U.S. patent application number 13/284094 was filed with the patent office on 2012-05-03 for holographic sensor.
Invention is credited to Jeffrey Blyth, Abid Hussain, Satyamoorthy Kabilan, Mei-Ching Lee, Christopher Robin Lowe, Felicity Kate Sartain, Xiaoping Yang.
Application Number | 20120107944 13/284094 |
Document ID | / |
Family ID | 9954578 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120107944 |
Kind Code |
A1 |
Lowe; Christopher Robin ; et
al. |
May 3, 2012 |
Holographic Sensor
Abstract
A sensor for the detection of an analyte comprising a cis-diol
moiety, which comprises a holographic element comprising a medium
and a hologram disposed throughout the volume of the medium,
wherein an optical characteristic of the element changes as a
result of a variation of a physical property occurring throughout
the volume of the medium, and wherein the medium is a polymer
comprising a group of formula (i) ##STR00001## wherein n is 0, 1,
2, 3 or 4; each X (if present) is independently is an atom or group
which, via an electronic effect, promotes formation of a
tetrahedral geometry about the boron atom; and Y is a spacer which,
when n is 0 or otherwise optionally, is an atom or group which, via
an electronic effect, promotes formation of a tetrahedral geometry
about the boron atom. Such a sensor may be used for the detection
of glucose.
Inventors: |
Lowe; Christopher Robin;
(Cambridge, GB) ; Blyth; Jeffrey; (Cambridge,
GB) ; Kabilan; Satyamoorthy; (Cambridge, GB) ;
Hussain; Abid; (Cambridge, GB) ; Yang; Xiaoping;
(Cambridge, GB) ; Sartain; Felicity Kate;
(Cambridge, GB) ; Lee; Mei-Ching; (Cambridge,
GB) |
Family ID: |
9954578 |
Appl. No.: |
13/284094 |
Filed: |
October 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10545275 |
Oct 17, 2005 |
8048680 |
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PCT/GB2004/000576 |
Feb 13, 2004 |
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13284094 |
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Current U.S.
Class: |
436/95 |
Current CPC
Class: |
Y10T 436/144444
20150115; G02B 5/32 20130101; G03H 2260/12 20130101; Y10T
436/143333 20150115; G03H 1/02 20130101 |
Class at
Publication: |
436/95 |
International
Class: |
G01N 33/66 20060101
G01N033/66 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2003 |
GB |
0305587.8 |
Claims
1. A sensor for the detection of an analyte comprising a cis-diol
moiety, which comprises a holographic element comprising a medium
and a hologram disposed throughout the volume of the medium,
wherein an optical characteristic of the element changes as a
result of a variation of a physical property occurring throughout
the volume of the medium, and wherein the medium comprises a
polymer comprising a group of formula (i) ##STR00006## wherein X is
an atom or group which, via an electronic effect, promotes
formation of a tetrahedral geometry about the boron atom of the
--B(OH).sub.2 group; and Y is a linker to the remainder of the
polymer.
2. The sensor according to claim 1, wherein X is
electron-withdrawing.
3. The sensor according to claim 2, wherein X is selected from the
group consisting of halogen, nitro and cyano.
4. The sensor according to claim 3, wherein X is fluorine.
5. The sensor according to claim 1, wherein X comprises --C(O)--
and/or --NH--.
6. The sensor according to claim 1, wherein X is in the ortho
position relative to the --B(OH).sub.2 group.
7. The sensor according to claim 6, wherein X comprises an amide or
amine group which is capable of forming an intramolecular bond to
the --B(OH).sub.2 group, thereby forming a ring.
8. The sensor according to claim 6, wherein X is capable of forming
an intramolecular bond to the --B(OH).sub.2 group via a resonance
or mesomeric effect.
9. The sensor according to claim 6, wherein X is capable of forming
an intramolecular bond to the --B(OH).sub.2 group via lone pair
donation.
10. The sensor according to claim 9, wherein the lone pair donation
is from a nitrogen atom.
11. The sensor according to claim 9, wherein the lone pair donation
is from an oxygen atom.
12. The sensor according to claim 11, wherein the oxygen atom is a
carbonyl oxygen.
