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Carbon monoxide (CO) is regarded as one of the most important gaseous transmitters, playing a vital role in biological systems; meanwhile, abnormal levels of CO can be correlated with conditions such as lung disease, Alzheimer's disease, and cardiovascular disease. CO-releasing molecules (CORMs) are chemical agents used to release CO as an endogenous, biologically active molecule in order to treat diseases. CO-releasing molecule-3 (CORM-3), as a convenient and safe CO donor and therapeutic drug molecule, has been widely used to release exogenous CO in living cells to study the physiological and pathological roles of CO in living systems. Herein, we designed a NIR-emitting probe (NIR-CORM-3) with a large Stokes shift based on a 4-(dimethylamino)cinnamaldehyde lepidine derived fluorophore. A 4-nitrobenzyl group was selected as the CORM-3 recognizing moiety, and the probe is able to selectively and sensitively respond to CORM-3 (within only 15 min). Upon encountering CORM-3, NIR-CORM-3 releases a fluorophore with a response at 670 nm, and it shows a remarkable Stokes shift (up to 250 nm). In addition, NIR-CORM-3 has low cytotoxicity and exhibits outstanding NIR imaging abilities in living cells and mice.

Many viscous microenvironments exist in living systems. For instance, at the cellular level, the viscosity of subcellular organelles (mitochondria, lysosomes, endoplasmic reticulum, nucleus, etc.) is much greater than that of cytoplasm; at the organismal level, compared with normal states of health, blood, or lymphatic fluid viscosity will increase to some extent in diabetes, hypertension, inflammation, tumors, and so on. However, due to the design shortcoming, there is a lack of efficient tools for detecting biomolecules in viscous living systems. Herein, we propose a rational design strategy for constructing ratiometric fluorescent probes with superior response signal-to-background (S/B) ratio in viscous systems based on rigid-fluorophore-molecular rotor platform, and a practical sulfur dioxide (SO2) probe (RFC-MRC) based on conmarin-cyanine dyad was prepared as a proof-of-concept. The probe performs a significant enhancement (71.5-fold) of ratiometric response signal stimulated by SO2 in viscous aqueous media. The cationic probe can selectively in mitochondria and was successfully utilized to sense SO2 in living HeLa cells through ratiometric fluorescence imaging. What's more, in the fluorescence imaging experiments of monitoring SO2 in apoptotic cells using probe RFC-MRC, a more obvious superior of S/B ratio was observed in the early apoptotic cells than in the lately apoptotic cells.

A turn-on fluorescent probe, containing a naphthalimide platform and benzothiazole modified by the 2,4-dinitrobenzenesulfonyl (DNBS) group, was designed as an efficient fluorescent probe for sensitive detection of biological thiols and H2S species regulated by a photoinduced electron transfer (PET) mechanism. This probe shows a speedy response to analytes and has the ability to detect thiols and H2S in aqueous and living organisms via an obvious turn-on fluorescence response.

Herein, an interplaying ICT-FRET-based ratiometric fluorescent chemosensor (NapN3–PCM), capable of precisely determining H2S concentration by the dual fluorescence fluctuation mode of two distinct emission bands, was elaborately designed and synthesized. Importantly, it was successfully applied to detect H2S levels in living cells and zebrafish using ratiometric fluorescence imaging.

Herein, a mitochondria-targeted ratiometric fluorescent probe for SO2 was proposed based on the FRET coumarin–phenylchromenylium dyad. The probe showed two distinct emission bands centered at 485 and 650 nm. Upon exposure to SO2, the acceptor emission was inhibited, and a significant enhancement in donor fluorescence was simultaneously induced; this resulted in a satisfactory ratiometric fluorescence signal. Importantly, the probe was biocompatible and successfully applied to monitor SO2 in live HeLa cells and zebrafish.

Novel vehicle technology has become a hot research topic in the aerospace field in recent years. In order to improve the aerodynamic shape and stealth performance, a conformal antenna must be used. This puts strict requirements on the longitudinal height, volume and weight of the antenna. At the same time, the relevant electronic equipment on the aircraft platform also puts forward higher demands on the antenna for broadband, dual polarization, high gain, and low side lobes. Therefore, the low-profile, miniaturized broadband dual-polarization conformal antenna has become a research hotspot in recent years. This paper presents a form of double-layer patch micro-strip antenna with strip-line fed H-shaped slot coupled feed, which has broadband dual-polarization characteristics. At the same time, an 8x8 array antenna was designed. The test results show that the bandwidth of the standing wave less than 1.5 is 25%, and the overall height is 1.3mm, which is Very suitable for electronic equipment of novel aircraft platform.

