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					Biosensors:
A tutorial
review
SARAJU P. MOHANTY
AND ELIAS KOUGIANOS


AS THE POTENTIAL threat of bioterror-
ism increases, there is great need for a
tool that can quickly, reliably, and accu-
rately detect contaminating bioagents in
the atmosphere. Biosensors can essen-
tially serve as low-cost and highly effi-
cient devices for this purpose in addi-
tion to being used in other day-to-day
applications.

What’s a biosensor?
    The history of biosensors started in
1962 with the development of enzyme
electrodes by scientist Leland C. Clark.
Since then, research communities from
                                                                                                                           © PHOTO DISC
various fields such as very large scale
integration (VLSI), physics, chemistry,
and material science have come togeth-       ment, such as an enzyme, recognizes a         dous potential for commercialization in
er to develop more sophisticated, reli-      specific analyte and the sensor element       other fields of application such as
able, and mature biosensing devices.         transduces the change in the biomole-         biosensor-based instruments in food
Applications for these devices are in the    cule into an electrical signal. The           and beverage production, environmen-
fields of medicine, agriculture, biotech-    bioelement is very specific to the ana-       tal sampling, and noninvasive instru-
nology as well as the military and           lyte to which it is sensitive. It does not    ments for clinical analysis. However,
bioterrorism detection and prevention.       recognize other analytes. Depending on        commercial adoption has been slow
    What is a biosensor? Various defini-     the transducing mechanism used, the           because of several technological diffi-
tions and terminologies are used             biosensors can be of many types               culties. For example, due to the pres-
depending on the field of application.       such as: resonant biosensors, optical-        ence of biomolecules along with semi-
Biosensors are known as immunosen-           detection biosensors, thermal-detection       conductor materials, biosensor contami-
sors, optrodes, chemical canaries, reso-     biosensors, ion-sensitive field-effect        nation is a major issue.
nant mirrors, glucometers, biochips,         transistor (ISFET) biosensors, and elec-
and biocomputers. Two commonly               trochemical biosensors. The electro-          Basic concepts
cited definitions by S.P.J. Higson and       chemical biosensors, based on the                As demonstrated in Fig. 1, a biosen-
D.M. Frazer, respectively, are “a biosen-    parameter measured, can be further            sor consists of a bioelement and a sen-
sor is a chemical sensing device in          classified as conductimetric, ampero-         sor element. The bioelement may be an
which a biologically derived recognition     metric, and potentiometric.                   enzyme, antibody, living cells, or tissue.
entity is coupled to a transducer, to            Biosensors can have a variety of bio-     The sensing element may be electric
allow the quantitative development of        medical, industry, and military applica-      current, electric potential, and so on. A
some complex biochemical parameter,”         tions, as shown in Fig. 2. A major appli-     detailed list of different possible bio-
and “a biosensor is an analytical device     cation is in blood glucose sensing            elements and sensor-elements is shown
incorporating a deliberate and intimate      because of its abundant market poten-         in Fig. 3. Different combinations of bio-
combination of a specific biological ele-    tial. However, biosensors have tremen-        elements and sensor-elements constitute
ment (that creates a recognition event)
and a physical element (that transduces
the recognition event).”
    The name biosensor signifies that
the device is a combination of two                                                                                       Electrical
                                                  Analyte               Bioelement               Transducer
                                                                                                                          Signal
parts: a bioelement and a sensor ele-
ment. The basic concepts of a biosen-                                                Biosensor
sor’s operation can be illustrated with
the help of Fig. 1. A specific bioele-       Fig. 1 A schematic representation of biosensors



MARCH/APRIL 2006                                 0278-6648/06/$20.00 © 2006 IEEE                                                   35
                                                          Biosensors




                             Clinical                                                                     Nonclinical


              In Vivo                    In Vitro



                         Short-                                                                                                Environmental
      Long-Term                                                                           Single          Reactive
                          Term          Singleshot        Multi-Analyses                                                         Bioagent
     Implantable                                                                         Analysis         Monitoring
                        Invasive                                                                                                 Detection


