WO2023100203A1

WO2023100203A1 - Optical sensor, support for said optical sensor and detection system to detect the presence and/or concentration of an analyte in a solution

Info

Publication number: WO2023100203A1
Application number: PCT/IT2021/000057
Authority: WO
Inventors: Nunzio CENNAMO; Francesco ARCADIO; Luigi Zeni; Girolamo D'agostino
Original assignee: Universita' Degli Studi Della Campania "Luigi Vanvitelli"
Priority date: 2021-12-03
Filing date: 2021-12-03
Publication date: 2023-06-08

Abstract

Optical sensor (10) for detecting the presence and/or concentration of an analyte in a solution, the optical sensor (10) comprising a guiding layer (11) suitable for guiding electromagnetic waves in the visible light wavelength range, the guiding layer (11) extending lengthwise along a longitudinal extension direction Y of a system of cartesian axes XYZ, the guiding layer (11) comprising: • a first portion (12) suitable for operating as a multi-mode waveguide for electromagnetic waves in the visible light wavelength range; • a second concave portion (13) made in a single piece with the first portion (12); said optical sensor (10) comprising on the upper surface of the second portion (13) in succession to each other along a vertical direction Z a first metal layer (17) and a receptor layer (18), the receptor layer (18) being arranged to bind to the molecules of the analyte to be detected.

Description

OPTICAL SENSOR, SUPPORT FOR SAID OPTICAL SENSOR AND DETECTION SYSTEM TO DETECT THE PRESENCE AND/OR CONCENTRATION OF AN ANALYTE IN A SOLUTION

The present invention refers to an optical sensor, to a support for such optical sensor and to a detection system for detecting the presence and/or concentration of an analyte in a solution .

As it i s known in various f ields of application, di f ferent types of sensors are currently available for the selective detection of part icular molecules of interest in solutions , the so-called analytes .

In particular, waveguide optical sensors are known, for example in plastic optical fibres (POP ) or planar waveguides , for monitoring the variation of ref ractive index of a receptor, through the physical e f fect of the surface plasmon resonance ( SPR) . In these cases , the chemical receptor is often a polymeri c fi lm in whi ch the shape of the target molecule, or of a mixture of target molecules is imprinted when measuring a class of substances is wished, through the technology known as Molecularly Imprinted Polymer (MIP ) .

Typi cally, the POF plastic optical f ibres used to make the aforesaid optical sensors have diameters ranging from a few hundreds of μm to 1 mm and have a core made of PMMA or other sil icone or epoxy material transparent in the visible .

In these sensors , the plastic optical fibre is modi fied, eliminat ing the cladding unti l reaching the core for at least a st retch of the length thereof , for example about 1 cm, by lapping creat ing a sect ion in the shape of D . In this lapping process about 200-300 μm of core are usually removed. A metal layer is deposited on the flat portion of the modified fibre, usually gold, for example about 60 nm thick, on top of which a layer of a molecularly imprinted polymer (MIP) lower than 1μm thick is deposited. The molecularly imprinted polymeric layer therefore comprises a plurality of reception sites for the molecules of the analyte whose presence is to be detected. On the flat portion of the modified fibre, before the metal layer, a photoresist layer lower than 1μm thick can be deposited to modify the bandwidth or to increase the intensity of the plasmon resonance.

The modified plastic optical fibre as mentioned above is characterized by its own surface plasmon resonance or SPR corresponding to the frequency or to the wavelength at which the so-called surface plasmons are generated at the molecularly imprinted metal-polymeric interface .

According to known methods, the fibre is immersed in the aqueous solution to be examined for at least the stretch in which the sensor structure has been made, thus allowing the combination of the analyte with the MIP. At this point the input fibre is fed with an optical signal, for example white light, and the frequency shift of the plasmon resonance is observed. On the basis of this frequency shift it is possible to obtain information regarding the presence of the analyte in the aqueous solution.

Optical sensors made in this way are, for example, those described in EP3502152A1 ; these sensors show a very good chemical sensitivity, in the order of nanograms/litre, and a high selectivity towards the searched molecule (target) . However, in the case in which these sensors are made individually of optical fibre, they require production procedures that involve rather artisanal processes, such as lapping of the cladding to realise the D-shaped section, which hinders large-scale production. On the other hand in the case in which such sensors are made of planar waveguides, they may require more or less complex measurement setups .

