Sensor Array Fabricated with Nanoscale Metal–Organic Frameworks for the Histopathological Examination of Colon Cancer

Recent Advances on the Metal-Organic Frameworks-Based Biosensing Methods for Cancer Biomarkers Detection

Sensitive and selective detection of cancer biomarkers is crucial for early diagnosis and treatment of cancer, one of the most dangerous diseases in the world. Metal-organic frameworks (MOFs), a class of hybrid porous materials fabricated through the assembly of metal ions/clusters and organic ligands, have attracted increasing attention in the sensing of cancer biomarkers, due to the advantages of adjustable size, high porosity, large surface area and ease of modification. MOFs have been utilized to not only fabricate active sensing interfaces but also arouse a variety of measurable signals. Several representative analytical technologies have been applied in MOF-based biosensing strategies to ensure high detection sensitivity toward cancer biomarkers, such as fluorescence, electrochemistry, electrochemiluminescence, photochemistry and colorimetric methods. In this review, we summarized recent advances on MOFs-based biosensing strategies for the detection of cancer biomarkers in recent three years based on the categories of metal nodes, and aimed to provide valuable references for the development of innovative biosensing platform for the purpose of clinical diagnosis.

Recent Insights into Nanotechnology in Colorectal Cancer

Colorectal cancer (CRC) is the third cancer among the known causes of cancer that impact people. Although CRC drug options are imperfect, primary detection of CRC can play a key role in treating the disease and reducing mortality. Cancer tissues show many molecular markers that can be used as a new way to advance therapeutic methods. Nanotechnology includes a wide range of nanomaterials with high diagnostic and therapeutic power. Several nanomaterials and nanoformulations can be used to treat cancer, especially CRC. In this review, we discuss recent insights into nanotechnology in colorectal cancer.

Smartphone Imaging Device for Multimodal Detection of Hydrogen Sulfide Using Cu-Doped MOF Sensors

Multimodal sensing platforms may offer reliable, fast results, but it is still challenging to incorporate biosensors with high discriminating ability in complex biological samples. Herein, we established a highly sensitive dual colorimetric/electrochemical monitoring approach for the detection of hydrogen sulfide (H2S) utilizing Cu-doped In-based metal-organic frameworks (Cu/In-MOFs) combined with a versatile color selector software-based smartphone imaging device. H2S can result in the enhancement of the electrochemical signal because of the electroactive substance copper sulfide (CuxS), the decrease of the colorimetric signal of the characteristic absorption response caused by the strong coordination effect on Cu/In-MOFs, and the obvious changes of red-green-blue (RGB) values of images acquired via an intelligent smartphone. Attractively, the Cu/In-MOFs-based multimodal detection guarantees precise and sensitive detection of H2S with triple-signal detection limits of 0.096 μM (electrochemical signals), 0.098 μM (colorimetric signals), and 0.099 μM (smartphone signals) and an outstanding linear response. This analytical toolkit provides an idea for fabricating a robust, sensitive, tolerant matrix and reliable sensing platform for rapidly monitoring H2S in clinical disease diagnosis and visual supervision.

Textural Precursor Compositions Harvested for Independent Signal Generators: Scaling Micron-Sized Flower-Like Metal-Organic Frameworks as Amplifying Units for Dual-Mode Glycoprotein Assay

In this work, a micron-sized flower-like metal-organic frameworks (MOFs)-based boronate-affinity sandwich-type immunoassay was fabricated for the dual-mode glycoprotein assay. For proof of concept, the flower-like MOFs were synthesized from transition Cu nodes and tetrakis (4-carboxyphenyl) porphyrin (TCPP) ligands by spontaneous standing assembly. In addition, the specificity toward glycoprotein involved the antigen recognition as well as covalent bonding via the boronate-glycan affinity, and the immediate signal responses were initiated by textural decomposition of the flower-like MOFs. Intriguingly, Cu nodes, of which the valence state is dominant by CuI species, can endow the Fenton-like catalytic reaction of the fluorogenic substrate for generating fluorescence signals. For benefits, TCPP ligands, in which each TCPP molecule has four guest donors, can provide multiple valences for the assembly of cyclodextrin-capped gold nanoparticles via host-guest interaction for colorimetry output. Albeit important, the scaling micrometer patterns for the flower-like MOFs carrying numerous Cu nodes and TCPP ligands can also function as amplifying units, signifying the output signal. The detection limit of the dual-mode glycoprotein assay can reach 10.5 nM for the fluorescence mode and 18.7 nM for the colorimetry mode, respectively. Furthermore, the merits of harvesting different signal generators toward the multimodal readout patterns can allow the mutual verification and make the analytical results more reliable. Collectively, our proposed assay may offer a new idea in combining the inherent textural merits from MOFs for dual signal generators, which can also emphasize accurate detection capability for glycoprotein assay.