                                          Home              Pathology                                      Pollution
                         Bedside
      Artificial                          Blood             Laboratory                     Fruit          Monitoring,              Anthrax,
                         Glucose
      Organs                             Glucose             Glucose                     Ripening        Fermentation              Plague,
                        Monitoring
                                         Monitor            Monitoring                                    Processes              and Cholera


Fig. 2 Potential applications of biosensors

several types of biosensors to suit a vast           Common types of biosensors                       chemiluminescence. In optical-diffrac-
pool of applications.                                    In resonant biosensors, an acoustic          tion-based devices, a silicon wafer is
    The bio and the sensor elements can              wave transducer is coupled with an               coated with a protein via covalent
be coupled together in one of the four               antibody, or bioelement. When the ana-           bonds. The wafer is exposed to UV
possible ways demonstrated in Fig. 4:                lyte molecule, or antigen, gets attached         light through a photo mask, and the
membrane entrapment, physical adsorp-                to the membrane, the mass of the mem-            antibodies become inactive in the
tion, matrix entrapment, and covalent                brane changes. The resulting change in           exposed regions. When the diced wafer
bonding. In the membrane entrapment                  the mass subsequently changes the res-           chips are incubated in an analyte, anti-
scheme, a semipermeable membrane                     onant frequency of the transducer. This          gen-antibody bindings are formed in
separates the analyte and the bioelement;            frequency change is then measured.               the active regions, thus creating a dif-
the sensor is attached to the bioelement.                In optical biosensors, the output            fraction grating. This grating produces
The physical adsorption scheme is                    transduced signal that is measured is            a diffraction signal when illuminated
dependent on a combination of van der                light. The biosensor can be made                 with a light source such as a laser. The
Waals forces, hydrophobic forces, hydro-             based on optical diffraction or electro-         resulting signal can be measured or can
gen bonds, and ionic forces to attach the
biomaterial to the surface of the sensor.
The porous entrapment scheme is based
on forming a porous encapsulation                                                        Biosensors
matrix around the biological material that
helps in binding it to the sensor. In the
case of the covalent bonding, the sensor
surface is treated as a reactive group to                                Bioelement                   Sensor Element
which the biological materials can bind.
    The typically used bioelement
                                                                             Enzyme                         Electric Potential
enzyme is a large protein molecule that
acts as a catalyst in chemical reactions
                                                                             Antibody                       Electric Current
but remains unchanged at the end of
the reaction. Figure 5 shows the work-
                                                                             Nucleic Acid                   Electric Conductance
ing principle of enzymes. An enzyme,
upon reaction with a substrate, forms a                                      Tissue                         Electric Impedance
complex molecule that, under appropri-
ate conditions, forms the desirable                                                                          Intensity and Phase of
                                                                             Microbial
product molecule releasing the enzyme                                                                             EM Radiation
at the end. The enzymes are extremely                                        Polysaccharide                 Mass
specific in their action: enzyme X will
change a specific substance A, not C, to                                                                    Temperature
another specific substance B, (not D),
as illustrated in Fig. 6. This extremely                                                                    Viscosity
specific action of the enzymes is the
basis of biosensors.                                 Fig. 3 Elements of biosensors



36                                                                                                                               IEEE POTENTIALS
      B        B       B        B             B       B                                    B    B    B       B         B    B       B       B
                                                                    Semipermeable
           B       B        B             B       B                   Membrane
                                                                                                                                                      Membrane

                           Sensor                                                                            Sensor

                            (a)                                                                                  (b)




       B       B   B        B         B       B       B   B                                B     B       B           B          B       B
                                                                         Porous                                                                        Covalent
                                                                      Encapsulation                                                                     Bond

                            Sensor                                                                           Sensor

                                (c)                                                                              (d)

Fig. 4 In biomaterial-sensor coupling, the bio and sensor elements can be coupled together in one of four ways: (a) membrane
entrapment, (b) physical adsorption, (c) matrix entrapment, and (d) covalent bonding.

