Leo M. H. Lai

Formation of Efficient Electron Transfer Pathways by Adsorbing Gold Nanoparticles to Self-Assembled Monolayer Modified Electrodes

The influence of the length of a self-assembled monolayer (SAM) linker on the electrochemical performance of electrode-linker-gold nanoparticle molecular constructs is investigated. Electrodes were first modified with amino-1-alkanethiols of four different lengths (C=2, 6, 8, and 11). The SAM showed progressively greater blocking ability to ruthenium hexamine as the length of the alkyl chain increased to the point where no significant Faradaic peak was observed for the amino-1-undecanethiol SAM. Upon the attachment of gold nanoparticles, distinct Faradaic electrochemistry of the ruthenium hexamine was observed for all four length SAMs with the electrochemistry being similar to that observed on a bare electrode. The charge transfer resistance to this Faradaic process was observed to be insensitive to the length of the intervening SAM, indicating it is electron transfer between the redox species and the nanoparticles, rather than tunneling across the SAM, which is the rate-limiting step. Some comments on the mechanism of charge transfer are provided. When forming multilayers of the linker-nanoparticle constructs, fabricated in a stepwise manner, whenever the distal species was the SAM the Faradaic process was blocked and whenever it was the nanoparticle a distinct Faradaic process was observed. With up to five layers of linker-nanoparticles, there was little increase in charge transfer resistance and again the charge transfer resistance was insensitive to the length of the linker.

Smart Tissue Culture: in Situ Monitoring of the Activity of Protease Enzymes Secreted from Live Cells Using Nanostructured Photonic Crystals

Monitoring enzyme secretion in tissue culture has proved challenging because to date the activity cannot be continuously measured in situ. In this Letter, we present a solution using biopolymer loaded photonic crystals of anodized silicon. Shifts in the optical response by proteolytic degradation of the biopolymer provide label-free sensing with unprecedented low detection limits (1 pg) and calculation of kinetic parameters. The enhancement in sensitivity relative to previous photonic crystal sensors constitutes a change in the sensing paradigm because here the entire pore space is responsive to the secreted enzyme rather than just the pore walls. In situ monitoring is demonstrated by detecting secretion of matrix metalloprotease 9 from stimulated human macrophages.

The Biochemiresistor: An Ultrasensitive Biosensor for Small Organic Molecules

New sensation: A resistance-based biosensor uses gold-coated magnetic nanoparticles (Au@MNPs) functionalized with the antibiotic enrofloxin (see picture; purple), which bind to anti-enrofloxin as analyte (blue). The Au@MNPs can be magnetically assembled between electrodes, and the measured resistance R is a function of analyte concentration.

Organic modification of mesoporous silicon rugate filters: the influence of nanoarchitecture on optical behaviour

The internal nanostructure and optical properties of mesoporous silicon rugate filters prepared on different p+ type silicon substrates are compared for applications in biosensing. Chemical derivatisation of the internal surface by undecenoic acid hydrosilylation results in red-shifting of the resonant wavelength of the filter, whereby the magnitude of the red shift is found to be a function of the pore morphology. The pore structure was found to play a significant role during infiltration of protein into the photonic crystal.

Thiol functionalisation of gold-coated magnetic nanoparticles: Enabling the controlled attachment of functional molecules

Gold-coated magnetite nanoparticles (Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs) have recently become the focus of research efforts which exploit the novel nano-architecture of these nanoparticles as platforms for magnetically controlled biomedical and analytical applications. To effectively utilise the Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs, thiol molecules can be bound onto the gold coating to provide a predictable surface for controlled attachment of functional molecules. Herein we present a facile process by which thiols with different moieties are attached to Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs. Dynamic light scattering and zeta-potential measurements were performed to study the effect of different thiols on the aggregation stability and surface charge of the Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs. The controlled attachment of an electroactive osmium complex is then demonstrated via voltammetric measurements. This work highlights importance of thiol molecule selection in enabling the fabrication of functional Fe<inf>3</inf>O<inf>4</inf>-Au<inf>coat</inf> NPs.

Silicon (100) surfaces modified by osmium bipyridine complexes

Tethered osmium bypiridine-pyridine complexes [Os(bpy)2Clpy-R] were prepared from chemically modified non-oxidized silicon (100) electrodes. Pyridinyl groups at the distal end of self-assembled monolayers (SAMs)-modified silicon surfaces were used to coordinatively bind a representative osmium bipyridil complex precursor [Os(bpy)2Cl2]. SAMs presenting the putative osmium ligand were prepared by a step-wise procedure using ‘click’ reactions of acetylene-terminated alkyl monolayers and isonicotinic acid azide derivatives. The redox properties of the modified Si(100) electrodes were characterized using cyclic voltammetry.