution to the lack of rapid detection methods across various fields. Unlike traditional nanozyme research, the development of nanozyme aptasensors is challenging as it requires the design of highly active nanozymes as well as the establishment of efficient and agile interactions between aptamers and nanozymes. Therefore, this review summarizes the active species and catalytic mechanisms of various nanozymes along with classical design options, discussing the future development of nanozyme aptasensors. It is anticipated that this review will inspire researchers in this domain, leading to the design of more enzymatically active nanozymes and advanced nanozyme aptasensors.

Immobilization of a novel bacteriophage PpZDSS02 onto the peroxidase-mimicking Cu-MOF for colorimetric sensing of Proteus penneri encompassing both promotion and inhibition mechanisms

A chromogenic system utilizing a novel bacteriophage-integrated nanozyme was established for Proteus penneri detection. Initially, a novel bacteriophage PpZDSS02 was isolated and identified, demonstrating exceptional biological properties and harboring genes that exhibit specific recognition ability. Afterwards, a PpZDSS02-integrated Cu-MOF nanozyme (Cu-MOF@PpZDSS02) with peroxidase-mimicking activity was prepared, catalyzing 3, 3', 5, 5'-tetramethylbenzidine (TMB) chromogenic reaction. Its peroxidase-mimicking activity can be modulated by P. penneri. Interestingly, low concentration of P. penneri can enhance its activity and high concentration of P. penneri inhibits its activity. Based on it, a visual quantification method with high sensitivity and specificity for P. penneri was achieved, offering a low limit of detection (3.3 CFU·mL-1). Moreover, Cu-MOF@PpZDSS02-based chromogenic system shows exceptional performance in the detection of authentic food samples, achieving ideal recoveries (89.00 % ∼ 111.81 %). These results indicate the potential application of Cu-MOF@PpZDSS02-based chromogenic system for colorimetric detection of P. penneri.

Aptamer-modulated Pt/Au/MIL-100(Fe) nanozymatic activity for the colorimetric detection of deoxynivalenol in grains

In this study, Pt/Au nanoparticles functionalized metal-organic frameworks (Pt/Au/MIL-100(Fe)) nanocomposite was employed as a nanozyme and a colorimetric aptasensor based on aptamer-modulated nanozymatic activity was developed for deoxynivalenol (DON) detection. The catalytic activity of Pt/Au/MIL-100(Fe) was initially inhibited by aptamers due to the blocking of surface-active sites. However, the presence of DON detached the aptamer from Pt/Au/MIL-100(Fe) surface, restoring the enzyme-mimicking activity of the nanocomposites and producing a measurable colorimetric signal for DON quantitation. The nanozyme showed stable catalytic activities with a relative standard deviation within 3 % for storage at 4 °C for 21 days. Meanwhile, the developed aptasensor demonstrated a good linear range of 50-5000 ng/mL with a limit of detection of 44.14 ng/mL. The recovery rates for detecting DON in positive wheat and maize flour samples were 98.59 %-106.27 %. The developed method is cost-effective and easy to fabricate, providing a powerful tool for DON detection in food.

Detection of Aflatoxin B1 in Wheat Based on Nucleic Aptamer Chemiluminescence Sensor

In this study, we developed a low-cost, high-sensitivity chemiluminescence competitive aptamer sensor for the detection of aflatoxin B1 (AFB1) in wheat samples. The optical fiber sensor was self-made, and it utilized biotin and streptavidin (SA) link aptamer and horseradish peroxidase (HRP) for the chemiluminescence detection, achieving competitive assay between the AFB1 and AFB1 antigen. We adjusted the experimental conditions of the sensor base on the date of optimization of the experimental conditions and chose coated antigens on the surface of carboxyl magnetic particles. Under conditions optimized by testing key parameters, the assay results showed that the chemiluminescence intensity and AFB1 concentration demonstrated a strong linear relationship (R2 = 0.995), the dynamic range was from 0.1 to 10 ng/mL with a detection limit of 0.09 ng/mL, and the aptamer exhibited good specificity and anti-interference ability. Testing the wheat samples showed that the spiked recovery rate ranged from 79.19% to 113.21%. The sensor possesses characteristics of low detection limits, simple manufacturing methods, and affordability, providing a novel solution for the development of low-cost and high-sensitivity AFB1 detection equipment.

