A novel "turn-on" fluorescent probe based on triphenylimidazole-hemicyanine dyad for colorimetric detection of CN- in 100% aqueous solution

Approaching the Zero-Power Operating Limit in a Self-Coordinated Organic Protonic Synapse

High-performance artificial synapse with nonvolatile memory and low power consumption is a perfect candidate for brainoid intelligence. Unfortunately, due to the energy barrier paradox between ultra-low power and nonvolatile modulation of device conductances, it is still a challenge at the moment to construct such ideal synapses. Herein, a proton-reservoir type 4,4',4″,4'''-(Porphine-5,10,15,20-tetrayl) tetrakis (benzenesulfonic acid) (TPPS) molecule and fabricated organic protonic memristors with device width of 10 µm to 100 nm is synthesized. The occurrence of sequential proton migration and interfacial self-coordinated doping will introduce new energy levels into the molecular bandgap, resulting in effective and nonvolatile modulation of device conductance over 64 continuous states with retention exceeding 30 min. The power consumptions of modulating and reading the device conductance approach the zero-power operating limits, which range from 16.25 pW to 2.06 nW and 6.5 fW to 0.83 pW, respectively. Finally, a robust artificial synapse is successfully demonstrated, showing spiking-rate-dependent plasticity (SRDP) and spiking-timing-dependent plasticity (STDP) characteristics with ultra-low power of 0.66 to 0.82 pW, as well as 100 long-term depression (LTD)/potentiation (LTP) cycles with 0.14%/0.30% weight variations.

Current Advances in Diazoles-based Chemosensors for CN- and FDetection

Advances in molecular probes have recently intensified because they are valuable tools in studying species of interest for human health, the environment, and industry. Among these species, cyanide (CN-) and fluoride (F-) stand out as hazardous and toxic ions in trace amounts. Thus, there is a significant interest in probes design for their detection with diverse diazoles (pyrazole and imidazole) used for this purpose. These diazole derivatives are known as functional molecules because of their known synthetic versatility and applicability, as they exhibit essential photophysical properties with helpful recognition centers. This review provides an overview of the recent progress (2017-2021) in diazole-based sensors for CN- and F- detection, using the azolic ring as a signaling or recognition unit. The discussion focuses on the mechanism of the action described for recognizing the anion, the structure of the probes with the best synthetic simplicity, detection limits (LODs), application, and selectivity. In this context, the analysis involves probes for cyanide sensing first, then probes for fluoride sensing, and ultimately, dual probes that allow both species recognition.

A simple colorimetric and fluorometric probe for rapid detection of CN- with large emission shift

In this work, a novel probe R was synthesized via Knoevenagel reaction between 3H-benzo[f]chromium-2-formaldehyde and ethyl cyanoacetate for selective detection of CN^- in both colorimetric and fluorescent signal channels. The recognition of CN^- was through the nucleophilic reaction of CN^- to C = C of probe R, which destroys π-conjugation and blocks the ICT effect of the probe, resulting in colorimetric and fluorometric responses. Probe R showed great sensitivity toward CN^-, with large fluorescent emission (595 nm) and low detection limit (0.70 μM). Moreover, probe R can detect exogenous CN^- in living cells.

Development of AIEE active fluorescent and colorimetric probe for the solid, solution, and vapor phase detection of cyanide: smartphone and food applications

Apart from environmental implications, the extreme toxicity of cyanide can lead to sudden human death upon prolonged exposure to it. Hence, rapid and low-level on-site detection of cyanide has earned paramount significance in the present era. Therefore, an AIEE active and piezofluorochromic Schiff base (probe 2) was synthesized which exhibited highly selective fluorescence enhancement based nanoscale (LOD; 6.17 nM) detection of CN^-. The interaction mode was attributed to the deprotonation of the probe by the cyanide that was confirmed through ¹H NMR titration, pH, theoretical studies, and switchable fluorescence response upon the addition of HCl. Advantageously, probe 2 displayed solid and vapor phase recognition of cyanide which is the first of its kind as far as we know. The excellent sensing potential of the probe was satisfactorily applied for the detection of cyanide in food, natural soil, and industrial wastewater. Additionally, probe 2 showed an immediate colorimetric response towards cyanide which was favorably integrated through a smartphone. Finally, the switchable fluorescence response of the probe was used to design an INHIBIT logic gate. Therefore, the multifunctional probe 2 displayed excellent practical potential for cyanide detection which was the ultimate goal of our work.

