iBRET Screen of the ABCD1 Peroxisomal Network and Mutation-Induced Network Perturbations

Mapping the network of proteins provides a powerful means to investigate the function of disease genes and to unravel the molecular basis of phenotypes. We present an automated informatics-aided and bioluminescence resonance energy transfer-based approach (iBRET) enabling high-confidence detection of protein-protein interactions in living mammalian cells. A screen of the ABCD1 protein, which is affected in X-linked adrenoleukodystrophy (X-ALD), against an organelle library of peroxisomal proteins demonstrated applicability of iBRET for large-scale experiments. We identified novel protein-protein interactions for ABCD1 (with ALDH3A2, DAO, ECI2, FAR1, PEX10, PEX13, PEX5, PXMP2, and PIPOX), mapped its position within the peroxisomal protein-protein interaction network, and determined that pathogenic missense variants in ABCD1 alter the interaction with selected binding partners. These findings provide mechanistic insights into pathophysiology of X-ALD and may foster the identification of new disease modifiers.

Light-Activated and Self-Driven Autonomous DNA Nanomachine Enabling Fluorescence Imaging of MicroRNA in Living Cells with Exceptional Precision and Efficiency

Owing to their favorable design flexibility and eminent signal amplification ability, DNA nanomachine-supported biosensors have provided an attractive avenue for intracellular fluorescence imaging, especially for DNA walkers. However, this promising option not only suffers from poor controllability but also needs to be supplied with additional driving forces on account of the frequent employment of metal ion-dependent DNAzymes. Aiming at overcoming these obstacles, we introduce some fruitful solutions. On one hand, innovative light-activated walking behavior induced by a photocleavage mode is established on the surfaces of gold nanoparticles, and such a photoselective sensing system can be perfectly prevented from pre-activating during the intracellular delivery process and made to achieve target identification only under irradiation using a moderate ultraviolet light source. On the other hand, this light-switchable sensing frame is encapsulated within a dissociable metal-organic framework (ZIF-8) to facilitate endocytosis and ensure sufficient internal cofactors (Zn²⁺) to realize a self-driven pattern in the acidic environment of the cell lysosome. Based on the abovementioned efforts, the newly constructed autonomous three-dimensional DNA walkers present satisfactory sensitivity (a limit of detection of down to 19.4 pM) and specificity (even distinguishing single-base changes) toward a model biomarker (microRNA-21). More importantly, the sensing method allows determination of the variations in targets in living cancer cells with exceptional precision and efficiency, offering a powerful assay platform for intracellular imaging.

3D Flower-like NiCo Layered Double Hydroxides: An Efficient Electrocatalyst for Non-Enzymatic Electrochemical Biosensing of Hydrogen Peroxide in Live Cells and Glucose in Biofluids

Herein, a hierarchical structure of flower-like NiCo layered double hydroxides (NiCo LDH) microspheres composed of three-dimensional (3D) ultrathin nanosheets was successfully synthesized via a facile hydrothermal approach. The formation of NiCo LDH was confirmed by various physicochemical studies, and the NiCo LDH-modified glassy carbon electrode was used as an efficient dual-functional electrocatalyst for non-enzymatic glucose and hydrogen peroxide (H₂O₂) biosensor. The host matrix of hydrotalcite NiCo LDH exhibits the enhanced electrocatalytic sensing performances with a quick response time (<3 s), wide linear range (50 nM-18.95 mM and 20 nM-11.5 mM) and lowest detection limits (S/N = 3) (10.6 and 4.4 nM) toward glucose and H₂O₂, and also it exhibits good stability, selectivity, and reproducibility. In addition, this biosensor was successfully utilized to the real-time detection of endogenous H₂O₂ produced from live cells and glucose in various biological fluids, and demonstrates that the as synthesized NiCo LDH may provide a successful pathway for physiological and clinical pathological diagnosis.