A novel four-modal nano-sensor based on two-dimensional Mxenes and fully connected artificial neural networks for the highly sensitive and rapid detection of ochratoxin A

Timely and accurate on-site detection of ochratoxin A (OTA) is extremely important for global public health. In this study, a fluorescence/colorimetric biosensor based on Ti3C2 nano-materials (Ti3C2-NMS) and a machine-learning (ML) based fluorescence/colorimetric intelligent learning system for detection of OTA concentration (COTA) were developed. The sensor was fabricated by functionalizing Ti3C2-NMS prepared by physical-exfoliation assisted metal-ion-induction using ssDNA. The Ti3C2-NMS exhibited good fluorescence quenching characteristics (FQC) and peroxidase-like activity (PLA). More surprisingly, the functionalization of Ti3C2-NMS by ssDNA further enhanced the FQC and PLA of the material, which could be used for dual-mode detection of OTA. When different COTA existed, ssDNA competitively bound to OTA, resulting in regular changes in fluorescence and colorimetric signals of the sensor, which realized the accurate and sensitive biosensing detection of OTA in two modalities. Based on a series of fluorescent/colorimetric RGB datasets collected by a self-developed application, a dual-channel ML model had been developed. This model can be integrated into mobile phones, clouds, and PCs to achieve intelligent sensing detection of OTA with the assistance of fully connected artificial neural networks. The method constructed had high specificity, low cost, and fast responsiveness, with a LOD as low as 1.58 pg mL-1, indicating excellent potential for application and promotion.

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.

Portable sensing of hydrogen peroxide using MOF-based nanozymes

Hydrogen peroxide (H2O2) is extensively used in water treatment and food preservation for its pathogen-killing efficacy. Excessive H2O2 intake, however, can lead to poisoning with symptoms such as abdominal pain and breathing difficulties. Additionally, small amounts of H2O2 may be generated during food preservation, necessitating careful control to meet safety regulations. Real-time detection of H2O2 is crucial for process safety and compliance. In this study, a Zr-MOF-based colorimetric fluorescent nanozyme sensor (NH2-UiO-67(Zr/Cu)) along with a smartphone-assisted portable device were developed for detecting H2O2. The sensor, NH2-UiO-67(Zr/Cu), combines the stable structural properties of Zr-MOF with ligand-generated fluorescence and exhibits peroxidase-like activity. The sensor demonstrated a detection range of 0-1000 μM, with limits of detection (LOD) of 0.0057 μM for the colorimetric assay and 0.0020 μM for the fluorescence assay. Additionally, we designed and developed a portable, smartphone-assisted device using 3D printing technology. This device offers a detection range of 0-750 μM, with LODs of 0.0093 μM in colorimetric mode and 0.0311 μM in fluorescence mode. The developed colorimetric fluorescent nanozyme sensor and portable device show significant potential for the rapid on-site detection of H2O2, offering a more convenient and reliable approach for quick identification of analytes in practical applications.

Au@Pt@Pd nanozymes based lateral flow immunoassay for quantitative detection of SARS-CoV-2 nucleocapsid protein in nasal swab samples

Three-metal-core-shell nanoparticles (Au@Pt@PdNPs) providing excellent peroxidase-like activity were applied in lateral flow immunoassay (LFIA), designated as Au@Pt@Pd-LFIA, for detecting the nucleocapsid protein (NP) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). An Au@Pt@Pd-LFIA was developed for quantitatively testing of SARS-CoV-2 NP with a range 0.12-31.25 ng/mL. The limit of detection (LOD) of Au@Pt@Pd-LFIA strip was 0.06 ng/mL, which was 16-fold or eightfold more sensitive than that of the gold lateral flow immunoassay (Au-LFIA) and the gold flower flow immunoassay (AF-LFIA) strips, respectively. For detection of clinical samples from nasal swabs using test strips, Au@Pt@Pd-LFIA had 84.09% sensitivity, 100% specificity, and 92.55% accuracy. In terms of detection time, the testing of Au@Pt@Pd-LFIA strip was 16 min similar to Au-LFIA (15 min) and AF-LFIA (10 min), but much shorter than ELISA (2 h). In conclusion, Au@Pt@Pd-LFIA is a sensitive, rapid, and simple test for quantitative detection of SARS-CoV-2 NP in nasal swab samples.

Propelling gold nanozymes: catalytic activity and biosensing applications

Recently, gold nanomaterials have been rapidly developed owing to their high stability, good biocompatibility, and multifunctionality. The unique catalytic activity of gold nanomaterials has driven the emergence of the concept for a "gold nanozyme." Understanding the characteristics of gold nanozymes is crucial for improving their catalytic performance as well as expanding their applications. In this review, we provide an overview of the intrinsic enzyme-like activities of gold nanozymes, including peroxidase-, catalase-, superoxide dismutase-, and glucose oxidase-like activities, and the catalytic mechanisms involved. In addition, strategies for modulating the catalytic activity of gold nanozymes and their applications in biosensing were discussed in detail. Moreover, we highlight the current challenges of gold nanozymes and look forward to attracting more attention for propelling the developments in this field.

