Enhanced electrochemiluminescence of Ru(bpy)3 2+ -doped silica nanoparticles by chitosan/Nafion shell@carbon nanotube core-modified electrode.

Although Ru(bpy)3 2+ -doped silica nanoparticles have been widely explored as the labelling tags for electrochemiluminescence (ECL) sensing different targets, the poor electrical conductive properties of the silica nano-matrix greatly limit their ECL sensitivity. Therefore, a novel scheme to overcome this drawback on Ru(bpy)3 2+ -doped silica nanoparticles ECL is desirable. Here, a new scheme for this purpose was developed based on electrochemically depositing a nanoscale chitosan hydrogel layer on the carbon nanotube (CNT) surface to form chitosan hydrogel shell@CNT core nanocomposites. In this case, the nanoscale chitosan hydrogel layer only formed on the CNT surface due to the superior electrocatalytic effect of CNT on H+ reduction compared with the basic glass carbon electrode. Due to both the superhydrophilic properties and polyelectrolyte features of nanoscale chitosan hydrogel on the CNT surface, chemical affinity as well as the electric conductivity between Ru(bpy)3 2+ -doped silica nanoparticles and CNT were obviously enhanced, and then the ECL effectivity of Ru(bpy)3 2+ inside silica nanoparticles was improved. Furthermore, based on the discriminative interaction of these Ru(bpy)3 2+ -doped silica nanoparticles towards both the ssDNA probes and the ssDNA probe/miRNA complex, as well as the specific adsorption effect of these nanoparticles on the nanoscale chitosan shell@Nafion/CNT core-modified glass carbon electrode, a highly sensitive ECL method for miRNA determination was developed and successfully used to detect miRNA in human serum samples.

Study of the controlled assembly of DNA gated PEI/Chitosan/SiO2 fluorescent sensor.

In this paper, polyethylenimine (PEI) and Chitosan were simultaneously one-step doped into silicon dioxide (SiO2 ) nanoparticles to synthesize PEI/Chitosan/SiO2 composite nanoparticles. The polymer PEI contained a large amount of amino groups, which can realize the amino functionalized SiO2 nanoparticles. And, the good pore forming effect of Chitosan was introduced into SiO2 nanoparticles, and the resulting composite nanoparticles also had a porous structure. In pH 7.4 phosphate buffer solution (PBS), the amino groups of PEI had positive charges, and therefore the fluorescein sodium dye molecule can be loaded into the channels of PEI/Chitosan/SiO2 composite nanoparticles by electrostatic adsorption. Furthermore, utilizing the diversity of DNA molecular conformation, we designed a high sensitive controllable assembly of DNA gated fluorescent sensor based on PEI/Chitosan/SiO2 composite nanoparticles as loading materials. The factors affecting the sensing performance of the sensor were investigated, and the sensing mechanism was also further studied.

Silica Modified Chitosan/Polyethylenimine Nanogel for Improved Stability and Gene Carrier Ability.

Although chitosan-based hydrogel has been widely used as a gene carrier material, further improvement in this aspect is still needed. Herein a new method was proposed for preparing the effective chitosan-based gene carrier nanogel. The new method based on the fact that supra-molecular interactions between silica, polyethylenimine (PEI) and chitosan could be used to self-assemble them together to form a rigid and stable gene carrier material in the reverse microemulsion system. When compared with chemical cross-linking route, the proposed method is simple and easy to adjust components of the resulting nanogel and, therefore, can improve its gene carrying ability. Our results showed that, doping of the PEI and silica into the chitosan hydrogel obviously increased its strength, stability and gene carrying ability.

Highly sensitive detection of copper ions by densely grafting fluorescein inside polyethyleneimine core-silica shell nanoparticles.

In this work, polyethyleneimine (PEI) core-silica shell nanoparticles were synthesized and used for densely grafting fluorescent receptor units inside the core of these particles to result in multi-receptor units collectively sensing a target. Herein, copper ion quenching of the fluorescence intensity of a fluorescein isothiocyanate (FITC) system was selected as a model to confirm our proof-of-concept strategy. Our results showed that, compared to free FITC in solution, a 10-fold enhancement of the Stern-Volmer constant value for Cu(2+) quenching of the fluorescence intensity of the grafted state of FITC in PEI core-silica shell nanoparticles was achieved. Furthermore, compared to a previous collective sensing scheme by densely grafting fluorescent receptor units on a silica nanoparticle surface, the proposed scheme, which grafted fluorescent receptor units inside a polymer nano-core, was simple, highly efficient and presented higher sensitivity.

Label-free sensitive electrogenerated chemiluminescence aptasensing based on chitosan/Ru(bpy)3²âº/silica nanoparticles modified electrode.

