Visual and Electrochemical Detection of let-7a: A Tumor Suppressor and Biomarker.

Let-7a, a type of low-expressed microRNAs in cancer cells, has been investigated as a promising biomarker and therapeutic target for tumor suppression. Developing simple and sensitive detection methods for let-7a is important for cancer diagnosis and treatment. In this work, the hybridization chain reaction (HCR) was initiated by let-7a via two hairpin primers (H1 and H2). After the HCR, the remaining hairpin H1 was further detected by lateral flow assay (LFA) and electrochemical impedance spectroscopy. For LFA, biotin-modified H1(bio-H1) and free H2 were used for HCR. With the decrease of let-7a concentration, the color of T line gradually increased. As for electrochemical methods, the H1'-AuNP-modified electrode was used for detection of bio-H1 based on the difference of impedance (ΔRct) detected without and with different concentrations of let-7a participating in the HCR. This method could detect let-7a in the range of 10.0 fM and 1.0 nM with detection limits of 4.2 fM.

Fluorescent intracellular imaging of reactive oxygen species and pH levels moderated by a hydrogenase mimic in living cells.

The catalytic generation of H2 in living cells provides a method for antioxidant therapy. In this study, an [FeFe]-hydrogenase mimic [Ru + Fe2S2@F127(80)] was synthesized by self-assembling polymeric pluronic F-127, catalytic [Fe2S2] sites, and photosensitizer Ru(bpy)3 2+. Under blue light irradiation, hydrated protons were photochemically reduced to H2, which increased the local pH in living cells (HeLa cells). The generated H2 was subsequently used as an antioxidant to decrease reactive oxygen species (ROS) levels in living cells (HEK 293T, HepG2, MCF-7, and HeLa cells). Our findings revealed that the proliferation of HEK 293T cells increased by a factor of about six times, relative to that of other cells (HepG2, MCF-7, and HeLa cells). Intracellular ROS and pH levels were then monitored using fluorescent cell imaging. Our study showed that cell imaging can be used to evaluate the ability of Ru + Fe2S2@F127 to eliminate oxidative stress and prevent ROS-related diseases.

Oral Metal-Organic Gel Protected Whole-Cell Biosensor for in Situ Monitoring Nitrosamines in the Gastrointestinal Tract.

Nitrite, a type of food additive, has been proved convertible to genotoxic nitrosamines in the gastrointestinal tract by intestinal flora. There is no appropriate method for in situ detection of nitrosamines. Herein, plasmid-introduced Saccharomyces cerevisiae, which can respond to nitrosamine-induced DNA damage and activate pMAG1-based DNA damage repair (DDR), was designed as whole-cell biosensors (WCBs) for monitoring the in situ generated nitrosamines by a reporter gene expressing enhanced green fluorescent protein (EGFP). In order to protect the validity of WCBs (pMAG1 yeast) from the gastric acid environment, a type of metal-organic gel (MOG), coordinated by Fe3+ and 2,2'-thiodiacetic acid (TDA), was prepared to embed the WCBs. The MOG(Fe-TDA) is gastric acid resistant and can deliver the pMAG1 yeast to the gut without compromising the performance of pMAG1 yeast to detect in situ generated nitrosamines. The genotoxicity of nitrosamines converted from nitrite was successfully detected in the gastrointestinal tract of mice.

Lanthanide Complexes for Tumor Diagnosis and Therapy by Targeting Sialic Acid.

Sialic acid (SA) is overexpressed on cell membranes of tumor cells, and increased serum SA concentration has been observed in tumor-bearing patients. Herein, a series of lanthanide-containing bimetallic complexes (TDA-M-Lns) for targeting SA were prepared via coordination among luminescent lanthanide ions (Ln3+ = Tb3+, Eu3+, Dy3+, or Sm3+), metal ion quenchers (M2+ = Cu2+ or Co2+), and the organic ligand 2,2'-thiodiacetic acid (TDA). SA can competitively coordinate with Ln3+, resulting in the "signal-on" of the Ln3+. Therefore, the TDA-M-Lns can be simply used for cost-saving detection of SA in the blood samples. Among the TDA-M-Lns, TDA-Co-Eu showed the highest sensitivity to detect SA in the blood of tumor-bearing mice. Furthermore, the TDA-Co-Eu was successfully used to target SA and deposit Eu3+ on the surfaces of tumor cells for the inhibition of tumor cell growth and migration. The therapeutic effect of TDA-Co-Eu on a Balb/c mouse liver tumor model was evaluated. It was proved that TDA-Co-Eu can be applied for SA detection as well as for inhibiting tumor growth.