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.

Virtual Screening and Validation of Affinity DNA Functional Ligands for IgG Fc Segment

The effective attachment of antibodies to the immune sensing interface is a crucial factor that determines the detection performance of immunosensors. Therefore, this study aims to investigate a novel antibody immobilization material with low molecular weight, high stability, and excellent directional immobilization effect. In this study, we employed molecular docking technology based on the ZDOCK algorithm to virtually screen DNA functional ligands (DNAFL) for the Fc segment of antibodies. Through a comprehensive analysis of the key binding sites and contact propensities at the interface between DNAFL and IgG antibody, we have gained valuable insights into the affinity relationship, as well as the principles governing amino acid and nucleotide interactions at this interface. Furthermore, molecular affinity experiments and competitive binding experiments were conducted to validate both the binding ability of DNAFL to IgG antibody and its actual binding site. Through affinity experiments using multi-base sequences, we identified bases that significantly influence antibody-DNAFL binding and successfully obtained DNAFL with an enhanced affinity towards the IgG Fc segment. These findings provide a theoretical foundation for the targeted design of higher-affinity DNAFLs while also presenting a new technical approach for immunosensor preparation with potential applications in biodetection.

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.

Immunochromatographic Strip Based on Tetrahedral DNA Immunoprobe for the Detection of Aflatoxin B1 in Rice Bran Oil

Aflatoxin B1 (AFB1), a widespread contaminant in food and feeds, poses a threat to the health of animals and humans. Consequently, it is significant to develop a rapid, precise and highly sensitive analytical method for the detection of AFB1. Herein, we developed an immunochromatographic strip (ICS) based on a tetrahedral DNA (TDN) immunoprobe for AFB1 determination in rice bran oil. Three sizes of TDN immunoprobes (AuNP-TDN13bp-mAb, AuNP-TDN17bp-mAb, AuNP-TDN26bp-mAb) were constructed, and the performance of these three immunoprobes, including the effective antibody labeling density and immunoaffinity, was measured and compared with that of the immunoprobe (AuNP-mAb) developed using the physical adsorption method. Subsequently, the optimal TDN immunoprobe, namely AuNP-TDN13bp-mAb, was selected to prepare the immunochromatographic strip (ICS) for the qualitative and quantitative detection of AFB1 in rice bran oil. The visual limits of detection (vLODs) of the ICS based on AuNP-TDN13bp-mAb and AuNP-mAb were 0.2 ng/mL and 2 ng/mL, with scanning quantitative limits (sLOQs) of 0.13 ng/mL and 1.4 ng/mL, respectively. The ICS demonstrated a wide linear range from 0.02 ng/mL to 0.5 ng/mL, with good specificity, accuracy, precision, repeatability, and stability. Moreover, a high consistency was observed between the constructed ICS and ultra-high-performance liquid chromatography (UPLC) in the quantification of AFB1. The results indicated that the introduction of TDN was beneficial for promoting efficient antibody labeling, protecting the bioactivity of immunoprobes, and increasing the sensitivity of detection, which would provide new perspectives for the achievement of the highly sensitive detection of mycotoxins.

Highly sensitive detection of aflatoxin B1 byCRISPR/Cas12a-assisted single nanoparticle counting

CRISPR (clustered regularly interspaced short palindromic repeats) and CRISPR-associated protein (Cas) have gained extensive applications in bioassays. However, CRISPR-based detection platforms are often hampered by limited analytical sensitivity, while nucleic acid-based amplification strategies are usually indispensable for additional signal enhancement with potential risks of amplification leakages. To address these challenges, an amplification-free CRISPR-based bioassay of aflatoxin B1 (AFB1) was proposed by applying single nanoparticle counting. Single-particle mode inductively coupled plasma mass spectrometry (Sp-ICPMS) has been regarded as a sensitive tool for nanoparticle counting since one nanoparticle can generate considerable signals above backgrounds. With AFB1, activator strands were introduced to initiate the trans-cleavage of CRISPR/Cas12a for cutting the nanoparticles-tagged-magnetic beads, which were transduced to nanoparticle count signals after separation. Finally, a pico-mole level limit-of-detections (LODs) with moderate selectivity was achieved. Certified reference materials (CRMs) analysis and recovery tests were conducted with promising results. To our best knowledge, this is the first report of the single particle counting-based CRISPR/Cas12a biosensing study.

