novel semiconductor materials for the development of

analytica chimica acta 615 (2008) 1–9
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/aca
Review
Novel semiconductor materials for the development of
chemical sensors and biosensors: A review
Nikos Chaniotakis
∗
, Nikoletta Sofikiti
Laboratory of Analytical Chemistry, Department of Chemistry, University of Crete,
Voutes 71003 Iraklion, Crete, Greece
article info
Article history:
Received 15 November 2007
Received in revised form
13 March 2008
Accepted 18 March 2008
Published on line 30 March 2008
Keywords:
Chemical sensor
Biosensor
Semiconductor
Gallium nitride
Indium nitride
Conductive diamond
Transduction
Surface potential
abstract
The aim of this manuscript is to provide a condensed overview of the contribution of certain
relatively new semiconductor substrates in the development of chemical and biochemical
field effect transistors. The silicon era is initially reviewed providing the background onto

which the deployment of the new semiconductor materials for the development of bio-
chem-FETs is based on. Subsequently emphasis is given to the selective interaction of novel
semiconductor surfaces, including doped conductive diamond, gallium nitride, and indium
nitride, with the analyte, and how this interaction can be properly transduced using semi-
conductor technology. The main advantages and drawbacks of these materials, as well as
their future prospects for their applications in the sensor area are also described.
© 2008 Elsevier B.V. All rights reserved.
Contents
1. Introduction 2
2. The silicon era 4
3. New semiconductor substrates 4
4. Diamond 5
5. GaN and III-nitrides 6
6. Forecasting the future 7
References 8
∗
Corresponding author. Tel.: +30 810545018; fax: +30 810545165.
E-mail address: (N. Chaniotakis).
URL: lytical
chemsitry.uoc.gr (N. Chaniotakis).
0003-2670/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.aca.2008.03.046
2 analytica chimica acta 615 (2008) 1–9
1. Introduction
The semiconductor technology has boomed since the inven-
tion of the transistor in 1948 [1]. Initially the semiconductor-
based transistors were based on the physicochemical
interfacial properties of mainly two semiconductors, silicon
and germanium. The important physical properties of the
transistors were related to the actual area and thickness of

the active layer, and the final size and shape of the complete
device. Most importantly, it has been known early on that the
chemical characteristics of the active area of the semicon-
ductor play a major role in determining the behavior and the
performance of the final device. This is indeed the case since
a close look at the interfacial processes involved during the
operation on transistors will reveal that it is without a doubt a
chemical process technology. Based on these facts it was clear
that the precise control of the surface chemistry was manda-
tory for the final optimization of the device performance. For
this reason there are some basic parameters that need to be
taken into account when new semiconductor materials are
to be developed and optimized, and which play a decisive
role in their applicability to biosensors. The chemical synthe-
sis (growth) of the material, the post-material treatment such
as doping or ion implantation and the final chemical surface
treatment are the three most important ones. The develop-
ment and optimization of these semiconductor technology
procedures has allowed for the growth or synthesis of materi-
als withvery well controlled and unique physical and chemical
characteristics, down to the atomic level.
The main parameter, which has been shown very early to
play a very significant role in the behavior of these mate-
rials, especially in their application to bio-FETs as well as
all other electrochemically based biosensors, is the-what-
is-called “work function”, “contact potential”, or “electrode
potential”. Even though there might be some fine differences
between these terms, for the purpose of this work we will refer
to all these terms as the “surface potential” of the semiconduc-
tor. Semiconductor surface potential plays an important role

