Tuning quantum dots emission on DNA tetrahedron/silica nanosphere/graphene oxide nanointerface for ratiometric fluorescence assay of Pb2+ in multiplex samples.

BACKGROUND: Assembling framework nucleic acid (FNA) nanoarchitectures and tuning luminescent quantum dots (QDs) for fluorescence assays represent a versatile strategy in analytical territory. Rationally, FNA constructs could offer a preferential orientation to efficiently recognize the target and improve detection sensitivity, meanwhile, regulating size-dependent multicolor emissions of QDs in one analytical setting for ratiometric fluorescence assay would greatly simplify operation procedures. Nonetheless, such FNA/QDs-based ratiometric fluorescence nanoprobes remain rarely explored. RESULTS: We designed a sensitive and signal amplification-free fluorescence aptasensor for lead ions (Pb2+) that potentially cause extensive contamination to environment, cosmetic, food and pharmaceuticals. Red and green emission CdTe quantum dots (rQDs and gQDs) were facilely prepared. Moreover, silica nanosphere encapsulating rQDs served as quantitative internal reference and scaffold to anchor a predesigned FNA and DNA sandwich containing Pb2+ binding aptamer and gQD modified DNA signal reporter. On binding of Pb2+, the gQD-DNA signal reporter was set free, resulting in fluorescence quenching at graphene oxide (GO) interface. Owing to the rigid structure of FNA, the fluorescence signal reporter orderly arranged at the silica nanosphere could sensitively respond to Pb2+ stimulation. The dose-dependent fluorescence signal-off mode enabled ratiometric analysis of Pb2+ without cumbersome signal amplification. Linear relationship was established between fluorescence intensity ratio (I555/I720) and Pb2+ concentration from 10 nM to 2 µM, with detection limit of 1.7 nM (0.43 ppb), well addressing the need for Pb2+ routine monitoring. The designed nanoprobe was applied to detection of Pb2+ in soil, cosmetic, milk, drug, and serum samples, with the sensitivity comparable to conventional ICP-MS technique. SIGNIFICANCE: Given the programmable design of FNA and efficient recognition of target, flexible tuning of QDs emission, and signal amplification-free strategy, the present fluorescence nanoprobe could be a technical criterion for other heavy metal ions detection in a straightforward manner.

Fluorometric determination of mercury(II) based on dual-emission metal-organic frameworks incorporating carbon dots and gold nanoclusters.

Carbon dots and gold nanoclusters co-encapsulated by zeolitic imidazolate framework-8 (CDs/AuNCs@ZIF-8) have been obtained at room temperature. The composite has been applied to the ratiometric fluorescence determination of mercury(II). The composite shows fluorescence emission maxima at 440 and 640 nm under 360 nm excitation, due to the CDs and AuNCs, respectively (associated quantum yields were 18% and 17%, respectively). In the presence of Hg2+, the fluorescence at about 640 nm is quenched, while the fluorescence at about 440 nm is unaffected. The CDs/AuNCs@ZIF-8 composite allows the sensitive detection of Hg2+, with the fluorescence intensity ratio (I640/I440) decreasing linearly with Hg2+ concentration over the range 3-30 nM. The fluorescence emission of the composite changes color from red to blue with increasing Hg2+ under UV excitation, which can easily be discerned visually. This visual detection of Hg2+ is due to the high fluorescence quantum yields of the CDs and AuNCs and the ~ 200 nm separation between the two emission maxima. Graphical abstract (A) Schematic diagram showing the operating principle of the determination for Hg(II). (B) Digital graph of the solutions in absence and presence of 30 nM Hg(II) under a portable UV lamp.

Embedding carbon dots and gold nanoclusters in metal-organic frameworks for ratiometric fluorescence detection of Cu2.

Herein, a dual-emission metal-organic framework based ratiometric fluorescence nanoprobe was reported for detecting copper(II) ions. In particular, carbon dots (CDs) and gold nanoclusters (AuNCs) were embedded into ZIF-8 (one of the classical metal-organic frameworks) to form CDs/AuNCs@ZIF-8 nanocomposites, which exhibited dual-emission peaks at UV excitation. In the presence of Cu2+, the fluorescence attributed to AuNCs can be rapidly quenched, while the fluorescence of CDs serves as reference with undetectable changes. Therefore, the CDs/AuNCs@ZIF-8 nanocomposites were utilized as a ratiometric fluorescence nanoprobe for sensitive and selective detection of Cu2+. A good linear relationship between the ratiometric fluorescence signal of CDs/AuNCs@ZIF-8 and Cu2+ concentration was obtained in the range of 10-3-103 µM, and the detection limit was as low as 0.3324 nM. The current ratiometric fluorescence nanoprobe showed promising prospects in cost-effective and rapid determination of Cu2+ ions with good sensitivity and selectivity. Furthermore, this nanoprobe has been successfully applied for the quantitative detection of Cu2+ in serum samples, indicating its value of practical application. Graphical abstract Carbon dots (CDs) and gold nanoclusters (AuNCs) were embedded into metal-organic frameworks (ZIF-8) to form CDs/AuNCs@ZIF-8 nanocomposites, which exhibited dual-emission peaks at 365 nm excitation. In the presence of Cu2+, the fluorescence emission peak at 574 nm can rapidly respond by quenching, while the fluorescence at 462 nm serves as reference with undetectable changes.

Terbium Functionalized Schizochytrium-Derived Carbon Dots for Ratiometric Fluorescence Determination of the Anthrax Biomarker.

Efficient and instant detection of biological threat-agent anthrax is highly desired in the fields of medical care and anti-terrorism. Herein, a new ratiometric fluorescence (FL) nanoprobe was elaborately tailored for the determination of 2,6-dipicolinic acid (DPA), a biomarker of anthrax spores, by grafting terbium ions (Tb3+) to the surface of carbon dots (CDs). CDs with blue FL were fabricated by a simple and green method using schizochytrium as precursor and served as an FL reference and a supporting substrate for coordination with Tb3+. On account of the absorbance energy transfer emission effect (AETE), green emission peaks of Tb3+ in CDs-Tb nanoprobe appeared at 545 nm upon the addition of DPA. Under optimal conditions, good linearity between the ratio FL intensity of F545/F445 and the concentrations of DPA was observed within the experimental concentration range of 0.5-6 µM with the detection limit of 35.9 nM, which is superior to several literature studies and significantly lower than the infectious dosage of the Bacillus anthracis spores. Moreover, the CDs-Tb nanoprobe could sensitively detect DPA in the lake water sample. This work offers an efficient self-calibrating and background-free method for the determination of DPA.

A novel ratiometric fluorescence nanoprobe based on aggregation-induced emission of silver nanoclusters for the label-free detection of biothiols.

In this work, a novel ratiometric fluorescence nanoprobe based on Au3+-triggered aggregation-induced emission (AIE) behavior of silver nanoclusters (Ag NCs) was designed for the label-free detection of biothiols. The probe was constructed by loading of Au3+ on g-C3N4 nanosheets surface and subsequently aggregating Ag NCs via ion binding. As Au3+ could conversely regulate the emission of g-C3N4 nanosheets and Ag NCs, the remove of Au3+ from nanoprobe by coordination with biothiols would change the emission ratio of nanoprobe that could be used for biothiols detection. The probe provided high sensitivity for glutathione (GSH) determination with the limit of detection as low as 0.8 µM and showed satisfying performance in human serum samples. This report may offer a new sight for the construction of ratiometric probe based on the AIE behavior of Ag NCs and broaden its applications in biosensing.