A novel fluorescent probe for rapid detection of sulfur dioxide in living cells

Sulfur dioxide is one of the reactive sulfur species, which has significant physiological functions in cells. Some physiological processes are closely related to SO₂ in organisms, and the high concentration of SO₂ in living cells can cause many diseases. In order to investigate the unique function of SO₂ at the subcellular level, developing a molecular tool which could detect of SO₂ within organelles is imperative. Hence, we developed a cationic dye named HQ-SO₂ as a new fluorescent probe to specifically monitor SO₂ , which was easy to obtain through one-step reaction. It took Michael addition reaction as the mechanism of reaction for detection of SO₂ . In addition, this probe showed a series of highly favorable properties such as rapid response rate, low cytotoxicity, high selectivity, low detection limit, and good photostability, which enabled the probe to track SO₂ in living cells.

Measuring calibration factors by imaging a dish of cells expressing different tandem constructs plasmids

Three-cube Förster resonance energy transfer (FRET) method is the most extensively applied approach for live-cell FRET quantification. Reliable measurements of calibration factors are crucial for quantitative FRET measurement. We here proposed a modified TA-G method (termed as mTA-G) to simultaneously obtain the FRET-sensitized quenching transition factor (G) and extinction coefficients ratio (γ) between donor and acceptor. mTA-G method includes four steps: (1) predetermining the ratio ranges of the sensitized emission of acceptor (F_C ) to the donor excitation and donor channel image (I_DD [(DA])) for all FRET plasmids; (2) culturing the cells which express every FRET plasmid in one dish respectively; (3) distinguishing and marking the cells expressing different FRET plasmids by detecting their F_C /I_DD (DA) values; (4) linearly fitting F_C /I_AA (DA) (acceptor excitation and acceptor channel image) to I_DD (DA)/I_AA (DA) for different kinds of cells. We implemented mTA-G method by imaging tandem constructs cells with different FRET efficiency cultured in one dish on different days, and obtained consistent G and γ values. mTA-G method not only circumvents switchover of different culture dishes but also keep the constant imaging conditions, exhibiting excellent robustness, and thus will expands the biological applications of quantitative FRET analysis in living cells.

Ratiometric Detection of Mercury (II) Ions in Living Cells Using Fluorescent Probe Based on Bis(styryl) Dye and Azadithia-15-Crown-5 Ether Receptor

Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg²⁺ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500-600 nm) to red (600-730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg²⁺ concentration in the 37 nM-1 μM range.

The Molecular and Pathophysiological Functions of Members of the LNX/PDZRN E3 Ubiquitin Ligase Family

The ligand of Numb protein-X (LNX) family, also known as the PDZRN family, is composed of four discrete RING-type E3 ubiquitin ligases (LNX1, LNX2, LNX3, and LNX4), and LNX5 which may not act as an E3 ubiquitin ligase owing to the lack of the RING domain. As the name implies, LNX1 and LNX2 were initially studied for exerting E3 ubiquitin ligase activity on their substrate Numb protein, whose stability was negatively regulated by LNX1 and LNX2 via the ubiquitin-proteasome pathway. LNX proteins may have versatile molecular, cellular, and developmental functions, considering the fact that besides these proteins, none of the E3 ubiquitin ligases have multiple PDZ (PSD95, DLGA, ZO-1) domains, which are regarded as important protein-interacting modules. Thus far, various proteins have been isolated as LNX-interacting proteins. Evidence from studies performed over the last two decades have suggested that members of the LNX family play various pathophysiological roles primarily by modulating the function of substrate proteins involved in several different intracellular or intercellular signaling cascades. As the binding partners of RING-type E3s, a large number of substrates of LNX proteins undergo degradation through ubiquitin-proteasome system (UPS) dependent or lysosomal pathways, potentially altering key signaling pathways. In this review, we highlight recent and relevant findings on the molecular and cellular functions of the members of the LNX family and discuss the role of the erroneous regulation of these proteins in disease progression.

Surface-Enhanced Raman Spectroscopy of Organic Molecules and Living Cells with Gold-Plated Black Silicon

Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR) while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with a nm-thin layer of plasmonic metal, i.e., gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surface-enhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 10⁸ due to a combination of electromagnetic and chemical mechanisms. This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cell nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristic protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics devices.

