Apparatus and method for detecting small changes in attached mass of piezoelectric devices used as sensors
First Claim
1. Apparatus for obtaining an indication of an amount of an analyte bound to a piezoelectric device, comprisingan electrical oscillator having a control terminal, the frequency of an output signal of the said oscillator being variable over a range in dependence upon the value of a control signal applied to the said control terminal,a piezoelectric device carrying a reagent for selectively binding an analyte to a surface of the device,launching and reception means coupled to the said device and to the said oscillator for use in launching acoustic waves at the output frequency of the said oscillator across the said device and for use in receiving acoustic waves propagating across the said device, andmeasurement means, with input coupled to the said launching and reception means and output coupled to the said control terminal, for deriving a signal representative of the time required for an acoustic wave to travel across the said device between launch and reception by the said launch and reception means, whereby the output frequency of the said oscillator depends on the speed of propagation of acoustic waves across the said device and therefore on the amount of analyte bound to said surface.
1 Assignment
0 Petitions
Accused Products
Abstract
In analysis, particularly for medical diagnostics, material can be selectively bound to the surface of a piezoelectric crystal by a reagent. The amount of material so bound affects the speed of propagation of an acoustic wave launched and received on the crystal surface by respective electrode pairs. Previously the crystal was used as a resonant element in an oscillator controlling the frequency of oscillation and so indicating the amount of bound material. However, the oscillator was either unstable or the range of bound masses too small to be of practical use. In the present invention delay between launch and reception of the acoustic wave provides a control signal for a voltage controlled oscillator. A much more stable system can therefore be constructed with a wide working range and high stability since the crystal is no longer the resonant element. Much greater sensitivity is also possible since the oscillator frequency may be greatly increased. A control signal representative of delay may be produced by a phase comparator comparing the phase of two input signals: one direct from the oscillator, and one from the reception of an acoustic wave on the crystal surface launched using a signal from the oscillator. The signal to the crystal may be modulated using a low frequency oscillator before it reaches the crystal to aid the oscillator in following frequency changes due to changing crystal surface conditions and the resulting signal may be summed with the output of a resonance oscillator before application to the crystal to aid the oscillator in initially settling to a stable frequency.
56 Citations
19 Claims
-
1. Apparatus for obtaining an indication of an amount of an analyte bound to a piezoelectric device, comprising
an electrical oscillator having a control terminal, the frequency of an output signal of the said oscillator being variable over a range in dependence upon the value of a control signal applied to the said control terminal, a piezoelectric device carrying a reagent for selectively binding an analyte to a surface of the device, launching and reception means coupled to the said device and to the said oscillator for use in launching acoustic waves at the output frequency of the said oscillator across the said device and for use in receiving acoustic waves propagating across the said device, and measurement means, with input coupled to the said launching and reception means and output coupled to the said control terminal, for deriving a signal representative of the time required for an acoustic wave to travel across the said device between launch and reception by the said launch and reception means, whereby the output frequency of the said oscillator depends on the speed of propagation of acoustic waves across the said device and therefore on the amount of analyte bound to said surface.
-
8. Apparatus for indicating the amount of material bound to the surface of a piezoelectric device, comprising
a piezoelectric device carrying a reagent for selectively binding an analyte to a surface of the device, the device having first and second electrocde means mounted on the surface thereof for launching and receiving, respectively, acoustic waves on the said surface, first and second contact means for making electrical contact with the first and second electrode means, respectively, a voltage-controlled oscillator having a control terminal, the frequency of the said oscillator being variable over a range in dependence on the magnitude of a d.c. control signal applied to the said control terminal, phase-comparator means, having first and second inputs and an output, for generating a d.c. output signal of magnitude representaive of any phase difference in signals applied to the said first and second phase-comparator inputs, the first input being coupled to the said oscillator and the second input being coupled to the second contact means, and the said phase comparator output being coupled to the said control terminal.
-
12. A method of obtaining an indication of the amount of analyte bound to a piezoelectric device, comprising the steps of
applying a reagent to the device which selectively binds an analyte to said surface, obtaining an output signal from an electrical oscillator having a frequency which is variable over a range in dependence upon the value of a control signal applied to the said oscillator, using the said oscillator output signal to generate a launch signal to launch an acoustic wave across the device, receiving the said acoustic wave, deriving, from the said oscillator output and the received acoustic wave, a delay signal representative of the time required by an acoustic wave to travel across the said device between launch and reception, and deriving the said control signal for the said oscillator from the said delay signal, whereby the frequency of the said oscillator provides an indication of the said speed of propagation and therefore the amount of analyte bound to said surface.
-
18. A piezoelectric device carrying a reagent for selectively binding an analyte to the surface of the said device,
the said device having first and second electrodes in close proximity for launching acoustic waves on the surface of the crystal, third and fourth electrodes in close proximity but spaced from the said first and second electrodes for receiving acoustic waves on the said surface, a first connection for use in coupling said first electrode to an oscillator, the second electrode having no low conductivity connection for coupling the said second electrode to the said oscillator, a second connection for use in coupling the said third electrode to phase comparison means, and a third connection for coupling the said fourth electrode to a ground connection between the said oscillator and the said measurement means.
Specification