Recent progress in the development of fluorescent probes for hydrazine

Received: 29 January 2018 Revised: April 2018 Accepted: 26 April 2018 DOI: 10.1002/bio.3505 REVIEW Recent progress in the development of fluorescent probes for hydrazine Khac Hong Nguyen1 Minghui Yang1 | | Yuanqiang Hao2 You‐Nian Liu | Wansong Chen1 | Yintang Zhang2 | Maotian Xu2 | 1 College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan Province, P R China Henan Key Laboratory of Biomolecular Recognition and Sensing, College of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu, Henan Province, P R China Correspondence Yuanqiang Hao, Henan Key Laboratory of Biomolecular Recognition and Sensing, College of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu, Henan Province, 476000, P R China Email: hao0736@163.com You‐Nian Liu, College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan Province, 410083, P R China Email: liuyounian@csu.edu.cn Abstract Hydrazine (N2H4) is an important and commonly used chemical reagent for the preparation of textile dyes, pharmaceuticals, pesticides and so on Despite its widespread industrial applications, hydrazine is highly toxic and exposure to this chemical can cause many symptoms and severe damage to the liver, kidneys, and central nervous system As a consequence, many efforts have been devoted to the development of fluorescent probes for the selective sensing and/or imaging of N2H4 Although great efforts have been devoted in this area, the large number of important recent studies have not yet been systematically discussed in a review format so far In this review, we have summarized the recently reported fluorescent N2H4 probes, which are classified into several categories on the basis of the recognition moieties Moreover, the sensing mechanism and probes designing strategy are also comprehensively discussed on aspects of the unique chemical characteristics of N2H4 and the structures and spectral properties of fluorophores KEY W ORDS Funding information National Natural Science Foundation of China, Grant/Award Numbers: 21476266, 21475084, 21505091, U1404215 and B061201; Innovation Scientists and Technicians Troop Construction Projects of Henan Province, Grant/Award Number: 41 | fluorescent probes, hydrazine, review I N T RO D U CT I O N in rocket fuel due to its high heat of combustion and since large volumes of hot gas are generated during its decomposition Hydrazine, coined by Emil Fischer in 1875, is an inorganic compound Ascribed to its other unique properties, including nucleophility, with the chemical formula N2H4.[1] Hydrazine can also be written as reductibility and double nucleophilic character, hydrazine also can be H2NNH2, called diamidogen, therefore it has basic (alkali) chemical utilized as an important reactant for many chemical products, including properties (Kb = 1.3 × 10−6) like ammonia At ambient conditions, textile dyes, pharmaceuticals and pesticides.[2–5] Despite its wide- hydrazine is a colourless fuming liquid with a faint ammonia‐like spread industrial applications, hydrazine is highly toxic Exposure to odour Since the by‐products are typically nitrogen gas and water, hydrazine may cause symptoms of irritation of the eyes, nose, and hydrazine often acts as a convenient reductant such as antioxidant, throat, dizziness, headache, nausea, pulmonary edema, seizures, coma oxygen scavenger and corrosion inhibitor Additionally, hydrazine is in humans, as well as damage to the liver, kidneys and the central ner- also used as a propellant in space vehicles or used as a component vous system.[6,7] The US Environmental Protection Agency (EPA) identified hydrazine as a potential carcinogen with a threshold limit of Abbreviations used: AIE, aggregation‐induced emission; DMSO, dimethyl sulfoxide; LOD, limit of detection; N2H4, hydrazine; NIR, near‐infrared; PBS, phosphate‐buffered saline; TICT, twisted‐intramolecular charge transfer; TPE, tetraphenylethylene Luminescence 2018;1–21 10 ppb.