be further amplified before measuring                         fuse through the polymer layer, causing                sinusoidal voltage (ac), which helps in
for improved sensitivity.                                     a change in the FET surface potential.                 minimizing undesirable effects such as
    Thermal detection biosensors exploit                      This type of biosensor is also called an               Faradaic processes, double layer charg-
one of the fundamental properties of                          enzyme field effect transistor and is pri-             ing, and concentration polarization.
biological reactions, namely absorption                       marily used for pH detection.                             Amperometric is a high sensitivity
or production of heat, that in turn                              Electrochemical biosensors are mainly               biosensor that can detect electroactive
changes the temperature of the medium                         used for the detection of hybridized                   species present in biological test sam-
in which the reaction takes place. These                      DNA, DNA-binding drugs, and glucose                    ples. Since the biological test samples
biosensors are constructed by combin-                         concentration. The underlying principle                may not be intrinsically electroactive,
ing immobilized enzyme molecules                              for this class of biosensors is that many              enzymes are needed to catalyze the pro-
with temperature sensors. When                                chemical reactions produce or consume                  duction of radioactive species. In this
the analyte comes in contact with the                         ions or electrons, causing some change                 case, the measured parameter is current.
enzyme, the heat reaction of the                              in the electrical properties of the solu-                 In the potentiometric type of sensor,
enzyme is measured and calibrated                             tion that can be sensed out and used as                the measured parameter is the oxida-
against the analyte concentration. The                        a measuring parameter. Electrochemical                 tion or reduction potential of an elec-
total heat produced or absorbed is pro-                       biosensors can be classified based on                  trochemical reaction. The working prin-
portional to the molar enthalpy and the                       the measuring electrical parameters as                 ciple relies on the fact that when a
total number of molecules in the reac-                        conductimetric, amperometric, and                      ramp voltage is applied to an electrode
tion. The measurement of the tempera-                         potentiometric. A comparative discus-                  in solution, a current flow occurs
ture is typically accomplished via a                          sion of these three types of electro-                  because of electrochemical reactions.
thermistor, and such devices are known                        chemical biosensors is given in Table 1.               The voltage at which these reactions
as enzyme thermistors. Their high sensi-                         The measured parameter in conduc-                   occur indicates a particular reaction and
tivity to thermal changes makes ther-                         timetric sensors is the electrical conduc-             particular species.
mistors ideal for such applications.                          tance/resistance of the solution. When
Unlike other transducers, thermal                             electrochemical reactions produce ions                 Glucose biosensors
biosensors do not need frequent recali-                       or electrons, the overall conductivity or                 The most commercially successful
bration and are insensitive to the optical                    resistivity of the solution changes. This              biosensors are amperometric glucose
and electrochemical properties of the                         change is measured and calibrated to a                 biosensors. These biosensors have been
sample. Common applications of this                           proper scale. Conductance measure-                     made available in the market in various
type of biosensor include the detection                       ments have relatively low sensitivity.                 shapes and forms such as glucose pens
of pesticides and pathogenic bacteria.                        The electric field is generated using a                and glucose displays.
    Ion sensitive biosensors are semicon-
ductor FETs having an ion-sensitive sur-
face. The surface electrical potential
                                                                             Substrate    +                                                  Enzyme
changes when the ions and the semicon-                                                         Enzyme            =         Substrate
                                                                                                                                            Complex
ductor interact. This change in the
potential can be subsequently measured.
The ISFET can be constructed by cover-                                        Product
                                                                                          Enzyme
ing the sensor electrode with a polymer                                                  Complex                     Product        +   Enzyme
layer. This polymer layer is selectively
permeable to analyte ions. The ions dif-                      Fig. 5 Working principle of enzymes



