Disposable sensor

Reliable measurements of L-lactate are of great interest in clinical chemistry, the dairy and vine industry, biotechnology, or sport medicine. In particular, blood lactate levels are indicative of various pathological states, including shock, respiratory insufficiencies, and heart and liver diseases. Silica sol-gel encapsulation of the lactate dehydrogenase and its cofactor was employed as a disposable sensor for L-lactate51. The sensor utilized the changes in absorbance or fluorescence from reduced cofactor nicotinamide adenine dinucleotide (NADH) upon exposure to L-lactate. 

Yang Z, Suzuki H, Suzuki S, Karube 1 (1996) Disposable sensor for biochemical oxygen demand. Appl Microbiol Biotechnol 46 10-14... 

KonigA,BachmannTT,Metzger JW,Schmid RD (1999) Disposable sensor for measuring N-BOD and inhibition of nitrification in wastewater. Appl Microbiol Biotechnol 15 112-117... 

The possible use of graphite-epoxy material by screen-printing technology opens the possibility of mass production of disposable sensors for heavy-metal analysis using stripping techniques. The utilization of these sensors for an extensive application in real heavy-metal samples is underway in our laboratories. 

Individual microelectrodes offer very small responses and one approach for overcoming this problem is to use many microelectrodes together in the form of an array to allow a cumulative and so larger response to be measured. Microelectrode arrays may be fabricated by a number of approaches although techniques such as photolithography or laser ablation have to date proved cost prohibitive for the mass production of disposable sensor strips. We have previously described a novel sonochemical fabrication approach [38,39] for the production of microelectrodes, that lends itself to the mass production of sensor arrays. 

Levels of lactate in buttermilk and yoghurt (and blood) were estimated using disposable sensors formed from screen-printed graphite laminated between two polymer sheets [18]. Platinum (deposited by sputter-coating) was the transducing surface. Layers of Nation were added to reduce interference and were surmounted by lactate oxidase in a mixture of polyethyleneimine and poly (carbamoyl) sulphonate hydrogel. The samples were measured in stirred buffer. A good correlation between biosensor results and those obtained with an enzyme kit was claimed but the data had a considerable amount of scatter—if the enzyme kit is taken as the reference method then a more severe analysis of the biosensor results [33] would not have shown them in a... 

The simplest way to deal with the problem of sensor lifetime is to circumvent it completely by using each sensor once. This requires the production of inexpensive, disposable sensor strips for a variety of anions, possibly by a method such as screen printing. An alternative method may be to further develop photoprocessable polymers, which can then be assembled into the final sensor by a process such as photolithography. 

A common form of disposable sensor is a long cardboard tube with the sensor elements built into one end. The tube is plunged into the molten steel and the measurements made within a few seconds. 

Acetylcholineesterase and choline oxidase Electrode was developed by co-immobilization of AChE with ChO H202. Disposable sensors constructed by co-immobilization in a gelatin membrane on Pt electrode or by immobilizing AChE in polyurethane on a thick-film metallized Pt electrode. A kinetically controlled bioenzyme sensor was also used at a low activity of ChE for determining inhibitors. [75]... 

The detection of OP compounds by biosensors modified with ChE-ChOx or ChE enzymes relies on an inhibition of catalytic activity of ChE enzymes by OPs. Therefore, it is a drawback of the sensors that the magnitude of the output signal correlates inversely with the concentration of OP compounds in the sample. The protocol in measurements is somewhat complicated because the substrate of ChE has to be added in the sample solution before measurements, resulting in multiple steps needed for OP detection. In addition, inhibition of ChE by OP compounds is usually irreversible and thus reactivation of ChE activity is required for repeated use of the sensors, although this problem can be circumvented by using disposable sensor tips. 

The first commercial SPR was launched hy Pharmacia Biosensor AB (presently Swedish BIAcore AB) in 1990. Since then, the device has been refined and now BIAcore [37] offers several models (BIACORE 3000, BIACORE 2000, BIACORE 1000, BIACORE X, J, Q, S51, and C models). The biosensors of BIACORE 1000 to 3000 are fully automated instruments, with a disposable sensor chip, an optical detection unit, an integrated micro-fiuidic cartridge, an autosampler, method programming and control software. Less expensive manually controlled alternatives cU e the BIACORE x and BiacoreQuant . 

It is used in combination with square wave anodic stripping voltammetry (SWASV) using a PalmSens portable instrument (Palm Instrument BV, Houten, The Netherlands) for the measurement of metals such as Cu (II), Cd (II) and Pb (II) (labile metallic complexes and free metals) in water. These disposable sensors require no calibration for use in the screening mode, so, many samples may be tested for the presence or the absence of metals in water. The quantification can also be performed using the standard addition method in less than 15 min. 

Differing from a typical analytical or sensing instrument, chemical sensors are relatively small in size, mobile or portable. If possible, chemical sensor should require minimum or no additional reagents, and also minimum sample transportation or preparation. For many applications, the possibility of producing the sensors at modest cost, and making disposable sensor a reality, is extremely attractive. This is particularly true in many biological and medical sensing applications. 

The direct fixation of the biocatalyst to the sensitive surface of the transducer permits the omission of the inactive semipermeable membranes. However, the advantages of the membrane technology are also lost, such as the specificity of permselective layers and the possibility of affecting the dynamic range by variation of the diffusion resistance. Furthermore, the membrane technology has proved to be useful for reloading reusable sensors with enzyme. In contrast, direct enzyme fixation is mainly suited to disposable sensors. This is especially valid for carbon-based electrodes, metal thin layer electrodes printed on ceramic supports, and mass-produced optoelectronic sensors. Field effect transistors may also be envisaged as basic elements of disposable biosensors. 

The integration of electronic signal processing and display into disposable sensors appears to be difficult. Hybrid systems comprising a disposable sensor and a separate, portable device are likely to prevail. 

Strong et al. developed an SPR biosensor for detection of TNT [41]. They used a SPREETA sensor (from Texas Instruments, USA) with disposable sensor chip coated with BSA-trinitrobenzen conjugate. The detection of TNT was performed by inhibition assay for TNT concentrations down to 1 p-gg for soil samples. The time needed for sample preparation (suspension followed by centrifugation) and analysis of the hquid supernatant were approximately 10 and 6 min, respectively. The sensor was shown to be regenerable using a solution with 0.1 M sodium chloride and 0.1% Triton X-100. 

Patra, D. and Mishra, A. K., A novel disposable sensor head for a fiber optic spectrofluorimeter. 

A fluorosensor for monitoring blood gases and pH in an extracorporal loop is commercially available [125]. Arterial or venous oxygen and carbon dioxide pressure, pH, and temperature can be determined continuously during cardiopulmonary bypass surgery. The system consists of a microprocessor-based instrument, bifurcated fiber-optic cables, and a disposable sensor head with fluorescent spots sensitive to the respective analytes. 

Two serious problems are encountered in the design, manufacture, and performance of in vivo sensors the lack of biocompatibility of the materials used and the poor long-term stability. The latter, however, plays only a minor role in the case of disposable optodes, which are in use only for the duration of a particular operation or test. Disposable sensor heads for clinical analytes seem to be the most promising candidates for practical use at present. Another problem results from the need for sterilization, which is difficult to solve in the case of biosensors with their thermally labile components such as enzymes. 

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