Visualization of endogenous hydrogen sulfide in living cells based on Au nanorods@silica enhanced fluorescence

Construction of a mitochondria-targeted near-infrared fluorescence turn-on fluorescent probe for H2S detection and imaging in living cells and drug-induced mice inflammatory models

The mechanism of the interaction between the signaling molecule hydrogen sulfide (H2S) and mitochondria and its related diseases is difficult to elusive. Thus it is urgent to develop effective methods and tools to visualize H2S in mitochondria and in vivo. In this work, a robust mitochondrial-targeting NIR fluorescence "turn-on" fluorescent probe, NIR1, was reported, by adopting a Changsha-OH near-infrared (NIR) dye as the NIR fluorophore, a 2,4-dinitrophenyl (DNB) moiety as both the responsive site of the H2S and the fluorescence quenching group of the NIR fluorophore, and an oxygen onium ion site as the mitochondria-targeting group, for the detection and analysis of H2S in living Raw 264.7 cells and drug-induced inflammatory mice models. NIR1 exhibited a much smaller background fluorescence signal in lack of H2S, whereas strong enhanced NIR fluorescence "turn-on" was detected in the presence of H2S, these results showed a low detection limit (30.2 nM) for quantitative detection of H2S in aqueous solutions with concentrations ranging from 0 to 1 μM H2S. These characteristics were beneficial to direct detection and imaging analysis of H2S in complicated biosystems. Therefore, first, NIR1 was applied for the NIR detection of mitochondrial H2S in living inflammatory cells with satisfactory results. Finally, NIR1 was applied to detect H2S in drug-induced inflammatory mice models with agreeable results, demonstrating that NIR1 as a molecular tool has an excellent practical application in the study of the interaction between inflammatory and H2S.

Comparative study of fluorescence core-shell nanotags with different morphology of gold core

The development of compact and highly active plasmonic nanotags tuned on the first transparency window of biological tissues is under demand for cell imaging applications. The optical activity of bare plasmonic nanoparticles is determined by morphology but the more complex core-shell systems require experimental verification as a shell may change the expected trends. A comparative study of fluorescence core-shell nanotags with different morphology of gold core is presented in this work. Four types of gold nanoparticles (nanostars, nanobones, short and long nanorods), differing in the surface roughness were used for preparation of complex nanotags with a polymer shell containing cyanine 5.5 dye inside and surface functionalized with folic acid as a model delivery vector. The obtained core-shell nanotags were characterized with transmission electron microscopy, UV-Vis absorption spectroscopy and zeta potential measurements. Imaging performance of the obtained nanotags was studied with a fluorescence microscope on human pancreatic cancer cells, indicating a successful internalization of all nanotags by cancer cells and fluorescence intensity depending on the spectral overlap between the dye, plasmonic band of gold core and laser wavelength. The tags based on gold nanorods showed the brightest fluorescence among the studied systems. Scanning electron microscopy of the cells incubated with nanotags proved their internalization in membrane and cytoplasm. The cell viability assay showed reduced cytotoxicity and good biocompatibility up to the concentration enough for cell imaging. The obtained results suggested that compact core-shell nanotags can be used for targeting the folate receptor positive tumor cells.

Recent advances in plasmon-enhanced luminescence for biosensing and bioimaging

Plasmon-enhanced luminescence (PEL) is a unique photophysical phenomenon in which the interaction between luminescent moieties and metal nanostructures results in a marked luminescence enhancement. PEL offers several advantages and has been extensively used to design robust biosensing platforms for luminescence-based detection and diagnostics applications, as well as for the development of many efficient bioimaging platforms, enabling high-contrast non-invasive real-time optical imaging of biological tissues, cells, and organelles with high spatial and temporal resolution. This review summarizes recent progress in the development of various PEL-based biosensors and bioimaging platforms for diverse biological and biomedical applications. Specifically, we comprehensively assessed rationally designed PEL-based biosensors that can efficiently detect biomarkers (proteins and nucleic acids) in point-of-care tests, highlighting significant improvements in the sensing performance upon the integration of PEL. In addition to discussing the merits and demerits of recently developed PEL-based biosensors on substrates or in solutions, we include a brief discussion on integrating PEL-based biosensing platforms into microfluidic devices as a promising multi-responsive detection method. The review also presents comprehensive details about the recent advances in the development of various PEL-based multi-functional (passive targeting, active targeting, and stimuli-responsive) bioimaging probes, highlighting the scope of future improvements in devising robust PEL-based nanosystems to achieve more effective diagnostic and therapeutic insights by enabling imaging-guided therapy.

