Polysiloxane-Based Molecular Logic Gate for Dual-Channel Visualizing Mitochondrial pH and Sulphite Changes during Cuproptosis.

Intracellular Cu-induced regulated cell death, characterized by the aggregation of lipidizing mitochondrial enzymes, is called cuproptosis. Mitochondria play a vital role in the metabolic regulation of cell injury and stressful immune responses. The pH levels and sulfur dioxide (SO2) content in mitochondria have important indicative roles in the regulation of cuproptosis. However, fluorescent probes that simultaneously detect changes in pH and SO2 in mitochondria during cuprotosis have not been reported. To fill this blank, in this study, we dexterously used functional polysiloxane as a fluorescent platform to propose a molecular logic gate probe P0-pH-SO2 for detecting changes in intramitochondrial pH and SO2 content through a dual-channel mode. In addition, we defined a new function to reflect the cellular state of the elesclomol-induced cuproptosis process based on the input and output of the relevant logic relationship. This new fluorescent molecular logic gate probe P0-pH-SO2 can be rapidly activated by mitochondrial sulfites to induce green fluorescence, while the red fluorescence is quenched with the proton in the mitochondria. Overall, this study developed a novel logic-gated molecular probe that provided a versatile strategy for monitoring the role played by intramitochondrial sulfites and H+ in cuproptosis. This work will open the way to broaden the applications of molecular logic gates and fluorescent polysiloxanes.

Versatile Switchable Targeted Polysiloxanes for High-Resolution Visualization of Mitochondrial and Lysosomal Interactions during Ferroptosis.

Ferroptosis is an iron-dependent process that regulates cell death and is essential for maintaining normal cell and tissue survival. The explosion of reactive oxygen species characterizes ferroptosis in a significant way. Peroxynitrite (ONOO-) is one of the endogenous reactive oxygen species. Abnormal ONOO- concentrations cause damage to subcellular organelles and further interfere with organelle interactions. However, the proper conduct of organelle interactions is critical for cellular signaling and the maintenance of cellular homeostasis. Therefore, investigating the effect of ONOO- on organelle interactions during ferroptosis is a highly attractive topic. To date, it has been challenging to visualize the full range of ONOO- fluctuations in mitochondria and lysosomes during ferroptosis. In this paper, we constructed a switchable targeting polysiloxane platform. During the selective modification of NH2 groups located in the side chain, the polysiloxane platform successfully constructed fluorescent probes targeting lysosomes and mitochondria (Si-Lyso-ONOO, Si-Mito-ONOO), respectively. Real-time detection of ONOO- in lysosomes and mitochondria during ferroptosis was successfully achieved. Remarkably, the occurrence of autophagy during late ferroptosis and the interaction between mitochondria and lysosomes was observed via the differentiated responsive strategy. We expect that this switchable targeting polysiloxane functional platform will broaden the application of polymeric materials in bioimaging and provide a powerful tool for further deeper understanding of the ferroptosis process.

Functional Polysiloxane Enables Visualization of the Presence of Carbon Monoxide in Biological Systems and Films.

As an essential gasotransmitter, carbon monoxide (CO) had gradually become a research hotspot in that it possessed important physiological functions and unique pharmacological properties. However, to date, no report has focused on the topic of detecting CO both in vivo and using films. To open up a new field of CO probes, for the first time, we designed a probe (PMAH-CO) that showed a distinctive ratio emission characteristic and displayed the quantitative distribution of CO in HeLa cells and zebrafish with a higher signal-to-noise ratio. Meanwhile, the fluorescent polysiloxane-based film (PMF) containing PMAH-CO exhibited an excellent response to CO. Due to the addition of the Si-O bond, the probe exhibited a broad transparency in the visible light range and had excellent photostability. Moreover, the probe was economically viable, easy to handle, and suitable for biological research. Hence, PMAH-CO and PMF would open up the road to broaden the application of silicone materials in the field of fluorescence imaging.

Intramolecular Spirocyclization Enables Design of a Single Fluorescent Probe for Monitoring the Interplay between Mitochondria and Lipid Droplets.