in the performance and characteristics of all devices involving
surface chemistry and thus semiconductor-based biosensors.
Fundamental studies of the surface potential of surfaces have
been vital in understanding the behavior of these materials, as
well as their applications in chemical sensors and biosensors
in general.
The surface potential of a material is of fundamental inter-
est to many areas of semiconductor sciences. Both the native
and the imposed potential can play a major role in the space
charge effect. The induced depletion or inversion layer, and
the Fermi energy shift or pinning, are parameters that are
directly related to, not only the chemical composition of the
bulk material, but also to the chemical equilibria that exists
between the surface of the semiconductor and the analyte
sensed. The surface potential, and therefore the nature of
the space charge double layer associated with the surface,
depends on the chemistry of the adsorbed layers on the elec-
trode surface, as it has been known since the early 1930s
[2,3]. This idea has been extended to the semiconductor sur-
face, especially after the invention of FETs in 1948 by Bardeen
and Brattain [1]. In 1954 Brattain and Bardeen actually mea-
sured for the first time the effect that different electrolytes,
such as HCl, KCl or KOH, had on the half-cell potential of
the germanium semiconductor [4]. In the same journal issue,
Bardeen and Morisson [5] presented the effect that different
electrolytes and gasses had on the properties of the semi-
conductor as manifested by the change in the surface space
charge barrier. In addition, the effect of both ions and pH on
the surface of semiconductors was reviewed a little later by
Boddy [6], showing both the dependence of surface potential in

germanium and in silicone semiconductors [7]. It was shown
in these early works that the surface chemistry of the material
is determined by the active chemical functionalities found at
the surface, and to a lesser degree by the crystal orientation. At
the same time, the type and amount of the surface chemical
functionalities depend on both the chemical composition of
the material itself, as well as, on any chemical post-treatment
of the surface.
The surface chemistry, or to be more precise the surface
chemical functionalities, can induce specific physicochemi-
cal properties of the semiconductor as presented early on by
Bardeen and Morrison [5], and proven by many other scientists
since then. Those are:
1. Work function or contact potential [8–13].
2. Rectification [14,15].
3. Chemical reactions with electron transfer [16,17].
4. Adsorption [18,19].
5. Surface recombination–photoconductivity [20,21].
6. Change in contact potential with light [22].
7. Surface conductance–channel effect [23].
8. Change in surface conductance with electrostatic
field–field effect [24–26].
9. Noise.
All these properties can be used as the basis for the
development of analytically useful devices, including chem-
ical sensors, biosensors, and bio-chem-FETs. This is due to
the fact that external chemical stimuli can drastically alter
these fundamental and easily measurable surface semicon-
ductor properties. Monitoring surface current, potential or
impedance characteristics can be directly related to the chem-

ical stimuli interrogating the semiconductor sensing surface,
as shown in Fig. 1.
These facts make semiconductors ideal matrices as sensor
elements and transducers for the development of a variety
of chemical sensor and biosensor systems, especially sur-
face active Potentiometric Ion Selective Electrodes (ISEs), Field
Effect structures (FETs), amperometric biosensors, Surface
Acoustic Wave sensors (SAWs), and Film Bulk Acoustic Res-
onators (FBARs).
The development of such sensing device is always based
on the affect resulting from the specific or selective inter-
action of an analyte with the semiconductor surface. Such
interaction will usually result in changes of the electrochem-
ical characteristics of the surface [27], as shown in Fig. 2. The
most important of these parameters are the space charge,
the field and the potential. Once this interaction has been
characterized, a variety of sensing schemes can be envisaged.
Potentiometric ISE are based on the induced potential gen-
erated at the semiconductor solution interphase, while the
analytica chimica acta 615 (2008) 1–9 3
Fig. 1 – Generic experimental setups employed for the design of chemical sensors and biosensors based on semiconductor
surfaces. (A) Surface Acoustic Waves (SAW) biosensor, (B) normal and light addressable electrochemical sensors, (C)
CHEMFET sensor, and (D) hall effect sensor.
Fig. 2 – Schematic diagram of the electrical parameter distribution for an electrochemically active semiconductor surface.
4 analytica chimica acta 615 (2008) 1–9
current that passes the devise is practically zero. On the other
hand, the development of a CHEMFET will depend on the
effect this surface potential will have on the characteristics
of the underlying semiconductor layers, and specifically on
the depletion layer of the gate. Similarly, the selectivity and