Enzyme-Immobilized Metal-Organic Frameworks: From Preparation to Application.

As a class of widely used biocatalysts, enzymes possess advantages including high catalytic efficiency, strong specificity and mild reaction condition. However, most free enzymes have high requirements on the reaction environment and are easy to deactivate. Immobilization of enzymes on nanomaterial-based substrates is a good way to solve this problem. Metal-organic framework (MOFs), with ultra-high specific surface area and adjustable porosity, can provide a large space to carry enzymes. And the tightly surrounded protective layer of MOFs can stabilize the enzyme structure to a great extent. In addition, the unique porous network structure enables selective mass transfer of substrates and facilitates catalytic processes. Therefore, these enzyme-immobilized MOFs have been widely used in various research fields, such as molecule/biomolecule sensing and imaging, disease treatment, energy and environment protection. In this review, the preparation strategies and applications of enzyme-immobilized MOFs are illustrated and the prospects and current challenges are discussed.

Cancer drug resistance related microRNAs: recent advances in detection methods.

Drug resistance is a significant factor that hinders the success of cancer chemotherapy. The widely recognized mechanisms of drug resistance include changes to cell proliferation, cycle/apoptosis, drug metabolism/transport, DNA damage and the epithelial to mesenchymal transition. MicroRNAs (miRNAs), short non-coding RNAs with lengths of approximately 19-25 nucleotides, are related to cancer drug resistance, which is regulated by the aforementioned mechanisms. Based on the importance of miRNAs in regulating drug resistance, it is also necessary to take appropriate miRNA detection methods into consideration. To date, a number of advanced miRNA detection methods with high specificity and sensitivity have been developed, such as isothermal amplification-based methods, nanomaterial-based methods, chromatography-based methods, mass spectrometry-based methods and so on. Herein, biogenesis of miRNAs, the relationship between miRNAs and cancer drug resistance, and miRNA detection methods are introduced and discussed to facilitate the development of non-invasive diagnosis and inhibition of cancer drug resistance.

Surface functionalized biomimetic bioreactors enable the targeted starvation-chemotherapy to glioma.

Altering the glucose supply and the metabolic pathways would be an intriguing strategy in starvation therapy toward cancers. Nevertheless, starvation therapy alone could be inadequate to eliminate tumor cells completely. Herein, a multifunctional bioreactor was fabricated for synergistic starvation-chemotherapy through embedding glucose oxidase (GOx) and doxorubicin (DOX) in the tumor targeting ligands (RGD) modified red blood cell membrane camouflaged metal-organic framework (MOF) nanoparticle (denoted as RGD-mGZD). Owing to the remarkable biointerfacing property, the designed RGD-mGZD could not only possess enhanced blood retention time inherited from red blood cells, but also preferentially target the tumor site after the modification with RGD peptide. Once the bioreactor reached the desired region, GOx promptly consumed the intratumoral glucose and oxygen to starve cancer cells for robust starvation therapy. More importantly, the aggravated acidic microenvironment at the tumor region was found to induce the decomposition of the MOF structure, thus triggering the release of DOX for reinforced chemotherapy. This bioreactor would further prompt the development of synergistic patterns toward cancer treatment in a spatiotemporally controlled manner.

Anti-cancer adjuvant drug screening via epithelial-mesenchymal transition-related aptamer probe.

Epithelial-mesenchymal transition (EMT) is implicated in the pathological processes of cancer metastasis and drug resistance. Anti-cancer drugs may also potentially lead to EMT, resulting in their reduced therapeutic effect. Therefore, the combination of these anti-cancer drugs with anti-EMT agents has been promoted in clinic. Screening anti-EMT drugs and evaluation of EMT process are highly dependent on EMT biomarkers on cell membrane. At present, the detection of EMT biomarker is mainly by Western blot method, which is time-consuming and complicated. In this work, for effectively screening anti-EMT drugs by evaluation of the EMT process, a type of aptamer probe based on aggregation-induced emission (AIE) was designed. The aptamer SYL3C was employed to target the EMT biomarker EpCAM on cell membrane. Two fluorophores, FAM and tetraphenylethene (TPE, an AIE dye), were modified at the two ends of SYL3C, respectively. This aptamer probe (TPE-SYL3C-FAM) can monitor the EpCAM expression, which can be recovered by anti-EMT drugs. By observation of the change in TPE emission intensity, the anti-EMT effect of drugs can be evaluated. The FAM emission was used as internal reference to reduce environmental interferences. This probe can be potentially used to screen anti-EMT agents as anti-cancer adjuvant drugs with high throughput.

