We develop a simple assay for highly selective and sensitive fluorescence detection of sulfide ions (S2−) using glutathione-protected gold nanoclusters (GSH-Au NCs). This approach was based on the much higher affinity of CuS than that of the Cu–GSH complex, which makes the fluorescence of the NCs quenched by Cu2+ recover upon addition of S2−. Importantly, the assistance of Cu2+ enables S2− detection in the “turn-on” mode, eventually enhancing detection sensitivity toward S2− about 15 times more compared to that in the “turn-off” mode. Under the optimal conditions, the linear fluorescence response toward S2− was given within the concentration range of 2 to 24 μM with a low detection limit of 0.7 μM. Also, the GSH-Au NCs show good reusability for S2− detection due to effective removal of the bridging reagent Cu2+ by S2−. This phenomenon is further exploited as an integrated logic gate and successfully employed for imaging S2− in living cells.

•A facile and highly sensitive colorimetric assay for glutathione (GSH) based on AuNPs was presented.•The assay was based on anti-aggregation of AuNPs via pH regulation.•Discriminative detection of GSH over Cys/Hcy was developed.•The assay was applied to detect GSH in serum and urine samples.Glutathione (GSH) plays a key role in biological systems and serves many cellular functions. Since biothiols all incorporate thiol, carboxylic and amino groups, discriminative detection of GSH over cysteine (Cys) and homocysteine (Hcy) is still challenging. Both Cys and Hcy can induce aggregation of AuNPs via the formation of zwitterionic networks, which is different from GSH. GSH induced aggregation of AuNPs by the hydrogen bonding between the carboxylic groups when pH <4.5, so pH plays a crucial part in our present work. By regulating the pH to 5.8, our proposed sensing system exhibits high selectivity and sensitivity towards GSH even in the presence of other biothiols, realizing the discriminative detection of GSH over Cys/Hcy based on anti-aggregation of AuNPs. In our work, 2-mercapto-1-methylimidazole (MMI) and GSH took the role of aggregation and anti-aggregation agent, respectively. A linear relationship between the intensity ratio A650 nm/A520 nm and the GSH concentration is obtained (R2 = 0.998) with a detection limit of 12.0 nM.

•A novel and facile colorimetric assay of cellular glutathione (GSH) level was developed based on the inhibition effect of GSH on the peroxidase-like activity of GSH stabilized gold nanoclusters.•This assay can be potentially used to identify normal and cancer cells by accurately evaluating cellular GSH level.•This assay bears some advantages in terms of ease operation, time saving, low cost, and good durability.Glutathione (GSH), the most abundant biothiol in cells, not only plays a pivotal role in protective and detoxifying functions of the cell, but also serves as a very important mediator in many cellular functions. Especially, the difference of GSH level between cancer cells and normal cells is regarded as one of most important physiological parameters for cancer diagnosis. It is thereby extremely necessary to develop a simple, sensitive, and reliable analytical method for detection of GSH in cells. On the basis of the inhibition effect of GSH on the peroxidase-like activity of GSH stabilized gold nanoclusters, here a novel and facile strategy for colorimetric detection of cellular GSH level was well established. In this sensing system, GSH can effectively inhibit the oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a blue colored product. Under the optimized conditions, the absorbance at 652 nm against GSH concentration shows a linear relationship within a range from 2 to 25 μM with detection limit of 420 nM. This excellent property allows our approach to be used to accurately evaluate the cellular GSH levels, and it is revealed that the overall GSH level in cancer cells was much higher than that in normal cells. The presented assay will enable a powerful tool for identifying cancer cells in a simple manner for biomedical diagnosis associated with GSH.Download high-res image (126KB)Download full-size image

An operationally simple colorimetric method for measuring glutathione (GSH) concentration was developed using anti-aggregation of gold nanoparticles (AuNPs) in this work. At a pH of 5.8, cysteine (Cys) could rapidly induce the aggregation of AuNPs, thereby resulting in color change and AuNPs absorbance ratio (A650 nm/A520 nm) change. However, the added glutathione (GSH) can cause the anti-aggregation process to occur. This method was based on the regulation of pH, which on one hand can selectively detect GSH over Cys by the process of anti-aggregation of AuNPs and on the other hand can distinguish GSH from homocysteine (Hcys), and cystine (Cye) through specific selectivity. Under optical conditions, the detection of GSH can be finished within 5 min. The concentration range of the probe is 0.1–1.0 μM and the limit of detection (LOD) can be reached to 20.3 nM.

