Cuvette for sampling and analysis

Disposable cuvette for essentially simultaneous sampling of a fluid and analyzing the sample. The new cuvette comprises a body member having at least one cavity defined by surrounding walls, into which cavity the sample is permitted to enter by capillary force through an inlet communicating said cavity with the exterior of the body member. According to the invention, the cuvette is characterized in that at least a portion of the walls facing the cavity consists of a semipermeable membrane, optionally with an integrated electrode and/or sensor system, and that at least one reagent or reagent system is incorporated in the cuvette.

The present invention concerns a disposable cuvette for essentially 
simultaneous sampling of a fluid and analyzing the sample. 
A cuvette for sampling a fluid, mixing the sample with a reagent and 
directly making optical analyses of the sample mixed with the reagent is 
previously known from U.S. Pat. No. 4,088,448. This cuvette comprises a 
body member including two planar surfaces defining an optical path and 
placed at a predetermined distance from one another to determine the 
optical path length and to define a cavity having an inlet communicating 
said cavity with the exterior of the body member. The cavity has a 
predetermined fixed volume, and the predetermined distance permits the 
sample to enter the cavity by capillary force. Furthermore, a reagent is 
coated on the cavity surface. 
This known cuvette has serveral advantages when compared with 
conventionally used devices. It permits sampling of a liquid, mixing and 
chemically reacting it with a suitable reagent e.g. colour development in 
the same vessel as the one used for the subsequent measurement. The 
cuvette disclosed in U.S. Pat. No. 4,088,448 thus simplifies the sampling 
procedure, reduces the number of utensils and--in most cases, depending on 
the type of analysis--considerably improves the accuracy of analysis by 
making the analyzing procedure independent of the operating technique of 
the operator making the analysis. 
The present invention concerns an improvement of this known cuvette. 
To this end, there has been developed a disposable cuvette for essentially 
simultaneous sampling of a fluid and analyzing the sample, comprising a 
body member having at least one cavity defined by surrounding walls, into 
which cavity a sample is permitted to enter by capillary force through an 
inlet communicating said cavity with the exterior of said body member, the 
cuvette being characterized in that at least a portion of the walls facing 
the cavity consists of a semipermeable membrane, optionally with an 
integrated electrode and/or sensor system, and that at least one reagent 
or reagent system is incorporated in the cuvette. 
One advantage of the improved cuvette is that it can be used for other 
types of measurements than optical analyses, which makes it applicable to 
analyses within a much broader range than the cuvette according to U.S. 
Pat. No. 4,088,448. Thus, according to the present invention, the 
measurement can be carried out by using different electrodes, the surfaces 
of which are pressed against the exterior surface of the semipermeable 
membrane. Furthermore, optical instruments may be used. Within the scope 
of the present invention are also electrode or sensor systems integrated 
with, i.e. applied on or incorporated in, the semipermeable membrane 
material. 
Another very important advantage as compared with the previously known 
cuvette is that the use of membranes makes it possible to separate sample 
media from reagent media, and interferences originating from substances, 
unsuitable pH, unsuitable redox environment etc. can be avoided. Thus, two 
or more reaction systems, which are incompatible, may be included in the 
new cuvette, as the semipermeable membrane acts as a barrier which 
prevents a component, e.g. a reagent contained in the cavity from entering 
and disturbing the reaction(s) in the membrane(s), and vice versa. This 
second advantage makes the field of application for the present cuvette 
even broader and useful for a wide variety of different analyses. 
Thus, the additional advantages according to the present invention emanate 
from the use of the semipermeable membrane and the possibility of 
combining this membrane with external or internal electrodes. 
Analyses based on the use of semipermeable membranes and electrodes are 
known in the art. However, using known techniques, difficulties are 
encountered in the handling of the sample, electrodes which often are 
sensitive to contamination, may be contaminated, evaporation of the sample 
may occur, and the sample may be subjected to the influence of different 
types of gases, such as the oxygen of the air. All these problems can be 
avoided by using the cuvette according to the present invention. 
According to the present invention, the body member may consist of glass or 
polymeric material. It is also quite possible to make the whole body 
member or one wall thereof of the semipermeable material which in this 
case preferably should be self-supporting. If not essentially 
self-supporting, the membrane could be used as a coating on the surface of 
the body member facing the cavity. The reagent, if any, coated on at least 
a portion of the body (body member) surface facing the cavity may be 
deposited by evaporation, freeze-drying, spraying or screen-printing, as 
known in the art. 