Circulating tumor DNA analysis for tumor diagnosis.

Tumor is a kind of abnormal organism generated by the proliferation and differentiation of cells in the body under the action of various initiating and promoting factors, which seriously threatens human life and health. Tumorigenesis is a gradual process that involves multistage reactions and the accumulation of mutations. Gene mutation usually occurs during tumorigenesis, and can be used for tumor diagnosis. Early diagnosis is the most effective way to improve the cure rate and reduce the mortality rate. Among the peripheral blood circulating tumor DNA (ctDNA), gene mutation in keeping with tumor cells can be detected, which can potentially replace tumor tissue section for early diagnosis. It has been considered as a liquid biopsy marker with good clinical application prospect. However, the high fragmentation and low concentration of ctDNA in blood result in the difficulty of tumor stage determination. Therefore, high sensitive and specific mutation detection methods have been developed to detect trace mutant ctDNA. At present, the approaches include digital PCR (dPCR), Bead, Emulsion, Amplification and Magnetic (BEAMing), Next Generation Sequencing (NGS), Amplification Refractory Mutation System (ARMS), etc. In this paper, the principle, characteristics, latest progress and application prospects of these methods are reviewed, which will facilitate researchers to choose appropriate ctDNA detection approaches.

Multiple adsorption properties of aptamers on metal-organic frameworks for nucleic acid assay.

Enrichment and detection of circulating free nucleic acids in biological samples have gained great attention for disease diagnosis or prognostic evaluation. Nanoscale metal-organic frameworks (NMOFs) have been used for aptamer-based nucleic acid sensing. In this work, different NMOFs, including ZIF-8, MIL-88, MIL-100, MIL-101, as well as Eu-TDA and Tb-TDA [prepared by the coordination of 2,2'-thiodiacetic acid (TDA) and Eu3+ or Tb3+], were investigated in nucleic acid sensing by employing their aptamer adsorption ability and fluorescence quenching capacity for the labeled dyes. Two types of dye aptamer, FAM-labeled aptamer (FAM-Ap) and TexasRedaptamer (TexasRed-Ap) were designed, and their adsorption properties on NMOFs-were compared. It was found that the TexasRed-Ap can be well used for nucleic acid (miR-21) extraction and sensing by linking with a pH-responsive nucleotide chain (TexasRed-Ap-pH) or with an additional random chain ssDNA-1' (TexasRed-Ap-a). After interacted with the target miR-21 in biosamples, the TexasRed-dsDNA + NMOFs composites can be collected, and the formed TexasRed-dsDNA can be released by changing pH value or addition of ssDNA-1, which is matched with ssDNA-1'. A linear relationship from 0.1 to 200 pM for miR-21 detection was obtained. The results show that the NMOFs can be used as promising platforms for nucleic acid extraction and fluorescent sensing.

Colorable Zeolitic Imidazolate Frameworks for Colorimetric Detection of Biomolecules.

We report a series of colorable zeolitic imidazolate framework (ZIF)-based nanomaterials prepared by encapsulating starches (amylopectin, dextrin, or amylose) or tannic acid in the frameworks of ZIFs and first applied them in colorimetric assay of microRNA/DNA by adding I2/KI or FeCl3 solutions as chromogenic reagents. We found that iodine molecules can lead to rapid degradation of the ZIF-8 framework, while ZIF-90 remains stable. Therefore, ZIF-90 was selected for encapsulating the starches or tannic acid, and then assembled with polyethylenimine (PEI) and aptamers of microRNA/DNA. After interacting with the target microRNA/DNA, the aptamers (Ap) move away from the surface of the prepared Ap-starch@ZIF-90 or Ap-tan@ZIF-90, and the I2/KI or FeCl3 solution is added into the system to interact the starches (amylopectin, dextrin, or amylose) or tannic acid to generate different colors. According to the absorbance spectra, good linear correlations between the logarithm of absorbance intensity and the concentration of microRNA (1-180 nM) can be observed, and the naked eye can distinguish the change from ∼60 to ∼180 nM with a concentration gradient of 20 nM. A similar colorimetric assay ability for pathogenic bacteria can also be realized by detecting the gene fragments IS200 and eaeA. The detection limits can be potentially optimized by changing the amount of adsorbed PEI and aptamers on the surface of Ap-starch@ZIF-90 (or Ap-tan@ZIF-90) nanoparticles. This method could be a promising alternative for simple and cost-effective assay of microRNA/DNA.