13. A sensor for the detection of an analyte comprising a cis-diol
moiety, which comprises a holographic element comprising a medium
and a hologram disposed throughout the volume of the medium,
wherein an optical characteristic of the element changes as a
result of a variation of a physical property occurring throughout
the volume of the medium, and wherein the medium comprises a
polymer comprising a group of formula (ii) ##STR00007## wherein Y
is a spacer providing a link to the remainder of the polymer, and
which comprises an amide or amine group which is capable of forming
an intramolecular bond to the --B(OH).sub.2 group, thereby forming
a ring.
14. The sensor according to claim 13, wherein said intramolecular
bond is formed via a resonance or mesomeric effect.
15. The sensor according to claim 13, wherein said intramolecular
bond is formed via lone pair donation.
16. The sensor according to claim 15, wherein the lone pair
donation is from a nitrogen atom.
17. The sensor according to claim 15, wherein the lone pair
donation is from an oxygen atom.
18. The sensor according to claim 17, wherein the oxygen atom is a
carbonyl oxygen.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This application is a continuation application of co-pending
application Ser. No. 10/545,275, filed Oct. 17, 2005, now U.S. Pat.
No. 8,048,680, which was filed as a National Stage Application of
International Application Number PCT/GB2004/000576, filed Feb. 13,
2004; which claims priority to Great Britain Application No.
0305587.8, filed Mar. 11, 2003; all of which are incorporated
herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a holographic sensor.
BACKGROUND OF THE INVENTION
[0003] WO-A-95/26499 discloses a holographic sensor, based on a
volume hologram. The sensor comprises a holographic element, the
element comprising an analyte-sensitive holographic support medium
having an optical transducing structure disposed throughout its
volume. Because of this physical arrangement of the transducer, the
optical signal generated by the sensor is very sensitive to volume
changes or structural rearrangements taking place in the
analyte-sensitive matrix as a result of interaction or reaction
with the analyte. For example, a sensor comprising a gelatin-based
holographic medium may be used to detect trypsin. Trypsin acts on
the gelatin medium, irreversibly destroying the integrity of the
holographic support medium.
[0004] WO-A-03/087899 describes a method for the continuous
detection of an analyte in a fluid involving the use of a
holographic sensor. The support medium of the sensor comprises a
group which is capable of reacting reversibly with the analyte.
Thus, when fluid is passed over the holographic element, any
analyte present can be detected continuously.
[0005] In particular, WO-A-03/087899 describes how a holographic
sensor formed by the polymerisation of monomers including
vinylphenylboronic acid may be used to detect glucose. The pendant
phenylboronic acid groups can react reversibly with a cis-diol
group of glucose, resulting in swelling of the holographic support
medium. A limitation of this technology is that the sensor is only
effective over a limited pH range; there remains the need for
sensors which can detect glucose continuously over a range of
conditions, in particular physiological conditions.
SUMMARY OF THE INVENTION
[0006] When a cis-diol-containing species binds a boronic acid,
RB(OH).sub.2, an unstable boronate ester results, the ester having
a trigonal planar conformation. The boronate ester normally
achieves stability by binding an electron-donating group, to form a
more stable, tetrahedral geometry. Typically, boronic acids attain
this tetrahedral geometry by binding OH.sup.-, forming
negatively-charged boronate esters. At relatively high pH, the
mechanism is believed to be slightly different. It is thought that
the boronic acid first binds OH.sup.-, to form tetrahedral
RB(OH).sub.3.sup.-, which then reacts with the cis-diol. The
tetrahedral RB(OH).sub.3.sup.- reacts more readily with a cis-diol
than the trigonal planar boronate ester.
[0007] Without wishing to be bound by theory, the inventors believe
that the glucose sensor of WO-A-03/087899 "works" because the
formation of a negatively-charged phenylboronate ester produces a
Donan potential, causing water to partition into the support
medium. Expansion of the medium is then observed as a shift in the
reflectance maxima to longer wavelengths. At low pH values, the
boronic acid groups may be unable to form negatively-charged
phenylboronate esters and, as a result, detection might not be
possible. This is probably why the glucose sensor of WO-A-03/087899
is only effective over a limited pH range.
[0008] The invention is based on the discovery of a class of
phenylboronic acid derivatives which allow for the detection of
glucose and other cis-diol-containing analytes across a wide range
of pH values. The inventors have realised that phenylboronic acids
can be modified to promote formation of a more reactive tetrahedral
conformation.
[0009] For example, the phenyl group may comprise one or
electron-withdrawing substituents which, by mediating their
electronic effects through the phenyl ring, promote formation of
RB(OH).sub.3.sup.-. As another example, a substituent may be
capable of forming an intramolecular bond with the boron atom,
forcing the boronate into a substantially tetrahedral conformation.
