This article provides notes on biosensors.
Biosensors are analytical devices that show potential for development in the clinical, diagnostic, food analysis, process control, and environmental areas. Examples of commercially available biosensors include enzyme electrode biosensors for detection of glucose in blood and single analytes in food, as well as biological oxygen demand (BOD) in waste water.
Biosensors historically have been viewed as a class of chemical sensors that use biological recognition rather than chemical reactions to measure small organic compounds such as glucose. The use of biological recognition coupled to a signal transducer (e.g. electrochemical, optical, thermal or acountic) has required a certain degree of multidisciplinary approaches.
Considering the need for field analytical methods in the environmental areas, the wide variety of biosensors reported for potential environmental applications provide an interesting opportunity. The recent introduction of a variety of applied methods and technologies such as flow injection analysis and fluorescent techniques as well as the use of genetically engineered microorganisms (GEMS) has further blurred the classical concept of a biosensor as an enzyme electrode.
A overview of biosensor components are shown in Fig. 12.2.
Biosensors are classified or grouped in several different ways:
1. Chemical sensors
2. Biosensors, with physical transducers
Recently reported biosensors for potential environmental applications measure a fairly broad spectrum of environmental pollutants including pesticides, organic compounds, metals, and biological parameters (Table 12.3). Although these prototype biosensors have been demonstrated primarily using laboratory standards in buffer solutions, a number have been tested using matrices such as waste water, surface water, and mixed organics.
In addition, several of these devices are undergoing field trials in environmental settings. Many of the compounds targeted by these biosensors reflect environmental pollutants of national concern. For example, a wide range of organophosphate and carbamate insecticides have been measured using cholinesterase-based biosensors.
For herbicide detection, antibody-base biosensors that measure triazines, imadazolinones, and 2, 4-D have been reported. Biosensors based on inhibition of Photo System II have been used to measure a wide array of herbicides and biosensors using GEMS have been used to measure pesticides such as meturon and propanil.
A variety of organic compounds shown to contaminate superfund sites throughout the United States can be detected by a number of reported biosensors. These include enzyme-based biosensors for detection of phenolics, organophosphates, and cyanide; antibody-based biosensors for PCBs, potent carcinogens such as benzo(a)pyrene, and explosives such as TNT and RDX; and microbial biosensors for toxicants such as benzene and ammonia.
GEMs have been incorporated into biosensors that are specific for particular heavy metals such as mercury and copper, or that respond nonspecifically to metals such as lead, cadmium, chromium, and manganese, as well as to other pollutants such as benzalkonium ions, laurel sulfate, and 3-chloro-benzene.
In addition to specific compounds, biosensors have been reported to measure a variety of biological parameters, including BOD, biomarkers of human exposure, potential carcinogens, bioremediation efficiency, and bacterial identification or enumeration.
The BOD biosensors have been developed arid tested primarily in Japan and Europe. The short response time (i.e., 15 min compared to 5 d for classical determinations), make these devices particularly useful in process control applications for waste water treatment in which rapid analyses are required.
Biomarkers of human exposure is another area currently gaining attention (see BIOMARKERS). Fiber optic antibody-based biosensor technology recently was developed for detection of DNA adducts such as benzo(a)pyrenetetrol.
This compound is a potent carcinogen and has been shown to be a frequent co-contaminant with other polycyclic aromatic hydrocarbons (PAHs). Biosensor methods also have been developed to measure potential carcinogens through their ability to intercalate into DNA. This DNA-based fiber optic biosensor detects a wide range of potentially carcinogenic polyaromatic hydrocarbons.
Although bacteria are not typically considered to be environmental pollutants, there are a number of circumstances where field monitoring for these microorganisms is important and biosensor methods may prove to be a cost-effective alternative to classical methods.
For example, when bioremediation is used for decontamination of toxic compounds in the environment, it is crucial (especially in the case of GEMs) that the fate and transport processes of these organisms is well defined. Biosensor demonstrated to detect organisms of clinical interest potentially could be developed for environmental applications.
Developing biosensors for environmental applications is not a trivial task, however, there appears to be sufficient evidence that biosensors can be configured to be selective, sensitive and inexpensive to manufacture.