Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving viable micro-organism
Patent
1997-11-03
1998-12-08
Leary, Louise N.
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving viable micro-organism
435 34, 435 4, 430945, C12Q 102, C12Q 104, C12Q 100
Patent
active
058467599
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the field of biophysics, more specifically to optical biosensors.
At present, live microorganisms in liquids are recorded by observation using an optical microscope and methods of bioluminescence and selective staining. A general disadvantage of these methods is the low degree of automation of measurement.
Closer to the applicant's method is an optical method for detecting mobile scattering centres. In this method laser radiation passes through the liquid being investigated and is scattered by the particles (brownian motion) and mobile microorganisms in the liquid, and the scattered radiation, interfering on an observation surface, forms a dynamic speckle-picture, whose Fourier-spectrum of fluctuation of intensity is recorded. Based on the half-width of this spectrum the diffusion coefficient is calculated, and using its value the presence of mobile microorganisms is assessed.
A disadvantage of this method is that in order to distinguish mobile microorganisms from brownian particles it is necessary to have a priori information about the sizes of the particles being studied, and this reduces the applicability of the method. For example, differentiating between spectrums does not work if there is low mobility of mobile microorganisms, or brownian particles of small size are present. In addition, it is necessary to measure the Fourier spectrum to a high degree of accuracy, and this makes it more difficult and more expensive to create instruments working in real time.
The proposed method makes it possible to overcome the disadvantages mentioned by measuring the mean intensity of fluctuation of the speckle-picture, in a frequency range restricted at the lower end, associated both with the concentration of brownian particles and with the mobility of microorganisms. At the same time, using the known method, measurement takes place of the investigated medium's turbidity, which is associated only with the concentration of brownian particles and mobile microorganisms and does not depend on the mobility of the mobile microorganisms. This makes it possible to distinguish, in the output signal, between the contribution made by the concentration of brownian particles and mobile microorganisms and the contribution associated with the mobility of the microorganisms. Restriction of the frequency range at the lower end makes it possible to reduce the contribution in the output signal from the brownian particle concentration, whose spectrum lies in the low-frequency field, and causes little change to the signal associated with the mobility of the microorganisms, lying in a higher-frequency field. This makes it possible to increase the sensitivity of the method when detecting weak signals from mobile microorganisms against the background of a strong signal from brownian particles. The proposed method is simpler since there is no need for information about particle sizes and there is no need to measure the Fourier spectrum.
BRIEF DESCRIPTION OF DRAWINGS
The method is illustrated by three diagrams.
FIG. 1 shows typical amplitude-frequency spectrums of output signals, where 1--Fourier spectrum for brownian particles, 2--Fourier spectrum for mobile microorganisms.
FIG. 2 shows integral values measured under the proposed method, where 3--amplitude-frequency characteristic curve for limiting the spectrum at the lower end, area 4--integral signal U.sub.1 for brownian particles, area 5--integral signal U.sub.2 for brownian particles plus mobile microorganisms.
FIG. 3 shows the dependence of signal U.sub.1 on turbidity of liquid T (solid line), where .DELTA.U is the contribution to the output signal caused by mobility of microorganisms.
DETAILED DESCRIPTION OF THE INVENTION
The method is implemented as follows.
Laser radiation, passing through the liquid being investigated, is scattered by the particles in the liquid, and, interfering on the surface of a photodetector, forms a dynamic speckle-picture. The amplitude-frequency spectrum of fluctuation of the photocurrent is a Lorentz line: ##EQU1## where U-
REFERENCES:
patent: 4368047 (1983-01-01), Andrade et al.
patent: 4467032 (1984-08-01), Lowke et al.
patent: 5371016 (1994-12-01), Berndt
Ageev Vladimir Gennadievich
Rastopov Stanislav Fedorovich
Leary Louise N.
Rusteck Limited
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