The electromagnetic environment faced by modern aircraft is becoming more and more complex, and the sensors on the aircraft are subject to more and more interference and threat. The data link formed by the sensor network among several aircraft can effectively improve the data transmission performance and anti-interference ability. Inter-aircraft data link emphasizes high communication rate, large coverage angle domain, small attitude constraint, low interception rate, high anti-interference and high airborne environmental adaptability. Therefore, it is required that inter-machine data link antenna should have the characteristics of high frequency, large bandwidth, high gain of circular polarization, narrow beam, low side lobe, wave velocity scanning, low profile, light weight, etc. In this paper, a double layer micro-strip antenna coupling fed by strip line U /H slot is presented, which has the above advantages. At the same time, a 5x4 array antenna is designed. The test results show that the standing wave bandwidth less than 1.5 is 24% and the overall height is 14mm, which is very suitable for inter-machine networking data link antenna sensor equipment.

With the development of communication frequency to K-band, array antenna has become a trend of communication antenna. The microstrip antenna has the characteristics of simple fabrication, easy integration and low cost. It has become a main antenna of array element antenna. With the continuous shortening of working wavelength, the actual processing degree of unit antenna becomes more complex, and the structural accuracy requirements become more stringent. In this paper, a linearly polarized K-band array element is proposed, which uses metallized via holes as electrical walls to reduce the degree of mutual coupling between elements. Finally, the simulation results show that the return loss of the unit antenna is less than -10dB in the whole required working frequency band, which meets the requirements of communication antenna.

Satellite communication is an indispensable part of modern communication. In recent years, with the rapid rise of 5G-Technology, satellite communication is developing towards high frequency, multi-polarization, wide spectrum and multi-mode, which requires the antenna to have the characteristics of low profile, wide-band, dual-polarization and high gain. The traditional waveguide dual-polarization antenna has some disadvantages, such as narrow bandwidth of VSWR, poor cross-polarization and port-isolation and so on. In this paper, a novel dual polarization waveguide slot antenna is proposed, which has the advantages of large bandwidth, high efficiency, low cross-polarization, high port-isolation, low profile and simple structure. At the same time, a 2 × 2 array in Ka band is designed. The simulation results show that in the frequency band range of 16%, the standing-wave ratio of the two polarities is less than 2, the radiation efficiency is more than 800%, the cross-polarization is less than -25dB, and the port isolation is more than 25dB.

An illuminating ICT-based formaldehyde-responsive fluorescent probe (PBD-FA) with long wavelength emission was judiciously designed and synthesized, which is suitable for detecting FA in aqueous solution and living cells, both with significant fluorescence signal-to-noise ratios.

A H2O2-responsive fluorescent chemosensor (CNBE) with a ratiometric emission signal was elaborately designed and synthesized. The ratio signal of the chemosensor was manipulated by an interplaying ICT-activated FRET mechanism. The ratiometric fluorescence imaging was successfully applied to detect H2O2 using CNBE in living cells and zebrafish.

An illuminating formaldehyde-responsive fluorescence probe (Naph-FA) with a turn-on emission signal was rationally designed and synthesized. The reaction-based probe undergoes successive condensation, 2-aza-Cope rearrangement and hydrolysis processes in response to formaldehyde, and the fluorescence signal was regulated by combinational PET and ICT mechanisms.

Biothiols, as reactive sulfur species (RSS), play important roles in human physiology, and they have a close connection of generation and metabolism pathways among of them. It is challenging to discriminate biothiols from each other due to the similar chemical structures and properties of them. Herein, we develop a fluorescent hybrid dyad (CS-NBD) for efficiently discriminating cysteine (Cys)/homocysteine (Hcy) from glutathione (GSH) and hydrogen sulfide (H2S) by a dual-channel detection method. CS-NBD performs inherently no fluorescence in ranging from visible to near infrared region. However, upon addition of Cys (2–150 μM)/Hcy (2–200 μM), CS-NBD generates significant fluorescence enhancement in two distinct emission bands (Green-Red), while encounter of GSH (2–100 μM) or H2S (2–70 μM) induces the fluorescence increase only in the red channel. The detection limit was determined to be 0.021 μM for Cys, 0.037 μM for Hcy, 0.028 μM for GSH, and 0.015 μM for H2S, respectively (S/N = 3). The interval distance between two emission bands is up to 163 nm, which is favourable to acquire the accurate data in measurement due to the reducing of crosstalk signals. CS-NBD is also successfully applied to distinguish Cys/Hcy in cellular context by dual-color fluorescence imaging.

