A cytosine-rich hairpin DNA loaded with silver nanoclusters as a fluorescent probe for uranium(IV) and mercury(II) ions

An electrochemiluminescence microsensor based on DNA-silver nanoclusters amplification for detecting cellular adenosine triphosphate

Adenosine triphosphate (ATP), as the primary energy source, plays vital roles in many cellular events. Developing an efficient assay is crucial to rapidly evaluate the level of cellular ATP. A portable and integrated electrochemiluminescence (ECL) microsensor array based on a closed bipolar electrode (BPE) was presented. In the BPE unit, the ECL chemicals and oxidation/reduction were separated from the sensing chamber. The ATP aptamer was assembled with single-stranded DNA (ssDNA) in the sensing chamber. ATP capture made the aptamer disassemble from the ssDNA and facilitated DNA-templated silver nanocluster (Ag NC) generation by the target-rolling circle amplification (RCA) reaction. The guanine-rich padlock sequence produced tandem periodic cytosine-rich sequences by the RCA, inducing Ag NC generation in the cytosine-rich region of the produced DNA strands through Ag+ reduction. The in situ Ag NC generation enhanced the circuit conductivity of the BPE and promoted the ECL reaction of [Ru(bpy)2dppz]2+/tripropylamine in the anodic reservoir. On this ECL microsensor, a good linear relationship of ATP was achieved ranging from 30 to 1000 nM. The ATP content in HepG2 cells was selectively and sensitively determined without complex pretreatment. The ATP amount of 25 cells could be successfully detected when a sub-microliter sample was loaded.

A fluorescence sensor for thiram detection based on DNA-templated silver nanoclusters without metal ion-mediator

In this work, we firstly found a strong competitive interaction between thiram and silver atoms of DNA-templated silver nanoclusters (DNA-AgNCs), leading to fluorescence quenching of DNA-AgNCs without additional metal ion-mediator. Furthermore, this thiram-induced fluorescence quenching phenomenon was used to develop a sensor for thiram detection. This fluorescence sensor exhibited good linearity with thiram concentration from 0.20 to 2.0 μM and 0.012-0.20 μM under optimized conditions, with a low detection limit of 0.2 μM and 0.01 μM, respectively. Moreover, this sensor showed superior selectivity towards thiram, and its practicability was verified in apples and soil. This study provides a convenient and rapid "mix and detect" approach for thiram detection within 10 min, suggesting its potential for rapid on-site evaluation of thiram in real samples.

A self-cascade system based on Ag nanoparticle/single-walled carbon nanotube nanocomposites as an enzyme mimic for ultrasensitive detection of L-cysteine

L-Cysteine, widely used in medicine and the food industry, is of great essentiality to organisms and the food quality. Given that current detection approaches require exacting lab conditions and tedious sample treatment, there is a pressing demand for developing a method that possesses advantages of user friendliness, prominent performance, and cost-effectiveness. Herein, a self-cascade system was developed for the fluorescence detection of L-cysteine based on the ingenious performance of Ag nanoparticle/single-walled carbon nanotube nanocomposites (AgNP/SWCNTs) and DNA-templated Ag nanoclusters (DNA-AgNCs). The fluorescence of DNA-AgNCs could be quenched on account of the adsorption of DNA-AgNCs on AgNP/SWCNTs by π-π stacking. With the cooperation of Fe²⁺, AgNP/SWCNTs with oxidase and peroxidase-like activities could catalyze the oxidation of L-cysteine to produce cystine and hydrogen peroxide (H₂O₂) and then break the O-O bond of H₂O₂ to generate a hydroxyl radical (·OH), which could cleave the DNA strand into different sequence fragments which subsequently peeled off from the AgNP/SWCNTs, resulting in a "turn-on" fluorescence response. In this paper, AgNP/SWCNTs with multi-enzyme activities was synthesized enabling the reaction to proceed in just one step. The successful preliminary applications for the L-cysteine detection in pharmaceutical, juice beverage, and serum samples indicated that the developed method exhibited great potential in medical diagnosis, food monitoring, and the biochemical field, which also broadened the horizon for follow-up research.