We report a facile yet effective strategy for the fluorescence assay of heparin based on assembly and disassembly of the glutathione-protected gold nanoclusters (GSH-Au NCs) modulated via the competitive interaction of cetyltrimethyl ammonium bromide (CTAB) with heparin and GSH. Firstly, CTAB can increase the fluorescence of Au NCs by forming a nanocomposite via electrostatic and hydrophobic self-assembly. By adding heparin to the assay, CTAB is removed from the nanocomposites because of its higher affinity for heparin, quenching the fluorescence signal. Such a fluorescence feature induced via assembly and disassembly of the NCs enables our assay to possess high selectivity and sensitivity. The linear response toward heparin was obtained over the range 0.1–1.6 μg mL−1 with a low detection limit of 0.075 μg mL−1. Furthermore, satisfactory sensing perfomance for heparin in human serum makes this method hold great promise in heparin-related biomedical applications.

A new method based on sodium dodecyl sulfonate (SDS)-coated Fe3O4 magnetic nanoparticles (MNPs) as an efficient solid-phase adsorbent was developed for the extraction and determination of basic orange 21 and basic orange 22 by using solid-phase extraction coupled with an HPLC technique. MNPs were prepared via the solvothermal method, and characterized by an infrared spectrometry and a transmission electron microscope. The adsorption capacity was evaluated as 76.8 and 93.5 mg/g for basic orange 21 and basic orange 22, respectively, through Langmuir adsorption isotherm model. The experimental conditions were optimized, including the amounts of Fe3O4 NPs (10 mg) and SDS (1.0 mL 2.0 mg/mL), pH value of media (4.5), elution solvent and volume (1.0 mL methanol), and the rate of organic solvent and water of sample solution (methanol/water = 5%, v/v). Under optimal experimental conditions, the two dyes showed good linearities in the range of 0.02–5.0 μg/mL (R = 0.9999) with the LODs of 0.88 and 0.53 μg/kg for basic orange 21 and basic orange 22, respectively. The presented method was applied successfully to determine basic orange 21 and basic orange 22 in various food samples including dried beancurd stick, yellow fish, drinks, and wine. The recoveries were 72.1–98.3% with RSD of 2.1–9.4%, respectively. And the extraction procedure only needed no more than 13 min. Notably, MNPs show a good adsorption performance for the two target dyes within a wide pH range and excellent reusability during at least eight times of extraction procedures.

This work presents a novel and facile strategy for the fabrication of gold–platinum bimetallic nanoclusters (Au–PtNCs) with adjustable Au/Pt molar ratios by a one-pot synthetic route. It was unexpectedly found that the prepared Au–PtNCs with an optimal Au/Pt molar ratio (1 : 1) could exhibit greatly enhanced peroxidase-like catalytic activity and chemical stability toward harsh conditions due to the synergistic effect of the two atoms, in contrast with pure AuNCs. These prominent advantages render Au–PtNCs capable of sensitive and selective colorimetric detection of glucose by means of a NCs–glucose oxidase (GOx) cascade-catalyzed system using 3,3′,5,5′-tetramethylbenzidine (TMB) as a chromogenic substrate. This assay can be used not only for visual detection of glucose by the naked eye but for reliable and convenient quantification in the range from 5 to 55 μM with a detection limit of 2.4 μM. Importantly, to widen the application of point-of-care testing (POCT) of glucose to biomedical diagnosis, an integrated agarose hydrogel-based sensing platform comprising NCs, GOx and TMB was rationally designed. It was demonstrated that this sensing platform could serve as a reagentless and instrument-free platform for direct visualization of glucose with different levels in human serum, as the results were in good accordance with those obtained from a free NC-involved detection system as well as from a commercial blood glucometer.