MARCH/APRIL 2006                                                                                                                                                  37
               Bio-Element Transducer             Bio-Element Transducer                       process, a small gold electrode is
                                                                                               immersed in a tissue culture medium.
                                              Analyte
                                                                                               When cells get attached and spread on
     Analyte                                                                                   the electrodes, the impedance mea-
                            Recognition                            No Recognition No           sured across the electrodes changes.
                                     Signal                                     Signal         This changing impedance can be used
                                                                                               for understanding the cell behavior in
                                                                                               the culture medium.
                                                                                                   The attachment and spreading behav-
Fig. 6 Specificity of enzymes is the basis of biosensors
                                                                                               ior of the cells are important factors for
                                                                                               this type of biosensor. Cancerous cells
                                                                                               can usually grow and reproduce (mito-
    The first historic experiment that          chemical reaction takes place at a spe-        sis) freely in a medium without being
served as the origin of glucose biosen-         cific applied potential. The cellulose         attached to any substrate/surface.
sors was carried out by Leland C.               acetate outer layer placed over the            Normal cells, on the other hand, need to
Clark. He used platinum (Pt) elec-              GOD membrane also provides a barrier           be attached to a surface before they
trodes to detect oxygen. The enzyme             for interfering substances. The ampero-        grow. After attachment, the shape of the
glucose oxidase (GOD) was placed                metric reading of the biosensor (current       cells becomes flat and no longer remains
very close to the surface of platinum           versus glucose concentration) shows            spherical. Figure 8 demonstrates this cell
by physically trapping it against the           that the relationship is linear up to a        behavior in a tissue culture medium.
electrodes with a piece of dialysis             specific glucose concentration. In other           The principle of measurement is as
membrane. The enzyme activity                   words, current increases linearly with         follows. The cells are grown on gold
changes depending on the surrounding            glucose concentration; hence it can be         electrodes. The electrodes are immersed
oxygen concentration. Figure 7 shows            used for detection.                            in a tissue culture medium that works as
the reaction catalyzed by GOD.                      The current and future applications        an electrolyte. A voltage is applied
Glucose reacts with GOD to form glu-            of glucose biosensors are very broad           through a resistance, and the magnitude
conic acid while producing two elec-            due to their immediate use in diabetic         and phase of the voltage are measured
trons, and two protons, thus reducing           self-monitoring of capillary blood glu-        with a lock-in amplifier. Since the current
GOD. The reduced GOD, surrounding               cose. These types of monitoring devices        is constant, the measured magnitude and
oxygen, electrons, and protons (pro-            comprise one of the largest markets for        phase can be assumed to be proportional
duced above) react to form hydrogen             biosensors today, and their existence          to impedance (resistance and capaci-
peroxide and oxidized GOD, which is             has dramatically improved the quality          tance). After some time, it is found that
the original form. This GOD can again           of life for people with diabetes.              the resistance and capacitance values
react with more glucose. The higher                                                            fluctuate frequently. This happens when
the glucose content, the more oxygen            A biosensor to monitor                         cells are alive and moving. This type of
is consumed. On the other hand, lower           cell morphology                                biosensor has several advantages. It is
glucose content results in more hydro-             Another type of biosensor can be            less time consuming compared to con-
gen peroxide. Hence, either the con-            used to monitor cell morphology in tis-        ventional methods, it is possible to auto-
sumption of oxygen or the production            sue culture environments. The sensing          mate and quantify cell morphology mea-
of hydrogen peroxide can be detected            principle used is known as electric cell-      surements, and the fluctuating pattern
with the help of platinum electrodes,           substrate impedance sensing. In this           can be used as the signature for a cell.
and this can serve as a measure for
glucose concentration.
    Disposable amperometric biosensors                                Glucose                               Gluconic Acid
for the detection of glucose are also
available. The typical configuration is a
button-shaped biosensor consisting of
                                                                                  Glucose Oxidase
the following layers: metallic substrate,
graphite layer, isolating layer, mediator
                                                               (a) Oxygen                                      (a) Hydrogen
modified membrane, immobilized                                                                                     Peroxide
                                                                    or
enzyme membrane (GOD), and a cellu-                           (b) Oxidized                                           or
lose acetate membrane. This biosensor                           Mediator                                        (b) Reduced
uses graphite electrodes instead of plat-                                                                           Mediator
inum electrodes, as originally used by
Clark. The isolating layer is placed on
the graphite electrodes, which can filter
out certain interfering substances, such
as ascorbic acid and uric acid while
allowing the passage of hydrogen per-                                                    Electrode
oxide and oxygen. The mediator modi-
fied membrane helps in keeping the
GOD membrane attached to the
graphite electrode when the electro-             Fig. 7 Clark’s experiment               Electrons



