Marine Pollution Bulletin 45 (2002) 24–34

www.elsevier.com/locate/marpolbul

Biosensors for marine pollution research, monitoring and control

oger a, Sergey Piletsky b, Anthony P.F. Turner b,*
Silke Kr€
a
Centre for Environment, Fisheries and Aquaculture Science (CEFAS), Pakefield Road, Lowestoft, Suffolk NR33 OHT, UK
b
Cranfield University, Silsoe, Bedfordshire MK45 4DT, UK

Abstract

Measurement of ecological, climatic and anthropogenic changes underpins the formulation of effective management strategies for
sustainable use and protection of the marine environment. Sensors are traditionally used in marine studies to determine physical
parameters, but there is increasing demand for real-time information about chemical and biological parameters. These parameters
are currently measured in samples collected at sea and subsequently analysed in the laboratory. Biosensors fuse the exquisite
sensitivity and specificity of living systems with the processing power of microelectronics to deliver simple, inexpensive measurement
systems for use in the field or deployment in situ. While their potential for use in the marine environment is enormous, much
published work to date has focussed on applications in freshwater and wastewater. Marine applications pose a substantial challenge
in the robustness required for remote application, but recent developments in portable medical devices and receptor design suggest
that these demands can now be realistically tackled.
Ó 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Marine biosensors; Decentralised measurements; Novel instrumentation; Analytical techniques; Chemical pollution; Pollution monitoring

1. Introduction rameters is enhanced to accommodate the required de-

centralised and high frequency observations. The way in
Pollution of the marine environment is a complex which novel instrumentation such as biosensors could
topic of immense scientific and political importance, as contribute to these measurements is the subject of this
is continuously reflected by the content of this bulletin. review.
In order to develop an understanding of marine pollu-
tion issues, which ultimately allows effective manage-
ment strategies to be developed and implemented, we 2. What are biosensors?
rely on both research and monitoring of the oceans. The
aim is to identify contaminant nature, sources, distri- Biosensors (Fig. 1) are analytical devices incorporat-
bution, concentration, persistence, uptake into biota ing a biological material, biologically derived material
and, arguably most importantly, effect on the ecosystem or biomimetic intimately associated with or integrated
or any part thereof. To meet the need for improved within a physicochemical transducer or transducing
assessment of ecosystem change over appropriate tem- microsystem, which may be optical, electrochemical,
poral and spatial scales, new measurement strategies thermometric, piezoelectric or magnetic (Turner, 1999).
based on continuous or semi-continuous observations A wide variety of receptors have been incorporated
are required (Kr€oger et al., 2000a,b). Sensors for tem- into biosensors including biocatalysts such as enzymes,
perature, conductivity, depth and turbidity have already organelles, intact microorganisms and tissues, and af-
been used to good effect in oceanography, but it is time finity elements such as antibodies, cell receptors, nucleic
that the measurement of chemical and biological pa- acids and biomimetic molecules (Turner, 2000). It is
important to appreciate that biosensors do not neces-
*
sarily measure a biological parameter, but use a bio-
Corresponding author. Tel.: +44-1525-863005; fax: +44-1525- logical sensing element to detect whatever the analyte
863360.
E-mail addresses: s.kroeger@cefas.co.uk (S. Kr€oger), a.p.turner@
of interest is––i.e. biosensors can and have been used
cranfield.ac.uk (A.P.F. Turner). to quantify chemical pollutants. Another important
URLs: http://www.cefas.co.uk, http://www.silsoe.cranfield.ac.uk. feature is the ability of biosensors to measure a class of
0025-326X/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 2 5 - 3 2 6 X ( 0 1 ) 0 0 3 0 9 - 5
 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34 25

Fig. 1. Generalised diagram of a biosensor.