A novel multifunctional logic gate based on a triple-chromophore (coumarin-NBD-flavylium, CNF) fluorescent biothiol probe with diverse fluorescence signal patterns was rationally designed and synthetized. On the new triad CNF, diverse logic operations such as OR, TRANSFER, INH, NOT, and YES logic gates were achieved by using biothiols and fluorescence signal patterns as the multiple inputs and outputs, respectively.

A novel vertical patch antenna (VPA) for pattern reconfiguration is proposed. It consists of a VPA and a monopole antenna, which can operate independently. Simulation and experimental results show that the radiation patterns can be easily steered between omnidirectional pattern of 18% bandwidths and bidirectional pattern of 17.8% bandwidths. The whole radiation pattern can cover a beam range of 0∼90° in elevation angle with the gain greater than 0dB.

A novel dual-polarized magneto-electric dipole antenna with wideband performance is presented in this communication. The folded jagged edges of the radiating patch contribute to a better impedance matching, as well as a compact size. The antenna is fed by a crossed coupling structure, thus dual-polarizations and a high port isolation are obtained. A parametric study is performed for providing practical design guidelines. Simulation results show that an impedance bandwidth of 100% for VSWR ≤ 2.0 from 1GHz to 3GHz is achieved. Stable radiation patterns with low crosspolarization levels are also obtained across the operation band.

A broadband antenna with intergrated structure is designed. The antenna patch designed with fractal structure, add another patch layer to obtain a wideband characteristics. It has an excellent impedance matching characteristics and a outstanding radiation characteristics. The antenna obtain a high gain reach 7.2 dBi, The experimental results are in good agreement with the simulation results.

Hydrogen peroxide (H2O2) plays a crucial role in many biological processes in the human body. As our understanding of the complexity of physiological H2O2 in lysosome, investigative tools are required to make sense of this interconnectivity. Toward this goal, we have developed a new example of a fast responsive and lysosome-targeted two-photon H2O2 fluorescent probe (Lyso-HP) with a large turn-on fluorescence signal (80-fold fluorescence enhancement). The addition of H2O2 to Lyso-HP results a dramatic fluorescence enhancement around 550 nm. The probe could image exogenous and endogenous H2O2 in living cells and the probe was located in lysosomes with high colocalization coefficient (0.96) compared with LysoTracker. The large fluorescence enhancement of the two-photon probe Lyso-HP renders it attractive for imaging H2O2 in living tissues with deep tissue penetration. Significantly, the probe is feasible for fluorescently monitoring H2O2 level changes in lysosomes and suitable for fluorescence imaging of H2O2 in living tissues with deep penetration by using two-photon microscopy.

We have described a ratiometric fluorescent formaldehyde probe (RFFP) based on the 6-hydroxy naphthalene chromophore for the first time. The probe is suitable for ratiometric detection of formaldehyde both in the solution and living biological samples with two distinct emission bands.

Ratiometric fluorescent probes with two well-resolved emission bands have attracted considerable attention, as they can be employed to carry out ratiometric measurements. The ratiometric measurements can alleviate to some extent the shortcomings of intensity-based probes induced by the probe concentration effects, influence of probe environment, and instrumental limitations. Herein, a colorimetric and ratiometric fluorescent probe (CP-H2S) based on a coumarin–pyronine FRET dyad was developed for the detection of H2S in vitro and in vivo. In an aqueous solution, the probe exhibits an inherent red emission of the pyronine unit excited from the coumarin unit by FRET process, whereas an encounter of CP-H2S and H2S suppresses the FRET process and elicits a new blue emission of the coumarin moiety with a concomitant decrease in the red emission. The spectral shift of these two distinct emission bands is up to 119 nm. Moreover, there was a 252.7-fold enhancement in the ratiometric fluorescence intensity signal, and the energy-transfer efficiency was found to be 96.7%. These desirable results suggest that the CP-H2S probe can significantly reduce the crosstalk signals and improve the accuracy of ratiometric measurements. Remarkable ratio of signals of the CP-H2S probe upon responding to H2S was also obtained in living cells imaging.

An innovative design strategy has been proposed to construct viscosity-sensitive fluorescent probes with superior sensitivity and high signal-to-background ratio (S/B) based on double-rotor molecular platform. As a proof-of-concept, a double-rotor-based fluorescent molecule (DRVP) containing two rotors, quinolinium and carbazole moieties, was developed to track viscosity using a strong ICT platform. The cationic probe DRVP is able to visualize the mitochondrial viscosity variations in living cells and zebrafish.

