An Indole-based Chromofluorogenic Probe for Detection of Trivalent Al3+, Ga3+, In3+ and Fe3+ Ions

An easily synthesizable indole-derived chromofluorogenic probe InNS has been demonstrated for recognition of trivalent metal ions (i. e., Al3+, Ga3+, In3+ and Fe3+). Both UV-Vis and emission spectral studies have been employed to assess the cation sensing ability of InNS in semi-aqueous medium. This probe exhibited a chromogenic response for these metal ions, and the related change was accompanied with the appearance of a new absorption near 376 nm. An obvious color change from pale yellow to dark yellow could also be noticed upon addition of the aforementioned metal ions to the probe's solution. Distinctively from the UV-Vis analysis, the fluorescence behavior of InNS was completely different; it displayed a 'turn-on' fluorescence response for only Al3+ among all the studied cations. The detection limit and the association constant (Ka) for Al3+ were determined to be 12.5 nM and 6.85×106 M-1, respectively. A potential 1 : 1 binding mode of Al3+-InNS has been established based on Job's plot, 1H NMR and DFT analyses. The reversibility experiment was conducted using strongly chelating EDTA ion, and a corresponding logic gate has been devised. In terms of practical applications, the InNS has been utilized to detect Al3+ in human breast carcinoma (MCF-7) cell lines displaying promising 'turn-on' bioimaging experiments.

Highly Selective Electrochemical Detection of 5-Formyluracil Relying on (2-Benzimidazolyl) Acetonitrile Labeling

The identification of formylpyrimidines in DNA is crucial for a better understanding of epigenetics. Although many techniques have been explored to detect their content, more accurate methods of formylpyrimidine determination are still required due to the relatively lower sensitivity or lack of selectivity in current methods. Herein, an electrochemical method based on the covalent bonding of the azido derivative of (2-benzimidazolyl) acetonitrile (azi-BIAN) and the aldehyde group of 5-formyluracil (5fU) was proposed for the selective detection of 5fU in the presence of 5-formylcytosine (5fC) and apyrimidinic (AP) sites. Target DNA containing 5fU was first treated with azi-BIAN and then incubated with DBCO-PEG4-Biotin to introduce a biotin group by copper-free click chemistry. Next, the sulfhydryl group was attached to the 5' end of above DNA through T4 polynucleotide kinase-catalyzed reaction. Subsequently, the labeled DNA was assembled onto the AuNPs-modified glassy carbon electrode (AuNPs/GCE) through Au-S bonds, and the streptavidin-horseradish peroxidase conjugate (SA-HRP) was further immobilized onto the surface of the above electrode by specific recognition between biotin and streptavidin. Finally, HRP catalyzed hydroquinone oxidation to benzoquinone to enhance the current signal, which was related to the amount of 5fU in nucleic acids. This method demonstrated a good linear relationship with 5fU concentrations ranging from 0.1 to 10 nM. Moreover, the level of 5fU in γ-irradiated nucleic acids was also successfully detected, indicating that the combination of molecule-depended chemical recognition and electrochemical sensing is a promising method for the selective and sensitive detection of 5fU.

Sequencing 5-Formyluracil in Genomic DNA at Single-Base Resolution

Albeit with low content, 5-formyluracil has been an important modification in genomic DNA. 5-formyluracil was found to be widely distributed among living bodies. Due to the equilibrium of keto-enol form, 5-formyluracil could be base-paired with guanine, thus inducing mutations in DNA. The highly reactive aldehyde group of 5-formyluracil could also cross-link with proteins nearby, preventing gene replication and expression. In certain cancerous tissues, the content of 5-formyluracil was found to be higher than the normal tissues adjacent to the tumor, and 5-formyluracil might be an important potential epigenetic mark. Nevertheless, the lack of a higher resolution sequencing technique has hampered the studies of 5-formyluracil. We adjusted the base-pairing of 5-formyluracil during the PCR amplification by changing the pH. Hence, we adopted the Alkaline Modulated 5-formyluracil Sequencing (AMfU-Seq), a single-base resolution analysis method, to profile 5-formyluracil at the genome scale. We analyzed the distribution of 5-formyluracil in the human thyroid carcinoma cells using AMfU-Seq. This technique can be used in the future investigations of 5-formyluracil.