Peptide-based colorimetric and fluorescent dual-functional probe for sequential detection of copper(Ⅱ) and cyanide ions and its application in real water samples, test strips and living cells

A novel dual-functional peptide probe FLH based on fluorescent "on-off-on" strategy and colorimetric visualization method was designed and synthesized. This new probe exhibited highly selective and rapid detection of Cu²⁺ with significant fluorescent "turn-off" response, with a visible colorimetric change from yellow to orange. The combination ratio of FLH to Cu²⁺ (1:1) was determined using ESI-HRMS spectra and Job's plot. The fluorescent emission showed a good linear response (R² = 0.9986) with a low detection limit of 1.5 nM. In addition, the FLH-Cu²⁺ complex displayed colorimetric changes and a fluorescent "off-on" response toward CN^- over a wide pH range from 7 to 12. This detection behavior was observed within 20 s, with a limit of detection (LOD) for CN^- at 12.7 nM. Based on stability and accuracy, FLH was next developed as dual-functional test strips, and was also successfully applied to detect Cu²⁺ and CN^- in two actual water samples. More importantly, the cytotoxicity studies indicated that FLH had good biocompatibility and low toxicity, and was successfully utilized for monitoring Cu²⁺ and CN^- in living cells through fluorescence imaging.

A novel peptide-based fluorescent probe with a large stokes shift for rapid and sequential detection of Cu2+ and CN- in aqueous systems and live cells

A novel fluorescent probe (DSD) was reasonably designed and synthesized with dansyl-labeled dipeptide (Dan-Ser-Asp-NH₂). DSD featured remarkably large Stokes shift (230 nm) and perfect water solubility, and exhibited high selectivity and rapid recognition toward Cu²⁺via fluorescence quenching. The detection limit of DSD for Cu²⁺ was 2.4 nM, indicated that DSD has excellent sensitivity. In addition, the stoichiometry between DSD and Cu²⁺ were detected as 1:1 by fluorescence titration, Job's plot and ESI-HRMS data. As designed, DSD-Cu²⁺ system was able to sequentially detect CN^- according to the displacement approach with fluorescence "off-on" response, and the detection limit for CN^- was calculated to be 41.9 nM. Specifically, the response time of DSD with Cu²⁺ and CN^- was less than 40 s, which rendered it suitable for real time detection in actual water samples. In addition, with the alternate addition of Cu²⁺ and CN^-, the reversible cycles could be repeated for at least 10 times, indicated that DSD was a promising reversibility probe. DSD showed low toxicity and good biocompatibility, and was successfully applied to detect Cu²⁺ and CN^- in living cells.

A highly sensitive chemosensor for rapid recognition of Cu2+ and HSO3- in 100% aqueous solution

Dual-responsive chemosensors have garnered much research interests owing to the ability of recognizing two analytes simultaneously. Herein, the chemosensor BPIS composed of hemicyanine and 2, 2'-dipyridylamine (DPA) was facilely synthesized for sensitive and expeditious recognition of Cu²⁺ and HSO₃^- in 100% aqueous solution. By adding Cu²⁺, BPIS showed substantial spectral changes accompanied by a noticeable color change from pink to yellow under daylight. The absorbance and fluorescence intensity were linearly correlated to the Cu²⁺ concentration, enabling the quantitative recognition of Cu²⁺. The limit of detection (LOD) for Cu²⁺ was down to 4.02 × 10^-9 M. The response time of BPIS towards Cu²⁺ was 10 s, imparting BPIS great potential in real-time detection of Cu²⁺. Meanwhile, BPIS manifested ratiometric fluorescence response by introducing HSO₃^- owing to the 1,4-addition between HSO₃^- and the unsaturated CC bond of BPIS. The color of the BPIS solution progressively faded from pink to colorless with increasing HSO₃^- concentration, and a LOD of 3.47 × 10^-9 M was obtained. In addition, BPIS-coated test paper was found to be an efficient tool for fast, sensitive, portable detection of Cu²⁺ and HSO₃^- by naked eyes. More importantly, the precise detection of Cu²⁺ and HSO₃^- in real water and sugars were realized, respectively, by capitalizing on BPIS as the signal tool.