[8] Thus, it is highly desirable to develop selective and sensitive assays for the detection of trace hydrazine Several traditional analytical wileyonlinelibrary.com/journal/bio techniques, including titrimetry,[9] voltammetry,[10–12] Copyright © 2018 John Wiley & Sons, Ltd NGUYEN ET AL chromatography,[13,14] and chemiluminescence[15] have been widely and selectivity The topics of this review are classified into several cat- used for hydrazine detection However, most of these approaches egories based on the different sensing mechanisms and recognizing have major disadvantages associated with the need for sophisticated moieties of these probes for hydrazine, including probes based on ace- instrumentation and time‐consuming manipulations, and the inability tyl, 4‐bromobutyryl, vinyl malononitrile, phthalimide, β‐diketone, to be miniaturized for in situ and in vivo studies levulinate and other moieties Alternatively, analytical techniques based on fluorescence sensor systems are very popular because fluorescence measurements are usually easy to perform, inexpensive, very sensitive (parts per billion/ | PROB ES B A SE D ON A CE TY L M O I ET Y trillion) with detection limits as low as sub‐parts‐per million, and able to be employed for in situ and in vivo monitoring.[16–22] Hydrazine Phenol acetate can be readily hydrazinolyzed by hydrazine to generate can act as a good nucleophile for a variety of transformations in syn- its phenolic analogue (Figure 2) Based on this reaction, several probes thetic chemistry, such as hydrazone formation, Wolff–Kishner reduc- containing phenol acetate moieties have been developed for sensing tion, heterocyclic chemistry, deprotection of phthalimides and so on of hydrazine Chang and co‐workers developed two phenylacetate‐ Recently, these characters of hydrazine have provide a starting point based fluorescent probes (1 and 2) for hydrazine detection by incorpo- for the development of a large number of efficient fluorescent hydra- rating zine probes (Figure 1) Although great efforts have been devoted in fluorophore scaffolds, respectively (Figure 3).[23] In a mixture of this area, a large number of important recent studies have not yet dimethyl sulfoxide (DMSO) and Tris buffer solution (pH 8.0, 10 mM, been systematically discussed in a review format to the best of our 1:1, v/v), probe is colourless and non‐fluorescent Treating the probe knowledge Herein, we make such an effort to summarize the rapid solution with 100 equivalents of hydrazine creates a strong absorption progress in the development of fluorescent hydrazine probes and band at 512 nm with a corresponding colour change from colourless highlight a variety of inventive strategies to achieve good reactivity to greenish yellow and a prominent green emission at 534 nm, which acetate group onto dichlorofluorescein and resorufin FIGURE Fluorescent hydrazine (N2H4) probes based on different reaction mechanisms FIGURE Proposed sensing mechanism of probe for hydrazine (N2H4) based on hydrazinolysis of phenol acetate NGUYEN ET AL increase with the concentration of hydrazine in the range 10–80 μM And the LOD of for hydrazine was determined to be 2.5 × 10−8 M Moreover, the probe was successfully utilized for imaging hydrazine in living MCF‐7 cell line and visualizing hydrazine in mice (Figure 4B) Pang and co‐workers designed a ESIPT (excited state intramolecular proton transfer) probe by masking the phenol group of flavonoid with the ethyl ester (Figure 5).[25] Hydrazine can selectively remove the ester protection group, leading to the recovery FIGURE hydrazine Structures and reactions of probes and with of flavonoid ESIPT Addition of 20 equivalents of hydrazine to the probe solution causes a large fluorescence enhancement, giving intense green fluorescence, which increases by about eight‐fold are the characteristic spectral features of free dichlorofluorescein Under optimized conditions, the fluorescence intensity of the probe Hydrazinolysis of probe also causes evident chromogenic and fluo- solution was nearly proportional to the hydrazine concentration rescent turn‐on type signals Both and exhibit excellent selectiv- range from to 50 μM with a calculated LOD of 1.0 × 10−5 M −8 ities for hydrazine with limits of detection (LODs) of 9.0 × 10 −8 and 8.2 × 10 M M, respectively, which is sensitive enough for industrial chemical detection The probe was also successfully used for monitoring hydrazine in live cells and zebrafish Sun et al developed a ratiometric fluorescent hydrazine probe Peng and co‐workers reported a NIR (near‐infared region) (Figure 6)[26] by incorporating an acetate moiety onto naphthalimide, ratiometric fluorescent probe (3) for hydrazine based on a a widely used scaffold for the construction of fluorescent probes.