Dual-ratiometric electrochemical aptasensor enabled by programmable dynamic range: Application for threshold-based detection of aflatoxin B1

Novel ratiometric electrochemical aptasensor based on broad-spectrum aptamer recognition for simultaneous detection of penicillin antibiotics in milk

To effectively monitor multi-residues of penicillin antibiotics (PENs) in milk, we developed a novel ratiometric electrochemical aptasensor enabling simultaneous detection of PENs. The aptasensor employed a broad-spectrum aptamer as a recognition element, niobium carbide functionalized with methylene blue (Nb2C-MB) as a reference signal generator, and a ferrocene-labeled aptamer (Fc-Apt) as an output signal. Electrodes were modified with Fe-N-C doped carbon nanotubes (Fe-N-C-CNTs) to amplify detection signals further. During detection, Fc-Apt binding to PENs decreased Fc current intensity (IFc) and increased MB current intensity (IMB). The simultaneous detection of PENs was achieved using IMB/IFc as a quantitative signal. Under optimal conditions, a good linear relationship between IMB/IFc and antibiotic concentration was observed, indicating the aptasensor had a robustness. The limits of detection of aptasensor for four penicillin antibiotics and their mixed targets were 0.093-0.191 nM. This work provides a new approach to multi-residue detection of the same class of antibiotics.

Wavelength-Resolved Janus Biosensing Interface for Ratiometric Electrochemical Analysis

The Janus interface, comprising multiple functional heterointerfaces with contrasting functionalities within a single interface, has recently garnered widespread research interest. Herein, a Janus biosensing interface is obtained via wavelength-resolved laser illumination. Deoxyribonucleic acid bridges the electrochemical probe of methylene blue (MB) and plasmonic gold nanoparticles (AuNPs), achieving a sensitive detection performance. MB shows differential electrochemical signals under front (I532front) and back (I650back) laser illumination at 532 and 650 nm, respectively, owing to the selective wavelength-resolved effect. Thus, the presence of a wavelength-resolved laser enabled the design of a biosensing interface with Janus properties. The change in the distance between MB and AuNPs induced by aflatoxin B1 (AFB1) indicates that a sensitive response of the Janus biosensing interface can be achieved. A ratiometric strategy is introduced to describe the electrochemical signals of the I532front and I650back for improved robustness. The obtained linear range is 0.0005-50 ng mL-1, with a detection limit of 0.175 pg mL-1. Our study demonstrated that the wavelength-resolved Janus interface enables an electrochemical biosensor with excellent sensitivity. This finding provides an efficient approach for improving biosensor performance.

Recent Progress of Electrochemical Aptasensors toward AFB1 Detection (2018-2023)

Food contaminants represent possible threats to humans and animals as severe food safety hazards. Prolonged exposure to contaminated food often leads to chronic diseases such as cancer, kidney or liver failure, immunosuppression, or genotoxicity. Aflatoxins are naturally produced by strains of the fungi species Aspergillus, which is one of the most critical and poisonous food contaminants worldwide. Given the high percentage of contaminated food products, traditional detection methods often prove inadequate. Thus, it becomes imperative to develop fast, accurate, and easy-to-use analytical methods to enable safe food products and good practices policies. Focusing on the recent progress (2018-2023) of electrochemical aptasensors for aflatoxin B1 (AFB1) detection in food and beverage samples, without pretending to be exhaustive, we present an overview of the most important label-free and labeled sensing strategies. Simultaneous and competitive aptamer-based strategies are also discussed. The aptasensors are summarized in tabular format according to the detection mode. Sample treatments performed prior analysis are discussed. Emphasis was placed on the nanomaterials used in the aptasensors' design for aptamer-tailored immobilization and/or signal amplification. The advantages and limitations of AFB1 electrochemical aptasensors for field detection are presented.

Recent progress in optical and electrochemical aptasensor technologies for detection of aflatoxin B1

AFB1 (Aflatoxin B1) contamination is becoming a global concern issue due to its extraordinary occurrence, severe toxicity, as well as the great influence on the economic losses, food safety and environment. Therefore, it is desirable to develop novel analytical techniques for simple, rapid, accurate, and even point-of-care testing of AFB1. Fortunately, aptamer, considered as a new generation bioreceptor and even superior to classic antibody and enzyme, has been emerged remarkable application in food hazards detection. Correspondingly, aptasensors have been well-established toward AFB1 determination with outstanding performance. In this article, we first discuss and summarize the recent progress in optical and electrochemical aptasensors to monitor AFB1 over the past three years. In particular, the embedding of advanced nanomaterials for their improved analytical performance is highlighted. Furthermore, the critical analysis on various signal transduction strategies for aptasensors construction is discussed. Finally, we reveal the challenges and provide our opinion in future opportunities for aptasensor development.

