Ultra-Sensitive Electrical Biosensor Unlocks Potential for Instant Diagnostic Devices

(Santa Barbara,
Calif.) A new quantum
mechanical-based biosensor designed by a team at University
of California, Santa Barbara offers tremendous potential for
detecting biomolecules at ultra-low concentrations, from instant point-of-care
disease diagnostics, to detection of trace substances for forensics and
security.

Kaustav Banerjee, director of the Nanoelectronics Research Lab
and professor of Electrical
and Computer Engineering at UCSB, and PhD student Deblina Sarkar have
proposed a methodology for beating the fundamental limits of a conventional
Field-Effect-Transistor (FET) by designing a Tunnel-FET (T-FET) sensor that is
faster and four orders of magnitude more sensitive. The details of their study
appeared in the April 2, 2012 issue of the journal Applied
Physics Letters.

“This study establishes the foundation for a new generation
of ultra-sensitive biosensors that expand opportunities for detection of
biomolecules at extremely low concentrations,” said Samir Mitragotri, professor
of Chemical Engineering and director of the Center for Bioengineering at UCSB. “Detection
and diagnostics are a key area of bioengineering research at UCSB and this
study represents an excellent example of UCSB’s multi-faceted competencies in
this exciting field.”

Biosensors based on conventional FETs have been gaining
momentum as a viable technology for the medical, forensic, and security
industries since they are cost-effective compared to optical detection
procedures. Such biosensors allow for scalability and label-free detection of
biomolecules – removing the step and expense of labeling target molecules with
fluorescent dye.

The principle behind any FET-based biosensor is similar to
the FETs used in digital circuit applications, except that the physical gate is
removed and the work of the gate is carried out by charged versions of the
biomolecules it intends to detect. For immobilizing these biomolecules, the
dielectric surface enclosing the semiconductor is coated with specific
receptors, which can bind to the target biomolecules – a process called
conjugation.

“The thermionic emission current injection mechanism of
conventional FET based biosensors puts fundamental limitations on their maximum
sensitivity and minimum detection time,” said Banerjee, who conceived the idea
in 2009 while studying the design of tunnel-FETs for ultra energy-efficient
integrated electronics.

“We overcome these fundamental limitations by making
Quantum Physics join hands with Biology” explained Sarkar, the lead author
of the paper. “The key concept behind our device is a current injection
mechanism that leverages biomolecule conjugation to bend the energy bands in
the channel region, leading to the quantum-mechanical phenomenon of
band-to-band tunneling. The result is an abrupt increase in current which is
instrumental in increasing the sensitivity and reducing the response time of
the proposed sensor.”

“The abruptness of current increase in an electrical switch
is quantified by a parameter called subthreshold swing and the sensitivity of
any FET based biosensor increases exponentially as the subthreshold swing
decreases. Thus, similar devices such as Impact-ionization- or
Nano-electromechanical-FETs are promising for biosensing applications,”
explained Banerjee.  “But since theT-FETs can be easily integrated in the
widely available silicon-based semiconductor technology, they can be mass
produced in a cost effective manner.”

According to the researchers, their T-FET biosensor is
expected to have tremendous impact on research in genomics and proteomics, as
well as pharmaceutical, clinical and forensic applications – including the
growing market of in-vitro and in-vivo diagnostics. Banerjee and Sarkar have
filed a patent disclosure for their technology, which the researchers
anticipate can be ready for the marketplace in as few as two years.