[27,28] heptamethine cyanine dye derivative (Figure 4).[24] In the presence Probe displayed a fluorescence maximum at 432 nm Upon addition of hydrazine in a mixture of acetate buffer (pH 4.5, 10 mM) and DMSO (1:9, v/v), undergoes a hydrazinolysis process to release enol form, which further transforms it into its corresponding ketone form, leading to large hypsochromic shifts in both absorption and emission maxima Specifically, the colour of the solution changes from cyan (784 nm) to pink (520 nm), and the emission band shifts from 810 nm to 582 nm The fluorescence intensity ratio at 582 and 810 nm (I582/I810) was found to linearly FIGURE Structure and reaction of probe with hydrazine FIGURE (A) Structure and reaction of probe with hydrazine (B) In vivo images of a mouse given a skin‐popping injection of probe and a subsequent skin‐popping injection of hydrazine with the effect over different time intervals The top images were taken with an excitation laser of 740 nm and an emission filter of 820 ± 20 nm, and the bottom ones were taken with an excitation laser of 480 nm and an emission filter of 600 ± 20 nm (Reprinted from ref 24) NGUYEN ET AL FIGURE (A) Structure and reaction of probe with hydrazine (B) Fluorescence images of 7860 cells, (a–c) cells incubated with 5; (d–f) cells treated with and hydrazine (a, d) Bright‐field images, (b, e) blue channel, (c, f) green channel (Reprinted from ref 26) of hydrazine, the emission intensity at 432 nm decreased gradually highly fluorescent moiety The fluorescence increase at 680 nm is with the simultaneous appearance of a new red‐shifted emission band directly proportional to the hydrazine concentration from to centred at 543 nm, affording the ratiometric detection The emission 40 μM with a LOD of 5.7 × 10−7 M Obviously, the response time of intensity ratio (I543/I432) showed a good linearity against the hydrazine toward hydrazine is about min, and the probe is also capable concentration in the range 0–10 μM, with a LOD of 2.1 × 10−8 M of visualizing hydrazine in MCF‐7 cells by two‐photon microscopy Probe has also been applied to image hydrazine in living cells (TPM) imaging (Figure 8B) (Figure 6B) Yin and co‐workers recently reported a ratiometric fluorescent Compound was reported as a NIR and turn‐on fluorescent hydrazine probe by incorporating an acetate moiety to a coumarin probe for hydrazine detection (Figure 7).[29] Reaction of the probe derivative (Figure 9).[33] Noticeably, this probe displayed a different rec- with hydrazine removes the acetate moiety, producing the highly ognition mechanism for hydrazine, in which the carbanyl group of the fluorescent NIR hemicyanine fluorophore In vitro experiments probe reacts with hydrazine affording a Schiff‐base intermediate and showed that a linear correlation existed between the fluorescence further forming a stable heterocyclic structure The probe exhibited a response and the concentration of the hydrazine in the range high sensitivity for hydrazine with a linear response range 0–10 μM 0–50 μM, with a LOD of 1.9 × 10−7 M Furthermore, the probe is Cell imaging experiments also demonstrated the capacity of probe capable of imaging hydrazine not only in living cells but also in living for monitoring hydrazine in live samples mice due to its efficient NIR emission, a critical feature for application in bioimaging.[30,31] Incorporation of the acetate moiety onto a variety of other fluorophore scaffolds has afforded probes in a range of colour Peng and co‐workers developed a two‐photon NIR fluorescent Reports of hydrazine based on coumarin and its derivatives probe for the detection of hydrazine (Figure 8).