Notes on Biosensors | Bio-Monitoring

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.