Highly efficient dual-mode detection of AFB1 based on the inner filter effect: Donor-acceptor selection and application

BACKGROUND

The utilization of inner filter effect (IFE) brings more opportunities for construction of fluorescence immunoassays but remains a great challenge, especially how to select best donor in the face of extensive fluorescent nanomaterials. Aflatoxin B1 possesses high toxicity among mycotoxins and is frequently found in agricultural products that may significantly threaten to human health. Therefore, with the help of signal transduction mechanism of IFE to develop a convenient and sensitive approach for AFB1 detection is of great significance in ensuring food safety.

RESULTS

Herein, the classical alkaline phosphatase (ALP) catalyzes hydrolysis of p-nitrophenylphosphate to produce p-nitrophenol (PNP) was employed as a model reaction, which intends to explore tunable multicolor fluorescence of gold nanoclusters (AuNCs) for matching PNP to maximize IFE efficiency. The luminescent green-emitting AuNCs were selected as an optimal donor in terms of excellent spectral overlap, high photoluminescence, and adequate system adaptability, thus achieving a 22-fold increase in sensitivity improvement compared to colorimetric method for ALP detection. The fluorescence quenching mechanism between PNP and AuNCs was validated as IFE by studying ultraviolet absorption, zeta potentials and fluorescence lifetime. In light of this, we integrated a highly specific antibody-antigen recognition system, efficient enzymatic reaction and excellent optical characteristics of AuNCs to develop dual-mode immunoassay for AFB1 monitoring. The sensitivity of fluorometric immunoassay was lower to 0.06 ng/mL, which obtained a 3.5-fold improvement compared to "gold standard" ELISA. Their practicability and applicability were confirmed in the tap water, corn, wheat and peanuts samples.

SIGNIFICANCE

This work provides an easy-to-understand screening procedure to select optimal donor-acceptor pairs in IFE analysis. Furthermore, we expect that integration of IFE-based signal conversion strategy into mature immunoassay not only extends the signal types, simplifies signal amplification steps, and reduces the false-positive/false-negative rates, but also provides a simple, convenient, and versatile strategy for monitoring of trace other contaminants.

Recent advances using MXenes in biomedical applications

An MXene is a novel two-dimensional transition metal carbide or nitride, with a typical formula of Mn+1XnTx (M = transition metals, X = carbon or nitrogen, and T = functional groups). MXenes have found wide application in biomedicine and biosensing, owing to their high biocompatibility, abundant reactive surface groups, good conductivity, and photothermal properties. Applications include photo- and electrochemical sensors, energy storage, and electronics. This review will highlight recent applications of MXene and MXene-derived materials in drug delivery, tissue engineering, antimicrobial activity, and biosensors (optical and electrochemical). We further elaborate on recent developments in utilizing MXenes for photothermal cancer therapy, and we explore multimodal treatments, including the integration of chemotherapeutic agents or magnetic nanoparticles for enhanced therapeutic efficacy. The high surface area and reactivity of MXenes provide an interface to respond to the changes in the environment, allowing MXene-based drug carriers to respond to changes in pH, reactive oxygen species (ROS), and electrical signals for controlled release applications. Furthermore, the conductivity of MXene enables it to provide electrical stimulation for cultured cells and endows it with photocatalytic capabilities that can be used in antibiotic applications. Wearable and in situ sensors incorporating MXenes are also included. Major challenges and future development directions of MXenes in biomedical applications are also discussed. The remarkable properties of MXenes will undoubtedly lead to their increasing use in the applications discussed here, as well as many others.

Artificial neural network-facilitated V2C MNs-based colorimetric/fluorescence dual-channel biosensor for highly sensitive detection of AFB1 in peanut

In this work, V2C Mxene nano-enzyme materials (V2C MNs) with excellent peroxidase-like activity and fluorescence quenching performance were prepared, and it was modified using 6-carboxyfluorescein-labelled aptamers (ssDNA-FAM) to construct a novel dual-mode sensor V2C@ssDNA-FAM, with detection limits of 0.0477 ng mL-1 and 0.2789 ng mL-1 of fluorescence (linear range of 0.1-550 ng mL-1) and colorimetric (linear range of 1-1000 ng mL-1) modes, respectively. Meanwhile, an ANN intelligent detection platform has been constructed, which could automatically track and analyze the fluorescence and colorimetric signal of the detection system through machine learning and immediately obtain the AFB1 concentration, and the detection limits of the fluorescence (linear range of 0.1-500 ng mL-1) and colorimetric (linear range of 1-800 ng mL-1) channels of it were 0.0905 ng mL-1 and 0.6845 ng mL-1, respectively. The recovery rates of fluorescence, colorimetric sensing detection and ANN-assisted fluorescence and colorimetric sensing detection of real samples ranged from 95.40% to 101.76%. The method constructed in this work was superior to most existing literature reports and had great potential for application in the field of food quality testing.