compounds and not just single chemicals. These so- enhances the response time leading to rapid measure-
called ‘‘summing parameters’’ include effects such as ment due to low diffusion times. This means that auto-
toxicity (Farre et al., 2001), carcinogenicity, mutage- matic analysers can have high sample throughput or
nicity, cytotoxicity (Castillo et al., 2001) and genotox- that single measurements can be delivered in real time.
icity (Billinton et al., 1998; Polyak et al., 2000, 2001), This speed, combined with the continuous output of a
which are virtually impossible to characterise using sensor means that a much more complete visualisation
conventional chemical analysis. Sensors developed for of dynamic phenomena can be obtained and, in certain
these biological effects are numerous and highly relevant circumstances, automatic corrective action can be trig-
to marine measurements but it is beyond the scope of gered.
this article to provide a detailed review of the field. The development of biosensors was originally driven
While broad classes of pollutant can be measured, bio- by medical applications. One of the most successful
sensors can also offer a high degree of specificity, often devices has been an electrochemical biosensor for glu-
distinguishing between stereo isomers of the same cose based on the enzyme, glucose oxidase (Cass et al.,
compound. Sensitivity too can be high. In the extreme 1984; Cardosi and Turner, 1990). The convenient pen-
case of electrochemical immunosensors as little as 10 20 sized instrument originally developed at Cranfield Uni-
mol of a substance has been measured (Jenkins et al., versity in collaboration with Oxford University has
1991), although this is quite exceptional and sensors proved a huge commercial success (Fig. 2). It also serves
more normally operate in the nanomolar to millimo- to illustrate some of the features and benefits discussed
lar range. The integration of the biological sensing ele-
ment with the electronic transducer system leads to a
compact design, which is easy to use, inexpensive and
portable.
Biosensor technology is also amenable to mass pro-
duction making sensor elements disposable and cheap
enough to be deployed at multiple sites. Another feature
of biosensors as opposed to bioassays or other analytical
methods is the way that the assay design is permanently
fixed in the construction of the device. This means that a
biosensor is designed to perform a particular analytical
task, measuring a set analyte or class of analytes in a
defined medium. While this leads to some restriction on
the breadth of use, it has the advantage of allowing the
sensor to be used directly in complex matrices without
sample preparation. This in turn leads to improved re-
producibility by avoiding operator error. The close Fig. 2. A range of electrochemical glucose biosensors sold by Abbott
proximity of the sensing element to the transducer also Diagnostics.
26 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34

above, offering an inexpensive, simple-to-use instrument 4. Biosensors for marine determinants