[32] The probe has (9–11),[34–36] fluorescein (12),[37] 1,4‐dihydroxyanthraquinone (13),[38] an acetate moiety as the reaction site for hydrazine and a 2‐(2‐(4‐ 1,8‐naphthalimide (14),[39] benzthiazole [41,42] (15),[40] the hydroxystyryl)‐4H‐chromen‐4‐ylidene) malononitrile complex as the dicyanomethylenedihydrofuran scaffold (16) fluorescent reporter unit The non‐fluorescent reacts with hydrazine derivative (17)[43] have been described The structures of these fluo- leading to the removal of an acetate group and the release of the rescent hydrazine probes are summarized in Figure 10 However, it and rhodamine FIGURE Structure and reaction of probe with hydrazine NGUYEN ET AL FIGURE (A) Structure and reaction of probe with hydrazine (B) Confocal microscope images of MCF‐7 cells (a–c) cells treated with 7; (d–i) cells treated with hydrazine and subsequent treatment of the cells with 7; (d–f) OPM image of cells upon excitation at 560 nm, emission window 650–750 nm; (g–i), TPM image of cells upon excitation at 820 nm, emission window 575–630 nm (Reprinted from ref 32) FIGURE Structure and reaction of probe with hydrazine should be pointed out that, the acetyl group located on the aromatic anions Thus, fluorescent probes with excellent selectivity for phenol is also a reaction site for BO3− anion, and several fluorescent hydrazine would be afforded by taking advantage of this special reac- probes have been develop for BO3− ions based on the acetyl tivity For exploiting the double nucleophilic ability of hydrazine, a [44–47] recognition moiety, − indicating that BO3 may interfere with the hydrazine detection by using this type of probe 4‐bromo butyrate group has been employed as the reaction moiety for the design of hydrazine probes This type of fluorescent probe is normally prepared via the incorporation of 4‐bromo butyrate onto a phenolic‐containing fluorophore The sensing process involves | P R O B E S B A S E D ON ‐ B R O MO BU T Y R Y L M O I ET Y two steps (Figure 11), hydrazine first nucleophilically substitutes bromine atom and then performs a nucleophilic attack on the ester carbonyl, followed by intramolecular cyclization to release the Hydrazine, also written as H2NNH2, can actually be regarded as a fluorophore simple molecule consisted of two amino groups, which implies that it Goswami et al firstly developed a fluorescent hydrazine probe (18) can perform two consecutive nucleophilic reactions This double employing 4‐bromo butyrate as the reaction moiety (Figure 12).[48] nucleophilic character is unique to hydrazine over other amines and The probe is designed in such a way that ESIPT of the HBT NGUYEN FIGURE 10 Structures of fluorescent hydrazine probes 9–17 with an acetate moiety FIGURE 11 Proposed sensing mechanism of 4‐bromobutyryl‐based probes for hydrazine ET AL (2‐(2'‐hydroxyphenyl)benzothiazole) moiety gets blocked by the Recently, our group reported a ratiometric fluorescent hydrazine substituted 4‐bromo butyrate group The presence of hydrazine can probe (20) based on the 1,8‐naphthalimide fluorophore (Figure 14) result in the release of the HBT moiety as well as the recovery of the [50] ESIPT of fluorophore through subsequent substitution, cyclization 4‐bromo butyrate moiety via a substitution‐cyclization‐elimination The probe operates by hydrazine‐mediated removal of the and elimination processes Moreover, live‐cell imaging experiments process to liberate the 1,8‐naphthalimide moiety Upon the treatment establish the utility of this probe for tracking hydrazine in live cells with hydrazine, the probe solution displayed a bathochromic shift in Incorporation of a 4‐bromo butyrate moiety onto a resorufin emission from 420 to 550 nm The emission intensity ratio (I550/I420) fluorophore afforded a turn‐on fluorescent probe (19) for N2H4 is found to be proportional to the concentration of hydrazine in the (Figure 13).