A novel and label-free electrochemical aptasensor based on exonuclease III and G-quadruplex DNAzyme for sensitive and selective detection of metronidazole

Green nitrogen and sulfur co-doped carbon dots derived from eggshell as a high performance aptasensing interface for non-invasive detection of metronidazole

BACKGROUND

The concentration monitoring of the banned metronidazole (MTZ) drug as the alarmed carcinogenic agent in human biofluids is medically essential. The electrochemical aptasensors are good candidates to overcome some presence challenges in the detection process.

RESULTS

Herein, an electrochemical aptasensor based on nitrogen and sulfur co-doped carbon dots (NcS-CDs) has been developed for the high-sensitive detection of MTZ for the first time. The N-S-CDs have been synthesized from eggshell waste and the aptasensing interface has been fabricated by the attachment of the N-S-CDs to the glassy carbon electrode surface to fix the high-density aptamer (Apt) sequences via silver nanocubes (AgNCs). The electrochemical signal of the redox probe has changed by trapping the MTZ on the Apt's arm onto the aptasensing interface. The molecular dynamic simulation visually confirmed how the Apt binds to the MTZ. The resulting aptasensor measured MTZ in a wide linear range value from 1 fM to 901.4 nM with a limit of detection value of 333.3 aM and high selectivity regarding some possible interferences.

SIGNIFICANCE

The results reveal that the novel aptasensor has high potential applicability for the non-invasive monitoring of MTZ in human saliva and urine, and also, the tap water analysis. Utilizing waste-derived nanomaterials for the aptasensor fabrication not only less the fabrication costs but also guarantees the greenness of the applied methodology according to sustainable chemistry principles as evaluated by two international index metrics.

Recent Advances in Electrochemical Aptasensors for Detection of Clinical and Veterinary Drugs

Nowadays, aptamer-based biosensors and electrochemical measurements represent one of the efficient tools for the detection of drugs in both medical and veterinary. Precise trace values analysis of chemicals, especially drugs, plays a crucial role in food and therapeutic safety evaluations that are often time-consuming and costly. Ultimately, accurate determination of therapeutic medications like antibiotics in food, environmental resources, and biological matrices is very important for protecting public health and drug monitoring (TDM) for effective treatment. This review highlights recent advancements in electrochemical aptasensors as an innovative approach offering high sensitivity, specificity, and rapid detection of clinical and veterinary drugs at lower costs. We provide a comprehensive overview of the advancements and discuss the challenges and prospects of electrochemical aptasensing in drug residue detection across various samples.

An electrochemical aptasensor for the detection of bisphenol A based on triple signal amplification assisted by gold nanoparticles, hemin/G-quadruplex DNAzyme, and exonuclease I

A triple signal amplified electrochemical aptasensor for the detection of bisphenol A (BPA) was developed for the first time based on gold nanoparticles (AuNPs), hemin/G-quadruplex DNAzyme, and exonuclease I (Exo I) assisted amplification strategies. The BPA aptamer (Apt) hybridized with the capture probe (CP) was fixed on the gold electrode (GE) to form the double-stranded DNA (dsDNA) structure. When BPA was present, the Apt was detached from the GE surface by specific recognition between the BPA and Apt, forming BPA-Apt complexes in solution. The complexes could be selectively digested by Exo I, releasing BPA to participate in the cycle for binding to other Apt in dsDNA. The hybridization of the CP and auxiliary DNA (aDNA) within the detect probe DNA (dpDNA)-AuNP-aDNA nanocomplex allowed the nanocomplex to connect to the GE surface. The dpDNA interacted with K+ and hemin to produce hemin/G-quadruplex DNAzyme, which catalyzed H2O2 reduction, accelerated methylene blue (MB) oxidization, and further amplified the electrochemical signal. The integration of triple signal amplification strategies with aptamer-specific recognition enabled sensitive and specific detection of BPA. Under optimized conditions, the aptasensor exhibited a linear range of 0.1 pM-10 nM, with a low detection limit of 76 fM. Moreover, the designed aptasensor was successfully applied to detect BPA in lake water, fruit juice, and honey samples.

Enhancing the substrate selectivity of enzyme mimetics in biosensing and bioassay: Novel approaches

A substantial development in nanoscale materials possessing catalytic activities comparable with natural enzymes has been accomplished. Their advantages were owing to the excellent sturdiness in an extreme environment, possibilities of their large-scale production resulting in higher profitability, and easy manipulation for modification. Despite these advantages, the main challenge for artificial enzyme mimetics is the lack of substrate selectivity where natural enzymes flourish. This review addresses this vital problem by introducing substrate selectivity strategies to three classes of artificial enzymes: molecularly imprinted polymers, nanozymes (NZs), and DNAzymes. These rationally designed strategies enhance the substrate selectivity and are discussed and exemplified throughout the review. Various functional mechanisms associated with applying enzyme mimetics in biosensing and bioassays are also given. Eventually, future directives toward enhancing the substrate selectivity of biomimetics and related challenges are discussed and evaluated based on their efficiency and convenience in biosensing and bioassays.