Recent advances of ratiometric sensors in food matrices: mycotoxins detection

The public health problem caused by mycotoxins contamination has received a great deal of attention worldwide. Mycotoxins produced by filamentous fungi widely distributed in foodstuffs can cause adverse impacts on humans and livestock, posing serious health threats. Particularly worth mentioning is that mycotoxins can accumulate in organisms and be enriched through the food chain. Improving early trace detection and control from the source is a more desirable approach than the contaminated food disposal process to ensure food safety. Conventional sensors are susceptible to interference from various components in intricate food matrices when detecting trace mycotoxins. The application of ratiometric sensors avoids signal fluctuations, and reduce background influences, which casts new light on developing sensors with superior performance. This work is the first to provide an overview of the recent progress of ratiometric sensors in the detection of mycotoxins in intricate food matrices, and highlight the output types of ratiometric signal with respect to accurate quantitative analysis. The prospects of this field are also included in this paper and are intended to have key ramifications on the development of sensing detection conducive to food safety.

Dual DNA recycling amplifications coupled with Au NPs@ZIF-MOF accelerator for enhanced electrochemical ratiometric sensing of pathogenic bacteria

Sensitive and accurate quantification of pathogenic bacteria is vastly significant to the related food safety. Herein, a sensitive ratiometric electrochemical biosensor was developed for the detection of Staphylococcus aureus (S. aureus) based on dual DNA recycling amplifications and Au NPs@ZIF-MOF accelerator. Gold nanoparticles-loaded Zeolitic imidazolate metal-organic framework (Au NPs@ZIF-MOF) as electrode substrate possessed a large specific surface area for nucleic acid adsorption, and as an accelerator promoted the transfer of electrons. The strong recognition of aptamer to target S. aureus could initiate the padlock probe-based exponential rolling circle amplification (P-ERCA, as the first DNA recycling amplification), generating large numbers of trigger DNA strands. The released trigger DNA further activated the catalytic hairpin assembly (CHA, as the second DNA recycling amplification) on electrode surface. Consequently, P-ERCA and CHA continuously brought about one target to many signal transduction, leading to an exponential amplification. To achieve the accuracy of detection, the signal ratio of methylene blue (MB) and ferrocene (Fc) (I_MB/I_Fc) was applied for intrinsic self-calibrating. Taking advantages of dual DNA recycling amplifications and Au NPs@ZIF-MOF, the proposed sensing system displayed high sensitivity for S. aureus quantification with a linear range of 5-10⁸ CFU/mL, and the limit of detection was 1 CFU/mL. Moreover, this system represented excellent reproducibility, selectivity, and practicability for S. aureus analysis in foods.

An accurate and ultrasensitive ratiometric electrochemical aptasensor for determination of Ochratoxin A based on catalytic hairpin assembly

Ochratoxin A (OTA) pollution in agricultural products has raised the pressing to develop sensitive, accurate and convenient detection methods. Herein, an accurate and ultrasensitive ratiometric electrochemical aptasensor was proposed based on catalytic hairpin assembly (CHA) for OTA detection. In this strategy, the target recognition and CHA reaction were both accomplished in the same system, which avoided tedious multi-steps operation and extra reagents, providing the advantage of convenience with only a one-step reaction and without enzyme. The labeled Fc and MB were used as the signal-switching molecules, avoiding various interferences and greatly improving the reproducibility (RSD: 3.197%). This aptasensor achieved trace-level detection for OTA with LOD of 81 fg/mL in the linear range of lower concentration (100 fg/mL-50 ng/mL). Moreover, this strategy was successfully applied to OTA detection in cereals with comparable results of HPLC-MS. This aptasensor provided a viable platform for accurate, ultrasensitive, and one-step detection of OTA in food.

Advanced biosensors for mycotoxin detection incorporating miniaturized meters

Advanced biosensors, considered as emerging technologies, are capable of accurate, quantitative and real-time analysis for point-of-care testing (POCT) applications. Moreover, the integrating of miniaturized meters into these advanced biosensors makes them ideally appropriate for portable, sensitive and selective detection of biomolecules. Miniaturized meters including PGMs (personal glucose meters), thermometer, pressuremeter, pH meter, etc. are the most accurate devices and wide availability in the market, exhibiting a promising potential towards detection of small molecule mycotoxins. In this article, we introduce and analyze the recent advancements for sensing of mycotoxins measured by handheld meters since the first report in 2012. Furthermore, limitations and challenges for versatile meters application against mycotoxins in food matrix are highlighted. By overcoming the bottleneck problems, we believe the miniaturized meters-based biosensor platform will provide great possibilities for mycotoxins analysis and launch them to the market.

Aptasensor for Detection of Influenza-A in Human Saliva

Access to low-cost, rapid, individualized diagnostics at point-of-care and point-of-need is vital to minimize the impact of highly infectious viruses, such as influenza. Herein, a biosensor for detecting hemagglutinin (HA), an abundant capsid protein in H1N1 viruses, is demonstrated. A gold working electrode was functionalized with a thiol-modified, HA-binding aptamer derivatized with a methylene blue modification for redox reporting. The aptamer was characterized by surface plasmon resonance to confirm its biorecognition activity for HA. The aptasensor was characterized by square wave voltammetry to quantify the sensor's response to varying concentrations of HA. The sensor exhibited a lower limit of detection of 1.5 pM with linear detection of up to 1.2 nM in both Tris buffer and simulated human saliva, thus encompassing the clinically relevant HA range in saliva. Average sensitivity was measured at 21.083 nA·nM-¹in Tris and 14.5 nA·nM-¹in artificial saliva across clinically relevant HA titers. Sensor stability across time was also investigated, providing a preliminary understanding of the translational viability of the aptasensors for mobile and remote diagnostic applications.

