The acoustic spectrophonometer: A novel bioanalytical technique based on multifrequency acoustic devices

Abstract

A measurement technique similar to optical absorption spectroscopy but based on evanescent acoustic waves is described in this paper. This format employs a planar spiral coil to vibrate a single crystal of quartz from 6 to 400 MHz, in order to measure multifrequency acoustic spectra. Consistency with the defined Sauerbrey and Kanazawa terms K1 and K2 when applied to multiple frequencies was found for these specific operating conditions in terms of a significant fit between the measured and calculated values: For an IgG surface density of 13.5 ng mm(-2) the measured value of K1 is 22.5 x 10(-6) and the calculated value is 20.4 x 10(-6), whilst for glycerol viscous loadings of 5.131 cP the measured value of K2 is 0.47 and the calculated value is 0.54. Thus for these specific surface loadings the multifrequency data fits to the predictions of the Sauerbrey model to within 10% and to Kanazawa model within 13%. However collective frequency shifts for 5.131 cP solutions of sucrose, dextran and glucose were found to exhibit an unanticipated additional variability (R2 < 0.4) with frequency, but retained a square root of frequency dependency within a factor 2 of the interpolated K2 values. The response to the 5.131 cP dextran solution was found to be significantly below the other isoviscous solutions, with a substantially reduced frequency shift and K2 value than would be expected from its bulk viscosity. In comparison with these viscous solutions, IgG protein films consistently produced linear frequency shifts with little scatter (R2 > 0.96) that were proportional to the operating frequency, and fully consistent with the Sauerbrey model under these specific conditions. A t-test value of 14.52 was calculated from the variance and mean of the two groups, and demonstrates that the acoustic spectrophonometer can be used to distinguish between the acoustic impedance characteristics of two chemical systems that are not clearly differentiable at a single operating frequency.

Magnetic acoustic resonance immunoassay (MARIA): a multifrequency acoustic approach for the non‐labelled detection of biomolecular interactions

“…Flat spiral coils of 30-40 turns, with a resistance of 1 Ohm, inductance of 0.5 mH and outside diameter of 5 mm, were wound from a 0.085 mm enamelled copper wire sourced from RS Electronics, UK, and fixed on a 0.25 mm thick epoxy laminate board with cyanoacrylate adhesive (Stevenson and Lowe, 1998;Stevenson et al, 2003aStevenson et al, , 2004Stevenson et al, , 2005. The two wire ends were joined as a twisted pair and connected by coaxial cable to the signal generator and the rest of the MARS system instrumentation.…”

“…Multifrequency operation results in the localization of the evanescent wave in a fluid layer that extends between 200 nm and 17 nm at 6.6 MHz and 1 GHz, respectively. This unique ability to focus the acoustic wave onto the chemical recognition layer, through variable penetration depth evanescent waves, allows bulk fluid events to be excluded, and the analysis directed towards interfacial processes associated with viscosity, elasticity and slippage (Sindi et al, 2001;Stevenson et al, 2003aStevenson et al, ,b, 2004.…”

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

“…In practice, this means that the collection of high fidelity spectral information from the microrheological relaxation of the interface is possible, a measurement never accomplished before with an acoustic device (Stevenson et al, 2003b). A signature of the absorbed molecular species can be collected from low MHz frequencies up to radio frequencies in excess of 1 GHz (Stevenson et al, 2003a) Thus, our instrument format provides a powerful analytical methodology that shares the same operating concept as the optical spectrophotometer.…”

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].…”

“…1b uses only a piezoelectric crystal and a hand wound spiral coil that is separated by a small air gap (~ 30 mm) [12,[13][14][15][16][17]. The hand wound spiral coil produces electric fields that penetrate the piezoelectric material to excite acoustic waves [15].…”