Rapid and ultrasensitive detection of DNA and microRNA-21 using a zirconium porphyrin metal-organic framework-based switch fluorescence biosensor

Recent advances of biocompatible optical nanobiosensors in liquid biopsy: towards early non-invasive diagnosis

Liquid biopsy is a non-invasive diagnostic method that can reduce the risk of complications and offers exceptional benefits in the dynamic monitoring and acquisition of heterogeneous cell population information. Optical nanomaterials with excellent light absorption, luminescence, and photoelectrochemical properties have accelerated the development of liquid biopsy technologies. Owing to the unique size effect of optical nanomaterials, their improved optical properties enable them to exhibit good sensitivity and specificity for mitigating signal interference from various molecules in body fluids. Nanomaterials with biocompatible and optical sensing properties play a crucial role in advancing the maturity and diversification of liquid biopsy technologies. This article offers a comprehensive review of recent advanced liquid biopsy technologies that utilize novel biocompatible optical nanomaterials, including fluorescence, colorimetric, photoelectrochemical, and Raman broad-spectrum-based biosensors. We focused on liquid biopsy for the most significant early biomarkers in clinical medicine, and specifically reviewed reports on the effectiveness of optical nanosensing technology in the detection of real patient samples, which may provide basic evidence for the transition of optical nanosensing technology from engineering design to clinical practice. Furthermore, we introduced the integration of optical nanosensing-based liquid biopsy with modern devices, such as smartphones, to demonstrate the potential of the technology in portable clinical diagnosis.

Metal-organic framework (MOF)-based biosensors for miRNA detection

MicroRNAs (miRNAs) play several crucial roles in the physiological and pathological processes of the human body. They are considered as important biomarkers for the diagnosis of various disorders. Thus, rapid, sensitive, selective, and affordable detection of miRNAs is of great importance. However, the small size, low abundance, and highly similar sequences of miRNAs impose major challenges to their accurate detection in biological samples. In recent years, metal-organic frameworks (MOFs) have been applied as promising sensing materials for the fabrication of different biosensors due to their distinctive characteristics, such as high porosity and surface area, tunable pores, outstanding adsorption affinities, and ease of functionalization. In this review, the applications of MOFs and MOF-derived materials in the fabrication of fluorescence, electrochemical, chemiluminescence, electrochemiluminescent, and photoelectrochemical biosensors for the detection of miRNAs and their detection principle and analytical performance are discussed. This paper attempts to provide readers with a comprehensive knowledge of the fabrication and sensing mechanisms of miRNA detection platforms.

Biomedical application of metal-organic frameworks (MOFs) in cancer therapy: Stimuli-responsive and biomimetic nanocomposites in targeted delivery, phototherapy and diagnosis

The nanotechnology is an interdisciplinary field that has become a hot topic in cancer therapy. Metal-organic frameworks (MOFs) are porous materials and hybrid composites consisted of organic linkers and metal cations. Despite the wide application of MOFs in other fields, the potential of MOFs for purpose of cancer therapy has been revealed by the recent studies. High surface area and porosity, significant drug loading and encapsulation efficiency are among the benefits of using MOFs in drug delivery. MOFs can deliver genes/drugs with selective targeting of tumor cells that can be achieved through functionalization with ligands. The photosensitizers and photo-responsive nanostructures including carbon dots and gold nanoparticles can be loaded in/on MOFs to cause phototherapy-mediated tumor ablation. The immunogenic cell death induction and increased infiltration of cytotoxic CD8+ and CD4+ T cells can be accelerated by MOF platforms in providing immunotherapy of tumor cells. The stimuli-responsive MOF platforms responsive to pH, redox, enzyme and ion can accelerate release of therapeutics in tumor site. Moreover, MOF nanocomposites can be modified ligands and green polymers to improve their selectivity and biocompatibility for cancer therapy. The application of MOFs for the detection of cancer-related biomarkers can participate in the early diagnosis of patients.

DNA-functionalized metal or metal-containing nanoparticles for biological applications

The conjugation of DNA molecules with metal or metal-containing nanoparticles (M/MC NPs) has resulted in a number of new hybrid materials, enabling a diverse range of novel biological applications in nanomaterial assembly, biosensor development, and drug/gene delivery. In such materials, the molecular recognition, gene therapeutic, and structure-directing functions of DNA molecules are coupled with M/MC NPs. In turn, the M/MC NPs have optical, catalytic, pore structure, or photodynamic/photothermal properties, which are beneficial for sensing, theranostic, and drug loading applications. This review focuses on the different DNA functionalization protocols available for M/MC NPs, including gold NPs, upconversion NPs, metal-organic frameworks, metal oxide NPs and quantum dots. The biological applications of DNA-functionalized M/MC NPs in the treatment or diagnosis of cancers are discussed in detail.