38                                                                                                                    IEEE POTENTIALS
DNA detection                                   can detect various biologically active       again. This happens when the tempera-
   The category of biosensors used for          materials like toxins, proteins, viruses,    ture is lowered. Thus, in one
DNA detection is also known as biode-           and bacteria in low concentrations. To       heating/cooling cycle the amount of
tectors. The objective is to isolate and        accomplish this, it uses a sandwich          sample DNA is doubled (one cycle time
measure the strength of single DNA-DNA          assay technique, in which antibodies         is about one minute). Typically, 25–40
or antibody-antigen bonds, which in turn        against a particular protein, virus, or      cycles are needed to produce approxi-
helps in detecting and characterizing sin-      bacterium are covalently bound to a          mately 1 billion copies. This amount is
gle molecules of DNA or antigen. In one         solid surface. The sample solution flows     sufficient for optical detection. While the
method, multiple copies of the sample           over the surface, and the antibodies         PCR is busy in copying DNA, identifica-
DNA are created using a polymerase              capture the virus present in the sample.     tion also could be made possible using
chain reaction (PCR). On the other hand,        Next, super paramagnetic beads, also         fluorescent DNA probes.
force amplified biological sensor (FABS),       coated with an antibody against the             In general, PCR consumes a great
bead arraycounter (BARC), and force dif-        virus, flow through the liquid and bind      deal of power because of the succes-
ferentiation assay (FDA) biosensors can         to the analyte. After washing away           sive heating/cooling cycles that take
perform many such measurements in a             excess beads, a number of beads              about 30 minutes. It was previously not
                                                                                             possible to fabricate portable battery
                                                                                             operated biodetectors that can do PCR.
                                    Cell                 Attachment                          However, using micro electromechani-
                                                                                             cal systems (MEMS), such kinds of
                                                                                             biodetectors (which are basically lab-
                                                                                             on-a-chip systems) have been devel-
                                      Substratum                                             oped. In these MEMS-based devices the
            Transfer
            of Cells                                                                         amount of reagent used is scaled down.
                                                                                             This type of biosensor has several
                                                                          Spreading
                                             Growth
                                                                                             advantage: they are many times faster
                                                                         Cell Mobility
          Daughter Cells                                                                     than conventional PCR, more efficient
                                                                                             in the number of DNA copies pro-
                                                                                             duced, easily designed to use small vol-
                                                                                             umes, and economical.