In any case, known optical sensors, whether fibre or planar waveguide, require the use of microfluidic systems when it is not possible to make the sensitive surface of the optical sensor interact with a drop of the solution containing the analyte of interest and deposited directly thereon. Therefore, in such cases, the application of the solution containing the analyte on the optical sensor is difficult, complex and onerous .

For example, to make biological material interact with the sensitive surface of a circular cross-section optical fibre during the measurement time, it may be necessary to let the solutions to be measured flow slowly over the sensitive area of the fibre for several minutes. For this purpose, a specific micro-pump, a flow cell and micro-channels should be used to carry out this measurement.

In addition, such known optical sensors have their own optical sensitivity, which cannot be varied according to the analyte to be detected without modifying the structure of the sensor itself. This makes them inflexible and unsuitable for the detection of a large number of analytes. The purpose of the present invention is to overcome the above-mentioned drawbacks and, in particular, to devise an optical sensor which enables to apply the solution containing the analyte to be detected to the sensor in a simple and immediate manner.

Another purpose of the present invention is to provide an optical sensor that can be used for different measurements requiring different optical sensitivities. A further object of the present invention is to provide a support for such an optical sensor which is very simple to couple to the sensor while allowing to obtain a stable and secure positioning necessary to carry out the measurements .

Another object of the present invention is to provide a detection system comprising such an optical sensor which is simple to assemble and usable in different configurations useful for different application areas. These and other purposes according to the present invention are achieved by making an optical sensor, a support for such optical sensor and a detection system as set forth in the independent claims.

Further characteristics of the optical sensor, the support for such optical sensor and the detection system are the subject of the dependent claims.

The features and advantages of the optical sensor, the support for such optical sensor and the detection system according to the present invention will be more apparent from the following description, which is illustrative and not limiting, referring to the attached schematic drawings in which:

- Figure 1 is a perspective view of an embodiment of an optical sensor according to the present invention; - Figure 2 is a view from above of the opt ical sensor of Figure 1 ;

- Figure 3 i s a sect ional view of the optical sensor of Figure 1 along the plane I I I-I I I ;

- Figure 4 is a perspect ive view of the optical sensor of Figure 1 housed in a support according to the present invention;

- Figure 5 is a view from above of the optical sensor of Figure 1 housed in a support according to the present invention ;

- Figure 6 i s a perspect ive schematic view of a first operational conf iguration of a detection system according to the present invention ;

- Figure 7 is a perspect ive schemat ic view of a second operational conf iguration of a detection system according to the present invent ion;

- Figure 8 is a graph showing the normalized intensity of the optical signal transmitted through a first embodiment of the opt ical sensor according to the present invention without the receptor layer placed in the detection system of Figure 6 as the refractive index of the solution placed above and in direct contact with the first metal layer varies ;

- Figure 9 is a graph showing the normalized intensity of the optical signal transmitted through a first embodiment of an optical sensor according to the present invention without the receptor layer placed in the detect ion system of Figure 7 as the re f ractive index of the solution placed above and in direct contact with the first metal layer varies ;

- Figure 10 is a graph showing the normali zed intensity of the optical signal transmitted through a second embodiment of an optical sensor according to the present invention without the receptor layer placed in the detection system of Figure 7 as the refractive index of the solution placed above and in direct contact with the first metal layer varies.

With reference to the figures, an optical sensor to detect the presence and/or concentration of an analyte in a solution, indicated as a whole with 10, is shown.

In the present discussion, for simplicity's sake of explanation, reference will be made to an illustrated system of cartesian axes XYZ in which the transverse axis X, the longitudinal axis Y and the vertical axis Z are the axis of extension in width, the axis of longitudinal extension and the axis of extension in height of the optical sensor 10, respectively.

Furthermore, the terms "upper", "lower", "lateral" refer to the configurations of the optical sensor 10 as illustrated .

Such an optical sensor 10 comprises a guiding layer 11 adapted to guide electromagnetic waves in the wavelength range of visible light, i.e. between about 350 nm and 750 nm.

Preferably, the guiding layer 11 consists of a material having a refractive index comprised between 1.4 and 1.5 at wavelengths of visible light.

For example, the guiding layer 11 consists of polymeric material of the silicone or epoxy type or of vitreous material.

The guiding layer 11 may, for example, be produced using 3D printing techniques or numerical control machines (CNC) .

The guiding layer 11 extends lengthwise along a longitudinal extension direction Y and has a first portion 12 suitable for operating as a multi-mode waveguide for electromagnetic waves in the visible light wavelength range and a second concave portion 13 made in a single piece with the first portion 12 subsequently to said first portion 12 along the extension direction Y.

