Qun Huo

A One-Step Homogeneous Immunoassay for Cancer Biomarker Detection Using Gold Nanoparticle Probes Coupled with Dynamic Light Scattering

A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements. A spherical gold nanoparticle with a core diameter around 37 nm and a gold nanorod with a dimension of 40 by 10 nm were first conjugated with two different primary anti-PSA antibodies and then used as optical probes for the immunoassay. In the presence of antigen f-PSA in solution, the nanoparticles and nanorods aggregate together into pairs and oligomers through the formation of a sandwich type antibody-antigen-antibody linkage. The relative ratio of nanoparticle-nanorod pairs and oligomers versus individual nanoparticles was quantitatively monitored by DLS measurement. A correlation can be established between this relative ratio and the amount of antigen in solution. The light scattering intensity of nanoparticles and nanoparticle oligomers is several orders of magnitude higher than proteins and other typical molecules, making it possible to detect nanoparticle probes in the low picomolar concentration range. f-PSA in the concentration range from 0.1 to 10 ng/mL was detected by this one-step and washing-free homogeneous immunoassay.

A One-Step Highly Sensitive Method for DNA Detection Using Dynamic Light Scattering

A one-step homogeneous DNA detection method with high sensitivity was developed using gold nanoparticles (AuNPs) coupled with dynamic light scattering (DLS) measurement. Citrate-protected AuNPs with a diameter of 30 nm were first functionalized with two sets of single-stranded DNA probes and then used as optical probes for DNA detection. In the presence of target DNA, the hybridization between target DNA and the two nanoparticle probes caused the formation of nanoparticle dimers, trimers, and oligomers. As a result, the nanoparticle aggregation increased the average diameter of the whole nanoparticle population, which can be monitored simply by DLS measurement. A quantitative correlation can be established between the average diameter of the nanoparticles and the target DNA concentration. This DLS-based assay is extremely easy to conduct and requires no additional separation and amplification steps. The detection limit is around 1 pM, which is 4 orders of magnitude better than that of light-absorption-based methods. Single base pair mismatched DNAs can be readily discriminated from perfectly matched target DNAs using this assay.

A Nanochannel Array-Based Electrochemical Device for Quantitative Label-free DNA Analysis

A strategy for label-free oligonucleotide (DNA) analysis has been proposed by measuring the DNA-morpholino hybridization hindered diffusion flux of probe ions Fe(CN)(6)(3-) through nanochannels of a porous anodic alumina (PAA) membrane. The flux of Fe(CN)(6)(3-) passing through the PAA nanochannels is recorded using an Au film electrochemical detector sputtered at the end of the nanochannels. Hybridization of the end-tethered morpholino in the nanochannel with DNA forms a negatively charged DNA-morpholino complex, which hinders the diffusion of Fe(CN)(6)(3-) through the nanochannels and results in a decreased flux. This flux is strongly dependent on ionic strength, nanochannel aperture, and target DNA concentration, which indicates a synergetic effect of steric and electrostatic repulsion effects in the confined nanochannels. Further comparison of the probe flux with different charge passing through the nanochannels confirms that the electrostatic effect between the probe ions and DNA dominates the hindered diffusion process. Under optimal conditions, the present nanochannel array-based DNA biosensor gives a detection limit of 0.1 nM.

A Functional Nuclear Epidermal Growth Factor Receptor, Src and Stat3 Heteromeric Complex in Pancreatic Cancer Cells

Evidence is presented for the nuclear presence of a functional heteromeric complex of epidermal growth factor (EGFR), Src and the Signal Transducer and Activator of Transcription (Stat)3 proteins in pancreatic cancer cells. Stat3 remains nuclear and associated with Src or EGFR, respectively, upon the siRNA knockdown of EGFR or Src, demonstrating the resistance of the complex to the modulation of EGFR or Src alone. Significantly, chromatin immunoprecipitation (ChIP) analyses reveal the nuclear EGFR, Src and Stat3 complex is bound to the c-Myc promoter. The siRNA knockdown of EGFR or Src, or the pharmacological inhibition of Stat3 activity only marginally suppressed c-Myc expression. By contrast, the concurrent modulation of Stat3 and EGFR, or Stat3 and Src, or EGFR and Src strongly suppressed c-Myc expression, demonstrating that the novel nuclear heteromeric complex intricately regulates the c-Myc gene. The prevalence of the transcriptionally functional EGFR, Src, and Stat3 nuclear complex provides an additional and novel mechanism for supporting the pancreatic cancer phenotype and explains in part the insensitivity of pancreatic cancer cells to the inhibition of EGFR, Src or Stat3 alone.

