Multivalent binding of small guest molecules and proteins to molecular printboards inside microchannels

Fluorescent silica nanoparticles as nano-chemosensors for the sequential detection of Pb2+ ions and bacterial-spore biomarker dipicolinic acid (DPA) in aqueous solution

Herein, we report fluorescein-labelled silica nanoparticles (FSNP) which serve as fluorescent nano-chemosensors for sequential detection of Pb2+ (which is a toxic heavy metal) and dipicolinic acid (DPA) (which is a distinctive indicator biomarker of bacterial spores) with high sensitivity and selectivity. The fluorescence of FSNP is quenched because of the complex formation between Pb2+ ions and surface amide groups, however, the fluorescence is recovered in contact with DPA, resulting from the association of DPA with surface bound Pb2+ ions. FSNP-Pb2+ complexes show high sensitivity towards DPA with a low detection limit of 850 nM which is approximately seventy times lower than the infectious dosage of bacterial spores (60 μM). Lateral flow test platform was further developed to show the applicability and practicability of our system.

Interactions between shape-persistent macromolecules as probed by AFM

Water-soluble shape-persistent cyclodextrin (CD) polymers with amino-functionalized end groups were prepared starting from diacetylene-modified cyclodextrin monomers by a combined Glaser coupling/click chemistry approach. Structural perfection of the neutral CD polymers and inclusion complex formation with ditopic and monotopic guest molecules were proven by MALDI-TOF and UV-vis measurements. Small-angle neutron and X-ray (SANS/SAXS) scattering experiments confirm the stiffness of the polymer chains with an apparent contour length of about 130 Å. Surface modification of planar silicon wafers as well as AFM tips was realized by covalent bound formation between the terminal amino groups of the CD polymer and a reactive isothiocyanate-silane monolayer. Atomic force measurements of CD polymer decorated surfaces show enhanced supramolecular interaction energies which can be attributed to multiple inclusion complexes based on the rigidity of the polymer backbone and the regular configuration of the CD moieties. Depending on the geometrical configuration of attachment anisotropic adhesion characteristics of the polymer system can be distinguished between a peeling and a shearing mechanism.

Dendrimer-encapsulated Pd nanoparticles as catalysts for C–C cross-couplings in flow microreactors

Dendrimer-encapsulated Pd nanoparticles anchored within continuous flow microreactors are efficient for C–C cross-coupling reactions. This is witnessed by the good catalytic performance for the Heck–Cassar and Suzuki–Miyaura couplings.

Cyclodextrin-based molecular machines

This chapter overviews molecular machines based on cyclodextrins (CDs). The categories of CD-based molecular machines, external stimuli for CD-based molecular machines, and typical examples of CD-based molecular machines are briefly described.

A supramolecular approach to enzyme immobilization in micro-channels

A supramolecular assembly scheme is developed to enable the facile in-situ immobilization of enzymes in a microfluidic channel system. A combination of orthogonal supramolecular interactions of host (β-cyclodextrin)-guest (adamantane) and biotin-Streptavidin (SAv) interactions are employed to generate reusable homogeneous enzyme layers in microchannels. The structural integrity and catalytic activity of the immobilized enzyme calf-intestine alkaline phosphatase (AlkPh) is demonstrated. From the kinetic analysis of a dephosphorylation reaction, the specificity constant k(cat)/K(M) for immobilized alkaline phosphatase in the channels is on the order of 10(5) M(-1) s(-1) and comparable to known literature values in other environments. These observations are ascribed to the good access of the substrate to favorably oriented enzymes across the microchannel. Therefore, this study demonstrates the great potential for adopting a supramolecular assembly scheme to immobilize enzymes in microfluidic devices.

A supramolecular sensing platform for phosphate anions and an anthrax biomarker in a microfluidic device

A supramolecular platform based on self-assembled monolayers (SAMs) has been implemented in a microfluidic device. The system has been applied for the sensing of two different analyte types: biologically relevant phosphate anions and aromatic carboxylic acids, which are important for anthrax detection. A Eu(III)-EDTA complex was bound to β-cyclodextrin monolayers via orthogonal supramolecular host-guest interactions. The self-assembly of the Eu(III)-EDTA conjugate and naphthalene β-diketone as an antenna resulted in the formation of a highly luminescent lanthanide complex on the microchannel surface. Detection of different phosphate anions and aromatic carboxylic acids was demonstrated by monitoring the decrease in red emission following displacement of the antenna by the analyte. Among these analytes, adenosine triphosphate (ATP) and pyrophosphate, as well as dipicolinic acid (DPA) which is a biomarker for anthrax, showed a strong response. Parallel fabrication of five sensing SAMs in a single multichannel chip was performed, as a first demonstration of phosphate and carboxylic acid screening in a multiplexed format that allows a general detection platform for both analyte systems in a single test run with μM and nM detection sensitivity for ATP and DPA, respectively.

Redox strategy for reversible attachment of biomolecules using bifunctional linkers

Soft attachment of streptavidin to β-cyclodextrin-modified pegylated SAMs was efficiently performed in a reversible and repetitive way via orthogonal bifunctional linkers involving streptavidin-biotin recognition and redox-driven multivalent host-guest (β-cyclodextrin-ferrocene) interactions.

Chemical strategies for generating protein biochips

Protein biochips are at the heart of many medical and bioanalytical applications. Increasing interest has been focused on surface activation and subsequent functionalization strategies for immobilizing these biomolecules. Different approaches using covalent and noncovalent chemistry are reviewed; particular emphasis is placed on the chemical specificity of protein attachment and on retention of protein function. Strategies for creating protein patterns (as opposed to protein arrays) are also outlined. An outlook on promising and challenging future directions for protein biochip research and applications is also offered.