In this work, a label-free and sensitive electrogenerated chemiluminescence (ECL) aptasensing scheme for K(+) was developed based on G-rich DNA aptamer and chitosan/Ru(bpy)3(2+)/silica (CRuS) nanoparticles (NPs)-modified glass carbon electrode. This ECL aptasensing approach has benefited from the observation that the G-rich DNA aptamer at the unfolded state showed more ECL enhancing signal at CRuS NPs-modified electrode than the binding state with K(+), which folds into G-quadruplex structure. As such, the decreasing ECL signals could be used to detect K(+). Compared to other aptasensing K(+) approaches previously reported, the proposed ECL sensing scheme is a label-free aptasensing strategy, which eliminates the labeling, separation, and immobilization steps, and behaves in a simple, low-cost way. More importantly, because the proposed ECL sensing mechanism utilizes the nanosized ECL active CRuS NPs to sense the nanoscale conformation change from the aptamer binding to target, it is specific. In addition, due to the great conformation changes of the aptamer's G-bases on CRuS NPs and the excellent ECL enhancing effect of guanine bases to the Ru(bpy)3(2+) ECL reaction, a 0.3 nM detection limit for K(+) was achieved with the proposed ECL method. On the basis of these advantages, the proposed ECL aptasensing method was also successfully used to detect K(+) in colorectal cancer cells.

A highly sensitive fluorescent nanoprobe for the amplified detection of formaldehyde.

Non-conjugated polymer nanoparticles (PNPs) have been widely reported for analytical applications; however, the development of an effective fluorescence signal-amplification scheme based on PNPs remains challenging. In this study, polyethyleneimine-based polymer nanoparticles (PEI-PNPs) were synthesized for interrogating the fluorescence signal-amplification analytical application of the PNPs. The PEI-PNPs with an aggregated PEI polymer structure were able to confine a large density of sub-fluorophores on an individual nanoparticle, enabling the realization of a signal-amplification effect. Herein, formaldehyde (FA) was utilized for enhancing the fluorescence intensity of the PEI-PNPs as a model to confirm our proof-of-concept strategy. Our results showed that a more than 9-fold signaling-enhancing ability for the sensing of FA was observed using the PEI-PNPs prepared with a higher PEI concentration. The possible mechanism for the FA amplified sensing was studied. In particular, the FA-recognition units were sub-fluorophores of PEI-PNPs, which were simultaneously formed with the preparation of the PEI-PNPs avoiding the leakage effect of dyes. We believe that the water-soluble and biocompatible PEI-PNPs are promising candidates for the detection of endogenous FA in living systems.

The synthesis of PEI core@silica shell nanoparticles and its application for sensitive electrochemical detecting mi-RNA.

Although the silica-based nanoparticles (NPs) have been widely explored as the labels for sensing different targets, the simple and novel scheme, to impose a large number of signal molecules inside silica NPs, is challenge. Herein, a new scheme for this purpose was developed. This new strategy was based on densely doped polyethyleneimine (PEI) inside silica nanoparticles and forming the PEI@silica nanoparticles. Then, the Cu2+ was selected as the electrochemical signal molecule model to be loaded in PEI@silica nanoparticles the based on the strong coordination reaction of Cu2+ with PEI and test its signal amplification ability. Our results showed that 7.6 × 105 Cu2+signal ions could be loaded in a single PEI@silica nanoparticles. Thereafter, based on the discriminating interaction of this PEI/Cu2+/SiO2 NPs towards both ssDNA probes and ssDNA probe/mi-RNA complex, as well as the specific adsorption effect of this NPs on chemically modified electrode, a highly sensitive electrochemical method for detecting mi-RNA was developed and successfully used to detect mi-RNA in the human serum samples.

Preparation of Nafion-Ru(bpy)3(2+)-chitosan/gold nanoparticles composite film and its electrochemiluminescence application.

In this research, it was found that a composite film could be formed by mixing Nafion with chitosan on the graphite electrode surface. Then, based on the strong absorption of both chitosan for AuCl(4)(-) and Nafion for Ru(bpy)(3)(2+), respectively, the gold nanoparticles and electrochemiluminescence (ECL) active molecules, Ru(bpy)(3)(2+), were effectively incorporated into the composite film of chitosan with Nafion. Lastly, based on the interaction of Ru(bpy)(3)(2+) with Nafion inside the Nafion-chitosan/gold nanoparticles film, Ru(bpy)(3)(2+) was successfully immobilized within this composite film. In this case, a new composite film for fabricating Ru(bpy)(3)(2+)-based ECL sensors was developed. The performances of this composite film were characterized by transmission electron microscopy (TEM), electrochemistry and electrochemiluminescence methods. Our results showed that: firstly, the gold nanoparticles in the resulting composite film could act as conducting pathways to connect Ru(bpy)(3)(2+) sites; the electrode surface accelerated the charge transport through the composite film, and the diffusion coefficient of Ru(bpy)(3)(2+) within this composite film modified electrode was 65 times higher than that of the pure Nafion film modified electrode. Secondly, due to its unique polymeric cationic character and better film-forming properties, chitosan could improve the compact structure of pure Nafion and greatly enhance the mass-transfer speed of Ru(bpy)(3)(2+). Then, the co-reactant tripropylamine (TPA) inside the composite film could offer better ECL performances such as more rapid ECL response speed, longer-term stability and higher sensitivity compared with the performances of pure Nafion film.