Eye-Readable and Wearable Colorimetric Sensor Arrays for In Situ Monitoring of Volatile Organic Compounds

Wearable sensors utilize changes in color as a response to physiological stimuli, making them easily recognizable by the naked eye. These colorimetric wearable sensors offer benefits such as easy readability, rapid responsiveness, cost-effectiveness, and straightforward manufacturing techniques. However, their applications in detecting volatile organic compounds (VOCs) in situ have been limited due to the low concentration of complex VOCs and complicated external interferences. Aiming to address these challenges, we introduced readable and wearable colorimetric sensing arrays with a microchannel structure and highly gas-sensitive materials for in situ detection of complex VOCs. The highly gas-sensitive materials were designed by loading gas-sensitive dyes into the porous metal-organic frameworks and further depositing the composites on the electrospun nanofiber membrane. The colorimetric sensor arrays were fabricated using various gas-sensitive composites, including eight dye/MOF composites that respond to various VOCs and two Pd2+/dye/MOF composites that respond to ethylene. This enables the specific recognition of multiple characteristic VOCs. A microfluidic channel made of polydimethylsiloxane (PDMS) was integrated with different colorimetric elements to create a wearable sensor array. It was attached to the surface of fruits to collect and monitor VOCs using the DenseNet classification method. As a proof of concept, we demonstrated the feasibility of the wearable sensing system in monitoring the ripening process of fruits by continuously measuring the VOC emissions from the skin of the fruit.

Plasmon-Stimulated Colorimetry Biosensor Array for the Identification of Multiple Metabolites

Rationally designing highly catalytic and stable nanozymes for metabolite monitoring is of great importance because of their huge potential in early disease diagnosis. Herein, a novel nanozyme based on hierarchically structured CuS/ZnS with a highly efficient peroxidase (POD)-mimic capability was developed and synthesized for multiple metabolite determination and recognition via the plasmon-stimulated biosensor array strategy. The designed nanozyme can simultaneously harvest plasmon triggered hot electron-hole pairs and generate photothermal properties, leading to a sharply boosted POD-mimic capability under 808 nm laser irradiation. Interestingly, because of the interaction diversity of the metabolite with POD-like nanomaterials, the unique inhibitory effect of metabolites on the POD-mimic activity could be the signal response as the differentiation. Thus, utilizing TMB as a typical chromogenic substrate in the addition of H2O2, the designed colorimetric biosensor array can produce diverse fingerprints for the three vital metabolisms (cysteine (Cys), ascorbic acid (AA), and glutathione (GSH)), which can be precisely identified by principal component analysis (PCA). Notably, a distinct fingerprint of a single metabolite with different levels and metabolite mixtures is also achieved with a detection limit of 1 μM. Most importantly, cell lysis could be effectively discriminated by the biosensor assay, implying its great potential in clinical diagnosis.

Monosystem Discriminative Sensor toward Inorganic Anions via Incorporating Three Different Luminescent Channels in Metal-Organic Frameworks

Because there are great demands of distinguishing multiple chemically similar analytes, chemical sensors for multivariate analyses have been developed rapidly in the past few decades. However, designing luminescent discriminative sensors based on a monosystem has been a challenge until now. In this work, we first develop a triemitting luminescent discriminative platform named RGB@TLU-2 with three different emission centers: blue-emitting center (BDC-NH₂), green-emitting (Tb@BDC-SO₃^-), and red-emitting center (rhodamine B, RhB). The different luminescent mechanisms (ligand emission, LMET emission, guest emission) in these emission centers endow RGB@TLU-2 with high cross-reactivity, which is essential for discriminating applications. To balance the three luminescent centers, all variables in the synthesis process are optimized carefully. Surprisingly, the RGB@TLU-2 shows a variety of luminescent response patterns when immersed into 12 inorganic anions. Two unsupervised multidimensional analysis methods, (principal component analysis and hierarchical cluster analysis), are used to explore the relationship between these anions. On the basis of the luminescent response of analytes, 5 response modes are obtained and 12 inorganic anions are classified into 6 groups. The sensing mechanisms are discussed in detail. Detection limits of typical anions Cr₂O₇^2-, PO₄^3-, ClO^-, and NO₂^- are calculated as 2.895 × 10^-8, 6.353 × 10^-6, 1.134 × 10^-5, and 4.56 × 10^-4 mol/L, respectively. Furthermore, the RGB@TLU-2 also shows the ability to distinguish 4 (Fe³⁺, Fe²⁺, Cu²⁺ and Cr³⁺) of 12 metal ions and 3 (Trp, Pro, and Arg) of 11 amino acids.

Fluorescent Ensemble Sensors and Arrays Based on Surfactant Aggregates Encapsulating Pyrene-Derived Fluorophores for Differentiation Applications

Surfactant assemblies have drawn great attention in fabricating fluorescent sensors as they can provide advantages such as easy preparation, low cost, aqueous detection, high fluorescence stability, high sensitivity to external stimuli, etc. We have devoted the past few years to fluorescent cross-reactive sensors and arrays that are advantageous in differentiating similar analytes and analyzing mixed samples. In this Spotlight on Applications, we introduce our recent advances in developing surfactant assembly-based fluorescent sensors and arrays for discrimination applications. Besides using surfactant assemblies encapsulating fluorophores to fabricate multiple-element-based sensor arrays, we particularly proposed to take advantage of modulation effect of dynamic surfactant assemblies on the photophysical properties of encapsulated fluorophores to construct single-system-based discriminative sensors, which have been successfully applied in differentiation of multiple metal ions and various proteins. The applications of surfactant assembly-based sensors for the detection and discrimination of thiols, amino acids, and explosives are also introduced. Finally, the prospects of further efforts for improving surfactant ensemble sensors and their challenges are discussed.