sensitivity of semiconductor-based FBARs will depend on both
the initial physical characteristics of the material, as well as
the induced physical changes upon chemical interaction of
the analyte with the sensing surface. Finally, amperometric
sensors are dependent on changes in either the conductance
of the material, or changes in the activity of redox species
available within the sensor element.
It is thus clear from the above that creating chemical
sensors or biosensors from semiconductors requires precise
chemical control of the surface chemistry. Only under these
conditions the analytical characteristics of the sensor such as
selectivity, sensitivity, detection limit, response time, and sig-
nal stability can be optimized. Since analyte recognition and
detection is a result of the perturbation of the electro optical
properties of the semiconductor surface and subsurface layers
there must be a specific and reversible chemical interaction
of the analyte with the semiconductor sensing element. As
the material science community evolved and was able to have
complete control of the growth process, more and more these
materials were used for the development of sensors.
2. The silicon era
In the late 1960s, the use of silicon as a matrix for integrated
sensor–transducer systems had begun [28,29]. Silicon-based
devices for the in vivo measurement of electrophysiological
measurements had already been developed. The revolution
came from a publication of Bregveld [23], in which he showed
that Si-based devices, the so-call pH-FETs, can be used to mea-
sure pH in very small volumes, and with good accuracy. This Si
technology came to maturation with the commercialization of
these pH sensors in the mid-80’s, while they were the platform

for the development of other ion-selective FETs and bio-FETs
up to date. When SiO
2
, or other metal oxides or nitrides such
as Al
2
O
3
,Ta
2
O
5
, SnO
2
, and Si
3
N
4
are used as the chemical
recognition element, the resulting sensor is highly selective
for the hydrogen ion, due to the very strong hydrogen bond-
ing that exists with the oxide layer. The oxides can coordinate
reversibly with the hydrogen ion in solution, affecting the sur-
face potential of the sensing element. These surface potential
changes affect the gate potential in the same way as a metal
gate field effect transistor (MEGFET) works, altering the signal
of the pH-FETs. The Si technology offered considerable advan-
tages in the microsensing area, due to the ability to integrate
the sensing element directly with the readout circuit to obtain,
self-contained microsensor devices with high sensitivities and

signal to noise ratios, thus allowing for the development of
large sensor arrays highly useful in the area of biochips.
One of the major obstacles to overcome during the design
of a continuous sensing system is the long-term storage and
operational stability of the sensing element. Even though SiO
2
and its related metal tin oxide substrates are very selective
substrates for the detection of hydrogen ions, their stability
in harsh environments is limited. Treatment with very acidic
or basic solution, or fluoride containing solutions should thus
be avoided since it can be detrimental to the analytical behav-
ior of these systems. Surface etching and oxidation in these
solutions will result in the drastic decrease in the sensitivity,
while the response time increases considerably. In addition
the proper isolation between the devices and the chemical
solutions, as well as the sensitivity to light are still issues to
be completely resolved. It is therefore a challenge to develop
inert semiconductor electrodes.
The bio-chemical sensors developed up until very recently
were based on the pH sensitive FETs. Any chemical or bio-
logical process that can result in changes of the pH can be
combined with a pH-FET transducer, resulting in what is called
CHEMFET of BIOFET. In all of these devices, the surface poten-
tial developed at the surface of the semiconductor is based on
the direct interaction of the ligand with the exposed atoms
of the semiconductor, as shown in Fig. 5 [30]. This chemical
interaction (chemisorption or coordination) of the charged or
polarized analytes with the semiconductor surface induces
a surface potential. It is important to recognize this fact,
which is much more pronounced and important for the design

