Zhong-Peng Lv

Creating protein-imprinted self-assembled monolayers with multiple binding sites and biocompatible imprinted cavities.

Imprinted monolayers have several advantages over bulk imprinted polymers such as excellent mass transfer of molecules into and out of imprinted sites and transduction of binding signals detected in real time. Protein-imprinted self-assembled monolayers (SAMs) were created with multiple binding sites and biocompatible imprinted cavities from functional thiols and novel disulfide compounds containing an oligoethylene glycol (OEG) terminal moiety and two amide groups incorporated in the chain (DHAP) in a biologically benign solution. DHAP played an important role in the formation of multiple binding sites and biocompatible cavities in addition to resisting nonspecific protein binding. The created protein-imprinted SAMs exhibited the excellent ability of specific binding of target proteins determined by multiple binding sites and imprinted cavities. The strategy generates tailor-made monolayer surfaces with specific protein binding and opens the possibility of controlled assembly of intellectual biomaterials and preparation of biosensors.

Bifunctional quantum dot-decorated Ag@SiO2 nanostructures for simultaneous immunoassays of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF)

Bifunctional nanostructured ensembles of quantum dot (QD)-decorated Ag@SiO2 nanoparticles embedded with Raman reporters p-aminothiophenol (PATP) were intentionally prepared for simultaneous immunoassays of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). The maximum SEF intensity was optimized with a silica shell spacer of about 9 nm. The SERS sensitivity was significantly improved due to the large Raman scattering cross-section of the coupling reaction product of PATP, generated on the Ag cores upon irradiation of laser during the SERS measurements. The antibody-immobilized QD-decorated Ag/PATP@SiO2 nanocomposites were used for antigen immunoassays using SERS and SEF with high sensitivity. This progress demonstrates the crucial role of rational design/control of multifunctional nanostructures in biodetection and bioimaging.

Charge-Transfer Supra-Amphiphiles Built by Water-Soluble Tetrathiafulvalenes and Viologen-Containing Amphiphiles: Supramolecular Nanoassemblies with Modifiable Dimensions

In this study, multidimensional nanoassemblies with various morphologies such as nanosheets, nanorods, and nanofibers are developed via charge-transfer interaction and supra-amphiphile self-assembling in aqueous phase. The charge-transfer interactions between tetrathiafulvalene derivatives (TTFs) and methyl viologen derivatives (MVs) have been confirmed by the characteristic charger-transfer absorption. (1) H NMR and electrospray ionizsation mass spectrometry (ESI-MS) analyses also indicate supra-amphiphiles are formed by the combination of TTFs and MVs head group through charge-transfer interaction and Coulombic force. X-ray single crystal structural studies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) reveal that both linkage pattern of TTFs in hydrophilic part and alkane chain structure in hydrophobic part have significant influence on nanoassemblies morphology and microstructure. Moreover, gold nanoparticles (AuNPs) are introduced in the above supramolecular nanoassemblies to construct a supra-amphiphile-driven organic-AuNPs assembly system. AuNPs could be assembled into 1D-3D structures by adding different amount of MVs.

Tuning Electron-Conduction and Spin Transport in Magnetic Iron Oxide Nanoparticle Assemblies via Tetrathiafulvalene-Fused Ligands.

We report a strategy to coat Fe3O4 nanoparticles (NPs) with tetrathiafulvalene-fused carboxylic ligands (TTF-COO-) and to control electron conduction and magnetoresistance (MR) within the NP assemblies. The TTF-COO-Fe3O4 NPs were prepared by replacing oleylamine (OA) from OA-coated 5.7 nm Fe3O4 NPs. In the TTF-COO-Fe3O4 NPs, the ligand binding density was controlled by the ligand size, and spin polarization on the Fe3O4 NPs was greatly improved. As a result, the interparticle spacing within the TTF-COO-Fe3O4 NP assemblies are readily controlled by the geometric length of TTF-based ligand. The shorter the distance and the better the conjugation between the TTFs HOMO and LUMO, the higher the conductivity and MR of the assembly. The TTF-coating further stabilized the Fe3O4 NPs against deep oxidation and allowed I2-doping to increase electron conduction, making it possible to measure MR of the NP assembly at low temperature (<100 K). The TTF-COO-coating provides a viable way for producing stable magnetic Fe3O4 NP assemblies with controlled electron transport and MR for spintronics applications.