for home blood glucose monitoring, based on a mass-
producible and disposable enzyme electrode. This gra- 4.1. Nutrients
phic illustration of utility has encouraged workers to
seek wider applications for the technology and envi- Two key nutrients regularly measured in the marine
ronmental monitoring has proved an attractive target environment are nitrate and nitrite. The compounds are
(Bilitewski and Turner, 2000). While the immediate essential for phytoplankton growth and thus form the
commercial returns from environmental sensors are basis for marine productivity. Considering them as
substantially less than from medical diagnostics, public pollutants is only justified in particular cases, when their
demand and government funding has generated a major input from the anthropogenic sources, as outlined
research effort. Much of this work, however, has been above, far exceeds requirements and leads to undesirable
directed at fresh water monitoring and adaptation of effects generally described as euthrophication. Nutrient
this powerful analytical technology to the marine envi- measurements can conveniently be made using biologi-
ronment is just beginning. cal sensing systems, particularly with metabolic sensors.
A nitrate sensor was constructed using nitrate reductase
immobilised in an electrogenerated polymer, which si-
3. Important topics in marine pollution research, moni- multaneously entrapped the enzyme and connected it
toring and control electrically to the electrode (Cosnier et al., 1994). En-
zyme-based nitrate measurements were also made using
There are different pathways by which contaminants an optical transducer and selecting a periplasmic enzyme
can be introduced into the marine environment: direct from the denitrifying bacteria Thiospaera pantotropha
inputs, riverine contributions, and drawdown from the immobilised in an optically transparent sol–gel matrix
atmosphere. Examples for direct inputs include dis- (Aylott et al., 1997), which increased the enzyme sta-
charges of industrial or domestic effluents, chemicals bility while allowing for unhindered optical detection.
released in conjunction with oil exploration or the de- The enzyme nitrite reductase isolated from Alcaligenes
commissioning of oil platforms, and chemicals origi- faecalis has been successfully employed in the con-
nating from agricultural run-off such as fertilisers and struction of an amperometric sensor (Sasaki et al.,
pesticides. Anti-biofouling agents leaching from ship 1998).
paints (TBT and booster biocides) and other releases Using whole microorganisms rather the isolated en-
from ships, including events such as accidents involving zymes, a nitrate (NO3 ) biosensor has been constructed
oil tankers or ships carrying hazardous chemicals, also based on immobilised denitrifying bacteria (Agrobacte-
contribute to the pollution of the seas. Pollutants rium radiobacter) and electrochemical quantification of
reaching the marine environment mainly through ri- the nitrous oxide (N2 O) released (Larsen et al., 1997). By
verine inputs include agricultural run-off as well as in- careful selection of the denitrifying strain and continu-
dustrial discharges and substances released from sewage ous supply of electron donors and other nutrients from
treatment plants, most importantly nutrients and pol- a built-in reservoir to the immobilised cells, a very selec-
lutants such as surfactants, plasticisers (nonylphenol), tive and stable system was obtained. The described
steroid hormones, and other pharmacological products. biosensor was subsequently used in the determination of
Atmospheric pollutant inputs are equally diverse and the microscale distribution of nitrate, nitrate assimi-
include emissions from power plants, other industrial lation, nitrification and denitrification in sediment
sites and general traffic. In addition to chemicals intro- (Lorenzen et al., 1998). Nitrification kinetics have also
duced into the marine environment from external been elucidated using biosensors (Ficara et al., 2000).
sources, contaminants of biological origin such as algal
toxins found in shellfish cause concern and bacterial or 4.2. Anti-biofouling agents
viral contamination of waters can have pathogenic ef-
fects either following direct exposure or by uptake Organotin compounds are used as biocides in anti-
through the food chain. fouling paints on marine structures, including the hulls
From the above diverse pollutant issues, it is apparent of commercial and leisure craft. Because of its high
that the range of determinants important to measure is toxicity and negative effects on non-target biota, TBT
wide, but an equally broad range of different biosensors use has been carefully monitored (Waldock et al., 1993;
have been developed that measure relevant analytes. As Law et al., 1994; volume 258 of Science of the Total
mentioned above only a few biosensors have been Environment, 2000 and references therein). Among the
developed, to date, directly for marine applications. best-documented effects of organotins on biota are di-
Therefore we will also highlight important technology rect toxicity, shell thickening in oysters, a decline in
that could usefully be adapted to the marine challenge in recruitment of their juvenile stages, and endocrine
future years. disruption (imposex). Much of the evidence for
 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34 27

