Facile, rapid one-pot synthesis of multifunctional gold nanoclusters for cell imaging, hydrogen sulfide detection and pH sensing

In this study, we have developed a facile, rapid one-pot strategy for synthesis of orange fluorescent gold nanoclusters (MBISA-AuNCs) at room temperature by using 2-Mercapto-5-benzimidazolesulfonic acid (MBISA) as both reducing and protecting reagent. The prepared AuNCs exhibited prominent advantages including high fluorescent quantum yield, good water solubility, excellent biocompatibility and low toxicity. Based on these superior properties, the AuNCs have been multi-talented applied in cell imaging, hydrogen sulfide detection and pH sensing. Confocal fluorescence imaging showed that the MBISA-AuNCs could enter living cells and distribute in the cytoplasm. Additionally, the obtained AuNCs could visualize H₂S fluctuations in living cells without interference of autofluorescence based on their high sensitivity and selectivity detection for H₂S with a linear range of 2.7 × 10^-11-8.5 × 10^-4 M and a detection limit of 0.024 nM. Most strikingly, the AuNCs exhibited strong pH dependent behavior and responded linearly, rapidly and reversibly to minor pH fluctuations within the range of 2.01-12.00. Therefore, the AuNCs could also image pH fluctuations in live cells with negligible autofluorescence and provided a new method of analysis to visualize monitoring wide pH range change in live cells.

An etching based fluorescent probe for sensitive detection of hydrogen sulfide in cells

Hydrogen sulfide (H₂S) is one of the most crucial gas signaling agents that mediate many physiological and pathological processes. However, rapid high-efficiency detection and imaging of H₂S in living cells is very challenging. Herein we reported a simple fluorescent nanoprobe using FAM-DNA/AgNP nanocomposites for fast and sensitive H₂S detection based on surface silver displacement. In contrast to the conventional principles for fluorescence turn-on analyte detection, the present work demonstrated a sensitive and selective AgNP based optosensor for the assay of H₂S. Compared with the majority of the reported H₂S probes, complex synthesis procedures and costly equipment are not involved in this assay.

Engineering of Electrochromic Materials as Activatable Probes for Molecular Imaging and Photodynamic Therapy

Electrochromic materials (EMs) are widely used color-switchable materials, but their applications as stimuli-responsive biomaterials to monitor and control biological processes remain unexplored. This study reports the engineering of an organic π-electron structure-based EM (dicationic 1,1,4,4-tetraarylbutadiene, 1²⁺) as a unique hydrogen sulfide (H₂S)-responsive chromophore amenable to build H₂S-activatable fluorescent probes (1²⁺-semiconducting polymer nanoparticles, 1²⁺-SNPs) for in vivo H₂S detection. We demonstrate that EM 1²⁺, with a strong absorption (500-850 nm), efficiently quenches the fluorescence (580, 700, or 830 nm) of different fluorophores within 1²⁺-SNPs, while the selective conversion into colorless diene 2 via H₂S-mediated two-electron reduction significantly recovers fluorescence, allowing for non-invasive imaging of hepatic and tumor H₂S in mice in real time. Strikingly, EM 1²⁺ is further applied to design a near-infrared photosensitizer with tumor-targeting and H₂S-activatable ability for effective photodynamic therapy (PDT) of H₂S-related tumors in mice. This study demonstrates promise for applying EMs to build activatable probes for molecular imaging of H₂S and selective PDT of tumors, which may lead to the development of new EMs capable of detecting and regulating essential biological processes in vivo.

Red-emitting fluorescent probe for detecting hypochlorite acid in vitro and in vivo

Due to the importance of hypochlorous acid (HClO) in biological and industrial, development of fluorescent probes for HClO has been an active research area. Here, a new red-emitting ratiometric fluorescent probe (P) was synthesized and well defined characterization via NMR, HR-MS, and fluorescence spectrum, which serves as a selective and sensitive probe for ClO^- group. The probe showed a ratiometric fluorescent response to hypochlorite at the emission intensities ratio (I₄₈₀/I₆₁₂) increasing from 0.28 to 27.46. The emission intensities ratio (I₄₈₀/I₆₁₂) was linearly enhanced (I₄₈₀/I₆₁₂ = 0.064 X + 0.096) with the ClO^- concentration range from 1 to 30 μM. The detection limitation for ClO^- in aqueous solution is 0.47 μM. Moreover, this biocompatible red-emitting ratiometric fluorescent probe was utilized to the fluorescence imaging of ClO^- in living cells and Zebrafish.