The interplay between mitochondria and lipid droplets (LDs) plays a central role in regulating the ß-oxidation and storage of fatty acids (FA) and is also engaged in responding to external stimuli such as nutrient deficiency. However, a single fluorescent probe enabling the discriminative and simultaneous visualization of the two organelles has not been reported yet, which brings limitation for the in-depth study on their interplay. In this work, utilizing the intramolecular spirocyclization reaction of rhodamine dyes that can dramatically change the optical and soluble properties, we have designed a new single fluorescent probe for labeling LDs and mitochondria in clearly separated dual-emission channels. The newly designed "biform" probe, MT-LD, presented in a ring-opened form in mitochondria to give a strong red emission, while it underwent the intramolecular spirocyclization reaction to target LDs showing an intense blue fluorescence. In this manner, MT-LD can label LDs and mitochondria in blue and red fluorescence, respectively. With this robust probe, the increase of mitochondria-LD contact and peridroplet mitochondria (PDM) amount during oleic acid treatment and starvation-induced autophagy has been successfully revealed. The interaction between the two organelles was also visualized in different tissues, which revealed an obviously higher level of mitochondria-LD contact and PDM amount in brown adipose tissue and lung tissue. This work provides a promising molecular tool to investigate the interplay between mitochondria and LDs and promotes studies on FA metabolism and autophagy.

Binding Reaction Sites to Polysiloxanes: Unique Fluorescent Probe for Reversible Detection of ClO-/GSH Pair and the in Situ Imaging in Live Cells and Zebrafish.

PDMS is biocompatible, economically viable, transparent, and facile to handle and thus is suitable for fluorescent microscopy and biological research. However, there has been no report about polysiloxane-based fluorescent probes applied in bioimaging. In this report, a two-photon polysiloxane-based reversible luminescent probe (P1) was fabricated for the first time. P1 is a powerful tool for detecting the ClO-/GSH cycle in situ both in live cells and in zebrafish. This work demonstrates the potential of polysiloxane-based fluorescent probes for versatile in vivo or in vitro applications in the future.

Triphenylamine Schiff base as a lipid droplet-targeted fluorescent probe using Si-O-Si as a bridge for the detection of Cr6+ applied in bio-imaging.

Lipid droplets are known to play an important role in many cellular activities, as revealed by recent studies. Additionally, hexavalent chromium is considered extremely toxic because it readily passes through cellular membranes and easily accumulates in living cells. In this study, a novel lipid droplet-targeted fluorescent probe (Si-LDS) for recognition of Cr6+ in living cells was designed and synthesized using triphenylamine derivatives and organosiloxane. Si-LDS detected Cr6+ with high selectivity and sensitivity. The novel probe was successfully applied to cell imaging of exogenous Cr6+ in HeLa cells, and Si-LDS was able to localize mainly in the lipid droplets of HeLa cells. Si-LDS is the first lipid droplet-targeted fluorescent probe for monitoring Cr6+.

Novel fluorescent probe with a bridged Si-O-Si bond for the reversible detection of hypochlorous acid and biothiol amino acids in live cells and zebrafish.

Herein, we report the design of a novel fluorescent probe consisting of a naphthalimide fluorophore and a silicone small molecule for the reversible detection of hypochlorous acid and biothiol amino acids. The response mechanism of BSi-1 is based on the concept of the S-based oxidation/reduction. The probe was found to be suitable for imaging HOCl in HeLa, RAW 264.7 cells and zebrafish, demonstrating its utility in biological applications.

Silica Nanoparticles with Up-conversion Fluorescence Based on Triplet-Triplet Annihilation Mechanism for Specific Recognition of Apoptosis Cells.

Discrimination of live and apoptotic cells is a crucial task in the research of pharmacology, biology, pathology, and medicine science. Recently, up-conversion (UC) luminescent materials have appealed much attention due to their unique ability to convert low energy excitation photons to high energy ones. However, UC fluorescence has not been employed in the field of discrimination of live and apoptotic cells. We present a facile and costless Stöber method to fabricate robust silica nanoparticles (SiO2 UCNPs) exhibiting several merits, such as narrow size distribution and UC luminescence. SiO2 UCNPs could discriminate live and apoptosis cells by taking advantage of the unique surface property of SiO2 UCNPs for the first time. This work is also the first demonstration of the use of single photon excited UC fluorescence derived from nanoparticles for biological recognition of a specific type of cells.

Ionic S(N)i-Si Nucleophilic Substitution in N-Methylaniline-Induced Si-Si Bond Cleavages of Si2Cl6.