•An ultrasensitive fluorescence “turn-on” assay for Cu2 + based on p-dimethylaminobenzamide-based derivative was presented.•The probe exhibits excellent selectivity and a very high tolerance to other common ions by the naked eye and fluorescence spectra.•The assay was applied to detect Cu2 + on the test kits and in living cells.•Compound BDIH showed a very low background.A new p-dimethylaminobenzamide derivative based compound BDIH has been synthesized. Cu2 + turned on the fluorescence of compound BDIH with a 1:2 binding stoichiometry. The fluorescent color of compound BDIH shows an evident change from colorless to bright blue upon the addition of Cu2 +, which could be visibly detected by the naked eye under UV light at 365 nm. More importantly, the detection limit was found to be 0.64 nM which is far lower than the maximal allowed concentration of the WHO limit (31.5 μM) for drinking water. This selective “turn-on” fluorescence sensor was used to identify Cu2 + in living cells using confocal fluorescence microscopy, indicating that compound BDIH has a potential application for selective detection of Cu2 + in organism.

•A highly sensitive fluorescence “turn-on” assay for Cu2+ based on p-dimethylaminobenzamide-based derivative was presented.•The probe exhibits excellent selectivity over other ions and compounds by the naked eye and fluorescence spectra.•The assay was applied to detect Cu2+ on the test kits and in living cells.•Compound DTBL showed zero background.•The assay exhibited an excellent tolerance to coexisting components.A novel p-dimethylaminobenzamide-based Schiff base derivative DTBL was synthesized via a simple reaction and utilized as a “turn-on” fluorescent indicator for copper ion (Cu2+). It showed extraordinary high selectivity toward Cu2+ in MeCN–H2O (v/v = 3:2, pH = 5) HOAc-NaOAc buffer solution, and the fluorescence intensity change were noticeable for the Cu2+ detection even in the presence of different kinds of foreign ions and compounds at very high concentrations. The 2:1 stoichiometry of DTBL-Cu2+ complex was calculated from Job’s plot based on fluorescence titrations. The good linear relationship easily exhibited a dynamic response range for Cu2+ from 0 to 3.4 μM and the detection limit (0.32 nM) of DTBL for Cu2+ was far lower than the maximum allowable level of the WHO limit (30 μM) for drinking water. Moreover, the adaptability of DTBL for biological applications was also demonstrated by fluorescence imaging of intracellular Cu2+ in living cells. The results indicate that DTBL should be available for the research on the biological and environmental applications associated with Cu2+.

•A highly sensitive and simple colorimetric strategy for Hg2+ detection is developed using gold nanoparticles.•The assay was based on anti-aggregation of AuNPs which could lower false positive signals.•The assay was applied to detect Hg2+ in real water and milk powder samples.•The colorimetric assay showed excellent sensitivity compared to other assays.A highly sensitive and simple colorimetric strategy for Hg2+ detection is introduced based on anti-aggregation of gold nanoparticles (AuNPs). 2-Mercaptobenzothiazole (MBT) can cause the aggregation of AuNPs due to strong covalent Au–S bond formation resulting in color change from red to blue. However, the presence of Hg2+ led the AuNPs to remain in the dispersed state because MBT prefers to interact with Hg2+ rather than AuNPs. Based on the anti-aggregation mechanism, Hg2+ can be detected by observing the color change of AuNPs solution containing MBT. The minimum detectable quantity is 0.1 μM by the naked eyes, and the limit of the detection (LOD) is 6.0 nM by UV–vis spectroscopy with the linear range from 0.05 to 1.0 μM. Furthermore, the developed detection system is also environmental-friendly and inexpensive, which has been successfully used in lake water and milk powder samples detection.