State-of-the-art progress of switch fluorescence biosensors based on metal-organic frameworks and nucleic acids

Metal-organic frameworks (MOFs) have captured substantial attention of an increasing number of scientists working in sensing analysis fields, due to their large surface area, high porosity, and tunable structure. Recently, MOFs as attractive fluorescence quenchers have been extensively investigated. Given their high quenching efficiency toward the fluorescence intensity of dyes-labeled specific biological recognition molecules, such as nucleic acids, MOFs have been widely developed to switch fluorescence biosensors with low background fluorescence signal. These strategies not only lead to specificity, simplicity, and low cost of biosensors, but also possess advantages such as ultrasensitive, rapid, and multiple detection of switch fluorescence methods. At present, researches of the analysis of switch fluorescence biosensors based on MOFs and nucleic acids mainly focus on sensing of different types of in vitro and intracellular analytes, indicating their increasing potential. In this review, we briefly introduce the principle of switch fluorescence biosensor and the mechanism of fluorescence quenching of MOFs, and mainly discuss and summarize the state-of-the-art advances of MOFs and nucleic acids-based switch fluorescence biosensors over the years 2013 to 2020. Most of them have been proposed to the in vitro detection of different types of analytes, showing their wide scope and applicability, such as deoxyribonucleic acid (DNAs), ribonucleic acid (RNAs), proteins, enzymes, antibiotics, and heavy metal ions. Besides, some of them have also been applied to the bioimaging of intracellular analytes, emerging their potential for biomedical applications, for example, cellular adenosine triphosphate (ATP) and subcellular glutathione (GSH). Finally, the remaining challenges in this sensing field and prospects for future research trends are addressed. Graphical abstract.

A Multichannel Pattern-Recognition-Based Protein Sensor with a Fluorophore-Conjugated Single-Stranded DNA Set

Recently, pattern-recognition-based protein sensing has received considerable attention because it offers unique opportunities that complement more conventional antibody-based detection methods. Here, we report a multichannel pattern-recognition-based sensor using a set of fluorophore-conjugated single-stranded DNAs (ssDNAs), which can detect various proteins. Three different fluorophore-conjugated ssDNAs were placed into a single microplate well together with a target protein, and the generated optical response pattern that corresponds to each environment-sensitive fluorophore was read via multiple detection channels. Multivariate analysis of the resulting optical response patterns allowed an accurate detection of eight different proteases, indicating that fluorescence signal acquisition from a single compartment containing a mixture of ssDNAs is an effective strategy for the characterization of the target proteins. Additionally, the sensor could identify proteins, which are potential targets for disease diagnosis, in a protease and inhibitor mixture of different composition ratios. As our sensor benefits from simple construction and measurement procedures, and uses accessible materials, it offers a rapid and simple platform for the detection of proteins.

A carbon-based polymer dot sensor for breast cancer detection using peripheral blood immunocytes

We constructed a carbon-based polymer dot (CPD) sensor to detect breast cancer based on the differences of peripheral blood cells, providing a new minimally invasive method for cancer diagnosis. This simple and extensible system exhibits clinically relevant accuracy in terms of cancer identification, making it an attractive strategy for diagnosis and prognosis.

Hemin-Bridged MOF Interface with Double Amplification of G-Quadruplex Payload and DNAzyme Catalysis: Ultrasensitive Lasting Chemiluminescence MicroRNA Imaging

Here, we report a double-amplified sensing platform for ultrasensitive chemiluminescence (CL) miRNA detection in real patients' blood in which a hemin-bridged metal-organic framework (MOF) is employed as a functional interface to boost the payload and catalysis of G-quadruplex (G4) DNAzymes. Hemin is here used as the organic ligand for the MOF synthesis, which endows the MOF with an intrinsic peroxidase-like catalytic activity. Most importantly, the MOF surface provides a large amount of binding sites for polymeric G4 DNAzymes that are produced by miRNA-triggered rolling circle amplification reactions, and meanwhile, the interfaced G4 DNAzymes on MOFs (G4/MOFzymes) display an about 100-fold higher catalytic activity than those in solution. By using the G4/MOFzyme catalysts in the luminol/H₂O₂ CL system, the amplification detection of two acute myocardial infarction (AMI)-related miRNAs (low to 1 fM seen with naked eyes) is achieved in human serum with a smartphone as a portable imaging detector, which provides a facile methodology for point-of-care (POC) diagnosis of AMI. Compared with previous smartphone-based counterparts not requiring sophisticated equipment, this new facile methodology shows both 6 orders of magnitude higher sensitivity and an ∼50-fold longer duration for CL miRNA imaging. These unique features allow our developed G4/MOFzymes to be further employed as a novel luminescent ink for printing commonly used patterns.