Direct detection of potassium and lead (II) ions based on assembly-disassembly of a chiral cyanine dye /TBA complex

Novel fluorescence strategy based on G-quadruplex structure-switching aptamer for enrofloxacin detection in food and environmental samples

Enrofloxacin (ENR) is widely used in the prevention and treatment of animal infectious diseases, so it is necessary to strengthen the residue detection of this drug in animal-derived food and water environments. In this work, for the first time, we engineered assembly a split ENR aptamer into the G-quadruplex (G4) region to form a new aptamer (G4-ENRA) that provides a more sensitive signal-reporting function while retaining target-specific recognition ability of the aptamer. This rational design effectively overcomes the issue of difficulty in identification probe development. Under the optimized conditions, a response range of 0.05-20 µM and limit of detection of 26.7 nM were obtained by directly detecting fluorescence signals, displaying a comparative advantage over the previously reported methods. Moreover, this method demonstrated satisfactory performance for the ENR detection in various real food and environmental samples, with the detection recoveries ranging from 95.87 % to 104.36 %, illustrating promising applicability prospects.

A portable microfluidic electrochemical sensing platform for rapid detection of hazardous metal Pb2+ based on thermocapillary convection using 3D Ag-rGO-f-Ni(OH)2/NF as a signal amplifying element

Heavy metal pollution is causing a great threat to ecological environment and public health, which needs an efficient strategy for monitoring. A portable microfluidic electrochemical sensing system was developed for the determination of heavy metal ions. Herein, the detection of Pb²⁺ was chosen as a model, and a microfluidic electrochemical sensing chip relying on a smartphone-based electrochemical workstation was proposed for rapid detection Pb²⁺ with the assistance of thermocapillary convection result from the formed temperature gradient. The 3D Ag-rGO-f-Ni(OH)₂/NF composites, prepared by one-step hydrothermal method without any Ni precursor salt, were used to further amplify electrochemical signals under the synergistic effect of thermocapillary convection. The thermocapillary convection could accelerate the preconcentration process and shorten the detection time (save 300 s of preconcentration time). The fabricated system exhibited the exceptional competence for monitoring of Pb²⁺ range from 0.01 μg/L to 2100 μg/L with a low detection limit (LOD) of 0.00464 μg/L. Furthermore, this portable system has been successfully demonstrated for detecting Pb²⁺ (0.01 μg/L to 2100 μg/L) in river water (LOD = 0.00498 μg/L), fish (LOD = 0.00566 μg/L) and human serum samples (LOD = 0.00836 μg/L), and the results were consistent with inductively coupled plasma-mass spectrometry (ICP-MS). The proposed novel sensing platform provides a cost-effectiveness, rapidly responding and ease-to-use pathway for analysis of heavy metal ions in real samples and shows great potential in point-of-care testing.

A label-free G-quadruplex aptamer fluorescent aptasensor for visual and real-time kanamycin detection in lake and human samples

Antibiotic abuse is considered a serious problem affecting human health, necessitating that great attention be paid to explore robust, simple and sensitive methods for rapid evaluation. In this paper, we developed a fluorescent aptasensor for visual and real-time kanamycin detection by taking advantage of the label-free strategy based on H-aggregate disassembly of a chiral cyanine dye induced by a G-quadruplex aptamer. The good sensitivity and selectivity enabled this aptasensor to have a detection limit as low as 43 nM and have high specificity for kanamycin recognition. Furthermore, this assay was successfully applied for the detection of kanamycin in lake water and urine with excellent recoveries.