The first portion 12 has a first free end 14 which coincides with a first longitudinal end of the guiding layer 11.

The second portion 13 has a free edge 16 comprising a second longitudinal end of the guiding layer 11 opposite the first longitudinal end.

Preferably, the first portion 12 has a cylindrical or D-shaped or rectangular cross-section.

Preferably, the first portion 12 has an elongated shape along the extension direction Y.

The guiding layer 11 may therefore have a spoon shape such as the one shown in Figure 1.

Preferably, the first portion 12 has a length along the direction Y comprised between 3 cm and 10 cm and a base surface area comprised between 100 μm² and 1 mm².

The second portion 13 is preferably concave polyhedral and has a plurality of converging flat faces 15 which may have any polygonal shape, preferably triangular or trapezoidal or mixed.

Each face 15 defines with respect to the plane XY an angle comprised preferably between 0° and 90°.

For example, as an extreme case, the guiding layer 11 may be made with the second portion 13 in the form of a cuvette with one face substantially parallel to the plane XY and the other faces inclined substantially 90° with respect to the plane XY .

The angles comprised between the faces 15 and the plane XY may vary from face to face and thus be di fferent from each other .

Preferably, the number of faces 15 is comprised between 3 and 10 .

In the case where the second portion 13 is polyhedral , the free edge 1 6 is formed by the free edges of the faces 15 .

The optical sensor 10 comprises on the upper surface of the second portion 13 in succession to each other along the vertical direct ion Z orthogonal to the plane XY a first metal layer 17 and a receptor layer 18 .

The receptor layer 18 , in particular, is des igned to bind to the molecules of the analyte to be detected and may be of either synthetic or natural origin .

The extension of the receptor layer 18 def ines the sensitive portion of the optical sensor 10 .

For example, a receptor layer 18 of synthetic origin may be a layer of molecularly imprinted polymer material compri sing a plurality of receptor site s arranged to capture molecules of the analyte to be detected; for example , the layer of molecularly imprinted polymer material may comprise EGDMA, or DVB and has a thickness of les s than 1 μm .

For example , a naturally occurring receptor layer 18 may be a layer of ant ibodies , or aptamers capable of binding to molecules of the analyte to be detected .

In any case , the receptor layer 18 and the first metal layer 17 have optical properties , dimensions , and shape such that , when the optical signal propagat ing in the guiding layer 11 hit s the first metal layer 17 , a surface plasmon i s excited at the interface between the fi rst metal layer 17 and the receptor layer 18 at a certain wavelength . Thi s determined wavelength corresponds to the wavelength of the surface plasmon resonance or SPR .

Preferably, the first metal layer 17 is deposited on the upper surface of the guiding layer 11 and is thus in direct contact therewith .

In such a case , the first metal layer 17 is preferably made of Gold or Silver or other metal s , having a thicknes s compri sed between 20 nm and 80 nm, preferably 60 nm .

In a particular embodiment , at least a second metal layer 19 may be interposed between the first metal layer 17 and the upper surface of the guiding layer 11 . In such a case, for example , the at least one second metal layer 19 may be made of Chromium or Titanium or of TiO2 or ZrO2 or a combination thereof with thicknes ses between 30 nm and 100 nm and the first metal layer 17 of Gold with thickness comprised between 10 nm and 80 nm; ; however, other pairs of metals may be provided, both to improve performance and adhes ion to the guiding layer 11 .

The optical sensor 10 may be integrated into a detection system 50 according to the present invention , which wi ll be described below .

Said detection system 50 comprises a support 51 having a substantial ly flat base having on the top a receiving seat for the optical sensor 10 and a plurality of reces sed visible channels 1 , 2 , 4 , 5 , 7 or buried channels 3 , 6 , 8 posit ioned respectively at the free end 14 of the first port ion 12 and at predetermined points of the free edge 16 of the second portion 13. All of these channels 1, 2, 3, 4, 5, 6, 7, 8 are adapted to house launch/reading optical fibres.

A launch optical fibre 21 means an optical fibre intended to be coupled with an optical source 23 included in the detection system 50.

A reading optical fibre 22 means an optical fibre intended to be coupled with an optical detection device 24 included in the detection system 50. The receiving location of the support 51 has a complementary shape to that of the optical sensor 10. The support 51 can be made of metal or resin, using 3D printing techniques or CNC machines.

Depending on where the optical launch/reading fibres are positioned, the optical path following the optical signal within the guiding layer 11 varies.

