Visualization and colorimetric determination of clenbuterol in pork by using magnetic beads modified with aptamer and complementary DNA as capture probes, and G-quadruplex/hemin and DNA antibody on the metal-organic framework MIL-101(Fe) acting as a peroxidase mimic

Structural optimization, characterization, and evaluation of binding mechanism of aptamers against bovine pregnancy-associated glycoproteins and their application in establishment of a colorimetric aptasensor using Fe-based metal-organic framework as peroxidase mimic tags

A truncated aptamer (designated A24-3) was identified that specifically binds to bovine pregnancy-associated glycoproteins (bPAG9) with a low dissociation constant (2.04 nM) through two truncation approaches. Circular dichroism spectroscopy indicated that A24-3 formed parallel G-quadruplexes, which was subsequently confirmed using nuclear magnetic resonance (NMR) spectroscopy. Furthermore, a molecular dynamics simulation was employed to investigate the recognition mechanism of A24-3 and bPAG9. Interaction analysis showed that A24-3 folded into a parallel G-quadruplex structure with three G-tetrads, primarily through numerous hydrogen bonds and hydrophobic and π-π interactions. Finally, a novel colorimetric aptasensor was developed for detecting bPAG9 using A24-3 and an Fe-based metal-organic framework as target recognition elements and enzyme mimics, respectively. The method demonstrated a broad detection range from 0.5 to 50 ng/mL, with a low detection limit of 0.03 ng mL-1, and exhibited a good recovery (91.0-102%) for bPAG9-spiked serum samples. Additionally, the aptasensor was successfully applied to detecting the pregnancy-specific biomarker bPAGs in serum samples.

Recent progress of metal-organic framework-based nanozymes with oxidoreductase-like activity

Nanozymes, a class of synthetic nanomaterials possessing enzymatic catalytic properties, exhibit distinct advantages such as exceptional stability and cost-effectiveness. Among them, metal-organic framework (MOF)-based nanozymes have garnered significant attention due to their large specific surface area, tunable pore size and uniform structure. MOFs are porous crystalline materials bridged by inorganic metal ions/clusters and organic ligands, which hold immense potential in the fields of catalysis, sensors and drug carriers. The combination of MOFs with diverse nanomaterials gives rise to various types of MOF-based nanozyme, encompassing original MOFs, MOF-based nanozymes with chemical modifications, MOF-based composites and MOF derivatives. It is worth mentioning that the metal ions and organic ligands in MOFs are perfectly suited for designing oxidoreductase-like nanozymes. In this review, we intend to provide an overview of recent trends and progress in MOF-based nanozymes with oxidoreductase-like activity. Furthermore, the current obstacles and prospective outlook of MOF-based nanozymes are proposed and briefly discussed. This comprehensive analysis aims to facilitate progress in the development of novel MOF-based nanozymes with oxidoreductase-like activity while serving as a valuable reference for scientists engaged in related disciplines.

Aptamer-modified metal organic frameworks for measurement of food contaminants: a review

The measurement of food contaminants faces a great challenge owing to the increasing demand for safe food, increasing consumption of fast food, and rapidly changing patterns of human consumption. As different types of contaminants in food products can pose different levels of threat to human health, it is desirable to develop specific and rapid methods for their identification and quantification. During the past few years, metal-organic framework (MOF)-based materials have been extensively explored in the development of food safety sensors. MOFs are porous crystalline materials with tunable composition, dynamic porosity, and facile surface functionalization. The construction of high-performance biosensors for a range of applications (e.g., food safety, environmental monitoring, and biochemical diagnostics) can thus be promoted through the synergistic combination of MOFs with aptamers. Accordingly, this review article delineates recent innovations achieved for the aptamer-functionalized MOFs toward the detection of food contaminants. First, we describe the basic concepts involved in the detection of food contaminants in terms of the advantages and disadvantages of the commonly used analytical methods (e.g., DNA-based methods (PCR/real-time PCR/multiplex PCR/digital PCR) and protein-based methods (enzyme-linked immunosorbent assay/immunochromatography assay/immunosensor/mass spectrometry). Afterward, the progress in aptamer-functionalized MOF biosensors is discussed with respect to the sensing mechanisms (e.g., the role of MOFs as signal probes and carriers for loading signal probes) along with their performance evaluation (e.g., in terms of sensitivity). We finally discuss challenges and opportunities associated with the development of aptamer-functionalized MOFs for the measurement of food contaminants.

Functionalized pyrite nanozyme probe and imprinted polymer modified with hydrophilic layer for rapid colorimetric analysis of glycoprotein in serum

The biological molecules used in the sandwich detection method have problems such as complex extraction processes, high costs, and uneven quality. Therefore we integrated glycoprotein molecularly controllable-oriented surface imprinted magnetic nanoparticles (GMC-OSIMN) and boric acid functionalized pyrite nanozyme probe (BPNP) to replace the traditional antibody and horseradish peroxidase for sensitive detection of glycoproteins through sandwich detection. In this work, a novel nanozyme functionalized with boric acid was used to label glycoproteins that were captured by GMC-OSIMN. The substrate in the working solution catalyzed by the nanozyme labeled on the protein underwent visible color changes to the naked eye, and the generated signal can be quantitatively detected by a spectrophotometer, and the best color development conditions of the novel nanozyme under the influence of many factors were determined through multi-dimensional investigation. The optimum conditions of sandwich are optimized with ovalbumin (OVA), and it was extended to the detection of transferrin (TRF) and alkaline phosphatase (ALP) in the application. The detection range for TRF was 2.0 × 10^-1-1.0 × 10⁴ ng mL^-1 with a detection limit of 1.32 × 10^-1 ng mL^-1, The detection range for ALP was 2.0 × 10^-3-1.0 × 10² U L^-1 with the detection limit of 1.76 × 10^-3 U L^-1. This method was subsequently used to detect TRF and ALP levels in 16 liver cancer patients, and the standard deviation of the test results of each patient was less than 5.7%.