N-Methylaniline-induced Si-Si bond cleavage of Si2Cl6 has been theoretically studied. All calculations were performed by using DFT at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) levels. An ionic SN i-Si nucleophilic substitution mechanism, which is a newly found nucleophilic substitution in silicon-containing compounds, is proposed in the N-methylaniline-induced Si-Si bond cleavage in Si2Cl6. Unlike general S(N)i-Si nucleophilic substitutions that go through a pentacoordinated silicon transition state, ionic nucleophilic substitution goes through a tetracoordinated silicon transition state, in which the Si-Si bond is broken and siliconium ions are formed. Special cleavage of the Si-Si bond is presumably due to the good bonding strength between Si and N atoms, which leads to polarization of the Si-Si bond and eventually to heterolytic cleavage. Calculation results show that, in excess N-methylaniline, the final products of the reaction, including (NMePh)(3-n) SiHCl(n) (n=0-2) and (NMePh)(4-n) SiCl(n) (n=2-3), are the Si-Si cleavage products of Si2Cl6 and the corresponding amination products of the former. The ionic S(N)i-Si nucleophilic substitution mechanism can also be employed to describe the amination of chlorosilane by N-methylaniline. The suggested mechanisms are consistent with experimental data.

Color-Transformable Silicone Elastomers Prepared by Thiol-Ene Reaction with Potential Application in UV-LEDs.

A series of high-efficiency, full-color fluorescent elastomers based on polysiloxane matrix prepared by an easy thiol-ene "click" reaction is reported here. It is found for the first time that the same elastomer can emit transformable colors by conveniently altering the excitation wavelength because of the effect of energy transfer and the "fluorescence switch" of lanthanide ions. A fluent change in emission colors can also be feasible and conveniently reproducible by varying the stoichiometric ratio of lanthanide ions and rhodamine-B in solution and in polymer elastomers. The obtained elastomers are further coated onto commercially available UV-LED cells from the solution medium followed by an in situ cross-linking step.

Polysiloxane-Based Autonomic Self-Healing Elastomers Obtained through Dynamic Boronic Ester Bonds Prepared by Thiol-Ene "Click" Chemistry.

Cross-linked silicone elastomers constructed with dynamic-covalent boronic esters are first synthesized by photoinitiated radical thiol-ene "click" chemistry. The resultant samples can be cut with a sharp knife into two pieces and then healed via the reversibility of the boronic ester cross-linkages to restore the original silicone sample within 30 min. Regulation of luminescent properties is achieved by incorporating organic dye into the elastomers through a "one-pot" thiol-ene reaction. The proposed synthesis procedure demonstrates a new strategy to produce boronic acid silicone materials capable of self-healing without external forces.

From polymer to monomer: cleavage and rearrangement of Si-O-Si bonds after oxidation yielded an ordered cyclic crystallized structure.

Polymerization reactions are very common in the chemical industry, however, the reaction in which monomers are obtained from polymers is rarely invesitgated. This work reveals for the first time that oxone can break the Si-O-Si bond and induce further rearrangement to yield an ordered cyclic structure. The oxidation of P1, which is obtained by reaction of 2,2'-1,2-ethanediylbis(oxy)bis(ethanethiol) (DBOET) with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (MM(Vi)), with oxone yielded cyclic crystallized sulfone-siloxane dimer (P1-ox) after unexpected cleavage and rearrangement of the Si-O-Si bond.

Polysiloxane-based luminescent elastomers prepared by thiol-ene "click" chemistry.

Side-chain vinyl poly(dimethylsiloxane) has been modified with mercaptopropionic acid, methyl 3-mercaptopropionate, and mercaptosuccinic acid. Coordinative bonding of Eu(III) to the functionalized polysiloxanes was then carried out and crosslinked silicone elastomers were prepared by thiol-ene curing reactions of these composites. All these europium complexes could be cast to form transparent, uniform, thin elastomers with good flexibility and thermal stability. The networks were characterized by FTIR, NMR, UV/Vis, and luminescence spectroscopy as well as by scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The europium elastomer luminophores exhibited intense red light at 617 nm under UV excitation at room temperature due to the (5)D0 →(7)F2 transition in Eu(III) ions. The newly synthesized luminescent materials offer many advantages, including the desired mechanical flexibility. They cannot be dissolved or fused, and so they have potential for use in optical and electronic applications.