A Water-Soluble Hydrogen Sulfide Donor Suppresses the Growth of Hepatocellular Carcinoma via Inhibiting the AKT/GSK-3β/β-Catenin and TGF-β/Smad2/3 Signaling Pathways

Hepatocellular carcinoma (HCC) is a disease with high morbidity, high mortality, and low cure rate. Hyaluronic acid (HA) is widely adopted in tissue engineering and drug delivery. 5-(4-Hydroxyphenyl)-3H-1, 2-dithiol-3-thione (ADT-OH) is one of commonly used H₂S donors. In our previous study, HA-ADT was designed and synthesized via coupling of HA and ADT-OH. In this study, compared with sodium hydrosulfide (NaHS, a fast H₂S-releasing donor) and morpholin-4-ium (4-methoxyphenyl)-morpholin-4-ylsulfanylidenesulfido-λ5-phosphane (GYY4137, a slow H₂S-releasing donor), HA-ADT showed stronger inhibitory effect on the proliferation, migration, invasion, and cell cycle of human HCC cells. HA-ADT promoted apoptosis by suppressing the expressions of phospho (p)-protein kinase B (PKB/AKT), p-glycogen synthase kinase-3β (GSK-3β), p-β-catenin, and also inhibited autophagy via the downregulation of the protein levels of p-Smad2, p-Smad3, and transforming growth factor-β (TGF-β) in human HCC cells. Moreover, HA-ADT inhibited HCC xenograft tumor growth more effectively than both NaHS and GYY4137. Therefore, HA-ADT can suppress the growth of HCC cells by blocking the AKT/GSK-3β/β-catenin and TGF-β/Smad2/3 signaling pathways. HA-ADT and its derivatives may be developed as promising antitumor drugs.

Novel near-infrared spectroscopic probe for visualizing hydrogen sulfide in lysosomes

Considering the scarcity of hydrogen sulfide (H₂S) probes with subcellular organelle targeting, especially probes with near-infrared (NIR) emission wavelengths fluorophores, our group has been working to overcome this problem and looking forward to providing potential practical tools for exploring the relationship between the physiology and pathology of H₂S at subcellular level. In this paper, a novel colorimetric and NIR fluorescent probe SHCy-H₂S for the specific detection of H₂S in lysosome over other biological thiols was designed and synthesized. The xanthene-benzothiozolium fluorophore was chosen to provide fluorescence emission maxima over 735 nm, and 2,4-dinitrophenyl group was chosen as fluorescence quenching group and specific H₂S response site. Impressively, SHCy-H₂S exhibited high selectivity, fast response and detection limit as low as 0.116 μM for H₂S, marked obvious color changes in naked-eye and fluorescence. Specially, SHCy-H₂S was capable of specifically imaging endogenous lysosomal hydrogen sulfide, providing a potential tool for exploring the function of H₂S at subcellular level.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Emerging analytical tools for the detection of the third gasotransmitter H2S, a comprehensive review

BACKGROUND

Hydrogen sulfide (H2S) is currently considered among the endogenously produced gaseous molecules that exert various signaling effects in mammalian species. It is the third physiological gasotransmitter discovered so far after NO and CO. H2S was originally ranked among the toxic gases at elevated levels to humans. Currently, it is well-known that, in the cardiovascular system, H2S exerts several cardioprotective effects including vasodilation, antioxidant regulation, inhibition of inflammation, and activation of anti-apoptosis. With an increasing interest in monitoring H2S, the development of analysis methods should now follow.

AIM OF REVIEW

This review stages special emphasis on the several analytical technologies used for its determination including spectroscopic, chromatographic, and electrochemical methods. Advantages and limitations with regards to the application of each technique are highlighted with special emphasis on its employment for H2S in vivo measurement i.e., biofluids, tissues.

KEY SCIENTIFIC CONCEPTS AND IMPORTANT FINDINGS OF REVIEW

Fluorescence methods applied for H2S measurement offer an attractive non-invasive and promising approach in addition to its selectivity, however they cannot be considered as H2S-specific probes. On the other hand, colorimetric assays are among the most common methods used for in vitro H2S detection, albeit their employment in vivo H2S measurement has not yet been possible . Separation techniques such as gas or liquid chromatography offer higher selectivity compared to direct spectrophotometric or fluorescence methods especially for suitable for endpoint H2S measurements i.e. plasma or tissue samples. Despite all the developed analytical procedures used for H2S determination, the need for highly selective, much work should be devoted to resolve all the pitfalls of the current methods.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes

A fluorescent probe for the monitoring of H₂S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H₂S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H₂S in biological samples. Their applications in real-time monitoring of H₂S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H₂S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.

