Microbiosensor based on an integrated thermopile

Optical sensor arrays for chemical sensing: the optoelectronic nose

A comprehensive review is presented on the development and state of the art of colorimetric and fluorometric sensor arrays. Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties. This provides a high dimensionality to chemical sensing that permits high sensitivity (often down to ppb levels), impressive discrimination among very similar analytes and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, both in the gas and liquid phases.

Thermal Biosensor and Microbiosensor Techniques

This chapter describes principles and features of thermal biosensors and microbiosensors and includes a discussion of different thermal transducers. A number of instrumental concepts are described in detail from larger flow injection instruments to miniaturized devices and chip designs with thermal arrays. A thermal–electrochemical hybrid sensor is also presented. The chapter contains many descriptions of actual assays from different fields, such as process and in vivo monitoring, multianalyte determination, operation in organic solvents, and environmental analysis.

Theory and Experiments of MEMS Thermal Biosensors

This paper presents a theoretical and experimental investigation of MEMS thermal biosensors in flow-through measurements of metabolites. A model is developed to consider convective heat transfer effects and enzyme kinetics using the Michaelis-Menton theory. Numerical solutions from the model are compared with experimental data obtained from a prototype MEMS thermal biosensor. Satisfactory agreement is found between the theoretical and experimental results, indicating that the model is useful for designing MEMS thermal biosensors with optimized performance.

Noninvasive picoliter volume thermometry based on backscatter interferometry

Using the on-chip refractive index (RI) detector based on backscatter interferometry, sensitive, small volume, noninvasive thermometry can be performed. The current optical configuration for the on-chip interferometric backscatter detector (OCIBD) is quite simple and consists of an unfocused laser, an unaltered chip with a hemispherical channel and a photodetector. Alignment is straightforward with the only requirement being that the beam fully fills the channel. The interaction of an unfocused laser beam with the uncoated etched channel with a curvature within the silica plate (chip) produces fringes whose positional changes scale with respect to the refractive index (RI), n, of the fluid in the channel. Due to the inherently high value of dn/dT for most fluids and the high sensitivity of OCIBD to RI changes, the measurement of small temperature variations in sub-nanoliter volumes is possible. Performing OCIBD with a 75 microm diameter laser beam on a silica chip that contains an etched channel with a 40 microm radius facilitates noninvasive thermometry on a N-(2-hydroxyethyl)piperazine-(2-ethanesulfonic acid) (HEPES) solution in a 188 x 10(-12) L probe volume with a temperature resolution of 9.9 x 10(-4) degrees C, at the 99% confidence level.

Thermal biosensors in biotechnology

The application of enzyme thermistor devices for the continuous monitoring of enzymatic processes is described. Different hardware concepts are presented and discussed, practical results are also given. These devices were used to analyze the enantiomeric excess in biotransformation processes and for thermal immunoanalysis. In addition, the biosensors were applied for the monitoring and control of an L-ornithine producing process and for the application in hemodialysis monitoring. A review section discusses the use of thermal biosensors for monitoring biotechnological processes in general.

Principles and applications of flow injection analysis in biosensors

In practical applications biosensors are often forced to operate under less than optimal conditions. Because of their construction, and the physical processes and chemical reactions involved in their operation, compromise conditions are frequently required to synchronize all events taking place. Therefore, and in order to implement functions such as periodic calibration, conditioning and possible regeneration of the biosensor, and, very importantly, to yield the freedom to select the optimum detection means, it is advantageous to use these devices in a flow-through mode, particularly by employing the flow injection (FI) approach. The capacity of FI, as offering itself as a complementary facility to augment the performance of biosensors, and in many cases as an attractive alternative, is demonstrated by reference to selected examples, comprising assays based on enzymatic procedures with optical and thermal detection procedures, and via description of a recently introduced technique for immunoassays, termed flow injection renewable surface immunoassays, which promises to entail powerful potentials and to yield compatible or better economy of operation than existing approaches.