Sequential Flow Controllable Microfluidic Device for G-Quadruplex DNAzyme-Based Electrochemical Detection of SARS-CoV-2 Using a Pyrrolidinyl Peptide Nucleic Acid

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a significant health issue globally. Point-of-care (POC) testing that can offer a rapid and accurate diagnosis of SARS-CoV-2 at the early stage of infection is highly desirable to constrain this outbreak, especially in resource-limited settings. Herein, we present a G-quadruplex DNAzyme-based electrochemical assay that is integrated with a sequential flow controllable microfluidic device for the detection of SARS-CoV-2 cDNA. According to the detection principle, a pyrrolidinyl peptide nucleic acid probe is immobilized on a screen-printed graphene electrode for capturing SARS-CoV-2 DNA. The captured DNA subsequently hybridizes with another DNA probe that carries a G-quadruplex DNAzyme as the signaling unit. The G-quadruplex DNAzyme catalyzes the H2O2-mediated oxidation of hydroquinone to benzoquinone that can be detected using square-wave voltammetry to give a signal that corresponds to the target DNA concentration. The assay exhibited high selectivity for SARS-CoV-2 DNA and showed a good experimental detection limit at 30 pM. To enable automation, the DNAzyme-based assay was combined with a capillary-driven microfluidic device featuring a burst valve technology to allow sequential sample and reagent delivery as well as the DNA target hybridization and enzymatic reaction to be operated in a precisely controlled fashion. The developed microfluidic device was successfully applied for the detection of SARS-CoV-2 from nasopharyngeal swab samples. The results were in good agreement with the standard RT-PCR method and could be performed within 20 min. Thus, this platform offers desirable characteristics that make it an alternative POC tool for COVID-19 diagnosis.

Few Layer Ti3C2 MXene-Based Label-Free Aptasensor for Ultrasensitive Determination of Chloramphenicol in Milk

Quantitative detection of veterinary drug residues in animal-derived food is of great significance. In this work, a simple and label-free electrochemical aptasensor for the highly sensitive detection of chloramphenicol (CAP) in milk was successfully developed based on a new biosensing method, where the single- or few-layer Ti3C2 MXene nanosheets functionalized via the specific aptamer by self-assembly were used as electrode modifiers for a glassy carbon electrode (aptamer/Ti3C2 MXene/GCE). Differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), atomic force microscope (AFM), and so on were utilized for electrochemical and morphological characterization. Under the optimized conditions, the constructed aptasensor exhibited excellent performance with a wider linearity to CAP in the range from 10 fM to 1 μM and a low detection limit of 1 fM. Aptamer/Ti3C2 MXene/GCE demonstrated remarkable selectivity over other potentially interfering antibiotics, as well as exceptional reproducibility and stability. In addition, the aptasensor was successfully applied to determine CAP in milk with acceptable recovery values of 96.13% to 108.15% and relative standard deviations below 9%. Therefore, the proposed electrochemical aptasensor is an excellent alternative for determining CAP in food samples.

Efficient detection of metronidazole by a glassy carbon electrode modified with a composite of a cyclotriveratrylene-based metal-organic framework and multi-walled carbon nanotubes

Constructing a sensitive and efficient sensor for determination of metronidazole (MNZ) is crucial in food field. Herein, a new cyclotriveratrylene-based metal-organic framework (MOF), namely, [Cd₆L₂(cyclen)₂(H₂O)₂] (1), was constructed by self-assembly of functionalized 5,6,12,13,19,20-hexacarboxy-propoxy-cyclotriveratrylene (H₆L), 1,4,7,10-tetraazacyclododecane (cyclen) and Cd(II) cation under solvothermal condition. In 1, adjacent Cd(II) cations are linked by L^6- to produce a 2D polymeric structure with carboxylate and phenolic oxygen atoms. To enhance conductivity of 1, it was combined with conducting carbon materials, including mesoporous carbon (MC), reduced graphene oxide (RGO) and multi-walled carbon nanotubes (MWCNT), respectively, producing a series of composite materials. Remarkably, electrochemical tests showed that 1@MWCNT(1:1) featured a much better electrochemical detection performance for metronidazole (MNZ) than 1@MC and 1@RGO. The linear range for the detection of MNZ is up to 0.4-500 μM and the limit of detection (LOD) for MNZ reached 0.25 μM. Importantly, the fabricated sensor 1@MWCNT(1:1) was employed for the detection of MNZ in honey and egg with satisfactory result. High-performance liquid chromatography (HPLC) validated the high accuracy of the electrochemical method for the determination of honey and egg.

Ultrasensitive electrochemical aptasensor with Nafion-stabilized f-MWCNTs as signal enhancers for OTA detection

In this study, an ultrasensitive electrochemical (EC) aptasensor with Nafion-stabilized functionalized multi-walled carbon nanotubes (f-MWCNTs) as signal enhancers was established for ochratoxin A (OTA) determination. Herein, f-MWCNTs were prepared through functionalization with nitric acid. The incorporation of Nafion promoted a good dispersion of f-MWCNTs and prevented their leaching on the electrode, making a robust stability of the aptasensor. The Nafion-f-MWCNTs composites were used as the sensing substrates to largely enhance the electroactive surface area and the conductivity of the electrode, realizing a significant signal amplification. Carboxyl groups on the surface of f-MWCNTs readily exposed from Nafion membrane to couple with streptavidin, facilitating the immobilization of biotinylated aptamers to achieve selective recognition towards OTA. When OTA existed, aptamers preferentially combined with it, causing a noticeable decline in the current response. Under optimum conditions, a good linear relationship between the current changes and the logarithm of OTA concentration was observed from 0.005 ng/mL to 10 ng/mL, with a limit of detection low to 1 pg/mL for OTA. The specific, sensitive, and reproducible aptasensor succeeded in application in malt samples, confirming a great promise for more contaminants and providing a universal platform in complex matrices by simply replacing the corresponding aptamers.