The semipermeable membrane may be in the form of one separate membrane 
layer or two or more separate layers joined to each other to form a 
composite membrane. The various reagents may be coated on the membrane 
surface facing the cavity and applied thereto by evaporation, 
freeze-drying, spraying or screenprinting, etc. It is also possible to 
have the reagents deposited as a layer on separate surfaces of the 
membrane in such a way that this layer becomes an intermediate layer in 
the finished composite membrane. One or more such layers may be present. 
The semipermeable membrane may also be prepared in such a manner that the 
reagent or reagents are dispersed or dissolved throughout the whole 
membrane or one or more layers thereof. Another possibility is to prepare 
the membrane material in such a manner that the reagent molecules are 
covalently bound to the polymer molecules of the semipermeable membrane. 
The semipermeable membrane material is chosen in dependence on the kind of 
analysis to be performed and may be determined by a person skilled in the 
art. The membrane material might be hydrophilic or hydrophobic. Examples 
of different material which can be used according to the present invention 
are Teflon.RTM., silicon rubber, polyacrylates, polyvinyls, collagen and 
even crosslinked enzymes, etc.. Various substances could be incorporated 
in the membrane to give special selective properties, to perform a 
chemical reaction, etc. Including specific crown ethers in a polyvinyl 
membrane gives a membrane with selective properties for alkaline ions. 
Including glucose oxidase in a membrane makes it possible to measure 
glucose by the production of hydrogen peroxide or the decrease in oxygen 
concentration. 
The membrane may selectively permit penetration of only or essentially the 
substance/ion, which is relevant/interesting, and which can be detected 
by, for example, an electrode on the external surface of the membrane. 
Furthermore, the membrane may function as a discriminator in which only 
molecules/ions below a certain size can move freely. 
To perform measurements with electrodes on or in the improved cuvette, the 
membrane acts as a semipermeable barrier (with or without selective 
properties) which prevents the electrodes from being contaminated by the 
sample medium and/or the reagent. The membrane could participate in a 
chemical reaction through incorporated reagents and/or selectively permit 
free passage for the substances to be determined at the electrode. 
The electrode to be used according to the present invention may be a 
conventional potentiometric, i.e. ion-selective or amperometric electrode 
which, together with the semipermeable membrane of the cuvette, functions 
as an enzyme electrode or biosensor of the type described in e.g. P. 
Vadgama, Journal of Medical Engineering & Technology, Vol. 5, No. 6, 1981, 
293-298. 
Examples of electrodes to be used with the membrane cuvette of the present 
invention are conventional electrodes, such as a glass electrode (pH), a 
platinum, gold, or carbon electrode, and other more exclusive electrodes, 
such as solid state devices of the type CHEMFET or ISFET with their 
associated electronic parts. 
An example of a platinum/silver-silver chloride electrode system together 
with a composite membrane for determining glucose by amperometric 
measurement of consumed oxygen is given in a paper by Jean-Louis Romtte, 
B. Fromment & D. Thomas (Clin. Chim. Acta, 95 (1979) 249-253). 
An example of glass electrode application together with a composite 
membrane for determining urea by pH-measurement of produced ammonia is 
disclosed in a paper by M. Mascini and G.G. Guilbault (Anal. Chem., Vol. 
49, No. 6, May 1977, 795-798). 
As regards optical analyses to be performed with the present cuvette, there 
are two main possibilities: 
(A) the colour develops in the cavity; 
(B) the colour develops within the membrane. 
In (A), the two main surfaces of the cavity must have a predetermined or a 
determinable distance between one another to make it possible to determine 
the optical path length. The determinable distance may be obtained by 
applying an external force to the surface of an essentailly elastic 
membrane until the movement of the membrane is stopped against a spacer of 
predetermined thickness inserted in the cavity. 
In (B), the colour developing part (layer) of the membrane or the entire 
membrane must be of a predetermined thickness to accomplish a determined 
optical path length. 