Stretchable Electrochemical Biosensing Platform Based on Ni-MOF Composite/Au Nanoparticle-Coated Carbon Nanotubes for Real-Time Monitoring of Dopamine Released from Living Cells

Existing electrochemical biosensing platforms, using traditional rigid and unstretchable electrodes, cannot monitor the biological signaling molecules released by cells in a mechanically deformed state in real time. Here, a stretchable and flexible electrochemical sensor was developed based on nickel metal-organic framework composite/Au nanoparticle-coated carbon nanotubes (Ni-MOF composite/AuNPs/CNTs) for sensitive detection of dopamine (DA) released by C6 living cells in real time. A Ni-MOF composite was obtained by introducing Ni, NiO, and a carbon frame onto the surface of two-dimensional (2D) Ni-MOF nanosheets using an efficient one-step calcination method. The hybrid of Ni-MOF composite/AuNPs/CNTs that deposited on the poly(dimethylsiloxane) (PDMS) film endowed the sensor with excellent electrochemical performance with a wide linear range of 50 nM to 15 μM and a high sensitivity of 1250 mA/(cm² M) and also provided the sensor with desirable stability against mechanical deformation. Furthermore, the stretchable electrode also displayed good cellular compatibility while C6 living cells can be cultured and proliferated on it with strong adhesion. Then, the DA released by C6 living cells with chemical induction in both natural and stretched states was monitored using our stretchable and flexible electrochemical sensor in real time. This indicates that our new design of flexible Ni-MOF composite/AuNPs/CNTs/PDMS (NACP) film electrodes provides more opportunities for the detection of chemical signals released from cells and soft living organisms even under mechanically deformed states.

High-Yield Production of Water-Soluble MoS2 Quantum Dots for Fe3+ Detection and Cell Imaging

Uniform water-soluble MoS2 quantum dots (WS-MSQDs) were synthesized via a sequential combination of sintering/etching/exfoliation method and solvothermal route. The obtained WS-MSQDs with average size of approximately 3.4 nm exhibited sufficient water solubility and remarkable fluorescence properties. The WS-MSQDs were utilized as a probe for detection of Fe3+ ions with high selectivity and specificity. Furthermore, the WS-MSQDs exhibited high fluorescence stability under different conditions. Finally, the WS-MSQDs were successfully applied for the fluorescence imaging of Fe3+ in living cells, which exhibited practical potential for biomedical applications.

Nile-Red-Based Fluorescence Probe for Selective Detection of Biothiols, Computational Study, and Application in Cell Imaging

A new colorimetric and fluorescence probe NRSH based on Nile-red chromophore for the detection of biothiols has been developed, exhibiting high selectivity towards biothiols over other interfering species. NRSH shows a blue shift in absorption peak upon reacting with biothiols, from 587 nm to 567 nm, which induces an obvious color change from blue to pink and exhibits a 35-fold fluorescence enhancement at 645 nm in red emission range. NRSH displays rapid (<1 min) response for H₂S, which is faster than other biothiols (>5 min). The detection limits of probe NRSH towards biothiols are very low (22.05 nM for H₂S, 34.04 nM for Cys, 107.28 nM for GSH and 113.65 nM for Hcy). Furthermore, NRSH is low cytotoxic and can be successfully applied as a bioimaging tool for real-time monitoring biothiols in HeLa cells. In addition, fluorescence mechanism of probe NRSH is further understood by theoretical calculations.

In Vivo Biosynthesis of Inorganic Nanomaterials Using Eukaryotes-A Review

Bionanotechnology, the use of biological resources to produce novel, valuable nanomaterials, has witnessed tremendous developments over the past two decades. This eco-friendly and sustainable approach enables the synthesis of numerous, diverse types of useful nanomaterials for many medical, commercial, and scientific applications. Countless reviews describing the biosynthesis of nanomaterials have been published. However, to the best of our knowledge, no review has been exclusively focused on the in vivo biosynthesis of inorganic nanomaterials. Therefore, the present review is dedicated to filling this gap by describing the many different facets of the in vivo biosynthesis of nanoparticles (NPs) using living eukaryotic cells and organisms-more specifically, live plants and living biomass of several species of microalgae, yeast, fungus, mammalian cells, and animals. It also highlights the strengths and weaknesses of the synthesis methodologies and the NP characteristics, bio-applications, and proposed synthesis mechanisms. This comprehensive review also brings attention to enabling a better understanding between the living organisms themselves and the synthesis conditions that allow their exploitation as nanobiotechnological production platforms as these might serve as a robust resource to boost and expand the bio-production and use of desirable, functional inorganic nanomaterials.

