novel semiconductor materials for the development of

Semiconductor surface potential plays an important role in the performance and characteristics of all devices involving surface chemistry and thus semiconductor-based biosensors.. Fundam

a v a i l a b l e a t w w w s c i e n c e d i r e c t c o m

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / a c a

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

a r t i c l e i n f o

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

a b s t r a c t

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:nchan@chemistry.uoc.gr(N Chaniotakis)

URL: http://www.analytical 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

The semiconductor technology has boomed since the

inven-tion of the transistor in 1948[1] Initially the

semiconductor-based transistors were semiconductor-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 with very 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-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 inFig 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 inFig 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

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.

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 asig-nalyte 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 SiO2, or other metal oxides or nitrides such

as Al2O3, Ta2O5, SnO2, and Si3N4 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 sursur-face 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 SiO2

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

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 inFig 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-Table 1 – Summary of the analytical applications of

novel semiconductor materials

Gas sensing (H2, NH3, NOx, O2,

CO, H2O, 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 mechaniphysi-cal stability make these new semiconductor

materials ideal for the development of specific chemical

sen-sor and biosensen-sor systems.Table 1summarizes the analytical

applications of novel semiconductor materials

Diamond is a unique WBS (Eg= 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 sp3-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 Cl2 and F2 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, Cl2/400–500◦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 (C4F4I) 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 (0.38 mm 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

Fig 3 – The GaN (0 0 0 1) 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 biosensen-sors 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 (0 0 0 1)

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 inFig 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

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 inFig 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]

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 Additioorigi-nally, 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 biosensen-sor 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

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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