Perylene-Based Fluorescent Nanoprobe for Acid-Enhanced Detection of Formaldehyde in Lysosome

Injectable extracellular matrix-mimetic hydrogel based on electrospun Janus fibers

To date, the reported injectable hydrogels have failed to mimic the fibrous architecture of the extracellular matrix (ECM), limiting their biological effects on cell growth and phenotype. Additionally, they lack the micro-sized pores present within the ECM, which is unfavorable for the facile transport of nutrients and waste. Herein, an injectable ECM-mimetic hydrogel (IEMH) was fabricated by shortening and dispersing Janus fibers capable of self-curling at body temperature into pH 7.4 phosphate buffer solution. The IEMH could be massively prepared through a side-by-side electrospinning process combined with ultraviolet irradiation. The IEMHs with only 5 wt% fibers could undergo sol-gel transition at body temperature to become solid gels with desirable stability, sturdiness, and elasticity and self-healing ability. In addition, they possessed notable pseudoplasticity, which is beneficial to injection at room temperature. The results obtained from characterization analysis via scanning electron microscopy, total internal reflection fluorescence microscopy, nuclear magnetic resonance spectroscopy, and Fourier-transform infrared spectroscopy indicate that their sol-gel transition under physiological conditions stems from the synergistic action of the tight entanglements between thermally-induced self-curling fibers and the hydrophobic interaction between the fibers. An MTT assay using C2C12 myoblast cells was performed to examine the in vitro cytotoxicity of IEMHs for biomedical applications, and the cell viability was found to be more than 95%.

Semicarbazide-based fluorescent probe for detection of Cu2+ and formaldehyde in different channels

Two fluorescent sensors with the receptor semicarbazide respectively at 7- (CAA) and 3-position (CAB) of coumarin were designed and synthesized. CAA exhibits fluorescence turn-on response to Cu²⁺ by triggering the intramolecular charge transfer (ICT) process via Cu²⁺-catalyzed hydrolysis, and can detect formaldehyde (FA) at different channel by inhibiting the photo-induced electron transfer (PET). However, CAB displays quite different responses: the photophysical properties hardly changed in the presence of FA; while a three-stage fluorescence response of fast quenching, steady increasing and slowly decreasing was found upon addition of Cu²⁺. The high selectivity enabled CAA a good candidate for quantification of Cu²⁺ and formaldehyde as well as bioimaging Cu²⁺ in living cells. Good linear relationships between the fluorescence intensity and analyte concentration were observed in the range of 0.1-30 μM for Cu²⁺ and 1.0-50 μM for FA, and their detection limits (LOD) were calculated to be 0.43 μM and 1.92 μM (3δ/k), respectively.

A new quinoline based probe with large Stokes shift and high sensitivity for formaldehyde and its bioimaging applications

As a common reactive metabolite in living organisms, abnormal levels of formaldehyde may cause diseases such as cancer and Alzheimer's disease. Therefore, it is important to develop a sensitive and efficient method to understand the role of formaldehyde in physiology and pathology. Herein, a new fluorescent probe 4-phenyl-2-(trifluoromethyl) quinolin-7-hydrazino (QH-FA) was prepared for the detection of formaldehyde in near-total aqueous media with hydrazine as the reaction site and quinoline derivatives as the fluorophore. After reacting with formaldehyde, the hydrazine group formed methylenehydrazine and the fluorescence was significantly enhanced (223-fold) with large Stokes shift of 140 nm. Furthermore, the response of QH-FA to formaldehyde could be finished with in only 10 min with good selectivity, and can distinguish formaldehyde from other aldehydes. More remarkably, the estimated limit of detection of QH-FA is 8.1 nM, which is superior to those of previously reported formaldehyde fluorescent probes. At the end, we detected formaldehyde in cells and zebrafish using QH-FA in a near-total aqueous system and obtained fluorescence images by confocal microscopy.

