A Strategy for Chemical Sensing Based on Frequency Tunable Acoustic Devices

Abstract

A new acoustic sensor geometry, the magnetic acoustic resonant sensor (MARS), is described. The device comprises a circular 0.5-mm-thick resonant plate fabricated from a wide variety of nonpiezoelectric materials and coated on the underside with a 2.5-microm-thick aluminum film. Harmonic radial shear waves over at least a 2 orders of magnitude frequency range can be induced in the resonant plate by enhanced magnetic direct generation using a noncontacting rf coil and NdFeB magnet. Mass loading with adherent aluminum films produced frequency changes of 106 Hz/nm (40.8 Hz/ng-mm(-2)), while contact with viscous fluids resulted in maximum changes of 15 446 Hz/cP. At an operating frequency of 50 MHz, the device detected viscosity changes as low as 0.0006 cP. The adsorption of proteins such as human IgG and the binding of a complementary antigen, goat anti-human IgG, on the upper nonmetallized surface of the device has been monitored with a detection limit of approximately 75 ng/mL. The binding of substrates and allosteric effectors to glycogen phosphorylase b has provided evidence that the device is very sensitive to viscoelastic changes in adsorbed proteins. The MARS device generates radial shear acoustic waves over a broad bandwidth that are unaffected by the conductivity of the solution. These results suggest that simple metal, glass, crystalline, or polycrystalline plates can be used as a new type of tunable acoustic immunosensor.

The application of the acoustic spectrophonometer to biomolecular spectrometry: a step towards acoustic ‘fingerprinting’

“…Initial experiments with acoustic signals at single frequencies were conducted with high solution concentrations of IgG in order to produce monolayers that were relatively ordered and defined in orientation (Sindi et al, 2001).…”

“…Our group has been developing a radio frequency antenna/coil based system that completely separates the electronics from the device (Stevenson, 1996;Stevenson and Lowe, 1998;Sindi et al, 2001), and is designed for application as a biosensor. Unlike all other waveguide and resonant acoustic devices, there is no electronic component that is equivalent to the sensing element utilized.…”

3I-4 A Monolithic Spiral Coil Acoustic Transduction Sensor

“…are described elsewhere [3][4][5][6]. In contrast to the QCM and LFE sensors which are excited by two electrodes, a hand wound spiral coil has been used as the excitation source in two other acoustic wave sensors, namely the Magnetic Acoustic Resonant Sensor (MARS) [7][8][9][10][11][12] and the Electromagnetic Piezoelectric Acoustic Transduction Sensor (EMPAS) [12][13][14][15][16][17]. The MARS utilizes the same operating principles as Electromagnetic Acoustic Transducers (EMAT), a technology that has been used for more than 50 years on the macro scale [18][19][20] to test the structural integrity of metallic objects such as sheet metal [21] and materials characterization [22].…”

“…Instead of being used on the macro scale, the MARS utilizes the same basic configuration as EMAT but applies it on the micro scale to produce an acoustic wave sensor [10,11]. In the MARS configuration, an electrically excited hand wound spiral coil is placed near a metalized substrate that is exposed to a permanent magnetic field (See Fig.…”

“…As with other acoustic wave sensors the resonant frequency of the device shifts with changes on its surface [10,23]. Unlike other acoustic wave sensors however, the MARS configuration has the advantage of being capable of utilizing nonpiezoelectric substrates such as aluminum, silica glass, sapphire [10] and high-Q silicon membranes [11].…”