Microparticle sensor

Figure 5. Microparticle Sensor Design. In this design, microparticles release reagent into a polyacrylamide layer, reacting with analyte that has diffused in from the bulk solution.

Figure 6. Cumulative Release of HPTS from EVA Microparticles. Sensors were fabricated and soaked in pH 7.8 phosphate buffer. The release of HPTS from microparticles entrapped in polyacrylamide on sensor tips was monitored by measuring the increase in fluorescence intensity over 300 hours.

Figure 7. Microparticle Sensor Response Time. The arrows show when the sensor was placed in the respective pH buffer. Measurements were taken at various intervals over 20 minutes.

Figure 8. Microparticle Sensor Titration Curve. A sensor was place in a series of six buffers of different pHs. After the sensor signal stabilized, the intensity at the respective excitation and emission wavelengths was collected 405nm and 515nm 450nm and 515nm. The ratio at these intensities was plotted against pH.

Figure 9. Fluorescent Irreversible Indicators that are Adaptable to the Microparticle Sensor Design.

Figure 10. Proposed Adaptation of a Fluorescence Energy Transfer Immunoassay to the Microparticle Sensor Design. A mixture of two different microparticles, each containing different reagents, are entrapped physically in the polyacrylamide layer. The reagents released from the microparticles set up a competition reaction between the free and labeled antigens for the available binding sites of labeled-antibody. The immunocomplexes formed have different emission spectra, allowing quantitation of free antigen concentration.

There is a wealth of literature on transport and kinetics in microhetero-geneous catalytic systems [175,176], the influence of particle size [177], and complicated situations in which both catalytic microparticles and electron-transfer mediators are dispersed in a polymer matrix [176-179]. The designs and uses of this type of flow-through sensors have been thoroughly reviewed [180,181]. 

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Time-of-flight (TOF) measurement is popular in microflow measurements. The time of flow of a pulse of temperature or of molecular tracers from one point in a microchannel to another point is characterized to measure the flow rate. An emitter and a collector are integrated into TOF sensors. Various optimizations of these sensors have been carried out, using temperature pulses or electrochemical production of molecular tracers. These sensors calculate the flow rate at one point in the cross section of the channel and are calibrated with a known flow rate. Flow measurementusing microparticles captures the velocity profile at many such locations in the channel cross section and allows one to calculate the flow rate. Figure 4 shows the principle of a flow sensor using a CFD simulation of convective diffusion... 

Park W, Lee HS, Park H, Kwon S (2009) Sorting microparticles by orientation using wedged-fin and railed microfluidics. In TRANSDUCERS 2009-2009 international solid-state sensors, actuators and microsystems conference, Denver, Colorado, pp 429 32... 

The ubiquitous temperature effects on luminescent sensors can be referenced and compensated with dual luminophore preparatiOTis. Several approaches of dual optical sensors have been demonstrated, that can be used for simultaneous determination of oxygen and temperature, or CO2 and temperature, respectively [114,115]. Luminescent temperature indicators have also been employed as reference components in PSPs (see Sect. 3.1). These have foimd widespread application in fluid mechanics and aerodynamic wind tunnel tests. The real-time imaging of dynamic flow processes on model surfaces are of high significance for aerospace and car industry. To avoid interferences or energy transfer between the oxygen and temperature sensitive dyes, these can be incorporated into different types of polymer microparticles [116]. 

Examples of such chemosensors have been outlined including oxygen (or air pressure), pH, humidity, hydrogen peroxide, copper, and temperature sensors. However, the encapsulation of lanthanide probes in sohd state matrices or polymer nano- or microparticles can contribute to reduce the impact of interfering agents. Many polymers provide a selective permeability and block certain species. A number of copolymers, particularly block copolymers, are available that on the one hand are well suited for the immobilization of lanthanide complexes, and on the other hand hinder the diffusion of certain interfering species into the layer. 

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