A novel aptamer-G-quadruplex/hemin self-assembling color system: rapid visual diagnosis of invasive fungal infections

BACKGROUND

The clinical symptoms of invasive fungal infections (IFI) are nonspecific, and early clinical diagnosis is challenging, resulting in high mortality rates. This study reports the development of a novel aptamer-G-quadruplex/hemin self-assembling color system (AGSCS) based on (1 → 3)-β-D-glucans' detection for rapid, specific and visual diagnosis of IFI.

METHODS

We screened high affinity and specificity ssDNA aptamers binding to (1 → 3)-β-D-glucans, the main components of cell wall from Candida albicans via Systematic Evolution of Ligands by EXponential enrichment. Next, a comparison of diagnostic efficiency of AGSCS and the (1 → 3)-β-D-glucans assay ("G test") with regard to predicting IFI in 198 clinical serum samples was done.

RESULTS

Water-soluble (1 → 3)-β-D-glucans were successfully isolated from C. albicans ATCC 10,231 strain, and these low degree of polymerization glucans (< 1.7 kD) were targeted for aptamer screening with the complementary sequences of G-quadruplex. Six high affinity single stranded DNA aptamers (A1, A2, A3, A4, A5 and A6) were found. The linear detection range for (1 → 3)-β-D-glucans stretched from 1.6 pg/mL to 400 pg/mL on a microplate reader, and the detection limit was 3.125 pg/mL using naked eye observation. Using a microplate reader, the sensitivity and specificity of AGSCS for the diagnosis of IFI were 92.68% and 89.65%, respectively, which was higher than that of the G test.

CONCLUSION

This newly developed visual diagnostic method for detecting IFI showed promising results and is expected to be developed as a point-of-care testing kit to enable quick and cost effective diagnosis of IFI in the future.

Engineering a thermostable biosensor based on biomimetic mineralization HRP@Fe-MOF for Alzheimer's disease

The development of disease detection by biosensors represents one of the key components of medical science. However, millions of people are still misdiagnosed each year due to the poor efficacy and thermal instability of biosensors. Using horseradish peroxidase (HRP) as a paradigm, we offer a rational design strategy to optimize the thermostability and activity of biosensors by biomimetic mineralization. To overcome the weak thermostability of the biosensor, the mineralization of Fe-MOF forms an armor on HRP that protects against high temperature. Additionally, the biomimetic mineralization HRP@Fe-MOF can double-catalyze the TMB/H₂O₂ chromogenic system for color development. The biosensor can also be recycled through simple heat treatment due to the thermally stable aptamer and biomimetic mineralization HRP@Fe-MOF. The optical biosensor based on this sensitive spectral transformation was successfully developed for the measurement of AβO with an outstanding linear range (0.0001-10 nM) and a low limit of detection (LOD) of 0.03 pM. This promising platform will open up new avenues for the detection of AβO in the early diagnosis of Alzheimer's disease (AD).

A label-free aptasensor for clenbuterol detection based on fluorescence resonance energy transfer between graphene oxide and rhodamine B

A label-free aptasensor for clenbuterol was developed through the fluorescence resonance energy transfer mechanism by using an aptamer as the recognition element, rhodamine B as the fluorescence probe and graphene oxide as the fluorescence quencher.

A label-free reusable aptasensor for Alzheimer's disease

To early effectively detect amyloid-beta (Aβ) oligomers, a label-free reusable aptasensor was designed. This aptasensor based on a luminescent nanoscale lanthanum-based metal-organic framework (L-MOF)-armored single-stranded DNA antibody (MOF-armored-anti-DNA antibody) as signal tags and aptamer bound to magnetic beads (Apt-MB) as capture probe. The reusable aptasensor combines signal tag and capture probe with antigen-antibody interaction. When the reusable aptasensor is formed, the strong fluorescence intensity of L-MOF will "turn off" by photo-induced electron transfer from excited states to an unfilled d shell of iron cations on the nanoparticle surface. Upon the presence of Aβ oligomers in serum samples, they can be especially distinguished with the Aβ oligomers aptamer in capture probes and then signal tags are released into the solution for developing the fluorescence aptasensor under excitation/emission 365 nm/430 nm. Meanwhile, the aptamer was recovered from the complex of Aβ oligomers/Apt-MB by heat treatment. When the temperature returns to room temperature, the recovered aptamer in the capture probe can once again bound to the MOF-armored-anti-DNA antibody for reuse. The label-free reusable aptasensor system detection has high sensitivity and selectivity toward Aβ oligomers (LOD = 0.4 pg/mL) and an excellent linear range (0.001-100 ng/mL). This strategy is a fruitful step for the development of reusable aptasensor and may turn on new avenues for the applications of Aβ oligomer detection in clinical diagnosis.Graphical abstract.