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Surface-plasmon-resonance-based biosensors for food diagnostics

Identification

Key words surface plasmon resonance, SPR, biosensor, additive, residue, contaminant, pesticide, herbicide, veterinary drug, antibiotic, bacteria, pathogen, toxin, allergen, analysis
Latest version 2011/05/06
Completed by KU Leuven LFT

How does it work?

Primary objective analytical tool

detection and (semi)quantification of low levels of biological and chemical substances in foods (e.g. veterinary drugs, pathogenic bacteria/toxins, vitamins, pesticides, allergens) based on the principle of specific biological recognition.

Working principle Surface-plasmon-resonance (SPR)-based biosensor detection and quantification are based on label-free monitoring of the interaction between a target analyte in solution and a biomolecular recognition element immobilized on the sensor surface. In most cases, a specific antibody towards this target is used as recognition element. Assays rely in principle on the measurement of mass concentration changes (as a refractive index change) at the sensor surface, which are detected by use of the optical phenomenon of SPR. (1-3)
SPR.jpg
Briefly, SPR occurs in thin conducting films (mostly gold) at an interface between media of different refractive index. Under specific conditions of wavelength and angle of incidence, incident light excites plasmons (= electron charge density waves) in the gold film, resulting in absorption of energy (part of the energy of the light is transferred to the metal film). SPR is seen as a dip in the intensity of the reflected light. A change in the refractive index of the medium near the gold film alters the light characteristics (e.g., angle, wavelength) at which this dip in intensity occurs. Different types of SPR sensors are distinguished depending on which light characteristic is measured as SPR response (mostly SPR angle shift) in order to detect changes in mass concentration at the surface (as changes in refractive index). (1-3)

Practically, in an SPR biosensor, one interaction partner (mostly the biorecognition element) is immobilized on the sensor surface using an appropriate coupling method. Different immobilization chemistries and specific tailored surfaces have been described. Next, a sample containing the target analyte is brought into contact with the surface to allow interaction (often by a microfluidic system). The sensor surface is then regenerated with an appropriate washing solution for the next sample to be tested. Binding and dissociation events are followed on a sensorgram (= SPR response, as a measure for bound mass, vs. time). By comparing the SPR response of an unknown sample with those of known concentrations of analyte, quantification of the unknown samples is achieved. For low-molecular weight analytes (mass below ca. 5 kDa), the sensitivity/limit of detection can be enhanced by using sandwich (in which a second binder to the analyte is injected, sometimes even linked to nanoparticles), inhibition (with immobilized target molecule) or competitive assays, since binding of small compounds generates only small SPR responses (1-3).

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Additional effects Besides detection and quantification of target substances, SPR biosensors also allow the specific study of affinity, kinetics (association and dissociation rates), thermodynamics (based on binding data at different temperatures) and stoichiometry of interactions between biomolecules without the need for labelling (1,2).

The application field of SPR biosensors is not restricted to food analysis, but also includes medical diagnostics (e.g. cancer markers, antibodies, drugs, hormones etc.), environmental monitoring (e.g. pesticides, heavy metals, dioxins, PCBs etc.) and interaction analysis in the life sciences and drug discovery (1-3).

Important process parameters Several parameters directly impact the sensitivity , specificity and detection limit of the SPR-based biosensors (3), including:
  • Choice of (specific) bio-recognition element (antibody or other);
  • Choice of immobilization strategy (retaining biological activity and minimizing nonspecific binding to the surface);
  • Choice of detection format (direct, sandwich, inhibition or competition assay);
  • Choice of sample preparation/pretreatment.
Important product parameters

What can it be used for?

Products Basically, all kinds of food products are possible candidates to be analyzed by SPR biosensor technology, provided that an appropriate sample preparation is executed. This sample preparation can be restricted to dilution in a running buffer (for some liquid samples) or entail homogenization, extraction and/or centrifugation/filtration (for complex liquid and solid samples) (2).

Examples are water, milk, orange/apple juice, urine, honey, barley, wheat, corn, adipose tissue, muscle tissue, mussel, prawn, shrimp, etc (4,5).

