Discrimination of copper and silver ions based on the label-free quantum dots.

A simple and fast method for copper ions (Cu2+) and silver ions (Ag+) detection was established with cadmium telluride quantum dots (CdTe QDs) as fluorescent probes. In the presence of Cu2+ or Ag+, the fluorescence intensity of TGA-CdTe QD can be significantly quenched, which fitted a linear relationship between the fluorescence quenching degree (F0-F)/F0 and the concentration of metal ions. In this work, the lowest detected concentration for Cu2+ and Ag+ was 35.0 nM and 25.3 nM, respectively. In addition, the differentiation of Cu2+ and Ag+ at different concentrations was realized with the principal component analysis (PCA). Furthermore, Cu2+ was successfully detected in body fluids. This method provides a good potential for copper ions and silver ions detection with simplicity, rapidity, and excellent selectivity.

Förster Resonance Energy Transfer-Based Soft Nanoballs for Specific and Amplified Detection of MicroRNAs.

Förster resonance energy transfer (FRET) by using fluorescent carbon dots (CDs) as energy donors shows potential for biosensing and bioimaging. However, it remains underused and underestimated for CDs as a building block for FRET owing to the low efficiency and complex operation originating from the surface modification of CDs. To overcome these limitations, herein we develop a novel FRET soft nanoball (fretSNB) in which thousands of green CDs and black hole quencher 2 (BHQ-2) dyes are loaded, and FRET occurs from CDs to BHQ-2 dyes with the consequence of effective fluorescence quenching. These fretSNBs can be ruptured in the presence of phospholipase A2 (PLA2) released in a process of duplex-specific nuclease (DSN)-assisted target recycling amplification (TRA), making the fluorescence of CDs recovered. Thus, a dual amplification strategy is successfully developed for amplified detection of microribonucleic acids (miRNAs) in the concentration range 0.025-10 nM with a limit of detection (3σ) reaching 16.5 pM which is about 515 times lower than without fretSNBs. In addition, the developed strategy exhibits high selectivity for discrimination of a single nucleotide difference and capability to detect miRNAs extracted from cells, suggesting excellent potential in biomedical analysis and clinical diagnosis.

Metal-Mediated Gold Nanospheres Assembled for Dark-Field Microscopy Imaging Scatterometry.

Developing rapid, sensitive and intelligent optical probes is important for the growing need of microscope imaging analysis. Herein, we proposed a new strategy to assemble plasmonic nanoprobes in situ for dark-field microscopy imaging scatterometry by making use of the formation, disruption, and re-formation of cytosine-Ag+-cytosine (CAg+C) bonds. The CAg+C bond was formed at first through Ag+-mediated base pairing between C-contained aptamer and its C-mismatched complementary DNA. Owing to the subsequent binding of target with the aptamer, the CAg+C structure was disrupted, leading Ag+ to be quantitatively released. The released Ag+ ions can make the CAg+C bonds formed again between the C-contained sequence that modified gold nanospheres (AuNSs), and AuNS clusters thus formed in situ, which have strong plasmonic scattering signals owing to the coupling of localized surface plasmon resonance (LSPR). Therefore, the plasmonic scattering signals enhanced following the off-on mode under the dark field microscope from the 'zero' background to on. As a concept of proof, sensitive detections for Aflatoxin B1 (AFB1) in foods, carcinoembryonic antigen (CEA) in blood serum, and Ricin B in artificial sample, was successfully made by using of the in situ formed AuNS clusters, demonstrating that the newly developed metal-mediated strategy for assembling nanoprobes are universal.

Photothermal Soft Nanoballs Developed by Loading Plasmonic Cu2- xSe Nanocrystals into Liposomes for Photothermal Immunoassay of Aflatoxin B1.

Photothermal effects (PTEs) have been greatly concerned with the fast development of new photothermal nanomaterials. Herein we propose a photothermal immunoassay (PTIA) by taking mycotoxins (AFB1) as an example based on the PTEs of plasmonic Cu2- xSe nanocrystals (NCs). By loading plasmonic Cu2- xSe NCs into liposomes to form photothermal soft nanoballs (ptSNBs), on which aptamer of AFB1 previously assembled, a sandwich structure of AFB1 could be formed with the aptamer on ptSNBs and capture antibody. The heat released from the ptSNBs under NIR irradiation, owing to the plasmonic photothermal light-to-heat conversion through photon-electron-phonon coupling, makes the temperature of substrate solution increased, and the increased temperature has a linear relationship with the AFB1 content. Owing to the large amounts of plasmonic Cu2- xSe NCs in the ptSNBs, the PTEs get amplified, making AFB1 higher than 1 ng/mL detectable in food even if with a rough homemade immunothermometer. The proposal of PTIA opens a new field of immunoassay including developing photothermal nanostructures, new thermometers, PTIA theory, and so on.

A single gold nanoprobe for colorimetric detection of silver(i) ions with dark-field microscopy.

Highly sensitive colorimetric detection of silver(i) ions (Ag+) at the single-particle level was developed based on the color of a gold nanoparticle (AuNP) assembly captured by dark-field microscopy (DFM) imaging. Formation of C-Ag+-C bonding between cytosines was utilized to induce interparticle coupling of AuNPs modified with single-strand DNA, resulting in a color change as the signal transduction to quantify Ag+ under DFM imaging. This method allowed visual quantitation of Ag+ in the range of 0.05 nM-250.00 nM and a detection limit of 28.8 pM was achieved. Furthermore, we demonstrated its applicability for the colorimetric detection of Ag+ in a small quantity of real samples, showing the good potential of this developed method for environmental monitoring and drug quality control.