An enzyme-free turn-on fluorescent strategy for nucleic acid detection based on hybridization chain reaction and transferable silver nanoclusters

A fluorescence biosensor has been developed based on hybridisation chain reaction (HCR) amplification coupled with silver nanoclusters (AgNCs) for nucleic acid detection. The fluorescence was activated via end-to-end transfer of dark AgNCs caged within a DNA template to another DNA sequence that could enhance their red fluorescence emission at 611 nm. Such cluster-transfer approach allows us to introduce fluorogenic AgNCs as external signal transducers, thereby enabling HCR to perform in a predictable manner. The resulted HCR-AgNC biosensor was able to detect target DNA with a detection limit of 3.35 fM, and distinguish the DNA target from single-base mismatch sequences. Moreover, the bright red fluorescence emission was detectable with the naked eye, with concentration of target DNA down to 1 pM. The biosensor also performed well in human serum samples with good recovery. Overall, our cluster-transfer approach provides a good alternative to construct HCR-AgNC assay with less risk of circuit leakage and produce AgNCs in a controllable manner.

NH3 Plasma Functionalization of UiO-66-NH2 for Highly Enhanced Selective Fluorescence Detection of U(VI) in Water

Radioactive U(VI) in nuclear wastewater is a global environmental pollutant that poses a great threat to human health. Therefore, it is of great significance to develop a U(VI) sensor with desirable sensitivity and selectivity. Inspired by electron-donating group modification for enhancement of binding affinity toward U(VI), we report an amine group functionalization of UiO-66-NH₂, using a low-cost, environmentally friendly, and low-temperature NH₃ plasma technique as a fluorescence switching nanoprobe for highly sensitive and selective detection of U(VI). The resulting amine-functionalized UiO-66-NH₂ (LTP@UiO-66-NH₂) shows dramatically enhanced fluorescence emission and selective sensitivity for U(VI) on the basis of the quenching effect. The quenching efficiency increases from 58 to 80% with the same U(VI) concentration (17.63 μM) after NH₃ plasma functionalization. As a result, the LTP@UiO-66-NH₂ has the best K_sv (1.81 × 10⁵ M^-1, 298 K) and among the lowest LODs (0.08 μM, 19.04 ppb) compared with those reported in the literature. Intraday and interday precision and application in real environment experiments indicate stable and accurate U(VI) detection performance. Fluorescence lifetime and temperature-dependent detection experiments reveal that the quenching mechanism belongs to the static quenching interaction. The highly selective fluorescence detection is attributed to the selective binding of U(VI) by the rich functionalized amine groups of LTP@UiO-66-NH₂. This work provides an efficient fluorescence probe for highly sensitive U(VI) detection in water, and a new strategy of tailored plasma functionalization for developing a practical MOF sensor platform for enhanced fluorescence emission, sensitivity, and selectivity for detecting trace amounts of radioactive species in the environment.

A novel liquid crystal sensing platform for highly selective UO22+ detection based on a UO22+-specific DNAzyme

A label-free and selective sensor was established for uranyl ion (UO₂²⁺) detection based on a UO₂²⁺-dependent DNAzyme and liquid crystals (LCs). In the presence of UO₂²⁺, the substrate chains can be cleaved at the rA site by the DNAzyme strands. The cleaved products released from the DNAzyme strand will hybridize with the capture probes that are fixed on the LC sensing substrate to form double strands. The formation of double strands would disturb the original orientation and induce the rearrangement of liquid crystal molecules, resulting in the polarization images changing from uniform black to bright. Attributed to the specificity of the DNAzyme and the optical signal of the LC, a highly selective and label-free method was established with a detection limit of 25 nM. This approach showed satisfactory analytical performance and offered an inspiring platform for detecting other radioactive elements.

Sensitive detection of RNA based on concatenated self-fuelled strand displacement amplification and hairpin-AgNCs

Herein, a self-fuelled amplification strategy (SFAS) is proposed, in which two strand displacement amplification (SDA) processes were concatenated for the proliferation of ssDNA. The ssDNA then initiated a polymerase action and caused the destruction of hairpin-templated silver nanoclusters (AgNCs), resulting in decreased fluorescence for sensing miRNA-21. This SFAS-based sensor is less complicated in design and facile in operation, because of the easy concatenation of SDA and mutual enzymes used in the signal output process. The sensitivity of this SFAS-based miRNA sensor was 1.78 × 10^-11 M with a linear relationship in the range 0.02-1.0 × 10^-9 M, and the recoveries of this method ranged from 82.07% to 106.58% with an average RSD of 10.96%.

