Detection Of Multiple Metal Ions Research Articles

Simultaneous fluorescent detection of multiple metal ions based on the DNAzymes and graphene oxide

A novel fluorescent detection strategy for simultaneous detection of Cu2+, Pb2+ and Mg2+ based on DNAzyme branched junction structure with three kinds of DNAzymes and graphene oxide (GO) was presented. Three fluorophores labeled DNA sequences consisted with enzyme-strand (E-DNA) and substrate strand (S-DNA) were annealed to form DNAzyme branched junction structure. In the presence of target metal ion, the DNAzyme was activated to cleave the fluorophore labeled S-DNA. The S-DNA fragments were released and adsorbed onto GO surface to quench the fluorescent signal. The detection limit was calculated to be 1 nM for Cu2+, 200 nM for Mg2+, and 0.3 nM for Pb2+, respectively. This strategy was successfully used for simultaneous detection of Cu2+, Mg2+ and Pb2+ in human serum. Moreover, it had potential application for simultaneous detection of multiple metal ions in environmental and biological samples.

Facile and scalable preparation of highly luminescent N,S co-doped graphene quantum dots and their application for parallel detection of multiple metal ions.

Sensitive and selective detection of metal ions is important for environmental monitoring and biological studies because metal ions play crucial roles in many physiological and pathological processes including cellular metabolism, enzymatic activities, as well as DNA and RNA syntheses. In this work, new nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs) are synthesized and serve as fluorescence probes for parallel and specific detection of Fe3+, Cu2+ and Ag+ ions. The N,S-GQDs are synthesized based on one-step bottom-up molecular fusion in a hydrothermal process with a high yield of 87.8% and possibility of mass production. The as-prepared N,S-GQDs exhibit a single-layer graphene structure, high crystallinity and uniform size (∼2.1 nm). Successful co-doping of N and S atoms in the lattice of GQDs not only enables bright blue fluorescence with high absolute photoluminescence quantum yield (23.2%) but also provides unique selectivity towards some metal ions. With the help of different masking agents, N,S-GQDs are able to differentially detect Fe3+, Cu2+ and Ag+ ions in a mixture with low detection limits (8 nM, 250 nM and 50 nM, respectively). Moreover, detection of Fe3+, Cu2+ and Ag+ in complex biological (serum) and environmental samples (river water) is demonstrated.

Simultaneous imaging of Zn(2+) and Cu(2+) in living cells based on DNAzyme modified gold nanoparticle.

Trace Zn(2+) and Cu(2+) in living cells play important roles in the regulation of biological function. It is significant to simultaneously detect the cellular Zn(2+) and Cu(2+). Here, we present a novel two-color fluorescence nanoprobe based on the DNAzymes for simultaneous imaging of Zn(2+) and Cu(2+) in living cells. The probe consists of a 13 nm gold nanoparticle, DNAzymes that are specific for Zn(2+) and Cu(2+), and the substrate strands labeled with fluorophores at the 5' end and quenchers at the 3' end. The fluorescence of the fluoreophores is quenched both by the gold nanoparticle and the quencher. After the nanoprobes are transferred into the cells, the substrate strands would be cleaved in the presence of the Zn(2+) and Cu(2+) target, resulting in disassociation of the shorter DNA fragments containing fluorophores, which produce fluorescence signals correlated with the location and concentration of the Zn(2+) and Cu(2+). The nanoprobe exhibits high specificity, nuclease stability, and good biocompatibility. Moreover, the nanoprobe can simultaneously monitor the cellular Zn(2+) and Cu(2+) with an on-site manner, providing the information on localization and concentration of targets, which is significant to further research the Zn(2+)- and Cu(2+)-relative cellular events and biological process. The proposed method has shown great potential in the detection of multiple metal ions in living cells, which may help us to better understand the function of metal ions in the fields of biochemistry, molecular biology, and cellular toxicology.

Single (19)F probe for simultaneous detection of multiple metal ions using miCEST MRI.

