Silver nanoclusters capped silica nanoparticles as a ratiometric photoluminescence nanosensor for the selective detection of I- and S2.

A novel and efficient approach has been established for the synthesis of silver nanoclusters capped silica nanoparticles (SiO2@AgNCs). These nanoclusters (AgNCs) capped silica nanoparticles were utilized as a novel ratiometric photoluminescence (PL) nanosensor for extremely sensitive and selective detection of I- and S2- ions. The AgNCs were prepared in situ on the silica nanoparticles through polyethyleneimine (PEI) template approach. While dual PL emissions of AgNCs (at 500 nm) and luminescent silica nanoparticles (at 602 nm) formed the basis for the ratiometric sensing. The PL emission of AgNCs was strongly quenched by I- (or S2-), while that of luminescent silica nanoparticles was hardly affected. The PL emission intensity ratio of AgNCs and the luminescent silica nanoparticles was defined as I500/I602. A good linear relationship between the I500/I602 value and the concentration of I- (or S2-) was observed, and the limit of detection (LOD) was estimated to be 57 nM for I- and 62 nM for S2-. In addition, the fluorescence images of the SiO2@AgNCs nanosensor changed from white to orange upon exposure to different concentrations of I- (or S2-) (0-250 µM), which could be clearly distinguished by the naked eye. The SiO2@AgNCs nanosensor exhibited good selectivity against other analytes, and I- or S2- ions could be separately detected via the introduction of proper masking agents. Furthermore, the detection of I- and S2- in real water samples was also demonstrated.

Label-free fluorescence turn-on detection of microRNA based on duplex-specific nuclease and a perylene probe.

A novel fluorescence turn-on microRNA (miRNA) detection method based on duplex-specific nuclease (DSN) and a perylene probe is presented in this study. A positively charged perylene derivative (compound 1) was used as the fluorescent probe. Compound 1 exhibits strong monomer fluorescence in an aqueous buffer solution. It is well known that single-stranded DNA is a polyanion in nature. Thus, it can induce the aggregation of compound 1 through strong electrostatic, hydrophobic and π-π stacking interactions. As a result, the fluorescence of compound 1 was efficiently quenched. When the target miRNA was added, the formation of DNA-RNA hybridized duplex initiated the cleavage of the DNA strand by DSN cycle reaction, which resulted in disaggregation of compound 1. A fluorescence turn-on signal was detected, and a novel miRNA sensing method was therefore established. The presented method is label-free, simple, cost effective, sensitive and selective.

Aminophenylboronic-acid-conjugated polyacrylic acid-Mn-doped ZnS quantum dot for highly sensitive discrimination of glycoproteins.

Discrimination of glycoproteins with different glycans is a significant but difficult issue. We presented here a new strategy for strengthening the discrimination of glycoproteins by introducing a new signaling channel, fluorescence polarization (FP), into a "single probe with three signaling channels" sensor array. The single probe was aminophenylboronic-acid-conjugated poly(acrylic acid)-Mn-doped ZnS quantum dots, and the three signaling channels were FP, room temperature phosphorescence and light scattering. Ten glycoproteins, including ovalbumin, fibrinogen, transferrin, horseradish peroxidase, vascular endothelial growth factor, immunoglobulin G, avidin, hyaluronidase, cellulase R-10, and glucose oxidase, were involved for evaluating the discriminating capability. The introduction of the FP signaling channel improved the discriminating power of the sensor array, so that the 10 glycoproteins at 0.15 µM could be well discriminated both in PBS buffer and in the presence of human serum sample. The identification accuracy of the unknown samples was 96.25% (77 out of 80) at the 0.15 µM level and 97.50% (78 out of 80) at the 0.2 µM level. The integration of the signaling patterns with different responsive principles was demonstrated as the promising way to enhance the discrimination power of the single-probe-based sensor arrays.