Judicial selection of substituents allows the responsiveness of the
sensor to be optimised with respect to a particular set of
detection conditions.
[0010] Accordingly, a first aspect of the invention is a sensor for
the detection of an analyte comprising a cis-diol moiety, which
comprises a holographic element comprising a medium and a hologram
disposed throughout the volume of the medium, wherein an optical
characteristic of the element changes as a result of a variation of
a physical property occurring throughout the volume of the medium,
and wherein the medium comprises a polymer comprising a group of
formula (i)
##STR00002##
wherein
[0011] n is 0, 1, 2, 3 or 4;
[0012] each X (if present) is independently an atom or group which,
via an electronic effect, promotes formation of a tetrahedral
geometry about the boron atom; and
[0013] Y is a spacer which, when n is 0 or otherwise optionally, is
an atom or group which, via an electronic effect, promotes
formation of a tetrahedral geometry about the boron atom.
[0014] Such a sensor can be used in a method for the detection of
an analyte comprising a cis-diol moiety in a fluid, which comprises
contacting the fluid with the holographic element and detecting any
change of the optical characteristic of the element. The analyte
may comprise a plurality of cis-diol moieties; examples of such
analytes include glucose and tartaric acid (tartarate).
[0015] The polymeric medium may be obtained by the polymerisation
of monomers including a compound of formula (I)
##STR00003##
wherein
[0016] X, Y and n are as defined above; and
[0017] Z is a polymerisable group.
[0018] Another aspect of the invention is a device for the
detection of an analyte comprising a cis-diol moiety in a fluid,
which comprises a fluid conduit having an inlet, an outlet, and a
holographic element as defined above over which the fluid can flow,
wherein the device also includes a window whereby non-ionising
radiation can irradiate the holographic element. The analyte
concentration may change, while the fluid is static. Alternatively,
the fluid may be passed continuously over the element.
[0019] The variation arises as a result of reaction between the
medium and the cis-diol moiety of the analyte, wherein the reaction
and the variation are reversible. Since both the reaction and the
reverse reaction can occur, analytes such as glucose can be
continuously detected, possibly in real time
[0020] A sensor of the invention may be used to monitor a reaction
in vivo or in vitro, e.g. in a fermenter. It can be used for
kinetic measurement, and as an effective control system. The sensor
may be used, for example, to detect hyperglycaemia or
hypoglycaemia.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows the response of the hologram in terms of peak
diffraction wavelength readings.
[0022] FIG. 2 shows a calibration curve.
[0023] FIG. 3 shows that the addition of salt had no significant
effect on the hologram, showing that it could easily tolerate small
changes in salt concentrations.
[0024] FIG. 4 shows a calibration curve for response to glucose in
PBS pH 7.4 at 30.degree. G.
[0025] FIG. 5 shows a calibration curve.
[0026] FIG. 6 shows the response of the sensor to the five
analytes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] In addition to their use in holographic sensors, the present
invention also encompasses the novel phenylboronic acid compounds
themselves. Certain compounds and combinations of substituents are
preferred; in particular, see the subclaims.
[0028] The term "alkyl" as used herein refers to a straight or
branched chain alkyl moiety having from one to six carbon atoms.
The term includes, for example, methyl, ethyl, propyl, isopropyl,
butyl, tert-butyl, pentyl, hexyl and the like.
[0029] The term "alkoxy" as used herein refers to a straight or
branched chain alkoxy moiety having from one to six carbon atoms.
The term includes, for example, methoxy, ethoxy, propoxy and the
like.
[0030] The term "halogen" as used herein refers to fluorine,
chlorine, bromine or iodine.
[0031] The term "electronic effect" as used herein refers to a
direct or indirect effect on the boronic acid group, which promotes
formation of a tetrahedral conformation about the boron atom
relative to phenylboronic acid. The atom or group may, for example,
have an electron-withdrawing, electron-donating, resonance or
mesomeric effect on the phenyl ring of formulae (i) and (I) which,
in turn, effects the boronic acid group.
