Tingting Dong

Bare magnetic nanoparticles as fluorescence quenchers for detection of thrombin

Rapid and sensitive detection of thrombin has very important significance in clinical diagnosis. In this work, bare magnetic iron oxide nanoparticles (magnetic nanoparticles) without any modification were used as fluorescence quenchers. In the absence of thrombin, a fluorescent dye (CY3) labeled thrombin aptamer (named CY3-aptamer) was adsorbed on the surface of magnetic nanoparticles through interaction between a phosphate backbone of the CY3-aptamer and hydroxyl groups on the bare magnetic nanoparticles in binding solution, leading to fluorescence quenching. Once thrombin was introduced, the CY3-aptamer formed a G-quartet structure and combined with thrombin, which resulted in the CY3-aptamer being separated from the magnetic nanoparticles and restoration of fluorescence. This proposed assay took advantage of binding affinity between the CY3-aptamer and thrombin for specificity, and bare magnetic nanoparticles for fluorescence quenching. The fluorescence signal had a good linear relationship with thrombin concentration in the range of 1-60 nM, and the limit of detection for thrombin was estimated as low as 0.5 nM. Furthermore, this method could be applied for other target detection using the corresponding fluorescence labeled aptamer.

Aptamer and PNIPAAm co-conjugated nanoparticles regulate activity of enzyme with different temperature.

In this paper, we described a temperature responsive nano-system that can regulate activity of enzyme with different temperature. Temperature responsive polymer poly(N-isopropylacrylamide) (PNIPAAm), with low critical solution temperature of 32°C, was synthesized with thiol modification. PNIPAAm and thrombin aptamer were co-functionalized on the surface of gold nanoparticles for effective regulation of thrombin activity with different temperature. On the one hand, we studied the thermal responsive properties of this inhibitor via UV-visible spectroscopy. On the other hand, we investigated the regulation of thrombin activity by this platform with different temperature. The PNIPAAm chains could extend and shrink with different temperature, which suggested that PNIPAAm on the surface of gold nanoparticles could regulate interaction between thrombin and aptamer according to temperature changing. At 25°C, PNIPAAm was hydrophilic extended state, which blocked the interaction between thrombin and aptamer on the surface of gold nanoparticles, therefore thrombin activity had no change. On the contrary, at 37°C, PNIPAAm transformed from hydrophilic extended state to hydrophobic shrank state, allowing the aptamer to capture thrombin, inhibiting the activity of thrombin. More interestingly, this regulation was reverse to normal condition, where 37°C was always the optimum reaction temperature for most of human enzymes. This system we prepared was opposite, which was capable of inhibiting the thrombin activity at 37°C. Furthermore, this was the first report of regulation of thrombin activity using this temperature responsive platform.

A redox responsive controlled release system using mesoporous silica nanoparticles capped with Au nanoparticles

A novel redox responsive controlled release system based on the host-guest interaction between ferrocene modified mesoporous silica nanoparticles (MSN-Fc) and beta-cyclodextrin modified gold nanoparticles (Au@CD) was developed. FITC was used as the release molecule and it was loaded into the pores of MSN-Fc. With the addition of oxidant (H2O2), oxidized ferrocene leaves the hydrophobic cavity of b-CD, resulting in cargo controlled release. Due to the structural properties of the modified MSN, the continuously slow release behavior showed the prospect to be a sustained drug delivery system. This novel redox responsive system possessed stimuli-responsive controlled release and sustained release properties, and therefore has potential applications in sustained and targeted drug delivery.

Reversible regulation of thrombin adsorption and desorption based on photoresponsive-aptamer modified gold nanoparticles.

In the protein separation, adsorption and desorption of target protein have been using different buffer condition. Different buffer will change the structure and activity of target protein in some cases. This work describes the use of different wavelength light for remote regulation of adsorption and desorption of target protein in the same buffer solutions. A dynamic system that captured and released protein in response to light is reported. Matrix gold nanoparticles and light-responsive affinity ligand comprising thrombin aptamer (APT15), polyethylene glycol linker, and azobenzene-modified complementary sequence were used. UV light induced a trans-cis isomerization of the azobenzene that destabilized the duplex of aptamer and azobenzene-modified complementary sequence, resulting in thrombin binding to aptamer sequence. Visible light irradiation resulted in DNA duplex rehybridization and thrombin released. Our work demonstrates that different light wavelengths effectively regulated the adsorption and desorption of thrombin in the same buffer, and this system also can capture and release prothrombin from plasma with different wavelength light. Furthermore, this method can be widely applied to a variety of different protein separation process.

A reversible light-responsive assembly system based on host–guest interaction for controlled release

Here, we established a reversible light-responsive assembly system, which consisted of azobenzene grafted mesoporous silica nanoparticles (MSN–AZO) and cyclodextrin-functionalized Au nanoparticles (AuNP@CD). The assembly system was constructed by the host–guest interaction between azobenzene and β-cyclodextrin. For controlled release, the cargo molecule fluorescein isothiocyanate (FITC) in the pores of the MSNs can be regulated or triggered by different wavelengths. Under visible light irradiation, the azobenzene on the MSN surface exhibits a trans-configuration, and can bind with β-cyclodextrin on the AuNPs by host–guest interaction. Thus the mesopores were closed by the AuNP@CD caps and cargo molecules were locked in the pores. While under UV irradiation, the azobenzene changed to cis-configuration, which cannot bind with β-cyclodextrin, leading to the disaggregation of the caps from the outer surface of the MSNs. Thus the cargo molecules were released from the pores. This light-responsive triggered system may have potential applications in drug-controlled release, light-responsive devices and novel catalytic processes.