Ho-Man Chan

Group 9 metal-based inhibitors of β-amyloid (1–40) fibrillation as potential therapeutic agents for Alzheimer's disease

We report here the first application of Group 9 metal complexes (i.e.iridium(III) and rhodium(III)) as inhibitors of amyloid fibrillogenesis and as luminescent probes for Aβ1–40peptide. These complexes contained aromatic co-ligands to interact with the hydrophobic residues around the N-terminal domain of the Aβ1–40peptide, as well as solvato co-ligands to allow coordinative bond formation with histidine residues. We demonstrate that these complexes could inhibit Aβ1–40peptide aggregation in vitro, with potency superior to previous metal-based inhibitors reported. Furthermore, we have demonstrated the first example of luminescent detection of Aβ1–40peptides by transition metal complexes.

Folate-conjugated Fe3O4@SiO2@gold nanorods@mesoporous SiO2 hybrid nanomaterial: a theranostic agent for magnetic resonance imaging and photothermal therapy

In this paper, we investigated the functional imaging and targeted therapeutic properties of core@multi-shell nanoparticles composed of a superparamagnetic iron oxide (SPIO) core and gold nanorods (GNRs) in the mesoporous silica shells functionalized with folic acid (Fe3O4@SiO2@GNRs@mSiO2-FA). The as-synthesized five-component hybrid nanocomposite was revealed to have insignificant cytotoxicity. Intracellular uptake of the nanoparticles was studied in the folate receptor over-expressing human epidermoid carcinoma of the nasopharynx (KB) cells. Due to their magnetic/optical properties as well as the folate targeting potential, compared with Fe3O4@SiO2@GNRs@mSiO2 nanoparticles, higher cellular uptake efficiency was observed for Fe3O4@SiO2@GNRs@mSiO2-FA nanoparticles in KB cells. Characterizations were achieved using both dark field and magnetic resonance (MR) imaging techniques. The hyperthermia induced by Fe3O4@SiO2@GNRs@mSiO2-FA nanoparticles resulted in a higher cytotoxicity in KB cells. Thus, the Fe3O4@SiO2@GNRs@mSiO2-FA hybrid nanomaterial is an effective and promising MR imaging and photothermal therapy agent for folate-receptor over-expressing cancer cells.

Direct Quantification of Single-Molecules of MicroRNA by Total Internal Reflection Fluorescence Microscopy

MicroRNAs (miRNAs) express differently in normal and cancerous tissues and thus are regarded as potent cancer biomarkers for early diagnosis. However, the short length and low abundance of miRNAs have brought challenges to the established detection assay in terms of sensitivity and selectivity. In this work, we present a novel miRNA detection assay in single-molecule level with total internal reflection fluorescence microscopy (TIRFM). It is a solution-based hybridization detection system that does not require pretreatment steps such as sample enrichment or signal amplification. The hsa-miR-21 (miR-21) is chosen as target miRNA for its significant elevated content in a variety of cancers as reported previously. Herein, probes of complementary single-stranded oligonucleotide were hybridized in solution to miR-21 and labeled with fluorescent dye YOYO-1. The fluorescent hybrids were imaged by an electron-multiplying charge-coupled device (EMCCD) coupled TIRFM system and quantified by single-molecule counting. This single molecule detection (SMD) assay shows a good correlation between the number of molecules detected and the factual concentration of miRNA. The detection assay is applied to quantify the miR-21 in extracted total RNA samples of cancerous MCF-7 cells, HepG2 cells, and normal HUVEC cells, respectively. The results agreed very well with those from the prevalent real-time polymerase chain reaction (qRT-PCR) analysis. This assay is of high potential for applications in miRNA expression profiling and early cancer diagnosis.

Effect of surface-functionalized nanoparticles on the elongation phase of beta-amyloid (1-40) fibrillogenesis.

The influence of nanoparticles of various sizes and surface functionalities on the self-assembling fibrillogenesis of beta-amyloid (1-40) peptide was investigated. Functionalized nanoparticles including quantum dots and gold nanoparticles were co-incubated with monomeric Aβ(1-40) peptides under seed-mediated growth method to study their influences on the elongation phase of the fibrillogenesis. It is observed that charge-to-surface area ratio of the nanoparticles and the functional moiety and electrostatic charges of the conjugated ligands on the particle surfaces took crucial regulatory role in the Aβ(1-40) fibrillogenesis.