TBT-mediated effects on biota is based on empirical

observations in the field, but many described effects have
been reproduced in the laboratory and the link between
TBT and endocrine disruption is by now generally ac-
cepted (Matthiessen and Gibbs, 1998). With the in-
creasingly strict legislation regarding the use of TBT,
instruments that allow efficient decentralised compliance
monitoring will be required and work on the develop-
ment of a sensor system for TBT detection is in progress
in the CEFAS laboratory. In order to replace organo-
tins, anti-biofouling paints are now largely based on
copper and other biocides such as pesticides (see section
below) and it is well possible that increased monitoring
efforts will be required to elucidate the effects of these
compounds on the receiving environment.
Fig. 3. Herbicide monitor developed at the Technical University of
4.3. Pesticides Berlin based on earlier work at the Universities of Cranfield and Luton
(Rawson et al., 1989). The photograph shows the use of a fibre-optic
Many biosensors have been developed for the detec- based system, delivering light to immobilised photosynthetic bacteria
tion of pesticides in complex matrices (Kr€ oger and at the tip. Photosynthetic activity stimulated by the light is recorded
electrochemically using a mediator. When the tip is dipped in water
Turner, 2000). By far the most common biocatalysts in
containing herbicide, photosynthesis is inhibited and a reduction in
the development of pesticide biosensors based on inhi- current is recorded. Larger monitoring systems based on this principle
bition studies are cholinesterases. Acetylcholinesterase are in use in estuaries in Germany, The Netherlands and Korea.
(AChE) is an enzyme involved in signal transduction in
the central and peripheral nervous system. Organo-
phosphorus and carbamate pesticides inhibit choline- tions detail antibody production and immunosensor
sterase and are therefore powerful insecticides, but at the development for environmental analysis (Marco et al.,
same time exhibit high toxicity for other animals and 1995; Killard et al., 2000; Mascini, 2001; Mallat et al.,
humans. A review of electrochemical biosensors for 2001) and antibody production specifically for pesticide
pesticide detection using cholinesterase inhibition has analysis was reviewed by Hock et al. (1995). Antibodies
been written by Trojanowicz and Hitchman (1996) and do not only exhibit remarkable sensitivity and selectiv-
further refinements to this system continue to be re- ity, but it has been shown that they can retain their
ported (Nunes et al., 1999; Sturm et al., 1999; Hernan- recognition properties in challenging environments such
dez et al., 2000). as mixed aqueous/organic solvents (Kr€ oger et al., 1998;
An alternative biocatalytic approach is the use of in- Setford et al., 1999). Numerous immunosensors have
tact microorganisms. The most successful commercial been designed and developed for pesticides in natural
biosensor for environmental use is the biochemical ox- waters including recent reports for analytes such as
ygen demand sensor (Wittmann et al., 1997). This ex- Isoproturon (Mallat et al., 2001a), Paraquat (Mallat et
ploits immobilised microorganisms and an oxygen al., 2001b) and Irgarol (Penalva et al., 1999). Other
electrode to rapidly determine the amount of metaboli- important pollutants have been monitored with similar
sable organic material in a given sample. Various ap- technology such as PCBs (Kim et al., 2000; Laschi et al.,
proaches have been taken to adapt this measurement 2000), surfactants (Castillo et al., 2000), algal toxins
principle to the detection of metabolites and inhibitors (Marquette et al., 1999) and pathogens (Perez et al.,
in the environment including the selection of appropri- 1998).
ate strains and genetic manipulation to introduce spe-
cific transducible properties. A variation has been to use 4.4. Endocrine disruptors
photosynthetic bacteria coupled to electrochemical
transducers to monitor herbicides (Rawson et al., 1989) In addition to the endocrine disruptor effects caused
(an example is shown in Fig. 3). by organotins, there has been increased concern in re-
Another group of biological sensors relevant to con- cent years over the presence in the aquatic environment
taminant measurements is affinity sensors and in par- of other compounds with estrogenic properties, since
ticular immunosensors. Applying antibodies as their they may interfere with the normal endocrine function in
sensing elements, they can be tailored to a range of animals and affect development and reproduction (Sadik
different analytes. The affinity constants and cross- and Witt, 1999). Among these compound are the natu-
reactivity patterns of the selected antibodies determine rally occurring steroids estrone and 17b-estradiol, and
their selectivity and specificity. Many scientific publica- the synthetic contraceptive steroid 17a-ethinyl estradiol,
28 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34

