Selective fluorometric detection of pyrophosphate and stringent alarmone with copper(II)–2,6-bis(2-benzimidazolyl)pyridine complex

Pyrrole-quinazoline derivative as an easily accessible turn-off optical chemosensor for Cu2+ and resultant Cu2+ complex as a turn-on sensor for pyrophosphate in almost neat aqueous solution

A simple chemosensor, 6-(1H-pyrrol-2-yl)-5,6-dihydro-benzo[4,5]imidazo[1,2-c]quinazoline (1), was synthesized via simple nucleophilic addition reaction coupled with Schiff base condensation. The probe 1 is aggregation-induced emission-active and could be used as an on-off fluorescence sensor toward Cu²⁺ in H₂O/CH₃CN (99.5%, v/v) solution. Furthermore, the resultant Cu²⁺ complex selectively responded to pyrophosphate (PPi) among various anions based on fluorescent on-off signal. In addition, the probe could be used for detecting Cu²⁺ and PPi in HeLa cells.

Highly sensitive and visual detection of guanosine 3'-diphosphate-5'-di(tri)phosphate (ppGpp) in bacteria based on copper ions-mediated 4-mercaptobenzoic acid modified gold nanoparticles

Guanosine 3'-diphosphate-5'-di(tri)phosphate (ppGpp) plays a crucial role in the gene expression, metabolism, growth, and other significant processes of microorganisms. In this work, a facile sensitive and visual strategy for the detection of ppGpp has been established by developing a colorimetric probe of copper ions (Cu²⁺)-mediated 4-mercaptobenzoic acid (4-MBA) modified gold nanoparticles (AuNPs). The sensing process was characterized by transmission electron microscopy (TEM), zeta potential, dynamic light scattering (DLS) and UV-vis spectroscopy. The strategy not only achieves desirable performance over a wide concentration range (0.05-10 μM), but also exhibits excellent selectivity over other nucleotides and biomolecules. In addition, the results could be visualized by the naked eye. We have demonstrated the determination of ppGpp in Bacillus subtilis lysate samples.

A novel and simple solvent-dependent fluorescent probe based on a click generated 8-aminoquinoline–steroid conjugate for multi-detection of Cu(ii), oxalate and pyrophosphate

A novel and simple deoxycholic acid-based fluorescent probe was facilely constructed for solvent-dependent multi-detection of Cu²⁺, C₂O₄²⁻and P₂O₇⁴⁻.

Selective and sensitive colorimetric detection of stringent alarmone ppGpp with Fenton-like reagent

Stringent alarmone, namely, guanosine 3'-diphosphate-5'-diphosphate (ppGpp), is a global regulator that plays a critical role in the survival, growth, metabolism, and many other vital processes of microorganisms. Because of its structural similarity to normal nucleotides, it is also a challenge for the selective and sensitive detection of ppGpp nowadays. Herein, we developed a colorimetric method for the selective detection of ppGpp by inhibiting the redox reaction between Fenton-like reagent (composed of Fe(3+) and H2O2) with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). Owing to the strong coordination affinity between ppGpp and Fe(3+), the chromogenic reaction between ABTS and Fenton-like reagent, occurred in aqueous medium at 37 °C and resulted in a bluish-green solution, which was inhibited with the addition of ppGpp. This phenomenon forms the basis for the colorimetric detection of ppGpp, with a detection limit of 0.19 μM and good selectivity for ppGpp over other nucleotides and anions. Furthermore, the results could be visualized by the naked eye, and the sensitivity of the naked-eye observation could even be further improved with the aid of the introduction of a background color.

Environment-sensitive fluorescent supramolecular nanofibers for imaging applications

The combination of an environment-sensitive fluorophore, 4-nitro-2,1,3-benzoxadiazole (NBD), and peptides have yielded supramolecular nanofibers with enhanced cellular uptake, brighter fluorescence, and significant fluorescence responses to external stimuli. We had designed and synthesized NBD-FFYEEGGH that can form supramolecular nanofibers and emit brighter than its counterpart of NBD-EEGGH without the self-assembling property. The nanofibers of NBD-FFYEEGGH could specifically bind to Cu(2+), leading to the formation of fluorescence quenched elongated nanofibers. This fluorescence quenching property was enhanced in self-assembling nanofibers and could be applied for detection of Cu(2+) in vitro and within cells. In a further step, an enzyme-cleavable DEVD peptide was placed between NBD-FFY and the copper binding tripeptide GGH. The resulting self-assembling peptide NBD-FFFDEVDGGH also showed strong fluorescence quenching to Cu(2+). Upon the enzymatic cleavage to remove the Cu(2+)-binding GGH tripeptide from the peptide, the fluorescence was restored. The cellular uptake of nanofibers was better than that of free molecules because of endocytosis. The supramolecular nanofibers with fluorescence turn-on property could therefore be applied for detection of caspase-3 activity in vitro and within cells. We believe that the combination of environment-sensitive fluorescence and fast responses of supramolecular nanostructures would lead to a useful platform to detect many important analytes.

