Biosensor probe

Biosensor Probes. For the fiber optic biosensor used here, a portion of protective cladding on the exterior of the optical fiber is removed from the distal 10 cm of the fiber to expose a core of fused silica. This exposed region becomes the probe. Antibodies are covalently attached to the exposed core. When the probe is in contact with a sample containing an analyte, the immobilized antibody specifically binds the analyte from the bulk solution and concentrates it on the surface of the fiber within the evanescent zone. Any fluorophore associated with the analyte is also immobilized within the evanescent wave. Excitation of the fluorophore by light in the evanescent wave leads to fluorescent emission which generates a detectable signal. Two different methods of associating a fluorophore with the analyte are described below. 

Actual construction of a biosensor probe tailored for the detection of G4 is a multistep process. First, the exposed fused silica core of the probe is cleaned with concentrated hydrofluoric acid (HE), then the 200 im core is tapered to 65 im by concentrated HE. Tapering requires about 40 minutes. 3-Mercapto-proply-trimethoxy-silane reacts covalently with the surface hydroxyls to produce immobilized thiol groups. Next, the malimide reactive group of the heterobifunctional crosslinker N-succinimidyl-4-maleimidobutyrate is reacted with the immobilized thiol to yield a tethered succinimide capable of reacting with the primary amines of a protein. ... 

Table 2 Km values reported for soluble enzymes and maximum concentration values of the linear concentration range reported for each biosensor probe ...

Biosensors (qv) and DNA probes ate relatively new to the field of diagnostic reagents. Additionally, a neat-infrared (nit) monitoring method (see Infrared TECHNOLOGY AND RAMAN SPECTROSCOPY), a teagenfless, noninvasive system, is under investigation. However, prospects for a nit detection method for glucose and other analytes ate uncertain. 

In Vivo Biosensing. In vivo biosensing involves the use of a sensitive probe to make chemical and physical measurements in living, functioning systems (60—62). Thus it is no longer necessary to decapitate an animal in order to study its brain. Rather, an electrochemical biosensor is employed to monitor interceUular or intraceUular events. These probes must be small, fast, sensitive, selective, stable, mgged, and have a linear response. 

Scanning electrochemical microscopy can also be applied to study localized biological activity, as desired, for example, for in-situ characterization of biosensors (59,60). In this mode, the tip is used to probe the biological generation or consumption of electroactive species, for example, the product of an enzymatic surface reaction. The utility of potentiometric (pH-selective) tips has also been... 

FIGURE 6-4 Schematic of a first-generation glucose biosensor (based on a probe manufactured by YSI Inc.). 

Toxin (Enzyme Inhibition) Biosensors Enzyme affectors (inhibitors and activators) that influence the rate of biocatalytic reactions can also be measured. Sensing probes for organophosphate and carbamate pesticides, for the respiratory... 

Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

Electrogenerated chemiluminescence (ECL) has proved to be useful for analytical applications including organic analysis, ECL-based immunosensors, DNA probe assays, and enzymatic biosensors. In the last few years, the electrochemistry and ECL of compound semiconductor nanocrystallites have attracted much attention due to their potential applications in analytical chemistry (ECL sensors). 

Figure 5. The unmanned plane used to collect and identify aerosolized bacteria in field trials at Dugway Proving Ground, UT. The plane carried a ten-pound payload including a cyclone air sampler and 4-probe fiber optic biosensor.

Z.J. Liu, B.H. Liu, J.L. Kong, and J.Q. Deng, Probing trace phenols based on mediator-free alumina sol-gel-derived tyrosinase biosensor. Anal. Chem. 72, 4707-4712 (2000). 

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