Lighting-Up Tumor for Assisting Resection via Spraying NIR Fluorescent Probe of γ-Glutamyltranspeptidas

For the precision resection, development of near-infrared (NIR) fluorescent probe based on specificity identification tumor-associated enzyme for lighting-up the tumor area, is urgent in the field of diagnosis and treatment. Overexpression of γ-glutamyltranspeptidase, one of the cell-membrane enzymes, known as a biomarker is concerned with the growth and progression of ovarian, liver, colon and breast cancer compared to normal tissue. In this work, a remarkable enzyme-activated NIR fluorescent probe NIR-SN-GGT was proposed and synthesized including two moieties: a NIR dicyanoisophorone core as signal reporter unit; γ-glutamyl group as the specificity identification site. In the presence of γ-GGT, probe NIR-SN-GGT was transformed into NIR-SN-NH₂, the recovery of Intramolecular Charge Transfer (ICT), liberating the NIR fluorescence signal, which was firstly employed to distinguish tumor tissue and normal tissues via simple “spraying” manner, greatly promoting the possibility of precise excision. Furthermore, combined with magnetic resonance imaging by T2 weight mode, tumor transplanted BABL/c mice could be also lit up for first time by NIR fluorescence probe having a large stokes, which demonstrated that probe NIR-SN-GGT would be a useful tool for assisting surgeon to diagnose and remove tumor in clinical practice.

Ratiometric photoacoustic nanoprobes for monitoring and imaging of hydrogen sulfide in vivo

Detection and visualization of hydrogen sulphide (H2S) is crucial for understanding its physiological and pathological roles towards human health and diseases, but precisely tracking of H2S in vivo remains challenging due to the limitations of available analytical methods. In this study, we developed a novel ratiometric photoacoustic (PA) nanoprobe for selective detection and imaging of H2S in biological fluids, live cells, brain tissues and animals. The nanoprobe AzHD-LP was fabricated by encapsulation of a newly synthesized H2S-responsive near-infrared (NIR) dye (AzHD) within a liposome (LP). The as-prepared AzHD-LP exhibits a dramatically red-shift response of its absorption peak after reduction reaction of AzHD with H2S: the absorbance of AzHD-LP centered at 600 and 700 nm is decreased and increased, respectively, producing a turn-on ratiometric PA signal in the presence of H2S. Typically, under the excitation of a 532 nm and 700 nm pulsed laser, the selective detection and imaging of H2S was achieved in aqueous solution, living cells and brain tissues of Alzheimer's diseased mice. Moreover, after AzHD-LP conjugated with a tumor-targeting peptide - c(RGDyK) as RGD-AzHD-LP - ratiometric PA mapping of the intratumoral generated H2S in the HCT116 colon tumor-bearing live mice was demonstrated.

A visible-near-infrared fluorescent probe for peroxynitrite with large pseudo-Stokes and emission shift via through-bond energy and charge transfers controlled by energy matching

We reported a visible-near-infrared fluorescent probe for peroxynitrite detection with large pseudo-Stokes and emission shifts, based on through-bond energy transfer (TBET) in combination with intramolecular charge transfer (ICT). Pyrene was chosen as a fluorophore (acceptor), which has monomer/excimer fluorescence characteristics. A conjugated 1,2-dimethylenehydrazine structure was a linker and phenyl boronate was selected as a reaction site (donor) to design the probe (Py-PhB) using the chemical transformation from boronate to phenol, which results in the increase of the energy of the donor to match the energy of the acceptor and simultaneously achieves TBET and ICT between the donor (phenolate) and the acceptor (pyrene), leading to a fluorescence 'OFF-ON' in a red-shifted region and a large emission shift. The results show that the probe exhibits high selectivity to ONOO^- with a detection limit of 3.54 μM. Favorable ICT from phenolate to pyrene makes the probe possess a large monomer emission shift (183 nm), red-shifted to organe-red light (598 nm). TBET ensures the probe with a large pseudo-Stokes shift of 244 nm. Furthermore, its excimer emits a near-infrared light (720 nm), which is extremely beneficial for bioimaging. In short, this probe offers a novel design strategy for designing the TBET fluorescent sensors emitting red or NIR light with large pseudo-Stokes and emission shifts.