[49] Reaction of the probe with hydrazine in a HEPES buffer range 1.0–30.0 μM with a LOD of 2.7 × 10−7 M Moreover, the probe (10 mM, pH 7.4, containing 10% acetonitrile (CH3CN)) leads to the has been utilized for practical detection of gaseous hydrazine, as well release of fluorescent resorufin The fluorescence increase is directly as imaging hydrazine in live cells proportional to the hydrazine concentration in the range 10–200 μM By anchoring a 4‐bromo butyrate moiety onto a cyanine scaffold, with a LOD of about × 10−6 M The dramatic colour change of Lu and co‐workers developed a NIR ratiometric fluorescent probe (21) the probe solution from colourless to red upon the treatment with (Figure 15) for hydrazine detection.[51] Addition of hydrazine to a hydrazine demonstrated that 19 can serve as a ‘naked‐eye’ probe for solution of 21 in DMSO–H2O (1:4, v/v, phosphate‐buffered saline hydrazine Probe 19 also has been applied to image hydrazine in living (PBS) 20 mM, pH 7.4) induced a significant hypsochromic shift of cells (Figure 13B) the emission maximum from 810 to 627 nm The probe displayed high sensitivity (LOD = 1.2 × 10−8 M) and excellent selectivity over other interfering analytes Furthermore, the probe is capable of imaging exogenous hydrazine not only in living cells but also in living mice (Figure 15B) Installation of a 4‐bromo butyrate moiety onto different fluorophores has afforded a series of fluorescent hydrazine probes in a variety of colours (Figure 16) Based‐on fluorescein, Goswami et al FIGURE 12 Structure and reaction of probe 18 with hydrazine reported a ‘turn on’ fluorescent probe (22).[52] By utilizing NGUYEN ET AL FIGURE 13 (A) Structure and reaction of probe 19 with hydrazine (B) Confocal fluorescence images of Chinese hamster ovary (CHO) cells: cells incubated with 19 (a–c); image of cells after treatment with 19 and subsequent treatment of the cells with hydrazine for (e–g) (a and e) Bright‐field images; (b and f) red channel; (c and g) merged images (Reprinted from ref 49) FIGURE 14 Structure and reaction of probe 20 with hydrazine FIGURE 15 (A) Structure and reaction of probe 21 with hydrazine (B) Representative fluorescence images of the mice that were pre‐treated with 21 and subsequently incubated with hydrazine Images were taken after incubation of hydrazine for 0, 3, 6, and 10 (Reprinted from ref 51) dicyanomethylenedihydrofuran scaffold, Li and co‐workers prepared a far‐red fluorescent hydrazine probe (23) [53] of hydrazine in living cells Chen et al reported a highly sensitive fluo- Zhu and co‐workers rescent turn‐on probe (26) for hydrazine based on a coumarin developed two flavonoid‐based fluorescent hydrazine sensors (24 fluorophore.[56] Using the similar strategy, a new ESIPT hydrazine [54,55] and 25), and both of them have been applied to the detection probe (27) was also developed It displayed good water solubility and NGUYEN FIGURE 16 ET AL Structures of fluorescent hydrazine probes 22–28 with a 4‐bromo butyrate moiety can be performed in a PBS buffer (pH 7.4) solution with 1% etha- hydrazone The probe displays a dynamic range of 5.0 to 20.0 μM nol.[57] Lu et al reported a NIR fluorescent probe (28) for hydrazine for hydrazine with a LOD of 1.2 × 10−8 M Moreover, the probe has [58] by using a hemicyanine dye an excellent biocompatibility, and has been successfully applied to visualize hydrazine in live cells and zabrafish Kumar et al reported a N,N‐dimethylaminocinnamaldehyde‐based | P R O B E S B A S E D ON V I N Y L M A L O N O N I T R I LE ICT fluorescent probe (31) (Figure 20) for the ratiometirc detection of Previous studies have demonstrated that arylidene malononitrile can probe 31 exhibits an emission in the red region The addition of hydra- selectively react with hydrazine to yield a product of hydrazone zine to the solution of 31 in HEPES buffer–CH3CN (10 mM, pH 7.2, (Figure 17).