limited ability to predict bloom occurrence. At present

algal taxonomy is mostly performed by specialist in
laboratories on fresh or preserved samples using optical
microscopy, but there are cases of morphologically non-
distinct species with different toxicity where these
methods are inadequate. Molecular biological methods
of species identification based on characteristic nucleic
acid sequences are rapidly gaining recognition as valu-
able additions or alternatives to classical taxonomy
based on visual inspection of morphology (Medlin et al.,
1998; Scholin, 1998; Haley et al., 1999). Some sequence
information for organisms of interest is already pub-
lished and as world-wide sequencing efforts progress
increasingly comprehensive databases become available
Fig. 4. A portable surface plasmon resonance-base immunosensor for for molecular biological species identification. The
endocrine disrupting compounds developed at Cranfield. group around Chris Scholin at Monterrey Bay Research
Institute has made significant advances in the develop-
ment and application of RNA probes to algae species
which have been detected in surface waters and sewage identification and in the adaptation of these methods to
treatment plant effluents (Kelly, 2000; Rodgers-Gray user-friendly formats such as an automated sandwich
et al., 2000). A number of publications deal with the assay in microtiter plate form and whole cell assays
development of steroid sensors based on biological or using fluorescently labelled probes (Scholin et al., 1999).
biomimetic sensing elements. The natural sensing ele- In order to realise the full potential of these new meth-
ment most commonly used is the human estrogen re- ods the use of nucleic acid-sensor systems is desirable to
ceptor and examples include an acoustic biosensor for move to automated systems and sensors. Some ap-
estrogen determination using a sandwich-type monitor- proaches were presented at the International Conference
ing assay system with a piezoelectric sensor in com- on Harmful Algal Blooms and the Workshop on
bination with flow injection (Mo et al., 1999), and a Harmful Algal Bloom and Marine Biotoxin Monitoring
voltammetric sensor based on changes in electrode prop- (HAB, 2000; HAB-TECH, 2000). Much interesting
erties related to binding of the affinity ligand (Murata work on detection methods for algal toxin monitoring
et al., 2001). Estrogenicity has also been determined in has been conducted or is in progress and a separate re-
surfaces waters by using a biosensor to detect the key view of this specific topic would be desirable.
biomarker, vitollogenin, in fish (Sole et al., 2000) and an For taxonomy, nucleic acid sensors represent a sub-
portable immunosensor (Fig. 4) for detection of hor- group of affinity recognition-based sensors, in which the
mone mimics based on surface plasmon resonance has recognition event is the sequence specific hybridisation
been described (Sesay and Cullen, 2001). between a nucleic acid released from the target organism
and a specific, usually short probe sequence. By strictly
4.5. Molecular taxonomy controlling the environmental parameters, this interac-
tion can be made highly selective (thus taxonomically
Species identification is crucial to marine ecosystem relevant) and the number of publication describing dif-
monitoring. The species under investigation can include ferent types and formats of nucleic acid sensors is in-
anything from large animals such as whales or fish right creasing at great speed. Examples of DNA sensors
down to microscopic organisms such as zoo or phyto- include direct and indirect sensing devices and the util-
plankton. Particularly for the latter group––the very isation of different detection mechanisms, most notably
small or even single cell organisms––accurate taxonomy involving optical (Chen et al., 1998; Kai et al., 1999;
can be very difficult and sensor technology offers a Kricka, 1999; Pilevar et al., 1998; Sauer et al., 1999;
valuable alternative. A good example of such an appli- Trabesinger et al., 1999; Zhang et al., 1999; Guedon
cation is the increasing international pressure to monitor et al., 2000), electrochemical (Bardea et al., 1999; Moser
variations in phytoplankton ecology, as an indicator of et al., 1997; Palecek and Fojta, 2001; Wang and Kawde,
nutrient-driven eutrophication, and to develop better 2001; Mascini et al., 2001; Yan et al., 2001) and piezo-
methods for managing the consequences of the presence electric transducers (Tombelli et al., 2000). Furthermore
of toxic algae. Effective monitoring for presence, the use of DNA technology in the medical field requiring
changing species composition or bloom development high throughput screening and the analysis of very small
would preferentially be carried out using continuous sample volumes has led to the development of minia-
automated remote or in situ approaches because of the turised DNA arrays allowing multiple tests to be carried
episodic and sporadic nature of algal growth and our out in parallel (Marshall and Hodgson, 1998; Ramsay,
 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34 29

1998; Vo-Dinh et al., 1999; Wang, 2000; Westin et al.,

2001). Such arrays of probes, when made species specific
and combined into complete analytical systems for
marine monitoring, could revolutionise marine taxo-
nomy and ecosystem monitoring. Development work is
in progress at CEFAS based on some of the above
methods and electrochemical detection (Kr€ oger et al.,
2000a,b).