A caged 2-hydroxyethyl luciferin for bioluminescence imaging of nitroxyl in living cells

Nitroxyl (HNO), a one-electron reduction product of nitric oxide, demonstrates distinct biological and pharmacological activities. Here we designed a bioluminescent turn-on probe, HNO-8, that could be used to visualize HNO without the need for excitation light. HNO-8 was prepared by caging 2-hydroxyethyl luciferin with a triphenylphosphine unit, in which 2-hydroxyethyl luciferin as a novel substrate of firefly luciferase was characterized by stronger and more sustained bioluminescent signals than the most popular substrates of d-luciferin and 6'-aminoluciferin. In vitro experiments showed that HNO-8 could selectively respond to HNO generated from Angeli's salt(AS) in the range 1-50 μM, with a limit of detection of 0.196 μM. The probe was successfully applied for visualizing HNO in luciferase-transfected Huh7 cancer cells. We envision that HNO-8 could be used as a powerful bioluminescent sensor for researching HNO biological roles.

DNA-Driven Two-Layer Core-Satellite Gold Nanostructures for Ultrasensitive MicroRNA Detection in Living Cells

It is a significant challenge to achieve controllable self-assembly of superstructures for biological applications in living cells. Here, a two-layer core-satellite assembly is driven by a Y-DNA, which is designed with three nucleotide chains that hybridized through complementary sequences. The two-layer core-satellite nanostructure (C₃₀ S₅ S₁₀ NS) is constructed using 30 nm gold nanoparticles (Au NPs) as the core, 5 nm Au NPs as the first satellite layer, and 10 nm Au NPs as the second satellite layer, resulting in a very strong circular dichroism (CD) and surface-enhanced Raman scattering. After optimization, the yield is up to 85%, and produces a g-factor of 0.16 × 10^-2 . The hybridization of the target microRNA (miRNA) with the molecular probe causes a significant drop in the CD and Raman signals, and this phenomenon is used to detect the miRNA in living cells. The CD signal has a good linear range of 0.011-20.94 amol ng_RNA^-1 and a limit of detection (LOD) of 0.0051 amol ng_RNA^-1 , while Raman signal with the range of 0.052-34.98 amol ng_RNA^-1 and an LOD of 2.81 × 10^-2 amol ng_RNA^-1 . This innovative dual-signal method can be used to quantify biomolecules in living cells, opening the way for ultrasensitive, highly accurate, and reliable diagnoses of clinical diseases.

2D Nanoarchitectonics: Soft Interfacial Media as Playgrounds for Microobjects, Molecular Machines, and Living Cells

Soft and flexible two-dimensional (2D) systems, such as liquid interfaces, would have much more potentials in dynamic regulation on nano-macro connected functions. In this Minireview article, we focus especially on dynamic motional functions at liquid dynamic interfaces as 2D material systems. Several recent examples are selected to be explained for overviewing features and importance of dynamic soft interfaces in a wide range of action systems. The exemplified research systems are mainly classified into three categories: (i) control of microobjects with motional regulations; (ii) control of molecular machines with functions of target discrimination and optical outputs; (iii) control of living cells including molecular machine functions at cell membranes and cell/biomolecular behaviors at liquid interface. Sciences on soft 2D media with motional freedom and their nanoarchitectonics constructions will have increased importance in future technology in addition to popular rigid solid 2D materials.

