Biomedical Engineering Reference
In-Depth Information
h e growing technology problem around the globe has prompted the
researchers to come up with novel and nit y solutions to quickly detect
concealed explosives. Several decades of research that went into the devel-
opment of sensors of explosives and hazardous gases helped the research-
ers to identify dif erent popular detection techniques such as ion mobility
spectrometry (IMS), mass spectrometry etc. However these conventional
explosive detection techniques tend to be expensive and bulky besides hav-
ing a longer response time. However, in order to ei ciently detect explosives
at strategic locations and public spots, deployment of multiple sensors is
necessary; hence the recent demand is for development of extremely sensi-
tive and cost ef ective sensors that can be mass produced and networked.
Gravimetric sensors such as SAW sensors and QCM sensors are not small
enough to be deployed as arrays and these sensing technologies require
frequency measuring systems that are known to be expensive and large in
size. Hence MEMS systems such as microcantilevers have been found to be
suitable for explosive detection because of their advantages such as small
size, high sensitivity, low power consumption and versatility to integrate
multiple explosive detectors in a single miniature package.
Dif erent techniques for the detection of explosives in vapour phase
using microcantilevers have been reported in the literature [72-76] which
includes receptor based detection and receptor free detection. In recep-
tor based detection, microcantilevers are functionalized with receptors for
molecular recognition and the functionalization procedure is based on the
receptor and microcantilever surface chemistry. h e molecular recogni-
tion mechanisms in these cases are based on the weak interactions that can
be reversed making the microcantilever sensors reversible. As per litera-
ture, microcantilever that have been used for these applications are mostly
silicon or derived materials such as silicon dioxide and silicon nitride.
Polymer microcantilever sensor platform being a better sensing platform
in terms of sensitivity compared to conventional silicon based microcan-
tilever platform would be a good candidate for development for explosive
detectors.
h e polymer nanocomposite microcantilevers were functionalized
using a receptor coating, 4-MBA (4-mercaptobenzoic acid). h ey form
hydrogen bond with nitroaromatic based explosive molecules such as TNT.
[72]. 4-MBA can easily form a stable monolayer on gold surface through
thiol chemistry. h erefore one side of the microcantilever was coated with
30 nm of gold with a 5-7 nm of titanium as the adhesion layer in order
to facilitate for a selective functionalization of 4-MBA. h e functional-
ized microcantilevers along with non-functionalized microcantilevers as
reference microcantilevers were then attached to a PCB with respective
