Four-channel enzyme thermistor system for process monitoring and control in biotechnology

Mediatorless, Reversible Optical Nanosensor Enabled through Enzymatic Pocket Doping

Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic near-infrared fluorescence that benefits from indefinite photostability and tissue transparency, offering a promising basis for in vivo biosensing. Existing SWCNT optical sensors that rely on charge transfer for signal transduction often require exogenous mediators that compromise the stability and biocompatibility of the sensors. This study presents a reversible, mediatorless, near-infrared glucose sensor based on glucose oxidase-wrapped SWCNTs (GOx-SWCNTs). GOx-SWCNTs undergo a selective fluorescence increase in the presence of aldohexoses, with the strongest response toward glucose. When incorporated into a custom-built membrane device, the sensor demonstrates a monotonic increase in initial response rates with increasing glucose concentrations between 3 × 10^-3 and 30 × 10^-3 m and an apparent Michaelis-Menten constant of K_M (app) ≈ 13.9 × 10^-3 m. A combination of fluorescence, absorption, and Raman spectroscopy measurements suggests a fluorescence enhancement mechanism based on localized enzymatic doping of SWCNT defect sites that does not rely on added mediators. Removal of glucose reverses the doping effects, resulting in full recovery of the fluorescence intensity. The cyclic addition and removal of glucose is shown to successively enhance and recover fluorescence, demonstrating reversibility that serves as a prerequisite for continuous glucose monitoring.

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 biosensors for bioprocess monitoring and control

Biosensors are useful analytical devices that can be integrated with on-line process monitoring schemes. In this article, the principles and applications of these devices for bioprocess monitoring are considered. Several different types of biosensors are described, and the applications and limitations of flow injection analysis (FIA) for these applications are discussed. It is hoped that the background provided here can be useful to researchers in this area.

Applied biosensors

Biosensors are important analytical tools in clinical and environmental monitoring, biotechnological process control, medicine, and in the food and drink industry. This review devotes attention to the most common biosensor in biotechnology, the glucose biosensor, and to recent contributions to the rapidly growing field of optical biosensors. Trends and developments in these areas are discussed.

An integrated silicon thermophile as biosensor for the thermal monitoring of glucose, urea and penicillin

A new kind of calorimetric biosensor for the measurement of the heat (molar enthalpy change) of enzymatic reactions is presented. The device operates according to the Seebeck effect, the same principle on which thermocouples are based. The thermopile used in this work consists of an array of p-type silicon/aluminium strips integrated on a thin silicon membrane (5 microns). Its sensitivity is about 1 V output voltage per watt of heating power, corresponding to a temperature resolution in the order of 10(-5) K and a heating power resolution of some tenths of a mu W in the flow system used. Furthermore, this performance is obtained without any control of external temperature because of the high common-mode thermal noise rejection ratio of the thermopile. The universal technique of calorimetry combined with the specificity of biochemical reactions makes this biosensor very versatile, with a broad range of possible applications. Glucose oxidase together with catalase for the determination of glucose, urease and penicillinase for the monitoring of urea and penicillin G, respectively, were immobilized directly onto the back side of the thermopile. The sensor was operated in conjunction with flow injection analysis which, in addition to its traditional advantages, allows preconditioning of the samples. Thus, artefacts due to mixing effects were suppressed and interference caused by differences in ionic strength between sample and carrier was strongly decreased. Detection limits between 1 and 2 mM were reported in the flow injection conditions described.

Biosensors for process monitoring

A short review about the biosensor research activities for bioprocess monitoring in the F.R.G. after its reunification is given. The principles of biosensor applications are presented. In situ sensors and sensors based on the principles of flow injection analysis are studied. Some applications of a four-channel enzyme thermistor, bio-field effect transistors, and immunoanalysis systems for real process monitoring are presented.