A red-emitting fluorescent probe for hydrogen sulfide in living cells with a large Stokes shift

An azido-based fluorescent probe was developed for the sensitive and selective detection of H₂S with a red emission and a large Stokes shift. The probe was successfully applied to detect H₂S both in aqueous solution and in living cells.

A NIR fluorescent probe for the detection and visualization of hydrogen sulfide using the aldehyde group assisted thiolysis of dinitrophenyl ether strategy

A NIR fluorescent probe exploiting the aldehyde group assisted thiolysis of dinitrophenyl ether strategy for H₂S imaging in cells, tissues and mice.

Reaction-based bi-signaling chemodosimeter probe for selective detection of hydrogen sulfide and cellular studies

A new quinoline-indolium-based chemical probe (DPQI) was synthesized and characterized for selective detection of hydrogen sulphide (H₂S).

A novel long-wavelength fluorescent probe for selective detection of hydrogen sulfide in living cells

Sensitive detection of endogenous H₂S by a low cytotoxicity probe.

A turn-on endoplasmic reticulum-targeted two-photon fluorescent probe for hydrogen sulfide and bio-imaging applications in living cells, tissues, and zebrafish

As one of the important gas signal molecules, hydrogen sulfide (H₂S) is associated with many important physiological processes in living organisms. Organelles, especially endoplasmic reticulum (ER), play a crucial role in the cell metabolism. Accordingly, the detection of H₂S in the ER is of high interest. Toward this goal, we have described the development of the first ER-targeted fluorescent H₂S probe (Na-H ₂ S-ER). The new probe exhibited favorable features, such as a large turn-on fluorescence signal (45-fold fluorescence enhancement), high sensitivity and selectivity. The probe was successfully employed for imaging exogenous and endogenous H₂S in the living HeLa cells. Significantly, the new probe Na-H ₂ S-ER was employed to visualize H₂S in the ER of living cells for the first time. In addition, the probe was also successfully used for imaging H₂S in the living tissues up to a depth of 100 μm and in the living zebrafish.

A new H2S-specific near-infrared fluorescence-enhanced probe that can visualize the H2S level in colorectal cancer cells in mice

Near-infrared (NIR) fluorescence-based sensors capable of selective detection of H2S in vivo would be useful tools to understand the mechanisms of diseases. A new NIR fluorescence probe 1 was developed for the detection of endogenous H2S in colorectal cancer cells in mice. 1 displayed an 87-fold fluorescence enhancement at 796 nm (with excitation at 730 nm) when reacted with H2S in a buffer (pH 7.4). 1 was water-soluble, cell-membrane-permeable, had low cytotoxicity and high selectivity and sensitivity for H2S. The properties of 1 enable its use in monitoring endogenous H2S in living cells, tissues, and mice. The bioimaging results indicated that (1) d-Cys could induce endogenous H2S production in living cells and stimulate angiogenesis; (2) tail intravenous injection of 1 into mice generated strong fluorescence in the liver while intraperitoneal injection of d-Cys could further enhance fluorescence in the liver in vivo; (3) importantly, endogenous H2S in colorectal cancer cells (HCT116, HT29) in vitro and in murine tumor models could be quickly and selectively detected by intratumoral injection of 1. These results indicated that our new probe could serve as an efficient tool for the detection of cellular H2S in living animals and even for cancer diagnosis.