[59] This specific reactivity of hydrazine combined with 99.5/0.5, v/v), the emission band at 582 nm shifts to 480 nm due to the synthetic ease of incorporating malononitrile onto fluorophores the conversion of cyano groups to hydrazone and the consequent possessing a vinyl aldehyde or benzaldehyde moiety has led to rapid inhibition of the ICT process within the probe molecule The probe progress in the development of fluorescent hydrazine probes The first displays an ultralow LOD of 8.87 × 10−9 M Furthermore, the fluorescent probe (29) based on this approach was developed by Peng probe has been applied for intracellular imaging of hydrazine and hydrazine.[62] Due to the efficient ICT from electron‐donating dimethylamino group to the electron‐withdrawing cyano groups, [60] and co‐workers (Figure 18) Probe 29 displays a strong emission with a maximum in the red region around 640 nm due to the intramo- the preparation of fluorescent test strips to detecting trace level of hydrazine in water lecular charge transfer (ICT) process from the 7‐N,N‐diethyl group to Incorporating dicyanovinyl group to derivated tetraphenylethylene the electron‐withdrawing vinyl malononitrile through a π‐conjugated (TPE) moieties, Liu and co‐workers devised a series of aggregation‐ system Upon reacting with hydrazine, the vinyl malononitrile can be induced emission (AIE) probes (32–34)[63] (Figure 21) for both fluores- converted to hydrazone, which inhibits the ICT process within the cence and colourimetric detection of hydrazine in solution as well as in probe and thus leads to ratiometric responses both in absorption solid state based on the probe‐stained paper strips These probes were and fluorescence signals In addition, this ICT‐based ratiometric probe designed on the basis of the different electron‐donating abilities of the is exploited to image hydrazine in living cells (Figure 18B) substituent groups Introducing the electron‐donating groups, such as The malononitrile trigger has been incorporated onto a phenothi- methoxyl and N,N‐dimethylamino, into the TPE structure, the yielded azine dye by Yang and co‐workers to give a fluorescent hydrazine probes (33 and 34) feature a more red‐shifted absorption and emission probe (30) (Figure 19).[61] Upon reaction with hydrazine in DMF–Tris in the visible region due to the enhanced ICT system Thus, probe 34 buffer (10 mM, pH 7.4, 7:3, v/v), the probe exhibits a distinct turn‐ gives the best response to hydrazine, and 34‐stained paper strip can on fluorescence response at 490 nm, which can be ascribed to the achieve sensing low‐level hydrazine vapour change in electronic structure of the probe due to the formation of The vinyl malononitrile as the recognition moiety has also expanded to develop family fluorescent hydrazine probes by using various fluorophore scaffolds or their derivatives, including benzothiazole (35),[64] carbazole (36),[65] acenaphthequinone (37),[66] anthraldehyde (38),[67] pydazoline (39),[68] naphthaoxazole (40),[69] formylated benzothiazole (41)[70] and dicyanomethylene‐4H‐chromene (42)[71] (Figure 22) Besides vinyl malononitrile, some other electron‐deficient alkene FIGURE 17 Proposed sensing mechanism of vinyl malononitrile‐ based probe for hydrazine structures also can react with hydrazine to form the hydrazone via a similar mechanism Based on this type of reaction, several new NGUYEN ET AL FIGURE 18 (A) Structure and reaction of probe 29 with hydrazine (B) Confocal fluorescence images of HeLa cells Cells incubated with 29 (top); image of cells after treatment with 29 and subsequent treatment of the cells with hydrazine (a, d) Bright‐field images; (b, e) green emission (540 ± 20 nm); and (c, f) red emission (640 ± 20 nm) (Reprinted from ref 60) fluorescent hydrazine probes have been reported recently (Figure 23) Two probes (43 and 44)[72,73] based on a recognition unit of 2‐cyano- | P R O B E S B A S E D ON P H T H A L I M I D E MOIETY acrylate have been designed by using two different signalling moieties, Compound Gabriel synthesis, named after the German chemist Siegmund Gabriel, (45)[74] was synthesized as a colorimetric and fluorogenic probe for pyridomethene is a classical approach for the preparation of primary amines, specifi- hydrazine detection based on the degradation of π‐conjugated cally transforming alkyl halides into primary amines Traditionally, this system utilizing reaction involves the N‐alkylation of phthalimide by a target primary 2‐benzothiazoleacetonitrile as a new recognition site, Lin and alkyl halide, followed by hydrazine‐mediated cleavage of the phthaloyl co‐workers reported a turn‐on two‐photon fluorescent hydrazine group to liberate the primary amines This strategies involved in probe (46).