G-quadruplex apurinic site-programmed chiral cyanine assemblies for specifically recognizing guanosine and guanine

DNA-tuned dye assemblies have received considerable attention toward developing various devices. Owing to easy conformation implementation, G-quadruplexes (G4s) have been extensively used as initiators to grow dye assemblies with controllable chiralities. However, programmed chirality regulation of dye assemblies for a given G4 sequence has not been realized in a straightforward manner. In this work, we replaced a middle guanine in the G-tracts of a human telomeric G4 with an apurinic site (AP site) to meet the programmed dye assemblies. Although all of the AP site replacements altered the G4 conformation from the hybrid to the antiparallel folding, the handedness of pinacyanol (PIN) assemblies grown on the AP site-containing G4 was programmably regulated. The G4 with the AP site at the 5'-most G-tract grew right-handed assemblies, while that with the AP site at the 3'-most G-tract grew left-handed assemblies. The handedness of assemblies almost totally mirrored each other within 450-700 nm. Interestingly, we found that the AP site provided a specific binding site for guanosine and guanine, and this binding event sensitively broke the chiral assemblies. Thus, dye assembly-based sensors can be easily established based on the chiral responses with a high selectivity and sensitivity. Our work first demonstrates the AP site programmed chirality regulation of G4-grown dye assemblies and will find wide application in chiral devices.

Advances in the Functional Nucleic Acid Biosensors for Detection of Lead Ions

Lead ions (Pb²⁺) are destructive to the natural environment and public health, so the efficient detection of Pb²⁺ is particularly important. Although the instrumental analysis methods have high accuracy, they require high cost and precise operation, which limits their wide application. Therefore, many strategies have been extensively studied for detecting Pb²⁺ by biosensors. Functional nucleic acids have become an efficient tool in this field. This review focuses on the recent biosensors of detecting Pb²⁺ based on functional nucleic acids from 2010 to 2020, in which DNAzyme, DNA G-quadruplex and aptamer will be introduced. The biosensors are divided into three categories that colorimetric, fluorometric and electrochemical biosensors according to the different reported signals. The action mechanism and detection effect of each biosensor are explained. Finally, the present situation of nucleic acid biosensor for the detection of Pb²⁺ is summarized and the future research direction is prospected.

Concurrent formation of H- and J-aggregates of dyes with chiralities individually determined by G-quadruplex handedness

DNA templated dye assemblies pave an easy way to regulate the optical properties of molecular aggregates. G-quadruplexes (G4s) provide versatile DNA platforms for the dye assemblies since their foldings can be easily tuned by cation ions and sequences. In this work, we found that the G4 handedness can be used to control the aggregate chirality of a dye of 3,3'-diethylthiacarbocyanine (DiSC₂(3)). The left-handed and right-handed G4s can template the concurrent formation of the J- and H-aggregates of DiSC₂(3) with emergence of the featured absorption spectra. However, the chiral J-aggregate of DiSC₂(3) can be formed only on the left-handed G4s, while the chiral H-aggregate is otherwise grown only on the right-handed G4s, as confirmed by the induced circular dichroism (ICD) spectra with the characteristic splitting bands. Additionally, these G4s even at tens of nM level are efficient to produce these chiral aggregates, demonstrating the high sensitivity of G4s in creating these optically active dye assemblies. The possible growth sites of the aggregates are proposed by the sequence length-dependent assemblies. Our work will provide a new way to control the chiral assemblies of dye aggregates via the G4 handedness.

Second Generation G-Quadruplex Stabilizing Trimethine Cyanines

G-Quadruplex DNA has been recognized as a highly appealing target for the development of new selective chemotherapeutics, which could result in markedly reduced toxicity toward normal cells. In particular, the cyanine dyes that bind selectively to G-quadruplex structures without targeting duplex DNA have attracted attention due to their high amenability to structural modifications that allows fine-tuning of their biomolecular interactions. We have previously reported pentamethine and symmetric trimethine cyanines designed to effectively bind G-quadruplexes through end stacking interactions. Herein, we are reporting a second generation of drug candidates, the asymmetric trimethine cyanines. These have been synthesized and evaluated for their quadruplex binding properties. Incorporating a benz[c,d]indolenine heterocyclic unit increased overall quadruplex binding, and elongating the alkyl length increases the quadruplex-to-duplex binding specificity.