A new amine moiety-based near-infrared fluorescence probe for detection of formaldehyde in real food samples and mice

A new amine moiety-based near-infrared fluorescent probe (Probe-NH₂) is developed for detection of formaldehyde in food samples and mice. Probe-NH₂ is constructed and synthesized from the IR-780 via two-step reactions as a hemicyanine skeleton bearing an amino moiety. The response mechanism is based on Schiff base reaction that formaldehyde reacts with amine group to form the corresponding imines. Probe-NH₂ for detection of formaldehyde exhibits excellent analytical performance, including near-infrared fluorescence emission at 708 nm, high selectivity and sensitivity, also provides a response time as low as 30 min with a detection limit of 1.87 μmolL^-1. Notably, we constructed a simple, rapid and visual formaldehyde detection platform based on paper chips in the near-infrared region for the first time. The accurate detection of formaldehyde in real food samples is of great significance, Probe-NH₂ was detected in dried beancurd sticks, endive sprout, frozen shrimp and squid, with good recoveries of 99.60%-112.72%, indicating the reliability of Probe-NH₂ for spiked determination of formaldehyde in contaminated foods. More importantly, Probe-NH₂ has been successfully applied to the detection of endogenous formaldehyde in mice.

Modulating TTA efficiency through control of high energy triplet states

An ideal annihilator in triplet-triplet annihilation photon upconversion (TTA-UC) can achieve a maximum of 50% quantum efficiency. This spin statistical limit depends on the energies of the triplet states of the annihilator molecule, with only 20% quantum efficiencies possible in less-optimal energy configurations (E _T2 ≤ 2E _T1 ). Our work utilises three perylene analogues substituted with phenyl in sequential positions. When substituted in the bay position the isomer displays drastically lowered upconversion yields, which can be explained by the system going from an ideal to less-ideal energy configuration. We further concluded position 2 is the best site when functionalising perylene without a wish to affect its photophysics, thus demonstrating how molecular design can influence upconversion quantum efficiencies by controlling the energetics of triplet states through substitution. This will in turn help in the design of molecules that maximise upconversion efficiencies for materials applications.

Activity-based fluorescent probes for sensing and imaging of Reactive Carbonyl species (RCSs)

This review explains various strategies for developing fluorescent probes to detect reactive carbonyl species (RCS). There are sevaral number of mono and diacarbonyls among 30 varieties of reactive carbonyl species (RCSs) so far discovered, which play pivotal roles in pathological processes such as cancer, neurodegenerative diseases, cardiovascular disease, renal failure, and diabetes mellitus. These RCSs play essential roles in maintaining ion channels regulation, cellular signaling pathways, and metabolisms. Among RCSs, Carbon moxide (CO) is also utilized for its cardioprotective, anti-inflammatory, and anti-apoptotic effects. Fluorescence-based non-invasive optical tools have come out as one of the promising methods for analyzing the concentrations and co-localizations of these small metabolites. There has been a tremendous eruption in developing fluorescent probes for selective detection of specific RCSs within cellular and aqueous environments due to its high sensitivity, high spatial and temporal resolution of fluorescence imaging. Fluorescence-based sensing mechanisms such as intramolecular charge transfer (ICT), photoinduced electron transfer (PeT), excited-state intramolecular proton transfer (ESIPT), and fluorescence resonance energy transfer (FRET) are described. In particular, probes for dicarbonyls such as methylglyoxal (MGO), malondialdehyde (MDA), along with monocarbonyls that include formaldehyde (FA), carbon monoxide (CO) and phosgene are discussed. One of the most exciting advances in this review is the summary of fluorescent probes of dicarbonyl compounds.

Biological applications of chiral inorganic nanomaterials

Chirality is common in nature and plays the essential role in maintaining physiological process. Chiral inorganic nanomaterials with intense optical activity have attracted more attention due to amazing properties in recent years. Over the past decades, many efforts have been paid to the preparation and chirality origin of chiral nanomaterials; furthermore, emerging biological applications have been investigated widely. This review mainly summarizes recent advances in chiral nanomaterials. The top-down and bottom-up preparation methods and chirality origin of chiral nanomaterials are introduced; besides, the biological applications, such as sensing, therapy, and catalysis, will be introduced comprehensively. Finally, we also provide a perspective on the biomedical applications of chiral nanomaterials.