Dispersion of carbon nanotubes and polymer nanocomposite fabrication using trifluoroacetic acid as a co-solvent

We herein report the dispersion of multi-walled carbon nanotubes (MWCNTs) using trifluoroacetic acid (TFA) as a co-solvent. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents. Our study demonstrates that MWCNTs can be effectively purified and readily dispersed in a range of organic solvents including dimethyl formamide (DMF), tetrahydrofuran (THF), and dichloromethane when mixed with 10 vol.% trifluoroacetic acid (TFA). X-ray photoelectron spectroscopic analysis revealed that the chemical structure of the TFA-treated MWCNTs remained intact without oxidation. The dispersed carbon nanotubes in TFA/THF solution were mixed with poly(methyl methacrylate) (PMMA) to fabricate polymer nanocomposites. A good dispersion of nanotubes in solution and in polymer matrices was observed and confirmed by SEM, optical microscopy, and light transmittance study. Low percolation thresholds of electrical conductivity were observed from the fabricated MWCNT/PMMA composite films. Further enhancement in the dispersion of MWCNTs was achieved by adding a conjugated conducting polymer, poly(3-hexylthiophene) (P3HT), to the dispersion, wherein TFA also serves as a doping agent to the conducting polymer. The ternary nanocomposite MWCNT/P3HT/PMMA exhibited an extremely low percolation threshold of less than 0.006 wt% of MWCNT content. This low percolation threshold is attributed to a good dispersion of MWCNTs and enhanced conductivity of the nanocomposites by conjugated conducting polymer.

A Novel Photoscissile Poly(ethylene glycol)‐Based Hydrogel

drawbacks, such as slow gelation rate, need for potentially toxic initiators, and thermal or storage instability. In addition, a limited number of these photoinduced systems demonstrate photoreversibility. [2,3,9,10] Andreopoulos et al. [3] have synthesized a partially reversible hydrogel via photopolymerization of cinnamylidene-terminated PEG. The physical properties of the hydrogel membrane such as pore size and swellability were controlled in a predictive way by alternating the wavelength (>300/254 nm) and sequence of irradiation. The photoreversibility efficiency of the PEG-cinnamylidene hydrogel, however, was compromised by photoscission light inefficiency, cinnamylidene photodegradation, and side polymerization reactions. [10] In the work reported here, we designed a new photocrosslinked and photoscissile hydrogel based on an eight-branched PEG with nitrocinnamate as pendant groups. Cinnamate is known to undergo trans‐cis isomerization and [2+2] cycloaddition upon UV irradiation at wavelengths longer than 290 nm, and the formed cyclobutane ring can be cleaved to regenerate the starting cinnamate groups at wavelengths below 260 nm. [11] The photocrosslinking property of cinnamates has been broadly utilized in the field of photolithography and the semiconductor industry. [12] However, the application of nitrocinnamate photoreactivity in PEG chemistry, especially in PEG-based hydrogel formation, has rarely been reported. [6,13] On the other hand, cinnamate derivatives possess excellent thermal and storage stability superior to cinnamylidene systems. [14] PEG-cinnamylidene polymers have been shown to be unstable and undergo gelation when they are kept at room temperature for a period of a few weeks. Nitrocinnamate demonstrates the stability characteristics of the unsubstituted cinnamate and at the same time is 350 times more photoreactive. [11,15]

Photothermal ablation of amyloid aggregates by gold nanoparticles.