A practical example of (B) is a cuvette designed to perform an analysis of 
urea in serum or urine. The cavity contains urease and an alkaline buffer 
system in dry form which, when dissolved in the sample medium, give free 
ammonia from urea, and the membrane incorporates an indicator (=a reagent) 
for ammonia. The membrane is manufactured from a polymer, the 
hydrophobicity of which is sufficienty high to prevent the alkaline buffer 
from interfering with the indicator, but is permeable to ammonia. The 
indicator is a solvent soluble pH-indicator with an indicator interval 
within the acid range. 
Different approaches to the analyses may be made by using different types 
of electrodes, different types of membranes and different reaction routes, 
as recognized by a person skilled in the art.

The cuvette illustrated in FIGS. 1 and 1a comprises a body wall 10 of glass 
or polymeric material, and a body wall 11 of semipermeable membrane 
material. The walls define a cavity 12 which is intended to accommodate a 
liquid sample and the dimension of which is such that it can be filled by 
capillary force. Two channels 13 extend from opposite sides of the cuvette 
and open into the cavity 12. Thus, a sample can here be drawn straight 
through the cuvette, which may be advantageous in certain cases. The 
cavity 12 might be supplied with a reagent (that is an agent to react with 
the sample drawn into said cavity) by evaporation, freeze-drying, 
spraying, screen-printing or in another suitable manner according to the 
manner in which the cuvette is manufactured. 
The wall 11 of semipermeable membrane material may be manufactured in such 
a manner that a reagent system is incorporated in the memebrane, e.g. 
dispersed or dissolved therein. It is also possible to manufacture the 
membrane in such a way that the components (molecules) of the reagent 
system are covalently bound to the polymers constituting the membane 
material. Another possibility is to build up a semipermeable membrane of 
two or more layers and apply the reagent systems as intermediate layers 
between two adjacent membrane layers. One or more such layers and 
intermediate layers may be present. All types of combinations of 
incorporation of the reagent system apparent to those skilled in the art 
fall within the scope of the present invention. 
In FIG. 2a, 10 is a body wall of polymeric supporting material. 11 is a 
semipermeable membrane optically composed of several layers. 12 is the 
cavity accommodating the sample. Elevations 14 determine the optical path 
length. When the sample is drawn into the cavity 12, air is pressed out 
through the slit 15. The body wall 10 and the semipermeable membrane 11 
are joined together (welded or glued) along the joint 16. The area 17 
indicates a suitable measuring zone. 
In FIG. 3 a measuring electrode is brought into contact with the 
semipermeable membrane 11 in the cuvette disclosed in FIGS. 2a and 2b. In 
this special embodiment, the electrode consists of a platinum electrode 18 
and a reference silver/silver chloride electrode 19. 20 designates the 
glass body surrounding the platinum electrode 18. 
In FIG. 4 cuvette of the FIGS. 2a and 2b is adapted for optical measuring. 
Thus, 21 here designates a light source e.g. monochromatic light. 22 
indicates the light path towards the cuvette. 23 indicates the light path 
of unabsorbed light after the cuvette, and 24 is an optical detector. 
The cuvette as shown in FIG. 5 has four parallel-connected cavities 25, 25' 
which are connected to a common channel, 26' by branch channels 27 which 
continue on the opposite side of the cavities and open into the atmosphere 
to prevent air inclusions in the cavities when samples are drawn 
thereinto. Different reactive systems may be included in different 
cavities and/or the membrane material defining the whole or part of the 
cavity. 
FIG. 5a shows a section of the cuvette according to FIG. 5 along line 
II--II. 
The embodiment of the present invention according to FIGS. 6 and 6a 
consists of elastic semipermeable material. The inlet channel 28 
communicates the exterior of the cuvette with the cavity 12. 
While the invention has been described with reference to preferred 
embodiments thereof, it will be understood by those skilled in the art 
that various changes in form and details may be made without departing 
from the spirit and scope of the invention. Many alternative container 
designs can be conceived which give the advantageous results herein 
disclosed. 
Further, it is obvious that any analytical procedure can be adapted to the 
invention herein disclosed. The cuvette is particularly suitable for 
routine blood chemistry, such as glucose, blood urea nitrogen, albumin, 
bilirubin, total protein, etc., and numerous other analytical tests. 
Accordingly, all substitutions, additions and modifications to which the 
present invention is readily susceptible, without departing from the 
spirit and scope of this disclosure, are considered part of the present 
invention.