A simple but novel compound of 4-aminoantipyrine derivative (NTBL) was synthesized and used for sensing Cu2+. Its applications in colorimetric detections of Cu2+ in aqueous solution and on the simple colorimetric paper-made test kits were performed. Upon addition of Cu2+, compound NTBL could give rise to a vivid color change from colorless to purple which was easily observed by the naked eye. However, compound NTBL did not show any observable change upon interaction with other metal ions. Under optimized experimental conditions, NTBL exhibits a dynamic response range for Cu2+ from 0 to 8.5 μM, with the detection limit of 2.14 × 10−7 M. The response of the colorimetric chemosensor for Cu2+ is reversible. Most importantly, both the color and absorbance changes of the chemosensor are remarkably specific for Cu2+ in the presence of other metallic cations (even those that exist in high concentration), which meets the selective requirements for biomedical and environmental monitoring application.

The authors demonstrate a single-step histidine assay that is based on the use of silver nanoparticles modified with sulfanilic acid (SAA-AgNPs). The presence of histidine leads to a visually detectable gradual color change from bright yellow via orange to purple. The effect is assumed to be mainly due to strong π-π stacking, electrostatic interaction, and hydrogen bonding between SAA and histidine. The assay has a 52.7 nM detection limit and works in the 0 to 3.5 μM concentration range. It is selective over other compounds when using appropriate masking agents. The method has been successfully applied to the colorimetric determination of histidine in (spiked) serum samples. Recoveries ranged between 97 % and 107 %, and relative standard deviations are <0.92 % (for n = 3). The method was also applied to detect polyhistidine-tagged cysteine (His-His-His-His-His-His-Cys) which can be quantified in concentrations down to 5.57 nM. This finding links the method to His-tag technology.

Copper ions (Cu2+) in the central nervous system play a crucial role in the physiological and pathological events, so simple, selective, and sensitive detection of cerebral Cu2+ is of great importance. In this work, we report a facile yet effective fluorescent method for sensing of Cu2+ in rat brain using one kind of lanthanide coordination polymer nanoparticle, adenosine monophosphate (AMP) and terbium ion (Tb3+), i.e., AMP-Tb, as the sensing platform. Initially, a cofactor ligand, 5-sulfosalicylic acid (SSA), as the sensitizer, was introduced into the nonluminescent AMP-Tb suspension, resulting in switching on the luminescence of AMP-Tb by the removal of coordinating water molecules and concomitant energy transfer from SSA to Tb3+. The subsequent addition of Cu2+ into the resulting SSA/AMP-Tb can strongly quench the fluorescence because the specific coordination interaction between SSA and Cu2+ rendered energy transfer from SSA to Tb3+ inefficient. The decrease ratio of the fluorescence intensities of SSA/AMP-Tb at 550 nm show a linear relationship for Cu2+ within the concentration range from 1.5 to 24 μM with a detection limit of 300 nM. The method demonstrated here is highly selective and is free from the interference of metal ions, amino acids, and the biological species commonly existing in the brain such as dopamine, lactate, and glucose. Eventually, by combining the microdialysis technique, the present method has been successfully applied in the detection of cerebral Cu2+ in rat brain with the basal dialysate level of 1.91 ± 0.40 μM (n = 3). This method is very promising to be used for investigating the physiological and pathological events that cerebral Cu2+ participates in.

Low-level cadmium ion (Cd2+) exposure contributes much toward the causation of chronic disease. Due to its low permissible exposure limit, overexposures may occur even in situations where trace quantities of Cd2+ exist. So far, no effective treatment for Cd2+ toxicity has been reported. Prevention of further exposure is the most important step in management of patients suggestive of Cd2+ intoxication. Development of sensors for Cd2+ is of great interest to ensure early diagnosis and improve management. We propose here a simple, low-cost (0.1$ per sample) yet very sensitive (limit of detection is 3.0 nM) and selective colorimetric assay for rapid (2 min) determination of Cd2+ based on 5-sulfosalicylic acid functionalized silver nanoparticles (SAA–AgNPs). This method shows excellent selectivity for Cd2+ over the other 16 metal ions. It is also precise and highly reproducible in determining Cd2+ in real samples such as tap water, milk, serum, and urine with recoveries ranging from 93 to 110%, indicating the wide practical application to samples suspected of Cd2+ exposure.