For example, different measurement configurations can be considered for the embodiment of Figures 4 and 5; the launch/reading optical fibres can be arranged in the first channel 1 and in the second channel 2, or in the third channel 3 and in the fourth channel 4, in the fifth channel 5 and in the sixth channel 6, in the seventh channel 7 and in the eighth channel 8, respectively . The optical sensor 10 has different performances in these different measurement configurations.

For example, let us consider the graph illustrated in Figure 8 which refers to an optical sensor 10 having a guiding layer 11 made of polystyrene, the first metal layer 17 made of Gold with a thickness of 60 nm in direct contact with the upper surface of the guiding layer 11 and lacking the receptor layer 18. The measurements were carried out using the measurement configuration shown in Figure 6, with the launch/reading optical fibres positioned in the first channel 1 and the second channel 2 and placing the first metal layer 17 in contact with liquids of different refractive index.

As can be seen in Figure 8, the optical sensor 10 is capable of detecting a wide range of refractive indices from approximately 1, 332 to 1, 408. In addition, in such a case a narrower resonance is obtained (with an easier-to-read minimum for the operator) with an optical sensitivity reduced to about 400 nm/RIU, wherein optical sensitivity (S) is defined as the variation of the resonance wavelength (A) as the refractive index of the dielectric material (n) placed above the first metal layer 17 varies (S=AX/An) .

Consider now the same optical sensor 10 used for the measurements of Figure 8 using the measurement configuration illustrated in Figure 7 with the launch/reading optical fibres positioned in the third channel 3 and in the fourth channel 4 and placing the first metal layer 17 in contact with liquids of different refractive index.

In that case, as can be seen in Figure 9, the optical sensor 10 is capable of detecting a wide range of refractive indices from approximately 1, 332 to 1, 408.

In this case, as evinced by Figure 9, a high optical sensitivity of about 1200 nm/RIU and a broadening of the resonance was achieved, making it more difficult for the operator to read.

By varying the material and technology used to make the guiding layer 11 of the optical sensor 10, the plasmonic response thereof can be modified.

For example, in the case in which the guiding layer 11 is made of resin by means of 3D printing, the guiding properties of such guiding layer 11 depend both on the type of photosensitive resin and on the printing quality, i.e. on the parameters used in the printing process itself, such as, for example, printer resolution, i.e. the height of the individual layer, exposure time to ultraviolet (UV) light and so on. In this respect, by way of example, consider an optical sensor 10 made of a photosensitive resin transparent to visible light through a 3D printer with the same geometric characteristics as the optical sensor 10 used for the measurements in Figure 8 and Figure 9. Figure 10 shows the measurements made with such an optical sensor 10 using the measurement configuration illustrated in Figure 7 with the launch/reading optical fibres positioned in the third channel 3 and in the fourth channel 4 and placing the first metal layer 17 in contact with liquids of different refractive index. As can be seen, in this case the optical sensor 10 is able to detect a wide range of refractive indices from 1, 332 to 1,371 and an optical sensitivity of approximately 800 nm/RIU was achieved.

The detection system 50, according to the present invention, enables the implementation of the detection method which will be described below.

Such a method is based on the observation of the variation of the plasmon resonance excitation in the case in which the receptor layer 18 is contacted with the solution containing the analyte to be detected with respect to a reference case. In any case, when the analyte binds to the receptor layer 18 , the optical properties thereof, that is the refractive index, varies . The detection method is based on the fact that the variation of the optical properties of the receptor layer 18 due to the bond with the analyte involves the shi ft of the wavelength of the surface plasmons resonance . This spectral shift i s linked to the concentration value of the analyte in the solution . P referably, the opt ical source 23 emit s an optical s ignal in a predetermined range of wavelengths , for example in the red wavelength range , and the concentration of the analyte is then determined on the basis of the intensity variation of the optical signal detected in case of presence of the analyte with respect to an opt ical reference signal detected in case of absence of the analyte . The variation between the intensit ies of the two signals is linked to the frequency shift of the surface plasmon resonance and, therefore , to the concentration of the analyte to be detected . In thi s case , the optical source 23 may for example be an LED emitting in the visible wavelengths , the optical detect ion device 24 may for example be a photodiode . Alternat ively , the opt ical signal generated by the optical source 23 is white l ight , for example in a range between 350 nm and 750 nm, and the concentration of the analyte is then determined on the basi s of the spect ral shi ft of the surface plasmon resonance detected by means of a spectrophotometer with respect to the optical reference signal detected in case of absence of the analyte . In this case , the optical source 23 may for example be a halogen lamp, the optical detection device 24 may for example be a spectrophotometer .