of chemical sensors and biosensors than the inherent band
bending due to layered structure or to crystal structure end.
The development of novel semiconductor matrices for
application is the area of chemical sensors and biosensors
is based on the fact that the surface of the new materials
must possess certain chemical and physical properties that
can deal with the drawbacks of the Si technology, and which
have been extensively analyzed in the last decades. Those
are the selectivity to species other than hydrogen ion, the
chemical stability of the surface to extreme chemical envi-
ronments, the ability for surface functionalization, increased
signal sensitivity and stability, and the biocompatibility of the
final device. New semiconductor materials with well-defined
surface chemistry, which are stable in aqueous solutions and
can selectively interact with analytes other than the hydro-
gen ion, can thus be very valuable tools in the design of novel
chemical sensors.
3. New semiconductor substrates
In recent years there is an intense effort in the design of new
semiconductor materials other than Si, for use in power elec-
tronics and other microelectronic applications [31,32] in order
to deal with the problems associated with the use of the Si-
based electronic devices. Among these materials, emphasis
has been given to those with relatively large band gap (Wide-
Bandgap Semiconductors, WBSs) due to their application in
UV lasers and photonics. But besides that, some of these
materials, such as silicon carbide (SiC), gallium nitride (GaN),
and diamond are proven to be unique materials for a variety
of applications mainly due to the fact that they are overall
more efficient in many electronic processes, since they can

withstand larger voltages, they have higher thermal conduc-
tivity, and they are more stable over time and thus are more
reliable. Moreover, the aforementioned WBG materials have
excellent reverse recovery characteristics, and for this reason
they require less time and energy to return to the base line
signal. In addition they are less susceptible to electromag-
analytica chimica acta 615 (2008) 1–9 5
Table 1 – Summary of the analytical applications of
novel semiconductor materials
Gas sensing (H
2
,NH
3
,NOx,O
2
,
CO, H
2
O, combustion gases,
ethanol, organic vapours,
hydrocarbons, fluorocarbons)
GaN [33–42]
InN [43]
AlN [44–46]
SiC [47–53]
Ion sensing
GaN [54–60]
InN [61]
Diamond [62,63]
Other electroanalytical applications Diamond [64–74]

Bio-electrochemical applications
Diamond [75–77]
GaN [78–80]
Electrocatalysis Diamond [81–83]
Shear mode acoustic
wave biosensors
AlN [84–88]
GaAs [89]
netic interference (EMI), while the devices based on them can
operate at higher frequencies. This unique chemical, physi-
cal and mechanical stability make these new semiconductor
materials ideal for the development of specific chemical sen-
sor and biosensor systems. Table 1 summarizes the analytical
applications of novel semiconductor materials.
4. Diamond
Diamond is a unique WBS (E
g
= 5.45 eV) since it possesses
several distinct properties including extreme hardness, high
electrical resistance, chemical inertness, high thermal con-
ductivity, high electron and hole mobility, and optical
transparency. These properties appoint this material ideal for
various highly demanding applications [90,91]. Since diamond
is one of nature’s best insulators doping is required for its
use in electrochemical studies. Chemical Vapor Deposition
(CVD) methods [89,90] can produce highly conductive boron
doped diamond films [92]. The surface of as-grown undoped
and boron-doped diamond films is relatively nonpolar, with
the surface carbon atoms terminated by hydrogens [93]. This
fact, along with the sp

3
-hybridization of carbon atoms in dia-
mond and the steric hindrance of such surfaces, are the main
reasons for the chemical inertness of diamond.
Despite that, there are several notable exceptions to the
generally low reactivity of diamond. First of all diamond sur-
faces can be oxidized by several post-growth treatments, such
as oxygen-ambient annealing [94], oxygen-plasma treatment
[93] or anodic polarization [95]. All these oxidizing techniques
result in an increase of surface O/C ratio and the presence of
carbon–oxygen bonds. An important characteristic of this sur-
face is that this oxygen termination can partially regenerated
by subsequent acid washing and hydrogen-plasma treatment
[93].
Another very useful modification of diamond surface is
the halogenation using atomic and molecular chlorine and
fluorine [96,97]. Although molecular Cl
2
and F
2
have been
used as reagents, the reaction conditions are such that atomic
radical species are produced. Since the reaction conditions
required are very extreme (for example, Cl
2
/400–500
◦
C), and
thus unsuitable for large-scale implementation, the photo-
chemical radical production is usually preferred [98].