Heavy metal pollution can exert severe effects on the environment and human health. Simple, selective, and sensitive detection of heavy metal ions, especially two or more, using a single probe, is thereby of great importance. In this study, we report a new and facile strategy for discriminative detection of Hg2+ and Cd2+ with high selectivity and sensitivity via pH-modulated surface chemistry of the glutathione-capped gold NCs (GSH-Au NCs). By simply adjusting pH values of the colloidal solution of the NCs, Hg2+ could specifically turn off the fluorescence under acidic pH, however, Cd2+ could exclusively turn on the fluorescence under alkaline pH. This enables the NCs to serve as a dual fluorescent sensor for Hg2+ and Cd2+. We demonstrate that these two opposing sensing modes are presumably due to different interaction mechanisms: Hg2+ induces aggregation by dissociating GSH from the Au surface via robust coordination and, Cd2+ could passivate the Au surface by forming a Cd-GSH complex with a compact structure. Finally, the present strategy is successfully exploited to separately determine Hg2+ and Cd2+ in environmental water samples.

•A fluorescent off-on probe for trace thiocyanate (SCN−) was exploited.•The assay for SCN− is ultrasensitive with detection limit 0.09 nM.•The method cost is 0.2$ per sample with the aid of fluorescence spectrometer.•The operation is ultraselective and relatively fast response time within10 min.Thiocyanate (SCN−) is a small anion byproduct of cyanide metabolism. Several methods have been reported to measure SCN− above the micromolar level. However, SCN− is derived from many sources such as cigarettes, waste water, food and even car exhaust and its effect is cumulative, which makes it necessary to develop methods for the detection of trace SCN−. In this paper, a simple and ultrasensitive turn-on fluorescence assay of trace SCN− is established based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and fluorescein. The detection limit is 0.09 nM, to the best of our knowledge, which has been the lowest detection LOD ever without the aid of costly instrumentation. The fluorescence of fluorescein is significantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN−, the fluorescence is turned on due to the competition action between SCN− and fluorescein towards the surface of AuNPs. Under an optimum pH, AuNPs size and concentration, incubation time, the fluorescence enhancement efficiency [(IF−I0)/I0] displays a linear relationship with the concentration of SCN− in the range of 1.0 nM to 40.0 nM. The fluorescein–AuNP sensor shows absolutely high selectivity toward SCN− than other 16 anions. The common metal ions, amino acids and sugars have no obvious interference effects. The accuracy and precision were evaluated based on the recovery experiments. The cost effective sensing system is successfully applied for the determination of SCN− in milk products and saliva samples.A simple and ultrasensitive turn-on fluorescence assay of trace thiocyanate (SCN−) is established based on the fluorescence resonance energy transfer (FRET) between the gold nanoparticles (AuNPs) and fluorescein. The limit of detection is 0.09 nM which has been the lowest ever reported without the expensive instrumentation to our best of knowledge.

A simple and low-cost assay for melamine is introduced that is making use of silver nanoparticles (AgNPs) functionalized with chromotropic acid (CTA). The surface of the AgNPs was capped with chromotropic acid which warrants the NPs to remain in stable and dispersed form. The presence of melamine induces the aggregation of the CTA-AgNPs due to the hydrogen bond interaction between CTA and melamine. This is accompanied by a color change from yellow to orange which can be observed with bare eyes. The method allows melamine to be quantified by absorptiometry with a linear response in the concentration range from 0.10 to 1.5 μM (R = 0.9996) and a detection limit of 36 nM which was much lower than the safe limits (20 μM in both the USA and EU, 8 μM for infant formula in China, 1.2 μM in the CAC review for melamine in liquid infant formula). The assay displays high selectivity to melamine over its structural analogs such as cyanuric acid, 2,4,6-trimethy-1,3,5-triazine, and phloroglucinol owing to the fact that only melamine can act as the hydrogen donor to form hydrogen bonds with the sulfo groups of the CTA-capped AgNPs. The method was successfully applied to the determination of melamine in spiked liquid milk and the average recovery was 99 %. Most amino acids and a high content of calcium do not interfere in this assay.

