Commercial Instrumentation And Future Perspectives

The majority of reported biosensor research has been directed towards the development of devices for clinical markets; however, driven by the need for better methods for food surveillance, research into this technology is also expanding to encompass food applications. Table 6 shows some examples of commercial biosensor instrumentation available for toxic compounds and pathogens analysis in food.

A number of instruments for food analysis are already commercially available. However, the commercial success of biosensors is limited to a small number of applications, where the market size justified more research, validation and development investment. These commercial devices are focused on few applications, such as the determination of saccharides (YSI), or the detection of bacterial toxins or pathogens (Research International).

The future commercial status and general acceptance of this technology will depend on the performance characteristics, sample throughput, associated costs, validation and acceptance by regulatory authorities.

A variety of laboratory prototype biosensors have been reported which measure a fairly broad spectrum of food contaminants and residues.

Immunoassays traditionally have been used as a single-analyte method, which has often been considered a limitation of the technology. However, several approaches are possible to overcome this limitation. An approach is to use a compact disk (CD)-based microarray system [139].

A microdot system was developed that utilized inkjet technology to print microdots on a CD. The CD was the solid phase for the immunoassay, and laser optics were used to detect the near-infrared fluorescent label. The advantage of the CD system is the ability both to conduct assays and to record and/or read data from the same CD. Since the surface of a single CD can hold thousands of dots, thousands of analyses can be made on a single sample simultaneously. Such high-density analyses could lead to environmental tasters where arrays of immunosensors are placed on Chips [205] or high-density plates. Because the CD

Table 6 Commercial devices

Name

Analyte

Description

Company

Analyte 2000™

Staphylococcal enterotoxin B,

4-Channel, single wavelength

Research International, 18706 142bd Ave, N.E.,

Escherichia coli 0157:H7, spores

fluorometer optimized for

Woodinville, WA, 98072, USA

performing evanescent-wave

(www.resrchintl.com)

fluoroimmunoassays

ANDREA

Direct measurement of molecular

The measurement of antibody-

DRE — Dr. Riss Ellipsometerbau GmbH, Feldstr.

locking and DNA-hybridization

antigen reactions is done by a

14 D-23909, Ratzeburg, Germany

new technique on the basis of

(www.dre.de)

ellipsometry. Ellipsometry is an

optical method, which simply

measures the state of polarization

of light that is reflected from a

substrate.

Autolab SPR SPRIT

Generic sensor for studding binding

SPR affinity based biosensor

Windsor scientific

interactions with low molecular

(http://www.ecochemie.nl/)

weight molecules

BIAcore (1000, 2000,

Hormones, vitamins, mycotoxins,

SPR affinity based biosensor

BIAcore AB, Rapsgatan 7, Uppsala, Sweden

3000, Q, A100,

antibiotics, low weight molecules

(www.biacore.com)

Flexchip)

FasTraQ is a biosensor

Generic sensor for studding binding

SPR affinity based biosensor

QUANTECH LTD,

interactions with low molecular

815 Northwest Parkway, Suite 100, Eagan, MN,

weight molecules

55121, USA

(http://www.quantechltd.com/)

IBIS

Generic sensor for studding binding

SPR affinity based biosensor

Windsor Scientific Limited, 264 Argyll Avenue,

interactions with low molecular

Slough Trading Estate, Slough,

weight molecules

Berkshire SL1 4HE, United Kingdom.

(www.windsor-ltd.co.uk)

MORITEX, SPR-670M

Generic sensor for studding binding

SPR affinity based biosensor

Moritex Inc., Japan

interactions with low molecular

(www.moritex.co.jp)

weight molecules

RAPTOR™

Staphylococcal enterotoxin B, Bacillus

Portable fluoroimmuno biosensor

Research International, 18706 142bd Ave, N.E.,

anthracis, Yersinia pesti, micotoxins,

Woodinville, WA, 98072, USA

spores

(www.resrchintl.com)

SPREETA™

Generic sensor for studding binding

Miniaturized SPR affinity based

Texas Instruments Inc., 12500 TI Boulevard,

interactions with low molecular

biosensor

Dallas, TX, 75243-4136, USA.

weight molecules

(www.ti.com)

format has the potential for high-density analyses, there will be the opportunity for easily generating multiple replicates of the same sample, including more calibration standards, thus improving data quality.