Except from these two small atomic radicals, larger organic
radicals have been also photochemically introduced onto dia-
mond surfaces. Such an example is the perfluorobutyl moiety
which has been successfully attached to diamond surfaces by
irradiating perfluorobutyl iodide (C
4
F
4
I) either using UV light
or X-rays [99,100]. Moreover, a quite big variety of long-chain
organic moieties have been also introduced on diamond sur-
faces by photochemical reactions. Although such compounds
are either functionalized alkanes or alkenes, it is proven that
alkenes significantly increase the attachment efficiency and
are thus used preferencially [101].
The main purpose of all the aforementioned chemical
modification methods is to provide diamond surface with
the appropriate binding groups (mainly primary amine and
carboxylic acid groups). These groups are required for fur-
ther functionalization of diamond surface with more complex
molecules, such as DNA or proteins, with the altimate goal of
diamond-based biosensor development.
At the same time diamond has attracted a lot of atten-
tion due to its unique electrochemical properties. In particular,
boron-doped, hydrogen-terminated, polycrystalline diamond
has a very wide working potential window (+3.0 to 3.5 V)
in aqueous and non-aqueous media, and low overpotential
for several redox analytes. In addition this material has low
and stable background current, leading to improved signal-to-
noise ratios [102]. Finally adsorption of polar molecules on its

surface is insignificant, leading to improved resistance to sur-
face deactivation and fouling. It should be mentioned though
that the surface chemistry of the diamond is strongly influ-
enced by the amount of boron doping [103,104].
All the above-mentioned properties, along with the fact
that diamond is considered highly biocompatible, make this
material ideal for the development of completely integrated
bioelectronic sensing systems. This seems to be true since
already a large number of diamond’s electroanalytical appli-
cations have been reported, in flow-injection analysis (FIA)
systems or ion and high-performance liquid chromatogra-
phy (IC & HPLC), for the detection of azide [63,64], metal
ions [63,65], nitrite [63], dopamine [63,66,67], chlorpromazine
[63], hydrazine, biogenic aliphatic polyamines [68,69], NADH
[70], uric acid [71], histamine and serotonin [72], and carba-
mate pesticides [73]. It is worth to be mentioned that, in all
the above cases, diamond demonstrated superior electrode
performance in terms of linear dynamic range, sensitivity,
limit of detection, response stability and long-term activity,
as compared with glassy carbon. In the field of electrocataly-
sis some interesting applications have also been reported, for
the oxidation of methanol and the reduction of oxygen, both
using a conductive, dimensionally stable diamond electrode
containing Pt nanoparticles [80–82]. Another very attractive
application of diamond, coming from the area of spectro-
electrochemistry, was reported in 2001 [105], concerning a
free-standing boron-doped diamond disc (0.38mm thick and
8 mm in diameter) used for the oxidation of ferrocyanide, or
the reduction of methyl viologen, and the simultaneous spec-
troscopic monitoring of the products through the disc. In the

