Biosensors, Porous Silicon

Abstract

Biosensors consist of a biologically active layer that responding to an analyte in solution and a powerful transducer that transforms and amplifies the reaction into a measurable signal. Biosensors can constantly measure the presence, absence, or concentration of specific organic or inorganic substances in short response time and ultimately at low cost. They are used commercially in health care, biotechnological process control, agriculture, veterinary medicine, defense, and environmental pollution monitoring. A common requirement of all of these applications is on‐site chemical information—preferably in real time—on some dynamic or rapidly evolving process. Most biosensors are based on molecular events as they take place at the cellular membrane or inside the cell involving enzyme cascades. Their perceived advantages over existing technologies include the ability to monitor broad or narrow spectra of analytes continuously in real time, and their weakness is the instability of the biological molecules outside their natural environment, which results in a restricted lifetime for the device. The challenge is to find a matrix for biomolecules that provides high compatibility of the material with biological substances, low‐cost fabrication, and special optical and electrical properties to generate a signal that measures the interaction between analytes in solution and the receptive biological layer. It is also desirable that it be compatible with conventional microfabrication techniques to miniaturize the device or to build individually addressable arrays. The high surface area in conjunction with its unique optical and electrical properties and its compatibility with silicon microelectronics fabrication techniques has led to the proposal that porous silicon may be a suitable material for building sensor devices. Several different transducer schemes have evolved based on thin film interference, capacitance changes, and the photoluminescent properties of porous silicon and these are discussed.