Modulation of Living Cell Behavior with Ultra-Low Fouling Polymer Brush Interfaces

Ultra-low fouling and functionalizable coatings represent emerging surface platforms for various analytical and biomedical applications such as those involving examination of cellular interactions in their native environments. Ultra-low fouling surface platforms as advanced interfaces enabling modulation of behavior of living cells via tuning surface physicochemical properties are presented and studied. The state-of-art ultra-low fouling surface-grafted polymer brushes of zwitterionic poly(carboxybetaine acrylamide), nonionic poly(N-(2-hydroxypropyl)methacrylamide), and random copolymers of carboxybetaine methacrylamide (CBMAA) and HPMAA [p(CBMAA-co-HPMAA)] with tunable molar contents of CBMAA and HPMAA are employed. Using a model Huh7 cell line, a systematic study of surface wettability, swelling, and charge effects on the cell growth, shape, and cytoskeleton distribution is performed. This study reveals that ultra-low fouling interfaces with a high content of zwitterionic moieties (>65 mol%) modulate cell behavior in a distinctly different way compared to coatings with a high content of nonionic HPMAA. These differences are attributed mostly to the surface hydration capabilities. The results demonstrate a high potential of carboxybetaine-rich ultra-low fouling surfaces with high hydration capabilities and minimum background signal interferences to create next-generation bioresponsive interfaces for advanced studies of living objects.

Monitoring the Kinetics of the Cellular Uptake of a Metal Carbonyl Conjugated with a Lipidic Moiety in Living Cells Using Synchrotron Infrared Spectromicroscopy

Presented here is the exploitation of synchrotron infrared spectromicroscopy to evaluate the feasibility of monitoring the cellular uptake of rhenium-tris-carbonyl-tagged (Re(CO)₃) lipophilic chains in living cells. To this aim, an in-house thermostated microfluidic device was used to limit water absorption while keeping cells alive. Indeed, cells showed a high survival rate in the microfluidic device over the course of the experiment, proving the short-term biocompatibility of the device. We recorded spectra of single, living, fully hydrated breast cancer MDA-MB231 cells and could follow the penetration of the rhenium complexes for up to 2 h. Despite the strong variations observed in the uptake kinetics between individual cells, the Re(CO)₃ complex was traced inside the cells at low concentration and shown to enter them on the hour time scale by active transport.

Quantum Dots for Monitoring Choline Consumption Process of Living Cells via an Electrostatic Force-Mediated Energy Transfer

In this work, a ratiometric nanoprobe CdS/ZnS-FB was designed for H₂O₂ detection based on FRET assay. Furthermore, CdS/ZnS-FB could work for detecting choline (Ch) and acetylcholine (ACh) since H₂O₂ is the enzyme cascade reaction product. Significantly, the Jurkat T's choline consumption could also be quantitatively measured by monitoring FRET ratio (I₅₂₂/I₄₂₆). Thus, the biosensor could be applied as a universal tool for the detection of choline consumption of living cells, which provides a good potential for the applications in detecting chemical transmitter and cancer diagnosis.

An optical and non-invasive method to detect the accumulation of ubiquitin chains

The accumulations of excess amounts of polyubiquitinated proteins are cytotoxic and frequently observed in pathologic tissue from patients of neurodegenerative diseases. Therefore, optical and non-invasive methods to detect the increase of the amounts of polyubiquitinated proteins in living cells is a promising strategy to find out symptoms and environmental cause of neurodegenerative diseases, also for identifying compounds that could inhibit gathering of polyubiquitinated proteins. Therefore, we generated a pair of fluorescent protein [Azamigreen (Azg) and Kusabiraorange (Kuo)] tagged ubiquitin on its N-terminus (Azg-Ub and Kuo-Ub) and developed an Azg/Kuo-based Fluorescence Resonance Energy Transfer (FRET) assay to estimate the amount of polyubiquitin chains in vitro and in vivo. The FRET intensity was attenuated in the presence of ubiquitin-activating enzyme inhibitor, PYR-41, indicating that both fluorescent ubiquitin is incorporated into ubiquitin chains likewise normal ubiquitin. The FRET intensity was enhanced by the addition of the proteasome inhibitor, MG-132, and was reduced in the presence of the autophagy activator Rapamycin, designating that ubiquitin chains with fluorescent ubiquitin act as the degradation signal equally with normal ubiquitin chains. In summary, the above optical methods provide powerful research tools to estimate the amounts of polyubiquitin chains in vitro and in vivo, especially non-invasively in living cells.

