The present invention provides an apparatus and method for enhancing the response of a biometric sensor for sensing toxins by measuring the rate of change of sensor readings. An LED, optically coupled to the sensor and a photodiode, transmits light through the sensor to the photodiode. The photocurrent from the photodiode is converted to a digital sensor reading value proportional to the darkness of the sensor and is loaded into a microprocessor. In the microprocessor, the sensor readings are essentially differentiated to determine the rate of change of the sensor readings. The rate of change information is used to trigger an alarm condition indicative of a predetermined level of sensed toxins.

The present invention provides an apparatus and method for enhancing the response of a biometric sensor for sensing toxins by measuring the rate of change of sensor readings. An LED, optically coupled to the sensor and a photodiode, transmits light through the sensor to the photodiode. The photocurrent from the photodiode is converted to a digital sensor reading value proportional to the darkness of the sensor and is loaded into a microprocessor. In the microprocessor, the sensor readings are essentially differentiated to determine the rate of change of the sensor readings. The rate of change information is used to trigger an alarm condition indicative of a predetermined level of sensed toxins.

A detector system for sensing the presence of a toxic gas, such as carbon monoxide, and sounding an alarm. The presence of the gas is detected by passing light through a biomimetric sensing material that darkens in the presence of the gas. The system includes a housing containing a light emitter, a light detector and a mechanism for sounding an alarm. The sensing material is contained in a cell, which, together with a battery to power the system, are mounted in a drawer insertable into the housing, which has openings permitting ambient air to reach the sensing material. When fully inserted, the drawer positions the cell between the emitter and detector and brings battery contacts into connection with contact s for the light emitter and alarm. Both the battery and sensing material must be replaced periodically, typically about once every three years. The drawer is configured so that it cannot be inserted without a battery in place. Both the battery and cell are easily replaced in the drawer. A microporous filter is preferably placed between the cell and ambient air to prevent contamination by large airborne particles.

A three-dimensional structure of porous silicon considerably improves the anchorage of sensor-active material such as, for example, enzymes, antibodies, etc., on or in the substrate surface of chemical sensors, in particular silicon-based biosensors. This structure is produced by means of suitable etching which forms pore apertures adapted to the penetrability of the sensor-active material. The pore walls advantageously receive a non-conductive boundary layer which consists of oxides of Si and/or Al or Ta or silicon nitride and are preferably 1-100 nm thick. The porous layer is advantageously between 10 nm and 100 .mu.m thick and the pores are preferably in the form of branched ducts whose average diameter is 1 nm-10 .mu.m and in particular 10-1000 nm. The sensor-active material can optionally be distributed in a glass, solid, plastics or polymer membrane.

Disclosed are oxygen concentration and/or pressure sensing devices and methods which incorporate photoluminescent silica aerogels. Disclosed sensors include a light proof housing for holding the photoluminescent aerogel, a source of excitation radiation (e.g., a UV source), a detector for detecting radiation emitted by the aerogel, a system for delivering a sample gas to the aerogel, and a thermocouple. Also disclosed are water resistant oxygen sensors having a photoluminescent aerogel coated with a hydrophobic material.