Biosensors

BIOSENSORS

Senior investigator: Dr. Camilla Baratto

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Single Nanowire Transistor (SNT) based biosensors

The development of electrically addressable devices for label-free detection of DNA and of other biological macromolecules has the potential to impact on basic biological research as well as screening in food safety and medical bioterrorism applications. The main purpose of this activity is to develop a new and innovative technology based on a single metal oxide nanowire for electrical label-free biosensing of variuos target molecules with extreme sensitivity and good selectivity, providing a pathway to integrated, high-throughput, multiplexed DNA detection.

Figure 1. Working principle of a single metal-oxide biotransistor with ODN probes (left) in buffer solution, (right) after hybridization with complementary ODNs.

The sensors are basically transistors that are “switched” on or off  (that is, between a high-current and a low-current state) by a binding of a molecule to their surface (see Figure 1). When the nanowire is grafted with single strand ODN (probe), DNA hybridization, in presence of complementary ODN strand (target), induces a modification of the size of the sufrace space charge region, detectable as a current variation through the wire.  On the contrary, in presence of non-complementary DNA strand, current remains at a stable value (see Figure 2).

Figure 2. Current variation in presence of the complementary and non-complementary ODN of a SnO2 thin film grafted with single strand ODN.

Polyaniline nanostructures for enhanced molecularly imprinted polymer-based sensing

The aim of this work is the development and characterisation of conductive polyaniline (PANI) nanostructures for applications in electrochemical sensing. We explored a simple, cheap and fast route to grow polyaniline (PANI) nanotubes (see Figure 3) arranged in an ordered structure directly on an electrode surface by electrochemical polymerisation, using an alumina nanoporous membrane as a template.

Figure 3. SEM images of (left) Alumina membrane used as a template for the electrochemical deposition, (right) PANI nanotubes after membrane dissolution

Among conducting polymers, polyaniline (PANI) has generated great interest because it is inexpensive, easy to process and dope, has high conductivity and the raw materials for its synthesis are readily available. The deposited nanostructures were used as a functional substrate for the development of a molecularly imprinted polymer-based sensor (see Figure4). Thus, we were able to exploit the intrinsic advantages of nanostructures as optimal transducers and the well known benefits of molecularly imprinted polymers (MIPs) as receptors.

Figure 4. Scheme of the tempate synthesis of PANI nanostructures. From left to right: gold sputtered on the back of an alumina membrane; NPEDMApolymerisation inside the pores og the membrane; membrane dissolution in NaOH; MIP grafting on the PANI nanotubes

A novel hybrid material, N-phenylethylene diamine methacrylamide (NPEDMA) was employed as monomer, combining two orthogonal polymerisable functionalities, an aniline group and a methacrylamide. In this way, the polymerisation of NPEDMA resulted in a conductive layer which allowed direct electrical connection between the electrode and the MIP. The molecular recognition of catechol by the hybrid nanostructured-MIP sensor was investigated. Compared to an analogue non-nanostructured sensor, the detection limit was one order of magnitude lower.

This activity is carried out in collaboration with F. Berti and Prof. G. Marrazza from University of Firenze, Chemistry Department, and with  Cranfield University, Cranfield Health, Smart Materials group, directed by Prof. S. Piletsky and  Prof. A. P. F. Turner.

References

F. Berti, S. Todros,  D. Lakshmi, M. J. Whitcombe, I. Chianella, M. Ferroni, S. A. Piletsky, A. P. F. Turner, G. Marrazza, Quasi-monodimensional polyaniline nanostructures for enhanced molecularly imprinted polymer-based sensing, Biosensors and Bioelectronics 26 (2010) 497-503

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Micro and nano electromechanical transducers

Electro-mechanical effects in devices at the micro- and nanoscale can be innovatively exploited to sense a range of different phenomena occurring in the physical, chemical or biochemical domains. The responses can be measured with high sensitivity by electronic means through suitable mechanic-electrical effects, thereby obtaining a class of extremely promising sensors in the field of micro-electro-mechanical systems (MEMS). The mechanical response can either affect acoustic waves propagating in the device, such as in acoustic-wave and resonant microsensors, or display as a static effect, such as the bending of micro- and nano-cantilevers, or be a combination of both. The proposed research line will focus on the development and investigation, from both theoretical and applicative sides, of micromechanical devices belonging to the classes of acoustic-wave (AW) sensors and microcantilever (MC) sensors. This latter research will be carried out in collaboration with the Chemistry for Technology laboratory (Chem4Tech) of Brescia University directed by Prof. Laura Depero and involving Dr. Paolo Bergese.