A platinum shell for ultraslow ligand exchange: unmodified DNA adsorbing more stably on platinum than thiol and dithiol on gold

Due to the ultraslow ligand exchange rate on Pt, non-thiolated DNA is adsorbed on platinum nanoparticles (PtNPs) more stably than thiolated and even dithiolated DNA on AuNPs. Adsorption kinetics, capacity and stability are systematically compared as a function of DNA sequence. The Pt conjugates can tolerate extreme pH, salt, and thiol molecules. Taking advantage of the optical properties of AuNPs and the extreme stability of DNA on PtNPs, DNA-functionalized Au@Pt NPs are prepared using a cost-effective and more stable bioconjugation method. The DNA-directed assembly of non-thiolated DNA conjugates is also demonstrated.University of Waterloo || Natural Sciences and Engineering Research Council || Foundation for Shenghua Scholar of Central South University || National Natural Science Foundation of China || Grant No. 21301195 China Scholarship Council || CSC, Grant No. 20140637011

Infrared Optical Response of Metallic Graphene Nanoribbons

We investigate theoretically the infrared optical response characteristics of metallic armchair/zigzag-edge graphene nanoribbons (A/ZGNRs) to an external longitudinally polarized electromagnetic field at low temperatures. Within the framework of linear response theory at the perturbation regime, we examine the optical infrared absorption threshold energy, absorption power, dielectric function, and electron energy loss spectra near the neutrality points of the systems. It is demonstrated that, by some numerical examples, the photon-assisted direct interband absorptions for AGNR exist with different selection rules from those for ZGNR and single-walled carbon nanotube at infrared regime. This infrared optical property dependence of GNRs on field frequency may be used to design graphene-based nanoscale optoelectronic devices for the detection of infrared electromagnetic irradiations

Dependence of electronic and optical properties on a high-frequency field for carbon nanotubes

We study theoretically the electronic structure, transport and optical properties for a zigzag single-wall carbon nanotube connected to two normal conductor leads under the irradiation of an external electromagnetic field at low temperatures, with particular emphasis on the features of high-frequency response. Using the standard nonequilibrium Green's function techniques, we examine the time-averaged density of states, the conductivity, the dielectric function and the electron energy loss spectra for the system with photon polarization parallel with the tunneling current direction, respectively. Through some numerical examples, it is shown that the density of states is strongly dependent on the incident electron energy, the strength and frequency of the applied field. For higher electron energies in comparison with lead-nanotube coupling energy, the system conductance decreases with increasing the field strength and increases with increasing the field frequency respectively, and shows some oscillation structures. Moreover, the optical functions for the system have also a rich structure with the variation of field frequency. It may demonstrate that this transport dependence on the external field parameters can be used to give the energy spectra information of carbon nanotubes and to detect the high-frequency microwave irradiation.Comment: 6 Revtex pages, 4 figures. to be appeared in JA

Tandem Phosphorothioate Modifications for DNA Adsorption Strength and Polarity Control on Gold Nanoparticles

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Applied Materials & Interfaces, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see Zhou, W., Wang, F., Ding, J., & Liu, J. (2014). Tandem Phosphorothioate Modifications for DNA Adsorption Strength and Polarity Control on Gold Nanoparticles. ACS Applied Materials & Interfaces, 6(17), 14795–14800. https://doi.org/10.1021/am504791bUnmodified DNA was recently used to functionalize gold nanoparticles via DNA base adsorption. Compared to thiolated DNA, however, the application of unmodified DNA is limited by the lack of sequence generality, adsorption polarity control and poor adsorption stability. We report that these problems can be solved using phosphorothioate (PS) DNA. PS DNA binds to gold mainly via the sulfur atom and is thus less sequence dependent. The adsorption affinity is ranked to be thiol > PS > adenine > thymine. Tandem PS improves adsorption strength, allows tunable DNA density, and the resulting conjugates are functional at a low cost.University of Waterloo || Natural Sciences and Engineering Research Council || Foundation for Shenghua Scholar of Central South University || National Natural Science Foundation of China || Grant No. 2130119

Aptamer-based biosensors for biomedical diagnostics

Aptamers are single-stranded nucleic acids that selectively bind to target molecules. Most aptamers are obtained through a combinatorial biology technique called SELEX. Since aptamers can be isolated to bind to almost any molecule of choice, can be readily modified at arbitrary positions and they possess predictable secondary structures, this platform technology shows great promise in biosensor development. Over the past two decades, more than one thousand papers have been published on aptamer-based biosensors. Given this progress, the application of aptamer technology in biomedical diagnosis is still in a quite preliminary stage. Most previous work involves only a few model aptamers to demonstrate the sensing concept with limited biomedical impact. This Critical Review aims to summarize progress that might enable practical applications of aptamers for biological samples. First, general sensing strategies based on the unique properties of aptamers are summarized. Each strategy can be coupled to various signaling methods. Among these, a few detection methods including fluorescence lifetime, flow cytometry, upconverting nanoparticles, nanoflare technology, magnetic resonance imaging, electronic aptamer-based sensors, and lateral flow devices have been discussed in more detail since they are more likely to work in a complex sample matrix. The current limitations of this field include the lack of high quality aptamers for clinically important targets. In addition, the aptamer technology has to be extensively tested in a clinical sample matrix to establish reliability and accuracy. Future directions are also speculated to overcome these challenges.University of Waterloo || Natural Sciences and Engineering Research Council || Foundation for Shenghua Scholar of Central South University |

Spin Accumulation in a Quantum Wire with Rashba Spin-Orbit Coupling

We investigate theoretically the spin accumulation in a Rashba spin-orbit coupling quantum wire. Using the scattering matrix approach within the effective free-electron approximation, we have demonstrated the three components of spin polarization. It is found that by a few numerical examples, the two peaks for the out-of-plane spin accumulation 〈Sz〉 shift to the edges of quantum wire with the increase of propagation modes. The period of intrinsic oscillations 〈Sx/y〉 inversely proportions to the Rashba SOC strength. This effect may be used to differentiate the intrinsic spin accumulation from the extrinsic one