A novel ratiometric fluorescent chemosensor for detecting malononitrile and application assisted with smartphone

Malononitrile can be transformed into hypertoxic hydrogen cyanide which induces severely jeopardizes to human beings and environment. However, an effective detection technology for malononitrile was still lacking, which means that it is necessary to develop new sensitive analysis technology for malononitrile. Here in, a high sensitive fluorescent probe NQBS for detecting malononitrile was designed and synthesized from the derivative of natural product nopinone. NQBS could selectively recognize malononitrile from 26 kinds of competitive compounds in N, N-dimethylformamide (DMF) solution. The detection limit of NQBS for malononitrile was calculated to be 1.96 μM at the concentration range of 0-25 μM. In addition, the sensing mechanism of NQBS towards malononitrile was proved with high resolution mass spectrometer (HRMS), nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), and density functional theory (DFT) calculation analysis as Knoevenagel condensation process and intramolecular cyclization reaction. With the assistance of smartphone and color recognition software, NQBS was well applied in the on-site recognition of malononitrile in real time by analyzing the change trend of the red-greenblue (RGB) value of the NQBS solution.

A novel near-infrared fluorimetric method for point-of-care monitoring of Fe2+ and its application in bioimaging

Iron is one of the essential trace elements in the human body, which is involved in many important physiological processes of life. The abnormal amount of iron in the body will bring many diseases. Therefore, a novel near-infrared fluorimetric method was developed. The method is based on a fluorescent probe (E)-4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)-N, N-diethylaniline oxide (DDED) which uses N-oxide as a recognition group to real-time monitoring and imaging of Fe²⁺ in vivo and in vitro. The method exhibits excellent selectivity and high sensitivity (LOD = 27 nM) for Fe²⁺, fast reaction rate (< 4 min), extremely large Stokes shift (＞ 275 nm), low cytotoxicity. The strip test strongly illustrates the potential application of DDED in real environment. In particular, DDED has been successfully applied to real-time monitoring and imaging of Fe²⁺ in HepG² cells and zebrafish. That is, the method has great potential for the detection of Fe²⁺ in living systems.

A Highly Selective Turn-on Fluorescent and Naked-eye Colourimetric Dual-channel Probe for Cyanide Anions Detection in Water Samples

A highly selective turn-on fluorescent and naked-eye colourimetric dual-channel probe for cyanide anions (CN-) has been designed and characterized. In the mixed solution (DMSO / H₂O, 9:1, v / v), only CN- could cause an increase in the UV absorption intensity and the corresponding fluorescence intensity increased, and other anions had no significant effect on the probe. After treatment with cyanide in the probe solution, the solution showed a noticeable colour change, from light yellow to purple. Moreover, a fluorescence spectrophotometer can be used to observe that the fluorescence intensity of the solution is significantly enhanced. The response of the colourimetric and fluorescent dual-channel probe to CN- was attributed to nucleophilic addition, and the mechanism was determined by ¹H NMR spectroscopy. In addition, this probe was used to detect CN- in actual water samples, including river water, drinking water, and tap water. The spiked CN- recovery rate is very high (97.2%-100.06%), and analytical precision is also very high (RSD < 2%), which shows its feasibility and reliability for detecting cyanide ions in actual water samples.

A dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH 3 -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg2+ are better than to other metal ions (Ag+, Al3+, Ba2+, Cd2+, Co3+, Cu2+, Cr3+, Fe3+, Ga2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+). According to the standard curve diagram, the detection limits of CH 3 -R6G and CN-R6G were determined to be 1.34 × 10-8 and 1.56 × 10-8 M, respectively. Reaction of the probes with Hg2+ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH 3 -R6G and CN-R6G have been successfully used for imaging Hg2+ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg2+ in vivo.

Two highly sensitive fluorescent probes based on cinnamaldehyde with large Stokes shift for sensing of HSO3- in pure water and living cells

Two simple and novel fluorescent probes (CDC1 and CDC2) have been designed and prepared here for sensing HSO₃^- with large Stokes shifts (about 250 nm). The synthesized probes can react with HSO₃^- just in 2 min, followed by the obvious color change from blue to colorless. The colorimetric and ratiometric absorbance response of the probes to HSO₃^- is due to the addition of HSO₃^- to the electron-deficient C=C double bond group, which prevents significant intramolecular charge transfer (ICT). Besides, CDC1 and CDC2 can detect HSO₃^- in pure water and detection limits of CDC1 and CDC2 reached 4.59 nM and 8.19 nM, respectively. Considering the delicate difference in the two prepared probes' molecular structures, CDC1 containing the carboxyl group has a more significant fluorescence intensity change response to HSO₃^- in pure water than CDC2 (with sulfinyl group). Beyond better response characteristics, CDC1 also has lower cytotoxicity and better biocompatibility compared with CDC2, which could be chosen to detect HSO₃^- in living cells. With these superior properties, probe CDC1 could have a potential application in the fields of environmental and biological detection.