Polymeric microenvironment enhancing polarity response sensitivity for discriminating lipid droplets in cancer cells.

Cellular micro-environment analysis via fluorescence probe has become a powerful method to explore the early-stage cancer diagnosis and pathophysiological process of relevant diseases. The polarity change of intracellular lipid droplets (LDs) is closely linked with disorders or diseases, which result in various physiological and pathological processes. However, the efficient design strategy for lipid droplet polarity probes with high sensitivity is lacking. To overcome this difficulty, two kinds of LDs-targeting and polarity-sensitive fluorescent probes containing carbazole and siloxane groups were rationally designed and synthesized. With the carbazole-based rotor and bridge-like siloxanes, two probes (P1 and P2) behave high sensitivity to polarity changes and show different fluorescent intensity in normal and cancer cells. Notably, polysiloxanes groups promoted the response sensitivity of the probes dramatically for the polymeric microenvironment. In addition, due to the polarity changes of LDs in cancer cells, the distinct fluorescent intensities in different channels of laser scanning confocal microscope were observed between NHA cell and U87 cells. This work could offer an opportunity to monitor the dynamic behaviors of LDs and further provide a powerful tool to be potentially applied in the early-stage diagnosis of cancer.

Polarity responsive polysiloxanes with twisting intramolecular charge transfer effect for monitoring lipophagy process and the detection of volatile organic compounds.

Polarity plays a critical role in biology and materials science, serving as a complex parameter. Imbalances in polarity within subcellular organelles are closely associated with various diseases. Moreover, volatile organic compounds (VOC) with low polarity pose significant health and safety risks, therefore, researchers have shown great interest in accurately detecting polarity. However, precise observation of polarity changes within organisms and identification of low-polarity volatile organic solvents are formidable challenges. To overcome these difficulties, we developed a versatile polymeric twisting intramolecular charge transfer (TICT) effect Polysiloxane-n (PDMS-n), utilizing polysiloxane molecular chains as "smart guides" to connect TICT molecules, inspired by the concept of "threading a needle." With the aid of PDMS-n, the process of polarity changes during cellular lipophagy was monitored in situ with high accuracy. Remarkably, the polarity changes of the local microstructure of the PDMS films were successfully visualized. PDMS-Films were also constructed, which enabled the recognition of Dichloromethane (DCM) gas during swelling. This work will contribute to the understanding of changes in cellular physiological processes, and facilitate the sensitive detection of VOCs.

Polysiloxane-based hyperbranched fluorescent probe for dynamic visualization of HClO in lysosomes and vivo.

As a type of reactive oxygen species, hypochlorous acid (HClO) is associated with inducing oxidative stress in lysosomes. Once its concentration is abnormal, it may lead to lysosomal rupture and subsequent apoptosis. Meanwhile, this may provide new inspiration for cancer treatment. Therefore, it is crucial to visualize HClO in lysosomes at the biological level. So far, numerous fluorescent probes have emerged to identify HClO. However, fluorescent probes that combine low biotoxicity with lysosome-targetable properties are scarce. In this paper, hyperbranched polysiloxanes were modified by embedding perylenetetracarboxylic anhydride red fluorescent cores with naphthalimide derivative green fluorophores to synthesize novel fluorescent probe (PMEA-1). PMEA-1 was a lysosome-targetable fluorescent probe with unique dual emission, high biosafety, and good response speed. PMEA-1 exhibited excellent sensitivity and responsiveness to HClO in PBS solution and could dynamically visualize HClO fluctuations in cells and zebrafish. Simultaneously, PMEA-1 also had monitoring ability for HClO produced in the process of cellular ferroptosis. In addition, the bioimaging results indicated that PMEA-1 was capable of accumulating within the lysosomes. We anticipate that PMEA-1 will broaden the application of silicon-based fluorescent probes in the field of fluorescence imaging.

Hyperbranched polysiloxane-based probe with enhanced lipophilicity for visualizing ONOO- fluctuations in endoplasmic reticulum.