The development of class-selective antibodies is another approach to multi-analyte analysis. The analyst may design haptens that will generate antibodies that recognize an epitope common to several compounds. Examples of class-selective immunoassays that have been developed are mercapturates [206], glucuronides [207], pyrethroids [208], organophosphate insecticides [209] and benzoylphenylurea insecticides [210].

Rather than have one antibody that can detect a class, a third approach is to analyse a sample using multiple immunoassays, each with a known cross-reactivity spectrum, and determine the concentration of the analytes and confidence limits mathematically [211]. A drawback to using class-selective assays or assays with known cross-reactivity is that for a given antibody, the sensitivity for each analyte vary, and the sensitivity for some analytes may not be sufficient, hence selection of well-characterized antibodies will be a critical step.

Some of the other important keys in the future of immunoassays and immunosensors development are to allow more stability of biological components, more robustness assays, more repeatability between different batches of production when disposable elements are involved, and the integration of new technologies coupled to biosensors, such as the PCR.

On the other hand, there are at least two other developments that are expected to have significant impact, the laboratory on a chip (LOC) [212] and nano-technology [213]. The concept of LOC entails miniaturization of all the essential components of analytical instrumentation (e.g., sample preparation, components, reaction with appropriate reagents and detection) by micro fabrication on a chip. Some of the components in LOC technology have already been released on the market (GeneChip® from Affimatrix). Nanotechnology refers to the exploitation of processes to generate and utilize structures, components and devices with a size range from 0.1 nm (atomic and molecular scale) to 100 nm or larger in some cases, by control at atomic, molecular and macromolecular levels. It has been suggested that nanoscale sensors and ultra miniaturized sensors could lead to the next generation of biotechnology-based industries.

There are several companies manufacturing SPR instruments for studying bio-molecular interactions [214,215]. Each company produces different SPR systems equipped with a variety of options usable for specific applications. Some of these companies are Biacore, SENSIA, Windsor scientific, Quantech, Texas, NTT and Moritex (formerly, Nippon Laser and Electronics). SPR instruments from Biacore have been widely used by the sensor researchers around the world.

Finally, among the variety of biomimetic recognition schemes utilizing supra-molecular approaches MIPs have proven their potential as synthetic receptors in numerous applications, and their advantages compared to biochemical recognition systems include thermal stability, storage endurance and lower costs.

In particular, the areas of, food and beverage analysis require analytical tools capable of discriminating chemicals with high molecular specificity. Furthermore, food and process safety control issues favour the application of on-line in situ analytical methods with high molecular selectivity. While biorecognition schemes frequently suffer from degrading bioactivity and long-term stability when applied in real-world sample environments, MIPs serving as synthetic antibodies have successfully been applied as stationary phase separation matrix, and biomimetic recognition layer in chemical sensor systems. Current research demonstrates the progression of MIP chemistry and the potential of these materials to solving a wide variety of food analytical problems.

The combination of MIPs with a range of transducers to produce on line and real time sensors is expected, and their potential has been demonstrated, but limitations described previously should be addressed. The majority of applications of MIPs are directed to low molecular weight, organic soluble analytes of interest in the pharmaceutical industry (e.g., chiral drug separation), but new applications have been developed in environment and food industry. Several new approaches to MIP production (e.g., surface imprinting) are expected to allow MIPs to be prepared in aqueous media.

Other new approaches in development are Magnetic MIPs and Cathalytic MIPs (also referred to as enzyme mimics or plastizyme).

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