5. Emerging technique: molecular imprinting

One of the critical requirements in the development of

marine biosensors is their robustness. Antibodies, en-
zymes and receptors can suffer from lack of stability.
Fig. 5. Scheme of molecularly imprinted polymerisation.
One of the emerging techniques, offering some advan-
tages with respect to receptor stability is molecular im-
printing. plate and experimental conditions chosen for polymer
Molecular imprinting is a generic technology, which preparation and analysis.
introduces recognition properties into synthetic poly- More than 400 templates have been used successfully
mers using appropriate templates. The typical recipe for for the preparation of MIPs with examples ranging from
MIP preparation includes mixing together the target inorganic ions (Tsukagoshi et al., 1993), peptides and
compound (template) with a corresponding functional proteins (Liao et al., 1996), drugs (Mullett and Lai,
monomer (most frequently––methacrylic acid) and 1998), steroids (McNiven et al., 1997; Rachkov et al.,
cross-linker (e.g. ethylene glycol dimethacrylate) in 1998) and whole cells (Dickert et al., 2001). MIPs have
appropriate solvents (chloroform, acetonitrile) and a number of advantages in comparison with natural
polymerising this mixture using UV or chemical initia- biomolecules (Table 1).
tion (Fig. 5). Subsequent removal of the template leaves The high specificity and stability of MIPs render them
binding sites in the polymer with geometry and orien- promising alternatives to the enzymes, antibodies, and
tation of functional groups complementary to these of natural receptors used in sensor technology (Levi et al.,
the template molecule and capable of molecular recog- 1997; Jenkins et al., 1997). Environmental monitoring
nition in a manner similar to natural receptors (Wulff, and remote sensing are considered as particularly at-
1995; Mayes and Mosbach, 1997). tractive areas for application of MIP sensors. Relevant
Practically any type of compounds can be used as examples of this undertaken at Cranfield include de-
template for the preparation of specific polymers, al- velopment of artificial receptors and MIP sensors for
though, the performance of the polymers, their affinity algal toxins (e.g. microcystin-LR, domoic acid) and
and specificity vary depending on the type of the tem- man-made substances (e.g. pesticides and herbicides).

Table 1
Comparison of natural biomolecules used in sensors (enzymes, receptors, antibodies) and MIPs
Natural biomolecules MIPs
Variable stability depending on structure and source Stable at low/high pHs, pressure and temperature and
over long time intervals
High price of some enzymes and receptors, easy supply of others Generally inexpensive and easy to prepare if sufficient
template is available
Evolved for aqueous environment, often poor performance in non-aqueous media Work in organic solvents, recognition in aqueous envi-
ronment more difficult
Integration of different biomolecules in multisensor unit can be difficult due to varying Due to minimal operational requirements of MIPs, the
operational requirements (pH, ionic strength, temperature, substrate) design of MIP-based multisensor is relatively easy
At times poor compatibility with micromachine technology (operational parameters) Polymers are fully compatible with micromachine tech-
nology
Very high affinity constants and catalytic turnover rates Affinity constants improving, generally still lower. Very
limited catalytic activity
Ethical considerations can be important (animal sources) No need for animal use/experimentation
Where biological effect of pollutant is known, biomolecules can be highly relevant Can be produced even for analytes where the
sensing element as they are the actual target biological target is not yet known
30 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34

