Nanosized Pt and PtRu colloids were prepared by a microwave-assisted polyol process and transferred to a toluene solution of decanthiol. Vulcan XC-72 was then added to the toluene solution to adsorb the thiolated Pt and PtRu colloids. TEM examinations showed nearly spherical particles and narrow size distributions for both supported and unsupported metals. The carbon-supported Pt and PtRu nanoparticles were activated by thermal treatment to remove the thiol stabilizing shell. All Pt and PtRu catalysts (except Pt 23 Ru 77 ) showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Pt 23 Ru 77 alloy was more typical of the hexagonal close-packed (hcp) structure. The electro-oxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results showed that the alloy catalyst was catalytically more active than pure platinum. The heat-treated catalyst was also expectedly more active than the non-heat-treated ones, because of the successful removal of the organic shell, which might interfere with reactant adsorption in the methanol oxidation reaction. Pt 52 Ru 48 /C had the best electrocatalytic performance among all carbon-supported Pt and PtRu catalysts.

Surface plasmon resonance (SPR) spectroscopy is employed for the study of biotinylated DNA assembly on streptavidin modified gold surfaces for target DNA hybridization. Two immobilization strategies are involved for constructing streptavidin films, namely, (1) physical adsorption on biotin-containing thiol treated surfaces through biotin-streptavidin links and (2) covalent attachment to 11-mercaptoundecanoic acid (MUA) treated surfaces through amine coupling. To understand the structural properties of the streptavidin films, a quartz crystal microbalance with energy dissipation monitoring (QCM-D) is used to monitor the streptavidin immobilization procedures. The simultaneously measured frequency (Deltaf) and dissipation factor (DeltaD) changes, together with the SPR angle shifts (Deltatheta), suggest that the streptavidin film assembled on the biotin-containing surface is highly rigid with a well-ordered structure while the streptavidin film formed through amine coupling is highly dissipative and less structured. The subsequent biotinylated DNA (biotin-DNA) assembly and target hybridization results show that the streptavidin film structure has distinct effects on the biotin-DNA binding amount. On the streptavidin matrix, not only the probe DNA density but also the strand orientation mediated by the streptavidin films has distinct effects on hybridization efficiency. Particularly, the molecularly ordered streptavidin films formed on the biotin-containing surfaces ensure a well-ordered DNA assembly, which in turn allows for a higher efficiency in target DNA capture and for a higher sensitivity in the hybridization analysis when compared to the biotin-DNA assembled on the less structured streptavidin films formed through amine coupling.

A growing number of peptides capable of specifically recognizing inorganic materials have been reported, incrementally increasing the potential to harness peptides as a biological linker to bridge biomolecules and inorganic materials at nanometer scale. In this study, we identified disulfide bond constrained heptapeptides with specific binding affinity to SiO2 and TiO2 using a phage display technique. Interestingly, two of the phage surface displayed peptides enriched with basic amino acid residues, STB1 (HKKPSKS) and STB2 (TKRNNKR), showed a cross binding affinity to both metal oxides. To understand the underlying binding mechanism, binding behaviors of phage particles harboring the STB1 (a high-frequency heptapeptide exhibiting dual binding affinity to both metal oxides) were investigated in a wide pH range using quartz crystal microbalance with energy dissipation measurement (QCM-D). It was found that the binding of STB1-harboring phages to the two metal oxides was clearly mediated by the peptide moiety displayed on the phage surface in a pH-dependent manner, indicating that the binding is largely governed by electrostatic interaction. Furthermore, the interpretation of QCM-D signals (i.e., frequency shift and dissipation shift), with the aid of AFM image analysis of the phage particles bound on the surface of the two metal oxides, elucidated whether the nature of phage (or the displayed peptide) binding to the metal oxides is largely specific or nonspecific.