[75] By conjugating hemicyanine to a coumarin fluorophore, Gabriel synthesis has been successfully adapted for the development Ni and co‐workers developed a NIR‐emissive (λex = 580 nm, of fluorescent hydrazine probes, typically by incorporating phthalimide λem = 660 nm) hydrazine selective probe (47) of the probe and phenanthroimidazole triggered by hydrazine [76] By Reaction of 47 with into amine‐containing fluorophores (Figure 24) The first two hydrazine gives a coumarin hydrazone derivative and a corresponding phthalimide‐based fluorescent hydrazine probes (49 and 50) were blue‐shift emission, and thus a ratiometric fluorescence response is reported simultaneously by Lin, Cui and their co‐workers by using achieved Based on a similar hemicyanine linked electron‐deficient 4‐aminonaphthalimide as the fluorescent reporters (Figure 25).[78,79] alkene structure, Ban et al synthesized a mitochondria‐targeted In a mixture of PBS buffer (10 mM, pH = 7.2) and ethanol (1:9, v/v), ratiometric fluorescent hydrazine probe (48).[77] probe 49 exhibits a UV–vis absorption band and a fluorescence emission band at 344 and 467 nm, respectively Upon reaction with hydrazine, the phthalimide group was cleaved, the released 4‐aminonaphthalimide displays a yellow colour (λabs = 467) and emits yellowish‐green fluorescence (λem = 528) The probe demonstrates an ultralow LOD of 4.2 × 10−9 M, and is capable of imaging intracellular hydrazine Probe 50 exhibits similar highly specific ratiometric FIGURE 19 Structure and reaction of probe 30 with hydrazine FIGURE 20 Structure and reaction of probe 31 with hydrazine response for hydrazine over other primary amines 10 NGUYEN ET AL DMSO (1/9, v/v), the probe only shows extremely weak fluorescence at 475 nm (ɸ = 0.093), and addition of hydrazine leads to a ‘switched on’ emission (ɸ = 0.4983) with a bathochromic shift to 512 nm The probe has also successfully exploited to detect gaseous and intracellular hydrazine Notably, Cui et al reported a multi‐responsive optical probe (52) for the specific detection of hydrazine (Figure 27).[81] On the basis of a Gabriel‐type reaction, hydrazinolysis of 52 can produce 7‐ amino‐4‐methylcoumarin as a chromogenic and fluorogenic reporter, FIGURE 21 hydrazine Structures and reactions of probes 32–34 with and luminol as a chemiluminescence probe The ratiometric fluorescence response of the probe 52 toward hydrazine is highly selective over other interfering substances, with a linear dynamic range of 0.1 By installing phthalimide onto the dansyl fluorophore, Zhao and to 1.0 μM and a LOD of × 10−7 M The probe is also used to detect co‐workers synthesized a turn‐on fluorescent hydrazine probe (51) hydrazine in vapour state Furthermore, the probe has also been (Figure 26).[80] In a solution of HEPES buffer (pH 7.0, 20 mM) and applied for the detection of hydrazine in HeLa cells (Figure 27B) FIGURE 22 Structures of fluorescent hydrazine probes 35–42 with a malononitrile moiety FIGURE 23 Structures of fluorescent hydrazine probes 43–48 possessing electron‐deficient alkene structure FIGURE 24 Proposed sensing mechanism of phthalimide‐based probe for hydrazine ... concentration of hydrazine in the range 10–80 μM And the LOD of for hydrazine was determined to be 2.5 × 10−8 M Moreover, the probe was successfully utilized for imaging hydrazine in living MCF‐7 cell line... good linearity against the hydrazine toward hydrazine is about min, and the probe is also capable concentration in the range 0–10 μM, with a LOD of 2.1 × 10−8 M of visualizing hydrazine in MCF‐7... possessing a vinyl aldehyde or benzaldehyde moiety has led to rapid inhibition of the ICT process within the probe molecule The probe progress in the development of fluorescent hydrazine probes The first