The invention relates to a chemical and/or biochemical integrated-optical sensor, a multiple arrangement of a plurality of such sensors and a method for integrated-optically sensing a substance, according to the preambles of the independent claims.
Many present and upcoming applications of chemical and/or biochemical microsystems, especially for application areas such as medical, food and environmental, require the detection of several analytes being simultaneously present in a liquid. One well-known and advantageous type of detection is optical. An important class of such optical sensors are integrated optical (IO) sensors comprising a chip with a waveguide and sensing biolayers. An example for this type of device is disclosed in WO 92/19976. Other patents have also been applied for in recent years and work has been published by various groups worldwide.
Different sensing principles are being used in IO chemical and/or biochemical sensors. These principles and arrangements allow one to integrate many sensing pads or sensors on one single chip for realizing on-chip referencing and complex analyte sensing.
In this document, the term xe2x80x9csensorxe2x80x9d stands for xe2x80x9csensingxe2x80x9d elements used for chemical and/or biochemical measurements as well as for xe2x80x9creferencingxe2x80x9d elements used for reference measurements. This is to avoid ambiguities, since there are many aspects which apply to both, sensing and referencing sensors, and referencing sensors can be considered to just represent a special type of measuring sensors, used to perform on-chip referencing.
It is known from the state of the art to arrange IO sensors in an array pattern. However, only one-dimensional IO sensor arrays permit independent simultaneous (xe2x80x9cparallelxe2x80x9d) measurements. More complex, e.g., two-dimensional, sensor arrays seriously suffer from crosstalk between the various IO channels, i.e., the optical signals cannot be separated in an acceptable way.
A further disadvantage of known multiple IO sensor arrangements is that the sensors require too much of chip area, leading to very big chips and also to a small ratio between active and passive area. (In this document, the term xe2x80x9cactive areaxe2x80x9d denotes the area of the IO sensor in which an interaction of the measurand with the light takes place.) They also need too much of (bio-)chemical area, since this is not efficiently used. Another problem with presently known array detection schemes is that the efficiency of on-chip referencing is limited by the large distance between sensing and referencing sensors due to their large size.
It is an object of the invention to provide a multiple arrangement of IO sensors which makes possible independent simultaneous (xe2x80x9cparallelxe2x80x9d) measurements with the sensors. It is a further object to provide an IO sensor for use in such a multiple arrangement. It is still a further object to indicate a method for integrated-optically sensing a chemical and/or biochemical substance using such a sensor.
The invention also aims at removing other drawbacks of the state-of-the art solutions for achieving high-density array IO sensors. In particular, it is another object of the invention to provide a multiple arrangement of IO sensors with:
more efficient on-chip referencing,
chip and system miniaturization, i.e., more sensors per chip area (in the case of a two-dimensional sensor) or per volume (in the case of a three-dimensional sensor),
less chemicals needed for chip biocoating, and
less analyte volume needed due to reduced chip area for performing same task.
To take full advantage for practical applications, the following constraints shall be taken into account:
the sensitivity is maintained or increased with respect to the conventional solutions, and
the dynamic range is maintained or increased with respect to the conventional solutions.
The objects are resolved by the IO sensor, the multiple arrangement of IO sensors and the method as defined in the independent claims.
The integrated-optical chemical and/or biochemical sensor according to the invention comprises a resonant waveguide grating structure defining a surface plane; means for emitting electromagnetic radiation towards the resonant waveguide grating structure, the means for emitting electromagnetic radiation comprising means for varying at least one parameter of the emitted electromagnetic radiation, the mutual arrangement of the resonant waveguide grating structure and the means for emitting electromagnetic radiation being such that the angles of incidence with respect to a normal line on said surface plane are greater than xe2x88x9290xc2x0 and smaller than +90xc2x0; and detector means for detecting electromagnetic radiation excident from the resonant waveguide grating structure under angles of excidence with respect to a normal line on said surface plane greater than xe2x88x9290xc2x0 and smaller than +90xc2x0.
The multiple one-, two- or three-dimensional arrangement according to the invention comprises a plurality of sensors as defined above.
The method for integrated-optically sensing a chemical and/or biochemical substance according to the invention comprises the steps of emitting electromagnetic radiation towards the resonant waveguide grating structure, the angles of incidence with respect to a normal line on said surface plane being greater than xe2x88x9290xc2x0 and smaller than +90xc2x0; exciting a resonant electromagnetic field in the resonant waveguide grating structure by means of the emitted electromagnetic radiation; causing an interaction of the substance with the resonant electromagnetic field; varying at least one parameter of the emitted electromagnetic radiation; and detecting electromagnetic radiation excident from the resonant waveguide grating structure under angles of excidence with respect to a normal line on said surface plane greater than xe2x88x9290xc2x0 and smaller than +90xc2x0.
According to the invention, the functionality of the measuring pads is increased. The measuring pad geometry is adapted to the sensing principle, to the overall chip geometry, and to the particular application. The efficiency of light collection (in general: xe2x80x9coptical transfer processesxe2x80x9d) is enhanced. Use is made of additional on-chip and/or off-chip and/or general degrees of freedom. The area required for performing the sensing task is reduced, especially by reducing the area required by a single measuring pad in an array, and by increasing the ratio between active and passive chip area.
Hence, a much higher density of sensors results for single-chip IO sensor arrangements, leading to several advantages as is described below. As an example, we will consider advantages for on-chip referencing, which is eased due to the smaller distance, and because multiple referencing sensors can be used per sensing pad, e.g. one on top and one below or left and right or distributed around etc. This is especially important for sensors with very high sensitivities, since they are more affected by unspecific effects such as temperature and signal drift due to chemical and physical fluctuations and chip deformation.