Two-Photon Enzymatic Probes Visualizing Sub-cellular/Deep-brain Caspase Activities in Neurodegenerative Models

Recent Advance in Single-Molecule Fluorescent Biosensors for Tumor Biomarker Detection

The construction of biosensors for specific, sensitive, and rapid detection of tumor biomarkers significantly contributes to biomedical research and early cancer diagnosis. However, conventional assays often involve large sample consumption and poor sensitivity, limiting their further application in real samples. In recent years, single-molecule biosensing has emerged as a robust tool for detecting and characterizing biomarkers due to its unique advantages including simplicity, low sample consumption, ultra-high sensitivity, and rapid assay time. This review summarizes the recent advances in the construction of single-molecule biosensors for the measurement of various tumor biomarkers, including DNAs, DNA modifications, RNAs, and enzymes. We give a comprehensive review about the working principles and practical applications of these single-molecule biosensors. Additionally, we discuss the challenges and limitations of current single-molecule biosensors, and highlight the future directions.

Novel Förster Resonance Energy Transfer probe with quantum dot for a long-time imaging of active caspases inside individual cells

With the goal to investigate biological phenomena at a single-cell level, we designed, synthesized and tested a molecular probe based on Förster resonance energy transfer (FRET) between a highly luminescent quantum dot (QD) as a donor and a fluorophore or fluorescence quencher as an acceptor linked by a specific peptide. In principle, QD luminescence, effectively dissipated in the probe, is switched on after the cleavage of the peptide by a protease and the release of the quencher. We proposed a novel synthesis strategy of a probe. A two-step synthesis consists of: (i) Conjugation of CdTe QDs functionalized by -COOH groups of succinic acid on the nanoparticle surface with the designed specific peptide (GTADVEDTSC) using a ligand-exchange approach; (ii) A fast, high-yield reaction of amine-reactive succinimidyl group on the BHQ-2 quencher with N-terminal of the peptide. This way, any crosslinking between individual nanoparticles and any nonspecific conjugation bonds are excluded. The analysis of the product after the first step proved a high reaction yield and nearly no occurrence of unreacted QDs, a prerequisite of the specificity of our luminescent probe. Its parameters evaluated as Michaelis-Menten description of enzymatic kinetics are similar to products published by other groups. Our research is focused on the fluorescence microscopy analyses of biologically active molecules, such as proteolytic active caspases, playing important roles in cell signaling regulations in normal and diseased states. Consequently, they are attractive targets for clinical diagnosis and medical therapy. The ultimate goal of our work was to synthesize a new QD luminescent probe for a long-time quantitative monitoring of active caspase-3/7 distribution in apoptotic osteoblastic MC3T3-E1 cells treated with camptothecin. As a result of comparison, our synthetized luminescent probe provides longer imaging times of caspases than commercial products. The probe proved the stability of the luminescence signal inside cells for more than 14 days.

Two-Photon Fluorescent Probes for Detecting Enzyme Activities in Live Tissues

Enzyme regulation is crucial in living organisms to catalyze various biosyntheses to maintain several physiological functions. On the contrary, abnormal enzyme activities can affect bioactivities leading to various serious disorders including cancer, Alzheimer's disease, Parkinson's disease, heart disease, and so on. This biological significance led to the development of various techniques to map specific enzyme activities in living systems to understand their role and distribution. Two-photon microscopy (TPM) in particular has emerged as a promising system for in situ real-time bioimaging owing to its robustness, high sensitivity, and noninvasiveness. It was achieved through the use of a two-photon (TP) light source of an optical window (700-1450 nm) beneficial in deeper light penetration and extraordinary spatial selectivity. Therefore, developing enzyme sensors utilized in TPM has significance in obtaining in vivo enzyme activities with minimal perturbation. The development of an efficient detection tool for enzymes has been continuously reported in the previous literature; here, we meticulously review the TP design strategies that have been attempted by researchers to develop enzyme TP fluorescent sensors that are proving very useful in providing insights for enzyme investigation in the biological system. In this review, the representative TP enzymatic probes that have been made in the past 5 years and their applications in tissue imaging are discussed in brief. In addition, the prospects and challenges of TP enzymatic probe development are also discussed.

Light emitting probes – approaches for interdisciplinary applications

Luminescent probes are key components of sensors to detect numerous bio- and chemical-analytes with high sensitivity and specificity. Sensing is the response of events like self-immolation, FRET, electron/charge transfer, etc. upon interaction.

Mitochondrial Targeting of Probes and Therapeutics to the Powerhouse of the Cell

Mitochondria, colloquially known as "the powerhouse of the cell", play important roles in production, but also in processes critical for cellular fate such as cell death, differentiation, signaling, metabolic homeostasis, and innate immunity. Due to its many functions in the cell, the mitochondria have been linked to a variety of human illnesses such as diabetes, cancer, and neurodegenerative diseases. In order to further our understanding and pharmaceutical targeting of this critical organelle, effective strategies must be employed to breach the complex barriers and microenvironment of mitochondria. Here, we summarize advancements in mitochondria-targeted probes and therapeutics.

Fluorescence imaging of drug target proteins using chemical probes

Fluorescence imaging can provide valuable information on the expression, distribution, and activity of drug target proteins. Chemical probes are useful small-molecule tools for fluorescence imaging with high structural flexibility and biocompatibility. In this review, we briefly introduce two classes of fluorescent probes for the visualization of drug target proteins. Enzymatically activatable probes make use of the specific enzymatic transformations that generally produce a fluorogenic response upon reacting with target enzymes. Alternatively, specific imaging can be conferred with a ligand that drives the probes to target proteins, where the labeling relies on noncovalent binding, covalent inhibition, or traceless labeling by ligand-directed chemistry.

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Fluorescence imaging of drug target proteins is useful for studying their localization and interaction with drugs.

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Enzymatically activatable probes provide high-contrast imaging and a readout of enzyme activity.

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Targeted probes favor specific imaging of non-enzymatic proteins, and LD chemistry allows for traceless labeling.

Smart fluorescent probes for in situ imaging of enzyme activity: design strategies and applications

Enzymes play critical roles in the physiological and pathological processes of living systems. To provide detailed pictures of enzyme activity at the molecular and cellular levels, interdisciplinary studies of chemistry and biology have led to the emergence of many smart fluorescent probes, which emit fluorescence or show a shifted signal only upon interaction with their targets. With distinct advantage of a higher signal-to-noise ratio than traditional ‘always on’ probes, smart fluorescent probes enable sensitive detection of enzymes with clinical significance. In this review, we summarize the design strategies and selected applications of smart fluorescent probes for in situ imaging of enzyme activity. Current challenges and future developments in this field are also discussed.