Reaction-based fluorescent and chemiluminescent probes for formaldehyde detection and imaging

Formaldehyde (FA), a reactive carbonyl species, is classified as Group 1 carcinogen by International Agency for Research on Cancer (IARC) in 2004. In addition, clinical studies have implicated that elevated levels of FA have been associated with different kinds of diseases, such as neurodegenerative diseases, diabetes, and chronic liver and heart disorders. However, in addition to the direct inhalation of FA in the environment, most organisms can also produce FA endogenously by demethylases and oxidases during the metabolism of amino acids and xenobiotics. Since FA plays an important role in physiological and pathological processes, developing reliable and efficient methods to monitor FA levels in biological samples is crucial. Reaction-based fluorescent/chemiluminescent probes have provided robust methods for FA detection and real-time visualization in living organisms. In this highlight, we will summarize the major developments in the structure design and applications of FA probes in recent years. Three main strategies for designing FA probes have been discussed and grouped by different reaction mechanisms. In addition, some miscellaneous reaction mechanisms have also been discussed. We also highlight novel applications of these probes in biological systems, which offer powerful tools to discover the diverse functions of FA in physiology and pathology processes.

Systematic investigation of the aza-Cope reaction for fluorescence imaging of formaldehyde in vitro and in vivo

Increasing evidence has highlighted the endogenous production of formaldehyde (FA) in a variety of fundamental biological processes and its involvement in many disease conditions ranging from cancer to neurodegeneration. To examine the physiological and pathological relevance and functions of FA, fluorescent probes for FA imaging in live biological samples are of great significance. Herein we report a systematic investigation of 2-aza-Cope reactions between homoallylamines and FA for identification of a highly efficient 2-aza-Cope reaction moiety and development of fluorescent probes for imaging FA in living systems. By screening a set of N-substituted homoallylamines and comparing them to previously reported homoallylamine structures for reaction with FA, we found that N-p-methoxybenzyl homoallylamine exhibited an optimal 2-aza-Cope reactivity to FA. Theoretical calculations were then performed to demonstrate that the N-substituent on homoallylamine greatly affects the condensation with FA, which is more likely the rate-determining step. Moreover, the newly identified optimal N-p-methoxybenzyl homoallylamine moiety with a self-immolative β-elimination linker was generally utilized to construct a series of fluorescent probes with varying excitation/emission wavelengths for sensitive and selective detection of FA in aqueous solutions and live cells. Among these probes, the near-infrared probe FFP706 has been well demonstrated to enable direct fluorescence visualization of steady-state endogenous FA in live mouse brain tissues and elevated FA levels in a mouse model of breast cancer. This study provides the optimal aza-Cope reaction moiety for FA probe development and new chemical tools for fluorescence imaging and biological investigation of FA in living systems.

Biomineralization of Aggregation-Induced Emission-Active Photosensitizers for pH-Mediated Tumor Imaging and Photodynamic Therapy

As an efficient, noninvasive, and high spatiotemporal resolved approach, photodynamic therapy (PDT) has high therapeutic potential for cancer treatment, whereas its development still faces a number of challenges, such as the lack of efficient and stable photosensitizers (PSs) and the inadequate ability of PSs to accumulate at tumor sites and target responses. Herein, a pH-responsive calcium carbonate (CaCO₃)-mineralized AIEgen nanoprobe was prepared by using bovine serum albumin as the skeleton and loaded with a mitochondria-specific aggregation-induced emission (AIE)-active PS of 1-methyl-4-(4-(1,2,2-triphenylvinyl)styryl)quinolinium iodide (TPE-Qu⁺), which exhibits superior singlet oxygen (¹O₂)-generation ability and meanwhile possesses a bright near-infrared fluorescence emission. The biomineralized nanoparticles have small sizes (100 ± 10 nm) with good water dispersion and stability. With an increase in acidity (pH = 7.4-5.0), the internal TPE-Qu⁺ molecules are released gradually and accumulated in the mitochondria due to their hydrophobicity and electropositivity and then generate fluorescence emission and PDT under an external light source. Tumor inhibition and low acute toxicity were further successfully confirmed by the intracellular uptake test and 4T1-tumor-bearing mouse model.