Self-assembling protein platform for direct quantification of circulating microRNAs in serum with total internal reflection fluorescence microscopy

MicroRNA (miRNA) has recently emerged as a new and important class of cellular regulators. Strong evidences showed that aberrant expression of miRNA is associated with a broad spectrum of human diseases, such as cancer, diabetes, cardiovascular and psychological disorders. However, the short length and low abundance of miRNA place great challenges for conventional techniques in the miRNA quantification and expression profiling. Here, we report a direct, specific and highly sensitive yet simple detection assay for miRNA without sample amplification. A self-assembled protein nanofibril acted as an online pre-concentrating sensor to detect the target miRNA. Locked nucleic acid (LNA) of complimentary sequence was served as the probe to capture the target miRNA analyte. The quantification was achieved by the fluorescence intensity measured with total internal reflection fluorescence microscopy. A detection limit of 1 pM was achieved with trace amount of sample consumption. This assay showed efficient single-base mismatch discrimination. The applicability of quantifying circulating mir-196a in both normal and cancer patients serums was also demonstrated.

Direct quantification of circulating miRNAs in different stages of nasopharyngeal cancerous serum samples in single molecule level with total internal reflection fluorescence microscopy.

MicroRNAs (miRNAs) are small noncoding RNAs that regulate human gene expression at the post-transcriptional level. Growing evidence indicates that the expression profile of miRNAs is highly correlated with the occurrence of human diseases including cancers. Playing important roles in complex gene regulation processes, the aberrant expression pattern of various miRNAs is implicated in different types and even stages of cancer. Besides localizing in cells, many of these miRNAs are found circulating around the body in a wide variety of fluids such as urine, serum and saliva. Surprisingly, these extracellular circulating miRNAs are highly stable and resistant to degradation, and therefore, are considered as promising biomarkers for early cancer diagnostic via noninvasive extraction from body fluids. Unfortunately, the abundance of these small RNAs is ultralow in the body fluids, making it challenging to quantify them in complex sample matrixes. Establishing a sensitive, specific yet simple assay for an accurate quantification of circulating miRNAs is therefore desirable. Our group previously reported a sensitive and specific detection assay of miRNAs in single molecule level with the aid of total internal reflection fluorescence microscopy. In this work, we advanced the assay to differentiate the expression of a nasopharyngeal carcinoma (NPC) up-regulator hsa-mir-205 (mir-205) in serum collected from patients of different stages of NPC. To overcome the background matrix interference in serum, a locked nucleic acid-modified molecular beacon (LNA/MB) was applied as the detection probe to hybridize, capture and detect target mir-205 in serum matrix with enhanced sensitivity and specificity. A detection limit of 500 fM was achieved. The as-developed method was capable of differentiating NPC stages by the level of mir-205 quantified in serum with only 10 μL of serum and the whole assay can be completed in 1 h. The experimental results agreed well with those previously reported whereas the quantity of miR-205 determined by our assay was found comparable to that of quantitative reverse transcription polymerase chain reaction (qRT-PCR), supporting that this assay can be served as a promising noninvasive detection tool for early NPC diagnosis, monitoring and staging.

Monitoring of DNA-protein interaction with single gold nanoparticles by localized scattering plasmon resonance spectroscopy.

We reported a sensitive detection system for measuring DNA-protein interaction at single plasmonic metal nanoparticles level by Localized Scattering Plasmon Resonance (LSPR) spectroscopy. As a proof of concept, DNA molecules were conjugated to gold nanoparticles (AuNPs) through gold-thiol chemistry and the resulted complex was served as single-particle probes of human topoisomerase I (TOPO). By recording the changes in Rayleigh light scattering signal of the individual nanoparticles upon protein binding, DNA-protein interaction was monitored and measured. The λmax shifts in LSPR spectrum of individual AuNP was found to be highly correlated with the amount of TOPO that bound onto. This technique provides a sensitive and high-throughput platform to screen and monitor accurately the specific biomolecular interactions. It is capable of revealing information such as particle-particle variations that might be buried in conventional bulk measurement.

N-Acetyl-L-cysteine capped quantum dots offer neuronal cell protection by inhibiting beta (1–40) amyloid fibrillation

This is the first work that revealed the neuro-protective effect of functionalized quantum dots against the cytotoxicity induced by beta-amyloid peptides. This study gives insight into the future treatment of Alzheimers disease. It opens many avenues for the development of the next generation nanotechnology for biomedical and therapeutic applications.