A two-photon NIR-to-NIR fluorescent probe for imaging hydrogen peroxide in living cells

Hydrogen peroxide (H₂O₂), one of the reactive oxygen species (ROS), plays vital roles in diverse physiological processes. Imbalance of the H₂O₂ is concerned with serious diseases such as cardiovascular disorders, neurodegenerative diseases, Alzheimer's disease and cancer. Therefore, it is critical to develop efficient methods for monitoring H₂O₂ in vivo. In this work, a two-photon excitation (860nm) NIR fluorescent turn-on probe TPNR-H₂O₂ for H₂O₂ based on Dicyanomethylene-4H-pyran fluorophore is reported, which can be used in solution detection with 13.2-fold NIR fluorescence enhancement, fast response (completed within 40min), excellent sensitivity (DL 72.48nM), and lower cellular auto-fluorescence interference. Importantly, the perfect photostability of TPNR-H₂O₂ clearly demonstrated that the probe could be applied to imaging intracellular H₂O₂ for a long time without photobleaching. In addition, through two-photon imaging, this probe was cell permeable and used to monitor the level of endogenous and exogenous H₂O₂ with promising biological application.

A novel two-photon fluorescent probe for hydrogen sulfide in living cells using an acedan–NBD amine dyad based on FRET process with high selectivity and sensitivity

The first NBD amine based two-photon fluorescence probe L using a FRET strategy was developed for the H₂S detecting in vitro and in vivo. The probe L not only afforded high selectivity and sensitivity for H₂S detecting, but also dispalyed a linear response to H₂S with a low detection limit 24 nM.

A NIR fluorescent chemodosimeter for imaging endogenous hydrogen polysulfides via the CSE enzymatic pathway

Sodium polysulfides (Na₂S_n, n > 1) as important raw materials in the chemical industry can afford hydrogen polysulfides (H₂S_n, n > 1) under physiological conditions.

Fluorescent Probes for Sensing and Imaging within Specific Cellular Organelles

Fluorescent probes have become powerful tools in biosensing and bioimaging because of their high sensitivity, specificity, fast response, and technical simplicity. In the last decades, researchers have made remarkable progress in developing fluorescent probes that respond to changes in microenvironments (e.g., pH, viscosity, and polarity) or quantities of biomolecules of interest (e.g., ions, reactive oxygen species, and enzymes). All of these analytes are specialized to carry out vital functions and are linked to serious disorders in distinct subcellular organelles. Each of these organelles plays a specific and indispensable role in cellular processes. For example, the nucleus regulates gene expression, mitochondria are responsible for aerobic metabolism, and lysosomes digest macromolecules for cell recycling. A certain organelle requires specific biological species and the appropriate microenvironment to perform its cellular functions, while breakdown of the homeostasis of biomolecules or microenvironmental mutations leads to organelle malfunctions, which further cause disorders or diseases. Fluorescent probes that can be targeted to both specific organelles and biochemicals/microenvironmental factors are capable of reporting localized bioinformation and are potentially useful for gaining insight into the contributions of analytes to both healthy and diseased states. In this Account, we review our recent work on the development of fluorescent probes for sensing and imaging within specific organelles. We present an overview of the design, photophysical properties, and biological applications of the probes, which can localize to mitochondria, lysosomes, the nucleus, the Golgi apparatus, and the endoplasmic reticulum. Although a diversity of organelle-specific fluorescent stains have been commercially available, our efforts place an emphasis on improvements in terms of low cytotoxicity, high photostability, near-infrared (NIR) emission, two-photon excitation, and long fluorescence lifetimes, which are crucial for long-time tracking of biological processes, tissue and body imaging with deep penetration and low autofluorescence, and time-resolved fluorescence imaging. Research on fluorescent probes with both analyte responsiveness and organelle targetability is a new and emerging area that has attracted increasing attention over the past few years. We have extended the diversity by developing organelle-specific responsive probes capable of detecting changes in biomolecular levels (reactive oxygen species, fluoride ion, hydrogen sulfide, zinc cation, thiol-containing amino acids, and cyclooxygenase-2) and the microenvironment (viscosity, polarity, and pH). Future research should give more considerations of the "low-concern" organelles, such as the Golgi apparatus, the endoplasmic reticulum, and ribosomes. In addition, given the tiny sizes of subcellular organelles (20-1000 nm), we anticipate that clearer visulization of the cellular events within specific organelles will rely on super-resolution optical microscopy with nanoscopic-scale resolution.

Efficient visualization of H2S via a fluorescent probe with three electrophilic centres

A meticulous design strategy of incorporating three electrophilic centres in an optical probe (FLA) led to the achievement of high sensitivity and rapid response time (40 s) towards H₂S detection.