Recent advances in selective formaldehyde detection in biological and environmental samples by fluorometric and colorimetric chemodosimeters

Formaldehyde, a highly reactive carbonyl species, has been widely used in day-to-day life owing to its numerous applications in essential commodities, etc.; the extrusion of formaldehyde from these sources basically leads to increased formaldehyde levels in the environment. Additionally, formaldehyde is endogenously produced in the human body via several biological processes. Considering the adverse effects of formaldehyde, it is highly important to develop an efficient and reliable method for monitoring formaldehyde in environmental and biological samples. Several chemodosimeters (reaction-based sensing probes) have been designed and synthesized to selectively detect the presence of formaldehyde utilizing the photophysical properties of molecules. In this review, we have comprehensively discussed the recent advances in the design principles and sensing mechanisms of developed probes and their biological/environmental applications in selective formaldehyde detection and imaging endogenous formaldehyde in cells. We have summarized the literature based on three different categories: (i) the Schiff base reaction, (ii) the 2-aza-Cope sigmatropic rearrangement reaction and (iii) miscellaneous approaches. In all cases, reactions are accompanied by changes in color and/or emission that can be detected by the naked eye.

A benzothiazole-based ratiometric fluorescent probe for detection of formaldehyde and its applications for bioimaging

We presented a new benzothiazole-based fluorescent probe for ratiometric sensing of formaldehyde. Upon treatment with formaldehyde, the alkylamine-functionalized probe can be converted to its aldehyde analogue via the target-mediated 2-aza-Cope rearrangement, which led to significant shifts in both absorption (from 392 to 452 nm) and emission (from 492 to 552 nm) bands. The sensing mechanism was confirmed by HPLC, UV/Vis and fluorescence spectroscopy. The probe is capable of sensing formaldehyde under physiological conditions with high selectivity over potentially competing biological analytes. The probe also displayed sensitive ratiometric fluorescence response (up to 35.7 fold) for formaldehyde with a low limit detection of 0.58 μM. Furthermore, the probe was successfully employed for ratiometric imaging of formaldehyde in living cells as well as in zebrafish.

De Novo-Designed Near-Infrared Nanoaggregates for Super-Resolution Monitoring of Lysosomes in Cells, in Whole Organoids, and in Vivo

As the cleaners of cells, lysosomes play an important role in circulating organic matter within cells, recovering damaged organelles, and removing waste via endocytosis. Because lysosome dysfunction is associated with various diseases-lysosomal storage diseases, inherited diseases, rheumatoid arthritis, and even shock-it is vital to monitor the movement of lysosomes in cells and in vivo. To that purpose, a method of optical imaging, super-resolution imaging technology (e.g., SIM and STORM), can overcome the limitations of traditional optical imaging and afford a range of possibilities for fluorescence imaging. However, the short wavelength excitation and easy photobleaching of super-resolution fluorescence probes somewhat problematize super-resolution imaging. As described herein, we designed a low-toxicity, photostable, near-infrared small molecule fluorescence probe HD-Br for use in the super-resolution imaging of lysosomes. The interaction of lysosomes and mitochondria was dynamically traced while using the probe's properties to label the lysosomes. Because the probe has the optimal near-infrared excitation and emission wavelengths, liver organoid 3D imaging and Caenorhabditis elegans imaging were also performed. Altogether, our findings indicate valuable approaches and techniques for super-resolution 3D and in vivo imaging.

Lysosome-targeted carbon dots for ratiometric imaging of formaldehyde in living cells

Formaldehyde (FA) is involved in many biological processes and is closely connected with many diseases including Alzheimer's disease and cancer. Therefore, methods for sensitive and selective detection of FA in living cells are highly demanded. As a new class of carbon nanomaterials, carbon dots (CDs) have attracted great attention owing to their robust photostability, good biocompatibility and environmental friendliness. In this manuscript, the first lysosome-targeted CDs for ratiometric fluorescence detection of FA were efficiently prepared from dexamethasone and 1,2,4,5-tetraaminobenzene through the microwave-assisted hydrothermal method. These CDs show highly selective and sensitive sensing ability towards FA with fast response and great changes of ratio values. The CDs exhibit robust photostability and good biocompatibility and were successfully employed in ratiometric fluorescence bioimaging of FA fluctuations in lysosomes of living cells, which demonstrates their great practicability in FA-related bioanalysis and biological studies.