Recent Developments in Fluorescent Materials for Heavy Metal Ions Analysis From the Perspective of Forensic Chemistry

Forensic chemistry deals with the analysis of various types of physical evidences related to crime, corresponding to the detection of target substances or elements in complex matrices. There is a vital need for highly selective, rapid, and sensitive biosensing technologies in heavy metal ions analysis especially those from living persons, autopsy, food, water, soil, and other identified substances at very preliminary stages. Fluorescent materials-based method for heavy metal ions detection is one of the most important analytical methods, resulting in the ability to measure analytes in complex matrices with unsurpassed selectivity and sensitivity. In this mini review, different fluorescent materials-based analytical methods aiming at several heavy metal ions detection are exclusively reviewed through a comprehensive literature survey. In addition, current challenges to achieve integrated evidence analysis process are briefly discussed to provide an outlook for heavy metal ions detection based on fluorescent analytical methods in the forensic chemistry field.

DNA-AgNCs as a fluorescence turn-off probe for dual functional detection of H2O2 and Fe(II) ions

A novel fluorescence probe (DNA-AgNCs) was synthesized for dually detecting hydrogen peroxide (H₂O₂) and ferrous ion (Fe(II)) in water samples. The assay is carried out through a dramatic "turn-off" fluorescence response of AgNCs by hydroxyl radical (OH), which is produced when H₂O₂ and Fe(II) are present simultaneously. Under the optimal conditions, the degree of fluorescence quenching of the DNA-AgNCs at 525 nm is linearly related to the concentration of H₂O₂ in the range of 0.3 to 450 pM, and Fe(II) in the range of 0.2 to 6.0 μM. The limit of detection (LOD) of H₂O₂ and Fe(II) are as low as 99 fM and 60 nM, respectively. Moreover, this method has the advantages of good specificity, high sensitivity, and can be successfully applied for detecting H₂O₂ and Fe(II) in the real water samples.

DNA-Hairpin-Templated Silver Nanoclusters: A Study on Stem Sequence

DNA hairpins are widely used to synthesize silver nanoclusters (AgNCs) with excellent optical properties due to their specific secondary structure. Hairpin-AgNCs have been popularly employed for sensoring applications, while no systematic study has been done about the effect of stem sequence on the fluorescence property of hairpin-AgNCs. In this presented work, the synthesizing conditions of hairpin-AgNCs were fully examined first. Then, the effect of percentage content and distribution of GC base pairs as well as stem length on the fluorescence property of hairpin-AgNCs were studied. Intriguing phenomena were observed and basic conclusions were drawn, which would be helpful to understand the hairpin-AgNCs comprehensively and instructional for the applications using hairpin-AgNC probes.

Specific Recognition of Uranyl Ion Employing a Functionalized Nanochannel Platform for Dealing with Radioactive Contamination

Radioactive contamination is a highly concerning global environmental issue along with the development of the nuclear industry. On account of sophisticated operations and high cost of instrument detection methods, numerous efforts have been focused on rapid and simple detection of pollution elements and uranium is the most common one. It is an enormous challenge to push the limit of determination as low as possible while carrying out ultrasensitive detection. Here, we report an intelligent platform based on functionalized solid nanochannels to monitor ultratrace uranyl ions. The platform has a detection limit of 1 fM, which is far below the value that traditional instrumental methods can reach. What is more, the system also exhibits uranyl removal property. The mesenchymal stem cells cultivated in media containing uranyl can achieve excellent viability in the presence of the membranes. This work provides a new choice for handling global radioactive contamination of water.

Label-free probes using DNA-templated silver nanoclusters as versatile reporters

DNA-templated silver nanoclusters (DNA-AgNCs) have demonstrated pervasive applications in analytical chemistry recently. As a way of signal output in DNA-based detection methods, DNA-AgNCs have prominent advantages: first, the recognition and synthesizing sequences are naturally integrated in one DNA probe without any chemical modification or connection; second, the emissive wavelength of DNA-AgNCs can be adjusted in a wide range by employing different sequences; third, DNA-AgNCs can be utilized for producing not only fluorescence, also electrochemiluminescence and electrochemical signals. Besides, they also show potential applications for cell imaging, and are considered to be one of the most ideal nanomaterials for in-vivo imaging due to their ultra-small particle size. In this review, a brief and comprehensive introduction of DNA-AgNCs is firstly given, then label-free probes using DNA-AgNCs are classified and summarized, lastly concluding perspectives are provided on the defects and application potentials.