Optical Sensor for Real-Time pH Monitoring in Human Tissue.

This article reports on a fiber-based ratiometric optical pH sensor for use in real-time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol-gel-based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model.

In situ generation of plasmonic cavities for high sensitivity fluorophore and biomolecule detection.

Plasmonic cavities are widely studied for the large amplifications in fluorophore emission intensity that they can achieve. Exploiting these properties for biological sensing applications requires strategies to selectively insert the target antigen into a resonant cavity, which are often of similar size or smaller than the target molecule. Here we demonstrate that using relatively simple solution processing, cavity structures can be grown at the stochastic locations where antigen binding takes place, which yields large enhancements in fluorophore emission intensities and over an order of magnitude improvement in bioassay response.

Controlled surface plasmon enhanced fluorescence from 1D gold gratings via azimuth rotations.

We demonstrate a method to maximise the fluorescence enhancement from a dye using gold coated diffraction gratings. Rotations about the azimuth provides a convenient approach to maximise the coupling between the grating and excitation source while achieving enhancements comparable to traditional optical configurations where the grating and in plane light vectors are parallel. This approach yields a 30 fold enhancement in the fluorescence signal over metal free substrates, while opening up the range of possible orientations and configurations suitable for fluorescence enhancement applications.

Cyanine5-doped silica nanoparticles as ultra-bright immunospecific labels for model circulating tumour cells in flow cytometry and microscopy.

In this work, ultra-bright fluorescent silica nanoparticles (NPs) labels have been shown to selectively bind to a model circulating tumour cell (CTC) line, MCF-7, a metastatic breast cancer by targeting epithelial cellular adhesion molecule (EpCAM) present on the MCF-7 cell membrane. Silica NPs approximately 40nm in diameter were doped with different concentrations of Cyanine5 dye molecules, using the reverse microemulsion method. The NPs were two orders of magnitude brighter than Cyanine5 free dye and the measured fluorescence intensity matched a homo-Förster Resonance Energy Transfer model.

Baking Powder Actuated Centrifugo-Pneumatic Valving for Automation of Multi-Step Bioassays.

We report a new flow control method for centrifugal microfluidic systems; CO₂ is released from on-board stored baking powder upon contact with an ancillary liquid. The elevated pressure generated drives the sample into a dead-end pneumatic chamber sealed by a dissolvable film (DF). This liquid incursion wets and dissolves the DF, thus opening the valve.

Investigating the colloidal stability of fluorescent silica nanoparticles under isotonic conditions for biomedical applications.

Fluorescent silica nanoparticle (NP) labels are of great interest in biomedical diagnostics, however, when used in bioassays under physiological conditions they rapidly agglomerate and precipitate from solution leading to high levels of non-specific binding. In this work, using size and zeta-potential data obtained from Dynamic and Electrophoretic Light Scattering analysis, the improvement in colloidal stability of silica NPs under physiological conditions was correlated with an increase in the concentration of three additives: (1) a protein, bovine serum albumin (BSA); (2) a neutral surfactant, Tween 20®; and (3) a charged surfactant, sodium dodecyl sulfate (SDS). The number of BSA molecules present in the NP corona at each concentration was calculated using UV-Vis spectroscopy and a bicinchoninic acid protein assay (BCA).

High efficiency ring-lens supercritical angle fluorescence (SAF) detection for optimum bioassay performance.

We present a polymer biochip with embedded optics which allows the detection of supercritical angle fluorescence (SAF) without losses due to total internal reflection within the substrate. The chip design comprises structured spherical and aspherical optical elements on the bottom, while the top is chemically functionalized for direct binding of biomolecules. Furthermore, this design facilitates integration in lab-on-a-chip systems with appropriate microfluidics.

A chemical quenching- and physical blocking-based method to minimize process-mediated aggregation of antibody-crosslinked nanoparticles for imaging application.

Critical limitation of nanoparticles (NP) is their aggregation after functionalisation and antibody cross-linking. We analysed the cause of this aggregation with respect to functionalities (carboxyls and amines) on the NP surface. We have devised a low cost novel method to reduce such aggregations during protein cross-linking and validated it by probing the platelet surface with platelet surface-specific anti-CD41 antibody conjugated NPs.

At-line bioprocess monitoring by immunoassay with rotationally controlled serial siphoning and integrated supercritical angle fluorescence optics.

In this paper we report a centrifugal microfluidic "lab-on-a-disc" system for at-line monitoring of human immunoglobulin G (hIgG) in a typical bioprocess environment. The novelty of this device is the combination of a heterogeneous sandwich immunoassay on a serial siphon-enabled microfluidic disc with automated sequential reagent delivery and surface-confined supercritical angle fluorescence (SAF)-based detection. The device, which is compact, easy-to-use and inexpensive, enables rapid detection of hIgG from a bioprocess sample.

