Mingqian Tan

Novel fluorescent europium chelate-doped silica nanoparticles: preparation, characterization and time-resolved fluorometric application

Novel fluorescent europium(III) chelate-doped silica nanoparticles were prepared and characterized as a new type of fluorescence probe for quantitative bioassay. The preparation was carried out in a water-in-oil (w/o) microemulsion consisting of a strongly fluorescent Eu3+ chelate, 4,4′-bis(1″,1″,1″,2″,2″,3″,3″-heptafluoro-4″,6″-hexanedion-6″-yl)-o-terphenyl–Eu3+ (BHHT–Eu3+), surfactant (Triton X-100), co-surfactant (n-hexanol, n-heptanol or n-octanol), aqueous phase (H2O or D2O) and oil phase (cyclohexane) by controlling the hydrolysis of tetraethylorthosilicate (TEOS). The effects of different co-surfactants and aqueous phases on the size and fluorescence lifetime of the nanoparticles were investigated. The results reveal that the size of the nanoparticles is decreased with a change of co-surfactants from n-hexanol to n-octanol, and the fluorescence lifetime of the nanoparticles is increased with a change of aqueous phase from H2O to D2O. A new method was established for the surface modification and bioconjugation of the nanoparticles. Nanoparticle-labeled streptavidin (SA) was used for the time-resolved fluoroimmunoassay of human hepatitis B surface antigen (HBsAg). The result shows that the new fluorescent europium(III) chelate-doped silica nanoparticles are suitable to be used as a fluorescence probe for highly sensitive bioassays.

Development of functionalized fluorescent europium nanoparticles for biolabeling and time-resolved fluorometric applications

A covalent binding-copolymerization method was developed to prepare silica-based fluorescent europium nanoparticles that can be used for biolabeling and highly sensitive time-resolved fluorescence bioassays. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion consisting of a conjugate of (3-aminopropyl)triethoxysilane bound to a fluorescent Eu3+ chelate, 4,4′-bis(1″,1″,1″,2″,2″,3″,3″-heptafluoro-4″,6″-hexanedion-6″-yl)chlorosulfo-o-terphenyl-Eu3+ (APS-BHHCT-Eu3+), free (3-aminopropyl)triethoxysilane (APS), tetraethyl orthosilicate (TEOS), Triton X-100, n-octanol, water, and cyclohexane by copolymerization of APS-BHHCT-Eu3+, APS, and TEOS with aqueous ammonia. Characterization by transmission electron microscopy and fluorometric methods indicate that the nanoparticles are spherical and uniform in size, 36 ± 4 nm in diameter, highly photostable, and strongly fluorescent, having a fluorescence quantum yield of 50.6% and a long fluorescence lifetime of 384 µs. The amino groups directly introduced to the surface of the nanoparticles by using free (3-aminopropyl)triethoxysilane in the nanoparticle preparation made the surface modification and bioconjugation of the nanoparticles easier. The nanoparticles were used for streptavidin labeling, and the nanoparticle-labeled streptavidin was used in sandwich-type time-resolved fluoroimmunoassays (TR-FIA) of carcinoembryonic antigens (CEA) and hepatitis B surface antigens (HBsAg) in human sera. The methods give detection limits of 1.9 pg ml−1 for CEA, and 23 pg ml−1 for HBsAg. The concentrations of HBsAg in 30 human serum samples were determined, and the results were compared with those independently determined by an established TR-FIA method using the BHHCT-Eu3+-labeled streptavidin. A good correlation was obtained with a correlation coefficient of 0.993.

Presence of photoluminescent carbon dots in Nescafe® original instant coffee: applications to bioimaging.

The presence of the carbon dots (C-dots) in food is a hotly debated topic and our knowledge about the presence and the use of carbon dots (C-dots) in food is still in its infancy. We report the finding of the presence of photoluminescent (PL) C-dots in commercial Nescafe instant coffee. TEM analysis reveals that the extracted C-dots have an average size of 4.4 nm. They were well-dispersed in water and strongly photoluminescent under the excitation of ultra-violet light with a quantum yield (QY) about 5.5%, which were also found to possess clear upconversion PL properties. X-ray photoelectron spectroscopy characterization demonstrates that the C-dots contain C, O and N three elements with the relative contents ca. 30.1, 62.2 and 7.8%. The X-ray diffraction (XRD) analysis indicates that the C-dots are amorphous. Fourier-transform infrared (FTIR) spectra were employed to characterize the surface groups of the C-dots. The C-dots show a pH independent behavior by varying the pH value from 2 to 11. The cytotoxicity study revealed that the C-dots did not cause any toxicity to cells at a concentration as high as 20 mg/mL. The C-dots have been directly applied in cells and fish imaging, which suggested that the C-dots present in commercial coffee may have more potential biological applications.

Peptide-targeted Nanoglobular Gd-DOTA monoamide conjugates for magnetic resonance cancer molecular imaging.