Copper Complex-Embedded Vesicular Receptor for Selective Detection of Cyanide Ion and Colorimetric Monitoring of Enzymatic Reaction

Detection of environmentally important ion cyanide (CN^-) has been done by a new method involving displacement of both metal and indicator, metal indicator displacement approach (MIDA) on the vesicular interface. Terpyridine unit was selected as the binding site for metal (Cu²⁺), whereas Eosin-Y (EY) was preferred as an indicator. About 150 nm sized nanoscale vesicular ensemble (Lip-1.Cu) has shown good selectivity and sensitivity for CN^- without any interference from other biologically and environmentally important anions. Otherwise, copper complexes are known for the interferences of binding with phosphates and amino acids. The Lip-1.Cu nanoreceptor also has the possibility to be used for real-time colorimetric scanning for the released HCN via enzymatic reactions. Lip-1.Cu has several superiorities over the other reported sensor systems. It has worked in 100% aqueous environment, fast response time with colorimetric monitoring of enzymatic reaction, and low detection limit.

Water-soluble fluorescent probe for simultaneous detection of cyanide, hypochlorite and bisulfite at different emission wavelengths

A fluorescent probe that responds at distinct wavelengths upon exposure to cyanide, hypochlorite, and bisulfite was synthesized. As a result, an easy to apply analytical methodology was developed for the detection of these ions. The feasibility of this method was evaluated by theoretical calculations. The probe exhibited excellent solubility in the test solution (H₂O: DMF = 99: 1, v: v) with low detection limits for cyanide, hypochlorite and bisulfite (4.5 × 10 ^-8 M, 4.9 × 10 ^-7 M and 4.3 × 10 ^-8 M respectively) showing distinct emission wavelengths for each ion without interference in practical application. Furthermore, the probe had low toxicity and was applied for the imaging experiments of cyanide, hypochlorite and bisulfite in living HeLa and MDCK cells.

A new colorimetric and ratiometric fluorescent probe for selective recognition of cyanide in aqueous media

A simple naphthopyran derivative (L) has been synthesized as a colorimetric and ratiometric fluorescent probe for cyanide sensing in the aqueous DMSO medium and paper strips. The nucleophilic addition of CN^- to this probe blocks the π-conjugation and the intramolecular charge transfer (ICT) transition between naphthopyran and benzoindolium moieties and consequently results in remarkable color and spectral changes. Upon addition of cyanide, L displayed a ratiometric fluorescence response with a blue shift of the peak position and a noticeable color change from fuchsia to colorless within 90s. The probe exhibits high selectivity and sensitivity toward CN^- over other anions and the detection limit was calculated to be 7.56×10^-7M, which is well below the WHO cyanide standard in drinking water (1.9μM). In addition, the excitation and emission of the probe were within the visible wavelength range, which could benefit an application of the probe in an inexpensive portable cyanide sensor. The sensing ability of L has been successfully applied in real water samples. Furthermore, test strips based on L were fabricated, which can act as convenient and efficient test kits for detecting CN^-.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu²⁺ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The detection limit of WM toward Cu²⁺ was 1.84 × 10^-7 M, which was lower than the concentration of Cu²⁺ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu²⁺ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu²⁺.

A dual-function colorimetric probe based on Carbazole-Cyanine dyad for highly sensitive recognition of cyanide and hypochlorous acid in aqueous media

A dual-function colorimetric probe (Cz-Cy7) with an electron-donating carbazole tethered at the central position of heptamethine cyanine was designed and synthesized, and the performance on CN^- and HClO detection were systematically investigated. With the addition of CN^-, Cz-Cy7 exhibited remarkable changes in both UV-vis and fluorescence spectra with a good linear relationship to CN^- concentration, and a discernible color change under daylight was observed. The limit of detection for CN^- was found to be 9.1 nM in DMF and 0.09 μM in DMF/H₂O. Meanwhile, Cz-Cy7 exhibited a highly sensitive response to HClO in the presence of other ROS (reactive oxygen species) based on the sensing mechanism of oxidative cleavage of olefinic C =  = C bond. The limit of detection for HClO was evaluated to be 14 nM in PBS buffer solution (containing 50% CH₃CN). More importantly, the probe Cz-Cy7 showed good recovery and analytical precision in real water samples for both CN^- and HClO detection, indicating it was feasible and reliable for practical application. Moreover, the test strips loaded with Cz-Cy7 were fabricated and validated to be a portable tool for the efficient detection of CN^- and HClO by the naked eye.