High-resolution ultrasonic spectroscopy

Abstract

Abstract. High-resolution ultrasonic spectroscopy (HR-US) is an analytical technique for direct and non-destructive monitoring of molecular and micro-structural transformations in liquids and semi-solid materials. It is based on precision measurements of ultrasonic velocity and attenuation in analysed samples. The application areas of HR-US in research, product development, and quality and process control include analysis of conformational transitions of polymers, ligand binding, molecular self-assembly and aggregation, crystallisation, gelation, characterisation of phase transitions and phase diagrams, and monitoring of chemical and biochemical reactions. The technique does not require optical markers or optical transparency. The HR-US measurements can be performed in small sample volumes (down to droplet size), over broad temperature range, at ambient and elevated pressures, and in various measuring regimes such as automatic temperature ramps, titrations and measurements in flow.

Acoustic characterisation of pH dependant reversible micellar casein aggregation

“…Acoustic techniques have been effectively used to study casein micelles in suspension. Ultrasonic attenuation measurements have been used to determine the behaviour of casein micelles in milk fractions [51] and to estimate the particle size [52,53] and zeta potential [54] of casein micelles. Ultrasonic velocity measurements have also been used to monitor calcium dissociation from casein micelles [55], gel formation involving casein micelles [56,57], casein concentration in skim milk [58], the phase separation of casein [59] and the stability of emulsions using casein as an emulsifier [60].…”

Advances in Analysis of Milk Proteases Activity at Surfaces and in a Volume by Acoustic Methods

“…Alternatively, within the last decades, low-intensity ultrasonic techniques, particularly ultrasonic velocimetry and spectroscopy, have been classified as nondestructive mechanical sensors for the online characterization of the state of biomolecules, as well as biochemical reactions, in native or processing media [ 71 , 72 ]. These techniques offer sensitivity measurements of the viscoelastic properties of analyzed samples determined by the molecular forces and dynamics involved in the process.…”

“…Ultrasonic spectroscopy (US) is a continuous ultrasonic wave-based analytical technique that utilizes a low amplitude, longitudinal deformation of high-frequency (1–20 MHz) acoustic waves propagating through the analyzed sample [ 71 ]. In contrast to traditional optical spectroscopic techniques, US probes the viscoelastic, rather than electric and magnetic, characteristics of the analyzed samples.…”

“…The resulting acceleration of the medium and mechanical momentum give rise to the well-known wave Equation (5), describing the propagation of the longitudinal wave in an isotropic medium, which is homogenous within the scale of an ultrasonic wave of low amplitude: where M is the modulus of longitudinal deformation, and is the effective inertial density of the medium. The detailed mathematical formulation and physical description of the propagation of a longitudinal ultrasonic wave have been previously well-discussed in the references [ 71 , 76 , 77 , 78 ]. Furthermore, under oscillation conditions where there are time delays between the stress and the strain, the displacement possess a complex characteristic [ 79 ].…”

“…The recent advances in ultrasonic spectroscopy for monitoring biocatalysts utilized today are based on the advanced principles of ultrasonic resonator techniques developed a couple of decades ago, as well as the optimal built-in resonator cell designs. The current resonator instrumentation is capable of exceptionally high-resolution ultrasonic velocity, down to 0.2 mm/sec, and an ultrasonic attenuation measurement of 0.2% [ 71 , 73 ]. This allows the resolving details of small changes in the molecular characteristics in the multi-steps or side reactions of bioprocesses, e.g., ionization reactions between titratable groups in protein solutions and the occurrence of protein aggregation concomitant with hydrolysis.…”