Dendrimer driven self-assembly of SPR active silver-gold nanohybrids.

A fourth generation PAMAM dendrimer has been successfully employed for the development of a single step synthesis strategy for self-assembled Ag-Au nanohybrid structures. The surface plasmon resonance properties and the degree of self-assembly of the nanohybrid are strongly correlated with the stoichiometry of the metals which gives rise to enhanced plasmonic properties. The enhanced plasmonic response of the nanohybrids is modeled and is validated experimentally in a model HRP (horseradish peroxidise) bioassay carried out on an SPR-based biochip platform.

Optimization of size, morphology and colloidal stability of fluorescein dye-doped silica NPs for application in immunoassays.

Fluorescent nanoparticle (NP) labels are of great interest for point-of-care medical diagnostics where high fluorescence signals combined with low limits of detection are required. In this work, hydrophilic and hydrophobic fluorescein dye derivatives were covalently doped into silica NPs. The NPs were prepared in a range of sizes from 16 to 80 nm using both ternary and quaternary microemulsion methods where the diameter varied linearly with changes in the water to surfactant ratio.

Synthesis and characterization of model silica-gold core-shell nanohybrid systems to demonstrate plasmonic enhancement of fluorescence.

In this work, gold-silica plasmonic nanohybrids have been synthesized as model systems which enable tuning of dye fluorescence enhancement/quenching interactions. For each system, a dye-doped silica core is surrounded by a 15 nm spacer region, which in turn is surrounded by gold nanoparticles (GNPs). The GNPs are either covalently conjugated via mercapto silanization to the spacer or encapsulated in a separate external silica shell.

Inhibition of neuroblastoma tumor growth by targeted delivery of microRNA-34a using anti-disialoganglioside GD2 coated nanoparticles.

Background: Neuroblastoma is one of the most challenging malignancies of childhood, being associated with the highest death rate in paediatric oncology, underlining the need for novel therapeutic approaches. Typically, patients with high risk disease undergo an initial remission in response to treatment, followed by disease recurrence that has become refractory to further treatment. Here, we demonstrate the first silica nanoparticle-based targeted delivery of a tumor suppressive, pro-apoptotic microRNA, miR-34a, to neuroblastoma tumors in a murine orthotopic xenograft model.

Synthesis and characterization of a Noble metal Enhanced Optical Nanohybrid (NEON): a high brightness detection platform based on a dye-doped silica nanoparticle.

A highly bright and photostable, fluorescent nanohybrid particle is presented which consists of gold nanoparticles (GNPs) embedded in dye-doped silica in a core-shell configuration. The dye used is the near-infrared emitting 4,5-benzo-5'-(iodoacetaminomethyl)-1',3,3,3',3'-pentamethyl-1-(4-sulfobutyl) indodicarbo cyanine. The nanohybrid architecture comprises a GNP core which is separated from a layer of dye molecules by a 15 nm buffer layer and has an outer protective, undoped silica shell.

Label-free optical characterization methods for detecting amine silanization-driven gold nanoparticle self-assembly.

Fluorescence lifetime correlation spectroscopy (FLCS) is presented as a single-step label-free detection method for probing the amine silanization-driven spontaneous 3D self-assembly of freestanding gold nanoparticles (GNPs) in solution. Unlike the conventional methods of studying self-assembly, for example, UV-vis spectroscopy and electron microscopy, FLCS utilizes the intrinsic gold fluorescence. The significance of this approach is to amalgamate the measurement of optical and hydrodynamic size properties simultaneously to achieve a more coherent description of the self-assembly pathway.

Dextran-coated silica nanoparticles for calcium-sensing.

This article describes the synthesis and characterisation of fluorescent composite nanoparticles consisting of a silica core and a dextran shell. The silica core contains a rhodamine-based reference dye, which allows ratiometric measurements and the dextran shell is labelled with the Ca(2+)-sensitive dye Fluo-4. The nanoparticles have an average hydrodynamic diameter of 95 nm, good colloidal stability and show a 2.

Signal enhancement of surface plasmon-coupled emission (SPCE) with the evanescent field of surface plasmons on a bimetallic paraboloid biochip.

We present a novel approach to the enhancement of surface plasmon-coupled emission (SPCE) using surface plasmon excitation in a bimetal (Ag/Au) layer and we validate the enhancement by presenting the results of a model human IgG immunoassay. Theoretical calculations using Fresnel's equations have been carried out to determine the optimum bimetallic composition and the resulting electric field enhancement. Signal enhancement of SPCE was confirmed using a range of bimetallic layers which were deposited on the surface of a high collection efficiency polymer array biochip and subsequently immobilized with Alexa Fluor 647 labeled anti-human IgG.