[0032] The phenyl ring is preferably substituted with one or more
electron-withdrawing groups. In this way, formation of
RB(OH).sub.3.sup.- may be promoted. When RB(OH).sub.3.sup.- reacts
with a cis-diol group of glucose, the resulting negatively-charged
phenylboronate ester produces a Donan potential, causing water to
partition into the support medium. Expansion of the medium is then
observed as a shift in the reflectance maxima to longer
wavelengths. In general, most sensors of the invention will detect
cis-diol-based analytes in this way.
[0033] Particularly when the analyte comprises a plurality of
cis-diol groups, it is preferred that the phenyl ring is
substituted with a group comprising an atom having a lone pair of
electrons, which can form an intramolecular (e.g. coordinate) bond
with the boron atom, forcing it into a tetrahedral conformation.
The boronic acid group may, as a result, be highly reactive. An
example of such a group is illustrated below:
##STR00004##
[0034] Although such a group is highly reactive to cis-diols, it is
thought to form an uncharged phenylboronate ester which, as it is
uncharged, cannot produce a Donan potential. Instead, it is
believed that, when the analyte comprises a plurality of cis-diol
moieties, it can bind two of these highly reactive phenylboronic
acid groups and effectively cross-link the support medium. This
cross-linking of the support medium causes it to contract,
resulting in a shift in the replay wavelength. Examples of analytes
which can be detected in this way are glucose and tartarate
(tartaric acid).
[0035] The interaction between the medium and analyte can be
detected remotely, using non-ionising radiation. The extent of
interaction is reflected in the degree of change of the physical
property, which is detected as a variation in an optical
characteristic, preferably a shift in wavelength of non-ionising
radiation.
[0036] The property of the holographic element which varies may be
its charge density, volume, shape, density, viscosity, strength,
hardness, charge, hydrophobicity, swellability, integrity,
cross-link density or any other physical property. Variation of the
or each physical property, in turn, causes a variation of an
optical characteristic, such as polarisability, reflectance,
refractance or absorbance of the holographic element.
[0037] The hologram may be disposed on or in, part of or throughout
the bulk of the volume of the support medium. An illuminating
source of non-ionising radiation, for example visible light, may be
used to observe variation(s) in the, or each, optical
characteristic of the holographic element.
[0038] More than one hologram may be supported on, or in, a
holographic element. Means may be provided to detect the or each
variation in radiation emanating from is the or each hologram,
arising as a result of a variation in the or each optical
characteristic. The holographic elements may be dimensioned and
arranged so as to sense two or more independent events/species and
to affect, simultaneously, or otherwise, radiation in two or more
different ways. Holographic elements may be provided in the form of
an array.
[0039] Preferred groups of formula (i) include:
##STR00005##
[0040] The holographic support medium may be obtained by the
polymerisation of monomers, wherein the monomers include a compound
of formula (I) Preferred monomers include: [0041]
2-(4-(acrylamidomethyl)phenylamino)methyl)phenylboronic acid;
[0042] 2-((3-methacrylamidopropylamino)methyl)phenylboronic acid;
[0043] 2-acrylamido-phenylboronic acid; [0044]
3-acrylamido-phenylboronic acid; and [0045]
3-acrylamido-6-fluoro-phenylboronic acid.
[0046] In addition to a compound of formula (I), the monomers may
include (meth)acrylamide and/or (meth)acrylate-derived co-monomers.
In particular, the monomer HEMA (hydroxyethyl methacrylate) is
readily polymerisable and cross-linkable. PolyHEMA is a versatile
support material since it is swellable, hydrophilic and widely
biocompatible. The monomers may also include co-monomers having
groups which are capable of intermolecular electron-donation, for
example secondary of tertiary amines.
[0047] Other examples of holographic support media which may be
modified to include boronate group are gelatin, K-carageenan, agar,
agarose, polyvinyl alcohol (PVA), sol-gels (as broadly classified),
hydro-gels (as broadly classified), and acrylates.
[0048] A parameter determining the response of a holographic
element is the extent of cross-linking. The number of cross-linking
points due to polymerisation of monomers should not be so great
that complex formation between polymer and analyte-binding groups
is relatively low, since the polymer film may become too rigid.
This may inhibit the swelling of the support medium.
[0049] The following Examples illustrate the invention, in
conjunction with the accompanying drawings.
Example 1
[0050] 3-Acrylamido-phenylboronic acid ("3-APB") was synthesised by
reacting 3-amino phenylboronic acid with an excess of acryloyl
chloride in an aqueous alkaline solution. The product was extracted
in acetone and dried using a rotary evaporator. The structure of
3-APB was confirmed using NMR. The purity was about 90%, TLC
showing very little contamination.