Self-assembly and molecular recognition of adenine- and thymine-functionalized nucleolipids in the mixed monolayers and thymine-functionalized nucleolipids on aqueous melamine at the air-water interface.

Self-assembly and molecular recognition of the monolayers composed of an equimolar mixture of adenine- and thymine-functionalized nucleolipids at the air-water interface have been investigated in detail using surface pressure-molecular area isotherms and in situ infrared reflection absorption spectroscopy (IRRAS). Prior to molecular recognition, the adenine moieties in the monolayer were almost oriented on an end-on mode through π-stacking and hydrogen bonding interactions, and the C-C-C planes of the alkyl chains were preferentially oriented perpendicular to the water surface, while the thymine moieties in the monolayer were involved in hydrogen bonding almost with a flat-on orientation. On aqueous subphases containing complementary bases, no significant molecular recognition was observed for the monolayers of individual nucleolipids. In the monolayer of equimolar mixture, molecular recognition occurred between the adenine and thymine moieties through hydrogen bonding probably with the development of cyclic structures of adenine-thymine-adenine-thymine quartets. Although molecular recognition between the monolayer of thymine-functionalized nucleolipids and aqueous melamine took place through triple hydrogen bonds, no melamine binding to the monolayer of equimolar mixture was observed, which reflects the formation of the quartets in the mixed monolayers at the air-water interface. FTIR and small-angle X-ray diffraction (XRD) results of the corresponding Langmuir-Blodgett films support the hydrogen bonding recognition and molecular orientation.

Tandem Assays of Protein and Glucose with Functionalized Core/Shell Particles Based on Magnetic Separation and Surface-Enhanced Raman Scattering

Tandem assays of protein and glucose in combination with mannose-functionalized Fe3 O4 @SiO2 and Ag@SiO2 tag particles have promising potential in effective magnetic separation and highly sensitive and selective SERS assays of biomaterials. It is for the first time that tandem assay of glucose is developed using SERS based on the Con A-sandwiched microstructures between the functionalized magnetic and tag particles.

Controlling the assembly and spin transport of tetrathiafulvalene carboxylate coated iron oxide nanoparticles

We report a solution phase based assembly method to tune the transport mechanism and magnetoresistance (MR) of Fe3O4 nanoparticles (NPs). The NP topological arrangement is altered by the NP coating of tetrathiafulvalene carboxylic acid (TTFCOOH) or its dicarboxylic analogue (TTF(COOH)2). Consequently, the transport mechanism of the assembly switches from tunneling to Mott hopping. The MR ratios of the Fe3O4 NP assemblies can be further tuned by the polarity of the solvent used in the ligand exchange process. The TTF(COO)2-coated Fe3O4 NP assembly has a 5% room temperature MR ratio, which is the highest value among all TTF-COO-Fe3O4 NP assemblies reported so far.

Structure-dependent electronic transition in a new type of π-electron delocalized multi-sulfur bis(dithiolene)nickel complex

Four new nickel bis(dithiolene) complexes with different substituent groups on their benzene rings were synthesized and characterized. X-ray structure analysis reveals that the anions of these Ni-complexes exhibit chair-like configurations. Magnetic measurements confirm that compounds 1–4 show antiferromagnetic interactions. The absorption spectra show strong and broad absorptions in the near-infrared region (700–1100 nm). Density functional theory (DFT) calculations indicate that the HOMO and LUMO energy levels are highly dependent on the electron donating/withdrawing abilities of the substituents. The electron-donating substituent results in a bathochromic-shift absorption, while the electron-withdrawing substituent leads to a hypsochromic-shift absorption band. Moreover, the results of solution-state electrochemical studies also show a good agreement with our findings in spectroscopic and DFT studies.