Ratiometric Luminescence Aptasensor Based on Dual-Emissive Persistent Luminescent Nanoparticles for Autofluorescence- and Exogenous Interference-Free Determination of Trace Aflatoxin B1 in Food Samples

Sensitive and accurate determination of aflatoxin B1 (AFB1) is of great significance to food safety and human health as it is recognized as the most toxic mycotoxin and carcinogenic. Herein, we report a ratiometric luminescence aptasensor based on dual-emissive persistent luminescent nanoparticles (PLNP) for the accurate determination of trace AFB1 in complex food samples without autofluorescence and exogenous interference. Dual-emissive PLNP ZnGa₂O₄:Cr_0.0001 was prepared first and acted as the donor for energy transfer as well as the signal unit with phosphorescence at 714 and 508 nm (the detection and the reference signal, respectively). AFB1 aptamer was then bonded on the surface of PLNP to offer specific recognition ability. Aptamer complementary DNA modified with Cy5.5 was employed as the acceptor for energy transfer and the quenching group to eventually develop a turn-on ratiometric luminescence aptasensor. The developed ratiometric luminescence aptasensor combined the merits of long-lasting luminescence, in situ excitation and autofluorescence-free of PLNP, exogenous interference-free and self-calibration reading of ratiometric sensor, as well as the high selectivity of aptamer, holding great promise for accurate determination of trace AFB1 in complex matrix. The developed ratiometric aptasensor exhibited excellent linearity (0.05-70 ng mL^-1), low limit of detection (0.016 ng mL^-1), and good precision (2.3% relative standard deviation for 11 replicate determination of 1 ng mL^-1 AFB1). The proposed ratiometric aptasensor was successfully applied for the determination of AFB1 in corn, wheat, peanut, millet, oats, and wheat kernels with recoveries of 95.1-106.5%.

Specifically triggered dissociation based ratiometric electrochemical sensor for H2O2 measurement in food samples

A novel ratiometric strategy based electrochemical sensor was developed to quantitative assay of H₂O₂ in different food samples. 4-aminophenylboronic acid pinacol ester (ABAPE) dissociation was specifically triggered by H₂O₂ to generate electro-active 4-aminophenol (4-AP), which not only can be oxidized to indirectly indicate the concentration of H₂O₂, but also endowed the sensor with high selectivity. Meanwhile, a reference probe of poly(thionine) (TH) was modified with ketjen black (KB) and gold nanoparticles (AuNPs) on electrode surface. KB and AuNPs displayed high electrocatalytic activity to 4-AP. A current ratio between 4-AP and TH (i/i_TH) showed a good linear relationship with the concentration of H₂O₂ in a range of 3.0 × 10^-7 - 1.0 × 10^-4 mol/L (0.010 ppm - 3.40 ppm) with a limit of detection of 2.6 × 10^-7 mol/L (0.009 ppm) (S/N = 3). Moreover, the ratiometric strategy based sensor possessed good accuracy, reliability, and stability, and successfully determined H₂O₂ in food samples with satisfactory results.

A nanozyme-catalysis-based ratiometric electrochemical sensor for general detection of Cd2+

AuPt–rGO showed good peroxidase-like activity for the oxidation of OPD to DAP (a novel internal reference) and achieved sensitive and reliable detection of Cd2+ based on a ratiometric strategy.

A novel COOH–GO–COOH–MWNT/pDA/AuNPs based electrochemical aptasensor for detection of AFB1

Aflatoxin B₁ (AFB₁), one of the most common mycotoxins in food matrixes, has been identified as the most toxic contaminant with mutagenic, teratogenic, immunosuppressive, and carcinogenic effects. In this study, an electrochemical aptamer sensor was developed for the on-site detection of AFB₁. Carboxylated graphene oxide (COOH–GO) and carboxylated multi-walled carbon nanotubes (COOH–MWNT) nanocomposites, dopamine polymers (pDA) and gold nanoparticles (AuNPs) were used to enhance the electrochemical activity and the biocompatibility of the screen-printed electrodes (SPE). Once AFB₁ was captured by the aptamer immobilized on the electrode surface, the redox current of [Fe(CN)₆]^3−/4− decreased. Therefore, the binding of aptamer (Apt) and AFB₁ can be reflected by the change of the peak current. The as-prepared sensor showed a wide detection range of 0.1 fg ml⁻¹–100 pg ml⁻¹ and a low detection limit of 15.16 ag ml⁻¹. It is also simple and low-cost, which shows great potential in practical application.

A novel COOH–GO–COOH–MWNT/pDA/AuNPs based electrochemical aptasensor was developed for detection of AFB₁.