Operations SPR biosensor methods have been described for detection and/or quantification of a wide variety of biological and chemical substances in complex food products. Targeted analytes include:
  • Pathogens: bacteria (Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, Campylobacter jejuni, a.o.), protozoa, fungi (1,3,5)
  • Toxins: staphylococcal enterotoxins, botulinum neurotoxins, domoic acid, mycotoxins (1,3,5)
  • Veterinary drug residues: growth-promoting hormones (e.g. β-agonists), antibiotics (e.g. penicillin, streptomycin, chloramphenicol) (2-6)
  • Pesticide and herbicide residues: atrazine, simazine (3,4)
  • Vitamins: Vit B2 (riboflavin), Vit B5 (pantothenic acid), Vit B8 (biotin), Vit B9 (folic acid), Vit B12 (cobalamine) (2,3)
  • Allergens: from peanut (Ara h1), egg white, sesame seed, hazelnut (3,7)
Solutions for short comings The ability to identify and quantify low levels of biological and chemical compounds that are relevant for food quality and food safety is of great importance to the food processing industry as well as to regulatory agencies. There is a need for sensitive and accurate techniques to rapidly detect the presence of contaminants. SPR is one such technique.

The main advantages of SPR-based detection over alternative analytical techniques (microbial assays, ELISA, PCR, chromatography a.o.) include ease of use, reduced assay time, sensitivity (although not for all cases), minimal sample preparation and versatility. SPR biosensors are capable of performing real-time detections, making on-line monitoring of food processing possible (rather than end-product testing) (1-6).

What can it NOT be used for?

Products The analysis by SPR biosensors is restricted to liquid samples (i.e. either a solution which is pumpable through a microfluidic system or a liquid in which a dipstick-like probe can be immersed). Consequently, solid foods should at least be homogenized and filtered/centrifuged. Sometimes, an extraction is required. “In situ” analysis is not possible.
Operations An SPR biosensor technique for a particular target analyte can only be designed if a specific bio-recognition element is available for that target (e.g. antibody or aptamer).

The size of the target also matters, since large targets (e.g. live bacteria) have extremely low rates of diffusion. To overcome this limitation, various treatment methods can be applied to create smaller fragments (e.g. heat-killing, cell lysis using ethanol or detergents) (1). For some analytes, current SPR biosensors do not reach the required limits of detection and further optimization is needed (1).

Other limitations Most current commercial SPR equipment is rather bulky in size and expensive, consequently not very suited for “field use”.
Risks or hazards Generally, there are no specific risks for the operators of this analytical technique. The risk may however be in the conclusions one draws from experimental results (see legal aspects).

Implementation

Maturity Quite a number of SPR sensor platforms from various manufacturers are available commercially. Besides, an even more diverse spectrum of tailor-made laboratory instruments have been described, including fiber optic SPR sensors (e.g. dipstick type). Systems often differ in SPR optical configuration, liquid handling system (flow cell, cuvette, microfluidic chip), level of automation and miniaturization, level of sensitivity and high-throughput capacity. In the context of food analysis, Biacore Q is worth mentioning, since is concerns a fully-automated, wizard-driven instrument, which is dedicated to safety and quality analysis (qualitative or quantitative) within the food industry. To make the analysis process as simple and consistent as possible, an extensive range of Qflex Kits have been created for use with the Biacore Q system (1-3).

The development of low-cost, compact, portable alternatives for field use (e.g. fiber optic SPR biosensors) is currently subject of lab-scale research (7-8). Procedures for a wide variety of analytes have been described in scientific literature. For specific analytes, ready-to-use analysis kits can even be purchased (e.g. QFlex Kits of Biacore) (2,9). For others, method implementation and optimization may be needed.

Modularity /Implementation SPR biosensors are capable of performing real-time detections, making on-line monitoring of food processing possible (rather than end-product testing) (1).

The biosensors may also be coupled offline or online with mass spectrometry devices for identification of interactants (4,9).

