Susan L. R. Barker

Subcellular optochemical nanobiosensors: probes encapsulated by biologically localised embedding (PEBBLEs)

Abstract Described here are arguably the worlds smallest stand-alone devices/sensors, consisting of multicomponent nano-spheres with radii as small as 10 nm, occupying ≈1 ppb of a typical mammalian cell’s volume. The probe is prepared from up to seven ingredients and is optimised for selective and reversible analyte detection, as well as sensor stability and reproducibility. Such a sensor probe encapsulated by biologically localised embedding (PEBBLE), is delivered into a cell by a variety of minimally-invasive techniques, including a pico-injector, a gene gun, liposomal incorporation and natural ingestion. These remote nano-optodes (PEBBLEs) have been prepared for pH, calcium, magnesium, potassium and oxygen. The sensor PEBBLEs can be inserted into a cell individually, in clusters (single analyte), in sets (multi-analyte) or in ensembles (single analyte, multiple locations).

Anion-selective liquid-polymer optodes with fluorescent pH chromoionophores, tunable dynamic range and diffusion enhanced lifetimes

Abstract The present work demonstrates the ability to extend coextraction based anion optodes into the fluorescence regime for the purpose of miniaturization. These optodes utilize standard ion-selective electrode ionophores with universal pH chromoionophores that have been selected for their fluorescence efficiency, photo-stability and p K a based tunability of the optimal activity range. The miniaturization of the photo-excitation zone enhances the optode lifetime, due to fast diffusion of unbleached chromoionophores into this zone. Specifically, we provide here examples of charged and neutral-carrier ionophore based fluorescent optodes, one highly selective for nitride and the other selective for thiocyanate. The ability to tune the dynamic range of the nitrite-selective optode is also demonstrated.

Fabrication, derivatization, and applications of plastic microfluidic devices

Control of the polymer surface chemistry is a crucial aspect in the development of plastic microfluidic devices. When commercially available plastic substrates are used to fabricate microchannels, differences in the electroosmotic flow (EOF) from plastic to plastic can be very high. Therefore, we have used polyelectrolyte multilayers (PEMs) to alter the surface of microchannels fabricated in plastics. The PEMs are easily fabricated and provide a means for controlling the flow direction and the electroosmotic mobility in the channels. Optimal modification of the microchannel surfaces was obtained by coating the channels with alternating layers of poly(allylamine hydrochloride) and poly(styrene sulfonate). The efficacy of the surface modification has been evaluated by measuring the electroosmotic flow mobility. When microchannels prepared in different polymer substrates were modified with PEMs, they demonstrated very similar electroosmotic mobilities. The PEMs have also been used to immobilize chemically selective molecules in the microchannels. In addition, relatively complex flow patterns, with simple arrangements of applied voltages, have been realized by derivatization of different arms of a single device with oppositely charged polyelectrolytes. Flow in opposite directions in the same channel is also possible; a positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows.

Derivatization of Plastic Microfluidic Devices With Polyelectrolyte Multilayers

Microchannels fabricated in plastic materials by room temperature imprinting demonstrate large variability in surface charge as a result of the fabrication procedure. Surface charged groups are primarily localized on the channel walls and not on the channel floor resulting in differences in adsorption properties in the channel. Polyelectrolyte multilayers can be used to effectively coat the plastic microchannel surface with high reproduciblity and excellent stability. We show that polyelectrolyte multilayers can be used to alter both direction and rate of flow in plastic microchannel devices.

Anion selective optodes: development of a fluorescent fiber optic sensor for the determination of nitrite activity

The response of state of the art anion optodes often cannot be described in a thermodynamically exact manner because the ionic strength within the membrane phase of such optodes changes during the course of a titration. Incorporating lipophilic charge sites in the anion optode membranes provides a constant ionic strength in the membrane phase, the ability to measure anion activities, and a more thermodynamically describable system. This configuration has been used to create a micrometer-sized nitrite-selective optode. Recent elucidation of the many biological roles of nitric oxide (NO) has spurred interest in sensitive and selective detection of this molecule. In biological systems NO is converted to NO2- within 30 sec and the biological concentration of NO2- is normally on the micromolar level. The optode we have prepared contains a selective vitamin B12 derivative ionophore, a fluorescent chromoionophore (ETH 2439 or ETH 5350), and lipophilic charge sites. These components are entrapped in a highly plasticized PVC matrix which is placed on the distal end of the fiber. Sensor characteristics such as limit of detection and reversibility are presented.