[0051] 3-APB was then copolymerised with acrylamide and
N,N'-methylene bisacrylamide, and a hologram recorded within the
polymer material. The response to glucose was then tested by
increasing the glucose concentration in phosphate-buffered saline
(PBS) solution at pH 7.4 in 0.5 mM steps.
[0052] FIG. 1 shows the response of the hologram in terms of peak
diffraction wavelength readings. The reaction with glucose was
fully reversible after the system was flushed twice with fresh
buffer. The sensor was also sensitive enough to pick up
concentrations of glucose as low as 0.5 mM (9 mg %) with a shift of
about 6 nm. This result was highly reproducible with errors of
about 5%, even when using a different hologram and
instrumentation.
[0053] FIG. 2 shows the calibration curve. The calibration was
approximately linear below 2 mM (36 mg %) glucose.
[0054] A control was also run where 2 mM KCl was added to the
system containing the hologram in PBS pH 7.4 instead of glucose.
This was to test the tolerance of the hologram to changes in
osmolarity; an increase in osmolarity could lead to a contraction
of the polymer. As shown in FIG. 3, addition of the salt had no
significant effect on the hologram, showing that it could easily
tolerate small changes in salt concentration.
Example 2
[0055] 3-APB, the synthesis of which is described in Example 1, was
recrystallised from an aqueous ethanolic solution with a purity of
about 98%; both NMR and TLC showed that there were no contaminants
present.
[0056] 3-APB was co-polymerised with acrylamide and N,N'-methylene
bisacrylamide to form a polymer comprising about 15 mole % of
purified 3-APB and about 1.55 mole % N,N'-methylene bisacrylamide
(cross-linker). A hologram was then recorded in the polymer.
[0057] A calibration curve for response to glucose in PBS pH 7.4 at
30 C. is shown in FIG. 4. The purified 3-APB had a response of
about 14 nm per millimolar glucose whereas the 90% pure 3-APB of
Example 1 had a response of only 11 nm per millimolar glucose for a
hologram with the same mole % of 3-APB.
[0058] A polymer comprising a 3-APB molar fraction of 25% was
synthesised using the same amount of cross-linker (1.55 mole %) and
the same amount of solids per unit volume of solvent. A hologram
was recorded within the polymer and then calibrated. The
calibration curve is shown in FIG. 5.
[0059] The increased amount of 3-APB increased the sensitivity of
the hologram for glucose by over 70%. This allowed small changes in
glucose concentration to be accurately detected.
Example 3
[0060] 2-Acrylamido-phenylboronic acid ("2-APB") was synthesised by
reacting 2-aminophenylboronic acid with an excess of acryloyl
chloride in an aqueous alkaline solution. The product was extracted
in acetone and dried using a rotary evaporator. The structure of
2-APB was confirmed using NMR. The purity was shown to be greater
than 90%.
[0061] 2-APB was then copolymerised with acrylamide and
N,N'-methylene bisacrylamide to form a co-polymer with 20% 2-APB
and 1.5% N,N'-methylene bisacrylamide (cross-linker). A hologram
was then recorded within the polymeric medium. The resulting
holographic sensor was then tested for its response to glycerol,
ethylene glycol, lactate, tartaric acid and glucose. Testing was
conducted using PBS (pH 7.4) at 30.degree. C.
[0062] The response of the sensor to the five analytes is shown in
FIG. 6. It is evident that the sensor is unresponsive to changes in
glycerol, ethylene glycol and lactate concentration. The sensor is,
however, sensitive to change in the levels of tartaric acid and
glucose; this was observed as a blue shift in the peak diffraction
wavelength, indicating that the support medium contracted in the
presence of these analytes.
[0063] This selectivity to tartaric acid and glucose is believed to
be attributable to the fact that both these analytes contain two
cis-diol groups; the other analytes tested contain only one. Thus,
tartaric acid and glucose can bind two 2-APB groups and,
effectively, cross-link the holographic support medium, causing it
to contract.
[0064] The response to tartaric acid is greater than for glucose
because the two cis-diol sites of tartarate are identical and thus
of equal affinity for 2-APB. The cis-diol sites of glucose are
slightly different. If such a sensor were to be used to monitor
physiological levels of glucose, then the greater response to
tartaric acid would not be a problem since the latter is not found
free in solution in the body.
* * * * *