FRET based ratiometric switch for selective sensing of Al3+ with bio-imaging in human peripheral blood mononuclear cells

FRET based ratiometric switch for selective sensing of Al³⁺ with bio-imaging in human peripheral blood mononuclear cells (PBMCs).

Progressive aggregation-induced emission strategy for imaging of aluminum ions in cellular microenvironment

A progressive aggregation-induced emission (AIE) strategy is established based on two diverse stimulus-responsive patterns of copper nanoclusters (CuNCs) for imaging of aluminum ions (Al³⁺) in cellular microenvironment. The non-emissive CuNCs were facilely synthesized with l-glutathione (GSH) as both stabilizing agent and reducing agent, and demonstrated the excellent AIE characteristics in the ethanol/water mixture. Moreover, the dispersed CuNCs can be aggregated to give the AIE behavior in aqueous solutions by reducing the pH value, and could be further aggregated with 94-fold reinforce by introducing Al³⁺ ascribe to the strong coordination ability between Al³⁺ and the functional groups of GSH, demonstrating the progressive AIE process. Under endocytosis, the progressive AIE strategy can be employed to distinguish the Al³⁺ in the locations of lysosome against other organelles due to the acidic microenvironment of lysosome. The progressive AIE advantages of CuNCs provide a new concept for signal transduction, and have the promising applications in decoding the functions of intracellular biomolecules.

Selective monitoring ATP using a fluorogenic Al(III)-probe complex in aqueous medium

A simple commercially available probe 8-hydroxyjulolidine-9-aldehyde (HJ) has been developed as a turn-on fluorescent probe specifically for Al³⁺ and characterized systemically. The probe HJ for Al³⁺ ion exhibits strong green fluorescence under ultraviolet light. The HJ acted as an OFF-ON-OFF type fluorescent probe for Al³⁺ and ATP in nearly 100% aqueous media. The 1:1 binding stoichiometry between probe and Al³⁺ has been established from Job's plot and HRMS studies. The limit of detection for Al³⁺ ion is found to be 5.75 × 10^-8 M. The large association constant between HJ and Al³⁺ ion is 1.05 × 10⁵ M^-1. Detailed insights of probe-metal interaction mechanisms have been studied by the density functional theory (DFT) as well as the time dependent-DFT (TDDFT) calculations. Moreover, benefiting from the water solubility and biocompatibility of the probe HJ and its HJ-Al³⁺ complex, they have also been successfully applied to detect Al³⁺ and ATP by bioimaging in onion epidermal cells and adult zebrafish respectively.

Facile Clamp-Assisted Ligation Strategy for Direct Discrimination and Background-Free Quantification of Site-Specific 5-Formylcytosine

Quantification of site-specific 5-formylcytosine (5fC) in DNA is highly significant to better understand its biological functions. However, it is still a big challenge to precisely discriminate 5fC from cytosine (C), 5-hydroxymethylcytosine (5hmC), 5-methylcytosine (5mC), and 5-carboxycytosine (5caC) owing to their similar structures that will interfere the quantification of 5fC. To solve this issue, a novel peptide nucleic acid (PNA) clamp-assisted ligation amplification strategy coupled with a 5fC-selective chemical conversion route is employed, through which 5fC can be precisely quantified with other interfering signals completely suppressed. As a result, as low as 200 aM of site-specific 5fC-containing DNA target can be accurately determined at single-base resolution in a background-free manner.

Turn-On Fluorescent Sensors for the Selective Detection of Al3+ (and Ga3+) and PPi Ions

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of L1-L4 in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between L4 and Al³⁺/Ga³⁺ ions. The solution-generated [L-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.