Fluorescence resonance energy transfer (FRET)-based nanoarchitecture for monitoring deubiquitinating enzyme activity.

A novel nanoarchitecture (MSN-Tb-UbR) was prepared by modifying rhodamine B-labelled Ubs (Ub-Rs) on the surface of mesoporous silica nanoparticles (MSNs) loaded with Tb3+-complexes. The MSN-Tb-UbR exhibits ratiometric sensing ability for DUB (UCH-L1) with good sensitivity and selectivity.

Development of biological metal-organic frameworks designed for biomedical applications: from bio-sensing/bio-imaging to disease treatment.

Metal-organic frameworks (MOFs) are built using various organic ligands and metal ions (or clusters). With properties of high porosity, tunable chemical composition, and potential for post-synthetic modification, they have been applied in biomedicine, especially in bio-sensing, bio-imaging, and drug delivery. Since organic ligands and metal centers (ions or clusters) in the structure of MOFs can directly influence the property, function, and performance of MOFs, strict screening of organic ligands and metal centers is necessary. Especially, to improve the application of MOFs in the field of biomedicine, biocompatible organic ligands with low toxicity are desirable. In recent years, biological metal-organic frameworks (bio-MOFs) with ideal biocompatibility and diverse functionality have attracted wide attention. Endogenous biomolecules, including nucleobases, amino acids, peptides, proteins, porphyrins and saccharides, are employed as frameworks for MOF construction. These biological ligands coordinate with diverse metal centers in different ways, leading to the structural diversity of bio-MOFs. In this review, we summarize the organic ligand selectivity in constructing different types of bio-MOFs and their influence in biomedical applications with attractive new functions.

Regulating Fluorescent Aptamer-Sensing Behavior of Zeolitic Imidazolate Framework (ZIF-8) Platform via Lanthanide Ion Doping.

Nanoscale metal-organic frameworks (NMOFs) have been proved to be effective quenching platforms for fluorescent detection of DNA via fluorophore-quencher pairs. Zeolitic imidazolate framework-8 (ZIF-8) is one type of the most promising NMOFs because of its excellent biocompatibility and easy preparation. However, ZIF-8 is rarely used as platforms for fluorescence sensing of DNA because of its bad fluorescence quenching property. In this study, lanthanide ions were doped into ZIF-8 to regulate its fluorescence quenching behavior. The La3+ doped ZIF-8 (ZIF-8-La) showed the best quenching efficiency on dye-labeled DNA. The signal-to-background ratio was around 3 times higher than ZIF-8. Furthermore, a core-shell La3+-doped ZIF-8 (CS-ZIF-8-La) was designed to modify more La3+ on the surface of ZIF-8. Compared with ZIF-8-La, the CS-ZIF-8-La exhibited the same fluorescence sensing behavior toward positive-dye-labeled DNA, but showed completely contrary quenching property on the negative-dye-labeled DNA. On the basis of this phenomenon, CS-ZIF-8-La was successfully used as quenching platform for designing a ratiometric sensor for DNA and microRNA.

Mitochondria: promising organelle targets for cancer diagnosis and treatment.

Mitochondria, the energy supply factories for cell-life activities, play important roles in controlling epigenetics, differentiation and initiation, and the execution of apoptosis. These functions of the mitochondria contribute to cell adaptation to challenging microenvironment conditions. In past decades, mitochondrial malfunction has been revealed to be closely related to the occurrence and development of a variety of human disorders, including cancer and multiple neurodegenerative diseases. The disturbance of the mitochondrial genome (mtDNA) or mitochondrial vital functions, e.g., the production of adenosine triphosphate (ATP) and the generation of reactive oxygen species (ROS), can potentially be involved in disease pathogenesis. Recent research has shown that the precise monitoring of mitochondrial environments can provide potential directions for cancer diagnosis. Furthermore, mitochondrial-targeted cancer treatment exhibits unparalleled superiority for enhanced tumor therapy. Therefore, in this review, we focus on mitochondrial-based cancer diagnosis via monitoring mitochondrial respiration or mitophagy. Current approaches using mitochondrial-based cancer treatments, including targeting mitochondrial ATP, mitochondrial membrane permeability, and mitochondrial ROS levels and mtDNA, are also summarized. This review will provide insights into mitochondrial-mediated tumor monitoring and mitochondrial-based therapy.