We report on a simple method for the determination of traces of aluminum(III) in water at pH 7.4 by using silver nanoparticles (Ag-NPs) functionalized with 8-hydroxyquinoline-5-sulfonate. The modified Ag-NPs undergo (a) a distinct color change from yellow to deep orange, and (b) a strong fluorescence enhancement upon addition of Al(III). Both the ratio of absorbances at 530 and 392 nm, and the intensity of fluorescence at 492 nm can serve as the analytical information. The absorption-based calibration plot increases linearly in the 0.1 to 4.0 μM Al(III) concentration range. The detection limit is 2.0 nM which is much lower than the permissible level (7.4 μM) for drinking water as defined by the World Health Organization. The method was successfully applied to the determination of Al(III) in samples of lake water, tap water and boiler water, and the recoveries were from 98 to 105 %. The assay also was applied to the determination of Al(III) in living mouse myeloma cells via fluorescence imaging. A linear relationship was obtained between relative fluorescence intensity (F/F0) and the concentration of Al(III) in the 0.05 μM to 4 μM concentration range. The detection limit is 15 nM.

•An easy-to-make colorimetric and fluorometric sensor 1 for Pb2+ was obtained.•The assay carried in aqueous solution with low limit detection as 37 nM mol L−1.•The high selectivity and sensitivity of 1 for Pb2+ was for 1’s distinctive structure.•1−Pb2+ shows longer wavelength absorption and emission and strong fluorescence.A new compound, 2-boronobenzaldehyde-(2′-hydroxyl-4′-sulfonic acid) naphthalene hydrazone (1), was synthesized and its structure was characterized by proton nuclear magnetic resonance, mass and element analyses. The presence of Pb2+ led 1 to undergo colorimetric and fluorescent changes, which were detectable with the naked eye. Thus, a dual spectral response for Pb2+ detection was introduced. In KH2PO4–NaOH buffer aqueous solution (pH 6.0), 1 exhibited fluorescence enhancement at 568 nm and hyperchromicity at 595 nm upon the addition of Pb2+. The fluorescent intensity change was proportionate to the concentration of Pb2+ with a dynamic working range of 5.0 × 10−7 mol L−1 to 1.0 × 10−4 mol L−1 and a detection limit of 3.7 × 10−8 mol L−1. The fluorometric method was successfully applied for the detection of Pb2+ water of Qianhu Lake and soil in Nanchang university campus. The recoveries were 111–116% for water and 97.6% for soil respectively, determined via the standard addition method.Graphical abstractA 1:1 metal-ligand complex between lead ion and compound 1 was formed which resulted in color change from red to blue and enhancement of fluorescence at 568 nm.

Simple structural compounds 1 to 3 were synthesized. The presence of Cu2+ resulted in the fluorescence and absorption spectra change of 1 and 2, which indicated that 1 and 2 showed a highly selective response to Cu2+ over other metal ions. However, 3 showed no selectivity for metal ions, which means that the compound could bind with several metal ions, such as, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, Fe3+, Mg2+, Ca2+, and Co2+, except Cu2+ and Ag+. The different spectral responses were attributed to the difference in binding sites for 1 and 3.

We report on a simple strategy for the determination of zinc ion by using surface-modified quantum dots. The probe consists of manganese-doped quantum dots made from zinc sulfide and capped N-acetyl-L-cysteine. The particles exhibit bright yellow-orange emission with a peak at 598 nm which can be attributed to the 4T1→6A1 transition of Mn(II). This bright fluorescence is effectively quenched by modifying the sulfur anion which suppresses the radiative recombination process. The emission of the probe can then be restored by adding Zn(II) which causes the formation of a ZnS passivation layer around the QDs. The fluorescence enhancement caused is linear in the 1.25 to 30 μM zinc concentration range, and the limit of detection is 0.67 μM.