The local presence and concentration of metal ions in biological systems has been extensively studied ex vivo using fluorescent dyes. However, the detection of multiple metal ions in vivo remains a major challenge. We present a magnetic resonance imaging (MRI)-based method for noninvasive detection of specific ions that may be coexisting, using the tetrafluorinated derivative of the BAPTA (TF-BAPTA) chelate as a 19F chelate analogue of existing optical dyes. Taking advantage of the difference in the ion-specific 19F nuclear magnetic resonance (NMR) chemical shift offset (Δω) values between the ion-bound and free TF-BAPTA, we exploited the dynamic exchange between ion-bound and free TF-BAPTA to obtain MRI contrast with multi-ion chemical exchange saturation transfer (miCEST). We demonstrate that TF-BAPTA as a prototype single 19F probe can be used to separately visualize mixed Zn2+ and Fe2+ ions in a specific and simultaneous fashion, without interference from potential competitive ions.

Metal ion-mediated assembly of DNA nanostructures for cascade fluorescence resonance energy transfer-based fingerprint analysis.

Contamination of heavy metal ions in an aquatic environment poses a serious threat to human health. More seriously, heavy metal ions are usually present in the environment in a mixture, and the synergetic toxicity of multiple heavy metal ions is revealed (Aragay et al. Chem. Rev. 2011, 111, 3433; Chu et al. Aquat. Toxicol. 2002, 61, 53). Unfortunately, most of the existing methods based on DNA sequences are focusing on the detection of one type of metal ions. Simple and multiplexed detection of multiple metal ions has been poorly investigated and remains challenging. Here, we re-engineered the DNA sequences for Pb(2+), Hg(2+), and Ag(+), through which the binding of multiple metal ions initiated the self-assembly of these DNA sequences. On the basis of our rationally designed multicolor fluorescent labeling of the DNA sequences, cascade fluorescence resonance energy transfer (FRET) occurred. As a result, a fingerprint fluorescent spectrum was produced to indicate the presence of a single type of metal ions or multiple metal ions. The major advantages of our cascade FRET fingerprint technology include the following: (1) the "mix and read" detection mode in homogeneous solution is simple without the need of complicated instruments; (2) only single excitation is required to provide the cascade FRET fingerprint spectrum; (3) multiplexed detection capability can be realized intuitively and sensitively.

Aptamer biosensing platform based on carbon nanotube long-range energy transfer for sensitive, selective and multicolor fluorescent heavy metal ion analysis

Coupling nanomaterials with biomolecular recognition events represents a new direction in nanotechnology toward the development of novel molecular diagnostic tools. A novel aptamer biosensor based on multi-walled carbon nanotube (MWCNT) long-range energy transfer has been developed for sensitive, selective and multicolor fluorescent detection of Hg2+, Ag+ and Pb2+ ions in homogeneous solution. The fluorescent dye-labeled aptamer is adsorbed on MWCNTs due to their strong π–π stacking interactions, leading to quenching of fluorescence of the dye. Desorption of the dye-labeled aptamer from MWCNTs, through the specific binding of the aptamer with its target, resulted in the restoration of the fluorescence signal of the dye. Due to the non-covalent assembly between the aptamer and MWCNTs, highly efficient long-range energy transfer from the dyes to MWCNTs takes place. In the presence of metal ions, the binding between the aptamer and metal ions will disturb the interaction between the aptamer and MWCNTs, and release the dye-labeled aptamer from the MWCNTs' surface, resulting in restoration of the fluorophore's fluorescence. Importantly, the high specific surface area of MWCNTs allows the quenching of multiple aptamer probes labeled with different fluorescent dyes, leading to a multicolor nanosensor for simultaneous detection of multiple metal ions in the same solution. As a proof of concept, we demonstrated that a three-color nanosensor can rapidly and simultaneously detect three metal ions (i.e. Hg2+, Ag+ and Pb2+) in a single solution. This MWCNT-based sensing platform exhibits high sensitivity and selectivity toward Hg2+, Ag+ and Pb2+versus other metal ions, with a limit of detection of 15 nM for Hg2+, 18 nM for Ag+ and 20 nM for Pb2+.