Fluorescent Disulfide-functional Coordination Polymers for Sensitive Detection of Hydrogen Peroxide.

A new type of fluorescent coordination polymer (NCPCd) based on disulfide carboxylate ligand was prepared by using one-pot synthesis for sensitive detection of reactive oxygen species (ROS). With the reaction between NCPCd and ROS, the morphology of the NCPCd was transformed from nanorods to hexagon particles, then broken into nano-fragments. Meanwhile, the fluorescence of NCPCd (at 421 nm) was quenched accordingly. For designing the highly sensitive probe for ROS, Rhodamine 6G (R6G) was doped in NCPCd. In the presence of ROS, the fluorescence of NCPCd moiety at 421 nm was quenched, but the R6G moiety was released from the broken nanorods and the fluorescence at 555 nm from R6G moiety was recovered. The R6G doped NCPCd (NCPCd-R) can be used as a highly sensitive and selective probe for hydrogen peroxide (H2O2) with detection limit of 12.4 nM. Moreover, the NCPCd-R was further extended to the glucose sensing combined with glucose oxidase (GOx) to oxidate glucose and generate H2O2, demonstrating the potential for practical applications.

Insight into the Unique Fluorescence Quenching Property of Metal-Organic Frameworks upon DNA Binding.

Metal-organic frameworks (MOFs) have been successfully used as efficient quenchers for fluorescent DNA detection. However, the surface charge property of MOFs can inevitably affect their fluorescence quenching behavior. Herein, nanoscale MOFs (NMOFs), including MOF nanosheets and nanoparticles, have been employed to investigate the relationship between the fluorescence quenching and surface properties of NMOFs. We find that the positively and negatively charged NMOFs exhibited totally opposite fluorescence quenching properties toward negatively charged FAM-labeled double-stranded DNA (dsDNA). On the contrast, they show negligible influence on the sensing of positively charged TAMRA-labeled dsDNA. This study provides a new insight of the fluorescence quenching property of NMOFs and offers a new concept for construction of ratiometric fluorescence DNA biosensors.

A simple way to fine tune the redox potentials of cobalt ions encapsulated in nitrogen doped graphene molecular catalysts for the oxygen evolution reaction.

Co2+ ions encapsulated in nitrogen doped graphene were applied as an oxygen evolution catalyst. Their redox potentials were tuned using different counter anions as liable ligands, and the redox potential related catalytic rates were explored. It was proposed that the electron density of Co2+ ions was a general descriptor for activity.

Functional Interfaces Constructed by Controlled/Living Radical Polymerization for Analytical Chemistry.

The high-value applications of functional polymers in analytical science generally require well-defined interfaces, including precisely synthesized molecular architectures and compositions. Controlled/living radical polymerization (CRP) has been developed as a versatile and powerful tool for the preparation of polymers with narrow molecular weight distributions and predetermined molecular weights. Among the CRP system, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) are well-used to develop new materials for analytical science, such as surface-modified core-shell particles, monoliths, MIP micro- or nanospheres, fluorescent nanoparticles, and multifunctional materials. In this review, we summarize the emerging functional interfaces constructed by RAFT and ATRP for applications in analytical science. Various polymers with precisely controlled architectures including homopolymers, block copolymers, molecular imprinted copolymers, and grafted copolymers were synthesized by CRP methods for molecular separation, retention, or sensing. We expect that the CRP methods will become the most popular technique for preparing functional polymers that can be broadly applied in analytical chemistry.

Biocompatible chiral monolithic stationary phase synthesized via atom transfer radical polymerization for high performance liquid chromatographic analysis.

Novel biocompatible chiral monolithic stationary phase was prepared by reverse and direct atom transfer radical polymerization (ATRP) methods. By taking advantages of the controlled/living property of ATRP method, the chiral monolith was prepared by reverse ATRP (RATRP) firstly. An attractive feature of RATRP is the prepared polymer containing a terminal radically transferable atom that can initiate another post-polymerization reaction by direct ATRP. Then, the biocompatible poly(hydroxyethyl methacrylate) (PHEMA) was grafted on the surface of the chiral monolith by direct ATRP as a diffusion barrier for proteins. This biocompatible chiral monolith was successfully used as restricted access stationary phase for determination of enantiomers in biological samples with direct injection by high-performance liquid chromatography (HPLC).