A new compound, 2,5-di-[2-(4-hydroxy-phenyl)ethylene]-terephthalonitrile (DHPEPN), was synthesized. The interaction between bovine serum albumin (BSA) and DHPEPN in Tris–HCl buffer solution (pH 7.4) was investigated using fluorescence and UV–vis absorption spectroscopy. The mechanism of BSA fluorescence quenched by DHPEPN is discussed according to the Stern–Volmer equation. The binding constant and the thermodynamic parameters ΔH, ΔS, ΔG at different temperatures were calculated. The results indicate that the van der Waals interaction and hydrogen bonding play major roles in the binding process. The distance between BSA and DHPEPN is estimated to be 3.59 nm based on the Förster resonance energy transfer theory. The spectral changes of synchronous fluorescence and three-dimensional fluorescence suggest that both of the microenvironment of DHPEPN and the conformation of BSA are changed during binding between DHPEPN and BSA.Graphical abstractA new compound, 2,5-di-[2-(4-hydroxy-phenyl)ethylene]-terephthalonitrile (DHPEPN) is synthesized and used as fluorescent probe for protein. With increasing the amount of BSA, the fluorescence intensity of DHPEPN was enhanced and emission band slightly blue shifted. At the same time a good linear response of fluorescence intensity as a function of BSA concentration was obtained.Highlights► A new compound, 2,5-di-[2-(4-hydroxy-phenyl)ethylene]-terephthalonitrile (DHPEPN), was synthesized and characterized by 1H NMR, IR, and mass spectrometry data. ► The interaction between DHPEPN and bovine serum albumin was investigated using fluorescence and UV–vis absorption spectroscopy. ► The binding constant and the thermodynamic parameters ΔH, ΔS, ΔG of the binding process between DHPEPN and bovine serum albumin were calculated.

A new compound, 1-[p-(dimethylamino)benzoyl]-4′-phenyl-semicarbazide (1) was synthesized and showed highly selective response to Cu2+ over other metal ions such as Pb2+, Mg2+, Fe2+, Co2+, Zn2+, Cd2+, Hg2+, Ni2+, Ca2+, Ag+, Na+, K+, and Li+. The control compound, 1-[p-(dimethylamino)benzoyl]-4-phenyl-thiosemicarbazide (2), showed different fluorescence spectral response to Cu2+. A 1:1 complex between Cu2+ and 1 was formed while 1:1 and 1:2 complexes between Cu2+ and 2 were formed. The binding model between the receptor (1 or 2) and Cu2+ was supported by IR spectra, mass spectra, and computation model. 1 possessed higher selectivity towards Cu2+ compared with 2 owing to the difference of complexation ability between urea and thiourea groups.

The interaction between 1-Zn (N-p-(dimethylamino)benzamido-N′-phenylthiourea-zinc) complex and serum albumins was studied. In the presence of proteins such as BSA or HSA, the fluorescence spectrum of 1 did not change. However, the fluorescence intensity of its zinc complex (1-Zn) was greatly enhanced. It was ascribed to the fact that zinc ion promoted the interaction between 1 and proteins. Therefore, it was concluded that zinc ion could facilitate bioactivity of thiourea derivative drugs. Energy transfer occurred between 1-Zn and the proteins, which led to decrease of proteins’ emission and increase of 1-Zn’s emission. The fluorescence quenching of serum albumins by 1-Zn was considered as a static quenching process. The binding constants between 1-Zn and serum albumins were estimated as 1.02×1012 mol−1 L for BSA and 1.32×1010 mol−1 L for HSA, respectively, and the number of binding sites was 2 for both. The effect of 1-Zn on the conformation of serum albumins was further investigated using synchronous fluorescence spectrometry and the results implied that tyrosine residues of proteins were closer to 1-Zn than tryptophan residues.

