Mary Manning

Surface immobilisation of antibody on cyclic olefin copolymer for sandwich immunoassay

In this work, the surface functionalisation of the commercially available cyclic olefin copolymer (COC) materials, Zeonor and Zeonex, has been studied. The methodology employed involved oxidation in oxygen plasma, functionalisation of the oxidized surface with aminopropyl triethoxy silane and, finally, attachment of antibody using covalent linker molecules. 1,4-Phenylene diisothiocyanate was selected as the most suitable cross-linker for the attachment of protein, as assessed by fluorescent intensity measurements on immobilised FITC-labelled IgG antibody. The modification method was characterised by contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. The data are consistent with the deposition of a polymeric film of the silane chemisorbed to the oxidised plastic surface. The functionalised surfaces were employed in a sandwich immunoassay format using the reagents goat anti-human IgG (G alphaHIgG) and fluorescently labelled G alphaHIgG (Cy5-G alphaHIgG) as capture and detection antibodies, respectively, and with human IgG (HIgG) as the model analyte. The lowest concentration of HIgG detected was 0.1 ng ml(-1), with a relative standard deviation of 15%. Non-specific binding effects were also assessed. The method and supporting data demonstrate that simple approaches to surface functionalisation can be adapted to plastic-based devices.

Asymmetric Pentagonal Metal Meshes for Flexible Transparent Electrodes and Heaters

Metal meshes have emerged as an important class of flexible transparent electrodes. We report on the characteristics of a new class of asymmetric meshes, tiled using a recently discovered family of pentagons. Micron-scale meshes were fabricated on flexible polyethylene terephthalate substrates via optical lithography, metal evaporation (Ti 10 nm, Pt 50 nm), and lift-off. Three different designs were assessed, each with the same tessellation pattern and line width (5 μm), but with different sizes of the fundamental pentagonal unit. Good mechanical stability was observed for both tensile strain and compressive strain. After 1000 bending cycles, devices subjected to tensile strain showed fractional resistance increases in the range of 8-17%, while devices subjected to compressive strain showed fractional resistance increases in the range of 0-7%. The performance of the pentagonal metal mesh devices as visible transparent heaters via Joule heating was also assessed. Rapid response times (∼15 s) at low bias voltage (≤5 V) and good thermal resistance characteristics (213-258 °C cm2/W) were found using measured thermal imaging data. Deicing of an ice-bearing glass coupon on top of the transparent heater was also successfully demonstrated.

Investigation of Potential Distribution and the Influence of Ion Complexation on Diffusion Potentials at Aqueous-Aqueous Boundaries within a Dual-Stream Microfluidic Structure

The occurrence of reactions at boundaries between adjacent miscible but unmixed aqueous streams coflowing in a microfluidic channel structure has been studied by simulation of the diffusion potentials that develop between the two coflowing aqueous electrolyte streams and by measurement of the effects of aqueous ion complexation on diffusion potentials. The microfluidic structure consisted of a Y-shaped microchannel with off-chip electrodes immersed in electrolyte reservoirs connected by capillaries to the Y-microchannel. The time-dependent, one-dimensional Nernst-Planck equation employing the electroneutrality condition was solved numerically to calculate the diffusion potentials established at the boundary between the two coflowing aqueous streams. Under the experimental conditions (channel length and width, flow rate) employed, it was shown that the use of the Henderson equation was appropriate. It was also shown that the cross-channel diffusion potential remained constant from the entrance of the channel to the exit. The influence of cation complexation by a neutral ionophore was investigated by experimentally measured diffusion potentials. It was found that potassium complexation by the cyclic polyether 18-crown-6 altered the experimental diffusion potential, whereas the interaction of sodium or lithium cations with the ionophore did not perturb the diffusion potential. The results are consistent with the literature data for aqueous-phase complexation of these cations by this ionophore. The results of these investigations demonstrate that relatively simple diffusion potential measurements between coflowing streams in microchannels may be used as a basis for study of ion complexation reactions occurring at boundaries between miscible fluids.

Hybrid CMOS compatible active/passive quenching module

This paper demonstrates the experimental results of combining new state-of-the-art Geiger mode avalanche photodiodes with an integrated hybrid active/passive quenching circuit. This creates an ultra-compact form factor for a low-light level detection module. Both devices, the photodiode and the quenching circuit, are fabricated using conventional CMOS process technology and wafer substrates. The photodiodes operate at low voltage levels (30 V to 40V). Detector active areas are of various dimensions (10μm to 50μm) and shapes (circular, cylindrical or square). The integrated active/passive quenching circuit is included on a 2.5 mm × 2.5 mm die, which has the functionalities of bias conditioning, passive/active quench, output signal generation and active recharge. The prototypes are hybrid packaged onto a PCB substrate. The module is characterised for detecting very low level optical signals such as the single photon activities. Parameters such as dark counts, timing jitter, and responsivity will be shown for the compact detection module. Our findings show that the proposed avalanche photodiode operation is considerably faster than the conventional discrete systems and the module size is greatly reduced.

Silicon photomultipliers for improved biomolecule detection

There is a need for low cost, miniature, integrated optical systems for bioassay monitoring to meet the growing in vitro and point-of-care diagnostics markets. To this end, we are investigating the use of silicon photomultipliers (SiPM) as device upon which to base our technology development. SiPMs have been used successfully in many high-energy physics applications, but their application as a fully integrated biological detection platform has not been shown. In this paper we will present a new detection platform for the measurement of fluorescent biomolecules at much lower concentrations than commercially available systems. Our results show approaches that demonstrate the use of SiPM for the detection of fluorescent proteins and fluorescent-labelled DNA sequences. The SiPM and sample platforms are integrated so that the minimum distance separating the detector from the sample is realised. In addition, direct immobilisation of the DNA sequences onto the SiPM surface is achieved. This combined approach shows improved sensitivities for both the fluorescent proteins and fluorescent-labelled DNA. We are presenting results that show the use of SiPM as a successful technology for the measurement of fluorescent biomolecules at improved lower concentrations.

Bioassay platform for fiber coupled avalanche photodiode for improved biomolecule detection

For future fully integrated sensing applications, a CMOS sensor will be required. New CMOS photon counting sensors have recently become available and these devices provide high quantum efficiency, photon counting sensitivity, low power and new devices in arrays and with on-chip electronics. In biological applications, photon counting is focused on the detection of low intensity fluorescence signals from fluorophores conjugated to proteins or nucleic acid biomarkers from fluorescent proteins. We describe the development of a novel microtitre plate reader format, or bioassay platform that incorporates arrays of photon counting detectors for multiple parallel readout and data acquisition. Using Pyrex wafers, we have designed and fabricated custom-made reaction wells using Pyrex and deep ion trench etched silicon, which produce optically clear structures to facilitate fluorescence detection in biological samples volumes of 2 nL to 2 μL. For initial verification of the system, a new photon counting detector from SensL is used to determine the effectiveness of the wells as the bioassay platform. The compact unit consists of a fibre coupled silicon photon counting sensor, thermoelectric cooler, thermoelectric controller, active quenching circuit, power supplies, and an USB interface to the operating software. Included in the module is a counter with time binning capability. Sensitivity increases of more than two orders of magnitude in fluorescence detection are expected over commercially available instruments. This system demonstrates that a miniaturized, low cost solution is possible for fluorescence bioassay detection, which can be used to meet growing demands in the in vitro diagnostics and Point of Care markets.