Highly selective detection of bacterial alarmone ppGpp with an off-on fluorescent probe of copper-mediated silver nanoclusters

In this study, a facile strategy for highly selective and sensitive detection of bacterial alarmone, ppGpp, which is generated when bacteria face stress circumstances such as nutritional deprivation, has been established by developing an off-on fluorescent probe of Cu(2+)-mediated silver nanoclusters (Ag NCs). This work not only achieves highly selective detection of ppGpp in a broad range concentration of 2-200 μM, but also improves our understanding of the specific recognitions among DNA-Ag NCs, Cu(2+), and ppGpp. The present strategy, together with other reports on the Ag NCs-related analytical methods, has also identified that Ag NCs functionalized with different molecules on their surfaces can be engineered fluorescent probes for a wide range of applications such as biosensing and bioimaging.

Spectral study on the unique enhanced fluorescence of guanosine triphosphate by zinc ions

Binding effect of guanosine triphosphate (GTP) with metal ions is involved in many biologically important processes, and so its investigation has been one interesting research focus for many chemical and biochemical research groups. In this contribution, we presented the unique fluorescence recovery and enhancement of GTP induced by Zn(II) based on the spectrofluorometric method. When excited at 280 nm, GTP is hardly fluorescent at the alkaline condition. However, the presence of Zn(II) caused an obvious fluorescence emission of GTP at 346 nm, and the binding molar ratio between GTP and Zn(II) had been proved to be 1. The investigations of binding property of various nucleotides with metal ions demonstrated that this fluorescence recovery and enhancement of GTP with Zn(II) was highly specific, which could successfully discriminate GTP from other structurally similar nucleotides including GDP and GMP. Furthermore, similar fluorescence response of the bacterial alarmone ppGpp to Zn(II) had also been identified.

A ratiometric fluorescence recognition of guanosine triphosphate on the basis of Zn(II) complex of 1,4-bis(imidazol-1-ylmethyl) benzene

As one vital member among the family of phosphates, guanosine triphosphate (GTP) not only plays a very important role in many critical biological processes but also closely associates with definite pathological states. Based on the ratiometric fluorescence response of the zinc complex of 1,4-bis(imidazol-1-ylmethyl) benzene (bix) in this contribution, a highly selective recognition of GTP has been successfully developed. The fluorescence of bix-Zn(II) at 289 nm decreased in the presence of GTP with the appearance of one new emission band at 341 nm, resulting in ratiometric fluorescence changes with the concentration of GTP. With that, ratiometric fluorescence recognition for GTP could be effectively established, and so GTP could be successfully discriminated from other structurally similar anions, including ATP and PPi. Furthermore, bix-Zn(II) also has a ratiometric fluorescence response to DNA sequences containing guanine.

Highly selective visual distinction of pyrophosphate from other phosphate anions with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene in the presence of copper(II) ions

Pyrophosphate (PPi), as a biologically related phosphate anion, plays very important roles in organisms. Here, a highly selective visual method for distinction of PPi was made with commercial available 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) in the presence of copper(II). The yellow solution of 5-Cl-PADAB exhibits strong absorption at 450.5 nm, and addition of Cu(II) results in a red solution with a new absorption band at 506.0 nm. Upon titration with PPi, the absorption band at 506.0 nm decreases with blueshift, while another new absorption band in the region from 562.0 nm to 750.0 nm appears which gradually splits into two peaks, and the color accordingly changes from red to cyan. Further addition of PPi, the new absorption peaks gradually disappear, and the mixture shows the absorption of 5-Cl-PADAB and recovers to yellow from cyan. This process is highly selective for PPi since other phosphate anions such as nucleotides cannot induce such spectral and color changes. With this method, the detection of PPi concentration in human urine was made with satisfactory results.