The endoplasmic reticulum, a cellular signaling regulator, participates in the synthesis and secretion of many proteins, glycogen, lipids and cholesterol substances. Peroxynitrite (ONOO-) is a highly oxidative and nucleophilic agent. Abnormal fluctuations of ONOO- induce oxidative stress in the endoplasmic reticulum, further disrupting the normal function of protein folding and transport and glycosylation modification, ultimately leading to neurodegenerative diseases, cancer and Alzheimer's disease. Up to now, most probes have tended to achieve targeting functions by introducing specific targeting groups. However, this approach increased the difficulty of the construction process. Therefore, a simple and efficient construction strategy for fluorescent probes with excellent specificity targeting the endoplasmic reticulum is lacking. To overcome this difficulty and put forward an efficient design strategy for the endoplasmic reticulum targeted probes, in this paper, we constructed alternating rigid and flexible polysiloxane-based hyperbranched polymeric probes (Si-Er-ONOO) by bonding perylenetetracarboxylic anhydride and silicon-based dendrimers for the first time. Efficient and specific targeting of the endoplasmic reticulum was successfully achieved by the excellent lipid solubility of Si-Er-ONOO. Furthermore, we observed different effects of metformin and rotenone on the changes of ONOO- volatility in the cellular and zebrafish internal environment by Si-Er-ONOO. We believe that Si-Er-ONOO will expand the application of organosilicon hyperbranched polymeric materials in bioimaging and provide an excellent indicator of reactive oxygen species fluctuations in biological systems.

A ratiometric fluorescent probe based on spiropyran in situ switching for tracking dynamic changes of lysosomal autophagy and anticounterfeiting.

Autophagy is the controlled breakdown of cellular components that dysfunctional or nonessential, and the decomposition products are further recycled and synthesized for the normal physiological activities of cells. Lysosomal autophagy has been implicated in cancer, neurological disorders, Parkinson's disease, etc. Therefore, it is necessary to develop a fluorescent probe that can clearly describe the process of lysosomal autophagy. However, there are currently limited fluorescent probes for ratiometric monitoring of the autophagic process in dual channels. To solve this problem, a fluorescent probe based on spiropyran with lysosomal targeting and pH response for ratiometric monitoring the autophagy process of lysosomes were designed. The sensitive response of the probe to pH in vitro was verified by UV and fluorescence spectrum tests. Meanwhile, the probe demonstrated the ability to monitor the intracellular pH fluctuations. In addition, the application of Lyso-SD in the field of anti-counterfeiting has been proposed based on the obvious photoluminescence ability of Lyso-SD under UV irradiation.

A novel coumarin-TPA based fluorescent probe for turn-on hypochlorite detection and lipid-droplet-polarity bioimaging in cancer cells.

A novel fluorescent compound, named C-TPA, based on coumarin (acceptor) and triphenylamine (donor) was facilely designed and fabricated through a one-step Suzuki coupling reaction. As a donor group, triphenylamine can efficiently enhance the fluorescence intensity and photostability of coumarin, and thus improve the detection efficiency. C-TPA-S was obtained from C-TPA treated with Lawesson's reagent and C-TPA-S can be used for the turn-on detection of hypochlorite through oxidative desulfurization with a low detection limit of 0.12 µM. Moreover, the intramolecular charge transfer process between the donor and acceptor group endows C-TPA with solvatochromism property and makes C-TPA a good candidate for polarity detection. The C-TPA with bright green fluorescence was highly efficient for imaging the microenvironment of polarity both in living cells and tissues with high selectivity and photostability, which can be applied in the diagnosis for the cancer cells.

A fluorescent probe based on POSS for facilitating the visualization of HClO and NO in living cells and zebrafish.

The main production area of HClO and NO is the mitochondria and has modulatory effects on multiple human diseases. Simultaneous detection of signaling molecules such as HClO and NO is an important approach for exploring the complex relationship between HClO and NO in mitochondria. However, most probes can detect only one species or are unable to complete the monitoring of HClO and NO in the NIR channel. There are only few reports on reasonable tools that can simultaneously monitor the presence of HClO and NO in the NIR channel. In this work, to solve this difficulty, a POSS-assisted NIR fluorescent probe with dual-response was rationally devised and developed. The probe Mito-Cy possessed high specificity and responsiveness to HClO and NO in spectral experiments. Notably, the probe exhibited excellent responsiveness and sensitivity to HClO and NO in living cells and the zebrafish model.