From the description given, the characteristics of the optical sensor, the support and the detection system according to the present invention are clear, as well as the the related advantages are clear .

The optical sensor, according to the present invention, has a second portion which, being concave, forms a tray suitable for containing the solution with the analyte of interest, a tray supported by the first portion. Such a feature ensures the ease of use of the optical sensor and prevents the use of microfluidic systems, which are essential when it is not possible to make the sensitive surface of the optical sensor interact with a drop of the aqueous solution containing the analyte of interest and deposited directly thereon.

The optical sensor, according to the present invention, is also very simple to manufacture as the guiding layer can be easily formed by a 3D printing process.

The support according to the present invention is very simple to couple to the optical sensor, which allows the optical sensor to be changed immediately and easily. The optical sensor can therefore be used for a single use i.e. be disposable. This is very important if not essential in those operating conditions in which the optical sensor is to be used to detect high level biohazard analytes such as SARS-CoV-2 or other viruses that are hazardous to the safety of operators .

Since, as we have seen, the optical sensitivity of the optical sensor depends on the measurement configuration set up on the detection system, it is possible to use the same optical sensor to carry out different measurements requiring different sensitivities simply by changing the positioning of the launch/ reading optical fibres.

Finally, it is clear that the optical sensor and the detection system thus conceived are susceptible to numerous modifications and variants, all falling within the scope of the invention; furthermore, all the details are replaceable with other technically equivalent elements. In practice, the materials used, as well as dimensions, can be of any type according to the technical requirements .

Claims

1) Optical sensor (10) for detecting the presence and/or concentration of an analyte in a solution, said optical sensor (10) comprising a guiding layer (11) suitable for guiding electromagnetic waves in the visible light wavelength range, said guiding layer (11) extending lengthwise along a longitudinal extension direction Y of a system of cartesian axes XYZ, said guiding layer (11) comprising: - a first portion (12) suitable for operating as a multi mode waveguide for electromagnetic waves in the visible light wavelength range;

- a second concave portion (13) made as a single piece with said first portion (12) ; said optical sensor (10) comprising on the upper surface of said second portion (13) in succession to each other along a vertical direction Z a first metal layer (17) and a receptor layer (18) , said receptor layer (18) being arranged to bind to the molecules of the analyte to be detected.

2) Optical sensor (10) according to claim 1 wherein said first portion (12) has an elongated shape along the direction Y and a cylindrical or D-shaped or rectangular cross-section. 3) Optical sensor (10) according to claim 1 or 2 wherein said second portion (13) is concave polyhedral and has a plurality of converging flat faces (15) of any polygonal shape, each of said faces (15) defining an angle preferably comprised between 0° and 90° with respect to the plane XY .

4) Optical sensor (10) according to claim 3 wherein the angles comprised between said faces (15) and the plane XY are different from each other.

5) Optical sensor (10) according to claim 3 or 4 wherein the number of said faces (15) is comprised between 3 and 10. 6) Optical sensor (10) according to any one of the preceding claims wherein between the first metal layer (17) and the upper surface of the guiding layer (11) at least a second metal layer (19) is interposed.

7) Optical sensor (10) according to any one of the preceding claims wherein said receptor layer (18) is of synthetic origin.

8) Optical sensor (10) according to any one of the preceding claims wherein said receptor layer (18) is of natural origin. 9) Support (50) for optical sensors comprising a substantially flat base having at the top a receiving seat suitable for housing an optical sensor (10) according to one or more of the preceding claims, said receiving seat having a shape complementary to that of said optical sensor (10) , said support also having a plurality of visible hollow channels (1, 2, 4, 5, 7) and/or buried channels (3, 6, 8) positioned respectively at predetermined points of a free edge (16) of the second portion (13) . 10) Detection system (50) for detecting the presence and/or the concentration of an analyte in a solution comprising :

- an optical sensor (10) according to one or more of the preceding claims; - a support (51) according to claim 9, said optical sensor (10) being housed in said receiving seat of said support (51) ; - a launch optical fibre (21) and a reading optical fibre (22) positioned in two respective channels of said channels (1, 2, 3, 4, 5, 6, 7, 8) ;

- an optical source (23) associated with said launch optical fibre (21) and an optical detection device (24) associated with said reading optical fibre (22) .