Consumer aspects Not applicable. It will be in the consumers’ interest to detect f.i. allergens, but it is not expected that the consumers will have a specific attitude towards the detection method .
Legal aspects Certification of an analysis (e.g. to reach minimum required performance limits) requires documented evidence for the quality of several assay parameters (specificity, accuracy, repeatability, reproducibility, limit of detection, etc.) and provides assurance that an independent third party has tested the assay and found that the product fulfills all performance claims. Several analyses of the Qflex Kits of Biacore, for instance, received AOAC approval after rigorous performance trials carried out in independent laboratories (2,6).

Local legislation should be checked to obtain appropriate certifications if claims are made based on analytical results.

Environmental aspects Given the limited sample preparation and the principle of detection, SPR biosensors often require reduced use of (organic) solvents (for extraction and/or elution) compared to alternative analytical techniques (chromatography, microbial assays, ELISA, PCR, etc).

Further Information

Institutes KU Leuven MeBioS, University of Twente, University of Regensburg, University of Cambridge-Chemical Engineering
Companies
References 1. Homola, J. (2006). Surface Plasmon Resonance Based Sensors. Berlin , Germany: Springer.

2. Schasfoort, R.B.M., Tudos, A.J. (2008). Handbook of Surface Plasmon Resonance. Cambridge, UK: RSC Publishing.

3. Homola, J. (2008). Surface plasmon resonance sensors for detection of chemical and biological species. Chemical Reviews, 108, 462-493.

4. Petz, M. (2009). Recent applications of surface Plasmon resonance biosensors for analyzing residues and contaminants in food. Monatshefte für Chemie, 104, 953-964.

5. Ricci, F., Volpe, G., Micheli, L., Palleschi, G. (2007). A review on novel developments and applications of immunosensors in food analysis. Analytica Chimica Acta, 605, 111-129.

6. Huet, A.-C., Fodey, T., Haughey, S.A., Weigel, S., Elliot, C., Delahaut, P. (2010). Advances in biosensor-based analysis for antimicrobial residues in foods. Trends in Analytical Chemistry, 29, 1281-1294.

7. Pollet, J., Delport, F., Janssen, K.P.F., Tran, D.T., Wouters, J., Verbiest, T., Lammertyn, J. (2011). Fast and accurate peanet allergen detection with nanobead enhanced optical fiber SPR biosensor. Talanta, 83, 1436-1441.

8. Fernandez, F., Hegnerova, K., Piliarik, M., Sanchez-Baeza, F., Homola, J., Marco, M.-P. (2010). A label-free and portable multichannel surface plasmon resonance immunosensor for on site analysis of antibiotics in milk samples. Biosensors and Bioelectronics, 26, 1231-1238.

9. Situ, C., Buijs, J., Mooney, M.H., Elliot, C.T. (2010). Advances in surface plasmon resonance biosensor technology towards high-throughput, food-safety analysis. Trends in Analytical Chemistry, 29, 1305-1315.

Several parameters directly impact the sensitivity , specificity and detection limit of the SPR-based biosensors (3), including:

  • Choice of (specific) bio-recognition element (antibody or other);
  • Choice of immobilization strategy (retaining biological activity and minimizing nonspecific binding to the surface);
  • Choice of detection format (direct, sandwich, inhibition or competition assay);
  • Choice of sample preparation/pretreatment.warning.png"Several parameters directly impact the sensitivity , specificity and detection limit of the SPR-based biosensors (3), including:
  • Choice of (specific) bio-recognition element (antibody or other);
  • Choice of immobilization strategy (retaining biological activity and minimizing nonspecific binding to the surface);
  • Choice of detection format (direct, sandwich, inhibition or competition assay);
  • Choice of sample preparation/pretreatment." cannot be used as a page name in this wiki.

Sensors and Indicators 2.1.2 chemical, biological not applicable biotechnology, nanotechnology Web of Science (surface plasmon resonance AND food), PhD thesis literature review WikiSysop :Template:Review document :Template:Review status



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Created by LiesbethV on 21 June 2011, at 13:18