Effective imaging of a cancer molecular biomarker is critical for accurate cancer diagnosis and prognosis. CLT1 peptide was observed to specifically bind to the fibrin-fibronectin complexes presented in tumor extracellular matrix. In this study, we synthesized and evaluated CLT1 peptide-targeted nanoglobular Gd-DOTA monoamide conjugates for magnetic resonance (MR) imaging of the fibrin-fibronectin complexes in tumor. The targeted nanoglobular contrast agents were prepared by conjugating peptide CLT1 to G2 and G3 nanoglobule (lysine dendrimers with a cubic silsesquioxane core) Gd-DOTA monoamide conjugates via click chemistry. The T(1) relaxivities of peptide-targeted G2 and G3 nanoglobules were 7.92 and 8.20 mM(-1) s(-1) at 3T, respectively. Approximately 2 peptides and 25 Gd-DOTA chelates were conjugated onto the surface of 32 amine groups of G2 nanoglobule, and 3 peptides and 43 Gd-DOTA chelates onto the surface of 64 amine groups of G3 nanoglobule. The peptide-targeted nanoglobular contrast agents showed greater contrast enhancement than the corresponding nontargeted agents in tumor at a dose of 0.03 mmol-Gd/kg in female athymic mice bearing MDA-MB-231 human breast carcinoma xenografts. The targeted MRI contrast agents have a potential for specific cancer molecular imaging with MRI.

Enhanced photoluminescence and characterization of multicolor carbon dots using plant soot as a carbon source.

Carbon dots (C-dots) are a class of novel fluorescent nanomaterials, which have drawn great attention for their potential applications in bio-nanotechnology. Multicolor C-dots have been synthesized by chemical nitric acid oxidation using the reproducible plant soot as raw material. TEM analysis reveals that the prepared C-dots have an average size of 3.1 nm. The C-dots are well dispersed in aqueous solution and are strongly fluorescent under the irradiation of ultra-violet light. X-ray photoelectron spectroscopy characterization demonstrates that the O/C atomic ratio for C-dots change to from 0.207 to 0.436 due to the chemical oxidation process. The photo bleaching experiment reveals that the C-dots show excellent photostability as compared with the conventional organic dyes, fluorescein and rhodamine B. The fluorescence intensity of the C-dots did not change significantly in the pH range of 3-10. To further enhance the fluorescence quantum yield, the C-dots were surface modified with four types of passivation ligands, 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), poly-L-lysine (PLL), cysteine and chitosan and the fluorescence quantum yields of the TTDDA, PLL, cysteine and chitosan passivated C-dots were improved 1.53-, 5.94-, 2.00- and 3.68-fold, respectively. Fourier-transform infrared (FTIR) spectra were employed to characterize the surface groups of the C-dots. The bio-application of the C-dots as fluorescent bio-probes was evaluated in cell imaging and ex vivo fish imaging, which suggests that the C-dots may have potential applications in biolabeling and bioimaging.

Development of multicolor carbon nanoparticles for cell imaging

Multicolor carbon nanoparticles (CNPs) were prepared, characterized and developed as fluorescent probes for cell imaging. The fluorescent CNPs were prepared with a facile hydrothermal oxidation route by using linear polysaccharide cellulose and cyclic oligosaccharide cyclodextrin as carbon sources. The characterizations by transmission electron microscopy show that the prepared cellulose-CNPs and cyclodextrin-CNPs are spherical, well-dispersed in water with average diameters of 100 nm and 76 nm, respectively. Under the excitation of UV light, the CNPs are strongly luminescent with an excitation-dependent emission behavior and bathochromic emission properties. The fluorometric methods show that the cellulose-CNPs and cyclodextrin-CNPs are strongly fluorescent with fluorescence quantum yield of 7.47% and 4.49%, respectively. The multicolor CNPs have excellent photostability toward photobleaching. Strong near-infrared fluorescence of the carbon nanoparticles was observed with a 632.8 nm excitation wavelength laser. The oxidative metal ions like Hg(II), Cu(II) and Fe(III) show an quench effect on the fluorescence intensity of the CNPs. The multicolor CNPs were successfully used as fluorescent probes for mouse melanoma cells imaging. The results indicate that the multicolor CNPs derived from cellulose and cyclodextrin may have a great potential for the applications in bioimaging.