same year, the construction of an electrolyte-solution-gate
diamond field-effect transistor (SGFET) was reported for the
first time [106], and after 2 years, in 2003, the first anion-
sensitive diamond SGFET was reported from the same group
6 analytica chimica acta 615 (2008) 1–9
Fig.3– TheGaN(0001)wurtzite crystal. The outer most
atomic layer of the material (Ga) is theoretically
non-bonded, allowing for a strong interaction with
overlaying coordinating ligands.
as well [61,62]. The first bio-electrochemical application of
diamond was reported in 2002, concerning the direct elec-
trochemistry of cytochrome c at nanocrystalline boron-doped
diamond [74]. Since then, many other bio-electrochemical
applications have been reported, such as the direct obser-
vation of DNA hybridization via simple measurement of
interfacial impedance, using DNA-modified diamond thin
films [75], or the in vitro measurement of norepinephrine
(NE)-release from a test animal’s mesenteric artery, using a
Pt-microelectrode coated with a thin film of boron-doped dia-
mond [76].
5. GaN and III-nitrides
GaN, AlN and InN are the so-called III-nitride semiconductor
materials. Some of these semiconductors have been the sub-
ject of intense research lately, due to their very high electron
mobility, high energy band gap, and biocompatibility. These
properties are very important in the design of chemical sen-
sors and biosensors for remote, in vivo, and low detection level
measurements. III-Nitrides prefer to crystallize in the wurtzite
crystal structure (Fig. 3). The important feature to understand,
in wurtzite crystal structures and in particular the (0001)ori-

entation is the fact that the outer most atomic layer has three
bonds to the underlying nitrogen atomic plane while the forth
unoccupied bond (tangling bond) is available for interaction
with ligands that exist within the close proximity test envi-
ronment. The type of ligands that can interact chemically with
this surface will thus depend on the chemistry of the surface
layer of the material. Extensive studies [107] have proven that
there is an induce polarity in these bonds, with the more elec-
tropositive atoms being electron deficient relative to nitrogen
atoms, as shown in the case of GaN in Fig. 4 [108].
Up until very recently, the growth of these materials was
not very well controlled, and thus their availability for sen-
sor applications was very limited. Of these, the polar GaN
c-plane is the first of the III-nitrides to be available at high
crystal quality and because of this it has been more exten-
sively studied for sensor applications. In particular, of the two
possible orientations of the c-plane GaN, the Ga-face is the
one almost exclusively used. This is due to the fact that this
material is very robust, inert to etching, while at the same
time it has available free bonding for coordination with Lewis
base-type ligands. In addition it can be chemically function-
alized, thus allowing the possibility to generate multi-layer
chemical systems [78]. On the other hand the N-face struc-
ture is not chemically stable; it etches easily, while at the same
time it cannot coordinate with bases due to the unfavorable
electronic charge density distribution.
Since most of the published work is based on the c-plane
GaN Ga-face, we will concentrate on this particular substrate
for the remaining of this section. Based on theoretical results
the outer most layer of the GaN, and in particular the Gal-

lium atoms, will be partially electron deficient, and will thus
interact preferentially with Lewis bases, such as thiols, organic
alcohols [109] and anions [59]. This surface chemical inter-
action will have considerable effect on the physicochemical
characteristics of the GaN substrate. To start with, it will
develop an interfacial layer which will be negatively charged
(Fig. 5).
As a result, potentiometric or impedometric sensors selec-
tive to the specific ligand can be developed. The calibration
curve of such a pair of sensors to chloride ion is shown in
Fig. 6 [59]. In the case of a GaN-based CHEMFET, the interaction
of Lewis bases with the surface will drastically influence the
internal band structure of the semiconductor. As a result, the
carrier density in the surface-near two-Dimensional Electron
Gas (2DEG) of GaN will be determined by this band bend-
ing. Since, under normal growth conditions, GaN acts as a
p-type semiconductor, it is expected that there is going to
be a decrease in the current upon increasing of the nega-
tive surface charge. The V–I curves of a GaN-based CHEMFET,
as it is shown in Fig. 7 [110], prove that indeed this is the
case.
Fig. 4 – Gallium nitride (GaN) electronic charge density
distribution. The numbers on the contour line are indicated
in equiv./atomic volume units. Reproduced with
permission from Ref. [107].
analytica chimica acta 615 (2008) 1–9 7
Fig. 5 – Schematic diagram of the Ga-face GaN-solution
interface. The potential and impedance changes appear
between the semiconductor and the solution, and across
the Helmholtz layers.