Quantifying the inhibitory effect of Bcl-xl on the action of Mff using live-cell fluorescence imaging

Mitochondrial fission regulates mitochondrial function and morphology, and has been linked to apoptosis. The mitochondrial fission factor (Mff), a tail‐anchored membrane protein, induces excessive mitochondrial fission, contributing to mitochondrial dysfunction and apoptosis. Here, we evaluated the inhibitory effect of Bcl‐xl, an antiapoptotic protein, on the action of Mff by using live‐cell fluorescence imaging. Microscopic imaging analysis showed that overexpression of Mff induced mitochondrial fragmentation and apoptosis, which were reversed by coexpression of Bcl‐xl. Microscopic imaging and live‐cell fluorescence resonance energy transfer analysis demonstrated that Bcl‐xl reconstructs the Mff network from punctate distribution of higher‐order oligomers to filamentous distribution of lower‐order oligomers. Live‐cell fluorescence resonance energy transfer two‐hybrid assay showed that Bcl‐xl interacted with Mff to form heterogenous oligomers with 1 : 2 stoichiometry in cytoplasm and 1 : 1 stoichiometry on mitochondria, indicating that two Bcl‐xl molecules primarily interact with four Mff molecules in cytoplasm, but with two Mff molecules on mitochondria.

Mitochondrial fission factor (Mff)‐mediated mitochondrial fission is positively correlated with the self‐oligomerization of Mff. Bcl‐xl directly interacts with Mff to prevent Mff‐mediated mitochondrial fission and apoptosis. Bcl‐xl interacts with Mff to form heterogenous hexamers with 1 : 2 stoichiometry in cytoplasm and heterogenous tetramers with 1 : 1 stoichiometry on the mitochondrial membrane, respectively.

Refractive-Index-Insensitive Nanolaminated SERS Substrates for Label-Free Raman Profiling and Classification of Living Cancer Cells

Surface-enhanced Raman spectroscopy (SERS) has emerged as an ultrasensitive molecular-fingerprint-based technique for label-free biochemical analysis of biological systems. However, for conventional SERS substrates, SERS enhancement factors (EFs) strongly depend on background refractive index (RI), which prevents reliable spatiotemporal SERS analysis of living cells consisting of different extra-/intracellular organelles with a heterogeneous distribution of local RI values between 1.30 and 1.60. Here, we demonstrate that nanolaminated SERS substrates can support uniform arrays of vertically oriented nanogap hot spots with large SERS EFs (>10⁷) insensitive to background RI variations. Experimental and numerical studies reveal that the observed RI-insensitive SERS response is due to the broadband multiresonant optical properties of nanolaminated plasmonic nanostructures. As a proof-of-concept demonstration, we use RI-insensitive nanolaminated SERS substrates to achieve label-free Raman profiling and classification of living cancer cells with a high prediction accuracy of 96%. We envision that RI-insensitive high-performance nanolaminated SERS substrates can potentially enable label-free spatiotemporal biochemical analysis of living biological systems.

Latent Redox Reporter of 4-Methoxyphenol as Electrochemical Signal Proxy for Real-Time Profiling of Endogenous H2O2 in Living Cells