Novel multiparametric approach to elucidate the surface amine-silanization reaction profile on fluorescent silica nanoparticles.

This Article addresses the important issue of the characterization of surface functional groups for optical bioassay applications. We use a model system consisting of spherical dye-doped silica nanoparticles (NPs) that have been functionalized with amine groups whereby the encapsulated cyanine-based near-infrared dye fluorescence acts as a probe of the NP surface environment. This facilitates the identification of the optimum deposition parameters for the formation of a stable ordered amine monolayer and also elucidates the functionalization profile of the amine-silanization process.

Ratiometric fluorescence-based dissolved carbon dioxide sensor for use in environmental monitoring applications.

The focus of this work is on the development and characterisation of a fluorescence-based ratiometric sol-gel-derived dissolved carbon dioxide (dCO(2)) sensor for use in environmental monitoring applications. Fluorescence-based dCO(2) sensors are attractive as they facilitate the development of portable and low-cost systems that can be easily deployed outside the laboratory environment. The sensor developed for this work exploits a pH fluorescent dye 1-hydroxypyrene-3,6,8-trisulfonic acid, ion-paired with cetyltrimethylammonium bromide (HPTS-IP), which has been entrapped in a hybrid sol-gel-based matrix derived from n-propyltriethoxysilane along with the liphophilic organic base.

Fluorescence lifetime analysis and fluorescence correlation spectroscopy elucidate the internal architecture of fluorescent silica nanoparticles.

Fluorescence lifetime (FL) analysis and fluorescence correlation spectroscopy (FCS) have been successfully employed to reveal detailed information about the internal architecture of fluorescent silica nanoparticles (NPs). The dual-component lifetime behavior shows a two-domain dye distribution in the NP as a function of solvent accessibility. The introduction of an undoped silica shell serves to stabilize the outer dye fraction that is manifest as an increase in lifetime.

Demonstration of a surface plasmon-coupled emission (SPCE)-based immunoassay in the absence of a spacer layer.

The technique of surface plasmon-coupled emission (SPCE) involves the coupling of light which is emitted from a fluorophore into the surface plasmon of an adjacent thin metal film, giving rise to highly directional emission. We have combined the advantages of SPCE with the high light collection efficiency of supercritical angle fluorescence by carrying out an immunoassay on a paraboloid array biochip in the absence of the conventional SPCE spacer layer normally used to minimize metal quenching of the fluorescence. In this work, we have successfully demonstrated an SPCE-based assay by utilizing the protein assay layer as the spacer layer.

Fabrication and performance evaluation of highly sensitive hybrid sol-gel-derived oxygen sensor films based on a fluorinated precursor.

This paper describes the fabrication and performance of a range of highly sensitive luminescence-based oxygen sensor films based on the fluorinated sol-gel precursor 3,3,3-trifluoropropyltrimethoxysilane (TFP-TMOS). The oxygen-sensitive ruthenium complex [Ruthenium(II)-tris(4,7-diphenyl-1,10-phenanthroline)] dichloride, [Ru(dpp)(3)](2+) was entrapped in a wide range of ORMOSILs (organically modified silicates) matrices composed of alkyl and TFP-TMOS sol-gel precursors in different relative ratios. The influence of TFP-TMOS on sensor sensitivity, humidity-sensitivity and long-term stability was investigated and performance was compared to that of similar but non-fluorinated films.

Enhancing the analytical performance of immunoassays that employ metal-enhanced fluorescence.

In this work, we used a model assay system (polyclonal human IgG-goat antihuman IgG) to elucidate some of the key factors that influence the analytical performance of bioassays that employ metal-enhanced fluorescence (MEF) using silver nanoparticles (NPs). Cy5 dye was used as the fluorescent label, and results were compared with a standard assay performed in the absence of NPs. Two sizes of silver NPs were prepared with respective diameters of 60 +/- 10 and 149 +/- 16 nm.

Surface plasmon-coupled emission (SPCE)-based immunoassay using a novel paraboloid array biochip.

We have carried out a human IgG immunoassay on a novel disposable optical array biochip using surface plasmon-coupled emission (SPCE) detection. The work successfully combines the advantages of the highly directional SPCE emission profile and enhanced surface plasmon excitation with the high light collection efficiency achieved using supercritical angle fluorescence (SAF). This is achieved using an array of transparent paraboloid polymer elements which have been coated with a thin gold layer to facilitate SPCE.