We have prepared a turn-on fluorescent probe for biothiols based on bromoketo coumarin (KC-Br). The emission intensity of the coumarin chromophore is modulated by both the heavy atom effect and internal charge transfer (ICT) process. The probe KC-Br is intrinsically nonfluorescent; however, after being reacted with thiols, the bromide moiety is substituted by the -SH group, which elicits a significant fluorescence increase. We surmised the free -NH2 group would further react with carbonyl in the Cys/Hcy-substituted intermediate product yielding to Schiff base compound KC-Cys/KC-Hcy, but not in compound KC-GSH. The ICT effect has a stronger influence in compound KC-GSH than that in compound KC-Cys/KC-Hcy, resulting in compound KC-GSH having a stronger fluorescence. Thus, the probe has a good selectivity for GSH over other various biologically relevant species and even two other similar biothiols (Cys/Hcy) and could image glutathione (GSH) in living cells. We expect the design concept presented in this work would be widely used for the design of fluorescent probes for distinguishing among biothiols.

Hydrogen sulfide (H2S), traditionally considered to be a toxic gas with the typical smell of rotten eggs and an antioxidant or scavenger for reactive oxygen species (ROS) [1], has recently emerged as a member of the endogenous gaseous transmitter family of signaling molecules including nitric oxide (NO) and carbon monoxide (CO) [2–3]. The endogenous H2S is produced by the enzymes (such as cystathionine β-synthase, cyst a t h i o n i n e γ l y a s e , a n d 3 -me r c a p t o p y r u v a t e sulphurtransferase) catalysis action of cysteine or cysteine derivatives in mammalian tissues [4–6]. H2S plays an important physiological role in many biological processes, for instance, ischemia reperfusion injury, vasodilation, apoptosis, insulin signaling, and oxygen sensing [7–11]. However, abnormal levels of H2S is associated with various diseases, like Alzheimer’s disease [12], Down’s syndrome [13], diabetes [10], and liver cirrhosis [14]. Therefore, it’s very significant for monitoring H2S using sensitive, selective, and watersoluble fluorescent probe in the native biological environment. Fluorescence imaging has been widely used as a powerful tool for monitoring biomolecules within the context of living systems with high spatial and temporal resolution [15–16]. Naphthalimide dye is the favorable building block for constructing fluorescent probes because of its excellent photophysical properties, such as high extinction coefficients, excellent quantum yields, and great photostability. In addition, azido group is well-known for sensitively and selectively responding to H2S, the electron withdrawing azide is very easy reduced by H2S affording the electron donating amine [17–26]. Thus, in this work, we employed the naphthalimide chromophore as the signal reporter and azido group as the responding site for H2S to construct a H2S probe based on internal charge transfer (ICT) process (Scheme 1). In addition, to enhance the water solubility, we introduced a hydrophilic alcoholic group to the naphthalimide core. Prior to react with H2S, we supposed that probe Nap-N3 has negligible fluorescence. However, interaction of naphthalimide azide with H2S affords 4-amino-1,8-naphthalimide, which would elicit a significant fluorescence enhancement via ICT process caused by the electron donating amine and the electron withdrawing amide. So, probe Nap-N3 might be employed as a turn-on fluorescent probe for detecting H2S.

Heptamethine cyanines are favorable for fluorescence imaging applications in biological systems owing to their near-infrared (NIR) absorption and emission. However, it is very difficult to quench the fluorescence of NIR dyes by the classic photoinduced electron transfer mechanism due to their relatively high-lying occupied molecular orbital energy levels. Herein, we present a simple and effective “capping” approach to readily tune the fluorescence of NIR cyanines. The resulting new functional NIR CyBX (X = O, N, or S) dyes not only retain the intact tricarbocyanine scaffold, but also have a built-in switch to regulate the fluorescence by spiro-cyclization. When compared to traditional cyanines, novel CyBX dyes have a superior character in that their NIR optical properties can be readily tuned by the intrinsic spiro-cyclization mechanism. We expect that this “capping” strategy can be extended across not only the visual spectrum but also to structurally distinct fluorophores.