                        Spreading                                   Mitosis                  A holographic biosensor
                                                                                             for screening pancreatic disorders
                                                                                                 Holograms are photographs of three-
                                                                                             dimensional impressions on the surface
                                                                                             of light. To make a hologram one
                                                                                             needs to photograph light waves. When
                                                                                             an object wave meets a reference wave,
                                       Cell Division                                         a standing wave pattern of interference
                                                                                             is created which can be photographed,
Fig. 8 A cell in tissue culture medium                                                       thus creating a hologram. A hologram is
                                                                                             generally recorded on silver halide film.
                                                                                             The film consists of a base material of
single easy operation. In these cases,          remain bound to the surface through          glass or plastic. A photoactive layer
magnetic microbeads are used to pull on         the virus. By determining the number of      called emulsion is on top. This emul-
DNA-DNA or antibody-antigen bonds               beads, the concentration of virus in the     sion layer is made up of gelatin, which
with a known force, and the strengths of        original sample is calculated.               is a colorless/yellowish protein. Silver
the presumed bonds are tested by                     The biodetectors are used to identify   and halide materials float in the gelatin
observing with a micromechanical sensor         a small concentration of DNA (of             layer. They chemically react to form
(FABS) or with a magnetoresistive sensor        microorganisms like viruses or bacteria)     silver halide molecules. When light
(BARC) whether the beads detach from            in a large sample. This relies on com-       energy travels into the gelatin, it is trans-
the surface. This kind of biosensor is          paring sample DNA with DNA of known          ferred to the silver halide molecule.
extremely useful in the detection of            microorganisms (probe DNA). Since the            Biosensors that use holograms as the
anthrax, ricin, botulinum, and other            sample solution may contain only a           sensing element have been produced.
pathogens.                                      small number of bioorganism molecules,       This biosensor can have potential appli-
   FABS is needed for monitoring the            multiple copies of the sample DNA            cations in screening pancreatic disor-
concentration of various biological             need to be created for proper analysis.      ders at lower price. The bioelement
agents that may possibly be present in          This is achieved with the help of a PCR.     used is bovine pancreatic trypsin
the environment. FABS is designed in            PCR starts by splitting samples of dou-      inhibitor (BPTI), which is an enzyme.
such a way that it is fully automated,          ble-helix DNA into two parts by heating      To screen pancreatic disorders, trypsin
compact, and rugged and can be imple-           it. If the reagents contain proper growth    needs to be detected in the duodenal
mented remotely. The assay is also a            enzymes, then each of these strands will     fluid or a stool sample. By proper use
rapid process as it may warn of a               grow the complementary missing part          of BPTI, trypsin detection can be made
potential threat to human health. FABS          and form the double-helix structure          possible.