Metal Nanoparticles-Enhanced Biosensors: Synthesis, Design and Applications in Fluorescence Enhancement and Surface-enhanced Raman Scattering

Metal nanoparticles (NP) that exhibit localized surface plasmon resonance play an important role in metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS). Among the optical biosensors, MEF and SERS stand out to be the most sensitive techniques to detect a wide range of analytes from ions, biomolecules to macromolecules and microorganisms. Particularly, anisotropic metal NPs with strongly enhanced electric field at their sharp corners/edges under a wide range of excitation wavelengths are highly suitable for developing the ultrasensitive plasmon-enhanced biosensors. In this review, we first highlight the reliable methods for the synthesis of anisotropic gold NPs and silver NPs in high yield, as well as their alloys and composites with good control of size and shape. It is followed by the discussion of different sensing mechanisms and recent advances in the MEF and SERS biosensor designs. This includes the review of surface functionalization, bioconjugation and (directed/self) assembly methods as well as the selection/screening of specific biorecognition elements such as aptamers or antibodies for the highly selective bio-detection. The right combinations of metal nanoparticles, biorecognition element and assay design will lead to the successful development of MEF and SERS biosensors targeting different analytes both in-vitro and in-vivo. Finally, the prospects and challenges of metal-enhanced biosensors for future nanomedicine in achieving ultrasensitive and fast medical diagnostics, high-throughput drug discovery as well as effective and reliable theranostic treatment are discussed.

Reactive Sulfur Species: A New Redox Player in Cardiovascular Pathophysiology

Hydrogen sulfide has emerged as an important gaseous signaling molecule and a regulator of critical biological processes. However, the physiological significance of hydrogen sulfide metabolites such as persulfides, polysulfides, and other reactive sulfur species (RSS) has only recently been appreciated. Emerging evidence suggests that these RSS molecules may have similar or divergent regulatory roles compared with hydrogen sulfide in various biological activities. However, the chemical nature of persulfides and polysulfides is complex and remains poorly understood within cardiovascular and other pathophysiological conditions. Recent reports suggest that RSS can be produced endogenously, with different forms having unique chemical properties and biological implications involving diverse cellular responses such as protein biosynthesis, cell-cell barrier functions, and mitochondrial bioenergetics. Enzymes of the transsulfuration pathway, CBS (cystathionine beta-synthase) and CSE (cystathionine gamma-lyase), may also produce RSS metabolites besides hydrogen sulfide. Moreover, CARSs (cysteinyl-tRNA synthetase) are also able to generate protein persulfides via cysteine persulfide (CysSSH) incorporation into nascently formed polypeptides suggesting a new biologically relevant amino acid. This brief review discusses the biochemical nature and potential roles of RSS, associated oxidative stress redox signaling, and future research opportunities in cardiovascular disease.

Ultrasensitive and label-free detection of ATP by using gold nanorods coupled with enzyme assisted target recycling amplification

Abnormal concentration of adenosine triphosphate (ATP) is directly asscociate with several diseases. Thus, sensitive detection of ATP is essential to early diagnosis of disease. Herein, we described an ultrasensitive strategy for ATP detection by using positively charged gold nanorods ((+)AuNRs) as an efficient fluorescence quenching platform, coupled with exonuclease Ⅲ (Exo Ⅲ) assisted target recycling amplification. To construct the sensor, DNA template that contained ATP aptamer was used for the formation of Ag nanoclusters signal probe (DNA/AgNCs), the structure of it could change to duplex after the interaction of it with ATP. Such DNA template or duplex DNA product could electrostatically adsorb onto (+)AuNRs surface, resulting in the quenching of the fluorescence signal due to the vicinity of AgNCs to (+)AuNRs. With the addition of Exo Ⅲ, DNA duplex could be hydrolyzed and released from (+)AuNRs surface, leading to the recovery of a strong fluorescent signal, while ATP could be regenerated for next target recycling. Combing the good fluorescence quenching ability of (+)AuNRs and the Exo Ⅲ assisted signal amplification, a low detection limit of 26 pM was achieved for ATP detection. Notably, the proposed method can be successfully applied for detecting ATP in serum samples, indicating a potential application value in early cancer diagnosis.

Surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles

A comprehensive survey on the methods for the surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles is presented. The review highlights various strategies for covalent attachment and electrostatic binding of molecules and molecular ions to core-shell nanoparticles with a focus on plasmonically active silver and gold nanoparticles encapsulated by SiO₂ and TiO₂ shells.

Molecular engineering of a colorimetric two-photon fluorescent probe for visualizing H2S level in lysosome and tumor

As a multifunctional signaling molecule, hydrogen sulfide (H₂S) plays an essential role in diverse physiological and pathological processes. The two-photon fluorescence probes detecting H₂S selectively in vivo could be useful tools to better study the mechanism of diseases. Then, an efficient two-photon lysosome-specific probe 1 has been developed to detect endogenous H₂S in living cells and mice. Probe 1 displays excellent properties with 28-fold fluorescence enhancement, marked color changes in naked-eye and fluorescence, high selectivity and sensitivity, and low detection limit (0.22 μM) to H₂S. These remarkable properties of probe 1 enable its practical applications in detecting H₂S in environment (wastewater) and food (beer). Moreover, as a two-photon probe under near infrared excitation at 790 nm, probe 1 can monitor the level changes of endogenous H₂S of lysosome and tumor in living system with good membrane permeability and high imaging resolution. Specially, the probe detecting H₂S distribution in lysosome could provide more evidences to explain the association of target-organelle and H₂S.