Enhancement of Surface Graft Density of MPEG on Alginate/Chitosan Hydrogel Microcapsules for Protein Repellency

Alginate/chitosan/alginate (ACA) hydrogel microcapsules were modified with methoxy poly(ethylene glycol) (MPEG) to improve protein repellency and biocompatibility. Increased MPEG surface graft density (n(S)) on hydrogel microcapsules was achieved by controlling the grafting parameters including the buffer layer substrate, membrane thickness, and grafting method. X-ray photoelectron spectroscopy (XPS) model was employed to quantitatively analyze n(S) on this three-dimensional (3D) hydrogel network structure. Our results indicated that neutralizing with alginate, increasing membrane thickness, and in situ covalent grafting could increase n(S) effectively. ACAC(PEG) was more promising than ACC(PEG) in protein repellency because alginate supplied more -COO(-) negative binding sites and prevented MPEG from diffusing. The n(S) increased with membrane thickness, showing better protein repellency. Moreover, the in situ covalent grafting provided an effective way to enhance n(S), and 1.00 ± 0.03 chains/nm(2) was achieved, exhibiting almost complete immunity to protein adsorption. This antifouling hydrogel biomaterial is expected to be useful in transplantation in vivo.

Synthesis and evaluation of nanoglobular macrocyclic Mn(II) chelate conjugates as non-gadolinium(III) MRI contrast agents

Because of the recent observation of the toxic side effects of Gd(III) based MRI contrast agents in patients with impaired renal function, there is strong interest on developing alternative contrast agents for MRI. In this study, macrocyclic Mn(II) chelates were conjugated to nanoglobular carriers, lysine dendrimers with a silsesquioxane core, to synthesize non-Gd(III) based MRI contrast agents. A generation 3 nanoglobular conjugate of Mn(II)-1,4,7-triaazacyclononane-1,4,7-triacetate-GA amide (G3-NOTA-Mn) was also synthesized and evaluated. The per ion T(1) and T(2) relaxivities of G2, G3, G4 nanoglobular Mn(II)-DOTA monoamide conjugates decreased with increasing generation of the carriers. The T(1) relaxivities of G2, G3, and G4 nanoglobular Mn(II)-DOTA conjugates were 3.3, 2.8, and 2.4 mM(-1) s(-1) per Mn(II) chelate at 3 T, respectively. The T(1) relaxivity of G3-NOTA-Mn was 3.80 mM(-1) s(-1) per Mn(II) chelate at 3 T. The nanoglobular macrocyclic Mn(II) chelate conjugates showed good in vivo stability and were readily excreted via renal filtration. The conjugates resulted in much less nonspecific liver enhancement than MnCl(2) and were effective for contrast-enhanced tumor imaging in nude mice bearing MDA-MB-231 breast tumor xenografts at a dose of 0.03 mmol Mn/kg. The nanoglobular macrocyclic Mn(II) chelate conjugates are promising nongadolinium based MRI contrast agents.

Preparation, characterization and application of fluorescent terbium complex-doped zirconia nanoparticles.

Novel zirconia-based fluorescent terbium nanoparticles have been prepared as a fluorescent nanoprobe for time-resolved fluorescence bioassay. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion consisting of a strongly fluorescent Tb3+ complex, N,N,N1, N1-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-phenylpyridine]tetrakis(acetate)-Tb3+(BPTA-Tb3+), Triton X-100, hexanol, and cyclohexane by controlling co-condensation of Zr(OCH2CH3)4 and ZrOCl2. The characterizations by transmission electron microscopy and fluorometric methods indicate that the nanoparticles are uniform in size, 33± 4 nm in diameter, and have a fluorescence quantum yield of 8.9% and a long fluorescence lifetime of 2.0 ms. The zirconia-based fluorescent terbium nanoparticles show high stability against basic dissolution in a high pH aqueous buffer compared to the silica-based nanoparticles. A surface modification and bioconjugation method for the fluorescent nanoparticles was developed, and the nanoparticle-conjugated streptavidin (SA) was used for time-resolved floroimmunoassy (TR-FIA) of human prostate specific antigen (PSA). The result shows that the zirconia-based fluorescent terbium nanoparticles are useful as a fluorescent nanoprobe for time-resolved fluorescence bioassay.

A non-invasive NMR and MRI method to analyze the rehydration of dried sea cucumber

Sea cucumbers possess high-value and bioactive components that have been used for human food and pharmaceuticals in treating a wide number of ailments. Most of the sea cucumber products on the market are dehydrated due to the immediate autolysis that occurs upon removal of the sea cucumber from seawater. Rehydration of the dried products is necessary to obtain sea cucumbers with the highest water content. In this study, a rapid and non-invasive NMR and MRI method was introduced to analyze the rehydration process for dried sea cucumber. The spin–spin relaxation time (T2) weighted NMR signal, obtained by a CPMG pulse sequence and processed by the chemometric method, was used to identify lightly dried and salted dried sea cucumber. The water uptake and distribution during the rehydration process was monitored by NMR 1H T2. Structural changes were analyzed by MRI with T1 and T2 weighted imaging. The results indicated that the proper presoaking and rehydration time was 24 and 96 h, respectively, for lightly dried sea cucumber. Good linear correlation during the rehydration process was observed between the NMR parameters and texture profile analysis parameters including the hardness, chewiness, and rehydration ratio of lightly dried sea cucumbers. The NMR and MRI method has the potential to noninvasively analyze the rehydration process of dried sea cucumber.