Hydrogen peroxide (H₂O₂) plays a persuasive role in the human cell physiology. Developing an efficient assay platform and a highly sensitive tracking and quantification of H₂O₂ in a physiological system is crucial to understand the neoplastic changes and/or redox homeostasis of cells. In this study, a novel turn-on latent electrochemical redox probe coupled with electrocatalytic signal amplification strategy is proposed. A custom-made readily available turn-on latent electrochemical probe 4-methoxyphenylboronic acid pinacol ester (4-MPBP) have been designed for the selective detection of endogenous H₂O₂ in live cells. The electrochemical probe composed of a latent electrochemical reporter (4-methoxy phenol, 4-MP) bearing a recognition unit (boronic acid pinacol ester) for H₂O₂ sensing. The selective analyte-triggered chemical transformation releases free electrochemical reporter 4-MP. The amount of H₂O₂ was evaluated electrochemically at glassy carbon electrode (GCE) with a broad detection range of 0.5 μM-1 mM. An amplified signal response of released 4-MP to build a highly sensitive assay tool has been achieved via replacing the GCE transducer electrode with polydopamine@carbonnanotube-molebtinumdisulfie hybrid modified GCE as it delivered an exceptional dynamic detection range of 0.01-100 μM. The innovative blend of electrochemical molecular probe strategy, with electrocatalytic signal amplification technique has delivered outstanding assay performance at trace level sensing of H₂O₂. Next, we set up a platform for real-time in vivo monitoring of the endogenously produced H₂O₂ in Caco-2 and MCF-7 cells through spermine-polyamine analogue and phorbol 12-myristate 13-acetate induction in SSAT/PAO gene and protein kinase C, respectively. As expected, the 4-MPBP latent probe coupled with electrocatalytic signal amplification strategy delivered outstanding performance for in situ H₂O₂ release and tracking over time.

Visualizing Proteasome Activity and Intracellular Localization Using Fluorescent Proteins and Activity-Based Probes

The proteasome is a multi-catalytic molecular machine that plays a key role in the degradation of many cytoplasmic and nuclear proteins. The proteasome is essential and proteasome malfunction is associated with various disease pathologies. Proteasome activity depends on its catalytic subunits which are interchangeable and also on the interaction with the associated regulatory cap complexes. Here, we describe and compare various methods that allow the study of proteasome function in living cells. Methods include the use of fluorescently tagged proteasome subunits and the use of activity-based proteasome probes. These probes can be used in both biochemical assays and in microscopy-based experiments. Together with tagged proteasomes, they can be used to study proteasome localization, dynamics, and activity.

Detecting Zn(II) Ions in Live Cells with Near-Infrared Fluorescent Probes

Two near-infrared fluorescent probes (A and B) containing hemicyanine structures appended to dipicolylamine (DPA), and a dipicolylamine derivative where one pyridine was substituted with pyrazine, respectively, were synthesized and tested for the identification of Zn(II) ions in live cells. In both probes, an acetyl group is attached to the phenolic oxygen atom of the hemicyanine platform to decrease the probe fluorescence background. Probe A displays sensitive fluorescence responses and binds preferentially to Zn(II) ions over other metal ions such as Cd2+ ions with a low detection limit of 0.45 nM. In contrast, the emission spectra of probe B is not significantly affected if Zn(II) ions are added. Probe A possesses excellent membrane permeability and low cytotoxicity, allowing for sensitive imaging of both exogenously supplemented Zn(II) ions in live cells, and endogenously releases Zn(II) ions in cells after treatment of 2,2-dithiodipyridine.

Quantitative FRET measurement based on spectral unmixing of donor, acceptor and spontaneous excitation-emission spectra

The spontaneous excitation-emission (ExEm) spectrum is introduced to the quantitative mExEm-spFRET methodology we recently developed as a spectral unmixing component for quantitative fluorescence resonance energy transfer measurement, named as SPEES-FRET method. The spectral fingerprints of both donor and acceptor were measured in HepG2 cells with low autofluorescence separately expressing donor and acceptor, and the spontaneous spectral fingerprint of HEK293 cells with strong autofluoresence was measured from blank cells. SPEES-FRET was performed on improved spectrometer-microscope system to measure the FRET efficiency (E) and concentration ratio (R _C ) of acceptor to donor vales of FRET tandem plasmids in HEK293 cells, and obtained stable and consistent results with the expected values. Moreover, SPEES-FRET always obtained stable results for the bright and dim cells coexpressing Cerulean and Venus or Cyan Fluorescent Protein (CFP)-Bax and Yellow fluorescent protein (YFP)-Bax, and the E values between CFP-Bax and YFP-Bax were 0.02 for healthy cells and 0.14 for the staurosporine (STS)-treated apoptotic cells. Collectively, SPEES-FRET has very strong robustness against cellular autofluorescence, and thus is applicable to quantitative evaluation on the protein-protein interaction in living cells with strong autofluoresence.