The development of new functional fluorescent dyes has attracted great attention. Herein we have described a novel strategy to design a unique type of cyanine dyes by attaching two indolium moieties at the α-positions of the pyrrole core. The new type of cyanine dyes is named as PyCy fluorophores. Importantly, PyCy dyes can exhibit an exceptional feature, fluorescence turn-on response at pH varying from acidic to near-neutral conditions, and a ratiometric fluorescence response at pH varying from near-neutral to basic conditions. By taking advantage of the fluorescence turn-on response of PyCy2 at pH varying from acidic to near-neutral conditions and emission properties of PyCy2, we have demonstrated that a small-molecule fluorescent probe can image pH variations in living cells. Furthermore, we have demonstrated that PyCy2 can sense real-time pH changes under alkaline conditions induced by enzymes based on the ratiometric fluorescence response of PyCy2 at pH varying from near-neutral to basic conditions. We expect that the new design strategy for PyCy fluorophores may prompt the development of a wide variety of cyanine derivatives with desirable properties.

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play a crucial role in many physiological processes. Cys production and metabolism is closely connected with Hcy and GSH; meanwhile, the dynamic antioxidant defenses network by Cys is independent of the GSH system, and Cys can serve as a more effective biomarker of oxidative stress. Hence, it is significant and urgent to develop an efficient method for specific detection of Cys over other biothiols (Hcy/GSH). However, most of the present Cys-specific fluorescent probes distinguished Cys from Hcy through response time, which would suffer from an unavoidable interference from Hcy in long-time detection. In this work, in order to improve the selectivity, we employed an improved aromatic substitution-rearrangement strategy to develop a ratiometric Cys-specific fluorescent probe (Cou-SBD-Cl) based on a new fluorescence resonance energy transfer (FRET) coumarin-sulfonyl benzoxadiazole (Cou-SBD) platform for discrimination of Hcy and GSH. Response of Cou-SBD-Cl to Cys would switch FRET on and generate a new yellow fluorescence emission with a 56.1-fold enhancement of ratio signal and a 99 nm emission shift. The desirable dual-color ratiometric imaging was achieved in living cells and normal zebrafish. In addition, probe Cou-SBD-Cl was also applied to real-time monitor Cys fluctuation in lipopolysaccharide-mediated oxidative stress in zebrafish.

The mitochondria-targeted turn-on fluorescent probe (Mito-FMP) based on a benzoxadiazole platform was developed for detection of malondialdehyde (MDA). Mito-FMP performed with large enhancement of the optical signal (774-fold) in response to MDA in an aqueous system and has the capability of monitoring endogenous MDA in HeLa cells and onion tissues.

A multi-signal fluorescent probe was engineered for simultaneously distinguishing and sequentially sensing cysteine/homocysteine, glutathione, and hydrogen sulfide in living cells., Biothiols, which have a close network of generation and metabolic pathways among them, are essential reactive sulfur species (RSS) in the cells and play vital roles in human physiology. However, biothiols possess highly similar chemical structures and properties, resulting in it being an enormous challenge to simultaneously discriminate them from each other. Herein, we develop a unique fluorescent probe (HMN) for not only simultaneously distinguishing Cys/Hcy, GSH, and H2S from each other, but also sequentially sensing Cys/Hcy/GSH and H2S using a multi-channel fluorescence mode for the first time. When responding to the respective biothiols, the robust probe exhibits multiple sets of fluorescence signals at three distinct emission bands (blue-green-red). The new probe can also sense H2S at different concentration levels with changes of fluorescence at the blue and red emission bands. In addition, the novel probe HMN is able to discriminate and sequentially sense biothiols in biological environments via three-color fluorescence imaging. We expect that the development of the robust probe HMN will provide a powerful strategy to design fluorescent probes for the discrimination and sequential detection of biothiols, and offer a promising tool for exploring the interrelated roles of biothiols in various physiological and pathological conditions.

Conformationally restricted analogues of the GFP chromophore have been synthesized. The spectroscopic properties of GCTPOC, a unique family with tunable two-photon action cross-sections, were investigated. GCTPOC could be used as a robust two-photon platform for development of a two-photon fluorescent thiol sensor, which could stain endogenous thiols both in vitro and in vivo.

The long wavelength (far-red to NIR) analyte-responsive fluorescent probes are advantageous for in vivo bioimaging because of minimum photo-damage to biological samples, deep tissue penetration, and minimum interference from background auto-fluorescence by biomolecules in the living systems. Thus, great interest in the development of new long wavelength analyte-responsive fluorescent probes has emerged in recent years. This review highlights the advances in the development of far-red to NIR fluorescent probes since 2000, and the probes are classified according to their organic dye platforms into various categories, including cyanines, rhodamine analogues, BODIPYs, squaraines, and other types (240 references).