Table 2
Affinity and sensitivity range of computationally designed molecularly
imprinted polymer in comparison with antibodies for the tem-
plate––microcystin-LR
Receptor Kd , nM Sensitivity range (lg l 1 )
MIP 0.3  0.08 0.1–100
Monoclonal antibody 0.03  0.004 0.025–5
Polyclonal antibody 0.5  0.07 0.05–10

The affinity and specificity of the synthesised polymers

was comparable with natural receptors and antibodies
(Table 2).
Different types of transducers, electrochemical, pi-
ezoelectric and optical were combined successfully with
imprinted polymers (Piletsky et al., 1998; Dickert et al.,
1999; Ji et al., 1999). As a result very stable sensor de-
vices were produced capable of withstanding a harsh
treatment with organic solvents, acids, base, and capable
of operating at a high pressure and at low and high
temperature (Kriz and Mosbach, 1994; Svenson and
Nicholls, 2001). Imprinted polymers have a very long
shelf and operational lifetime, characteristics that are
very important for the development of marine sensors.
The factors limiting the development of MIPs sensors
are: (i) absence of general protocol for MIP design; (ii)
poor performance of imprinted polymers in aqueous
solutions; (iii) difficult transformation of binding event
into an electrical signal. With further progress in poly-
mer science and engineering these problems will be Fig. 6. SmartBuoy with payload of different sensors and analytical
solved and we might expect to see the appearance of instruments. Above before and below after a four week deployment.
a new generation of MIP sensors for environmental
monitoring.
Potential frontrunner candidates with the highest level This is mainly an engineering challenge and has been
of readiness for a commercialisation are: sensors for overcome for the instruments available to date, but is
polycyclic hydrocarbons (Dickert et al., 1999), pesticides important to consider when selecting and developing
(Kr€oger et al., 1999; Sergeyeva et al., 1999; Yamazaki new technology. When integrating new sensors into
et al., 2001), organophosphate pesticides (Jenkins et al., measurement systems such as the CEFAS SmartBuoy
2001) and chloroaromatic acids (Lahav et al., 2001). (Fig. 6), it is important to obtain signal stability over
deployment periods of minimum 4–6 weeks, preferably
significantly longer. The SmartBuoy is a sampling plat-
form with a user-definable sensor and sampler array
6. What is required for existing and future systems to (Mills et al., 2001), for which new sensors are continu-
meet the marine challenge? ously developed and selected. Clearly any sensing ele-
ments used, or reagents employed, need to be stabilised
The potential benefit of using biosensors and biomi- to ensure functionality over the deployment intervals.
metic sensors for marine monitoring have been outlined Data from SmartBuoy instrumentation is relayed to
above and hopefully will stimulate some thoughts and shore in real-time using radio, cellular telephone or
discussions about worthwhile applications. Despite all satellite links (for details and on-line monitoring data
the promise the technology holds for future observa- see www.cefas.co.uk/monitoring). The advantage of this
tional strategies, some of the factors that present con- approach is not only the fast availability of the data but
siderable hurdles and can hold back application should also the inherent risk minimisation: even if at some point
also be considered. during the observation interval instrument loss occurs,
In order for high-frequency measurements to be made the data to that point is safe. Additionally, back-up data
successfully in situ, the instruments employed need to be loggers associated with the instrumentation are required
very robust in terms of possible physical impacts and to safeguard the user against loss of data due to tele-
functionality in a highly corrosive working environment. metry failure.
 S. Kr€oger et al. / Marine Pollution Bulletin 45 (2002) 24–34 31

Ideally sensors would be completely drift-free––a test that can be carried out to pre-screen samples, pos-
specification which is rarely achievable. Sensor drift is sibly helping to direct the sample collection effort for
acceptable if it can be accurately predicted and ac- further detailed chemical analysis.
counted for or if frequent re-calibration is part of the
measurement schedule. Sensor calibration can involve
strategies such as use of a stable on-board standard,
which is inserted between analyses and/or collection of References
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