Amyloid peptide (Abeta) is found in the brain and blood of both healthy and diseased individuals alike. However, upon secondary structure transformation to a beta-sheet dominated conformation, the protein aggregates. These aggregates accumulate to form neuritic plaques that are implicated in the pathogenesis of Alzheimers disease. Gold nanoparticles are excellent photon-thermal energy converters. The extinction coefficient of the surface plasmon band of gold nanoparticles is very large when compared to typical organic dyes. In this study, gold nanoparticle-Abeta conjugates were prepared and the photothermal ablation of amyloid peptide aggregates by laser irradiation was studied. Monofunctional gold nanoparticles were prepared using a recently reported solid phase modification method and then coupled to fragments of Abeta peptide, namely Abeta(31-35) and Abeta(25-35). The conjugates were then mixed with Abeta fragments in solution. The aggregated peptide formation was studied by a series of spectroscopic and microscopic techniques. The peptide aggregates were then irradiated by a continuous laser. With gold nanoparticle-Abeta conjugates present the aggregates were destroyed by photothermal ablation. Gold nanoparticles without Abeta conjugation were not incorporated into the aggregates and when irradiated did not result in photothermal ablation. With gold nanoparticle-Abeta conjugates the ablation was selective to the site of irradiation and minimal damage was observed as a result of thermal diffusion. In addition to the application of photoablation to a protein-based sample the nanoparticles and the chemistry involved provide an easily monofunctionalized photothermal material for the biological conjugation.

Protein complexes/aggregates as potential cancer biomarkers revealed by a nanoparticle aggregation immunoassay

Protein-protein interactions and protein complex/aggregate formation play an essential role in almost all biological functions and activities. Through a nanoparticle aggregation immunoassay, we discovered that some proteins are substantially more complexed/aggregated in cancer tissues than normal tissues. This study examined four biomarkers proteins, CA125, CEA (carcinoembryonic antigen), CA19-9 and PAP (prostatic acid phosphatase) in ovarian, colon and prostate tissue lysates. The most exciting results were observed from the PAP assay of prostate tissues: prostate cancer can be clearly distinguished from normal prostate and prostate with benign conditions such as BPH (benign prostate hyperplasia) based on the complex/aggregation level of PAP in prostate tissue lysates. The complex/aggregate level of a protein can be potential biomarkers for cancer detection and diagnosis.

Different Interaction Modes of Biomolecules with Citrate-Capped Gold Nanoparticles

In this study, we investigated the interaction between five biorelevant molecules and citrate-capped gold nanoparticles using dynamic light scattering, ζ-potential analysis, UV-vis absorption spectroscopy, and transmission electron microscopy. The five biomolecules are bovine serum albumin (BSA), two immunoglobulin G (IgG) proteins, immunoglobulin M (IgM), and a polysaccharide molecule, hyaluronan. BSA, IgG, and IgM are high abundance proteins in blood. Hyaluronan is a major component of the extracellular matrix. An abnormal level of hyaluronan in blood is associated with a number of medical conditions including rheumatoid arthritis and malignancy. Five different interaction modes were observed from these molecules. While BSA and IgM interact with the gold nanoparticles by forming electrostatic interactions with the citrate ligands, IgG and hyaluronan adsorb to the nanoparticle metal core by displacing the citrate ligands. BSA, rabbit IgG, and hyaluronan formed a stable monolayer on the nanoparticle surface. Human IgG and IgM caused nanoparticle cluster formation upon interacting with the gold nanoparticles. For the first time, we discovered that hyaluronan, a highly negatively charged polyglycosaminoglycan, exhibits an exceptionally strong affinity toward the citrate-gold nanoparticles. It can effectively compete with IgG to adsorb to the gold nanoparticles. This finding has exciting implications for future research: the molecular composition of a protein corona formed on a nanoparticle surface upon mixing the nanoparticle with blood or other biological fluids may vary according to the pathological conditions of individuals, and the analysis of these compositions could potentially lead to new biomarker discovery with diagnostic applications.

Cysteine-grafted chitosan-mediated gold nanoparticle assembly: from nanochains to microcubes

Molecule-mediated nanoparticle assemblies were obtained by the rational design and modification of chitosan, and grafting it onto gold nanoparticles, providing a new way for combining the virtues of synthetic and biological polymers. Using thiolate-functionalized chitosan molecules as soft templates, gold nanoparticles were found to self-organize into 1D nanochains via specific molecular recognition, or assemble into 2D needle-like crystals and 3D flower clusters through conformational change of the template. Such clusters may further re-crystallize into gold single crystal microcubes by way of a simple dialysis method. The as-prepared nano- and microstructures were characterized and the mechanism for the gold nanoparticle assembly process and microcrystal formation was revealed. This work demonstrates a simple and novel approach for fabricating well defined gold nano- and microstructures through a controlled nanoparticle self-assembly process.