It should be pointed out that the exact nature of the sur-
face chemistry of GaN is very important since any changes
will drastically influence the behavior of the final device. For
example, it is known that oxidation of the surface will gen-
erate a surface layer saturated with hydroxyl groups. In this
case, the behavior of the sensor will be reversed, since it will
now be sensitive to cations, and not to anions as in its origi-
nal state. Additionally, care must be taken so that the studies
used for the evaluation of these sensors do not involve any
pH changes, since this can interfere with the measurement
of the analyte ions. These studies of the GaN surface indicate
that the unique selectivity of the GaN surface is very impor-
tant for the future development of not only electrochemical
sensors and biosensors, but also optical fluorescent sensors.
Indium nitride (InN) is a semiconductor for which there
has been done very little work in the area of chemical sen-
Fig. 6 – Correlation between the activity of KCl and the
induced potential and interfacial capacitance of the Ga-face
GaN-solution interface. Reproduced with permission from
Ref. [59].
Fig. 7 – IDS–VDS characteristics of a GaN EGHEMT with
Lg=80␮m and Wg= 100 ␮m, measured in air (— black solid
line) and within aqueous solutions with pH 3.35 (··· red
dotted line), pH 6.84 (–·– blue dashed-dotted line) and pH
12.45 (– – magenta dashed line). Reproduced with
permission from Ref. [109]. (For interpretation of the
references to color in this figure legend, the reader is
referred to the web version of the article.)
sors and biosensors. InN is a chemically stable wurtzite crystal
which, as in the case of GaN, also has an induced polar surface.

The unique property though of this material is the fact that it
has very high surface electron concentrations [111]. This phe-
nomenon has been utilized for the development of a series of
gas sensors, and only in a few instances in the development
of solution chemical sensors. It has been found for example
that the InN surface shows a pronounced response to certain
solvents as shown by Hall mobility and sheet carrier density
measurements [110]. It is suggested that the near to surface
accumulated electrons, contribute considerably to the lateral
conductivity of thin InN films. Based on this, upon interac-
tion of a substance with the surface of InN, this will affect the
surface charge and thus it will modulate the current, or alter
the surface potential, providing the grounds for the develop-
ment of highly sensitive sensors. Up until now there are some
results indicating that this indeed is the case for gas sensing
[110,112]. Despite that, this material is relatively unexplored
as a matrix for chemical sensor and biosensor applications.
On the other hand, AlN is a material that even thought it
has not been used extensively as a substrate for chemical sen-
sor and biosensor development, it has been utilized for the
development of shear mode acoustic biosensors [86,87].
6. Forecasting the future
As the area of semiconductor synthesis evolves there is a very
significant opportunity for the development of a new era of
biosensors. While III-nitrites and doped diamond have already
shown that they can provide specific advantages for their use
in sensor science, at the same time new surfaces such as
SiC and other semiconductor materials are becoming widely
available, and might be useful for sensor applications. The
8 analytica chimica acta 615 (2008) 1–9

major problem of material availability and suitability for elec-
trochemical and optical transduction is being undertaken via
multidisciplinary research efforts.
In the near future it is expected that the nano-
semiconductor structures [113–117] will have a profound
effect on the capabilities of direct bio-chemical analysis. Not
only the quantum dots and quantum planar structures will
be a major player in this area, but it is also expected that
nanoporous and especially nanorods and nanocolumn arrays
will provide new directions for the development of chemi-
cal sensors and biosensors capable in tackling the modern
challenges of direct chemical analysis. These semiconduc-
tor materials will allow for the simultaneous emission and
detection of the signal, while it is envisioned that reagent-
less multi-parameter analysis will be achievable. For this,
coordinated research efforts embracing both synthetic and
analytical groups will facilitate the design and the materializa-
tion of these novel semiconductor-based analytical devices.
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