Chemistry Reference
In-Depth Information
analytical chemistry applications of devices that can integrate multiple laboratory functions (separation,
identification and quantification of the chemical and biological analytes) on a single chip able to handle very
small sample fluid volumes.
Although LOC technology already represents an established research field the efforts of scientists and
engineers are facing a continuous growth toward the synergy of this technology with nanotechnology and
material science in general; particularly nanomaterials. The development of novel sensors and biosensors
based on nanomaterials and nanostructures - called also nanobiosensors - is opening the way to cost-effective
devices that would be the perfect candidates to be integrated into LOC systems. The recent trends in the
development of nanomaterials-based biosensors, followed by the LOC technology and the applications of the
resulting synergic systems in diagnostics as well as other industries will be shown in the next sections.
18.2 Nanomaterials-based(bio)sensors
Nanotechnology is an emerging field, parallel to many knowledge areas where limits are established from 1 to
100 nm. Different applications can be distinguished such as: nanobiotechnology; nanomedicine; nanomaterials;
nanoelectronics; and nanosensors/nanodevices, nanotechnological instrumentation and nanometrology [2].
The application of nanomaterials in the development of sensors and biosensors represents one of the main
focuses of the current nanotechnology. The interesting optical and electrical properties are making
nanomaterials new building blocks for the design of various kinds of sensing and biosensing devices with
improved performance as well as cost-efficienct in comparison to conventional materials.
In order to quantify and analyse changing the operation of nanosensors is necessary to use transducers that
convert the chemical/biological recognition events to electrical/optical/piezoelectrical signals. Several kinds
of nanomaterials such as nanoparticles, nanotubes and other nanostructured materials are being used to
design various transducing platforms that lead to interesting nano(bio)sensing systems or nano(bio)sensors.
Transducing platforms based on optical detections such as light absorption and scattering induced by
nanoparticles used as labels have proved to be very interesting and have been extended not only to DNA [3]
and protein [4] analysis fields but also to other fields (i.e. heavy metal detection [5]. Surface plasmon
resonance enhancement by using nanoparticles is also an interesting optical transducing alternative that is
bringing advantages to this technique in terms of sensitivity. Between the different optical techniques, those
related to fluorescence measurements, including its quench monitoring while using nanoparticles as tracers
of biomolecules, are very interesting not only for the shown sensitivity but the possibility to achieve
multidetection through multiplexing alternatives [6].
Other kinds of transducers are the
electrochemical transducers
with two classes of biosensors; the
biocatalytic devices and the affinity sensors [7]. These transducers can be based on voltammetric/amperometric
measurements during which a potential is applied in the working electrode versus a reference electrode and
the current related to redox reactions occurring at the working electrode is measured. Amperometric detection
is commonly used with biocatalytic and affinity sensors because of its simplicity and low detection limit.
Transducers based on potentiometric measurements are related with the determination of the potential
difference between either an indicator or a reference electrode or two reference electrodes separated by a
perm-selective membrane, when there is no significant current flowing between them. Most common are ion-
selective electrodes (ISEs) based on thin films or selective membranes as recognition elements for pH, F
-
, I
-
,
CN
-
, Na
+
, K
+
, Ca
2+
and so on. or even gases (i.e. CO
2
, NH
3
) [8]. Impedance measurements - during which
resistive and capacitive properties of materials, while excited with a small amplitude sinusoidal ac typically
of 2-10 mV - are also being used. On other hand, the frequency is varied over a wide range to obtain the
impedance spectrum. The impedance based methods are very useful in affinity biosensors [9];
Conductimetry
,