MARCH/APRIL 2006                                                                                                                      39
    When the hologram is illuminated
                                               Table 1. Different electrochemical sensing characteristics.
by white light, constructive interfer-
ence gives a characteristic spectrum                                                       Electrochemical sensing
having spectral peaks described by the                               Conductimetric            Amperometric             Polentiometric
Bragg equation. The characteristic
                                               Measured Parameter    Condutance/Resistance           Current              Potential/Voltage
spectrum is dependent on the gelatin
matrix of the hologram. If the gelatin         Applied Voltage           Sinusoidal (AC)      Constant Potential (DC)      Ramp Voltage
molecules of the hologram film are             Sensitivity                    Low                      High
protease degraded the characteristic           Governing Equation    Incremental Resistance      Cottrell Equation         Nerst Equation
spectrum changes. This change is spe-          Fabrication               FET + Enzyme             FET + Enzyme             FET + Enzyme
cific to the type of degradation. The
                                                                                                   2 electrodes            Oxide electrode
reflected light from the hologram is
detected by spectrograph and charge-
coupled device detectors at intervals         large; cost, research should be focused          tions of MEMS,” in Proc. Electron Devices
of some minutes and is analyzed for           on the development of low-cost                   Meeting, 1996, pp. 239–242.
peak wavelength and reflectivity              biosensors. At present, with the threat             • M.A. Northrup, C. Gonzalez, D.
change with time. The major advan-            of bioterrorism omnipresent, the devel-          Hadley, R.F. Hills, P. Landre, S. Lehew,
tage of this biosensor is that very           opment of faster, reliable, accurate,            R. Saw, J.J. Sninsky, and R. Watson, “A
small trypsin levels can be detected          portable, and low-cost biosensors has            MEMS-based miniature DNA analysis
within a 60-minute period.                    become more important than ever.                 system,” in Proc. 8th Int. Conf. Solid-
                                                                                               State Sensors and Actuators, and
Conclusions                                   Acknowledgments                                  Eurosensors IX, Transducers ’95,
    We have discussed various biosen-            The authors would like to acknowl-            June 25–29, 1995, pp. 764–767.
sors in detail. The survey initially intro-   edge feedback on the contents of this               • N.V. Lavrik, M.J. Sepaniak, and
duces the basic concepts of the biosen-       article by Dr. Shekhar Bhansali,                 P.G. Datskos, “Cantilever transducers as
sor. A high-level overview of different       Department of Electrical Engineering,            a platform for chemical and biological
types of biosensors is also given.            University of South Florida.                     sensors,” Rev. Sci. Instrum., vol. 75,
Working principles, constructions,                                                             no. 5, July 2004, pp. 2229–2253.
advantages, and applications of many          Read more about it                                  • S.P.J. Higson, S.M. Reddy, and P.M.
biosensors are presented. In addition,            • B.D. Malhotra, R. Singhal, A.              Vadgama, “Enzyme and other biosen-
we should point out that during the last      Chaubey, S.K. Sharma, and A. Kumar,              sors: Evolution of a technology,” Eng.
two decades, advances in MEMS have            “Recent trends in biosensors,” Curr.             Science Educ. J., vol. 3, no. 1, pp. 41–48,
given rise to a whole new class of            Appl. Physics, vol. 5, no. 2, pp. 92–97,         Feb. 1994.
biosensors, which involve the transduc-       2005.
tion of mechanical energy and are                 • C.A. Marquette and L.J. Blum,              About the authors
based on mechanical phenomena.                “State of the art and recent advances in             Saraju P. Mohanty is an assistant pro-
    There are various technical difficul-     immunoanalytical systems,” Biosensors            fessor in the Department of Computer
ties for which some solutions exist, but      Bioelectron., vol. 21, no. 8, pp.                Science and Engineering, University of
still more research efforts are needed to     1424–1433, 2006.                                 North Texas. He received a Ph.D. in com-
find better alternatives. The areas in            • C. Aston, “Biological warfare              puter science and engineering from the
which research is needed are: contami-        canaries,” IEEE Spectr., vol. 38, no. 10,        University of South Florida in 2003, a
nation, bioelements and chemicals             pp. 35–40, Oct. 2001.                            master of engineering degree in systems
used in the biosensors need to be pre-            • C. Bartic and G. Borghs, “Organic          science and automation from the Indian
vented from leaking out of the biosen-        thin-film transistors as transducers for         Institute of Science, Bangalore, in 1999,
sor over time, a serious issue for non-       (bio)analytical applications,” Analyt.           and a bachelor of technology (first class
disposable ones; immobilization of bio-       Bioanalyt. Chem., vol. 384, no. 2,               honors) degree in electrical engineering
molecules to avoid contamination, bio-        pp. 354–365, Jan. 2006.                          from the College of Engineering and
molecules are attached to the transduc-           • C.R. Keese and I. Giaever, “A              Technology, Orissa University of
er as strongly as possible, but the prob-     biosensor that monitors cell morphology          Agriculture and Technology, Bhuba-
lem with this is that the behavior of         with electric fields,” IEEE Eng. Med. Biol.      neswar, India, in 1995. He is a member of
enzymes when absorbed on the surface          Mag., vol. 13, no. 3, pp. 435–445,               IEEE-CS and ACM-SIGDA and the author
is not well understood (the reaction of       June/July 1994.                                  of many journal and conference papers.
enzymes in free solutions is better               • CDC Emergency and Preparedness                 Elias Kougianos is an assistant pro-
understood); sterilization, if a sterilized   and Response. Available: http://www.             fessor in the Department of Engineering
probe is used, some sensor’s biomole-         bt.cdc.gov/bioterrorism/                         Technology at the University of North
cules may be destroyed whereas if                 • D.M. Fraser, “Glucose biosensors—          Texas. He has extensive industrial expe-
nonsterile probes are used some com-          The sweet smell of success,” Med.                rience in semiconductor process inte-
promises are needed; uniformity of bio-       Device Technol., vol. 5, no. 9, pp. 44–47,       gration, process and device simulation,
molecule preparation, fabrication of          1994.                                            and VLSI design. His current research
biosensors that can reproduce results             • G. Kovacs, Micromachined                   interests include analog and mixed
need such uniformity; selectivity and         Transducers: Sourcebook. New York:               signal circuit simulation and the appli-
detection range, should be more selec-        WCB/McGraw-Hill, 1998                            cation of stochastic techniques to the
tive and the detection range should be            • K. Peterson, “Biomedical applica-          solution of electromagnetic problems.



40                                                                                                                       IEEE POTENTIALS

				
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