The binding properties of curcumin with anions in acetonitrile were examined for the first time by UV–vis absorption and fluorescence spectroscopies. The results showed that curcumin highly and selectively responded to F− over other anions such as AcO−, H2PO4− and Cl− because of anionic complex formation via hydrogen bond. Curcumin gave rise to the red-shift of absorption spectra and its fluorescence was quenched with concomitant color change from yellow to purple upon addition of F−, which was detected by naked eyes. The addition of other anions such as AcO−, H2PO4−, HSO4−, NO3−, Cl− and Br− did not result in observable spectral change and solution color change. The binding constant between curcumin and F− was 2.0×105 mol−1 L and the recognizing mechanism was investigated as well.

A new Schiff-base compound, N′-(2-hydroxynaphthalenemethylene)-4-(2-hydroxyl naphthalenemethylenamine)benzoylhydrazine (1), was synthesized and the interaction between zinc complex (1-Zn) and bovine serum albumin (BSA) was investigated by fluorescence and absorption spectroscopies. A marked increase in the fluorescence intensity of 1-Zn was observed at 475 nm upon addition of BSA when excitation wavelength was set at 370 nm in pH 7.4 Tris–HCl buffer solution. Reversely, the intrinsic fluorescence of BSA could be quenched by 1-Zn complex. The quenching mechanism was suggested as static quenching according to the Stern–Volmer equation and the UV–vis absorption spectral change of 1-Zn upon addition of BSA. The binding constants Kb and the number of binding sites n were calculated. The effect of 1-Zn on the conformation of BSA was studied using synchronous fluorescence spectroscopy and three-dimensional fluorescence spectroscopy. In addition, the binding average distance r between the donor (BSA) and acceptor (1-Zn) was estimated based on the Förster's non-radiation energy transfer theory.

The zinc complex of 2-[2-(3, 5-bis(2-pyridylmethyl)aminomethyl-4-hydroxy-phenyl) ethylene]-5-methylpyrazine (1) could bind with the calf thymus deoxyribonucleic acid (ct-DNA). The binding behaviors between them were studied by fluorescence and absorption spectral assay. The absorption titration of 1-Zn with ct-DNA showed no bathochromic shift and hypochromic effect. No anisotropy increase was observed when ct-DNA was added to 1-Zn solution. They both proved the lack of intercalation interaction between 1-Zn and ct-DNA. The ionic strength experiment, Scatchard plot, study of interaction between 1-Zn and denatured ct-DNA all revealed that the interaction mode between 1-Zn and ct-DNA was electrostatic interaction. Binding constant was estimated to be 7.96×104 L moL−1.

A simple and sensitive fluorescence enhancement assay of trace cysteine (Cys) is presented. The method is based on the redox reaction between the Cu2+-morin complex and Cys. In Britton-Robinson buffer of pH 7.4, the addition of Cys to the Cu2+-morin system results in dramatic fluorescence intensity increase at 539 nm which is proportional to the concentration of Cys over the range of 6.52 × 10−7–2.20 × 10−5 mol L−1, with a limit of detection of 6.52 × 10−8 mol L−1. The method was applied to determine Cys in protein hydrolysate of fresh porcine blood and human urine, the recoveries being 91.3–94.1% and 95–98.6% respectively. The mechanism involved in the reaction was also studied.

A fluorescent assay of Hg2+ in neutral aqueous solution was developed using N-[p-(dimethylamino)benzamido]-N′-phenylthiourea (1). 1’s fluorogenic chemodosimetric behaviors towards various metal ions were studied and a high sensitivity as well as selectivity was achieved for Hg2+. It was because of a strongly fluorescent 1,3,4-oxadiazoles which was produced by the Hg2+ promoted desulfurization reaction. The spectra of ESI mass and IR provided evidences for this reaction. According to fluorescence titration, a good linear relationship ranging from 1.0 × 10−7 to 2.0 × 10−5 mol l−1 was obtained with the limit of detection as 3.1 × 10−8 mol l−1.