No abstract

We have demonstrated that mixed-base PNA oligomers are effective coagulants of citrate ion-coated gold and silver nanoparticles (AuNPs and AgNPs), and PNA-induced particle aggregation can be disrupted by hybridization of PNA with a specific DNA. Using particles' aggregation/dispersion as a measure, we have investigated how PNA and PNA-DNA complexes bind to AuNPs and AgNPs and modulate particles' stability differently relative to their DNA counterparts. We have made the following original discoveries: (1) mix-base PNA oligomers can induce immediate particle aggregation in a concentration- and chain-length-dependent manner; (2) PNA oligomers have a higher affinity to AuNPs and AgNPs than its ssDNA counterpart; (3) PNA-DNA complexes, although having a stable double helix structure similar to dsDNA, can effectively protect the particles from salt induced aggregation, and the protection effect of different nucleic acids are in the order of PNA-DNA complex > ssDNA > dsDNA; (4) all the characteristics are identical for AuNPs and AgNPs; and (5) AgNPs is more sensitive in response to destabilization effect and is proven a more sensitive platform for colorimetric assays. The control of particle aggregation and dispersion by PNA and PNA-DNA complexes has been used to detect a specific DNA sequence with single-base-mismatch resolution. zeta potential measurements have been conducted to reveal how distinct backbone properties of PNA and PNA-DNA complexes relative to their DNA counterparts contribute to the distinct binding characteristics.

Dual polarization interferometry (DPI) is used for a detailed study of antibody immobilization with and without orientation control, using prostate specific antigen (PSA) and its antibody as model. Thiol modified DPI chips were activated by a heterobifunctional cross-linker (sulfo-GMBS). PSA antibody was either directly immobilized via covalent binding or coupled via the Fc-fragment to protein G covalently attached to the activated chip. The direct covalent binding leads to a random antibody orientation and the coupling through protein G leads to an end-on orientation. Ethanolamine (ETH) was used to block remaining active sites following the direct antibody immobilization and protein G immobilization. A homobifunctional cross-linker (BS3) was used to stabilize the antibody layer coupled on protein G. DPI provides a real-time measurement of the stepwise molecular binding processes and gives detailed geometrical and structural values of each layer, i.e., thickness, mass, and density. These values evidence the end-on orientation of closely packed antibody on protein G layer and reveal structural effects of ETH blocking/deactivation and BS3 stabilization. With the end-on immobilized antibody, PSA at 10 pg/mL can be detected by DPI through a sandwich complex that satisfies the clinical requirement (assuming <30 pg/mL as clinically safe). However, the randomly immobilized antibody failed to detect PSA at 1 ng/mL. In a parallel study using surface plasmon resonance (SPR) spectroscopy, random and end-on antibody immobilization on streptavidin-modified gold surface was evaluated to further validate the importance of antibody orientation control. With the closely packed antibody layer on protein G surface, SPR can also detect PSA at 10 pg/mL.

12 years after the introduction of DNA-templated silver nanoclusters (DNA-AgNCs), exciting progress has been made and yet we are still in the midst of trying to fully understand this nanomaterial. The prominent excellence of DNA-AgNCs is undoubtedly its modulatable emission property, of which how variation in DNA templates causes emission tuning remains elusive. Based on the up-to-date DNA-AgNCs, we aim to establish the correlation between the structure/sequence of DNA templates and emission behaviour of AgNCs. Herein, we systematically present a wide-range of DNA-AgNCs based on the structural complexity of the DNA templates, including single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), triple-stranded DNA (tsDNA) and DNA nanostructures. For each DNA category, we discuss the emission property, quantum yield and synthesis condition of the respective AgNCs, before cross-comparing the impact of different DNA scaffolds on the properties of AgNCs. A future outlook for this area is given as a conclusion. By putting the information together, this review may shed new light on understanding DNA-AgNCs while we are expecting continuous breakthroughs in this field.

MutS protein is a mismatch binding protein that recognizes mispaired and unpaired base(s) in DNA. In this study, we incorporate the MutS protein-based mutation recognition into quartz crystal microbalance (QCM) measurements for DNA single-base substitution mutation and 1-4 base(s) insertion (or deletion) mutation detection. The method involves the immobilization of single-stranded probe DNA on a QCM surface, the hybridization of target DNA to form homoduplex or heteroduplex DNA, and finally the application of MutS protein for the mutation recognition. By measuring the MutS binding signal, DNA containing a T:G mismatch or unpaired base(s) is(are) discriminated against perfectly matched DNA at target concentrations ranging from 1nM to 5 microM. Furthermore, the QCM damping behavior upon MutS-DNA complex formation is studied using a Network Analyzer. The measured motional resistance changes per coupled MutS unit mass (deltaR/deltaf) are found to be indicative of the viscoelastic or structural properties of the bound protein, corresponding to different binding mechanisms. In addition, the deltaR/deltaf values vary remarkably when the MutS protein binds at different distances away from the QCM surface. Thus, these values can be used as a "fingerprint" for MutS mismatch recognition and also used to quantitatively locate the mutation site.