Nanosensors - Nanotechnologies for Water Environment Applications - page 417

13.3 Working Mechanisms and Types of Sensors

13.3.1 Working Mechanism of Sensors

Micro- and nano-sensors can be classified according to the type of bioreceptors,
transducers, and applications (Vo-Dinh and Cullum, 2000). Bioreceptors are biological
molecules (antibody, enzyme, protein, nucleic acid, cell etc.) that exploit the
biochemical interaction for analyte (antigen, nucleic acid) recognition. Transducers are
electrical/electronic components that convert the biological detection event into a
measurable signal. The conversion of biological event signal to a specific physical signal
differs for the type of transducer, e.g., i) an electrochemical transducer converts the
biochemical event to an electrical event by measuring the potential difference between
electrodes, ii) an optical transducer converts the biochemical event to a photochemical
event by measuring the difference in light intensity, and iii) a mechanical transducer
converts the biochemical event to an electrical event by measuring the difference in
mass or surface stress.

Cost Speed

Speed

Target Background

Specificity Sensitivity

Sensitivity

Sample Volume

Sample
throughput

Sample

Target
multiplexing

Target

throughput

multiplexing

Clinical sample Environmental sample

Figure 13.1 (a) Representation of parameters of interest during methods development
for micro and nano-scale sensors. Envelope shown by dark and dotted lines represents
the ideal and real scenario of biosensor development studies, (b) comparison of the level
of complexity for environmental and clinical samples applicable to sensors. High
volume, low amount of targets, and high amount of background in environmental
samples are bottlenecks in the widespread use of sensors in the water industry.

In general, a biosensor platform has three important components: i) bioreceptor,
ii) transducer, and iii) output system. The target species (antigens, nucleic acids), when
interacting with these bioreceptors, produces a biological signal, which is sensed by a
transducer and transformed into a measurable response (current, potential, or light
intensity etc.). The signal obtained at such small scale is quite low and noisy, which can
be further processed, amplified, and stored for analysis by an amplifier and