Xuezhong Du

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.

Synthesis and application of surface enhanced Raman scattering (SERS) tags of Ag@SiO2 core/shell nanoparticles in protein detection

A simple method has been developed to prepare silica-encapsulated Ag (Ag@SiO2) Raman tags, embedded with the reporter molecules 4-mercaptobenzoic acid (MBA), using environmental-friendly solvents (mixed solvents of ethanol and water) without vitreophilic pretreatment. The Ag@SiO2 Raman tags exhibited excellent stability resistance to high-concentration salts and long-term storage. Sensitivity of the Ag@SiO2 SERS tags could be enhanced by increasing MBA coverage and reducing the silica shell thickness, and the Ag@SiO2 SERS tags had versatility for bioassays. Myoglobin (Mb)-conjugated Ag@SiO2 Raman tags specifically bound to iminodiacetic acid (IDA)-functionalized wafers through the coordination interactions of IDA–Cu2+–histidine residues available on the Mb surfaces for SERS detection. Mb could be directly detected by means of the formation of the Mb-sandwiched structures via Cu2+ coordination between the IDA-functionalized wafers and IDA-modified Ag@SiO2–Au composite nanoparticles, where Au nanoparticles were adsorbed onto aminated Ag@SiO2 Raman tags followed by modifying with IDA. It is clear that the prepared Ag@SiO2 Raman tags can be applied for assays of other proteins or biomolecules if corresponding specific ligands are used and have potential application in immunoassays.

pH- and redox-triggered synergistic controlled release of a ZnO-gated hollow mesoporous silica drug delivery system

Hollow mesoporous silica spheres (HMSS) have a hierarchical mesoporous structure composed of a hollow cavity and mesoporous shell available for high capacity drug storage. The covalent attachment of ZnO quantum dots (QDs) to the HMSS outer surface as gatekeepers via disulfide-conjugated two amide linkages encapsulated the anticancer drugs doxorubicin (DOX) within the HMSS cavities and pores, and minimized premature release of the drug. The controlled release of the drug from the ZnO-gated HMSS delivery system was realized by the dissolution of ZnO QDs upon a decrease in pH and cleavage of the disulfide bonds, which indicates that the pH- and redox-responsive controlled release of the drugs could be synergically stimulated by tumor cells with weakly acidic environments and high-expressed glutathione. The constructed ZnO-gated HMSS delivery system has promising applications in site-specific drug release for tumor chemotherapy.

Iminodiacetic acid-functionalized gold nanoparticles for optical sensing of myoglobin via Cu2+ coordination.

A novel gold nanoparticle (AuNP)-based optical sensing system has been developed for the detection of myoglobin (Mb), which is of significant importance for early disease diagnosis. Two thiol molecules containing an iminodiacetic acid moiety (IDA) were synthesized. This detection is based on the Mb-induced aggregation of IDA-functionalized AuNPs resulting from the structures of Mb sandwiched between the functionalized AuNPs via Cu(2+) bridges in the coordination interactions of IDA-Cu(2+)-histidine residues available on the Mb surface, which was confirmed by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The induction aggregation resulted in a red shift in plasmon resonance band of the AuNPs concomitant with a change in solution color from red to purple. The qualitative and quantitative detections of Mb can be achieved by colorimetric observations and UV-vis spectral measurements, respectively. The selectivity of protein assay with the functionalized AuNPs was further investigated, and it is found that the optical sensing of histidine-rich proteins is closely related to number and distribution of surface histidine residues as well as size of proteins.

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.

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.