Biosensor model based on single hairpin structure for highly sensitive detection of multiple targets

Nowadays, due to the genetic information carried by nucleic acids, they can serve as a biomarker for the early diagnosis of diseases, including tumors and cardiovascular disease, among others, making genetic testing a hotspot of biomedicine. Therefore, we have designed a universal fluorescence biosensor that can detect multiple DNA sequences with good performance. In our designed biosensor, λ exonuclease is used due to its ability to digest double-stranded DNA from the phosphorylated 5'- end and promote the targeted cycle. The exonuclease is introduced into a DNA hairpin containing a target recognition sequence. Hence, with the target, λ exonuclease-assisted targeted recycling can be activated. The hydrolyzed DNA hairpin triggers a strand displacement reaction between the hairpin probe (H1) and F-Q double DNA strand (F-Q), increasing the distance between the fluorescent chain (F) and quenching chain (Q); thus the fluorescence signal is emitted. It is exciting that the detection limit of the biosensor is 300 fM, which is relatively low, and there is an excellent linear relationship between fluorescence intensity and target concentration. Moreover, the biosensor we designed has universal applicability in the detection of other genes, and the range of RSD is 1.28-2.45%. Hence, it has good application prospects and practical value in the early detection of some diseases and the design of fluorescent biosensors.

Quasi-intrinsic fluorescent probes for detecting the DNA adduct (ABPdG) based on an excited-state intermolecular charge transfer mechanism

N'-(2'-Deoxyguanosin-8-yl)-4-aminobiphenyl (^ABPdG) is one of the most representative carcinogenic DNA adducts formed by human exposure to 4-aminobiphenyl (4-ABP) during dye production, rubber-manufacturing processes and cigarette smoke. Accordingly, the ultrasensitive detection of ABP-derived adducts in DNA with minimal interference to the native structures becomes key for elucidating carcinogenesis mechanisms and mitigating the risk of cancer. In view of the lack of efficient optical emission in ^ABPG, we report a theoretical study on the photophysical properties of a set of quasi-intrinsic fluorescent C-analogues, which can form stable W-C base pairs with ^ABPG. It is found that fluorophore replacement and ring-expansion can bring a red-shifted absorption and bright photoluminescence due to additional π-conjugation. In particular, because the tricyclic cytosine analogue 1,3-diaza-2-oxophenoxazine (tC^O) possesses distinct optical properties, it is proposed as a biosensor to identify ^ABPG. The TDDFT-calculated absorption maximum of tC^O is red-shifted by 97 nm in comparison with that of the native C base, which contributes to selective excitation after incorporating into the nucleic acids. Although the fluorescence is insensitive to base pairing with natural guanine, the excited state intermolecular charge transfer (ESICT)-governed "OFF-ON" signal can be observed in the presence and absence of ^ABPG. Moreover, to evaluate the direct availability of the bright C-analogues with high selectivity for the deoxyguanosine adduct ^ABPG in DNA, we further investigated thoroughly the effects of its linking to deoxyribose on its absorption and emission, which shows little difference from that of experiment.

Carboxyl porphyrin as signal molecule for sensitive fluorescent detection of aflatoxin B1 via ARGET-ATRP

In this work, a novel fluorescent biosensor for sensitive detecting of aflatoxin B₁ (AFB₁) was constructed through activators regenerated by electron transfer for atom transfer radical polymerization (ARGET-ATRP) for the first time. The AFB₁ antigen was immobilized on the carboxy magnetic beads (MBs) by forming a sandwich-type "aptamer-antigen-antibody" immune system. Then, acrylamid (AM) was introduced through ARGET-ATRP to provide binding sites for the signaling molecules. Finally, carboxy porphyrins (TPP*) were connected with monomers through an amide bond and fixed on the MBs. Under the optimal experimental conditions, the fluorescence intensity and the logarithm of the concentration of AFB₁ showed a good relationship from 100 fg mL^-1 to 100 ng mL^-1, with the limit of detection (LOD) as low as 8.38 fg mL^-1. In addition, the method shows good selectivity and excellent reproducibility. More importantly, the biosensor has applied to the quantitative analysis of AFB₁ in four Chinese medicines, and this strategy could potentially serve as a novel means for sensitive detecting of AFB₁ in complex matrices.

Platform Formed from ZIF-8 and DNAzyme: "Turn-On" Fluorescence Assay for Simple, High-Sensitivity, and High-Selectivity Detection of Pb2

Lead contamination has posed a potential threat to the environment and food safety, arousing extensive concern. In this work, we fabricated a novel fluorescent sensing platform based on zeolitic imidazolate framework-8 (ZIF-8) and DNAzyme for monitoring Pb²⁺ in water and fish samples. ZIF-8 was proposed as a fluorescence quencher with the advantages of simple synthesis, low cost, and high quenching efficiency. The Pb²⁺-dependent GR5 DNAzyme containing the large ssDNA loop can be adsorbed onto ZIF-8 accompanied by fluorescence quenching. Upon binding with Pb²⁺, GR5 DNAzyme was activated and cleaved, leading to the release of FAM-labeled 5-base ssDNA, which restored the fluorescence. The "turn-on" assay can detect Pb²⁺ through the one-pot procedure in the range of 0.01-10.0 nM with a detection limit of 7.1 pM. The platform is promising for on-site monitoring of Pb²⁺ owing to the excellent performance of high sensitivity, low background, strong anti-interference ability, and simple operation.